Influence of tachycardia and arterial hypertension on infarct size in the pig

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Abstract
To investigate the clinically important but controversial question of how hypertension during coronary occlusion affects infarct size 24 pigs underwent 1 h occlusion of the mid left anterior descending coronary artery and 24 h reperfusion and were randomised to one of three treatment groups. In group 1 blood pressure was increased during the occlusion period by an infusion of methoxamine; in group 2 tachycardia was induced by atrial pacing; and in group 3 no intervention was performed. The area at risk and infarct size were quantified by digital planimetry of slices of myocardium previously marked with fluorescein and with triphenyl-tetrazolium. Methoxamine maintained mean aortic blood pressure at 117(SEM8) mmHg during occlusion, whereas the values were 80(6) mmHg in group 2 and 67(9) mmHg in group 3. Pacing increased heart rate to 146(1) beats-min−1 in group 2; it was 103(5) in group 1 and 99(8) in group 3. The pressure-rate product achieved was similar in groups 1 and 2 and significantly higher than in group 3. The pathological studies showed infarct size to be moderately but significantly larger in group 1 (14[3.5]% of the left ventricle) and similar in groups 2 (10.5[3.9]%) and 3 (10.1 [2.2]%). The ratio of infarct size to area at risk was also significantly higher (0.743[0.057]) in group 1 with no differences between group 2 (0.604[0.055]) and group 3 (0.613[0.027]). At similar pressure-rate product, infarct size was thus greater with hypertension but not with pacing alone, showing a deleterious effect of increasing blood pressure in this experimental model with negligible collateral blood flow.

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