Influence of left ventricular dysfunction on the role of atrial contraction: an echocardiographic-hemodynamic study in dogs.

OBJECTIVES: The purpose of this study was to understand the significance of an effective atrial systole and the interactions between atrial and ventricular function.
BACKGROUND: The significance of atrial function is controversial, particularly in the setting of left ventricular (LV) dysfunction.
METHODS: Serial, rapid pacing in five dogs that had undergone radiofrequency ablation and implantation of right atrial and ventricular pacemakers produced reversible atrial and ventricular dysfunction (alone and in combination). Atrial function (echocardiograph-determined transmitral diastolic flow, left atrial appendage emptying, and pulmonary venous flow), cardiac output, and right heart pressures were measured at matched paced heart rates of 80 beats/min.
RESULTS: Isolated rapid atrial pacing (LV ejection fraction approximately 60%) decreased atrial booster pump in the body and appendage of the left atrium, but increased the conduit function of the left atrium. Isolated LV dysfunction (LV ejection fraction approximately 34%) increased atrial booster pump function. The decreased atrial booster pump function in animals with combined atrial and ventricular dysfunction was incompletely compensated by the redistribution of the reservoir and conduit functions of the left atrium. As a result, cardiac output decreased and right heart pressures increased only after superimposed pacing.
CONCLUSIONS: In the presence of a normal left ventricle (LV), atrial failure has little effect on cardiac output and right heart pressures because of compensatory conduit function, but when early LV dysfunction coexists, changes in reservoir and conduit functions are insufficient to compensate for an impairment of atrial contraction.