Preconditioning myocardium with demand ischemia in the presence of a critical coronary artery stenosis.

ABSTRACT

The relative importance of adrenergic stimulation and demand ischemia as important preconditioning stimuli remains unclarified. The purpose of this investigation was to use a partial coronary stenosis to define the preconditioning role of demand ischemia. Dobutamine was infused intravenously before coronary occlusion in closed-chest swine with and without an artificial coronary stenosis in the mid-left anterior descending coronary artery. Control animals had no stenosis and did not receive dobutamine before occlusion. All three groups underwent 45 minutes of occlusion followed by 120 minutes of reperfusion. At baseline, regional myocardial blood flow in the area at risk was reduced in animals with a stenosis, but global left ventricular systolic function, measured by gated blood pool scan, was equivalent in all three groups. Animals with and without a stenosis received equivalent catecholamine stress with dobutamine, but only animals with a stenosis manifested ischemia during the infusion. At 2 hours after reperfusion, infarct size as a percentage of the area at risk was smaller in animals with a stenosis given dobutamine. Demand ischemia preconditions myocardium in closed-chest swine. Increased demand alone without ischemia had marginal preconditioning effects. This may have clinical relevance to patients with severe stenoses exposed to stressful stimuli before the development of myocardial infarction.