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Published on: April 13, 2015
Myocardial blood flow and function with critical coronary stenosis in exercising dogs
Insights
Critical coronary stenosis limits blood flow during exercise, causing a detrimental "steal" phenomenon. This reduces subendocardial perfusion and impairs heart muscle function, highlighting the risks of compromised coronary vasodilator reserve.
Area of Science:
- Cardiovascular Physiology
- Coronary Artery Disease Research
- Hemodynamics
Background:
- Critical coronary stenosis impairs myocardial blood flow (MBF) during hyperemia.
- Subendocardial vasodilator reserve is depleted, while subepicardial reserve remains.
- The functional significance of remaining subepicardial vasodilator reserve in critical stenosis is unclear.
Purpose of the Study:
- To investigate the role of subepicardial vasodilator reserve in dogs with critical coronary stenosis during exercise.
- To determine the impact of this reserve on regional myocardial blood flow and contractile function.
Main Methods:
- Utilized six exercising dogs instrumented for MBF (microspheres), regional function (sonomicrometers), and coronary blood flow velocity (CBFV, Doppler).
- Induced critical coronary stenosis using a hydraulic occluder.
- Measured hemodynamic and functional parameters during treadmill exercise.
Main Results:
- Critical stenosis limited CBFV and mean MBF to resting levels during exercise.
- A transmural "steal" phenomenon occurred: subendocardial MBF decreased 50%, while subepicardial MBF increased 104%.
- Systolic wall thickening significantly decreased, indicating impaired regional contractile performance despite available subepicardial reserve.
Conclusions:
- Subepicardial vasodilator reserve in critical coronary stenosis offers little benefit to regional contractile function during exercise.
- The
- steal
- effect may be deleterious, potentially reducing subendocardial perfusion and worsening systolic wall thickening.
Abstract:
Critical stenosis of coronary arteries does not alter myocardial blood flow (MBF) at rest, but eliminates hyperemia and corresponds to a degree of arterial narrowing that expends subendocardial vasodilator reserve. Because subepicardial vasodilator reserve remains with critical stenosis at rest, we tested the significance of this reserve in six exercising dogs chronically instrumented to measure MBF (microspheres), regional function (systolic wall thickening with sonomicrometers), and coronary blood flow velocity (CBFV, pulsed Doppler). Critical stenosis produced with a hydraulic occluder limited CBFV and mean MBF to the resting level during treadmill exercise, but MBF was maldistributed. Subendocardial MBF decreased 50% (P less than 0.05) and subepicardial MBF increased 104% (P less than 0.01) compared with resting control conditions, suggesting that a transmural "steal" phenomenon had occurred, with augmented MBF in the subepicardial region at the expense of subendocardial MBF. Systolic wall thickening decreased markedly from 31.5 +/- 6.8 to 9.4 +/- 2.0% (P less than 0.01) during exercise, indicating that use of subepicardial vasodilator reserve with critical stenosis had little sustaining effect on regional contractile performance. Rather, subepicardial vasodilator reserve is potentially deleterious, inasmuch as a steal effect could contribute to reduced subendocardial perfusion, the primary determinant of systolic wall thickening.
