Left ventricular pressure-length relation during exercise-induced ischemia

Abstract

The pressure-length relation in normal and ischemic segments was analyzed with use of left ventriculography and simultaneous micromanometry during supine exercise in 9 normal subjects and 12 patients with effort angina. Segmental analysis was done in the right anterior oblique projection using a long axis with three perpendicular, equidistant chords. The apical segment in the 12 patients with coronary artery disease represented the ischemic region. In 5 of the 12 patients with coronary artery disease, the basal segment that showed no exercise-induced deterioration in wall motion was used as an intrapatient control (nonischemic segment).In the 12 patients with coronary artery disease, left ventricular ejection fraction decreased (from 65% to 50%, p < 0.001), end-diastolic pressure increased (from 24 to 40 mm Hg, p < 0.001) and the lowest diastolic filling pressure increased (from 9 to 22 mm Hg, p < 0.001) during exercise-induced ischemia. In normal subjects, ejection fraction increased (from 64% to 70%, p < 0.01) with unchanged end-diastolic pressure, whereas the lowest diastolic filling pressure decreased during exercise (from 9 to 3 mm Hg, p < 0.01). Global left ventricular diastolic pressure-volume curves showed an upward and rightward shift during exercise-induced ischemia. Regional pressure-length curves of both nonischemic (n = 5) and ischemic (n = 12) segments were shifted upward in early diastole, but moved to a higher portion of the rest pressure-length curve without an upward shift during mid- to end-diastole. In contrast, the apical segment in normal subjects showed a downward shift during exercise. Regional stiffness increased during exercise-induced ischemia in the ischemic but not in the nonischemic segment.In conclusion, the global left ventricular diastolic pressure-volume relation shows an upward and rightward shift during exercise-induced ischemia, whereas the regional pressure-length curves of the nonischemic and ischemic segments show an upward shift only during early, but not during late, diastole. This early diastolic upward shift of the regional pressure-length curve is more pronounced in the nonischemic segment. Regional stiffness is increased only in the ischemic segment. Thus, there is a time-dependent upward shift of the regional pressure-length curve during exercise-induced ischemia that is probably due to delayed relaxation in the ischemic segment and increased viscous forces in the nonischemic segment.