Studies in Isolated Guinea Pig Papillary Muscles

The muscle is stimulated with a monophasic rectangular stimulus of 3 ms duration and at 1.5 times the stimulation threshold using a 1831A stimulator 

In contrast to the Purkinje fiber, the papillary muscle is a contractile tissue lending it also for the measurement of contractile force, together with the action potential configuration. Since effects on the inotropic state of the myocardium can also affect the action potential, this is a useful secondary measurement to have to interpret possible drug-induced effects. However, the contraction of the muscle makes the placement of the electrode more difficult and changes in the contractile function can lead to loss of the electrode placement in the course of a study. 

Arterially Perfused Wedge of Canine Left Ventricle 

The M cell is a unique myocardial cell type found in the deeper layers of the ventricular wall (Antzelevitch et al. 1999). These cells respond more sensitively to agents that block hERG channels and, as such, contribute to possible drug-induced transmural heterogeneity of ventricular repolarization and thereby the proarrhythmic potential. The perfused myocardial wedge preparation is design to allow the study of transmural differences in drug action on the action potential and may therefore provide a better assessment of possible proarrhythmic potential of a test article. 

Antzelevitch C, Sun Z-Q, Zhan Z-Q, Yan G-X (1996) Cellular and ionic mechanisms underlying erythromycin-induced long QT intervals and Torsade de Pointes. J Am Coll Cardiol 28 1836-1848 

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Yamazaki, K., Terada, H., Satoh, H., Naito, K., Takeshita, A., Uehara, A., Katoh, H., Ohnishi, K., Hayashi, H. (2006). Arrhythmogenic effects of arsenic trioxide in patients with acute promyelocytic leukemia and an electrophysiological study in isolated guinea pig papillary muscles. Circulation Journal 70 1407-14. 

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