Heart rate variability and baroreflex sensitivity in idiopathic dilated cardiomyopathy

Objective-To examine the relation between cardiac autonomic tone, assessed by baroreflex sensitivity and heart rate variability, and left ventricular function, arrhythmias on Holter monitoring, and clinical variables in patie nts with idiopathic dilated cardiomyopathy. Design-A prospective observational study. Patients-160 patients with idiopathic dilated cardiomyopathy and preserved sinus rhythm in the absence of antiarrhythmic drug treatment. Measures of h eart rate variability obtained by digital 24 hour Holter recordings include d the mean of all coupling intervals between normal beats (RRm), the standa rd deviation of the mean of normal RR intervals (SDNN), and the square root of the mean of the squared differences between adjacent normal RR interval s (rMSSD). Baroreflex sensitivity testing was performed using the phenyleph rine method. Results-Mean SDNN (SEM) was 112 (46)ms, and baroreflex sensitivity was 7.5 (5.0) ms/mm Hg. SDNN showed a weak correlation with baroreflex sensitivity (r = 0.19, p < 0.05) and with left ventricular ejection fraction (r = 0.29, p < 0.05). SDNN showed no significant correlation with age (r = -0.07), th e presence of non-sustained ventricular tachycardia (r = -0.13), or left ve ntricular end diastolic diameter (r = -0.07). In addition, baroreflex sensi tivity showed no significant correlation with age (r = -0.13), non-sustaine d ventricular tachycardia (r E -0.08), left ventricular end diastolic diame ter (r = 0.09), or ejection fraction (r = 0.14). Conclusions-The weak correlation between baroreflex sensitivity and heart r ate variability suggests that these two indices explore different aspects o f cardiac autonomic control in patients with idiopathic dilated cardiomyopa thy. The weak or absent correlation between baroreflex sensitivity, heart r ate variability, and other potential non-invasive risk predictors, includin g left ventricular ejection fraction, left ventricular end diastolic diamet er, and non-sustained ventricular tachycardia on Welter monitoring, indicat e that these variables may have independent prognostic value in idiopathic dilated cardiomyopathy.