Tachycardia induced reduction in coronary blood flow distal to a stenosis

Clinical and experimental data indicate that some coronary stenoses can rapidly change shape thereby influencing the hemodynamic severity of the stenosis. In 7 closed chest dogs, we examined the effects of distal coronary arteriolar vasomotor tone and myocardial oxygen demands on a coronary stenosis created by partial intraluminal occlusion, using a small balloon catheter. Myocardial blood flow (ml/g per min) was measured with 15-microns radioactive microspheres. Stenotic resistance was calculated as the mean pressure gradient across the stenosis divided by the mean blood flow through the stenosis. The mean pressure gradient was calculated as the ascending aortic pressure minus the left anterior descending coronary artery pressure distal to the stenosis. Coronary arteriolar vasodilation induced by pacing (170 beats/min) increased stenotic resistance (1.64 +/- 0.27 to 26.48 +/- 13.77 mmHg/ml per min, P less than 0.05) and decreased myocardial blood flow (endocardial 0.42 +/- 0.04 to 0.17 +/- 0.04, P less than 0.05, midcardial 0.35 +/- 0.03 to 0.13 +/- 0.04, P less than 0.05; epicardial 0.22 +/- 0.05 to 0.15 +/- 0.05). Five dogs fibrillated within 10 min of continuous tachycardia and partial arterial occlusion. The change in arteriolar vasomotor tone and decreased aortic pressure induced by pacing altered the severity of the stenosis and resulted in a reduction of blood flow to the myocardium.