Key result
Repolarization dispersion and early afterdepolarizations explain most TdP features despite some mechanistic gaps.
Why the study?
Recent studies suggested torsade de pointes may be precipitated by early afterdepolarizations, offering an alternative to the hypothesis attributing it to dispersion of repolarization.
This review highlights that while both dispersion of repolarization and early afterdepolarizations can explain most clinical features of torsade de pointes, the afterdepolarization hypothesis faces challenges in certain cases.
Both mechanisms explain most torsade de pointes; leaves open targeted experiments to resolve afterdepolarization inconsistencies.
Recent experimental and clinical studies suggest that torsade de pointes may be precipitated by early afterdepolarizations in the Purkinje or ventricular muscle fibers. This hypothesis offers an alternative to the earlier one that attributes torsade to the underlying dispersion of repolarization. This review lists the clinical conditions associated with torsade de pointes and examines the experimental background of the two proposed electrophysiologic substrates of torsade, namely, the dispersion of repolarization and the early afterdepolarizations. The strengths and weaknesses of the two hypotheses are compared in relation to the following characteristics of torsade de pointes: facilitation by slow heart rate, suppression by pacing, R on T phenomenon, difficulty of induction by programmed stimulation, aggravation by hypokalemia, manifestation of an idiosyncratic reaction to class IA antiarrhythmic drugs, spontaneous termination, suppression by magnesium salts and isoproterenol and induction by such drugs as sotalol, bepridil and prenylamine. It appears that most clinical observations can be explained by either mechanism, but in some cases difficulties are encountered for the afterdepolarization hypothesis.
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Borys Surawicz (1989) conducted a review in Torsade de pointes. Early afterdepolarizations vs. Dispersion of repolarization was evaluated. Dispersion of repolarization and early afterdepolarizations can explain most clinical features of torsade de pointes, though the afterdepolarization hypothesis faces difficulties in some cases.
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