Left ventricular dimensions and function during right ventricular pressure overload

The effects of right ventricular (RV) pressure overload on left ventricular (LV) function is controversial. Therefore, we examined LV dimensions and shortening after acute and chronic pulmonary artery (PA) constriction in six conscious dogs, preinstrumented with LV and RV catheters, an LV micromanometer, a PA inflatable cuff occluder, and ultrasonic crystals to measure an LV anteroposterior, a septal-lateral, and a free wall segment chord. Studies were performed before, immediately after, and 2, 4, and 6 wk after PA constriction. With acute cuff inflation, RV systolic- and end-diastolic pressures rose, but LV end-diastolic pressure fell. Both septal-lateral end-diastolic length and systolic shortening declined 4.1 +/- 0.7 mm and 5.9 +/- 2.3% respectively (P less than 0.01), whereas the anteroposterior and segment chords were unaffected. With chronic RV pressure overload septal-lateral shortening but not end-diastolic length returned to control levels. Also the first derivative of LV pressure (LV dP/dt) fell 540 +/- 164 mmHg/s by 6 wk compared with control, but this decline was reversed by volume expansion with dextran. We conclude that RV pressure overload displaces the septum toward the LV free wall; acutely this displacement is primarily at end diastole, but chronically it occurs at end systole as well, maintaining the septal contribution to LV ejection. Thus chronic RV pressure overload is associated with significant changes in LV diastolic shape but maintenance of normal LV function.