Oral Magnesium Prophylaxis Provides Spontaneous Resumption of Cardiac Rhythm in Patients Undergoing Cardiac Surgery

Y Besogul 0 1 R Aslan 0 1 0 Department of Cardiovascular Surgery, Osmangazi University Medical School and Research Hospital , Eskisehir, Turkey 1 Dr Yavuz Besogul Batkent mah.Costu sok, No. 67/22 Alpata evleri, Eskisehir, Turkey - >> Version of Record - Mar 1, 2009 What is This? Downloaded from imr.sagepub.com by guest on October 16, 2014 The Journal of International Medical Research 2009; 37: 318 324 [first published online as 37(2) 4] Oral Magnesium Prophylaxis Provides Spontaneous Resumption of Cardiac Rhythm in Patients Undergoing Cardiac Surgery Y BESOGUL AND R ASLAN Evidence is growing that magnesium supplementation in patients undergoing cardiac surgery is beneficial, however the best administration route has not been established. Previously, we showed that intra-operative direct flush infusion of magnesium into the aortic root before reperfusion was effective. The present study compared pre-operative oral administration of magnesium for 10 days with intra-operative flush infusion of magnesium for spontaneous resumption of cardiac rhythm and ventricular fibrillation in patients undergoing cardiac surgery with cardiopulmonary bypass (CBP). The rate of spontaneous resumption of cardiac rhythm, the number of shocks required for defibrillation, the energy required for defibrillation and the occurrence of postCPB ventricular tachyarrhythmias were not significantly different between the groups. Serum magnesium levels were minimally increased following administration of magnesium but were within the normal range at all times in both groups. Oral administration of magnesium might provide myoprotective effects during cardiac surgery, but larger trials with a greater statistical power need to be carried out in order to show this. For many years it has been recognized that magnesium levels play an important role in morbidity associated with heart surgery.1 As is widely known, hypomagnesaemia in patients undergoing heart surgery can cause cardiac arrhythmias or ventricular fibrillation.2,3 The magnesium ion has been proposed as an endogenous physiological calcium blocker, although the exact cardioprotective mechanism remains unclear.4 Total plasma hypomagnesaemia is common in patients undergoing heart surgery with cardiopulmonary bypass (CPB).5 Data from experimental studies have shown a significant improvement of left ventricular performance after global ischaemia when magnesium has been added to the cardioplegic solution.6,7 The magnesium ion favourably influences nitric Downloaded from imr.sagepu3b.c1om8by guest on October 16, 2014 oxide production by the coronary endothelium, attenuating the endothelial dysfunction caused by global ischaemia followed by reperfusion.8 Studies have demonstrated successful prevention of postoperative arrhythmias with magnesium administration.4,5,7 Prophylactic magnesium treatment remains controversial and the optimum method, dose and timing of administration have not been clearly determined. We have previously shown that intraoperative direct flush infusion of magnesium into the aortic root, before reperfusion, reduced the need for internal defibrillation and the occurrence of ventricular tachyarrhythmias.9 In the present study, the effects of oral magnesium prophylaxis were compared with those of intra-operative aortic flush infusion of magnesium on intraoperative reperfusion-induced arrhythmias, early post-operative outcomes and serum magnesium levels in patients undergoing cardiac surgery with CPB. Patients and methods STUDY DESIGN AND PATIENTS The study was a randomized, prospective, controlled trial of consecutive patients undergoing cardiac surgery with CPB. Inclusion criteria were: New York Heart Association (NYHA) class III or IV, and undergoing coronary artery bypass or mitral and/or aortic valve operations. Exclusion criteria were: renal and hepatic dysfunction, re-operation, pre-operative hypomagnesaemia (< 1.5 mg/dl), hypocalcaemia (< 8.5 mg/dl) or hypokalaemia (< 3.5 mEq/l), atrial fibrillation, chronic diarrhoea, hyper- or hypothyroidism, congestive heart failure of higher than NYHA functional class III and uncontrollable diabetes mellitus. The Ethics Committee of Osmangazi University Medical School and Research Hospital approved the study and all patients gave verbal informed consent to participate in the study. Patients were randomly divided into two groups: the patients in the pre-operative oral prophylaxis group (group I) received 2 1830 mg magnesium citrate (equivalent to 2 295.7 mg magnesium) daily for 10 days before surgery and this was resumed from the first post-operative day until the patient was discharged from hospital; and the patients in the intra-operative flush infusion group (group II) received 10 ml of 1.5 nmol/ml magnesium sulphate (equivalent to 0.146 mg/ml magnesium) infused into the aortic root over a 30-s period before crossclamp removal during surgery. SURGICAL PROCEDURES All operations were performed under fentanyl anaesthesia (1.5 mg/h fentanyl by infusion and 1% inhaled isoflurane) and neuromuscular blockade was achieved using 0.15 mg/kg pancuronium bromide. Intravenous heparin (300 IU/kg) was administered before cannulation for CPB and additional doses were given to maintain an activated clotting time of 480 s. During the CPB procedures, non-pulsatile flow rates of 2.4 l/min per m2 with moderate hypothermia (28 32 C) were used. Cold crystalloid cardioplegia containing 16 mmol magnesium (+4 C; Plegisol; Abbott Laboratories, Abbott Park, IL, USA) was used for myocardial protection. Group II received magnesium infused as described above. A membrane oxygenator and standard synthetic circuits were used for CPB. HAEMODYNAMIC MEASUREMENTS Haemodynamic measurements were made by standard radial, central venous catheterization. Serial plasma magnesium concentrations were recorded before surgery Downloaded from imr.sagepu3b.c1om9by guest on October 16, 2014 and at 6 h and 24 h after the operation. Additionally, spontaneous resumption of cardiac rhythm or spontaneous defibrillation, the number of shocks required for defibrillation, the energy required for defibrillation, the occurrence of ventricular tachyarrhythmias and temporary pacing required for bradyarrhythmias after completion of CPB were recorded. Heart rate and rhythm were continuously monitored and displayed during surgery. STATISTICAL ANALYSIS Group data are expressed as mean SD or medians. Clinical characteristics were evaluated by the Students t-test for twogroup comparisons. Intra-operative categorical data were analysed using the two-proportion z-test. Numerical data were compared using the MannWhitney U-test. P-values < 0.05 were considered statistically significant. The statistical power of the study was calculated in order to determine the number of patients in each group that would be required in order for all the measured between-group differences to be statistically significant. Results A total of 100 patient (...truncated)