Minimizing Unnecessary Right Ventricular Pacing

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Permanent pacemakers have been used to treat patients with symptomatic bradycardia for 45 years. The earliest pacemakers paced only the ventricle and were used primarily for patients with complete heart block. The need for atrial pacing became apparent as pacing for sinus node dysfunction became more common. Initially, only single-chamber pacing was possible in the atrium, and this was a good therapeutic approach for patients with sinus node dysfunction and intact conduction from the atria to the ventricles. Dual chamber (DDD) pacemakers have been available for more than 20 years, and dual chamber rate-responsive (DDDR) pacemakers have been implanted for more than 15 years. With the availability of such universal pacemakers, implantation of a DDDR pacemaker has become the usual practice in the US for almost all patients except those with permanent atrial fibrillation. A conventional pacemaker paces the right atrium and the right ventricle. At nominal settings for atrioventricular (AV) delay, such pacemakers will often pace the right ventricle with either fusion or complete capture even if intrinsic conduction is present. Only more recently has it become apparent that routine pacing of the right ventricle can be detrimental when it is not needed.

Concerns about deleterious effects of right ventricular pacing come in part from studies using devices capable of pacing the right ventricle in patients with no indication for the pacing. The Dual Chamber and single chamber ventricular pacemaker (VVI) Implantable Defibrillator Trial (DAVID)1 compared DDDR pacing with VVI pacing in patients with dual chamber implantable cardioverter-defibrillators (ICDs) in patients with an indication for an ICD, ejection fraction Ôëñ40% but no indication for pacing. The hypothesis was that the dual chamber pacing devices would improve the incidence of congestive heart failure (CHF), atrial fibrillation, hospitalization, and death. There was no protocol programming requirement to avoid pacing the right ventricle in patients with no need for ventricular pacing. Therefore, at nominal AV delay settings, many patients had right ventricular pacing a high percentage of the time (60% of all ventricular beats) despite having no AV block indication for pacing. The result was an increased incidence of the composite end-point of hospitalization for CHF and death in patients programmed to DDDR mode, compared with those programmed to VVI mode with ventricular pacing at a low rate, and consequently no pacing at all in most patients (1% overall).

The Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) also encountered unexpected problems related to worsening heart failure. The patients in MADIT II all had coronary artery disease and severe left ventricular dysfunction with ejection fraction (EF) <30% but no indication for pacing. Patients with defibrillators lived longer, but had more heart failure admissions, which was out of proportion to their increased longevity.2

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References
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