EFFECT OF HEART-RATE ON ZONAL TENSION AND ISCHEMIA FOLLOWING CORONARY-OCCLUSION - OPTIMAL RATE FOR TREPPE VERSUS ISCHEMIA

The optimal heart rate in the immediate period following acute coronary occlusion was controversial from the standpoint of arrhythmias and the extent of ischemic injury. The effect of heart rate on both local myocardial contractile ability and ischemia in 10 open chested dogs using strain gauge arches and epicardial electrograms was studied. After sinus node destruction, atrial pacing was instituted for rate control at 100/min and increased randomly to 150, 175, and 200/min. Before coronary occlusion, total tension and rate of tension rise progressively increased at higher rates while ST segments demonstrated no significant changes. After coronary artery occlusion, total tension and rate of tension rise in the ischemic zone decreased markedly and showed no significant change with increments in pacing rate. In the border zone, after the initial decrease in tension, pacing at 150 beats/min improved tension without a change in ST segments. However, when the rate was increased to 175 and 200 beats/min, although border zone tension increased further, ST segments rose significantly. Thus, a heart rate between 100-150/min provides the optimal range for increasing contractile ability in the nonischemic and border zones without adversely affecting the degree of ischemic injury.