916-88 Simultaneous Measurement of Left Ventricular Volume and Parasympathetic Activity During Head-up Tilt in Vasovagal Syncope

Abstract

Present study tested the hypothesis that the great decline of left ventricular volume (LVV) during Head-up tilt (HUT) triggers ventricular mechanoreceptor activation and subsequently increases parasympathetic activation associated with hypotension-bradycardia. We measured temporal changes of frequency domain heart rate variability indices (HRV) and LVV using M mode echocardiogarphy during HUT (80° up to 40 min) in 15 patients (pts, 50 ± 23 years) with syncope of undetermined etiology. HRV consisted of low (L, 0.04 Hzl, high (H, 0.15–0.40 Hz) and total (T, 0.01–1.00 Hz) components. For LVV analysis, EDV. ESV and EF were calculated using Teichholtz formula. HRV and LW indices were measured in consecutive 2 min segments throughout the study. Eight pts had positive tests (syncope was induced by HUT; Group 1, G1) and 7 pts in negative tests (Group 2, G2). Data were shown below [SSP, systolic blood pressure; mean in HR and SBP; Suo supine; Δ and Δ%, differenct es between values at 2 min of HUT and maximally changed values (Mx) during HUT; L/H, ratio of Land H components]. HR (bpm) SBP(mmHg) ΔH ΔLJH Δ%EDV Δ%ESV Δ%EF Gl (Su/Mx) 77/64 # 117/79 # 2.8 0.058 -53 + -49 * +23 G2(Su/Mx) 6S/75 # 132/124 -11.6 0.063 -19 -20 +22 * p < 0.05 vs G2 # P < 0.05 vs Su Before syncope, LVVs in G1 gradually and more profoundly declined than those in G2. The values of H significantly increased from supine to 2 min prior to syncope in G1. Also, the values of H at 2 min prior to syncope in G1 was significantly higher than those at Mx in G2 (14 ± 7 vs. 7 ± 4 ms, p < 0.05). Simultaneous measurements of LW and HRV during HUT are useful for evaluating pathophysiology of neurally mediated syncope. Preceding decrease of LVV can trigger exaggerated parasympathetic activity in patients with vasovagal syncope.