Role of Age on Cardiac Autonomic Profile in Patients With Neurally Mediated Syncope and Positive Response to Head Up Tilt Test

Abstract

Introduction The pathophysiology of neurally mediated syncope (NMS) remains controversial. Age related cardiac autonomic function in patients with NMS has not been systematically assessed. Objective To determine the characteristics of age related non-invasive cardiac autonomic function in patients with NMS Methods 1336 subjects with clinical diagnosis of NMS were assessed in the autonomic physiology laboratory at Fundacion Cardiovascular de Colombia. 815 patients had positive response to 70° head-up tilt test (HUT) standard to either a nitroglycerine or low-dose isoproternol protocols. Patients were divided in three study groups for comparison according to age: A = 66 years old (74±5). Non-invasive beat-to-beat (Finapress monitoring) heart rate (HR, bpm) and mean arterial blood pressure (MAP, mmhg) as well as short-term heart rate variability (HRV) and baroreflex gain (BRS, mmhg/msec) were measured using power spectral analysis and coherence and phase techniques respectively during supine 5 minutes (min) rest and during 5 min of 70°orthostatic stress (OS). HRV indexes, low-frequency (LF, normalized units: nu) and high-frequency (HF, nu) bands were obtained, and the LF/HF ratio was also calculated. In addition, cardiovagal function was assessed using 6 cycles per minute deep breathing test protocol (deep breathing difference DBD, bpm). One-way ANOVA and Student's t test were applied (significance test: p<0.05) Results Variables are shown as means ± SD. Significantly higher DBD was found in group A compared to groups B and C (20±8 vs. 14±8 and 20±8 vs. 15±11 respectively). HRV and BRS results are presented in the table above: ![Graphic][1] Conclusion Patients with NMS have characteristic age-related cardiac autonomic responses. Younger NMS patients have an increased chronotropic activity at rest and OS and a decreased vascular reactivity. Higher sympathovagal balance and progressive decrease in cardiovagal BRS were documented in older patients with NMS. Age related autonomic compensatory mechanisms during OS may trigger different vasovagal responses. [1]: /embed/graphic-1.gif