Ventricular arrhythmias following coronary artery occlusion in rats: is the diabetic heart less or more sensitive to ischaemia?

Rhythm disorders are common complications in diabetic patients, due to thei r enhanced sensitivity to ischaemia. However, experimental studies are inco nsistent, and both higher and lower vulnerability to injury has been report ed. Our objectives were to compare susceptibility to ventricular arrhythmia s in rats with prolonged duration of diabetes induced by streptozotocin (45 mg/kg, i.v,), utilising two different models. Following 8 weeks, either an aesthetised open-chest rats in vivo or isolated Langendorff-perfused hearts were subjected to 30 min regional zero-flow ischaemia induced by occlusion of LAD coronary artery. In addition, cardiac glycogenolysis and lactate pr oduction were measured. In open-chest rats, 90 % of the controls exhibited ventricular tachycardia (VT) which represented 55.4 % of total arrhythmias, whereby only 19.9 % of arrhythmias occurred as VT in 44 % of the diabetic rats (P < 0.05 vs controls). Duration of VT and ventricular fibrillation (V F) was reduced from 35.5 <plus/minus> 11.1 and 224.8 +/- 153.9 s in the con trols to 4.8 +/- 2.5 and 2.2 +/- 0.2 s in the diabetics, respectively (P < 0.05). Accordingly, severity of arrhythmias (arrhythmia score, AS) was also lower in the diabetics (2.0 <plus/minus> 0.38 vs 3.3 +/- 0.3 in the contro ls; P < 0.05). In the isolated hearts, high incidence of VF was decreased i n the diabetic hearts, and although VT occurred in almost all of the diabet ic hearts, the duration of VT and VF was substantially shorter (61.5 <plus/ minus> 14.5 and 5.5 +/- 0.5 s vs 221.5 +/- 37 and 398.5 +/- 55 s in the con trols, respectively; P < 0.05). AS was reduced to 2.9 <plus/minus> 0.12 fro m 4.1 +/- 0.3 in the controls (P < 0.05). Postischaemic accumulation of lac tate was lower in the diabetic than in the non-diabetic myocardium (20.4 <p lus/minus> 1.9 vs 29.5 +/- 2.9 mu mol/l/g w.wt.; P < 0.05). These results s uggest that rat hearts with chronic diabetes, despite some differences in t he arrhythmia profiles between the in vivo model and isolated heart prepara tion, are less sensitive to ischaemic injury and exhibit lower susceptibili ty to ventricular arrhythmias and reduced accumulation of glycolytic metabo lites.