Reversibility of Morphologic Changes Following Elective Cardiac Arrest

Abstract

The progression, or reversibility of acute changes in myocardial function and structure after periods of elective cardiac arrest from 30 to 60 minutes using anoxia alone and with mild hypothermia, deep hypothermia and potassium citrate was studied by physiologic, histochemical, and electron microscopic methods. Immediate postarrest morphologic changes were as described previously. Additionally, with arrest by profound hypothermia, with or without coronary perfusion, no morphologic changes were noted immediately after cardiac arrest. The myocardium of all dogs recovering from all types of arrest for 24 to 48 hours showed restoration of nuclear changes as compared with immediate postarrest biopsies. No animal whose heart had been arrested for 60 minutes by anoxia at normothermia survived. In one-half of the surviving animals, regardless of the type of arrest or duration of arrest, degenerative lesions suggestive of mitochondrial origin, and believed to be irreversible, were demonstrated in myocardial cells. These lesions as demonstrated by electron microscopy appeared to correlate with fatty degeneration of myocardial fibers as shown by light microscopy. Focal gross and microscopic areas of necrosis were observed in hearts of dogs recovering from potassium citrate arrest after 24 to 48 hours. Cardiac function, as measured by myocardial force, systemic arterial blood pressure, and pump support time after arrest, was variably impaired following the arrest period. Most severe impairment was noted after prolonged arrest with anoxia, or with mild hypothermia.