Freeze-thaw injury of rat heart across an intact diaphragm: a new model for the study of the response of myocardium to injury.

A new method for producing a circumscribed injury in rat myocardium is described. It utilises laparotomy and freeze-thawing across an intact diaphragm. Morbidity and mortality are negligible because the chest and pericardial cavities, the major coronary vessels, and the major branches of the conduction system remain intact. The size and location of the injury are reproducible and its sharp delineation facilitates accurate collection of samples from areas of interest. The myocytes are killed in the area of injury, whereas the capillary, nerve and connective tissue cells are killed centrally but preserved peripherally in a perimeter zone of injury in which capillaries remain patent. The reparative activities are initiated at the border between injured and uninjured myocardium; as they progress over the ensuing 6 weeks, the volume of damaged myocardium diminishes rapidly leaving only a rim of subepicardial scar tissue, and the thickness of ventricular muscle between the scar and endocardium returns almost completely to its pre-injury width. The mechanisms involved in the repair process are being investigated.