Noninvasive evaluation of pacemaker circus movement tachycardias

Programming a long paced atrioventricular interval may be risky in DDDR pacing

In patients with intermittent AV block and dual chamber pacemakers, a long paced AV interval of 200 msec or more can be selected to prolong pulse generator life (by avoiding the ventricular pace output) and to enable a more physiological and hemodynamically superior activation sequence. This case report describes the potential risks of programming a long paced AV interval in a patient with a DDDR pacemaker. T wave pacing, as described here, can occur if the conducted QRS complex is not sensed because it occurs during the ventricular blanking period (delivery of the atrial stimulus). This can be initiated by the mechanisms that induce apparent and actual P wave undersensing of the conducted QRS complex. In this case report apparent P wave undersensing and subsequent T wave pacing with ventricular capture (in a patient with intermittent AV block) occurred frequently during an exercise test done in the DDDR mode with a paced AV interval of 200 msec, according to the clinical evaluation protocol.

Demonstration of the feasibility of implantation of a skeletal muscle pulse generator for fecal incontinence in a patient with an implanted unipolar DDD pacemaker

Electromagnetic fields and myopotentials from skeletal muscle may interfere with the function of a cardiac pacemaker. A 65-year-old woman with a unipolar DDD cardiac pacemaker underwent dynamic graciloplasty (transposition of the gracilis muscle around the anal canal and subsequent implantation of a bipolar pulse generator to stimulate the gracilis muscle), for the treatment of fecal incontinence. This gracilis pulse generator is turned "off" with an external magnet to allow defecation. Appropriate functioning of these two pulse generators (the cardiac pacemaker and the gracilis pulse generator) was tested during implantation of the gracilis pulse generator and afterwards. It was demonstrated that the combination could be used safely in this patient.

Repetitive reentrant and non-reentrant ventriculoatrial synchrony in dual chamber pacing

Repetitive retrograde ventriculoatrial (VA) conduction in patients with dual chamber pacemakers may cause two forms of VA synchrony. (1) Endless loop tachycardia (pacemaker-mediated tachycardia) or repetitive reentrant VA synchrony occurs when the pacemaker senses retrograde P waves. Appropriate programming can prevent pacemaker reentrant tachycardia in almost all cases. However, the measures used to control tachycardia may themselves create new problems. (2) AV desynchronization arrhythmia or repetitive non-reentrant AV synchrony occurs when the pacemaker does not sense retrograde P waves. In this form of VA synchrony, the atrial stimulus is ineffectual because it falls in the atrial myocardial refractory period generated by the preceding unsensed retrograde P wave. A long atrioventricular interval and a relatively fast lower rate (or sensor-driven rate with DDDR pacing) favor the development of AV desynchronization arrhythmia and its unfavorable hemodynamic consequences.

Orthodromic and antidromic pacemaker circus movement tachycardia

Pacemaker circus movement tachycardia (PCMT) during DDD pacing is usually sustained by retrograde natural and antegrade electronic atrioventricular (AV) conduction. As PCMT is often initiated by a ventricular premature beat (VPB) one method of its prevention is the programming of an atrial stimulus synchronously following a ventricular extrasystole. A patient is described with preserved antegrade, but without retrograde, i.e., VA, conduction. The optional pacemaker mode of synchronous atrial stimulation following a VPB caused an unusual PCMT sustained by retrograde electronic and antegrade natural AV conduction. This PCMT is similar to a natural reentry tachycardia, the most common variety of which (based on retrograde conduction) is termed antidromic and that which we describe is orthodromic.

Long-term antitachycardia pacing experience for supraventricular tachycardia

A pacemaker was used to control drug-resistant reentrant supraventricular tachycardia (SVT) in 40 patients. An antitachycardia pacemaker was implanted in 37 for SVT; in one for ventricular tachycardia that could also be used to terminate SVT; in one SVT could be terminated with an activity rate variable pacemaker; and in one a DDD pacemaker was used for prevention and termination of SVT. Twenty patients had AV nodal reentrant tachycardias, eight had tachycardias due to a concealed accessory pathway, eight had a Wolff-Parkinson-White syndrome, three had reentrant atrial tachycardias, and one had atrial flutter. Twenty-two patients were paced from the right atrium, five from the coronary sinus, ten from the right ventricle, and three had a DDD pacemaker. During a total follow-up period of 1,503 (mean 38) months an estimated 16,240 episodes of tachycardia were terminated promptly at home, 58 required several attempts, 57 episodes lasted longer than 30 minutes but did not require medical attention, and 11 required hospital admission. Hospital admission for SVT decreased from one per patient-month (in the 3 months before implantation) to 1 per 137 patient-months after implantation. Additional reentrant tachycardias occurred in 13 patients. Antiarrhythmic drug therapy in combination with a conservative antitachycardia pacing mode was required in four patients paced from the atrium to avoid pacing induced atrial fibrillation. Antiarrhythmic drug therapy was used in 42% of patients to help control SVT.

CONCLUSIONS

(1) Drug-resistant SVTs can be safely and effectively managed on the long-term with antitachycardia pacemakers. (2) Rapid termination of SVT improved the quality-of-life significantly by avoiding prolonged episodes of tachycardia and repetitive hospital admissions.

Pacemaker endless loop tachycardia: termination by simple techniques other than magnet application

PURPOSE

Pacemaker endless loop (or reentrant) tachycardia (ELT) is often terminated by conversion to the asynchronous mode of pacing by simply placing a magnet over the implanted atrial tracking (DDD or VDD) pacemaker. We investigated three other simple methods of ELT termination--chest wall stimulation (CWS), provocation of myopotential oversensing, and chest thumping--that may be useful when the arrhythmia is unresponsive to magnet application or a magnet is unavailable.

PATIENTS AND METHODS

A modified CWS technique using an external pulse generator (pulse width = 40 msec) ordinarily used for transcutaneous cardiac pacing was tested in 74 patients (40 with unipolar and 34 with bipolar DDD devices). CWS inhibited the ventricular channel of all DDD pacemakers easily and reliably. CWS was then applied during ELT in 20 patients (10 with unipolar and 10 with bipolar DDD devices). Provocation of myopotential oversensing by the ventricular channel was attempted during ELT in 10 patients with unipolar DDD pacemakers. Chest thumping was tried during ELT in six patients.

RESULTS

CWS by the modified technique terminated ELT in all patients in whom the arrhythmia was induced. Myopotential oversensing resulted in successful ELT termination in six of the 10 patients. ELT was successfully terminated by chest thumping in four of six patients.

CONCLUSION

These simple techniques provide effective ways of ELT termination other than magnet application, and may be easily applied by physicians unfamiliar with the complexities of contemporary DDD pacemakers and their programmers.

Magnet unresponsive pacemaker endless loop tachycardia

Endless loop tachycardia is a well-known complication of DDD pacing and is almost invariably terminated by conversion to the asynchronous DOO mode upon application of a magnet over the pulse generator. Occasionally magnet application is ineffectual because the ventriculoatrial (VA) synchrony of endless loop tachycardia is converted directly or indirectly to an atrioventricular (AV) desynchronization arrhythmia, another form of VA synchrony. This occurs when a paced ventricular beat engenders an unsensed retrograde P wave and the continual delivery of an ineffectual atrial stimulus during the atrial myocardial refractory period creates self-perpetuating VA synchrony. Upon magnet removal, AV desynchronization arrhythmia reverts immediately to endless loop tachycardia. In the absence of access to programmers, magnet unresponsive endless loop tachycardia can be easily and reliably terminated by chest wall stimulation through inhibition of the ventricular channel of the DDD pulse generator.

Termination of ventricular tachycardia by chest wall stimulation during DDD pacing. A report of two cases

This report describes the use of chest wall stimulation (CWS) for the termination of ventricular tachycardia in two patients with dual chamber pulse generators functioning in the DDD mode. Rapid CWS induced burst ventricular pacing when CWS was selectively sensed by the atrial channel, whereupon the pulse generator triggered its ventricular output. In this way, by programming the pulse generators to the maximum upper rate, this CWS technique produced burst ventricular pacing at a rate of 175 to 180/minute that successfully terminated ventricular tachycardia in both patients. The same CWS technique also initiated ventricular tachycardia by burst ventricular pacing. This CWS technique may be useful for the termination of relatively slow ventricular tachycardia in patients with DDD pulse generators when the maximum rate of ventricular pacing cannot be otherwise increased.

Computer simulation of cardiac pacing

A mathematical model of the cardiac conduction system, including external pacemakers, has been developed. The heart is modeled as a network in which the impulse propagation is described by differential equations; several arrhythmia-generating mechanisms, such as modulated parasystole, reflection, macro and micro re-entry and block, can be simulated. Different kinds of pacemaker modes have been incorporated in the model, thus making it possible to simulate the interaction between the heart and the pacemaker. The model can be tuned by the user according to electrophysiological data so that pacemaker programs can be tested under different underlying conditions. During a simulation, the program generates ECG signals and pacemaker diagnostic diagrams. This model can be used for training and testing, and also as a support system when searching for the optimal pacing therapy for a particular patient.

Orthodromic pacemaker circus movement tachycardia

We report on the case of a 33-year-old woman with sick sinus syndrome who had an orthodromic pacemaker circus movement tachycardia (PCMT), with antegrade atrioventricular (AV) conduction and a retrograde pathway by means of a DDD (AV universal) pacemaker. This PCMT was provoked and sustained by premature ventricular contraction-synchronous atrial stimulation (PVC-SAS), which is a new feature for the prevention of antidromic PCMTs. The conditions for occurrence of this tachycardia were: PVC-SAS; atrial undersensing; first degree AV block. Recommendations for prevention of this pacemaker-mediated tachycardia are given.

Merits of various antipacemaker circus movement tachycardia features

Pacemaker circus movement tachycardia (PCMT) was a significant problem in first generations of DDD pacemakers. Programmability of the atrial refractory period proved to be an effective tool to prevent PCMT except in patients with very long ventriculoatrial (V-A) conduction intervals, because a long atrial refractory period severely limits the maximum tracking rate. In these patients, extension of the atrial refractory period after a VPB, bipolar atrial sensing, adaptation of atrial refractory period to atrial rate, and VPB synchronous atrial stimulation helped limit the incidence of PCMT. Rate smoothing and fallback behavior have given rise to other forms of PCMT. Once initiated, PCMT can be terminated by a single P wave or by means of an appropriately timed atrial stimulus. Recognition by means of continued upper rate pacing may not be helpful in patients with a long V-A conduction interval because their PCMT rate will be low, thus requiring a low upper rate to trigger. Therefore, absolute prevention of PCMT has not yet been achieved, but PCMT is no longer a significant problem in DDD pacing; recognition of PCMT should not be related to the ventricular upper rate limit.

Clinical usefulness of chest wall stimulation in patients with automatic tachycardia-terminating pacemakers

Chest wall stimulation may be used diagnostically and therapeutically in the follow-up of patients with automatic tachycardia-terminating pulse generators. In this report, we present our experience with chest wall stimulation in the follow-up of five patients with implanted Intermedics CyberTach 60 automatic tachycardia-terminating pacemakers (three for supraventricular tachycardia and two for ventricular tachycardia). Chest wall stimulation delivered at a rate faster than the rate detection criterion of the pulse generator often precipitates reentry tachycardia, making it possible to perform a noninvasive electrophysiologic study. In addition, chest wall stimulation may be invaluable in the termination of reentry tachycardia which is unsensed by an implanted pulse generator either because the rate is too slow, or below the rate detection criterion, or because the intracardiac signal does not attain the sensitivity of the pulse generator.

Paradoxical induction of endless loop tachycardia by magnet application over a DDD pacemaker

It is well known that removal of a testing magnet from a DDD pulse generator may cause endless loop tachycardia in patients with retrograde ventriculoatrial conduction; application of the magnet then terminates the tachycardia. We have observed the opposite response to the magnet and in this report we describe the paradoxical induction of endless loop tachycardia by magnet application over a DDD pulse generator and its persistence despite repeated removal and reapplication of the magnet. This unusual behavior occurred only in the "magnet off" function and is due to magnet-induced signals sensed by the atrial channel circuitry.

Improved method for evaluating ventriculoatrial conduction before implantation of atrial-sensing dual chamber pacemakers

Pacemaker-mediated tachycardia may occur when a spontaneous ventricular premature depolarization is retrogradely conducted to the atrium with a ventriculoatrial (VA) interval that exceeds the atrial refractory period of an atrial-sensing dual chamber pacemaker. Previous methods for evaluating VA conduction have failed to predict clinical occurrences of pacemaker-mediated tachycardia. In this study, maximal VA intervals after ventricular extrastimuli during atrial or atrioventricular (AV) sequential pacing were compared with intervals measured by the standard method of ventricular pacing. VA intervals were 201 +/- 53 ms during ventricular pacing and 224 +/- 52 ms after ventricular extrastimuli during atrial pacing (p = NS). VA intervals were 305 +/- 77 ms after ventricular extrastimuli during AV sequential pacing and were longer than VA intervals during ventricular pacing (p less than 0.001) or after ventricular extrastimuli during atrial pacing (p less than 0.01). Thus, the ventricular extrastimulus technique during AV sequential pacing reveals substantially longer VA intervals than does ventricular pacing and explains why pacemaker-mediated tachycardia might occur when pacemaker atrial refractory periods are designed or programmed according to VA intervals measured only during ventricular pacing.

Noninvasive evaluation of retrograde conduction times to avoid pacemaker-mediated tachycardia

Pacemaker-mediated tachycardia is a potential complication of atrioventricular (AV) universal DDD pacemakers when retrograde ventriculoatrial (VA) conduction is slower than the postventricular-atrial refractory period of the pulse generator. The propensity for pacemaker-mediated tachycardia was noninvasively assessed in 17 patients with a unipolar DDD pacemaker using chest wall stimulation. Low amplitude stimuli were delivered to chest wall electrodes through a programmed stimulator. Using this method, 13 of the 17 patients were found to have absent VA conduction or VA conduction time less than the postventricular-atrial refractory period. In the four patients with noninvasively measured VA conduction time greater than the postventricular-atrial refractory period, sustained pacemaker-mediated tachycardia was induced. Reprogramming of pacemaker parameters prevented repeat induction of pacemaker-mediated tachycardia in only one of four patients. The three remaining patients had clinical pacemaker-mediated tachycardia and underwent pacemaker programming to the DVI mode. A total of 13 patients continue to use DDD mode after a mean follow-up period of 9.5 +/- 5.4 months. Invasive measurement of VA conduction was performed in 13 of the 17 patients. The noninvasive method accurately predicted the invasive measurement in each case. Noninvasive evaluation of VA conduction accurately predicts the propensity for pacemaker-mediated tachycardia under a variety of clinical conditions. Serial testing can be performed after pacemaker reprogramming or drug intervention. Noninvasive evaluation of retrograde VA conduction should predict most clinical episodes of pacemaker-mediated tachycardia.

Programmability in DDD pacing

Safe and reliable DDD pacemakers with multiple programming capabilities have now been developed. Certain programmable parameters are basic, including mode, voltage (or current) output, pulse width, sensitivity and refractory periods in each chamber. Upper rate response as well as low rate settings and A-V delays are equally important. In certain models, the ability to program the blanking period has proven quite useful. The interrelationship between all these functions will assure the smooth overall performance of these sophisticated devices.