Spontaneous heart rate, propranolol, and ischaemia-induced ventricular fibrillation in the dog

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Abstract
Abrupt coronary occlusion was performed in anaesthetised, open-chest dogs with pre-occlusion arterial blood Po2 ranging from 8.0 to 10.7 kPa (60 to 80 mmHg). Ventricular fibrillation occurred in 15/19 dogs with high spontaneous heart rate (greater than 155 beats·min−1) and in 0/8 dogs with low spontaneous heart rate (less than 155 beats·min−1). Dogs with low spontaneous heart rate fibrillated when paced at a fast rate (200·min−1) (4/5). In dogs with high spontaneous heart rate fibrillation occurred in 0/5 dogs when propranolol reduced spontaneous heart rate, but in 3/5 dogs when reduction in spontaneous heart rate in response to propranolol was prevented by pacing.