Determinants of Impairment of Cardiac Filling During Progressive Pericardial Effusion

The progressive reduction in cardiac output—and later in arterial pressures—that develops during advancing degrees of pericardial effusion is usually attributed to a steady decrease in the venoatrial pressure gradient. Evaluation of changes in instantaneous pressures in the right and left atria at the end of ventricular diastole (Z pressure) and systole (V pressure) indicates that as pericardial pressure rises other determinants enter in the following order: (1) reduction in diastolic capacities of the atriums and ventricles; (2) decrease in venoatrial pressure gradient and preponderant rise of left atrial pressures due to the higher elasticity coefficient of this chamber; (3) blockage of atrial inflow during ventricular diastole; (4) impairment of atrial inflow during ventricular systole as its stroke volume diminishes to an extreme degree; and (5) inauguration of a vicious cycle in which a diminishing venopressure gradient decreases ventricular filling, while the consequent reduction in stroke volume attenuates the facilitating effect of ventricular ejection on the venoatrial gradient.