Acute complete heart block in dogs

Abstract

A study has been conducted immediately and up to 18 days after the surgical production of complete heart block in dogs. Immediately after surgery cardiac output, coronary flow, and mean arterial pressure were reduced in rough proportion to the degree of bradycardia. In time, these measures began to return toward preoperative levels. Paralleling the diminished left ventricular work was a diminished left ventricular oxygen consumption with little consequent change in myocardial efficiency. Small rises were detected in central venous pressure. At autopsy, the only unequivocal abnormality was myocardial hypertrophy which became measurable between 2 and 18 days after operation.

Fig. 1

A. Femoral arterial pressure before, during and after caval occlusion and section of the bundle of His. Calibration in mm. Hg. B. Electrocardiogram of sinus and idioventricular rhythm before and 15 minutes after surgically induced complete heart block. Different animal than A.

Fig. 2

Effect of complete heart block, 2:1 block, and control myocardotomy on cardiac output. Note how the magnitude of the cardiac-output fall is related to the degree of bradycardia. Values are expressed in per cent of preblock values, each animal serving as its own control.

Fig. 3

Cardiac outputs, expressed in per cent of preblock values, in 13 dogs in which complete heart block was produced and ventricular stimulation then conducted at the same rate as had been present before the lesion. Note the fall in output after block, with subsequent restoration to preoperative values during ventricular pacemaking.

Fig. 4

Changes in cardiac output and stroke volume in animals studied one to one and one half hours, two days, and 10 to 18 days after surgically induced complete heart block. Results are in per cent of preoperative values, each animal serving as his own control.

Fig. 5

Total oxygen consumption and arterial-venous difference at different times after surgically induced complete heart block. Results are in per cent of preoperative values, each animal serving as his own control.

Fig. 6

Changes in left ventricular coronary flow, mean femoral pressure, and coronary vascular resistance (CVR) at varying times after surgically induced complete heart block. Results are in per cent of preoperative values, each animal serving as his own control.

Fig. 7

Changes in left ventricular work, oxygen consumption, and efficiency at varying times after section of the bundle of His. Results are in per cent of preoperative values, each animal serving as his own control.

Fig. 8

Changes in heart weight. Note dogs sacrificed after 48 hours had no hypertrophy. Heart weights were abnormally high in animals sacrificed after 10 to 18 days. The percentage values were obtained by dividing the actual post mortem heart weights by the weights predicted on the basis of body weight.