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  • Title: A canine model of acute coronary artery stenosis: effects of deliberate hypotension.
    Author: Hickey RF, Verrier ED, Baer RW, Vlahakes GJ, Fein G, Hoffman JI.
    Journal: Anesthesiology; 1983 Sep; 59(3):226-36. PubMed ID: 6881588.
    Abstract:
    Coronary artery disease is considered a contraindication to inducing hypotension during surgery because the combined effects of stenosis and hypotension in reducing distal coronary artery perfusion pressure might produce myocardial ischemia. To study the effect of deliberate hypotension (mean systemic pressure, 50 mmHg) on regional myocardial perfusion, oxygenation, and lactate extraction, we constricted the left-anterior descending coronary artery (LADCA) in dogs. Two degrees of stenosis were studied: "critical" stenosis, which reduced resting coronary blood flow from 34.4 to 31.2 ml/min and abolished reactive hyperemia of the LADCA in response to 10 s of total coronary artery occlusion; and a more "severe" stenosis, which reduced resting coronary blood flow by 40%. LADCA pressure was measured distal to the stenosis, and LADCA perfusion pressure was obtained by subtracting the left ventricular end-diastolic pressure from the coronary artery diastolic pressure measured past the stenosis. Hypotension was induced by administering sodium nitroprusside, halothane at a high concentration, or trimethaphan. Lactate extraction and oxygen consumption were measured across the myocardium distal to the stenosis (from the coronary artery to the great cardiac vein) and across the whole heart (from the coronary artery to the coronary sinus). Regional myocardial blood flow was measured using radioactive microspheres. A transmural electrocardiogram was obtained from electrodes implanted in the subendocardium and the subepicardium in the distribution of the LADCA distal to the stenosis. Although the combination of critical stenosis and hypotension reduced regional myocardial blood flow and lowered LADCA perfusion pressure to 27 +/- 3 (SE) mmHg, myocardial ischemia did not occur, as evidenced by continued lactate extraction and no redistribution of transmural blood flow or change in ST segment. On the other hand, the combination of severe stenosis and hypotension reduced LADCA perfusion pressure to 17 +/- 2 (SE) mmHG and produced evidence of ischemia by regional lactate production, reduction of the subendocardial/subepicardial flow ratio, and depression of the ST segment.
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