Mechanisms of retarded apical filling in acute ischemic left ventricular failure

Background-We examined the hypothesis that retardation of apical filling as measured by color M-mode Doppler echocardiography in the diseased left ven tricle (LV) reflects a decrease in the intraventricular mitral-to-apical Methods and Results-In 9 open-chest anesthetized dogs, micromanometers were placed near the mitral tip and in the apical region. From the color M-mode Doppler images, the time delay (TB) between peak velocity at the mitral ti p and the apical region was determined as an index of LV flow propagation. Acute ischemic LV failure was induced by coronary microembolization. Induct ion of ischemia caused a marked increase in LV end-diastolic pressure and a decrease in LV ejection fraction. The time constant of LV isovolumic apica l pressure decay (tau) increased from 31+/-8 to 49+/-16 ms (P<0.001). The p eak early diastolic mitral-to-apical pressure gradient (Delta PLVmitral-ape x) decreased from 1.9+/-0.9 to 0.7+/-0.5 mm Hg (P<0.01), and TD increased f rom 5+/-3 to 57+/-26 ms (P<0.001). The slowing of flow propagation was limi ted to the apical portion of the LV cavity. The TD correlated with Delta PL Vmitral-apex (r=-0.94, P<0.01) and with tau (r=0.92, P<0.01). Before ischem ia, the mitral-to-apical flow propagation velocity far exceeded the velocit y of the individual blood cells, whereas during ischemia, flow propagation velocity approximated the blood Conclusions-Retardation of apical filling acute ischemic failure was attrib uted to a decrease in the mitral-to-apical driving pressure, reflecting slo wing of LV relaxation. The slowing of flow propagation appeared to represen t a shift in apical filling from a pattern of column motion to a pattern do minated by convection.