[Hemodynamic changes during increasingly rapid atrial pacing]

The cardiac output (Qc), indices of left ventricular function in the isovolumic period (dp/dt/Pt), max, and during the ejection period (EF, VCF), the end diastolic and end systolic ventricular volumes, the speed of ventricular filing, the module of elasticity of the ventricular chamber (kp) and the end systolic pressure-volume relationships were measured in 20 patients (11 normal in group I and 9 with and apparently primary cardiomyopathy in group II) at rest and during progressively rapid atrial pacing. The Qc was lower and the indices of left ventricular function in the isovolumic and ejectional phases, the end systolic pressure-volume relationship and speeds of ventricular filling were decreased in group II: kp was the same in both groups of patients. At progressively higher heart rates the cardiac output slightly in both groups, the systolic volume decreased, (dp/dt/Pt) max increased, the ejection fraction and VCF were unaltered. The speeds of filling and kp were unchanged. The end systolic pressure-volume relationship increased. In group I the reduction in systolic volume seemed to be related to a greater reduction in the end diastolic volume than in the end systolic volume. In group II, the reduction of the systolic volume was related only to a reduction of the end diastolic volume.