801–3 Differential Effect of d-Sotalol on QT Dispersion in Acute Drug Responders Versus Non-Responders

QT interval dispersion measured as interlead variability of QT, is a marker of dispersion of ventricular repolarization and, hence, of cardiac electrical instability. The influence of the new class III agent d-sotalol on QT dispersion (QT disp) was investigated in 20 patients (pts) with recurrent sustained ventricular tachycardia (VT) and/or ventricular fibrillation (VF). All pts had inducibile VT/VF at baseline and were electrophysiologically studied under oral d-sotalol (460±94 mg/day). In 10 pts d-sQTalol suppressed the induction of VT/VF, whereas 10 pts did not respond. QTand RR intervals of 3 consecutive beats were measured in 6 simultaneously recorded precordial leads (VI-V6) by two independent blinded investigators. Under oral d-sotalol, the QT disp was reduced in 9/10 responders but only in 4/10 non-responders, despite comparable doses of the drug in both groups. The relative changes between control and under d-sotalol therapy in responders and non-responders of corrected maximal QT (QTc max.), QT disp., dispersion of the QTc (QTc disp.) and adjusted QTc (adj. QTc disp) are presented as means±SD.respondernon-responderpΔ QTc max.32.9±69.227.5±41.4NSΔ QT disp.-30.3±16.820.3±38.20.001Δ QTc disp.-34±3118.5±37.80.003Δ adj. QTc disp-13.3±12.97.5±15.60.004Dosage480±103440±84NSThe new class III agent d-sotalol produced a significant reduction of QTc dispersion in responders in contrasts to non-responders.ConclusionQT dispersion may be potentially useful in the assessment of the efficacy of class III antiarrhythmic drugs. This effect may be due to homogenization of repolarization in both normal and diseased myocardium representing the arrhythmogenic substrate