Pacing On Ventricular Arrhythmias

Theoretically, biventricular pacing may alter the substrates responsible for ventricular arrhythmias and, on occasion, may possibly be associated with an increased risk for ventricular arrhythmias. However, currently available data indicate that biventricular pacing reduces the likelihood of ventricular tachyarrhythmias. In addition, there is evidence that biventricular pacing actually inhibits ventricular reentry. Several studies obtained from a small number of patients demonstrated that biventricular pacing may decrease the inducibility of ventricular tachycardia (19), the incidence of spontaneous ventricular arrhythmias (ectopy) (20), and the need for defibrillator therapy (21).

In rare cases, biventricular pacing may suppress refractory ventricular tachycardia in patients in whom it was not controlled by drugs or right ventricular DDD pacing (22). Proposed mechanisms for the protective benefits of biventricular pacing are (1) prevention of ventricular reentry, (2) improvements in cardiac function and myocardial perfusion, (3) reductions in sympathetic activity, or (4) decreases in QT dispersion (Fig. 5) (unpublished data).

Additional data have indicated that biventricular antitachy-cardia pacing may be even more effective than right ventricular antitachycardia pacing (17); however, there is controversy regarding this role of biventricular antitachycardia pacing (23). On the other hand, biventricular pacing has been associated with nonphysiological ventricular activation sequences that may augment transmural heterogeneity of repolarization and thus facilitate the genesis of ventricular arrhythmias (24).

To date, there is no evidence that biventricular pacing increases mortality during a 1-year follow-up period. However, it should be noted that such studies were not designed to determine the effects of biventricular pacing on overall survival. Interestingly, it has been suggested that it may be safe to implant a biventricular pacemaker without a backup defibrillator (23) because biventricular pacing does not appear to be associated

Defibrillator Implant Risks
Essentials of Human Physiology

Essentials of Human Physiology

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