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Global myocardial ischaemia improves intracardiac operating conditions but damages the myocardium. Propranolol should reduce this damage but may impair postoperative myocardial contractility. An assessment of its protective effect during 90 minutes of normothermic ischaemia in canine hearts has been made. The early and late changes of contractility caused by low-dose propranolol were also recorded. A comparison of cardiac isovolumic contractile force, velocity, and compliance was made in three groups of dogs given 30 microgram/kg of propranolol with or without 90 minutes of cardiac ischaemia, or cardiac ischaemia without propranolol. Contractile force and velocity were significantly reduced by the propranolol, but recovered fully after 90 minutes. Ischaemia without propranolol reduced force and velocity of contraction significantly more than ischaemia with propranolol. Propranolol thus reduces operative ischaemic damage without itself impairing postoperative function.
Brown et al. (Sun,) studied this question.