Abstract

Frequency potentiation and postextrasystolic potentiation of myocardial contractility were induced in 17 patients found not to have cardiac disease (group 1) and in 10 patients with coronary arterial disease (group 2). Atrial stimulation was performed starting at a rate of 110/min and going up to 200/min (frequency potentiation). Single, premature venriculr beats with decreasing coupling intervals were induced every fifteenth beat during basal atrial stimulation at 125/min, after which compensatory pauses were provided (posts used an an idex of contractility. With increasing heart rate dp/dt max was augmented equally, in both groups of patients, by frequency increases and premature beats (the coupling interval of the extrasystole being expressed as heart rate). dp/dt min and left ventrricular systolic pressure remained unchanged while left ventricular end-diastolic pressure decreased in both groups of patients with the two forms of potententiation. It was concluded that both these forms of potentiation have the same augmenting effect on myocardial contractility. Shortening the coupling intervals of premature beats caused a decreased in left ventricular end-diastolic pressure, suggesting that the Frank-Starling mechanism was not involved in postextrasystolic potentiation. Patients with coronary arterial disease had lower values of dp/dt max, dp/dt min, and higher values of left ventricular end-diastolic pressure during rest and stimulation procedures, while the systolic pressures equalled those in the control group. Though individual case values fromthe healthy and diseased hearts might be similar, it was only under the stress of potentiation that the true state of contractility was made apparent. Impairment of dp/dt min was not found without an impairment of dp/dt max in the presence of myocardial ischaemia.