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 the effect of heart rate during regional ischemia. BACKGROUND: Myocardial ischemia changes the transmittal flow velocity pattern due to disease-induced changes in the heart's diastolic properties. METHODS: Regional ischemia was produced in 12 pigs by partially occluding the 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 ischemia, at two heart rates, 70 and 90 beats/min. RESULTS: Regional ischemia had a significant effect on two determinants of filling: relaxation, which was slower, and chamber stiffness, which increased. These changes were associated with reduced contractility and increased myocardial stiffness, resulting in an early transmitral flow pattern that was flatter and narrower, but no change in the late flow pattern. Moderate increases in heart rate accelerated relaxation and decreased atrioventricular pressure gradient but had no effect on contractility or myocardial or chamber stiffness, resulting in an early transmitral flow pattern that was flatter and narrower and an increased late flow velocity. CONCLUSIONS: This model of regional ischemia leads to a flatter and narrower early transmitral flow velocity pattern and no change in late flow due to a combination of slowed left ventricular relaxation and increased chamber stiffness. Reflex increases in heart rate that accompany ischemia tend to mask this effect.