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Coronary patency and its relation to contractile reserve in hibernating myocardium
James A Fallavollita1, Michael Logue, John M Canty
1Veterans Affairs Western New York Health Care System, The University at Buffalo, 14214, USA. jaf7@buffalo.edu
Insights
Epicardial artery patency influences myocardial function in hibernating myocardium. Patent arteries allow for contractile reserve, while occluded arteries limit it due to exhausted subendocardial flow reserve.
Area of Science:
- Cardiovascular Physiology
- Myocardial Viability Assessment
Background:
- Hibernating myocardium, characterized by dysfunction and reduced resting flow, may retain contractile reserve.
- Epicardial artery patency is a potential predictor of subendocardial flow reserve and contractile function in these segments.
Purpose of the Study:
- To investigate the relationship between epicardial artery patency and subendocardial flow reserve in hibernating myocardium.
- To determine if epicardial artery patency predicts contractile reserve in chronically dysfunctional myocardial segments.
Main Methods:
- Chronic left anterior descending artery stenosis was induced in pigs to create hibernating myocardium.
- Flow, ventricular function, contractile reserve, and (18)F-2-deoxyglucose deposition were quantified.
Main Results:
- Hibernating myocardium was observed in both occluded and patent coronary artery groups.
- Collateral-dependent hibernating myocardium showed exhausted subendocardial flow reserve and limited contractile reserve.
- Hibernating myocardium distal to a patent artery exhibited preserved subendocardial flow reserve and greater contractile reserve.
Conclusions:
- Myocardial physiology and metabolism in hibernating segments depend on stenosis severity and subendocardial flow reserve.
- Limited contractile reserve in collateral-dependent hibernating myocardium is linked to exhausted subendocardial flow reserve.
- Metabolic imaging may be superior for assessing viability distal to complete coronary occlusions.
Objectives:
Recent clinical studies suggest that contractile reserve may occur in a minority of viable, chronically dysfunctional segments with reduced resting flow (hibernating myocardium). We hypothesized that epicardial artery patency might predict which segments have critically reduced subendocardial flow reserve and limited contractile reserve.
Methods:
Pigs were chronically instrumented with a fixed stenosis on the left anterior descending coronary artery (LAD) to produce hibernating myocardium. At least 3 months later, flow at rest and during adenosine vasodilation (microspheres), ventricular function and contractile reserve (contrast ventriculography), and (18)F-2-deoxyglucose (FDG) deposition (ex vivo tissue counting) were quantified.
Results:
Hibernating myocardium (regional dysfunction with reduced resting perfusion) was present in animals with an occluded (n=40) or patent (n=19) LAD. Viability was confirmed by histology and FDG deposition. In collateral-dependent hibernating myocardium, subendocardial flow did not increase above baseline levels during epinephrine or adenosine stimulation, consistent with exhausted subendocardial flow reserve at rest. This was associated with limited contractile reserve and regionally increased FDG deposition. In contrast, subendocardial flow reserve was present in hibernating myocardium distal to a patent artery. Contractile reserve during epinephrine infusion in this group was significantly greater than in animals with an occluded artery.
Conclusions:
The physiology and metabolism of hibernating myocardium was dependent upon stenosis severity and its effects on subendocardial flow reserve. In collateral-dependent hibernating myocardium, contractile reserve was limited in the setting of exhausted subendocardial flow reserve, thus supporting the hypothesis that metabolic imaging may be preferable for determining viability distal to a complete occlusion.