Digitalis in experimental acute myocardial infarction: Differential effects on contractile performance of ischemic, border and nonischemic ventricular zones in the dog

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The effects of digoxin (priming dose of 0.04 mg/kg body weight followed by infusion of 0.02 mg/kg per min) on local tension and length characteristics of the nonischemic, border and ischemic left ventricular zones were studied in 30 dogs using Walton-Brodie strain gauge arches and mercury-in-Silastic segment length gauges. Total tension in the nonischemic zone increased to 130.9 ± 5.3 percent ( P < 0.001) of the control level in association with parallel changes in preejection and ejection tension and rate of rise of tension when infusion of digoxin was instituted 15 to 30 minutes after ligation. Consistent increases in tension variables were noticed when infusion of digitalis was initiated 45 to 60 minutes or 2 to 3 hours after ligation. Segment length remained unchanged. In the border zone, total tension decreased to 68.9 ± 5.9 percent ( P < 0.01) 15 to 30 minutes after coronary occlusion and increased to 106.8 ± 9.7 percent ( P < 0.01) after infusion of digitalis. When infusion of digitalis was instituted 45 to 60 minutes or 2 to 3 hours after occlusion, similar increases in total tension and other tension variables were seen. Segment length again showed no significant changes. There was an increase in total tension in 5 of the 12 ischemic zones studied when digitalis was infused 15 to 30 minutes after coronary arterial ligation, whereas a consistent (3 to 5 percent) decrease in tension was observed when infusion of digitalis was instituted 45 to 60 minutes and 2 to 3 hours after coronary occlusion. There was no increase in segment length. In summary, digitalis uniformly increased contraction of the nonischemic and border zones after coronary arterial ligation, but the effects on contraction and aneurysmal bulging in the ischemic zone were minimal.