Simultaneous analysis of heart rate variability and myocardial contractility during head-up tilt in patients with vasovagal syncope.

Abstract

The aim of this study was to evaluate simultaneously cardiac autonomic activity, through heart rate variability (HRV) analysis, and cardiac inotropic changes during head-up tilt (HUT) in patients with recurrent vasovagal syncope. Twelve subjects implanted with a permanent dual-chamber pacemaker for recurrent vasovagal syncope characterized by marked bradycardia were studied. The tip of the right ventricular electrode was equipped with a sensor that measured peak endocardial acceleration (PEA) as an index of myocardial contractility. RR interval and PEA signals were acquired simultaneously and processed in the time and frequency (low frequencies [LF] and high frequencies [HF] of RR signal) domain during early HUT (T1), late HUT, or before syncope (T2). In the six subjects with positive HUT: (1) Abnormal heart rate oscillations were evidenced at T1 and discriminated this group from the negative group (LF/HF decreased by 46% from supine to T1, but increased by 55% in the negative group; P < 0.01 positive vs negative HUT). (2) Gradual diminution of the HF component was associated with an increase in PEA index during HUT with a correlation between PEA/RR interval (R = -0.8, P < 0.001), PEA/HF components (R = -0.6, P < 0.05). (3) Sympathetic stimulation responsible for changes in both HRV and PEA parameters occurred immediately before the faint (LF/LF+HF: 0.6 +/- 0.2 to 0.8 +/- 0.09; P < 0.05 T2 vs T1; PEA: 0.62 +/- 0.10G to 0.83 +/- 0.22G; P < 0.01 T2 vs T1). Our findings showed that a homogeneous subgroup of patients with recurrent vasovagal syncope and positive HUT exhibited abnormal cardiac autonomic and inotropic responses to an orthostatic stimulus. Continuous changes over time of HRV and PEA parameters highlight the dynamic behavior of the mechanisms leading to syncope.