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Contrasting effects of pharmacologic vasodilation on true collateral and overlap perfusion in ischemic myocardium
Insights
Chromonar, a coronary vasodilator, reduced true collateral blood flow but increased overlap perfusion in ischemic heart tissue in dogs. This suggests dual effects on myocardial perfusion sources during coronary occlusion.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
- Myocardial Perfusion
Background:
- Acute coronary occlusion leads to myocardial ischemia.
- Understanding perfusion in ischemic myocardium is crucial for therapeutic interventions.
- Two distinct perfusion pathways, collateral and overlap flow, exist in the heart.
Purpose of the Study:
- To investigate the independent effects of chromonar, a selective coronary vasodilator, on true collateral blood flow and overlap flow in ischemic myocardium.
- To determine the dose-dependent response of these perfusion pathways to chromonar.
- To elucidate the impact of pharmacologic vasodilation on different perfusion sources in the context of coronary occlusion.
Main Methods:
- Anesthetized dogs underwent acute coronary occlusion.
- Chromonar was administered intravenously at doses of 3.5 and 7.0 mg/kg.
- True collateral blood flow and transmural overlap flow were measured independently.
- Perfusion was assessed in subepicardial and subendocardial regions.
Main Results:
- Chromonar significantly reduced true collateral flow in a dose-dependent manner (P < 0.05).
- Transmural overlap flow was significantly increased by chromonar.
- True collateral flow reduction affected both subepicardial and subendocardial regions.
- Overlap perfusion increase was observed in both subepicardial and subendocardial layers.
Conclusions:
- Myocardial ischemia is supplied by two independent perfusion sources: true collateral flow and overlap flow.
- Pharmacologic vasodilation with chromonar has opposing effects on these pathways.
- Chromonar causes a "steal" of true collateral blood flow while enhancing overlap perfusion in ischemic myocardium.
Abstract:
The effects of chromonar (3.5 and 7.0 mg/kg i.v.), a selective coronary vasodilator, on true collateral blood flow and overlap flow (noncollateral perfusion due to overlapping end arteries of adjacent coronary vessels) were measured independently in anesthetized dogs following acute coronary occlusion. Collateral flow in the ischemic zone was significantly (P less than 0.05) reduced by chromonar in a dose-related manner while transmural overlap flow was increased. True collateral flow was distributed primarily to the subepicardium and chromonar produced a significant reduction in both subepicardial and subendocardial perfusion. Overlap perfusion was distributed equally across the left ventricular wall and chromonar increased perfusion to both subepicardium and subendocardium. The results indicate that there are two independent sources of perfusion of ischemic myocardium and that pharmacologic vasodilation with chromonar produces opposite effects on each: a steal of true collateral blood flow and an increase in overlap perfusion.