Predicting the effect of D,L-sotalol on ventricular tachycardia inducibility from the RR variability response

Aim-To find a rapid way of identifying non-responders to D,L-sotalol in pat ients with ventricular tachycardia. Methods-Programmed ventricular stimulation and RR variability were studied in the control state and 10 days after treatment with 160 to 320 mg of D,L- sotalol in 36 consecutive patients with ventricular tachycardia. Results-In 14 patients (group I) D,L-sotalol suppressed ventricular tachyca rdia inducibility. In 22 patients (group II) sustained ventricular tachycar dia remained inducible during D,L-sotalol treatment. The ventricular tachyc ardia rate was slowed in eight patients and unchanged or accelerated in 14. At baseline, heart rate variability was similar in both groups. During tre atment with D,L-sotalol, variables reflecting parasympathetic activity (pNN 50, rMSSD, and high frequency amplitude (HF)) increased in both groups: HF increased from (mean (SD)) 75 (68) to 146 (134) in group I (p < 0.05) and f rom 60 (49) to 125 (79) in group II (p < 0.05). Other variables were unchan ged in group I. In group II, the variables associated with sympathetic acti vity (coefficient of variance (CV), ratio of low frequency amplitude (LF) t o HF) decreased significantly: CV decreased from 13 (4) to 9 (2) (p < 0.001 ) and LF/HF from 4.74 (3.02) to 3.00 (2.02) (p < 0.05). Conclusions-The beta blocking effect of D,L-sotalol produced a significant improvement over control values in indices of parasympathetic tone in all t reated patients. However, the heart rate variability indices related to sym pathetic activity were decreased only in non-responders. This effect of D,L -sotalol on heart rate variability could help detect nonresponders to the d rug and avoid an electrophysiological study.