Pacing Treatment of Cardioinhibitory Syncope
September 1, 2000 4 minutes read
Pacing Treatment of Cardioinhibitory Syncope
Abstract & Commentary
Synopsis:Dual chamber pacing is effective in selected patients with recurrent neurally mediated syncope. However, in this study, the absolute recurrence rate for syncope even without treatment was low (0.44 episodes/yr) and repeat tilt table testing did not predict long-term outcome.
Source: Sutton R, et al, for the Vasovagal Syncope International Study (VASIS) Investigators. Circulation 2000;102:294-299.
Sutton and colleagues tested the effects of DDI pacing with rate hysteresis on reducing the risk of recurrent syncope in patients with cardioinhibitory syncope. Patients enrolled in the study all had neurally mediated syncope with at least three episodes in the last two years, a positive cardioinhibitory response during head-up tilt table testing, and either were older than 40 years of age or, if younger, had demonstrated failure of conventional drug therapy. Prior to enrollment, tilt table testing was performed using 60° head-up tilt for 45 minutes. The Vasovagal Syncope International Study (VASIS) criteria were used to classify a positive response. Category 2A responses were defined as a heart rate rising initially and then falling to a ventricular rate of less than 40 bpm for longer than 10 seconds with the blood pressure rising initially but then falling before the heart rate decrease. Type 2B responses were defined as a heart rate that rose initially and then fell to a ventricular rate of less than 40 bpm for longer than 10 seconds with the blood pressure rising initially and only falling after the onset of bradycardia. Sublingual nitroglycerin (300 m) with a repeat 20-minute tilt was permitted if the initial 45-minute tilt did not produce symptoms.
Eligible patients were assigned either to treatment with a dual chamber pacemaker programmed to the DDI mode at 80 bpm with rate hysteresis from 45 bpm. Patients in the no-pacemaker arm received no specific therapy. A follow-up head-up tilt test was performed within 15 days of enrollment in both groups. During follow-up, patients were monitored both clinically and by telephone interview. The primary study end point was recurrence of syncope. Outcomes were reported using both an intention-to-treat and an "on-therapy" analysis.
Forty-two patients were randomized into this study. They were followed for a mean of 3.7 ± 2.2 years. Initially, 19 patients were assigned to the pacemaker group and 23 patients were assigned to the no-pacemaker group. Three patients in the no-pacemaker group, however, received pacemakers within one month of randomization before any recurrence of syncope. Five other patients in the no-pacemaker group eventually received a pacemaker after more than one syncopal episode.
Patients in both groups were approximately 60 years of age. They had experienced a median of five episodes of syncope in their lifetime, with three episodes in the last year. Slightly fewer than half had suffered trauma secondary to syncope. Thirty-six of the 42 patients had asystole during their tilt study that lasted a mean of 13.9 ± 10.2 seconds.
Pacemaker therapy was apparently more effective than no therapy. In the intention-to-treat analysis, syncope recurred in only one patient in the pacemaker arm after 15 months. In contrast, recurrent syncope was noted in 14 of 23 patients in the no-pacemaker arm after a median of five months follow-up. Treatment analysis confirmed the efficacy of pacing. At one and three years, 45% and 57% of untreated patients had experienced recurrent syncope. Repeat tilt table testing was not helpful in evaluating responses to pacemaker therapy. The overall reproducibility of positive responses between the first and second tests in the no-pacemaker arm was only 61%. In the pacemaker arm, despite pacemaker therapy during head-up tilt, there were still 10 of 17 positive responses (59%).
Sutton et al conclude that dual chamber pacing is effective in selected patients with recurrent neurally mediated syncope. However, in this study, the absolute recurrence rate for syncope even without treatment was low (0.44 episodes per year) and repeat tilt table testing did not predict long-term outcome.
Comment by John P. DiMarco, MD, PhD
Recurrent neurally mediated syncope remains a vexing problem. Some of the difficulties in studying this syndrome are illustrated in this paper. Despite the fact that more than 1200 potentially eligible patients were screened at the institutions that participated in this trial, only 42 were eventually randomized and entered into the study. Patients either were not willing to accept the possibility of pacemaker implantation or did not want to randomly be assigned to a no-therapy group. However, even in the no-therapy group, the recurrence rate of syncope was only 1.7 ± 0.9 episodes per patient during a median follow-up of 3.7 years. Also, this was in a relatively old patient population. In a population with younger patients, acceptance of a permanent pacemaker might be even less desirable and the natural history is often less certain. The study also highlights the limitation of tilt table testing in the evaluation of these patients. Test-to-test reproducibility was only about 60% in the no-therapy group. Responses during pacemaker therapy were not predictive of long-term clinical outcome. Therefore, although useful to study the pathophysiology of neurally mediated syncope in general, the use of tilt table testing in individual patients remains limited.
Despite these limitations, one must agree with Sutton et al’s conclusions. In selected, elderly patients with recurrent syncope, pacemaker therapy can abort future episodes. Also, in selected patients, particularly those in whom injury has occurred with syncopal episodes, a trial of pacing seems indicated.
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