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.

The influence of changes in the size of ischemic region on ST-segment potential distribution in isolated canine hearts.

In order to investigate how a change in the size of a ischemic region is reflected in ST-segment mapping studies, we produced two different sizes of ischemic regions by occluding proximal or distal portions of the left circumflex artery for five minutes, using ten isolated canine heart preparations. We examined the relationship between the geometry of the ischemic region and ST-segment potential distribution on the epicardial surface and that in the "precordium", in which the heart was suspended. The extent of the ischemic region was reflected differently on epicardial and "precordial" sites, in that the magnitude of epicardial ST-segment elevation decreased (p less than 0.001) while the "precordial" one increased (p less than 0.01). In the epicardium the degree of ST-segment elevation was almost uniform over the ischemic region, whereas in the "precordium" it was maximal at sites overlying the center of the ischemic region and progressively decreased approaching the periphery. However, frequent occurrence of intraventricular conduction disturbance was observed near the center of the ischemic region. As a result, the magnitude of epicardial ST-segment elevation near the center became larger than in the periphery. These results suggest that the classical solid angle theory provides a useful approximation of the ST-segment deflection in very acute ischemic phase, until development of the intraventricular conduction delay.