Prevention of intraoperative myocardial injury by pretreatment with pharmacological agents

Low-dose propranolol for the protection of the left ventricle from ischaemic damage

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.

Ventricular fibrillation during cardiopulmonary bypass

Changes in ultrastructure after induced ventricular fibrillation were studied in the normothermic and nonhypertrophic canine heart using a transmural myocardial biopsy method. Comparisons were made between subendocardial and subepicardial layers by the quantitative evaluation of ultrastructural changes in mitochondria and glycogen granules. Slight abnormalities characterized by interstitial edema, mitochondrial derangement, contraction bands, swelling of capillary endothelium were demonstrated throughout the myocardium following ventricular fibrillation. The myocardium following ventricular fibrillation did not demonstrate differences in ultrastructure between the subendocardial and subepicardial layers. These pathologic fine structural changes were at least in part reversible. Quantification of ultrastructure showed that mitochondria and glycogen granules were well preserved. It was suggested that the myocardium following ventricular fibrillation may be less affected by the no-reflow phenomenon after restoring normal coronary circulation.