Objectives. This study was designed to increase asynchrony with sequential atrioventricular (AV) pacing and to study its effects on left ventricular isovolumetric relaxation, rapid filling and stiffness. Background. Left ventricular nonuniformity is a major determinant of diastolic function. Methods. Thirteen patients with coronary artery disease were studied by simultaneous equilibrium radionuclide angiography and cardiac catheterization during atrial and AV pacing. Ejection fraction and peak filling rate were measured by radionuclide angiography. Regional analysis was obtained by analyzing time-activity curves of four left ventricular sectors; systolic and diastolic asynchrony were evaluated as the coefficient of variation of time to end-systole and, respectively, time to peak filling rate in the four sectors. Cardiac index and left ventricular pressure were measured with high fidelity catheters at cardiac catheterization. The time constant of isovolumetric relaxation was derived from left ventricular pressure. Pressure-volume loops were assembled and constants of chamber stiffness were computed. Results. Atrioventricular pacing led to a decrease in cardiac index (3.7 ± 0.9 to 3.3 ± 0.8 liters/min per m2, p = 0.01) and peak filling rate (352 ± 125 to 287 ± 141 ml/s, p = 0.03; 2.4 ± 0.8 to 2.0 ± 0.8 end-diastolic counts/s, p = 0.02; 4 ± 1.3 to 3.2 ± 1.0 stroke counts/s, p = 0.008). The time constant of isovolumetric relaxation increased (57 ± 10 to 64 ± 12 ms, p = 0.04) and the global diastolic pressure-volume relation shifted upward. Conclusions. Atrioventricular pacing induces left ventricular asynchrony, which is associated with a slower rate of isovolumetric relaxation. The isovolumetric relaxation lasts after the filling phase has begun, thereby reducing the rate of rapid filling.
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