The Journal of Thoracic and Cardiovascular Surgery, Vol 73, 195-200, Copyright © 1977 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Studies of the effects of hypothermia on regional myocardial blood flow and metabolism during cardiopulmonary bypass. IV. Topical atrial hypothermia in normothermic beating hearts
N Cooper, JR Brazier, DH McConnell and GD Buckberg
This study compares (1) the effects of slowing heart rate by topical
hypothermia in hearts perfused at 37 degrees C. with bradycardia produced
by perfusion hypothermia (28 degrees C.) and (2) the consequences of
counteracting the bardycardic effects of perfusion hypothermia by atrial
pacing. Topical atrial hypothermia (myocardial temperature 37 degrees C.)
produced a level of bradycardia comparable to perfusion hypothermia (82 vs.
71 beats per minute), but reduced myocardial oxygen requirements 25 per
cent more than perfusion with 28 degrees C. blood. Myocardial oxygen uptake
per beat did not change with topical atrial hypothermia but increased 40
per cent with perfusion hypothermia. Counteracting the bradycardic effects
of perfusion hypothermia with atrial pacing (to 130 beats per minute)
reduced subendocardial flow 25 per cent, caused a redistribution of flow
away from the subendocardium, and produced evidence of ischemia on the
intracavitary electrocardiogram. This study shows that (1) topical atrial
hypothermia with systemic normothermia reduced myocardial oxygen demands as
effectively as perfusion hypothermia and (2) subendocardial ischemia
develops in beating empty hearts when the expected bradycardia of
hypothermia does not occur.
