ROLE OF INTERVENTRICULAR DISPERSION OF REPOLARIZATION IN ACQUIRED TORSADE-DE-POINTES ARRHYTHMIAS - REVERSAL BY MAGNESIUM

Objective: The mechanism of acquired torsade-de-pointes arrhythmias (T dP) is not clear but is suggested to be based on several parameters in cluding early afterdepolarizations (EADs) and/or dispersion of repolar ization (Delta APD). In our animal model of TdP (anaesthetized dogs wi th chronic AV block), we assessed the relevance of interventricular di spersion for the initiation of TdP. Methods: In 24 experiments, multip le endocardial monophasic action potential (MAP) recordings were made at baseline, after d-sotalol (2 mg/kg), and after MgSO4 (100 mg/kg, n = 11) to measure regional differences in action potential duration (AP D). Rate-dependent behavior of the interventricular Delta APD (APD of left minus right ventricle) and intraventricular dispersion was studie d under the different circumstances. Results: Dogs with induction of T dP by d-sotalol and pacing (11/20 = 55%) had longer cycle lengths of i dioventricular rhythm, longer QT-durations, increased presence of EADs (14/22 vs 5/18 MAPs, P < 0.05) and increased interventricular Delta A PD (135 +/- 55 vs 60 +/- 40 ms, P < 0.05) compared with non-inducible dogs. There were no differences in intraventricular dispersion. MgSO4 diminished Delta APD (110 +/- 45 to 55 +/- 60 ms, P < 0.05) and preven ted TdP (4/4). In contrast to intraventricular dispersion, interventri cular Delta APD is clearly bradycardia-dependent. Conclusions: Next to bradycardia, prolonged repolarization, and EADs, we propose that Delt a APD should be added to the relevant factors for the initiation of Td P. Interventricular dispersion is much larger than intraventricular di spersion and demonstrates a very strong bradycardia dependence.