Influence of Age on Magnitude and Timing of Vasodepression and Cardioinhibition in Tilt-Induced Vasovagal Syncope.

Abstract

Cardioinhibition may diminish with age, but the changing balance of cardioinhibition and vasodepression with age has not been quantified, leaving the mechanism of vasovagal syncope (VVS) in old ageunclear. This study sought to quantify age-related changes of vasodepression and cardioinhibition in tilt-induced VVS. We studied 163 cases of tilt-induced VVS, evoked using the Italian protocol with blood pressure, heart rate, and video-electroencephalographic monitoring. Presyncope was excluded. Cardioinhibition was defined as the heart rate decrease before syncope; asystolic pauses (≥3 seconds) were divided into early and late asystole, ie, beginning early enough to or too late to be the major cause of loss of consciousness. The log-ratio method was used to quantify contributions of cardioinhibition and vasodepression, assessed in 2 10-second periods before the onset of cardioinhibition and before syncope. With increasing age, cardioinhibition decreased, ie, heart rate decreased less and more slowly near syncope (P< 0.0001), while vasodepression increased. Asystolic pauses were less frequent in the older one-half of the group than the younger one-half (26% vs 57%; P< 0.00001), but when it did, late asystole occurred more often (58% vs 15%; P<0.001). The shift toward less cardioinhibition and more vasodepression with increased age probably reflects a physiological shift in circulatory control. The weakening of cardioinhibition with age may detract from the efficacy of pacing in older patients with VVS. Cardioinhibition-vasodepression balance should be considered in pacing decisions in older subjects with VVS.