HAeMODYNAMIC STUDIES IN PATIENTS WITH ARTIFICIAL PACEMAKERS

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Abstract
Thirty-five patients with complete heart block have been investigated. The conclusions are supported by clinical experience in a further 41 patients. Cardiac outputs measured 4 min after changes in rate were nearly independent of ventricular rate in 14 patients without evidence of myocardial disease, but were critically dependent upon rate in 14 patients with myocardial disease, both at rest and on exercise. There was an optimal ventricular rate at rest in most patients. At this rate cardiac output was maximal, venous pressure lowest, and atrial rate minimal. The optimal rates ranged from 55 to 90 beats a min with a mean of 71 beats. The optimal rates on exercise for patients with myocardial disease were very close to the optimal rates at rest. In all patients a fixed ventricular rate was acceptable if correctly chosen, and enabled moderate activity to be carried out. Artificial pacing increased the mean cardiac output in 28 patients from 2.9 l./min. to 4-4 1./min. Exercise with a fixed ventricular rate increased the mean cardiac output in 10 patients from 4.0 l./min. to 10-2 1./min. Of these 10 patients, 4 increased their output to 12 l./min. or more.