Abstract:
A low profile electrical adapter body releasably connects to the electrodes of a pacing lead connector, such as an IS-1. Spring steel lead connector holders and the twist-tolerant cable allow continuous ECG recording while manipulating the pacing lead. The adapter body includes two lead connector holders. A grip longitudinally aligns the lead connector within the adapter body. The grip is slidably attached to a twist-tolerant cable and releasably engages the adapter to form a single adapter assembly that enlarges the device for easier digital manipulation. A twist-tolerant cable connects the low profile adapter directly or indirectly to a medical test device such as a pacemaker analyzer.

Description:
FIELD OF THE INVENTION 
     The invention relates to a low-profile adapter for the temporary, uninterrupted electrical connection of a test device, such as a pacemaker analyzer, to an implantable cardiac pacemaker lead during its manipulation by the implanting surgeon. 
     BACKGROUND OF THE INVENTION 
     The Pacemaker-Lead System 
     When the heart fails to beat or beats irregularly, physicians may implant a pacemaker to ensure the regular beat of the heart. Pacemakers have implantable electrical leads, i.e., specially coated wires with electrodes at the tip that connect the pacemaker to the heart, usually to its inner wall via the venous system.  FIG. 1  depicts a pacemaker  10  and an implantable lead  20 . The pacemaker senses electrical activity and sends an electrical current through the implantable lead to the heart at appropriate intervals to regulate the heartbeat. The distal (i.e., most distant from the pacemaker) end  24  of the lead  20  is located typically on the endocardium of the heart. The proximal (i.e., closest to the pacemaker) end  22  of the lead  20  generally has a single or multiple coaxial contact assembly for insertion into and electrical coupling with pacemaker  10 . 
     Description of the Lead 
     Implantable leads have one or more distal “electrodes”, which are metallic contact surfaces for transmitting electrical signals into and from the heart tissue. One example of an electrode is distal end  24  of implantable lead  20  in  FIG. 1 . In an implantable lead, each electrode is attached to a unique contact (not shown) in lead connector  22  in  FIG. 1 . The number of electrode-contact circuits is also referred to as the number of “poles” the lead has. A stylet or a removable stiff wire  110  (see  FIG. 4 ) may be inserted into a central channel spanning the entire length of the pacing lead to stiffen the lead to facilitate its manipulation in the body. 
     Implantable leads have distal ends that are a) passively fixated, using “tines” or tiny wings that entangle with cardiac structures on the inside of the heart, or b) actively fixated, where the distal tip electrode consists of a corkscrew which is twisted out of the barrel of the distal lead and into the heart tissue.  FIG. 1  depicts the wings of a passively fixated tip  24 . Leads may be either unipolar, having just one distal tip electrode, or bipolar, with one tip electrode and a second ring electrode located on the lead shaft about 3-10 mm from the tip. Specialized leads may have 3 or more electrodes. 
     The IS-1 connector is currently the industry standard 3.2 mm, in-line, two-contact electrical connector. The IS-1 standard is defined by ISO 5841-3:1992, Rev 2000, Cardiac pacemakers—Part 3: Low-profile connectors (IS-1) for implantable pacemakers. An example IS-1 can be seen in  FIG. 3 . Proximal end  31  of IS-1 co-axial bipolar connector  30  has two electrodes  32 ,  34  and two sets of silicon sealing rings  33 ,  35 . In an actively fixated lead, a tiny torque wrench fits the most proximal contact on the IS-1 connector  30 . When turned, the wrench rotates the distal corkscrew electrode via a torquable conductor within the body of the lead. Typically 8 to 12 full turns are required to engage the corkscrew electrode. 
     Implanting the Lead 
     Implantation of pacing leads typically involves the insertion of the lead through a peripheral vein into the heart under X-ray fluoroscopic guidance and manipulation of the lead around the heart until a suitable permanent location is found. Indicators of adequate location include the anatomical location, the stability of the lead as it appears on the fluoroscope, and electrical characteristics, including adequate sensing of cardiac electrical activity at the site and a low pacing threshold, which is the minimum stimulating current necessary to contract the heart. Some of these indicators are determined by a pacemaker analyzer, such as the Medtronic PSA 5311.  FIG. 4 , while depicting certain aspects of the present invention, also generally represents a pacemaker analyzer  196  electrically connected to a pacing lead  120 . Manipulation of the lead requires a continuing series of push-pull movements, flexing, and multiple full axial rotations of the lead. 
     Prior Art 
     To electrically test the pacing lead&#39;s position, the prior art uses a relatively stiff speaker wire lead  70 ,  71  terminated by alligator clips  42  and  44  (see  FIG. 2 ) to connect from the pacemaker analyzer to the contacts on the lead connector (see  FIG. 3 ). The stiff cable and its bulky alligator clips do not readily allow manipulation of the lead while the clips are connected. This necessitates electrically “blind” manipulation of the lead with numerous iterations of lead manipulation without electrical feedback from the analyzer. Typically the lead is manipulated without the alligator clips connected. To measure the electrical quality of current particular pacing site the physician stops manipulating the lead, connects the alligator clips, and then measures the site quality. To resume testing additional sites the physician disconnects the alligator clips, manipulates the lead to another site without electrical feedback from the analyzer, stops manipulation, reconnects the alligator clips, etc. 
     Historically, pacing leads were typically placed into the relatively easy implant sites of the right ventricular apex and the right atrial appendage. Under these circumstances blind manipulation of the lead was tolerable, usually requiring only a limited number of connections and disconnections of the alligator clips and taking only 15 to 45 minutes. Failed lead implantations were rare. In the last 5 to 10 years, physicians have been implanting pacing leads in new and more difficult cardiac locations for more physiological pacing and to resynchronize cardiac contraction in heart failure. This approach has generally improved long term cardiac function. New pacing lead locations currently include the left cardiac veins, right ventricular septum or outflow tract, atrial septum, adjacent to His Bundle, in Bachman&#39;s bundle and inside Coronary Sinus, as well as on the epicardium. Finding the optimal pacing lead site has thus become far more challenging and time consuming, requiring numerous relocations of the lead and thus repeated testing using the alligator clips, with implant procedures taking 1.5 to 2 hours to complete, sometimes far longer and with not infrequent failures to secure an adequate pacing site. 
     This need for connection and reconnection is a disadvantage because it results in only intermittent testing of possible lead positions, adds to procedure time, distracts the physician from manipulation of the lead, may delay or even prevent the identification of the optimal pacing site, and adds to the risk of contamination of the lead and thus infection. Secondary unfavorable effects from prolonged implant procedures include an increase in operator fatigue, greater risk to the patient from anesthesia-related complications, higher cost per procedure, and higher risk of trauma, including heart perforation. 
     The prior art in lead adapters reflects attempts to allow compatibility of connection to various lead connector geometries or to improve security of lead connection, but none address safety and manipulability of the connected lead during implantation. A typical coaxial pacing lead IS-1 connector to which this invention may connect is described in U.S. Pat. No. 4,951,687. U.S. Pat. No. 6,038,481 to Werner et al describes a lead adapter between pacing leads and a pacemaker analyzer but the adapter is too large, heavy and cumbersome to allow lead manipulation that involves multiple rotations of the lead and connector. The Werner et al design also does not accommodate the small torque wrench required for actively fixated leads. Furthermore, Werner et al teaches securing the adaptor to the connector. U.S. Pat. No. 5,782,892 depicts a large lead adapter designed to securely accommodate different lead connector geometries but which is unsuitable to manipulation of the lead. U.S. patent application No. 2003/0120327 depicts a simpler, smaller adapter but is designed for connection to temporary pacing leads with different connectors to those of permanent leads and not suitable for manipulation of the leads. U.S. Pat. No. 6,921,295 describes a large complex adapter to join, upsize, and adapt leads with different connector geometries. It is unsuitable for manipulation during implantation. 
     In view of the current state of the art, it is desirable to have a pacing lead adapter that remains connected to the lead during manipulation of the lead to provide continuous measurement of lead parameters. This same adapter, however, must disconnect readily if required by the physician and in case of inadvertent pull on the adapter to prevent potentially lethal tearing of the lead out of the heart, especially in the case of an actively fixated lead. Such an adapter would need to be small, light, and have a low profile above the lead, and its connecting cable should be light and pliable enough so that the physician can hold the pacing lead in his hands and push, pull, move and twist the lead many times without any impediment from the adapter or its attached cable. Furthermore, the cable between the adapter and the pacemaker analyzer should also be compliant and twist-tolerant so as to not inhibit the rotation, twisting and bending of the pacing lead during its manipulation. 
     SUMMARY OF THE INVENTION 
     With today&#39;s increasing demands on cardiologists to locate pacing leads in diverse and challenging cardiac sites, the present invention provides the much-needed constant feedback during continuous manipulation, which the prior art does not have. The invention will allow shorter implant time, optimize lead locations that will in turn improve lead parameter values, reduce trauma to the heart, and lower the associated procedure risks and costs. 
     The preferred embodiment of the invention includes: (i) a low-profile, light-weight adapter assembly with two spring clip contacts for releasably holding the two contacts of a pacing lead connector such as the IS-1; (ii) the most proximal spring clip contact is preferably disposed at or near one end of the adapter body and is narrow enough to provide room on the lead connector&#39;s proximal electrode for a small torque wrench to rotate the lead connector in the case of actively fixated leads; (iii) a grip, removably engageable with the adapter body, with guides and a central slot for the pacing lead stylet to aid the physician to precisely locate the adapter onto the pacing lead connector; (iv) the proximal clip contact is designed such that it exerts sufficient force to make good electrical contact with the pacing lead connector contact, while allowing for the normal and intended functioning of the pacing lead, i.e., rotation of the lead connector contact; (v) a long, pliable twist-tolerant connection cable for connecting the adapter to the pacemaker analyzer; and, (vi) two electrical receptacles located on the pacemaker analyzer end of the adapter connecting cable that can connect to the industry standard two alligator clips used in all of the various proprietary pacemaker analyzer connecting cables, or alternatively, a specific electrical plug for connection into specific pacemaker analyzers. 
     The clip contacts preferably have a controlled spring force to ensure the adapter does not readily lose electrical connection from the pacemaker analyzer during manipulation. At the same time the clips&#39; spring force is limited and size and geometry, so designed that the lead connector will disengage from the pacemaker lead if the connector cable is accidentally pulled. This is important, because an accidental force on or rapid extraction of the lead, especially an actively fixated lead, may damage cardiac structures or even cause a potentially lethal tear in the heart. 
     The removable grip engages the tiny adapter body to form a single, larger assembly for easier handling with the fingers and locates the adapter&#39;s clip contacts precisely and effortlessly onto the lead connector contacts and sealing rings. In a preferred embodiment of the invention the removable grip, once removed, slides back along the twist-tolerant connecting cable but cannot be removed from the cable. This prevents the grip from getting lost in case it is needed again. Also, this configuration prevents the grip from falling into an open wound, or from being inadvertently left behind in the wound. 
     The present invention has numerous advantages over the prior art. It allows continuous measurement of intracardiac electrocardiogram (IECG) signals and pacing thresholds during manipulation of the lead. It improves the likelihood that the physician will locate the optimal pacing site. It eliminates the need to maneuver alligator clips on and off the lead connector numerous times during implantation, thus further reducing procedure time. The invention connects the lead connector&#39;s electrodes precisely, securely, and with controlled high-quality contact, reducing the chance of a bad connection, loss of the connection, or induced noise from an intermittent connection. The contacts further reduce the potential for damage to the lead connector, especially the soft sealing rings, by the alligator clips. In addition, the absence of repeated connections and disconnections reduces the chance for contamination of the lead connector, which in turn reduces the possibility of infection. Earlier procedural success also reduces the potential for damage to or perforation of the myocardium from prolonged manipulation of the lead inside the heart. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and elements characteristic of the invention are described below and set forth in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to its structure and method of operation, may best be understood by reference to the detailed description which follows and the knowledge of those skilled in the art, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a drawing of a prior art pacemaker and an implantable pacemaker lead. 
         FIG. 2  is a drawing of prior art alligator clips. 
         FIG. 3  is a drawing of prior art alligator clips attached to the electrodes of an IS-1 lead connector. 
         FIG. 4  is a view of the present invention connected to an implantable lead at the distal end and to an electrical device at the proximal end. 
         FIG. 5  is an exploded view of the invention with the grip and adapter engaging each other to form a single assembly. 
         FIG. 6  is an exploded view of the invention, a lead connector, and an implantable pacing lead. 
         FIG. 7  is an exploded view of the grip having been slid down the twist tolerant cable and onto the low-profile adapter to form a single assembly. 
         FIG. 8  is an elevation view of the adapter assembled on an IS-1 connector, including the torque wrench for rotating the tip end of the lead connector electrode. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The Adapter Body, the Grip, and the Adapter Assembly 
       FIGS. 4-8  depict the invention, which connects pacemaker analyzer  196  to pacing lead  120 . In  FIG. 4 , the adapter assembly  165  attaches to the proximal end  122  of pacemaker lead  120 .  FIGS. 6 and 7  depict the low-profile adapter body  150  and grip  160 , and how the lead connector  130  is secured to adapter body  150  with adapter clip contacts  152 ,  154 . The adapter assembly  165  consists of a small body  150  and an attached larger grip  160 , allowing an easier finger grip of the adapter. Both pieces are preferably made from medical grade plastic. The adapter body  150  and grip  160  releasably engage to form adapter assembly  165 . This allows the pacing lead with the small adapter attached to be gripped and twisted without the adapter getting stuck in the hand or being brushed off the lead. The adapter assembly  165  is mounted on distal end  172  of twist-tolerant cable  170  while its proximal end  174  attaches to an electrical receptacle  180  or other type of electrical connector for connecting to equipment such as pacemaker analyzer  196 .  FIG. 6  shows how adapter body  150  with grip  160  removed is constructed to have a low profile so as to protrude less than approximately  3  pacing lead diameters above the lead connector. For example, if the ordinary lead diameter is approximately 3.5 mm, then preferably the low profile is less than about 3×3.5 mm =11.5 mm. 
       FIGS. 6-8  show in detail how adapter assembly  165  is connected to lead connector  130 . Lead connector  130  is, in this example, an IS-1 connector with cylindrical contacts  132 ,  134 . Guide arm  162  of grip  160  helps to align adapter along the lead connector  130 . The guide arm  162  includes slot or notch  166  to accommodate a stylet and includes flanges  167  on the inside of the arm for setting the required standoff of the adapter from the lead connector during attachment. 
     Attaching the Adapter Body and Grip to the Pacing Lead 
     To attach adapter assembly  165  to the lead, the physician first aligns the assembly parallel to and above lead connector  130  with stylet  110  inserted, as in  FIG. 6 , and then tilts guide arm  162  of grip  160  towards the lead connector  130 . He then pushes stylet slot  166  over the stylet  110  and then slides guide arm  162  towards lead  130  until it abuts against the proximal end  139  of connector  130 . In the absence of a stylet, guide arm  162  has flanges  167  on the inside that locate it correctly onto proximal end  139 . This procedure precisely aligns the contacts  152 ,  154  in adapter body  150  with cylindrical contacts  132  and  134  of lead connector  130  respectively. The physician then pushes the rest of adapter assembly  165  onto lead connector  130 , which snaps first the smaller clip contact  154  onto lead connector contact  134  (i.e., onto the narrower tip cylindrical contact on an IS-1) and then snaps clip contact  152  onto lead connector contact  132 . 
     Note that the adapter assembly  165  cannot be connected with incorrect orientation because of the different diameters of the two contact pairs  152 ,  132  and  154 ,  134 . Correct orientation is, however, facilitated by the adapter&#39;s guide arm  162 , which makes correct orientation readily apparent. Also, the outer part of the grip  160  may be marked, or shaped to indicate the correct orientation. For example, it could be wider at the distal end and narrower at the proximal end. In addition, adapter body  150  could have orientation marking or shaping for instances when it is positioned on the pacemaker lead connector  130  without grip  160  in place. Further, the receptacle  180  could also be marked, so that the electrical contacts are identified with the corresponding lead connector electrodes. 
     Other embodiments of the device could combine the alignment and placement features of the grip  160  and the adapter body  150  into one part. For example, guide arm  162  could be integral with the adapter  150 ; it could be hinged; or, it could be designed to snap off, once alignment on the pacemaker lead had been achieved. 
     The Adapter Body on the Lead 
     Once adapter  165  is connected to lead connector  130 , grip  160  can be removed. The design of grip  160  allows it to be gently twisted off the adapter body  150  (removal not shown). Grip  160  is then slid along cable  170  away from the adapter body  150 , which remains attached to lead connector  130  by clip contacts  152 ,  154 . In the case of an IS-1 lead connector, the ridges and valleys of stops  210 ,  220  in adapter body  150  interlock with sealing rings  133 ,  135  on the pacing lead connector  130 . These features prevent adapter body  150  from sliding along its longitudinal axis off lead connector  130 . 
     The present invention includes flexible lead connector holders, which in the preferred embodiment are clip contacts  152 ,  154  that have a spring force that releasably retains or holds lead connector  130 . Clip contacts  152 ,  154  are preferably fabricated from a biocompatible, flexible, conductive metal such as surgical spring steel such as PH17. The clip contacts are approximately 0.2 mm to 0.3 mm thick. They are shaped into partially open tubes with diameters of approximately 2.65 and 1.6 mm and openings of approximately 2.1 mm and 0.95 mm. The preceding dimensions correspond to contacts that will fit an IS-1 connector, with the smaller dimensions corresponding to the IS-1 tip electrode. 
     The contacts must securely hold lead connector  130  yet have a controlled breakaway force that permits the contacts  152  and  154  to snap off the lead connector contacts  132 ,  134  if excessive force is applied to the adapter. Such force, if transmitted to an implanted lead, and especially one that is actively fixated, could damage cardiac structures. The preferred breakaway force is approximately 300-400 gm or 3-4 Newtons. The amount of breakaway force is controlled by the design of the lead connector holders, which in the preferred embodiment are clip contacts  152 ,  154 . 
     Contacts can alternatively be constructed from a shaped, spring metal wire such as nitinol or beryllium-copper alloy. Other configurations with other metal contacts can perform the same function. For example, the sheet metal contacts could be configured as a set of three leaves or fingers so that electrical contact is made at a number of points. In the preferred embodiment of the invention, contacts  152 ,  154  perform the dual function of releasably retaining or holding lead connector  130  in adapter  150  while also providing electrical contact to maintain a continuous electrical signal. Other embodiments of the invention also exist. For example, contacts  152 ,  154  could simply be lead connector holders made of plastic or some other flexible material and located differently than shown. Meanwhile additional electrical contacts, separate from the structure that is releasably retaining lead connector  130 , could provide the necessary conductivity for the electrical signals. 
       FIGS. 5-8  demonstrate an additional advantage of the present invention in relation to active fixation leads.  FIG. 6  shows how contact  154  in adapter body  150  is narrower than contact  152  and is located flush with edge of adapter body  150 , leaving a portion (width “A”) of the lead connector&#39;s proximal tip contact  134  uncovered. This configuration permits access with a small torque wrench  115 , typically supplied-in kits with active fixation leads, for rotating the tip contact to screw distal tip electrode  124  (see  FIG. 4 , corkscrew tip not shown) of lead  120  into the heart. For the first time in clinical practice this allows the continuous monitoring of a cardiac electrogram while the physician screws in the tip of an actively fixated lead. This improvement will avoid unnecessary heart trauma from a full deployment of the fixing corkscrew, about 10 to 12 turns, if electrical characteristics are unacceptable after the first turn. In the case of a rotating active lead, it should be emphasized that metal contact  154  must maintain good electrical contact with, but not exert excessive force or friction on, the lead connector. Otherwise continuous manipulation could be impeded or the lead contact could be scratched. 
     The electrical spring contacts are designed of steel or other material soft enough and formed without sharp edges, thus preventing damage to the pacemaker lead contacts. Without scratching, scoring, or scraping metal from the pacemaker leads, no residue will occur, metallic or otherwise. In addition, matching ridges and valleys of stops  210 ,  220  inside adapter body  150  protect the outer jacket and sealing rings of the pacemaker. 
     The invention works equally well for unipolar and bipolar lead connectors. In the former case, one contact is electrically inactive. As those of skill in the art will appreciate, the invention is not necessarily limited to IS-1 connectors, and could easily be adapted to other connectors. The adaptation to other pacemaker connectors could be in the form of a different size for each type of pacemaker connector or a single device with a range of fittings to allow it to be used with a number of different pacemaker connector sizes. 
       FIG. 4  includes another significant feature of the present invention: the twist-tolerant connecting cable  170  which uses a thin, floppy cable or wire to allow unimpeded manipulation of pacing lead  120 . The preferred thickness of the cable is on the order of 1.5-2.5 millimeters, with a PVC jacket and a preferred length of about 1.5 meters. The cable should be long enough, thin enough, and flexible enough to allow manipulation of the implantable lead while readily absorbing the twisting caused by the rotation of the lead-connector assembly. At the same time the cable should not apply more than a minimal torque to the connection between the lead and the IS-1 connector, and preferably it should not be so long that it easily drags on the floor. Cable length, however, could reasonably vary from 1 to 2 or more meters, depending on the set-up in the implanting laboratory. The conductors in  170  should not be too thin, which would add significant resistance to the electrical circuit. Cable construction may employ two parallel or twisted pair of 28-32 AWG conductors with a tough but thin, pliable insulation jacket. A PVC jacket is preferred, because silicone rubber is typically not robust enough. PET and Teflon are stiffer than the PVC, and therefore less desirable. 
     Other Aspects of the Invention 
     Those of skill in the art will understand and appreciate that variations of the present invention can be made without departing from the spirit and scope of the claims. For example, in the preferred embodiment grip  160  is permanently attached to cable  170  so grip  160  slides between clip  150  and receptacle  180 . The invention, however, should not be so limited. While different manufacturers of pacemaker analyzers have different sockets for accepting cables, most are equipped with cables terminated with alligator clips, such as alligator clips  192 ,  194  that would connect to receptacle  180 . Here, too, the invention should not be limited to what is described. Twist-tolerant cable  170  could be configured to connect directly to an electrical device like a pacemaker analyzer, or even to connect wirelessly. If the invention is configured to include a connection at distal end  174  of cable  170 , the connection need not be limited to the electrical receptacle  180  or the alligator clips  192 ,  194 . 
     One preferred embodiment of the invention may be supplied as an inexpensive, sterilized, and disposable unit for single use. During normal use, assembly  165  and twist tolerant cable  170  remain in the sterile field. Receptacle  180  may be non-sterile, and alligator clips  192 ,  194  and wires  197 ,  198  need not be sterilized. It is intended, however, that the scope of the invention cover a device in which some, all, or none of the invention is reusable. 
     In another configuration the invention or some components of the invention could be pre-connected and pre-packaged together with the pacemaker lead. Furthermore, this invention is not limited to permanent pacemaker leads. It can also be potentially utilized with the leads used with temporary pacemakers or indeed any electrical lead placed within the body for either therapeutic or diagnostic use. 
     Terms such as lead, electrode, contact, and connector sometimes have different or overlapping meanings to physicians, equipment designers, and others of ordinary skill in the art. The meaning will sometimes depend on the context in which those terms are used. For example, contacts  132 ,  134  of lead connector  130  may also be referred to as electrodes or electrode contacts. Similarly, contacts  152 ,  154  may be referred to as contacts, clips, springs, electrodes, or connector holders, depending upon the context. Terms such as connected can have a broad meaning. For example, in  FIG. 2  alligator clips are directly connected (mechanically and electrically) to wire or electrode  47 . In  FIG. 5 , pacemaker analyzer  196  is connected (electrically but not mechanically) to pacing lead  120 . In clinical practice, lead connector  130  is sometimes referred to simply as the lead. It will be clear to those of skill in the art how those terms are used in the art and in the present context to describe the invention. 
     While the present invention has been described in conjunction with specific, preferred embodiments, it will be evident to those of skill in the art that alternatives, modifications, and variations of the invention are possible. Therefore, it is contemplated that the appended claims will embrace any such alternatives, modifications, and variations of the invention, which will fall within the spirit and scope of the claims.