Pharmacological modification of the dispersion of repolarization in the heart: Importance of the m cells

Several in vitro and in vivo investigations have provided data supporting t he existence of M cells in the deep subepicardial layers of the ventricles in a number of species. Characterized by unique electrophysiological and ph armacological features, this population of cells is regarded to have a sign ificant role in creating dispersion of repolarization in the ventricular wa ll and thus contribute importantly to arrhythmogenesis, in particular to in tramural reentry and triggered activity. Focusing on M cells, the authors s ummarize recent findings and concepts concerning the pharmacological hetero geneity of different cell and tissue types found within the ventricles and explore how these differences may contribute to electrocardiographic manife stations. On the basis of literarary data and of their own results they con clude that studying the electrical and pharmacological inhomogeneity within the ventricular wall may provide a better understanding of the pathophysio logical processes that give rise to cardiac rhythm disturbances and the mec hanisms by which antiarrhythmic agents act to suppress and in some cases ag gravate arrhythmias.