Method and apparatus for detecting left ventricular lead displacement based upon EGM change

Displacement or migration of a left ventricular lead located within the coronary sinus or coronary veins of the heart is detected by comparing an electrogram (EGM) waveform pattern from the lead with a stored baseline EGM waveform pattern. Based upon the extent of lead migration, if any, a lead displacement may produce an annunciating response. The patient may be alerted, an electrical stimulus applied through the lead may be adjusted to compensate for lead migration, or an alternative electrode on the lead may be used for EGM sensing and pacing.

BACKGROUND OF THE INVENTION

The present invention relates generally to cardiac rhythm management systems. In particular, the present invention relates to detection of lead displacement or migration of a sensing/pacing lead, such as a left ventricular lead within the coronary sinus, coronary veins or one or more epicardial or pericardial locations.

In 1957, the first wearable, battery-powered cardiac pacemaker was used to keep a young patient alive. The first implantation of a permanent pacemaker followed in 1958. Since then, pacemaker technology has continually improved and has become the treatment of choice to treat symptoms due to bradycardia. The pacing lead is usually introduced transvenously into the right atrium or right ventricle, and electrical pulses from the implanted pacemaker are applied by the lead via metal electrodes that are in contact with cardiac muscle.

More recently, cardiac resynchronization therapy using bi-ventricular pacing has been introduced to treat patients with heart failure. More than twenty million people worldwide suffer from heart failure, with about two million new cases diagnosed each year. With some patients, heart failure disease affects the synchronous beating action of the left ventricle and right ventricle until the left ventricle cannot pump blood efficiently to supply the body with oxygen and nutrients. These patients tend to tire easily, have a poor quality of life, and their health may deteriorate rapidly resulting in a need of a heart transplant or death.

Cardiac resynchronization therapy helps to coordinate the left ventricle and right ventricle of the heart in patients with moderate to severe heart failure. It helps to improve the pumping power of the heart, can make the patients feel better, increase their energy levels, and improve their exercise capacity.

Cardiac resynchronization therapy systems typically include a left ventricular lead to provide stimulation to the left ventricle, together with conventional pacing leads placed in the right atrium and right ventricle.

The left ventricular lead is oftentimes introduced via the coronary sinus into the coronary venous system to achieve appropriate (synchronous) left ventricular stimulation although a variety of epicardial or pericardial locations can also be utilized. Different patients have different cardiac venous anatomy. As a result, delivery of a left ventricular lead can be challenging. In addition, heart failure can result in cardiac remodeling or change of shape. In contrast to the electrodes of the right atrial pacing lead and the right ventricular pacing lead, which are typically affixed to cardiac muscle by a fixation mechanism such as tines or a screw tip, the electrode (or electrodes) of the left ventricular lead are positioned within a blood vessel and are not affixed by a fixation mechanism. Given the location and the lack of tissue fixation, maintaining the position of the left ventricular lead on a long-term basis can be difficult to achieve. The inventors suggest that in approximately twenty percent (20%) of patients, the left ventricular lead suffers some dislocation, and stimulation may become less effective because the electrode is no longer positioned in the clinically optimal position.

BRIEF SUMMARY OF THE INVENTION

Dislodgement or migration of a lead is detected by comparing an EGM pattern representing heart activity sensed by an electrode of the lead with a previously stored baseline EGM pattern. The baseline pattern represents a characteristic EGM from the electrode of the lead when the electrode was at a position that provided appropriate stimulation.

DETAILED DESCRIPTION

FIG. 1shows cardiac resynchronization therapy (CRT) system10, which restores ventricular synchronization in heart H by delivering pacing pulses to one or more chambers of heart H. InFIG. 1, heart H is shown in a partially cutaway view illustrating right atrium RA, left atrium LA, right ventricle RV, left ventricle LV, coronary sinus CS, and coronary venous system CVS.

CRT system10includes pacemaker12, right atrial (RA) lead14, right ventricular (RV) lead16, and left ventricular (LV) lead18. As shown inFIG. 1, pacemaker12includes housing or canister20, header22and can electrode24. The circuitry and power source of pacemaker12are located within housing20. The circuitry communicates with leads14,16, and18through electrical connectors within header22. Can electrode24is formed on or is a part of the outer surface of housing20, and acts as a remote indifferent electrode with respect to one or more of the electrodes carried by leads14,16, and18.

As shown inFIG. 1, RA lead14is a bipolar endocardial lead that is passed through a vein into right atrium RA of heart H. RA lead14includes lead body30, connector32, distal tip attachment mechanism34, distal tip RA pace/sense electrode36, and proximal ring RA pace/sense electrode38. Lead body30contains a pair of electrically insulated conductors, which extend from connector32to pace/sense electrodes36and38. Connector32is inserted into a connection bore within header22to provide an electrical connection between pace/sense electrodes36and38and the circuitry within pacemaker housing20. The distal end of RA lead14is attached to the wall of right atrium RA by attachment mechanism34, which may be, for example, a screw or tined fastener.

RV lead16is a bipolar endocardial lead that is passed through right atrium RA and into right ventricle RV. RV lead16includes lead body40, connector42, distal tip attachment mechanism44, distal tip RV pace/sense electrode46, and proximal ring RV pace/sense electrode48. Lead body40of RV lead16contains a pair of electrically insulated conductors, which extend from connector42to pace/sense electrodes46and48. Connector42is at the proximal end of RV lead16, and is inserted into a connection bore of header22to provide an electrical connection between the pacemaker circuitry within housing20and pace/sense electrodes46and48. Distal tip electrode46is placed in contact with the apex of right ventricle RV and is fixed in place by attachment mechanism44. LV lead18includes lead body50, connector52and LV pace/sense electrode54. Lead body50contains an electrically insulated conductor, which extends from connector52at the proximal end of lead18to electrode54at the distal end of lead18(although other unipolar and bi-polar pace/sense vectors can be used). Connector52is inserted into a bore within header22to provide electrical connection between LV pace/sense electrode54and the pacemaker circuitry within housing20.

In this embodiment, LV lead18is passed through right atrium RA into coronary sinus CS and then into a cardiac vein of coronary vein system CVS. LV lead18is shown as a unipolar lead, so that sensing of electrogram (EGM) signals and application of pacing pulses through LV pace/sense electrode54is performed with respect to one of the other electrodes24,36,38,46, or48of CRT system10. Alternatively, LV lead18can carry more than one electrode and perform as a bipolar lead or a multipolar lead.

LV lead18is configured so that LV pace/sense electrode54will lodge within a cardiac vein and will remain in position despite having no mechanical attachment mechanism (e.g., embedded into myocardial tissue or a portion of a vessel wall), comparable to attachment mechanism34of RA lead14or attachment mechanism44of RV lead16. LV pace/sense electrode54is positioned within the cardiac vein during implantation to achieve desired synchronous pacing performance.

Experience has shown that pacing leads can dislodge from their implanted position. This is particularly the case with a left ventricular lead placed within the coronary venous system CVS. With the present invention, dislodgement or migration of LV lead18is detected by EGM pattern comparison. At the time of implantation, when LV pace/sense electrode54is in its desired final position, an EGM waveform is sensed and stored within memory of pacemaker12. This stored EGM waveform acts as a baseline (paced or sensed) EGM pattern from which periodic comparison can be made.

At time intervals selected by pacemaker12(or selected by an external device in communication with pacemaker12), an algorithm stored in pacemaker logic causes an EGM waveform to be sensed, stored, and then compared with the baseline pattern. The interval can be programmed by the physician, and can produce a beat-to-beat comparison or a comparison after an elapsed time period, such as every minute, every hour, every day, every week, or longer. Although the EGM waveform can be sensed and stored at any time desired, periods of inactivity of the patient (e.g. at night while sleeping) may be advantageous to reduce possible noise in the waveform produced by patient movement. In addition, a comparison of the baseline signal collected in the same manner (e.g., with the patient positioned in a prone or supine manner).

Upon recognition of a change in the current EGM pattern with respect to the baseline pattern indicating dislodgement or migration of LV pace/sense electrode54, an annunciating response is produced. This response can be a warning sound or other perceptible signal that indicates to the patient that the patient should visit a physician for further investigation of the electrode location. Alternatively, the annunciating response can cause a change in the pacing pulses applied through LV pace/sense electrode54to compensate for a position change. In still another embodiment, which will be described in more detail with respect toFIG. 7, the annunciating response can cause pacemaker12to switch to a different LV pace/sense electrode that provides an EGM pattern closest to the baseline pattern.

Control system60controls the functions of pacemaker12by executing firmware and program software algorithms stored in associated RAM and ROM. Control system60may also include additional circuitry including a watchdog circuit, a DMA controller, a block mover/reader, a CRC calculator, and other specific logic circuitry coupled together by an on-chip data bus, address bus, power, clock, and control signal lines. Control and timing functions can also be accomplished in whole or in part with dedicated circuit hardware or state machine logic rather than a programmed microcomputer.

Input signal processing circuit62receives signals from RA lead14, RV lead16, LV lead18and can electrode24. The outputs of input signal processing circuit62include digitized EGM waveforms and sense event signals derived from the EGM signals sensed by leads14,16, and18.

Input signal processing circuit62includes a plurality of channels for sensing and processing cardiac signals from electrodes coupled to leads14,16, and18. Each channel typically includes a sense amplifier circuit for detecting specific cardiac events and an EGM amplifier circuit for providing the EGM waveform signal to control system60, where the EGM waveform is sampled, digitized and stored.

Therapy delivery system64delivers cardiac pacing pulses to leads14,16, and18to control the patient=s heart rhythm and to resynchronize heart chamber activation. Delivery of the cardiac pacing pulses by therapy delivery system64is under the control of control system60. Delivery of pacing pulses to two or more heart chambers is controlled in part by the selection of programmable pacing intervals, which can include atrial-atriol (A-A), atrial-ventricular (A-V) and ventricular-ventricular (V-V) intervals.

Therapy delivery system64can optionally be configured to include circuitry for delivering cardioversion/defibrillation therapy in addition to cardiac pacing pulses for controlling a patient=s heart rhythm. Accordingly, leads14,16, and18can additionally include high voltage cardioversion or defibrillation shock electrodes.

Electrical energy for pacemaker12is supplied from battery66through power supply/power on reset (POR) circuit68. This includes power to operate the circuitry controlling operation of pacemaker12, as well as electrical stimulation energy for delivery to heart H, and power for telemetry signal transmissions. Power supply/POR circuit68provides low voltage power Vlo, power on reset (POR) signal, reference voltage VREF, elective replacement indicator signal ERI and high voltage power Vhi (if pacemaker12also has cardioversion/defibrillator capabilities).

Clock signals for operation of the digital logic within pacemaker12are provided by crystal oscillator70and system clock72.

Uplink and downlink telemetry capabilities are provided through telemetry transceiver74and antenna76. External programmer90can receive stored EGM data, as well as real-time generated physiologic data and nonphysiologic data from control system60. In addition, programming data can be supplied from external programmer90to control system60.

FIG. 2also shows magnetic field sensitive switch78and magnetic switch circuit80, which issue a switch closed (SC) signal to control system60when magnet94is positioned over the subcutaneously implanted pacemaker12. Magnet94may be used by the patient to prompt control system60to deliver therapy or to store physiologic data.

FIG. 3shows a block diagram of the operation of the present invention. At the time of implant, leads14,16, and18are moved into position. With LV lead18, LV pace/sense electrode54is advanced until appropriate left ventricular stimulation can be achieved. When LV pace/sense electrode54is at the proper position, a command is provided from external programmer90to control system60to record an EGM from LV pace/sense electrode54. Control system60controls input signal processing circuit62so that an EGM waveform signal from LV pace/sense electrode54is amplified and supplied to control system60, where it is digitized (step100) and stored in memory (step102). The recorded and stored EGM waveform represents a baseline EGM pattern which will be used for later comparison with subsequent EGM patterns derived from LV pace/sense electrode54. Said baseline EGM pattern can be collected with a patient in one or more of a known, preferably repeatable variety of situations (e.g., different body positions, medicinal regimes, pace/sense electrode configurations, and the like).

At the time of digitizing and storing the EGM waveform baseline pattern, control system60may also initiate a transmission of the waveform through telemetry transceiver74to external programmer90, so that the waveform can be reviewed. At the same time, or at a later point in time, the EGM baseline waveform stored in memory is processed by control system60(step104). This waveform processing or analysis can result in derived waveform parameters and characteristics for the EGM baseline pattern which can be used as a basis for comparing the EGM baseline pattern to subsequently generated EGM waveforms. The waveform parameters and characteristics can also be stored for subsequent use, rather than being derived each time a comparison needs to be made.

At a subsequent time, which can be a preset time interval or at a time selected and prompted through programmer90, control system60repeats the process of recording an EGM waveform from LV pace/sense electrode54(step106) and storing the digitized waveform in memory (step108). The current waveform stored in memory is then processed (step110) to derive waveform parameters and characteristics. Those parameters and characteristics are then compared (step112) with similar parameters and characteristics of the baseline EGM pattern. Based upon that comparison, an annunciating response may be generated (step114).

In some embodiments, multiple EGM waveforms are digitized and stored each time a comparison is to be made. The EGM waveforms can be averaged, or selected ones processed, or each can be processed and compared to the baseline.

FIGS. 4A and 4BandFIGS. 5A and 5Billustrate how the present invention can be used to detect migration or dislodgement of lead18. InFIG. 4A, LV pace/sense electrode54is shown in the same position illustrated inFIG. 1. This is the original or baseline position.FIG. 5Aillustrates a baseline EGM pattern derived with LV pace/sense electrode54in the position shown inFIG. 4A.

FIG. 4Bshows LV lead18having been dislocated so that LV pace/sense electrode54has migrated away from its original position to a more proximal position.FIG. 5Bshows corresponding EGM pattern produced with LV pace/sense electrode54in the position shown inFIG. 4B.

FIGS. 5A and 5Bshow differences in EGM patterns as a result of different lead positions. The changing lead position can result in a change in amplitude, a change in slope (up stroke/downstroke), frequency content, and/or time interval between the atrial and ventricular signals. By comparing waveform characteristics of a baseline EGM pattern and the current EGM pattern, a determination can be made as to whether the position of LV lead18(and particularly LV pace/sense electrode54) has changed sufficiently to warrant an annunciating response.

Although in the example shown inFIGS. 4A,4B,5A, and5B the direction of migration was illustrated as being toward coronary sinus CS, the invention is also applicable to dislodgement or migration in the direction of the coronary veins.

To illustrate the effect of different electrode positions within the coronary sinus and coronary veins, an animal experiment was performed. A lead was positioned in the coronary sinus of a goat, and the position of the electrode carried by the lead was changed within the coronary sinus and coronary venous system to determine whether the resulting EGM waveform pattern would change.

FIGS. 6A-6Lrepresent unfiltered bipolar EGM patterns derived with the electrode at 12 different positions within the coronary sinus/coronary veins. The first spike of each pattern refers to atrial activity, and the second spike to ventricular activity. FromFIGS. 6A-6L, it can be seen that amplitude, morphology and timing of the bipolar EGM pattern changes with electrode position. By using multiple parameters or characteristics of the EGM pattern (such as amplitude, shape, waveform, slope, frequency content, and time intervals), change in electrode position can be detected.

FIG. 7shows another embodiment of the present invention which is generally similar to that illustrated inFIG. 1. The difference, as illustrated inFIG. 7, is that LV lead18carries multiple LV electrodes54A-54N rather than a single electrode (LV pace/sense electrode54inFIG. 1). This requires that LV lead18contain a separate insulated conductor for each of the LV electrodes54A-54N.

At the time of implantation, pacemaker12ofFIG. 7is instructed to switch from electrode to electrode among LV electrodes54A-54N, so that the appropriate pacing site can be determined. The LV electrode at that pacing site is then selected for subsequent pacing and sensing. A baseline EGM pattern is derived and stored from the selected LV electrode.

In accordance with the present invention, EGM patterns are derived at a later time for comparison with the baseline pattern. Rather than comparing only one EGM pattern to the baseline, each of the multiple LV electrodes54A-54N can be considered by comparing the EGM pattern from each LV electrode54A-54N with the baseline pattern. The LV electrode producing the EGM pattern that is closest to the baseline pattern can then be selected for subsequent pacing and sensing.

The number, size and spacing of LV electrodes54A-54N depends on the length of possible migration or displacement. A 1 cm movement of LV lead18can have a major effect on the therapy delivered. As an example, with a length of 10 cm possible lead movement, ten ring electrodes of 3 mm length and 6 mm to 10 mm spacing can cover that length. Dislodgement tends to be in the direction of the coronary veins, so that a more proximal LV electrode will move into position to provide the therapy.