Optimal pacing mode for sick sinus syndrome.

To the Editor: I read with interest the article on the treatment of patients who have sick sinus syndrome (SSS) with single-chamber atrial pacing by Anderson et al.1 However, their finding of the annual risk of secondor third-degree atrioventricular (AV) block of only 0.6% per year contrasts somewhat with the reported findings that abnormal AV conduction was demonstrated in 57% to 67% of patients with SSS using invasive electrophysiologic techniques.2–4 Therefore, although Anderson et al1 demonstrated that abnormalities of AV conduction cause clinical problems only infrequently, it should be clear that a significant number of patients with SSS cannot be treated with atrial pacing alone. In these cases, dual chamber pacing (DDD or DDI, preferably with rate adaptation) should be the treatment of choice because the atrial transport function is then preserved. The choice should not be restricted to dual-chamber versus single-chamber atrial pacing only. Another viable option in the treatment of SSS in these patients is ventricular pacing, which was first reported in 1968.5 Ordinarily, pacing from a ventricular site would not be expected to affect atrial ectopic activity. However, after successful ventricular capture following transvenous catheter pacing, atrial tachyarrhythmias often no longer recur. Two explanations can be offered. First, the improvement of atrial function through improved coronary circulation secondary to the restoration of an effective regular ventricular rhythm may favorably affect the stimulation and fibrillation threshold of the atria.5 Second, ventricular pacing causes constant retrograde depolarization of the AV node and the atria and, by suppressing the nodal and atrial ectopic pacemakers, not only prevents atrial tachyarrhythmias but also protects against competitive rhythm.5 Ventricular inhibited (VVI) pacing should be the procedure of choice when the dominating atrial rhythm is fibrillation or flutter or when a stable atrial lead position with satisfactory electrophysiologic characteristics cannot be accomplished.