Refractoriness and Arrhythmia Development in Isolated, Chronically Infarcted Canine Hearts

In normal isolated, perfused canine ventricles, increased ventricular volume leads to shortening of refractoriness. To test the hypothesis that myocardium within an infarction zone is more susceptible to volume-induced changes in refractoriness than is normal myocardium, we measured strength-interval curves at low and high end-diastolic volumes at control and infarcted sites in 14 isolated, blood perfused, canine hearts with chronic (> 25 days) infarctions. In addition, the effect of volume load on inducing ventricular arrhythmias was studied at one to six sites in 11 hearts. Differences in refractoriness and inducibility at low (22±5 ml) and high (48±6 ml) end-diastolic volumes were compared. At control sites, volume load reduced the absolute refractory period from 178± 16.5 to 175± 16.7 msec (p <0.05), but no significant change in the relative refractory period occurred. At infarcted sites, the change in refractoriness with volume load was greater, and the absolute refractory period decreased from 171.5±21 to 160.6±26.3