Relationship between ventricular rate and cardiac output in mimic experimental atrial fibrillation

In treating atrial fibrillation (AF) the goal of ventricular rate reduction is still not determined. An animal model of AF was developed in which the relationship between ventricular rate and the parameters of cardiac function in AF can be studied. To simulate AF, complete heart block was chemically produced on open-chest dogs. Then, assisted by a portable computer, the ventricles were paced with a series of grossly irregular stimuli of predetermined rates, while atria were paced rapidly (500 beats/min). The resulting electrocardiogram and pressure were indistinguishable from the naturally occurring AF. It was found that in AF with ventricular rates that were lower than that of the control state, cardiac output was decreased. Cardiac output increased and reached a plateau when the ventricular rate increased to the level of the control state and then kept stable up to a rate of 320 beats/min. There was a discrepancy between the effective ventricular rate (rate of beats with pulse pressures > or = 25 mmHg in the femoral artery) and the electrical ventricular rate. When the electrical ventricular rate increased over the control ventricular rate the effective ventricular rate did not increase in a parallel manner. Rather, the effective ventricular rate leveled off at the control ventricular rate. This discrepancy may explain the parallel relationship between the effective ventricular rate and cardiac output.