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Reduction of systolic coronary blood flow in experimental left ventricular outflow tract obstruction
1Henry Ford Heart and Vascular Institute, Detroit, MI 48202.
Insights
Subaortic obstruction in dogs reduced systolic coronary blood flow (CBF) by increasing left ventricular pressure. This finding suggests that elevated LV pressure can impair coronary flow reserve, even with normal coronary arteries.
Area of Science:
- Cardiovascular Physiology
- Hemodynamics
- Coronary Circulation
Background:
- Aortic valvular stenosis is associated with diminished coronary reserve despite normal coronary arteries.
- The underlying mechanisms for reduced coronary blood flow (CBF) in valvular stenosis require further investigation.
Purpose of the Study:
- To investigate the impact of acute subaortic valvular obstruction on coronary blood flow (CBF).
- To elucidate the effects of elevated left ventricular (LV) pressure on coronary hemodynamics.
Main Methods:
- Acute subaortic obstruction was induced in seven open-chest anesthetized dogs using a catheter-tip balloon.
- Left ventricular pressure was elevated while maintaining constant aortic pressure (coronary perfusion pressure).
- Coronary blood flow (CBF) was measured in the left anterior descending artery under conditions of intact vasomotor tone and maximal vasodilation.
Main Results:
- In dogs with intact coronary vasomotor tone, subaortic obstruction significantly decreased systolic CBF (p < 0.001) but increased diastolic CBF (p < 0.05), with no change in total CBF.
- In dogs with maximal vasodilation, systolic CBF decreased, diastolic CBF remained unchanged, and total CBF decreased during obstruction.
- Elevated LV intracavitary pressure above coronary perfusion pressure reduced systolic CBF.
Conclusions:
- Acute subaortic obstruction can reduce systolic coronary blood flow (CBF).
- The findings suggest that elevated left ventricular (LV) pressure can compromise coronary flow reserve through autoregulatory compensation.
- This phenomenon highlights a potential mechanism for diminished coronary reserve in conditions like aortic valvular stenosis.
Abstract:
In aortic valvular stenosis, coronary reserve has been shown to be markedly diminished despite normal coronary arteries. To gain further insight into this phenomenon, we examined the effects of an acute subaortic valvular obstruction on coronary blood flow (CBF) in seven open-chest anesthetized dogs. Transient subaortic obstruction was produced by inflating a catheter-tip balloon in the left ventricular (LV) outflow tract. The degree of obstruction, a 26 +/- 3 mm Hg gradient across the aortic valve, was adjusted to achieve an elevation of LV pressure while maintaining a constant aortic pressure (coronary perfusion pressure). In seven dogs with intact coronary vasomotor tone, systolic left anterior descending CBF decreased from 20 +/- 9 ml/min during the control period to 13 +/- 3 ml/min during subaortic obstruction (p less than 0.001). Diastolic CBF increased from 52 +/- 9 to 58 +/- 10 ml/min (p less than 0.05), and total CBF remained unchanged. In three dogs with maximal coronary vasodilation, systolic CBF decreased during subaortic obstruction, diastolic CBF remained unchanged, and total CBF decreased. The present data suggest that elevation of LV intracavitary pressure above coronary perfusion pressure can reduce systolic CBF and lead to an autoregulatory compensation that taxes coronary flow reserve.