Experimental Study on Right Ventricular Function : Right Ventricular Systolic Time Intervals in Acute Pulmonary Embolism

Right ventricular systolic time intervals (RVSTI) in experimentally produced acute pulmonary embolism were studied to evaluate right ventricular function. Acute pulmonary embolism was produced in 12 healthy adult mongrel dogs by injected carbon grains (50 to 100 microns in diameter) suspected in physiological saline into the right atrium of the dogs through a catheter. The amount of carbon grains suspention into the right atrium was increased monitoring pulmonary artery mean pressure (PAm). Measurements for determining right ventricular function were made when PAm, elevated by injecting the carbon grains suspention, was reached to a stable level. These measurements were repeated twice to 5 times at difference PAm levels in each dog. Subfractions of RVSTI, prejection period (PEP), ejection time (ET) and PEP/ET, were obtained analysing intracardiac pressure curves which were recorded during standard procedures of cardiac catheterization. To eliminate the contribution of heart rate, RVSTI subfractions were corrected by the regression equation obtained from control dogs in which PAm was below 19 mmHg. The cordiac output was measured by dye dilution method and aortic blood gas was analyzed. Findings of electrocardiogram and phonocardiogram were also investigated. The experimental procedures were completed without any heart failure. The elevation of PAm was accompanied with the increase of PEP/ET, prolongation of PEP and shortening of ET, in 10 of 12 subjects, until PAm was below 40 mmHg. However, when PAm was over 40 mmHg, the decrease of PEP/ET, shortening of PEP and prolongation of ET, were observed. The mean rate of right ventricular isovolumic pressure rise increased together with the elevation of PAm. This increase was accelerated by the elevation of PAm across 40 mmHg. Therefore, it is conclusive that the measurement of the RVSTI is useful for pathophysiological evaliation of acute pulmonary embolism.