European Journal of Cardiovascular Medicine

Patients who undergo surgeries are at risk of developing new-onset postoperative cardiac arrhythmias, notably atrial fibrillation (AF), with an incidence ranging from approximately 20% to 50%. Despite advancements in surgical and anesthetic techniques, this trend has not seen a decline in recent years. Typically, these arrhythmias manifest within 24 to 96 hours post-surgery, and while they often follow a benign and self-limiting course without long-term complications, the associated burdens cannot be disregarded. AF can lead to hemodynamic disturbances due to reduced cardiac output and increased atrial and ventricular end-diastolic pressures. Additionally, complications such as thromboembolism, stroke, and palpitations contribute to extended hospital stays and heightened costs. Thus, the adverse clinical and financial impacts underscore the importance of enhancing preventive strategies and management protocols [1-4].

Various risk factors contribute to postoperative cardiac arrhythmias, with hypomagnesemia being a well-documented factor. Evidence supports the correlation between low serum magnesium levels (below 1.5 mEq/L) and arrhythmias, as well as the amelioration of arrhythmias through magnesium supplementation [4]. Patients with severe coronary artery disease are particularly prone to magnesium deficiency, which can worsen following cardiac surgery, typically declining on the first post-CABG day and gradually returning to preoperative levels by the fourth day [4]. Hence, prophylactic magnesium therapy is commonly employed to mitigate this undesirable outcome.

This study aimed to evaluate the effectiveness of oral versus intravenous magnesium administration in preventing postoperative hypomagnesemia among sutgical patients and to assess oral supplementation's potential in averting arrhythmias. Notably, there is a paucity of literature comparing oral and intravenous administration routes in this context, making this investigation novel in its approach.

This interventional clinical study involved 98 patients admitted for major surgery. Exclusion criteria included a history of renal or liver diseases, arrhythmias unresponsive to medical treatment, hypersensitivity to magnesium, and the use of magnesium-containing medications, antiarrhythmic drugs, beta-blockers, calcium channel blockers, and diuretics. Additionally, patients who required exploratory surgery due to bleeding or had intra-aortic balloon pump (IABP) insertion were excluded from the study.

Prior to surgery, patients were thoroughly briefed on the study protocol and provided consent. Patients were then randomly assigned to either the oral or intravenous (IV) group using a blocking method. Baseline serum magnesium levels and electrocardiographic studies were obtained. All surgeries were conducted by the same surgeon, and both the patients and the medical staff were blinded to the group assignments. Any arrhythmias occurring post-surgery were documented, along with the corresponding treatments. Three additional serum samples were collected when patients were transferred to the intensive care unit (ICU), and at 12 and 24 hours post-transfer. Magnesium levels below 2 mg/dL were classified as hypomagnesemia. Data were analyzed using IBM SPSS 20.0 with independent T-tests and chi-square tests, with results presented descriptively and analytically.

The study participants comprised 45 patients (45.92%) in the intravenous (IV) group and 53 patients (54.08%) in the oral group (Table 1). Serum magnesium levels for both groups up to 48 hours post-operation are illustrated in Figure 1. The initial magnesium level in the orally treated group was 2.07 ± 0.71 mg/dL, compared to 2.13 ± 0.61 mg/dL in the parenteral group. The preoperative hypomagnesemia difference between the groups was not significant (P-value = 0.56) (Table 2).

During the operation, the magnesium levels increased to approximately 3.8 to 4.2 mg/dL, which is expected due to perioperative magnesium administration. No hypomagnesemia was detected during the operation. Postoperatively, magnesium levels gradually declined, with a more rapid decrease observed in the first 12 hours. During this period, the oral group's magnesium levels were lower but parallel to the IV group. Overall, both groups exhibited hypomagnesemia without significant differences. Preoperative arrhythmia prevalence was 14.60% in the IV group and 6.83% in the oral group (OR: 0.44). However, during the operation, the oral group showed an advantage until the postoperative period, when both groups had the same prevalence (Table 3).

Table 1: Perioperative and demographic variables in study groups

Figure 1: Mean Serum magnesium concentrations in both groups up to 48 hours postop.

Table 2: Prevalence of hypomagnesemia (%) in study groups

Table 3: Prevalence of arrhythmias (%) in study groups

Magnesium, a crucial bivalent cation, plays a vital role in maintaining transmembrane gradients of sodium and potassium ions. It serves as a cofactor for adenosine-triphosphatase, the energy source for contractility, and offers protection to the myocardium against ischemic reperfusion injury. Following surgery, serum magnesium levels typically decline, normalizing within 3 to 5 days. This deficiency is associated with cardiovascular manifestations like hypertension, electrocardiogram (ECG) alterations, and both supraventricular and ventricular arrhythmias [5-8].

Various mechanisms have been proposed regarding magnesium deficiency's role in postoperative atrial fibrillation (AF), including hemodilution, shifts from extracellular to intracellular compartments, intraoperative diuretic usage, increased urinary loss, catecholamine discharge, and elevated epinephrine levels [1,2,9]. Magnesium therapy has been demonstrated to reduce cardiac arrhythmia incidence by extending the refractory period [10,11]. However, literature on prophylactic magnesium therapy lacks consistency regarding indications, dosages, and timing, with conventional methods involving systemic and cardioplegic supplementation [8]. The novelty of our study lies in exploring the oral route for magnesium administration, a novel approach in this context.

Numerous studies advocate for preoperative magnesium loading as a cost-effective and safe alternative for preventing postoperative arrhythmias [12-16], aligning with European and Canadian guidelines [17,18]. However, US guidelines and some studies question the routine use of magnesium, citing minimal benefits or lack thereof [19-23]. The conflicting results may stem from variations in study designs and quality. Nonetheless, our study suggests that both oral and intravenous magnesium may hold equal value in the specified settings.

Limitations of our study include the need for larger sample sizes and inclusion of a control group for future research.

The results of our study demonstrate that the administration of 1.6 gm of oral magnesium supplements is comparably effective to the administration of 2 gm of magnesium sulfate intravenously in the prevention of hypomagnesemia and arrhythmia. This finding is significant as it suggests a less invasive, more convenient, and potentially more cost-effective approach for managing these common postoperative complications. The equivalence in efficacy between the two routes of administration indicates that oral magnesium supplementation could serve as a viable alternative to intravenous therapy, which is often associated with higher costs, increased need for healthcare resources, and greater patient discomfort. Based on these findings, the authors propose that the oral administration of magnesium should be considered a promising treatment regimen for the prevention of hypomagnesemia and arrhythmia. Further large-scale studies are recommended to validate these results and to explore the long-term outcomes and safety profile of this treatment approach.

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