Pathophysiology and therapy of right ventricular dysfunction due to pulmonary embolism.

When shock complicates an acute increase in RV afterload, initial therapy should be directed toward restoration of an adequate BP (RV coronary perfusion pressure) and CO. Current results indicate that norepinephrine, a drug with direct inotropic and pressor effects, may be an excellent agent for acute resuscitation and short-term maintenance of hemodynamic stability when frank circulatory instability complicates pulmonary embolism. Following hemodynamic stabilization, thrombolytic therapy should be initiated. Recent evidence suggests that the lytic agent can be given by bolus technique, but more work is required to determine the optimum dosing regimen. In the absence of shock, when a moderate decrease in CO complicates pulmonary embolism, isoproterenol or hydralazine may be used to improve flow. However, both of these agents may decrease systemic vascular resistance and BP. Accordingly, the latter parameter should be carefully monitored to ensure that excessive falls in BP and RV coronary perfusion pressure do not occur. Whereas in certain conditions volume expansion is appropriate therapy to increase CO, in acute pulmonary hypertension with excessive RV afterload, volume expansion may worsen RV function. Recent canine studies indicate that an increase in vascular closing pressure is the predominant mechanism explaining the increase in PAP and apparent increase in PVR complicating pulmonary embolism. Accordingly, in addition to decreasing vascular resistance, therapy to decrease RV afterload could be directed toward decreasing the vascular response producing excessive closing pressures.