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Regional myocardial function is not affected by severe coronary depressurization provided coronary blood flow is
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Regional left ventricular function depends on subendocardial blood flow, not coronary perfusion pressure. This finding clarifies the impact of vasodilation on heart muscle performance and recovery after revascularization.
Area of Science:
- Cardiology
- Cardiovascular Physiology
Background:
- Distal vasodilation in coronary stenosis can decrease perfusion pressure, potentially impairing regional left ventricular function.
- This phenomenon may explain the clinical observation of improved regional dysfunction after coronary revascularization.
Purpose of the Study:
- To test the hypothesis that regional myocardial function correlates with regional coronary blood pressure when coronary flow remains constant.
- To investigate the relationship between coronary perfusion pressure and regional left ventricular contractile function.
Main Methods:
- Dogs were chronically instrumented with flow probes, pressure catheters, and sonomicrometers in the left circumflex coronary artery.
- Regional coronary vascular resistance was reduced using intracoronary dipyridamole while blood flow was controlled by a proximal occluder.
Main Results:
- Mean left circumflex artery pressure was significantly reduced (83 to 38 mm Hg) while circumflex coronary blood flow was maintained constant.
- Regional contractile function, measured by sonomicrometers, remained unchanged despite the drop in perfusion pressure.
Conclusions:
- Regional myocardial contractile function is primarily dependent on subendocardial blood flow.
- Coronary perfusion pressure, in the absence of altered flow, does not directly impact regional left ventricular function.
Abstract:
It has been suggested that vasodilation distal to a stenosis may cause a profound decrease in perfusion pressure and adversely affect regional left ventricular function. This phenomenon could explain the clinical concept of reversal of regional dysfunction by coronary revascularization. To evaluate the hypothesis that regional myocardial function parallels regional coronary blood pressure in the absence of changes in coronary flow, dogs chronically instrumented with left circumflex coronary artery flow probes, cuff occluders, pressure catheters and segmental function sonomicrometers were studied. By decreasing regional coronary vascular resistance with selective intracoronary dipyridamole and controlling blood flow with a proximal coronary cuff occluder, the mean left circumflex artery pressure was reduced from 83 +/- 3 to 38 +/- 2 mm Hg while circumflex coronary blood flow was maintained constant. Regional contractile function as measured by circumflex sonomicrometers was unchanged at constant circumflex subendocardial blood flow as measured by radioactive microspheres. These findings suggest that regional contractile function is dependent on subendocardial blood flow and is independent of coronary perfusion pressure.