A critical view of coronary reserve

Coronary flow reserve is reduced by pathologic acquired left ventricular hypertrophy, and is less in subendocardial than subepicardial layers of normal or hypertrophied hearts. In normal hearts, pacing-induced tachycardia at a rate of 250 beats/min does not alter coronary reserve in the outer half of the left ventricular wall. Pacing produces a linear decrease in coronary reserve in the inner half, although the decrease is attenuated if perfusion pressure is elevated, as in systemic hypertension. Strenuous exercise can quadruple coronary flow, but modest coronary flow reserve is preserved in normal hearts. Whether this occurs when there is ventricular hypertrophy is unknown and requires study. The concept of coronary flow reserve is important to the understanding of pathophysiology, but data must be interpreted with caution because pharmacologic agents may produce more vasodilatation than can be attained by endogenous stimuli, even when there is marked ischemia.