Ventricular tachycardia produced by a normally functioning AV sequential demand (DVI) pacemaker with "committed" ventricular stimulation

A case of a pseudomalfunction of a DDD pacemaker

DDD pacemaker pseudomalfunction occurred in a 65-year-old man. This was due to premature ventricular contraction (PVC) response option and cross-talk detection window, which are designed to protect against pacemaker related tachycardia or cross-talk. Pseudomalfunction disappeared by eliminating PVC response option.

Therapeutic and diagnostic benefits of intentional crosstalk mediated ventricular output inhibition

Ventricular output inhibition due to crosstalk is generally considered unsafe and something that should be avoided. Special circuits have been incorporated in some dual chamber pacing systems to absolutely prevent this from happening. However, in patients with intact atrioventricular conduction, crosstalk mediated ventricular output inhibition can be beneficial to the evaluation and management of the patient. Utilizing this technique, one can achieve single chamber atrial paced rates which greatly exceed the rates allowed by lower rate limit programming to facilitate an assessment of the integrity of AV nodal conduction and to both convert and suppress some pathological tachyarrhythmias. The methods of achieving crosstalk and its utilization in four patients is discussed in this report.

Noise reversion of a dual chamber pacemaker without noise

Three patients are reported whose DDD pacemakers reverted to the asynchronous mode in the absence of skeletal muscle or electromagnetic (EMI) interference. In all three cases, the basic cardiac rhythm was atrial fibrillation with fast ventricular response due to intrinsic AV conduction. Noise reversion was triggered by the patients' own ventricular activity at cycle lengths shorter than the ventricular refractory period of the pulse generator. In one patient, asynchronous AV sequential pacing during atrial fibrillation was noted shortly after resuscitation from ventricular fibrillation; however, the initiation of the malignant ventricular arrhythmia by the pacemaker remains unproven. The mechanism of noise reversion by rapid cardiac activity and possible solutions to the problem by adequate pacemaker design are discussed.

Atrial pacing bigeminy: a manifestation of crosstalk

Atrial pacing bigeminy, defined as atrial pacing with alternating short and long cycle lengths, was recorded in two out of five DDD-pacemaker implants. Another fascinating feature, the lowering of the effective pacing rate after programming to a higher rate, occurred in one patient. Both phenomena can be explained by crosstalk; appropriate programming resulted in normal DDD-function in all cases. These observations in our patients have led to some interesting conclusions regarding multiprogrammability and nominal settings.

Pacemaker-mediated tachycardia initiated by coincident P-wave undersensing and ventricular blanking period

Pacemaker-mediated tachycardias (PMT) have received much recent attention. We describe the course and treatment of a 60-year-old man with an AV universal (DDD) pacemaker who developed a pacemaker-mediated tachycardia. The tachycardia was initiated by the coincidence of an unsensed P-wave, a QRS that was also not sensed due to the ventricular blanking period, and a short right ventricular myocardial effective refractory period. Treatment consisted of reprogramming the atrial sensitivity of the device. Physicians should be aware of the potential for the ventricular blanking period to participate in the initiation of pacemaker mediated tachycardias.

Indications for and management of cardiac pacemakers

Cardiac pacemakers are now at the forefront of medical technology. The ability to provide pacing therapy adapted to the individual patient has resulted in significant patient benefit. Although the indications for cardiac pacing have changed little over the past decade, the types of pacemakers available for specific bradyarrhythmias have proliferated in leaps and bounds. This technology is complex and sophisticated and requires in-depth knowledge for appropriate utilization. Artificial replacement of the human conduction system is now a reality. Still other advances remain to be achieved in this area, mainly in sensor technology and pacing therapy for tachyarrhythmias. At the current rate of development, the outlook is indeed promising.

Dual chamber pacemakers: upper rate behavior

Upper rate management of a dual chamber pacemaker requires sensing of the atrium and limitation of ventricular response to desired levels. Limitation of ventricular rate response is accomplished by setting atrial channel refractoriness which consists of two separate and continuous intervals, the atrioventricular interval (AV interval) and the atrial refractory interval, after the ventricular pace or sense event (AR interval). A P-wave that falls within the total atrial refractory interval (TARI) remains unsensed and one that falls beyond the TARI is sensed. If the upper rate limit interval (URI) is programmed to equal the TARI, the upper rate limit will occur by development of sudden AV block. If the URI is of greater duration (lower allowed rate) than the TARI, the difference in interval between the two is the Wenckebach interval (WI) and is the duration of a response plateau, when the atrial coupling interval is less than the upper rate interval. All dual chamber timing cycles can be interpreted in terms of atrial refractoriness and upper rate limitation with consideration of the lower rate interval, and the ventricular refractory and blanking intervals.

Interpretation of dual chamber pacemaker electrocardiograms

A diagramming system has been developed to assist in interpreting dual chamber pacemaker electrocardiograms. The system is based on the ladder diagram principle but uses two separate ladders, one for the ECG allowing proper representation of atrial A-V and ventricular activation, and a second ladder diagram below it for pacemaker events. The system is applicable to all current single and dual chamber pacing modes and is easy to draw. The ladder diagram allows the logical sequence of timing events to be easily illustrated, and pacemaker malfunction becomes clearly recognizable as a conflict between the ECG events ladder and the pacemaker timing ladder. The system is easy to apply and may eventually prove suitable for automatic generation by computer utilizing sophisticated pacemaker telemetry.

Pseudo failure of sensing in patients with universal pacemakers and junctional rhythms

Ventricular fibrillation has been only rarely observed as a complication of cardiac pacing after the advent of demand pacemakers. Automatic AV sequential pacing (DDD) may provide the setting for ventricular fibrillation in patients with junctional rhythms. In this report we present two patients with implanted DDD pacemakers in whom ventricular pacemaker spikes were seen occurring on top of the T wave during episodes of junctional rhythm. This apparent lack of sensing of QRS complexes does not represent pacemaker malfunction, but rather, is the result of physiologic lack of sensing (blanking) which occurs 56 to 100 msec. following the output of the atrial and ventricular channels. During junctional rhythm when the atrial spike occurs at the beginning of a QRS complex the ventricular channel is blanked and does not sense the intrinsic ventricular activity and thus, ventricular output occurs during repolarization. Increasing the maximum pacemaker rate and decreasing the AV delay will reduce the chance occurrence of this phenomenon.