The natural history of carotid sinus syncope and the effect of cardiac pacing

Abstract

Therefore, a question arises as to what the real usefulness of pacing therapy is and which patients need this therapy. Lopes et al. 11 performed a retrospective analysis of 138 patients who were followed-up for � 5 years, thus adding an important contribution to the effect of cardiac pacing in CSS patients. Taking into account this study, in this article we tried to summarize the current knowledge about pacing therapy of this old syndrome. We performed a MedLine search among peer-review journals in the English language for articles dealing with the natural and unnatural history of CSS; we excluded case reports. We found 12 studies 6,7,11 – 20 which reported sufficient follow-up data for analysis. In total, we were able to analyse the natural history of 305 patients and the effect of cardiac pacing in another 601 patients affected by severe recurrent syncope. The results are shown in Figure 1. The studies were largely heterogeneous in regard to the selection of patients, duration, and position (supine or standing) of the carotid sinus massage, criteria for identification of mixed forms, and different mode of pacing (single- vs. dual-chamber). Despite these limitations, the figure suggests that syncopal recurrence rates during follow-up with pacing ranged between 0 and 20%, whereas the recurrence of syncope was always higher in untreated patients, with the rates between 20 and 60%. The specificity of carotid sinus massage increases if reproduction of spontaneous syncope during carotid massage is a requisite for positivity of the test. The so-called ‘Method of Symptoms’ requires a longer duration of the massage, in general for 10 s. The recent ESC guidelines on syncope 2 recommend that CSS be diagnosed if spontaneous symptoms are reproduced together with the documentation of an abnormal reflex. Figure 2 shows the results of metanalysis of three controlled studies 6,7,15 in which carotid sinus massage was performed according to the ‘Method of Symptoms’. The studies were sufficiently homogeneous (Mantel– Haenszel heterogeneity test: P ¼ 0.39). The mean length of the pause induced by the carotid sinus massage ranged from 5.2 to 7.3 s. During a mean observation period of up to 3.3 years, syncope recurred in 9% of patients treated with a pacemaker and in 38% of control untreated patients. The cumulative odds ratio was 0.15 (95% CI 0.06–0.36). Finally, in a registry of 169 consecutive patients treated with permanent pacemaker in our departments from 1988 to 1994, 19 the actuarial estimate of syncopal recurrence was 7% at 1 year, 16% at 3 years, and 20% at 5 years. Cardiac pacing seems less effective in preventing pre-syncope than syncope. Indeed, pre-syncope and minor symptoms have been reported in 25, 6 27, 7 and 43% 20 patients after pacemaker implant. Moreover, two randomized trials 6,7 failed to show the superiority of cardiac pacing compared with no pacing in reducing the rate of pre-syncope. It seems that pacing transforms syncope to pre-syncope probably because it is effective in counteracting the asystolic reflex that causes syncope but it is less effective against the vasodepressor component of the reflex which is frequently associated even with the so-called dominant cardioinhibitory forms. Lopes et al. 11 reported a lower 6% rate of