Influence of aortic stenosis on the hemodynamic importance of coronary artery narrowing in dogs without left ventricular hypertrophy

Coronary hemodynamic effects of controlled left ventricular outflow obstruction stimulating aortic valve stenosis were studied in 20 open-chest dogs, with and without graded coronary artery diameter narrowing. Aortic stenosis was regulated so that a mean left ventricular-aortic pressure gradient of 46 +/- 20 mm Hg (mean +/- standard deviation) was created as both heart rate and stroke volume were unchanged. In addition, during aortic stenosis, mean aortic pressure (105 +/- 17 to 84 +/- 15 mm Hg, p less than 0.05) and diastolic pressure time index/systolic pressure time index ratio (1.2 +/- 0.3 to 0.6 +/- 0.2, p less than 0.05) decreased and end-diastolic left ventricular pressure (7 +/- 4 to 14 +/- 6 mm Hg, p less than 0.05) increased. With no coronary narrowing, mean coronary flow increased during aortic stenosis (53 +/- 23 to 62 +/- 23 ml/min) as the percentage of diastolic flow increased (83 +/- 6 to 89 +/- 4) and endocardial/epicardial ratio decreased (1.14 +/- 0.16 to 0.95 +/- 0.24) (all p less than 0.05). Peak reactive hyperemic flow also decreased (168 +/- 85 to 125 +/- 73 ml/min, p less than 0.05). This value with no coronary narrowing was similar to peak hyperemic flow with 60% narrowing without aortic stenosis. With 90% coronary narrowing, mean coronary flow decreased with or without aortic stenosis. Transmural flow distribution also decreased but was lower during aortic stenosis (0.86 +/- 0.19 to 0.61 +/- 0.25, respectively; p less than 0.05). These data suggest that although mean coronary flow is increased during aortic stenosis, endocardial flow may be limited, and coronary reserve exposed during reactive hyperemia appears decreased. When a coronary artery is narrowed, aortic stenosis has an even more important hemodynamic influence on the coronary circulation.