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HBE = His bundle electrogram, PPM = permanent pacemaker, V stim = ventricular stimulation study, SHD = structural heart disease.

HBE = His bundle electrogram, PPM = permanent pacemaker, V stim = ventricular stimulation study, SHD = structural heart disease.

Fig. 4. An individual with recurrent AF was being treated with procainamide. He was noted to have a prolonged QT interval and runs of polymorphic ventricular tachycardia (PVT) (three simultaneous ECG leads are shown here). His ECG normalized when the procainamide was discontinued.

period of rapid pacing is initiated when the rate drops suddenly below a certain preset limit) has awakened interest in the use of pacing for these disorders. Recently, the results of the North American Vasovagal Pacemaker Study (VPS) were reported (52). Fifty-four patients with neurocardiogenic syncope and >6 syncopal episodes were randomized to dual-chamber pacing with a rate-drop response, or to no pacing. The pacing group experienced an 85.4% reduction in syncopal episodes (p < 0.00002). In an accompanying editorial, Benditt agreed that the technique has promise, but cautioned that there was no medical treatment arm for comparison. Moreover, the population was very carefully selected so that the results were not necessarily applicable to the majority of individuals with neurocardiogenic syncope. In addition, treatment groups were not blinded—a potential problem considering the placebo effect of permanent pacing noted in other clinical settings. More recently, the smaller VASIS study yielded similar results (52A). In this trial, the paced patients received a dual-chamber device programmed to the DDI mode with a hysteresis rate of 45 and a pacing rate of 80; the control group received no therapy. Currently, the only class I indication for pacing in these disorders is recurrent syncope caused by carotid sinus hypersensitivity (1). The Vasovagal Pacemaker Study II (VPS II), in which all patients undergo pacemaker implantation, but one-half are randomized to inactive pacing (in a double-blind crossover design), is currently underway. Another multicenter controlled trial, "Syncope and Falls in the Elderly—Pacing and Carotid Sinus Evaluation" (SAFEPACE) is ongoing in the United Kingdom, and should provide additional information.

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