Effects of diltiazem on triggered activity in canine 1 day old infarction

Triggered activity arising from a delayed after-depolarisation occurs in canine subendocardial Purkinje fibres 1 day following infarction. Standard microelectrode techniques were used to study small preparations (less than 50 mm2) in vitro. Diltiazem, 1 mg X litre-1, reversibly suppressed triggered activity by reducing maximum diastolic potential, action potential amplitude and the rate of depolarisation of the delayed after-depolarisation. Complete quiescence or exit block resulted. The effects of diltiazem were antagonised by elevating extracellular Ca ion concentration. These results suggest that automatic ectopic rhythms 1 day following myocardial infarction, that are the result of triggered activity, are dependent on transmembrane Ca ion movement which diltiazem can directly antagonise.