The interaction between early and atrial filling of the left ventricle effects of heart rate, atrioventricular delay, isoproterenol and methoxamine

To circumvent the confounding variables of heart rate (HR) and atrioventricular (AV) delay on the Doppler-derived filling patterns, the effects of isoproterenol and methoxamine were evaluated in 16 patients with programmable dual-chamber pacemakers at a similar HR and AV delay to their control states. HR was increased by increments of 10 beats/min at an AV delay of 150 ms and the AV delay was set at 100, 150, 200 and 250 ms at a HR of 80 beats/min. Measurements were obtained before and after isoproterenol (mean = 15 ± 2 ng/kg/min) at a HR of 90 beats/min and an AV delay of 100 ms, and before and after methoxamine (0.5-1 mg/min) at a HR of 80 beats/min and an AV delay of 150 ms. As HR was increased, the total velocity integral, peak (PE) and integrated (Ei) velocities progressively decreased as the peak (PA) and integrated atrial (Ai) velocities increased. The reduction in Ei was due to shortening of the early filling period and a small decrease in the PE velocity. An incremental increase in AV delay was associated with a stepwise increase in Ai and a decrease in Ei. The increase in Ai was due to an increase in both the atrial filling period and PA velocity, while the reduction in Ei was the result of shortening of the early filling period. With isoproterenol the total velocity integral increased. This was due entirely to an increase in the Ei, which, in turn, related to both an increase in the PE velocity and the early filling period. Methoxamine produced a 39% increase in systolic blood pressure, and was associated with a decrease in the total velocity integral. This decrease was attributed to a decrease in Ei velocities, which, in turn, was due to marked shortening of in the early filling period. The increase in Ai was due to an increase in the PA velocity since the atrial filling period was unchanged. It is concluded that when atrial systole occurs progressively earlier in diastole, due to either an increase in AV delay or HR, atrial filling increases as it overlaps to an increasing degree with early filling. If the onset of early filling is brought forward, the overlap between early and atrial filling decreases, while when early filling is delayed, early filling occurs later in diastole, increasing the overlap between the filling phases, and in such a way augments the atrial contribution to filling.