Changes in porcine transmitral flow velocity pattern and its diastolic determinants during partial coronary occlusion

OBJECTIVES To define the mechanical determinants of transmitral flow and th e effect of heart rate during regional ischemia. BACKGROUND Myocardial ischemia changes the transmitral flow velocity patter n due to disease-induced changes in the heart's diastolic properties. METHODS Regional ischemia mas produced in 12 pigs by partially occluding th e left anterior descending coronary artery until segment-length shortening in the ischemic region fell by 20%. Transmitral flow velocity patterns and their determinants were measured under two conditions, baseline and ischemi a, at two heart rates, 70 and 90 beats/min. RESULTS Regional ischemia had a significant effect on two determinants of f illing: relaxation, which was slower, and chamber stiffness, which increase d. These changes were associated with reduced contractility and increased m yocardial stiffness, resulting in an early transmitral flow pattern that wa s flatter and narrower, but no change in the late flow pattern. Moderate in creases in heart rate accelerated relaxation and decreased atrioventricular pressure gradient but had no effect on contractility or myocardial or cham ber stiffness, resulting in an early transmitral flow pattern that was flat ter and narrower and an increased late flow velocity. CONCLUSION This model of regional ischemia leads to a flatter and narrower early transmitral flow velocity pattern and no change in late how due to a combination of slowed left ventricular relaxation and increased chamber sti ffness. Reflex increases in heart rate that accompany ischemia tend to mask this effect. (C) 1999 by the American College of Cardiology.