Experimental Studies of the Excitability of Ventricular Musculature in Infarcted Region

Abstract

(1) The excitability of the myocardium in ischemic region produced by coronary artery ligation were studied on the canine heart through combined use of electric stimulation unit and specially devised multipolar electrode.
(2) The asynchronism of myocardia in recovery from the refractoriness was found in ischemic region. The refractory period observed in the ischemic myocardium became progressively shortened and the diastolic threshold be-came also progressively lowered with increasing ischemia until they reached their minima. After reaching their minima, they started to increase in their values again and finally the myocardium failed to respond even to the extra-ordinary stimulus. These findings were supposed as the cause of asynchronism of myocardia in recovery from the refractoriness.
(3) Markedly low conduction velocity was observed in the early stage of the relative refractory period in ischemic myocardium. The delay of ventricular activation time was also observed in the severely ischemic myo-cardium.
(4) The shorter the interval from the preceding excitation, the shorter was the refractory period.
(5) The threshold for a run of extrasystole and ventricular fibrillation, or the vulnerable threshold, was observed to be low in the ischemic myocard-ium.
(6) The above mentioned findings may account for the frequent occur-rence of ventricular fibrillation on the attack of myocardial infarction. The reason for this was discussed.