Potassium was added to achieve a plasma concentration of 4-6 mmolper liter. Peripheral venous blood samples were collected for Tn analysis in the case and the control groups, 24 hours after CABG. The heart surgery complications such as atrial fibrillation and the death in the hospitalization period and 3 months later were recorded and compared between the two groups. Functional class was measured pre- and post- operatively (3 months later) according to NYHA criteria. The duration from intubation point to the extubation point in ICU called intubation time. The duration from clamping the ascending aorta to the removal of clamp called clamp time. Pump time was the time that patients were on cardiopulmonary pump.

Randomization did not give an equal distribution of male and female patients. Mean ejection fraction before surgery in the case and control groups were 50.6% ± 8.1 and 49.5% ± 12.4, respectively (Table 3). Mean ejection fraction before discharge in the case and control groups were 44.1 ± 6.8 and 46.3 ± 14.9, respectively. There was not a significant difference in the mean ejection fraction between the two groups before and after CABG (P > 0.05, Table 4). There were not significant changes in ejection fraction (EF1-EF2) in the case and control groups after CABG (P > 0.05).

Before operation, all patients were on beta-blockers and aspirin; the latter was stopped 5 days before surgery. A large number were also taking cholesterol-lowering medications (statins) and angiotensin-converting enzyme inhibitors.

In this study, despite the theoretical protective effects of GIK listed above and the increase in functional class, no cardioprotective effect of GIK was observed. We did not find a significant difference in ejection fraction between the two groups. Maybe, our results supported the findings of other studies,13 but there was no difference between GIK and non-GIK-treated patients. Before concluding that GIK confers no protective effect on the myocardium during CABG surgery, other possible reasons for our negative findings should be considered. We used a high dose of GIK, as recommended in other studies,24, 25 but continued this only 12 hours after surgery. It might be of more benefit if started before surgery and continued for 24-48 hours after surgery, as suggested by other studies. Some researchers examined the effect of GIK on complications of mitral valve replacement and demonstrated increased myocardial glycogen content after an infusion of GIK, 12 hours before the operation.26 This reduced complications such as hypothermia and arrhythmia after surgery. Lazar and colleagues27 found better cardiac performance and faster recovery from urgent CABG in patients with unstable angina given GIK infusion for 12 hours after operation. These patients had greater cardiac output, a significantly lower incidence of atrial fibrillation (13.3 vs. 53.3%, P = 0.02) and a shorter stay in intensive care. GIK might be beneficial in patients with decreased cardiac reserve, poor left ventricular function and/or cardiogenic shock. Patients with a high risk of death may be more likely to benefit from metabolic therapy.28 Patients with insulin-dependent diabetes might benefit particularly from GIK, as shown in the DIGAMI study for patients with myocardial infarction.29 A recent study by Lazar and colleagues found better cardiac performance and faster recovery after CABG in a group of 40 diabetic patients.30 Postoperative GIK infusion for 48 hours was of benefit in patients with refractory cardiac failure after hypothermic cardiac arrest for CABG.31 Other authors have been using cardiac index (CI) to evaluate the benefits from GIK in myocardial revascularization surgery. A randomized clinical trial published in 2000 compared the diabetic patients undergone myocardial revascularization surgery using GIK (n=20) or conventional treatment with insulin subcutaneously (n=20). CI has been shown to increase in the intervention group (CI at the 18^th hour postoperative: 2.88 ± 0.50 vs. 2.2 ± 0.39 L/min/m² in the case and control groups, respectively, 95% CI 0.38-0.97, P < 0.0001).10 Szabó et al11 have studied the diabetic patient undergone to myocardial revascularization surgery and randomized to the case group with high doses of insulin (n=10) or conventional treatment (n=10). In the case group there was a significant increase in the CI (2.3 ± 0.1 vs. 2.9 ± 0.2 L/min/m², P = 0.017). An essay published in 2000 evaluated 45 patients undergone to myocardial revascularization surgery without cardiopulmonary pump and randomized to GIK or saline solution. It was not found any difference between the groups regarding CI and SvO₂ (mixed venous oxygen saturation) as well as in the enzymatic variables CPK-MB and troponin I.12 The Insulin Cardioplegia Trial13 evaluated the use of 10-IU insulin-fortified cardioplegia vs. placebo in high-risk patients undergone myocardial revascularization surgery due to unstable angina. A total of 1127 patients were randomized. There was no significant difference regarding mortality rate and the event of enzymatic infarction and/or low cardiac output syndrome. This study was criticized by not considering some existing evidences, such as low insulin dose administered in a single moment and not maintained the intervention in the postoperative period.32 A meta-analysis published in 2004, which included 11 studies evaluating the GIK administered in the CABG postoperatively or in the valve replacement relating to 468 patients, estimated an 11.4% increment in the CI of patients who received GIK infusion with a decrease in the atrial fibrillation in the postoperative period.