Exercise-induced ischemia: The influence of altered relaxation on early diastolic pressures

Abstract

Left ventricular pressure (LVP) decay and early diastolic pressures were studied at rest and during exercise in three groups of patients. Patients in the ischemia group (n=15) had coronary artery disease and developed new regional wall motion abnormalities documented by biplane LV cineangiography during exercise. Patients in the control group (n=4) had a normal exercise response. Patients in the scar group (=5) had prior infarction, akinetic scars and no ischemia with exercise. Isovolumic pressure data were used to compute the time constant (T) of LVP decay (from the linear relation of LVP and negative dP/dt) and an extrapolated baseline pressure (P(B)) at dP/dt = 0. During exercise in the ischemia group, minimal LV diastolic pressure (P(L)) increased from 9 ± 3 to 21 ± 5 mm Hg (p<0.001), end-systolic volume increased from 38 ± 7 to 55 ± 8 ml/m2 (p<0.001) and P(B) rose from -10 ± 7 to 11 ± 8 mm Hg (p<0.01); T decreased (from 55 ± 9 to 37 ± 8 msec, p<0.01), although inadequately, compared with the decrease in the control group (from 49 ± 15 to 22 ± 2 msec, p<0.01). Relaxation at P(L) during exercise was incomplete in the ischemia group (2.2 ± 0.4 T) and complete in the control group (3.8 ± 0.7 T, p<0.05). The time course of LVP fall was extrapolated from the isovolumic period into the passive LV filling phase. The extrapolated pressure at the time P(L) occurred (P(E)) rose from 0 ± 4 to 20 ± mm Hg with ischemia (p<0.001). Thus, the characteristics of LVP decay can account for the elevated early diastolic pressures during ischemia. In contrast, the scar group maintained a low P(L) during exercise (11 ± 3 to 8 ± 3 mm Hg), even though T decreased inadequately (from 66 ± 10 to 36 ± 5 msec, p<0.01), because P(B) did not shift upward. Ischemia-related pressure elevations involve both delayed relaxation and a pressure baseline shift. During exercise, LVP decay is normally adjusted to maintain low diastolic pressures; with exercise-induced ischemia, LVP decay is abnormal and early diastolic pressures are severely elevated.