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

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 10min in supine (Su), HUT (80°) was performed up to 40min. Power spectra of low (L, 0.04Hzl, high (H, 0.15–0.40Hz) and total (T, 0.01–1.00Hz) 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.ResultsMx 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±13105±3/87±1315±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±928±17/28±1G3 (Su/Mx)71±13/90±20*138±15/115±15*15±12/6±4*16±10/14±1336±18/26±16mean±SD*p<0.05. vs Su#P<0.05 vs G2, G3H 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.ConclusionsUnusual autonomic responses to orthostatic stress can cause prolonged asystole, and this autonomic nerve dysfunction may lead to sudden cardiac death associated with cardiovascular collapse