Effects of exercise stress on left ventricular end diastolic pressure-length strain relations in dogs with and without coronary stenosis

Objective: The aim was to elucidate the alterations of left ventricular diastolic properties, taking into account changes in unstressed length during exercise stimuli with and without coronary stenosis. Methods: Left ventricular end diastolic pressure-length strain relations using segment length normalised to Lagrangian strain, and the rate of relaxation, were studied in seven open chest anaesthetised dogs with and without coronary stenosis on both left anterior descending and circumflex coronary arteries (approximately 30% resting flow reduction) during simulated dynamic exercise. Regional segment length was measured with ultrasonic crystals placed in the left anterior descending subendocardial region, and unstressed segment length at zero transmural pressure was obtained by occluding the vena cava. Results: Peak negative dP/dt was decreased and isovolumetric left ventricular relaxation time constant increased by coronary stenoses; however neither changed significantly during simulated exercise. Left ventricular end diastolic pressure was significantly increased by coronary stenoses, from 3.1(SEM 0.8) to 7.0 (0.9) mm Hg (p<0.05), and further increased to 15.5(1.1) mm Hg (p<0.01) during simulated exercise, although right ventricular end diastolic pressure did not change. Unstressed length was increased in coronary stenoses from 9.03(0.08) to 9.89(0.13) mm (p<0.01), and further increased to 10.34(0.14) mm (p<0.01) during exercise, whereas it tended to decrease without coronary stenosis, from 9.03(0.08) to 8.79(0.11) mm during exercise. Left ventricular end diastolic pressure-length strain relations progressively shifted upward and leftward with coronary stenoses and subsequent exercise, but shifted downward and rightward during exercise without coronary stenosis. Conclusions: The increase in unstressed length or volume may contribute to exercise induced left ventricular dilatation observed in patients in effort angina. End diastolic distensibility decreases in both mild supply induced and exercise induced ischaemia, whereas in the normal heart, left ventricular end diastolic distensibility increases during exercise.