1025-98 Exaggerated Sympathetic and Failed Withdrawal of Parasympathetic Activity During Head-up Tilt Precipitates a Life-threatening Cardiac Asystole

Abstract

A life-threatening cardiac asystole can be a malignant manifestation of vasovagal syncope induced by head-up tilt (HUT) testing. To investigate the mechanism of HUT-induced life-threatening cardiac asystole (T-LTAS), we measured a temporal change of frequency domain heart rate variability indices (HRV) in 25 patients (pts) with syncope of undetermined etiology. Three pts (37 ± 13 years, 2 male) had T-LTAS episode; asystole ≥ 10 seconds and cardiopulmonary resuscitation was necessary (Group 1, G1). Ten pts (48 ± 31 years, 6 male) had positive test (syncope was induced by HUT) but no asystole (Group 2, G2). and 12 pts (55 ± 20 years, 5 male) in negative test (Group 3, G3). After 10 min in supine (Su), HUT (80°) was performed up to 40 min. Power spectra of low (L, 0.04 Hzl, high (H, 0.15–0.40 Hz) and total (T, 0.01–1.00 Hz) frequency were measured in consecutive 2 min segments throughout the study. Maximally changed values (Mx) in HR, systolic blood pressure (BPs) and HRV during HUT were compared among 3 groups. Mx were obtained at 2 min or 4 min before the moment of T-LTAS or syncope in G1 and G2, respectively. HR (bpm) BP5 (mmHg) H(ms) L (ms) T (ms) G1 (Su/Mx) 60 ± 8/64 ± 13 105 ± 3/87 ± 13 15 ± 11/21 ± 6 # 20 ± 11/58 ± 41 # 30 ± 1/73 ± 29 # G2 (Su/Mx) 9/88 ± 21 * 126 ± 23/79 ± 13 * 11 ± 11/6 ± 4 * 14 ± 11/13 ± 9 28 ± 17/28 ± 1 G3 (Su/Mx) 71 ± 13/90 ± 20 * 138 ± 15/115 ± 15 * 15 ± 12/6 ± 4 * 16 ± 10/14 ± 13 36 ± 18/26 ± 16 mean ± SD * p < 0.05. vs Su # P < 0.05 vs G2, G3 H in G2 and G3 was decreased by HUT, whereas HUT did not decrease H in G1. H, L and T in G1 during HUT were significantly higher than those in G2 and G3, respectively. Findings were consistent with exaggerated sympathetic and failed withdrawal of parasympathetic activity during HUT in patients with T-LTAS. Unusual autonomic responses to orthostatic stress can cause prolonged asystole, and this autonomic nerve dysfunction may lead to sudden cardiac death associated with cardiovascular collapse.