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Regression and recovery of well-developed coronary collateral function in canine hearts after aorta-coronary bypass
N Watanabe1, S Yonekura, A G Williams
1Department of Physiology, Texas College of Osteopathic Medicine, Forth Worth, Texas 76107.
Insights
Coronary artery bypass grafting leads to rapid collateral vessel regression. Nitroglycerin can dilate these regressed vessels, but does not prevent regression after bypass graft occlusion.
Area of Science:
- Cardiovascular Physiology
- Surgical Research
Background:
- Coronary artery bypass grafting (CABG) restores blood flow, causing regression of collateral vessels.
- The speed of collateral regression and recovery after graft occlusion is debated.
- The efficacy of pharmacologic agents in accelerating collateral recovery is unclear.
Purpose of the Study:
- To investigate the rate of collateral regression after CABG.
- To determine the recovery of collateral function after acute bypass graft occlusion.
- To assess the effect of nitroglycerin on collateral recovery.
Main Methods:
- Utilized 14 canine hearts with collateralization via Ameroid occlusion of the left anterior descending coronary artery.
- Studied collateral function regression and recovery after opening and closing an aorta-coronary bypass.
- Measured peripheral coronary pressure, retrograde flow, collateral flow, and collateral resistance.
Main Results:
- Bypass perfusion significantly decreased collateral flow and increased collateral resistance.
- Acute bypass occlusion led to spontaneous decrease in collateral resistance.
- Nitroglycerin rapidly decreased collateral resistance but did not prevent subsequent regression.
Conclusions:
- Mature collateral function exhibits rapid, though not instantaneous, regression and recovery.
- Regressed collateral vessels demonstrate dilation capacity with nitroglycerin.
- Flow-dependent changes in collateral vascular tone influence early regression and recovery.
Abstract:
After restoration of antegrade blood flow by coronary artery bypass grafting to a region of myocardium supplied by well-developed collateral vessels, there is regression of collateral supply to that region. There is controversy as to how rapidly this regression occurs, how soon collateral flow might return after an acute occlusion of the bypass graft, and how effective pharmacologic agents such as nitroglycerin might be in accelerating this return. To investigate this problem, 14 canine hearts were collateralized by Ameroid occlusion of the left anterior descending coronary artery. Regression and recovery of well-developed collateral function were studied after opening and closing an aorta-coronary bypass. Before bypass, peripheral coronary pressure was 82 +/- 2 mm Hg, retrograde flow 63 +/- 7 ml/min, collateral flow 21 +/- 2 ml/min, and collateral resistance 0.96 +/- 0.13 mm Hg/ml/min. One hundred minutes of bypass perfusion significantly decreased peripheral coronary pressure by 27%, retrograde flow by 52%, and collateral flow by 42%, and significantly increased collateral resistance by 319%. When the bypass was acutely occluded for 30 minutes, collateral resistance decreased spontaneously by 37%. When intracoronary nitroglycerin was administered for 5 minutes immediately after bypass occlusion, collateral resistance rapidly decreased by 72%, but subsequent collateral regression was not alleviated. Increased flow through regressed collateral vessels during retrograde flow diversion was associated with a decrease in collateral resistance. Results demonstrate rapid but not instantaneous regression and recovery of mature collateral function in response to requirements of collateral-dependent myocardium. Regressed collateral vessels can be dilated by nitroglycerin. Flow-dependent changes in collateral vascular tone appear to be responsible for early regression and recovery of collateral function.