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Absence of coronary vascular reserve in myocardium distal to a fixed coronary stenosis
L W Klein1, A D Askenase, W S Weintraub
1Mid-Atlantic Heart and Vascular Institute, Presbyterian University of Pennsylvania Medical Center, Philadelphia 19104.
Insights
This study demonstrates that coronary vascular reserve is not fully exhausted during significant coronary artery stenosis. Even with reduced resting blood flow, the heart can still increase flow when needed.
Area of Science:
- Cardiovascular Physiology
- Coronary Circulation Research
Background:
- Assessing coronary vascular reserve is crucial for understanding myocardial oxygen supply and demand.
- Previous studies suggest vascular reserve may be limited in conditions of reduced coronary flow.
Purpose of the Study:
- To investigate whether coronary vascular reserve is depleted in the presence of a resting blood flow deficit caused by coronary artery stenosis.
- To evaluate the heart's ability to augment coronary blood flow under hyperemic conditions despite induced stenosis.
Main Methods:
- Canulation and perfusion of the left anterior descending or circumflex artery in dogs.
- Induction of moderate and severe coronary artery stenosis using a screw clamp.
- Measurement of coronary blood flow and subendocardial/subepicardial flow before and after stenosis and during adenosine infusion.
- Assessment of myocardial contractility using segment length crystals in a subset of experiments.
Main Results:
- Moderate stenosis reduced resting coronary flow, but adenosine infusion still increased flow.
- Severe stenosis led to a significant reduction in flow and decreased segmental shortening.
- Coronary flow increased with adenosine administration and further upon stenosis adjustment, indicating remaining vascular reserve.
- Subendocardial flow decreased with adenosine under stenosis but increased with perfusion pressure adjustment.
Conclusions:
- Coronary vascular reserve is not completely exhausted even with significant coronary artery stenosis and reduced resting flow.
- The heart retains the capacity for hyperemic flow augmentation, suggesting potential for therapeutic interventions.
- Findings challenge the notion of complete vascular reserve depletion in ischemic heart disease.
Abstract:
In a study to test the hypothesis that vascular reserve is exhausted in the setting of a resting blood flow deficit, the left anterior descending or circumflex artery was cannulated and perfused from the left carotid artery. After reactive hyperaemia had been assessed a stenosis was produced with a screw clamp. In the first experiment a moderate stenosis (diastolic perfusion pressure 40 mmHg) was produced in the left anterior descending artery (three dogs) or left circumflex artery (three dogs). Blood pressure was held constant with aortic constriction during intracoronary adenosine infusion (6 mumol.min-1). The stenosis was then adjusted to the preadenosine perfusion pressure. In the second experiment the anterior interventricular coronary vein was also isolated and segment length crystals were placed in the ischaemic and non-ischaemic zones. Severe stenosis (flow reduction of at least 50% and evidence of decreased segmental shortening) was produced in the cannulated left anterior descending artery (eight dogs). Intracoronary adenosine was given with aortic pressure held constant by transfusion and coronary venous drainage. In the first experiment resting coronary flow (ml.min-1) decreased from 41(3) to 29(6) (p less than 0.05) with stenosis. Coronary flow increased from 29(6) to 34(7) (p less than 0.05) with adenosine and to 50(10) (p less than 0.05) with stenosis adjustment. Subendocardial flow (ml.g-1.min-1) decreased from 0.89(0.26) to 0.78(0.23) (p less than 0.05) with adenosine and then increased from 0.94(0.49) with perfusion pressure adjustment. Subepicardial flow tended to increase with adenosine, and increased further with stenosis adjustment.(ABSTRACT TRUNCATED AT 250 WORDS)