Pacemaker-mediated tachycardias: a rapid bedside technique for induction and observation

Cardiology

Emergency cardiac problems are a frequent and significant occurrence in the daily life of the emergency physician. The first part of this article discusses some of the pearls and pitfalls of caring for the cardiac patient ranging from treating wide-complex tachycardia and troubleshooting pacemaker malfunction to diagnosing acute myocardial infarction in the setting of bundle branch blocks. The second part of this article updates the reader on several of the newer technologies and treatments, such as transesophageal echocardiography and intravenous amiodarone, now in use in the emergency department setting.

Atrial arrhythmia management with sensor controlled atrial refractory period and automatic mode switching in patients with minute ventilation sensing dual chamber rate adaptive pacemakers

Although a long postventricular atrial refractory period (PVARP) may prevent the occurrence of pacemaker mediated tachycardias and inadvertent tracking of atrial arrhythmias in dual chamber (DDD) pacing, the maximum upper rate will necessarily be compromised. We tested the feasibility of using minute ventilation sensing in a dual chamber rate adaptive pacemaker (DDDR) to shorten the PVARP during exercise in 13 patients with bradycardias (resting PVARP = 463 +/- 29 msec) to avoid premature upper rate behavior. Graded treadmill exercise tests in the DDD and DDDR modes at this PVARP resulted in maximum ventricular rates of 98 +/- 8 and 142 +/- 3 beats/min, respectively (P < 0.0001), due to chronotropic incompetence and upper rate limitation in the DDD mode, both circumvened with the use of sensor. In order to stimulate atrial arrhythmias, chest wall stimulation was applied for 30 seconds at a rate of 250 beats/min at a mean unipolar atrial sensitivity of 0.82 mV. Irregular ventricular responses occurred in the DDD mode (the rates at a PVARP of 280 and 463 +/- 29 msec were, respectively 92 +/- 5 and 66 +/- 3 msec; P < 0.0001). In the DDDR mode at a PVARP of 463 +/- 29 msec, regular ventricular pacing at 53 +/- 2 beats/min occurred due to mode switching to VVIR mode in the presence of repetitive sensed atrial events within the PVARP. One patient developed spontaneous atrial fibrillation on follow-up, which was correctly identified by the pacemaker algorithm, resulting in mode switch from DDDR to regular VVIR pacing and preservation of rate response. In conclusion, sensor controlled PVARP allows a long PVARP to be used at rest without limiting the maximum rate during exercise. In addition, to offer protection against retrograde conduction, a long PVARP and mode switching also limit the rate during atrial arrhythmias and allow regular ventricular rate responses according to the physiological demands.

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.

Prevention and termination of pacemaker-mediated tachycardia in a new DDD pacing system (Siemens-Pacesetter model 2010T)

The clinical incidence of Pacemaker-Mediated Tachycardia (PMT) has been substantially reduced with the availability of wide range postventricular atrial refractory period (PVARP) programmability in most current technology DDD pacemakers. However, patients may still be at clinical risk for PMT if the PVARP must be reduced to allow higher atrial tracking capability or VA conduction (VAC) is not periodically assessed to ensure adequate PVARP selection. A new DDD pacer (Siemens-Pacesetter Model 2010T) incorporates programmable responses to a sensed PVC to prevent PMT induction due to VAC following a PVC. In each of these responses, the PVARP is automatically extended to prevent detection of the retrograde P wave, thus preventing the PMT. Additionally, should a PMT occur for reasons other than a PVC, the selected PVARP extension algorithm is periodically invoked to terminate the PMT. This study was conducted to evaluate the operation and clinical benefit of these PVC response functions and PMT termination capabilities. The exact timing operation of the pacer during these responses is also reviewed.

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.

Atrial tracking (synchronous) pacing in a pediatric and young adult population

One hundred pediatric and young adult patients underwent implantation of an atrial tracking pacemaker. Seventy-four pacemakers paced in an atrioventricular (AV) sequential mode at the lower rate limit (DDD) while 26 paced in a ventricular demand mode at the lower rate limit (VDD). Five patients required reoperation during follow-up of 1 month to 2.5 years (mean 1.5 years). Six additional patients required programming to ventricular demand (3) or AV sequential (3) pacing, because of development of sinus bradycardia (2), atrial sensing problems (1) or pacemaker-mediated tachycardia (3). Pulse generators that could sense atrial signals less than 1.0 mV and had a programmable atrial refractory period did not require reprogramming out of the atrial tracking mode. No patient developed atrial flutter or fibrillation. Sensing problems during exercise occurred in 37% of the first 60 pacemakers but in none of the last 40, which had improved electronic components. Atrial tracking pacing is feasible in pediatric and young adult patients.

The dynamic nature of ventriculoatrial conduction

An endless loop tachycardia starts when the atrial sensory amplifier of a dual chamber pacemaker identifies an early atrial signal originating from a ventricular or atrial premature depolarization or from myopotential noise. The tachycardia will continue as long as ventriculoatrial conduction is sustained. By selecting the appropriate atrial sensitivity setting, postventricular atrial refractory period, or upper rate limit, it is possible to eliminate sustained endless loop tachycardia. Electrophysiological data obtained at the time of dual chamber pacemaker implantation can assist the physician when selecting these settings. This report summarizes our intraoperative data on ventriculoatrial conduction obtained from 432 consecutive patients. One hundred sixty-two patients had evidence of ventriculoatrial conduction including 14% of patients with antegrade complete heart block and 32% with 2:1 AVB. The majority of patients with preserved antegrade conduction had sustained retrograde conduction. During incremental ventricular pacing, ventriculoatrial conduction prolonged in the majority of patients, and with faster ventricular pacing rates, ventriculoatrial block developed. Ventriculoatrial block developed in half of the patients at a ventricular pacing rate exceeding 120 bpm. Analysis of these data suggests that by selecting an upper rate limit of 140 bpm, a postventricular atrial refractory period of 300 msec, and an atrioventricular interval of 125 msec, approximately 90% of patients will not have sustained endless loop tachycardia.

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.

Selective atrial sensing in dual chamber pacemakers eliminates endless loop tachycardia

With the introduction of dual chamber pacemakers that have multiple atrial amplitude sensing values, selective P wave sensing is possible. Five consecutive patients were studied who had 1) retrograde atrioventricular conduction, 2) anterograde atrial signals that were at least 1.4 times larger than their corresponding retrograde atrial signals, and 3) dual chamber pulse generators that are capable of discriminating this difference in atrial amplitude. In each patient the pacemaker was programmed in the DDD mode and the postventricular atrial refractory interval was at least 100 ms shorter than the individual's minimal retrograde conduction time. Two atrial sensitivity settings were evaluated in each patient: a high setting to ensure sensing of both anterograde and retrograde P waves, and a lower setting to allow sensing of anterograde P waves only. Ambulatory electrocardiographic monitoring demonstrated that with a high sensitivity setting, each patient sustained endless loop tachycardia (mean number of episodes 41, range 6 to 143) and that a low atrial sensitivity setting eliminated the tachycardia. With the lower atrial sensitivity setting, there was only sporadic atrial undersensing (1.5 episodes for each 1,000 P waves). This study demonstrates that atrial signals having different amplitudes can be selectively sensed. Additionally, dual chamber pulse generators with multiple atrial amplitude sensitivity values can discriminate anterograde from retrograde P waves, ensure anterograde sensing, reject retrograde P waves and eliminate endless loop tachycardia.

Noninvasive assessment of ventriculo-atrial conduction and early experience with the tachycardia termination algorithm in pacemaker-mediated tachycardia

Since the advent of physiologic dual chamber pacing systems, pacemaker-mediated tachycardia (PMT) has occurred and the need for invasive measurement of ventriculo-atrial conduction (VAC) has arisen. The variability in VAC and the potential for PMT often make it necessary to assess for the presence or absence of VAC at different points in time. We noninvasively evaluated 20 pacemaker patients for the presence or absence of VAC. We compared ventriculo-atrial conduction time (VACT) obtained with the atrial sense event maker with that obtained from Holter monitoring and invasive methods. The incidence of spontaneous (S) and induced (I) PMT and the efficacy of the tachycardia termination algorithm (TTA) was assessed. Fourteen of 20 had VAC with invasive or noninvasive methods. Twelve of 19 had PMT (63%); three were sustained (greater than 15 beats). We conclude that VACT assessed with the atrial sense event marker (ASEM) yielded a high correlation when compared to the Holter monitor data obtained utilizing our methodology. PMT is commonly a nonsustained (less than 15 beats) event, and the TTA is effective in sustained PMT. Myopotential sensing, atrial premature contractions and loss of atrial capture are common mechanisms in the initiation of PMT.

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.

Artificial circus movement tachycardias: incidence, mechanisms, and prevention

In a group of 45 patients treated with Medtronic 7000 and 7100 pulse generators for sick sinus syndrome or second or third degree atrioventricular block, an atrial synchronous mode of pacing was programmed in 34 cases and spontaneously occurring artificial circus movement tachycardias (ACMTs) were observed in nine. An analysis of conditions of occurrence, triggering mechanisms and patterns of ACMT, is presented. Various modalities of prevention are discussed. They resulted in suppression of ACMT in five patients and decrease of incidence in a sixth; the three remaining subjects were managed by definitive reprogramming in the DVI mode. Our conclusion is that correct prevention of ACMT requires the use of dual chamber pulse generators with programmable atrial refractory periods. For patients in whom a unit has already been implanted, careful observation of the triggering mechanism and pattern of ACMT may help in determining the most suitable way to prevent and suppress the arrhythmia.

Cardiac pacing in intensive care

Cardiac pacing techniques and equipment have developed dramatically in recent years. Bradycardias and tachycardias may be effectively treated by pacing. Bradyarrhythmias: It is generally accepted that pacing is indicated for a sustained symptomatic bradycardia. Prophylactic pacing for 'high-risk' bundle branch block in acute myocardial infarction is more controversial. A new era in cardiology has been introduced with the advent of 'physiological pacing', i.e. pacing of the heart with the maintenance of atrioventricular synchrony and varying the heart rate according to the body's metabolic leads. Modern pacing systems, which allow the atria and ventricles to contract in sequence, improve cardiac haemodynamics, result in subjective improvement and increase exercise tolerance. There are, however, pacemaker-associated and pacemaker-mediated tachyarrhythmias. Further advances in technology should overcome these problems. Tachyarrhythmias: Intracardiac electrocardiograms are often useful in the diagnosis of tachyarrhythmias, especially wide complex tachycardias. Rapid pacing of the atria in certain supraventricular tachycardias or of the ventricle in ventricular tachycardia is an alternative to cardioversion in many instances. This form of treatment is usually utilised in conjunction with drug therapy.

Pacemaker-mediated tachycardias: a new modality of treatment

Three patients with pacemaker interactive drug resistant tachycardia underwent invasive electrophysiological studies. In the first patient, the retrograde conduction of the artificial reciprocating tachycardia was provided by two right-sided accessory pathways and the antegrade conduction by an atrial synchronous pulse generator. In addition, AV-nodal tachycardia occurred alternately. In the second patient with intermittent atrial flutter, the AV node and, coincidentally, an AV sequential pulse generator provided high-rate antegrade conduction to the ventricles. In the third patient with surgical complete heart block, intermittent AV-nodal tachycardia induced retrograde atrial activation while an atrial synchronous pacemaker provided the antegrade conduction. Electrode catheter exploration of the heart allowed localization and closed-chest ablation of the accessory pathways or AV node by delivering two to seven 200-joule direct-current shocks through the appropriate electrode of the exploring catheter. Thereby, pacemaker-mediated arrhythmias could be controlled in these patients in the follow-up of 6 to 8 months.

A temporary external DDD pacing unit

A device for temporary external DDD pacing was developed using a modified permanent pulse generator, and temporary atrial and ventricular electrode catheters were inserted pervenously. The atrial lead was a J type and the ventricular lead had a remote anode in the superior vena cava. With a special clamp and appropriate connectors the permanent DDD pulse generator provided unipolar external DDD pacing. The device was evaluated in 13 patients to control bradyarrhythmias or for overdrive pacing in an attempt to control tachyarrhythmias. Nine patients were ambulatory; all had continuous electrocardiographic monitoring. The device was used for 1 to 12 days (mean 4.9). Eight patients benefited from temporary DDD pacing and 7 had permanent DDD pacemakers implanted. In 1 patient, atrial fibrillation developed, 2 patients had brief episodes of ventricular lead displacement and another required reprogramming because of loss of ventricular capture. Results suggest that the device is applicable for a clinical trial of DDD pacing before possible permanent implantation when attempting to improve cardiac output or control arrhythmias.