CORONARY BLOOD-FLOW RESERVE IN ACUTE AORTIC REGURGITATION

Objectives. This study sought to determine the impact of acute aortic regurgitation on coronary blood flow reserve and phasic epicardial coronary blood flow in closed chest dogs. Background. Hemodynamic changes in acute aortic regurgitation are known to precipitate myocardial ischemia, Coronary blood Bow reserve has not been studied in closed-chest experimental preparations with acute aortic regurgitation. Methods. Graded temporary acute aortic regurgitation was produced in 11 mongrel dogs. Phasic coronary blood flow velocities were measured using a Doppler guide wire. Coronary flow reserve was defined as the ratio of the time average of spectral peak velocity after administration of papaverine to that of the baseline state. Results. Under control conditions (mean [+/-SEM] diastolic blood pressure 82.2 +/- 4.5 mm Hg), coronary flow reserve was 3.51 +/- 0.27 with predominantly diastolic epicardial coronary blood flow. With mild acute aortic regurgitation (diastolic blood pressure 61.8 +/- 3.0 mm Hg), coronary flow reserve decreased to 2.38 +/- 0.27, with an increase in phasic systolic epicardial coronary blood flow. At the onset of moderate acute aortic regurgitation (diastolic blood pressure 42.1 +/- 0.9 mm Hg), coronary flow reserve declined further to 1.46 +/- 0.12, and the phasic systolic epicardial coronary blood flow became more prominent. With severe aortic regurgitation (diastolic blood pressure 29.2 +/- 2.2 mm Hg), coronary flow reserve reached 1.20 +/- 0.05, and the phasic epicardial coronary blood flow pattern was found to be predominantly systolic with retrograde diastolic flow. The ratio of diastolic to systolic pressure-time indexes with severe aortic regurgitation suggested subendocardial underperfusion. Conclusions. This study demonstrates a marked decline in coronary blood flow reserve and documents a progressive change in the phasic epicardial blood flow to a predominantly systolic pattern with increasing degrees of acute aortic regurgitation.