Study objectives: To examine the effects of low arterial BP (ABP) during reperfusion on the extent of myocardial infarction and on coronary blood flow (CBF) in an occlusion/reperfusion experimental model.
Design: Prospective, randomized animal study.
Setting: University hospital.
Participants: Normal pigs that were anesthetized, intubated, and mechanically ventilated.
Interventions: Twenty-seven open-chest pigs underwent occlusion of the mid left anterior descending (LAD) coronary artery for 1 h followed by reperfusion for 2 h. During reperfusion, the animals were randomly assigned to either continuous infusion of nitroglycerin in therapeutic doses and fluid infusion at rates to maintain a mean ABP ≥ 80 mm Hg (group 1, n = 13), or continuous nitroglycerin infusion at rates to maintain a mean ABP between 60 mm Hg and 75 mm Hg (group 2, n = 14).
Measurements and results: The hemodynamics and the coronary ABP distal to the occlusion were recorded throughout the experiment. In addition, the LAD CBF and peak hyperemia CBF before occlusion and during reperfusion periods were measured by transit-time flowmetry. At the end of the experiment, the infarcted left ventricular myocardial size was measured. There were no significant hemodynamic differences, including the distal coronary arterial pressure, between the two groups before or during the LAD artery occlusion period. During reperfusion, mean ABP was 90 ± 3 mm Hg in group 1 vs 69 ± 3 mm Hg in group 2 (p < 0.001). In group 1, the infarcted myocardium represented 50.3 ± 4.3% of the myocardium at risk, vs 69.4 ± 7.2% in group 2 (p < 0.001). During reperfusion, CBF and peak hyperemia CBF were significantly higher in group 1 than in group 2.
Conclusions: Low ABP during reperfusion increases the size of myocardial infarction and decreases CBF.