Antiarrhythmic effects of preconditioning in anaesthetised dogs and rats

The aim was to determine the relationship of the duration of short coronary artery occlusions and of the reperfusion period to the extent of the antiarrhythmic effect of preconditioning.

A prolonged occlusion of a coronary artery in 102 anaesthetised rats and 55 anaesthetised dogs was preceded by a variable number of preconditioning coronary artery occlusions, of varying duration and with variable reperfusion periods between them and the prolonged occlusion.

Preconditioning in both species reduced the severity of ischaemia induced arrhythmias, epicardial ST segment changes, and alterations in the degree of inhomogeneity of conduction during a subsequent prolonged coronary artery occlusion, provided that the reperfusion time was less than 30 min (in rats) and 1 h (in dogs). This antiarrhythmic effect of preconditioning was marked; eg, in dogs following two preconditioning occlusions survival from a combined ischaemia-reperfusion insult was 40% (cf, 0% in the controls).

Short preconditioning periods of myocardial ischaemia protect the myocardium against the arrhythmogenic effects of a more prolonged occlusion. The optimum time for this preconditioning occlusion in rats is 3 min and protection is still apparent 30 min later. In dogs, the protective effect is especially clear with two short (5 min) coronary artery occlusions. The protection in this species lasts for less than 1 h.