Susceptibility to ischemia-induced arrhythmias and the effect of preconditioning in the diabetic rat heart

Diabetic heart is suggested to exhibit either increased or decreased resist ance to ischemic injury, ischemic preconditioning suppresses arrhythmias in the normal heart, whereas relatively tittle is known about its effects in the diseased myocardium. Our objective was td investigate whether developme nt of diabetes mellitus modifies the susceptibility to ischemia-induced arr hythmias and affects preconditioning in the rat heart. Following 1 and 9 we eks of streptozotocin-induced (45 mg/kg, i.v.) diabetes, the hearts were La ngendorff-perfused at constant pressure of 70 mm Hg and subjected to test i schemia induced by 30 min occlusion of the left anterior descending (LAD) c oronary artery. Preconditioning consisted of one cycle of 5 min ischemia an d 10 min reperfusion, prior to test ischemia. Susceptibility to ischemia-in duced arrhythmias was lower in I-week diabetics: only 42% of diabetic heart s exhibited ventricular tachycardia (VT) and 16% had short episodes of vent ricular fibrillation (VF) as compared to VT 100% and VF 70% (including sust ained VF 36%) in the non-diabetics (P<0.05). Development of the disease was associated with an increased incidence of VT (VT 92%, not significantly di fferent fi om non-diabetics) and longer total duration of VT and VF at 9-we eks, as compared to 1-week diabetics. Preconditioning effectively suppresse d arrhythmias in the normal hearts (VT 33%, VF 0%). However, it did not pro vide any additional antiarrhythmic protection in the acute diabetes. On the other hand, in the preconditioned 9-weeks diabetic hearts, the incidence o f arrhythmias tended to decrease (VT 50%, transient VF 10%) and their sever ity was reduced. Diabetic rat hearts are thus less susceptible to ischemia- induced arrhythmias in the acute phase of the disease. Development of diabe tes attenuates increased ischemic tolerance, however, diabetic hearts in th e chronic phase can benefit more from ischemic preconditioning, due to its persisting influence.