Lack of association of heart rate variability parameters with head-up tilt-test responses in patients with syncope

Neurocardiogenic syncope is the most common type of syncope. Head-up tilt testing is the investigation of choice for diagnosis of patients with neurocardiogenic syncope. In this study, we aimed to findout any association between heart rate variability parameters and type of tilt-test response in patients with syncope.

Forty-nine cases with unexplained syncopal attacks were enrolled into our study and were grouped according to the tilt-test responses. Tilt test was performed in all patients after excluding other causes of syncope. In case of a negative basal tilt-testing, pharmacological tilt testing was performed after 30 min of 5 mg sublingual isosorbide dinitrate. Holter monitoring was done from the beginning of tilt testing upto two hours post-procedure. The heart rate variability parameters analyzed were the mean of all coupling intervals between normal beats, the standard deviation about the mean of all coupling intervals between normal beats, the mean of all 5-min standard deviations of mean of all coupling intervals between normal beats, the proportion of adjacent normal R-R intervals differing by > 50 ms, the root mean square of the difference between successive RRs, and the standard deviation of 5-min mean of all coupling intervals between normal beats and ratio between low and high frequencies.

In 35 patients, the tilt-test was positive, 16 were cardioinhibitor type (Group 1), four cases had a vasodepressor type response (Group 2) and 15 were mixed type (Group 3). Fourteen patients had a negative test result. The heart rate variability measures did not significantly differ among the study groups. The heart rate variability measures were compared between the tilt-test negative (Group 4) and the tilt-test positive groups (Groups 1, 2 and 3) and no statistically significant difference was found.