Single-site implantation methods for medical devices having multiple leads

Methods and devices include making an incision at a single site of a patient. The single site located at an anterior of a chest or abdomen. The method also includes inserting a tunneling tool through the incision at the single site and preparing a first tunnel to a subcutaneous posterior location. A path of the first tunnel at least one of i) extends over a plurality of Intercostal gaps of the chest or ii) extends along and within one of the intercostal gaps. The method also includes positioning a first lead having an electrode within the first tunnel and preparing a second tunnel to a subcutaneous parasternal location along the chest. The method also includes positioning a second lead having an electrode within the second tunnel and positioning a pulse generator within a subcutaneous pocket and operatively coupling the first and second leads to the pulse generator.

BACKGROUND

Embodiments of the present disclosure relate generally to implantable medical devices and methods, and more particularly to medical devices having pulse generators and multiple implanted leads.

Currently, implantable medical devices (IMD) are provided for a variety of cardiac applications. IMDs may include a “housing” or “canister” (or “can”) and one or more electrically-conductive leads that connect to the housing through an electro mechanical connection. IMDs contain electronics (e.g., a power source, microprocessor, capacitors, etc.) that control electrical activation of the leads to provide various functionalities. For instance, current IMDs may be configured for pacemaking, cardioversion, and/or defibrillation.

An implantable cardioverter-defibrillator (ICD) is one such medical device and it is designed to monitor heart rate, recognize certain events (e.g., ventricular fibrillation or ventricular tachycardia), and deliver electrical shock to reduce the risk of sudden cardiac death from these events. An ICD typically includes a pulse generator that is contained within a housing and one or more electrically-conductive leads that are controlled by the pulse generator. One conventional type of ICD uses transvenous leads in the right ventricle for detection and treatment of tachyarrhythmia. Although transvenous ICDs (or TV-ICDs) can prevent sudden cardiac death. TV-ICDs have certain drawbacks. For instance, obtaining venous access can be difficult and time-consuming, thereby prolonging the medical procedure. TV-ICDs are also associated with undesirable conditions or events, such as hemopericardium, hemothorax, pneumothorax, lead dislodgement, lead malfunction, device-related infection, and venous occlusion.

A second type of ICD, referred to as a subcutaneous ICD (or S-ICD), uses an electrode configuration that can reside entirely within the subcutaneous space. Unlike the transvenous types, the S-ICDs lack intravenous and intracardiac leads and, as such, can be less likely to have the undesirable conditions or events associated with TV-ICDs. The S-ICD typically includes a shock coil that extends parallel to the sternum in a pectoral region of the patient. The shock coil is flanked by two sensing electrodes. The sensing electrodes sense the cardiac rhythm and the shock coil delivers countershocks through the subcutaneous tissue of the chest wall.

The conventional S-ICD is implanted using three separate incisions: an axilla incision, an inferior parasternal incision near the xiphoid process, and a superior parasternal incision. More specifically, the pulse generator is positioned in a pocket of the axilla that is accessed through the axilla incision. The lead is implanted using the pocket and the two parasternal incisions. Like the TV-ICD, conventional S-ICDs have been effective in reducing the incidence of sudden cardiac death. However, the risk of infection or other complication increases with each incision. Accordingly, a need remains for an implantation method requiring fewer incisions while also providing an S-ICD configuration that may deliver a sufficient amount of energy for defibrillation.

SUMMARY

Embodiments set forth herein include implantable medical devices (SIMDs), systems that include SIMD, and methods of using and positioning the same. IMDs may include a pulse generator and multiple leads in which at least two leads are implanted through a single incision site. The leads may have one or more electrode segments. In some embodiments, the entire SIMD may be positioned subcutaneously (e.g., beneath the skin but above layers of skeletal muscle tissue, rib bones, and costal cartilage). In some embodiments, only designated elements of the SIMD are positioned subcutaneously. In other embodiments, at least some elements of the SIMD may be positioned submuscularly. For example, the pulse generator may be implanted submuscularly (e.g., under the serratus anterior muscle) or under the serratus anterior fascia but above muscle.

In accordance with embodiments herein, a method is provided that includes making an incision at a single site of a patient. The single site located at an anterior of a chest or abdomen of the patient. The method also includes Inserting a tunneling tool through the incision at the single site and preparing a first tunnel from the single site to a subcutaneous posterior location. A path of the first tunnel at least one of i) extends over a plurality of intercostal gaps of the chest or ii) extends along and within one of the intercostal gaps. The method also includes positioning a first lead having an electrode within the first tunnel and inserting the tunneling tool or a different tunneling tool through the incision at the single site and preparing a second tunnel from the single site to a subcutaneous parasternal location along the chest. The method also includes positioning a second lead having an electrode within the second tunnel and positioning a pulse generator within a subcutaneous pocket and operatively coupling the first and second leads to the pulse generator.

In some aspects, the path of the first tunnel extends beyond a posterior axillary line of the patient. The single site is the only site where an incision is made for positioning the first lead, for positioning the second lead, and for positioning the pulse generator. Optionally, the posterior location is within a region below the inferior angle of a scapula.

In some aspects, the method further comprises shaping the tunneling tool or the other tunneling tool based on an anatomical shape of the patient along the corresponding path.

In some aspects, the tunneling tool is surrounded by a removable sheath, wherein preparing the first tunnel includes moving the tunneling tool and the removable sheath through subcutaneous tissue to form the first tunnel and removing the tunneling tool such that the removable sheath remains within the first tunnel.

In some aspects, at least one of the first lead or the second lead is anchored to the deep fascia within the subcutaneous pocket at an anchor point. The anchor point is the only anchor point in which the at least one lead is anchored directly to patient.

In some aspects, a volume of the pulse generator is at most 40 milliliters.

In some aspects, the pulse generator is configured to generate a defibrillating energy of at most 50 Joules. The pulse generator and the electrode of the second lead have a common polarity.

In some aspects, the electrode of the first lead has an active length that is at least 12 centimeters (cm), and the electrode of the second lead has an active length that is at least 8 cm.

In some aspects, the electrode of the first lead includes an electrode patch positioned at the posterior location. The electrode patch has an active area that is at least 30 cm2.

In accordance with one or more embodiments herein, a method is provided that includes making an incision at a single site of a patient. The single site is located at an anterior of a chest of the patient. The method also includes inserting a first tunneling tool through the incision at the single site. The tunneling tool has an elongated shaft and a removable sheath that surrounds the elongated shaft. The method also includes displacing underlying tissue with the tunneling tool along a designated path to prepare a first tunnel. The first tunnel extends from the single site, over a plurality of intercostal gaps of the chest, and within one of intercostal gaps to a subcutaneous posterior location. The method also includes withdrawing the elongated shaft. The removable sheath maintains the first tunnel. The method also includes positioning a first lead having an electrode within the first tunnel and withdrawing the removable sheath. The method also includes inserting a second tunneling tool through the incision at the single site. The second tunneling tool has an elongated shaft and a removable sheath that surrounds the elongated shaft of the second tunneling tool. The method also includes displacing underlying tissue with the second tunneling tool along a designated path to prepare a second tunnel. The second tunnel extends from the single site to a subcutaneous parasternal location. The method also includes withdrawing the elongated shaft of the second tunneling tool. The removable sheath of the second tunneling tool maintains the second tunnel. The method also includes positioning a second lead having an electrode within the second tunnel and withdrawing the removable sheath of the second tunneling tool. The method also includes forming a subcutaneous pre-pectoral pocket. The method also includes positioning a pulse generator within the subcutaneous pre-pectoral pocket and operatively coupling the first and second leads to the pulse generator.

In some aspects, the path of the first tunnel extends beyond a posterior axillary line of the patient. The single site is the only site where an incision is made for positioning the first lead, for positioning the second lead, and for positioning the pulse generator.

In some aspects, the method also includes shaping at least one of the elongated shafts based on an anatomical shape of the patient along the corresponding designated path.

In some aspects, the pulse generator is configured to generate a defibrillating energy of at most 50 Joules. The pulse generator and the electrode of the second lead have a common polarity.

In some aspects, the first lead has an electrode with an active length that is at least 12 centimeters (cm). The second lead has an electrode with an active length that is at least 8 cm.

In accordance with one or more embodiments, a method is provided that includes making an incision at a single site of a patient. The single site is located at an abdomen of the patient. The method also includes inserting a first tunneling tool through the incision at the single site. The first tunneling tool having an elongated shaft and a removable sheath that surrounds the elongated shaft. The method also includes displacing underlying tissue with the first tunneling tool along a designated path to prepare a first tunnel. The first tunnel extends from the single site along an intercostal gap to a subcutaneous posterior location. The method also includes withdrawing the elongated shaft. The removable sheath maintains the first tunnel. The method also includes positioning a first lead having an electrode within the first tunnel and withdrawing the removable sheath. The method also includes inserting a second tunneling tool through the incision at the single site. The second tunneling tool has an elongated shaft and a removable sheath that surrounds the elongated shaft of the second tunneling tool. The method also includes displacing underlying tissue with the second tunneling tool along a designated path to prepare a second tunnel. The second tunnel extends in a superior direction from the single site to a subcutaneous parasternal location. The method also includes withdrawing the elongated shaft of the second tunneling tool. The removable sheath of the second tunneling tool maintains the second tunnel. The method also includes positioning a second lead having an electrode within the second tunnel. The method also includes withdrawing the removable sheath of the second tunneling tool and forming a subcutaneous abdominal pocket. The method also includes positioning a pulse generator within the abdominal pre-pectoral pocket and operatively coupling the first and second leads to the pulse generator.

In some aspects, the path of the first tunnel extends beyond a posterior axillary line of the patient. The single site is the only site where an incision is made for positioning the first lead, for positioning the second lead, and for positioning the pulse generator.

In some aspects, the method also includes shaping at least one of the elongated shafts based on an anatomical shape of the patient along the corresponding designated path.

In some aspects, the pulse generator is configured to generate a defibrillating energy of at most 50 Joules. The pulse generator and the electrode of the second lead have a common polarity.

In some aspects, the electrode of the first lead includes a patch electrode.

DETAILED DESCRIPTION

Embodiments set forth herein include implantable medical devices (SIMDs), systems that include SIMD, and methods of using and positioning the same. In certain embodiments, the SIMD is a subcutaneous implantable cardioverter-defibrillator (S-ICD) in which only one single incision site is used to position the first lead, the second lead, and the pulse generator. The pulse generator is positioned within a pocket that is accessed through the single incision site, and the first and second leads are positioned within tunnels that extend from the single incision site (or pocket). Particular embodiments include a pulse generator that is positioned within a pectoral region of a chest of a patient or within an abdominal region of the patient. In other embodiments, the SIMD is an implantable cardioverter-defibrillator (S-ICD) in which only one single incision site is used to position the first lead, the second lead, and the pulse generator, wherein the pulse generator is position submuscularly.

As used herein, the term “subcutaneously,” when used to describe implanting a device (e.g., pulse generator, lead body, electrode, etc.), means implanting the device beneath the skin but above layers of skeletal muscle tissue, rib bones, and costal cartilage. The device is typically positioned under or partially within the subcutaneous tissue. When the term “subcutaneous” is used to characterize the entire implantable medical system, the term means that most of the operating components of the system (e.g., the pulse generator, shocking electrodes, optional sensing electrodes, lead bodies) or each and every one of the operating components is beneath the skin, but above layers of skeletal muscle tissue, rib bones, and costal cartilage. Compared to transvenous ICD implantation, subcutaneous implantation may be less complex, less invasive, and less time-consuming.

An electrode represents an electrically conductive portion of the lead that is operable to deliver energy for antiarrhythmic therapy. Embodiments include an electrode configuration that includes at least three shock electrodes. A shock electrode may be, for example, a coil electrode, a ring electrode, a patch electrode, or the like. Each of the leads includes at least one electrode, and the pulse generator may include another electrode. As used herein, a pulse generator or a housing of the pulse generator “includes an electrode” when the housing forms or constitutes the electrode or when the housing (or other part of the pulse generator) has a discrete electrode attached thereto. Optionally, the electrode configuration may include additional sensing electrodes. Illustrated embodiments include a parasternal coil electrode and a posterior electrode (e.g., coil electrode or patch electrode) that is positioned below the inferior angle of a scapula. It is contemplated, however, that different types of electrodes may be used in these locations.

A lead typically includes a lead body having an elongated flexible tube or sleeve comprising, for example, a biocompatible material (e.g., polyurethane, silicone, etc.). The lead body may include a single lumen (or passage) or multiple lumen (or passages) within the flexible tube. A lead may have multiple electrical conductors (not shown) that electrically couple the electrode(s) of the lead to the pulse generator. The electrical conductors may be cabled conductors coated with PTFE (poly-tetrafluoroethylene) and/or ETFE (ethylenetetrafluoroethylene). The electrical conductors are terminated to the respective electrode. The lead body may be configured for receiving a guide wire or stylet that enable positioning of the lead.

Electrode configurations may reliably provide a sufficient amount of energy for antiarrhythmic therapy (e.g., defibrillation). Embodiments may enable pulse generators with defibrillation thresholds (DFTs) that are less than known systems. For example, the DFT in some embodiments may be at most 50 Joules. The DFT in certain embodiments may be at most 45 Joules or, more particularly, at most 40 Joules. Embodiments may also enable using pulse generators or canisters with a smaller volume than known systems. For instance, a volume of the pulse generator may be at most 40 milliliters or at most 35 milliliters.

Furthermore, the features, structures, or characteristics described herein may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obfuscation. The description is intended only by way of example, and simply illustrates certain example embodiments,

FIG. 1illustrates a graphical representation of an implantable medical system12that is configured to apply therapy to a heart (not shown). In particular embodiments, the system12may apply pacing therapy, cardiac resynchronization therapy (CRT), and general arrhythmia therapy, including defibrillation. The system12includes a subcutaneous implantable medical device (SMD)14that is configured to be implanted in a subcutaneous area exterior to the heart. The SIMD14is positioned in a subcutaneous pocket90. The system12also includes a first lead21having an electrode23and a second lead22having an electrode24that are configured for defibrillation. Optionally, each of the first and second leads21,22may include one or more additional electrodes (e.g., sensing electrodes).

The pulse generator15may be implanted subcutaneously and at least a portion of the first and second leads21,22may be implanted subcutaneously, in particular embodiments, the SIMD14is an entirely or fully subcutaneous SIMD. InFIG. 1, the SIMD14is positioned within a pectoral region. Optionally, the SIMD14may be positioned in a different subcutaneous region. The SIMD14may be configured to detect or sense cardiac activity (e.g., cardiac rhythm). The SIMD14is configured to deliver various arrhythmia therapies, such as defibrillation therapy, pacing therapy, antitachycardia pacing therapy, cardioversion therapy, and the like based on the cardiac activity.

The pulse generator15includes a housing or canister18. The pulse generator15also includes a pulse-generator (PG) electrode19. The pulse generator15or the housing18include an electrode when the housing18forms or constitutes the electrode or when the housing18(or other part of the pulse generator15) has a discrete electrode attached thereto. In particular embodiments, the housing18forms the PG electrode19. In other embodiments, as shown inFIG. 1, the PG electrode19is a discrete electrode attached to the housing18.

Each of the first and second leads21,22includes an elongated lead body60that extends from a PG-end portion62to a distal tip64. The PG-end portion62is operably connected to the pulse generator15. The PG-end portion62may include one or more electrodes (not shown) that electrically engage respective terminals (not shown) of the pulse generator15. More specifically, the PG end portion62may be inserted into a port of the pulse generator15where the terminals are located.

The elongated lead body60includes an elongated flexible tube or sleeve66comprising, for example, a biocompatible material (e.g., polyurethane, silicone, etc.). The lead body60may include a single lumen (or passage) or multiple lumen (or passages) within the flexible tube66. Each of the first and second leads21,22may also include a plurality of electrical conductors (not shown) that electrically couple the shocking electrode (and optionally sensing electrodes) to the pulse generator15. The electrical conductors may be cabled conductors coated with PTFE (poly-tetrafluoroethylene) and/or ETFE (ethylenetetrafluoroethylene). The lead body60may be configured for receiving a stylet that enable positioning of the lead. The electrical conductors are terminated to the respective electrodes. For example, the conductors may be terminated to an electrode (not shown) near the PG end portion62and a respective electrode (e.g., electrode23or electrode24) along a distal segment65that extends to and includes the distal tip64.

In the illustrated embodiment, each of the electrodes23,24is a single coil electrode. In other embodiments, however, the electrode23and/or the electrode24may include multiple different electrodes. In other embodiments, the electrode23and/or the electrode24may include a patch electrode. The electrodes23,24have respective active lengths. An active length68represents a length of the electrode (e.g., a coil electrode) that may be used to provide electrical energy. The active length68is measured between a proximal end70and a distal end72. For embodiments that include patch electrodes, the patch electrode may include an active area that may be used to provide the electrical energy.

In some embodiments, the active length of the parasternal electrode24is at least five (5) cm. In some embodiments, the active length of the parasternal electrode24may be at least seven (7) cm or, more particularly, at least nine (9) cm, in certain embodiments, the active length of the parasternal electrode24may be at least ten (10) cm or, more particularly, at least fifteen (15) cm.

In some embodiments, the active length of the posterior electrode23is at least ten (10) centimeters (cm). In some embodiments, the active length of the posterior electrode23may be at least twelve (12) cm or, more particularly, at least fifteen (15) cm. In certain embodiments, the active length of the posterior electrode23may be at least seventeen (17) cm or, more particularly, at least 20 cm. A maximum active length may be, for example, about 30 cm.

For embodiments, in which the posterior electrode23is a patch electrode, the patch electrode has an active area based on an active width and active length of the patch electrode. An active width of the electrode is measured perpendicular to the active length from an outer edge of the electrode to an opposite outer edge of the electrode. It should be understood that the patch electrode may include an array of individual electrodes. The active width of the patch electrode may be at least four (4) cm and an active length of the patch electrode may be at least 5 (cm). An active area (length times width) may be at least 30 cm2or, more particularly, at least 40 cm2. Examples of the active width and active length (w×l) include 3×6, 3×7, 3×8, 4×6, 4×7, 4×8, 5×6, 5×7, 5×8. The active area may be, for example, at least 15 cm2, at least 18 cm2, at least 20 cm2, at least 25 cm2, at least 30 cm2, or at least 40 cm2. It should be understood, however, that the active area of a patch electrode is not necessarily rectangular and may have other shapes.

The electrodes23,24may be positioned subcutaneously at a level that is suitable for providing a sufficient amount of energy for defibrillation. For example, the electrode23may be positioned subcutaneously at a level that approximately aligns with an apex of a heart of the patient. At least a portion of the electrode23may be positioned at or below an apex of the heart. For example, the electrode23may be positioned along an intercostal gap between the seventh and eighth ribs of the patient or along an intercostal gap between the sixth and seventh ribs of the patient. The electrode23may be positioned below the inferior angle of a scapula. It is contemplated, however, that the electrode23may be positioned at other levels with respect to the heart.

The electrode24may be positioned subcutaneously an extend parallel to a sternum of a patient (or a parasternal lime of the sternum). The electrode24may be spaced apart from the sternum by, for example, one to three centimeters. Although a typical location for the electrode24may be on a left side of the sternum, it is possible that the electrode24may be positioned along a right side of the sternum. It is contemplated, however, that the electrode24may be positioned at other levels with respect to the heart.

As described herein, for some embodiments, the subcutaneous pocket90is a pre-pectoral pocket located in the pectoral region. In other embodiments, however, the subcutaneous pocket90is an abdominal pocket located in the pectoral region. The shock vectors may be configured accordingly using a PG electrode of the pulse generator, the parasternal electrode24, and the posterior electrode23. In some embodiments, the electrical energy is generated by the PG electrode and the parasternal electrode and is directed to the posterior electrode.

FIG. 2illustrates a simple block diagram of at least a portion of the circuitry within the SIMD14. The SIMD14includes a controller30that may be coupled to cardiac sensing circuitry32and pulse sensing circuitry34. The controller30also utilizes or communicates with various other electronic components, firmware, software, and the like that generally perform sensing and pacing functions (as generally denoted by a pacemaker functional block36). While the examples herein are provided for pacing and defibrillation functions, the SIMD could be programmed to perform anti-tachycardia pacing, cardiac rhythm therapy, and the like. The cardiac sensing circuitry32is configured to detect one or more cardiac events (e.g., ventricular fibrillation, ventricular tachycardia, or other arrhythmia). The pulse sensing circuitry34is configured to detect event markers.

The controller30is configured to analyze incoming paced cardiac events (as sensed over the cardiac sensing circuitry32). Based on this analysis, the controller30in the SIMD14may perform various pacemaker related actions, such as setting or ending timers, recording data, delivery of therapy, and the like. The controller30of the SIMD14may also perform various cardioversion/defibrillation related functions. In the example ofFIG. 2, outputs38and40represent output terminals that are coupled through a switching circuit (in the functional module36) to corresponding electrodes on the housing of the SIMD14. Alternatively, the outputs38and40may be coupled to respective electrode on along the leads21,22(FIG. 1).

Inputs42-48are provided to the cardiac sensing circuitry32and pulse sensing circuitry34. By way of example, with reference to SIMD14, inputs42and44may be coupled to sensing electrodes that supply sensed signals to a sensing amplifier52. Inputs46and48may be coupled to the same or different sensing electrodes to provide sensed signals to a pulse amplifier54. An output of the sensing amplifier52is supplied to amplitude discriminator56, while an output of the pulse amplifier54is supplied to amplitude discriminator58. Outputs of the amplitude discriminators56and58are then provided to the controller30for subsequent analysis and appropriate actions. The inputs42and44may be coupled to various combinations of the electrode23,24or the PG electrode19.

FIG. 3illustrates components of a delivery system100that may be used for implanting the medical system12(FIG. 1). In particular, the delivery system100may be used to create a tunnel within the patient and position a lead within the tunnel. To this end, the delivery system may include a plurality of elongated components, such as shafts, tubes, wires, and the like. The components may have inner passages or lumens that receive other components. The delivery system100may be a kit that includes components for multiple steps in the tunnel preparation and lead placement operations. During some operations, one or more of the components may not be utilized.

In the illustrated embodiment, the delivery system100includes a dissector102, an elongated tunneling tool104, a removable sheath106, and a lead guide108. The lead guide108may be a guide wire or a stylet. Although only a single tunneling tool104is shown, the delivery system or kit100may include one or more types of shafts and/or multiple shafts with different lengths. In some embodiments, the dissector102and the tunneling tool104may be combined and constitute a single component or only the tunneling tool104is used for dissecting tissue. In some embodiments, the dissector102may also function as a stopper or plug that prevents material from entering a lumen116of the tunneling tool104.

The dissector102has a distal tunneling end110and a proximal loading end111. The tunneling end110is configured to displace subcutaneous tissue and/or separate the subcutaneous tissue from other tissue layers (e.g., deep fascia layer) to form a tunnel along a designated path. The tunneling end110may be blunt or include portions that are sharpened. Optionally, the tunneling end110may include active components that may facilitate forming the tunnel. For example, the active component may be an ultrasonic device. The dissector102may be malleable but sufficient rigidly for displacing tissue and/or separating tissues.

The tunneling tool104includes an elongated shaft105. The tunneling tool104has a leading end114that includes an opening120and a trailing end117that includes a loading port118. A length of the tunneling tool104extends between the leading and trailing ends114,117and may be sufficiently sized for providing the designated tunnel. The tunneling tool104has an operator handle112for directing the tunneling tool104during tunnel preparation and lead placement. The tunneling tool104has at least one lumen116that extends from the loading port118in the operator handle112to the leading end114where the opening120is provided. The leading end114may be shaped to facilitate displacing tissue. Optionally, the leading end114may include active elements (e.g., ultrasonic device, telemetry device, imaging device, etc.). Optionally, a portion or segment of the tunneling tool104may be steerable.

The tunneling tool104comprises a biocompatible material and may have a predetermined shape based on an anatomy of the patient. The predetermined shape may be made during manufacturing. Optionally, the tunneling tool104may include a malleable material such that the tunneling tool104may be shaped after manufacturing but prior to insertion. For instance, the tunneling tool104may comprise medical grade stainless steel. The tunneling tool104may be shaped (e.g., during manufacture or after manufacture but prior to surgery) based on a path that will be taken by the tunneling tool104during the tunneling process. For example, the tunneling tool104may be shaped for curving about the chest to the posterior location, or the tunneling tool104may be shaped to move along a path from the subcutaneous pocket to the sternum. The path is a function of an anatomical contour or shape of the patient's body along the corresponding path.

In the illustrated embodiment, the removable, sheath106is a splittable along a length of the removable sheath106. The dashed line107inFIG. 3represents where the removable sheath106may be separated. The removable sheath106may be perforated or otherwise weakened along the dashed line107to facilitate splitting the removable sheath106in a designated manner. As described below, the lead guide108interacts with the lead for positioning a lead at a designated location.

FIG. 4illustrates a method180for implanting a medical system, such as the implantable medical system12(FIG. 1), using the delivery system100(FIG. 3). The method180is described with reference toFIGS. 5-7. The method180may be applicable for abdominal pockets, pre-pectoral pockets, or other pockets within the patient body. With reference toFIG. 5, the method180includes making, at182, an incision122at a single site124of a patient body126. The incision122may be held open using forceps (not shown). Optionally, the single site124may receive more than one incision to provide a larger access point to the underlying tissue. For example, a first incision may be made through the skin followed by a second incision that intersects the first incision.

At184, the tunneling tool104of the delivery system100is inserted through the incision122at the single site124. In some embodiments, the removable sheath106may surround the tunneling tool104during insertion. Optionally, the removable sheath106may be advanced along the tunneling tool104after insertion. At186, a tunnel128within the underlying tissue is prepared. More specifically, the tunneling tool104is advanced along a path125through tissue of the patient until a distal end130of the delivery system100is positioned proximate to a designated location131(e.g., a subcutaneous posterior location or a subcutaneous parasternal location). As used herein, the “distal end of the delivery system” is the end of the component of the delivery system that leads (or is in front of) other components of the delivery system. The distal end may change based on the component being used. For example, the distal end130may include the tunneling end110of the dissector102, the leading end114of the tunneling tool104, or both when the tunneling and leading ends110,114are essentially even.

The designated location131may be the desired location for placing an electrode or may be a location that is proximate to the desired location. A user may grip the operator handle112, the elongated shaft105, and/or the dissector102and drive the distal end130along the designated path125. As the distal end130of the delivery system100moves along the path125, the distal end130displaces and/or separates layers of tissues. Prior to insertion or during the tunneling operation, the tunneling tool104and the dissector102may be shaped to conform to the path125. Alternatively or in addition to having a predetermined shape, the tunneling tool104and/or the dissector102may be steered as the distal end130moves through the tissue.

In the illustrated embodiment, the dissector102of the delivery system100leads the tunneling tool104along the path125. The tunneling end110of the dissector102displaces tissue (e.g., subcutaneous tissue132) and/or separates the subcutaneous tissue132from an underlying deep fascia layer134. In other embodiments, the dissector102of the delivery system100is even or flush with respect to the leading end114of the tunneling tool104as the tunneling tool104is advanced below the skin. In such instances, the leading end114displaces tissue and/or separates the subcutaneous tissue172from an underlying deep fascia layer174.

After the tunnel128is prepared, the tunneling tool104and the dissector102may be withdrawn from the tunnel128. In some embodiments, the removable sheath106may remain within the underlying tissue to maintain the tunnel128. As such, the tunneling tool104is withdrawn from the removable sheath106.

With respect toFIG. 6, a lead140may be positioned, at188, within the tunnel128. More specifically, the lead140is inserted through a port of the delivery system100. In the illustrated embodiment, the removable sheath106remains. The lead140is inserted through a port141and advanced through the tunnel128maintained by the removable sheath106. The lead guide108(FIG. 3) may be used to move the lead140. In some embodiments, the lead guide108is a stylet and the lead140includes a lumen (not shown) that is sized and shaped to receive the stylet. For example, an end of the stylet engages an interior surface of the lead140at an end of the lumen and pushes the lead140to the designated location131.

In other embodiments, the lead guide108may be a guide wire. The lead140may include a lumen that extends entirely through the lead140. Prior to inserting the lead140, the guide wire may be advanced through the tunnel128such that a distal end of the guide wire is proximate to the designated location131. With the guide wire positioned, a proximal end of the guide wire may be inserted into the lumen of the lead140, and the lead140may be advanced through the tunnel128using the guide wire to direct the lead140. Yet in other embodiments, the lead140may be advanced through the tunnel128without the use of a guide wire.

Optionally, positioning the lead140, at188, may be facilitated by imaging and/or tracking systems. For example, the lead140may be configured to communicate telemetry signals that indicate where the electrode146is located within the patient. Alternatively or in addition to the telemetry system, an imaging system (e.g., fluoroscopy) may be used to identify where the electrode146is located within the patient.

The lead140includes a lead body142having at least one inactive segment144and at least one electrode146. In the illustrated embodiment, the electrode146is a coil electrode, but it is contemplated that other electrodes may be used. For example, the electrode146may be an array of electrodes. The electrode146is a shock electrode. Optionally, sensing electrodes may be positioned adjacent to the electrode146or other portions of the lead body142.

After the lead140is positioned within the tunnel128and the electrode146is located at the designated position131, the removable sheath106may be removed. For example, the removable sheath106may be split along its length as the removable sheath106is withdrawn from the tunnel128. As the tunnel128is withdrawn, the subcutaneous tissue132may collapse upon the lead140.

Lead placement may then be repeated, at198. More specifically, a different tunnel may be prepared by inserting the delivery system100through the same incision at the single site124. The delivery system100may utilize the same or different components. For example, a different tunneling tool and a different dissector may be used to prepare the second tunnel. In a similar manner as described above, another lead150(shown inFIG. 7) may be positioned within the second tunnel.

With respect toFIG. 7, a subcutaneous pocket152may be formed, at190(FIG. 4), through the incision at the single site124. The subcutaneous pocket152may be formed by displacing and/or removing portions of the subcutaneous tissue132. It should be understood, however, that the subcutaneous pocket152is not required to be formed as a separate step and/or after lead positioning. The subcutaneous pocket152may be formed in stages and/or at different times during the method180. For example, the subcutaneous pocket152may be formed after positioning the multiple leads, after positioning only one or some of the leads, or prior to positioning the leads.

At192, the leads140,150may be operatively coupled to a pulse generator154. For example, the leads140,150may have terminals (not shown) at proximal ends of the leads140,150that are inserted into ports (not shown) of the pulse generator154, thereby completing assembly of an implantable medical system156. The implantable medical system156may be tested to determine if the system is operating properly.

At194, the pulse generator154may be positioned within the subcutaneous pocket152. At196, the pulse generator154and the leads140,150may be immobilized within the patient to reduce the likelihood that the leads140,150or the pulse generator154may migrate. For example, the leads140,150may be anchored to the deep fascia134using suture sleeves158. In some embodiments, the suture sleeves158and attachment to the pulse generator154are the only anchoring mechanisms used to immobilize the leads140,150within the patient. Optionally, the pulse generator154may also be anchored to the deep fascia134. After immobilizing the implantable medical system156, the incision122at the single site124may be closed.

In particular embodiments, the single site124is the only site where an incision is made for positioning the lead140, for positioning the lead150, and for positioning the pulse generator154. As such, a medical system may be subcutaneously implanted using only a single site and, possibly, making only a single incision. In other embodiments, however, an incision may be made to facilitate positioning one or more leads. For example, for some patients, another incision at a separate site may be made to position the posterior electrode.

The method may also include initiating the pulse generator, at191. For example, an external device (e.g., programmer) may be communicatively coupled to the pulse generator. The pulse generator may communicate identification data to the pulse generator (e.g., obtain model and serial number). The external device may generate a chart that correlates to the patient having the pulse generator. The external device may instruct the pulse generator to perform an electrode integrity check and measure parameters of the electrodes (e.g., impedance of shock electrode(s)). The external device and/or the pulse generator may determine a sensing configuration for the pulse generator based on cardiac activity. During initiation of the pulse generator, at191, therapy parameters may be selected by the user.

Optionally, the pulse generator may be implemented with the hardware, firmware and other components of one or more of implantable medical devices (IMDs) that include neurostimulator devices, implantable leadless monitoring and/or therapy devices, and/or alternative implantable medical devices, although implemented as a subcutaneous implantable medical device. For example, the SIMD may represent a cardioverter, cardiac rhythm management device, defibrillator, neurostimulator, leadless monitoring device, leadless pacemaker and the like. For example, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Pat. No. 9,333,351 “Neurostimulation Method And System To Treat Apnea” and U.S. Pat. No. 9,044,610 “System And Methods For Providing A Distributed Virtual Stimulation Cathode For Use With An Implantable Neurostimulation System”, which are hereby incorporated by reference. Additionally or alternatively, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Pat. No. 9,216,285 “Leadless Implantable Medical Device Having Removable And Fixed Components” and U.S. Pat. No. 8,831,747 “Leadless Neurostimulation Device And Method Including The Same”, which are hereby incorporated by reference. Additionally or alternatively, the IMD may include one or more structural and/or functional aspects of the device(s) described in U.S. Pat. No. 8,391,980 “Method And System For Identifying A Potential Lead Failure in An implantable Medical Device” and U.S. Pat. No. 9,232,485 “System And Method For Selectively Communicating With An Implantable Medical Device”, which are all hereby incorporated by reference in their entireties.

At193, a defibrillation test may be performed to determine a defibrillation threshold. The test may be administered prior to or after closing the incision. The defibrillation threshold is a quantitative estimate of the ability of the heart to defibrillate. The defibrillation threshold is typically defined as the minimum shock strength that causes defibrillation. The defibrillation threshold can be measured by changing the voltages in subsequent VF inductions in accordance with a predetermined protocol. For example, the stored voltages may be incrementally decreased for subsequent VF inductions until the first shock is unable to defibrillate. This may be referred to as a step-down to failure test. If a high defibrillation threshold is identified, it may be desirable to make adjustments to the system. For example, the leads could be repositioned, the leads could be switched-out, portions of the electrodes could be capped, or another lead may be added. The defibrillation testing may be performed using an external device (e.g., programmer) that is communicatively coupled to the pulse generator.

Another defibrillation test may including applying the same energy twice. The first electrical shock may be programmed to deliver an amplitude that is less than 10 Joules from the maximum capacity of the system. To verify the effectiveness of the shock, the same amplitude may then be applied a second time. At least three to five minutes may separate subsequent applications to allow hemodynamic recovery and to minimize the cumulative effect of the electrical shocks. If the electrical shock delivered by the implantable defibrillator is ineffective, a rescue shock can be delivered either by an external defibrillator or through the implanted defibrillator.

After closing the incisions, the method may also include sensing cardiac activity at195and analyzing, at197, the cardiac activity to determine whether a cardiac event-of-interest has occurred. In response to determining that a cardiac event-of-interest has occurred, a therapy may be applied, at199. For example, the pulse generator may sense subcutaneous signals (e.g., subcutaneous ECG signals) and a cardiac, rhythm using a combination of the electrodes. The pulse generator may process the cardiac signals (e.g., filter and/or amplify) and analyze the cardiac activity to determine whether an event that requires therapy is occurring. If the pulse generator determines that a cardiac event-of-interest is occurring, such as ventricular fibrillation, ventricular tachycardia, or other arrhythmia, the pulse generator may apply therapy (e.g., electrical shock) to the heart using a combination of the electrodes.

AlthoughFIGS. 3-7describe certain embodiments for implanting leads using the delivery system100, it should be understood that other delivery systems may be used, and that one or more operations (or steps) of the method180may be modified, replaced, or performed in different stages or at different times. One or more operations may also be added.

FIGS. 8 and 9are an anterior view and a lateral view, respectively, of a human thoracic cage that illustrates an electrode configuration of an implantable medical system (IMD)200in accordance with an embodiment. For reference, the heart is also shown. More specifically,FIGS. 8 and 9illustrate relative positions of a pulse generator202within a pectoral region203, a parasternal electrode204, and a posterior electrode206. The IMD200may be implanted using the method ofFIG. 4and using a delivery system, such as the delivery system100(FIG. 3).

For example, an incision (not shown) may be made within the pectoral region203at a single site210located at an anterior of a chest of the patient. A first tunneling tool may be inserted through the incision at the single site210. The tunneling tool may have, for example, an elongated shaft and a removable sheath that surrounds the elongated shaft. The tunneling tool may displace underlying tissue along a designated path to prepare a first tunnel. The first tunnel extends from the single site210, over a plurality of intercostal gaps212(FIG. 9) of the chest, and within one of intercostal gaps212to a subcutaneous posterior location214(FIG. 9).

After the first tunnel is formed, the elongated shaft may be withdrawn such that the removable sheath remains within the first tunnel and maintains the first tunnel. A first lead216may then be positioned within the first tunnel. The first lead216has the posterior electrode206(e.g., coil electrode) at a distal portion thereof. The removable sheath may then be withdrawn allowing the subcutaneous tissue to collapse around the first lead216.

As shown, the first lead216may wrap about the chest or torso of the patient. The electrode206may be positioned proximate to a scapula (not shown) of the patient. For example, the distal end of the electrode206may be positioned within an intercostal gap212and proximate to the tip or the inferior angle of the scapula. Transverse plane P1intersects the apex. Transverse plane P2intersects an upper portion of the heart, such as the atria. At least a portion of the electrode206may be positioned at or below the apex of the heart. For example, at least a majority of the electrode206may be positioned at or below the apex of the heart. The electrode204extends between the transverse planes P1and P2. The electrode204may extend from the transverse plane P2. The transverse planes P1and P2and placement of the electrodes204,206are based upon the size, shape, and location of the heart within the patient's body.

The electrode206may be at least partially positioned between a midaxillary line and a posterior axillary line of the patient. In some instances, a proximal end of the electrode206may be positioned beyond the midaxillary line or, possibly, the posterior axillary line of the patient. The midaxillary line is a coronal line extending along a surface of the body passing through an apex of the axilla. The posterior axillary line is a coronal line extending parallel to the midaxillary line and through the posterior axillary skinfold.

A second tunnel extending from the same single site210may also be prepared. The second tunnel may be prepared after the first tunnel or before the first tunnel. More specifically, a second tunneling tool may be inserted through the incision at the single site210. The second tunneling tool has an elongated shaft and a removable sheath that surrounds the elongated shaft of the second tunneling tool. The second tunneling tool may displace underlying tissue along a designated path to prepare the second tunnel. The second tunnel extends from the single site210to a subcutaneous parasternal location218. As described above, the elongated shaft may be withdrawn such that the removable sheath of the second tunneling tool maintains the second tunnel. A second lead220having the parasternal electrode204may be positioned within the second tunnel. The removable sheath may then be withdrawn allowing the subcutaneous tissue to collapse around the second lead220. As shown, the electrode204is positioned parasternally (e.g., within one to three centimeters from the sternum). An end of the electrode204may be located proximate to the xiphoid process. As shown, the electrode204may extend from a point at or above the transverse plane P2to a point at or below the transverse plane P1. A majority of the electrode206may be at or below the transverse plane P1. In some embodiments, at least 75% of the electrode206is at or below the transverse plane P1. In certain embodiments, at least 85% of the electrode206is at or below the transverse plane P1. In certain embodiments, at least 95% of the electrode206is at or below the transverse plane P1.

A subcutaneous pre-pectoral pocket may be formed prior to, during, or after the preparation of the first and second tunnels. The pulse generator202may be positioned within the subcutaneous pre-pectoral pocket and operatively coupled to the first and second leads216,220.

In the illustrated embodiment, the parasternal electrode204and the pulse generator202have the same polarity while the system provides electrical energy for defibrillation. As shown by the arrows inFIG. 9, the shock vector is directed from the parasternal electrode204and the pulse generator202to the posterior electrode206.

FIGS. 10 and 11are an anterior view and a lateral view, respectively, of a human thoracic cage that illustrates an electrode configuration of an implantable medical system (IMD)300in accordance with an embodiment. Relative positions of a pulse generator302within an abdominal region303, a parasternal electrode304, and a posterior electrode306. The IMD300may be implanted using the method ofFIG. 4.

For example, an incision (not shown) may be made within the abdominal region303at a single site310in the abdomen of the patient. A first tunneling tool may be inserted through the incision at the single site310. The tunneling tool may have, for example, an elongated shaft and a removable sheath that surrounds the elongated shaft. The tunneling tool may displace underlying tissue along a designated path to prepare a first tunnel. The first tunnel extends from the single site310along and through an intercostal gap312to a subcutaneous posterior location314.

After the first tunnel is formed, the elongated shaft may be withdrawn such that the removable sheath remains within the first tunnel and maintains the first tunnel. A first lead316may then be positioned within the first tunnel. The first lead316has the posterior electrode306at a distal portion thereof. Similar to the first lead216(FIGS. 8 and 9), the first lead316may wrap about the chest or torso of the patient and be positioned proximate to the tip or the inferior angle of the scapula.

InFIGS. 10 and 11, the posterior electrode306is a coil electrode. Alternatively, the posterior electrode may be a patch electrode406(shown inFIG. 12). Returning toFIGS. 10 and 11, the removable sheath may then be withdrawn allowing the subcutaneous tissue to collapse around the first lead316.

A second tunnel extending from the same single site310may also be prepared. The second tunnel may be prepared after the first tunnel or before the first tunnel. More specifically, a second tunneling tool may be inserted through the incision at the single site310. The second tunneling tool has an elongated shaft and a removable sheath that surrounds the elongated shaft of the second tunneling tool. The second tunneling tool may displace underlying tissue along a designated path to prepare the second tunnel. The second tunnel extends from the single site310to a subcutaneous parasternal location318. The second tunneling tool may move in a superior direction from the single site310to the subcutaneous parasternal location318.

As described above, only the elongated shaft may be withdrawn such that the removable sheath of the second tunneling tool maintains the second tunnel. A second lead320having the parasternal electrode304may be positioned within the second tunnel. The removable sheath may then be withdrawn allowing the subcutaneous tissue to collapse around the second lead320. As shown, the electrode304is positioned parasternally (e.g., within one to three centimeters from the sternum). An end of the electrode304may be located proximate to the xiphoid process.

A subcutaneous abdominal pocket may be formed prior to, during, or after the preparation of the first and second tunnels. The pulse generator302may be positioned within the subcutaneous abdominal pocket and operatively coupled to the first and second leads316,320.

In the illustrated embodiment, the parasternal electrode304and the pulse generator302have the same polarity while the system provides electrical energy for defibrillation. As shown by the arrows inFIG. 11, the shock vector is directed from the parasternal electrode304and the pulse generator302to the posterior electrode306.

With respect toFIG. 12, the parasternal electrode404and the pulse generator402have the same polarity while the system provides electrical energy for defibrillation. As shown by the arrows inFIG. 11, the shock vector is directed from the parasternal electrode404and the pulse generator402to the posterior patch electrode406.

FIG. 13illustrates a block diagram of an SIMD. The SIMD is capable of performing stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. The SIMD is hereinafter referred to as the device610. While a particular multi-element device is shown, this is for illustration purposes only. It is understood that the appropriate circuitry could be duplicated, eliminated or disabled in any desired combination to provide a device capable of monitoring impedance and/or cardiac signals, and/or treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation.

The housing640for the stimulation device610is often referred to as the “canister,” “can,” “case,” or “case electrode” and may be programmably selected to act as the shock electrode and/or as a return electrode for some or all sensing modes. The housing640may further be used as a return electrode alone or in combination with one or more other electrodes. The housing640further includes a connector (not shown) having a plurality of terminals647-652. To achieve sensing, pacing, and shocking in connection with desired chambers of the heart, the terminals647-652are selectively connected to corresponding combinations of electrodes.

The device610includes a programmable microcontroller660that controls the various modes of sensing and stimulation therapy. The microcontroller660includes a microprocessor, or equivalent control circuitry, designed specifically for controlling sensing impedance derivation and the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. The micro controller660includes the ability to process or monitor input signals (data) as controlled by a program code stored in memory. The details of the design and operation of the microcontroller660are not critical to the present invention. Rather, any suitable microcontroller660may be used.

The microcontroller660includes inputs that are configured to collect cardiac signals associated with electrical or mechanical behavior of a heart over at least one cardiac cycle. The cardiac signals may be from the cardiac sensing circuit682and representative of electrical behavior of the heart. The circuit682may provide separate, combined, composite or difference signals to the microcontroller660representative of the sensed signals from the electrodes. Optionally, the cardiac signals may be the output of the A/D circuit690that are representative of electrical behavior of the heart. The cardiac signals may be the output of the physiologic sensor607that are representative of mechanical behavior.

The microcontroller660includes a cardiac signal (CS) module661, a marker detection (MD) module663and a therapy module665(among other things). The CS module661is configured to analyze cardiac signals. The MD module663is configured to analyze signals sensed over the marker sensing channel and identify incoming event markers. The therapy module665is configured to modulate, over multiple cardiac cycles, at least one therapy parameter while the device610obtains a collection of at least one CSF indicators associated with different therapy parameters. The therapy module665is further configured to adjust a therapy configuration based on, among other things, the cardiac signals and based on the event markers.

The microcontroller660further controls a shocking circuit617by way of a control signal The shocking circuit617generates stimulating pulses of low (up to 0.5 Joules), moderate (0.5-10 Joules), or high energy (11 to 50 Joules), as controlled by the microcontroller660. Stimulating pulses may be applied to the patient's heart through at least two shocking electrodes.

One or more pulse generators670and672generate various types of therapy, such as pacing and ATP stimulation pulses for delivery by desired electrodes. The electrode configuration switch674(also referred to as a switch bank) controls which terminals647-652are connected to the pulse generators670,672, thereby controlling which electrodes receive a therapy. The pulse generators,670and672, may include dedicated, independent pulse generators, multiplexed pulse generators, shared pulse generators or a single common pulse generator. The pulse generators670and672are controlled by the microcontroller660via appropriate control signals to trigger or inhibit stimulation pulses. The microcontroller660further includes timing control circuitry which is used to control the timing of such stimulation pulses (e.g., pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A-A) delay, or ventricular interconduction (V-V) delay, etc.) as well as to keep track of the timing of refractory periods, PVARP intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc.

An electrode configuration switch674connects the sensing electronics to the desired terminals647-652of corresponding sensing electrodes. For example, a portion of the terminals may be coupled to electrodes configured to define a sensing and/or shocking vector that passes through the left ventricle. The switch674may connect terminals to the event marker sensing circuit684(which corresponds to the event marker sensing channel) and the microcontroller. The circuit684may amplify, filter, digitize and/or otherwise process the sensed signals from the select electrodes.

The switch674also connects various combinations of the electrodes to an impedance measuring circuit613. The impedance measuring circuit613includes inputs to collect multiple measured impedances between corresponding multiple combinations of electrodes. For example, the impedance measuring circuit613may collect a measured impedance for each or a subset of the active sensing vectors. Optionally, the impedance measuring circuit613may measure respiration or minute ventilation; measure thoracic impedance for determining shock thresholds; detects when the device has been implanted; measures stroke volume; and detect the opening of heart valves, etc.

The switch bank674includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. The switch674, in response to a control signal from the microcontroller660, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, co-bipolar, etc.) by selectively closing the appropriate combination of switches (not specifically shown). The outputs of the cardiac signal and event marker sensing circuits682and684are connected to the microcontroller660which, in turn, is able to trigger or inhibit the pulse generators670and672, respectively. The sensing circuits682and684, in turn, receive control signals from the microcontroller660for purposes of controlling the gain, threshold, the polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown).

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system690. The data acquisition system690is configured to acquire cardiac signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device610. The data acquisition system690samples cardiac signals across any pair of desired electrodes. The data acquisition system690may be coupled to the microcontroller660, or other detection circuitry, for detecting an evoked response from the heart in response to an applied stimulus, thereby aiding in the detection of “capture.” Capture occurs when an electrical stimulus applied to the heart is of sufficient energy to depolarize the cardiac tissue, thereby causing the heart muscle to contract.

The microcontroller660is further coupled to a memory694by a suitable data/address bus696. The memory694stores programmable operating, impedance measurements, impedance derivation and therapy-related parameters used by the microcontroller660. The operating and therapy-related parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, wave shape and vector of each stimulating pulse to be delivered to the patient's heart within each respective tier of therapy.

The operating and therapy-related parameters may be non-invasively programmed into the memory694through a telemetry circuit600in telemetric communication with the external device610, such as a programmer, trans-telephonic transceiver, or a diagnostic system analyzer. The telemetry circuit600is activated by the microcontroller660by a control signal. The telemetry circuit600advantageously allows data and status information relating to the operation of the device (as contained in the microcontroller660or memory694) to be sent to an external device101through an established communication link603.

The stimulation device610may include a physiologic sensor607to adjust pacing stimulation rate according to the exercise state of the patient. The physiological sensor607may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). The battery611provides operating power to all of the circuits shown inFIG. 7.