Postoperative atrial tachyarrhythmias in patients undergoing coronary artery bypass graft surgery without cardiopulmonary bypass: a role for intraoperative magnesium supplementation

Prevention of Atrial Fibrillation After Cardiac Surgery: A Review of Literature and Comparison of Different Treatment Modalities

Atrial fibrillation is the most common arrhythmia to occur after cardiac surgery, with an incidence of 10% to 50%. It is associated with postoperative complications including increased risk of stroke, prolonged hospital stays and increased costs. Despite new insights into the mechanisms of atrial fibrillation, no specific etiologic factor has been identified as the sole perpetrator of the arrhythmia. Current evidence suggests that the pathophysiology of atrial fibrillation in general, as well as after cardiac surgery, is multifactorial. Studies have also shown that new-onset postoperative atrial fibrillation following cardiac surgery is associated with a higher risk of short-term and long-term mortality. Furthermore, it has been demonstrated that prophylactic medical therapy decreases the incidence of postoperative atrial fibrillation after cardiac surgery. Of note, the incidence of postoperative atrial fibrillation has not changed during the last decades despite the numerous preventive strategies and operative techniques proposed, although the perioperative and postoperative care of cardiac patients as such has improved.

Predictors of postoperative atrial fibrillation after coronary artery bypass grafting: a prospective observational cohort study

Background

This study was conducted to determine the effect of certain predictors on the incidence of postoperative atrial fibrillation (POAF) during ICU stay after coronary artery bypass graft (CABG) surgery.

Results

We enrolled 123 patients in this study. The mean age was 57.4 ± 8.7 years, and the mean left atrial diameter was 4.1 ± 0.52 cm with male preponderance (76.4%). The incidence of POAF following CABG was 33.3%. There was no statistically significant association between POAF and smoking (P = 0.123). However, POAF was significantly associated with higher CHA2DS2-VASc score (P = 0.002), valve replacement (P < 0.001), and inotropic support (P = 0.005). Moreover, patients with POAF had significantly higher mean age (P = 0.031) and left atrial (LA) diameter (P < 0.001). Logistic regression showed that LA diameter (P < 0.001), potassium level at 36 h (P = 0.016), and female gender (P = 0.001) were independent predictors of POAF.

Conclusions

We had several significant epidemiological, clinical, and operative variables that were significantly associated with post-CABG AF, including older age, female gender, large LA diameter, valve replacement, higher CHA2DS2-VASc score, and postoperative inotropic support. However, only LA diameter, female gender, and potassium level at 36 h were independent predictors of POAF. Nevertheless, further large-scale studies are needed to confirm our findings.

The effect of magnesium sulfate on post off-pump coronary artery bypass grafting bleeding

BACKGROUND

Magnesium level alteration may cause coagulation abnormality resulting in bleeding complication after off-pump coronary artery bypass grafting. In this study, we investigated the effect of magnesium on the postoperative coagulation profile and bleeding in OPCAB patients.

METHODS

In a double blind clinical trial, six hundred patients were randomly allocated to two groups: group A (n=150) and group B (n=450). Group A received 50mg/kg of magnesium sulfate (MS) in 100ml 0.9% NaCl solution over 20min before the anesthesia induction. Group B or control group received only 100ml 0.9% NaCl solution at the same time points. OPCAB was performed with standard technique and device. Blood samples were collected 30min before and 6h after the surgery to analyze hemoglobin and blood coagulation tests. Postoperative exploration for bleeding, blood transfusion, and volume of transfusion was recorded. The two groups compared with t-test and χ(2) tests and p-valve <0.05 were considered as significant.

RESULTS

However, postoperative hemoglobin was statistically lower in group A compared with group B, but platelet, PT, and aPTT tests were not statistically different between two groups. The serum MS level, exploration for bleeding, volume of packed cell transfusion, and volume of postoperative bleeding were statistically different between group A vs group B.

CONCLUSION

Preoperative MS use may be associated with the postoperative platelet dysfunction and increased tendency to bleeding. This is an important risk factor for postoperative bleeding in the OPCAB in absence of CPB use.

Intravenous administration of magnesium and potassium solution lowers energy levels and increases success rates electrically cardioverting atrial fibrillation

BACKGROUND

External biphasic electrical cardioversion (CV) is a standard treatment option for patients suffering from acute symptoms of atrial fibrillation (AF). Nevertheless, CV is not always successful, and thus strategies to increase the success rate are desirable.

OBJECTIVE

The purpose of this study was to evaluate the effect of intravenously administered K/Mg solution on the biphasic CV energy threshold and success rate to restore sinus rhythm (SR) in patients with AF.

METHODS

The study consisted of 170 patients with persistent AF. The patients were randomly assigned to undergo biphasic CV either with (n = 84) or without (n = 86) pretreatment with K/Mg solution. An energy step-up protocol of 75, 100, and 150 W (J) was used.

RESULTS

Biphasic CV of AF was effective in 81 (96.4%) patients in the pretreatment and 74 (86.0%) patients in the control group (P = 0.005). The effective energy level required to achieve SR was significantly lower in the pretreated group (140.8 ± 26.9 J vs 182.5 ± 52.2 J, P = 0.02). No K/Mg-solution-associated side effects such as hypotension or bradycardia were observed.

CONCLUSION

Administration of K/Mg solution positively influences the success rate of CV in patients with persistent AF. Furthermore, significantly less energy is required to successfully restore SR and therefore K/Mg pretreatment may facilitate SR restoration in patients undergoing CV for AF.

Pharmacologic prophylaxis for atrial fibrillation following cardiac surgery: a systematic review

Atrial Fibrillation (AF) is the most common arrhythmia occurring after cardiac surgery. Its incidence varies depending on type of surgery. Postoperative AF may cause hemodynamic deterioration, predispose to stroke and increase mortality. Effective treatment for prophylaxis of postoperative AF is vital as reduces hospitalization and overall morbidity. Beta-blockers, have been proved to prevent effectively atrial fibrillation following cardiac surgery and should be routinely used if there are no contraindications. Sotalol may be more effective than standard b-blockers for the prevention of AF without causing an excess of side effects. Amiodarone is useful when beta-blocker therapy is not possible or as additional prophylaxis in high risk patients. Other agents such as magnesium, calcium channels blocker or non-antiarrhythmic drugs as glycose-insulin--potassium, non-steroidal anti-inflammatory drugs, corticosteroids, N-acetylcysteine and statins have been studied as alternative treatment for postoperative AF prophylaxis.

Postoperative Care of the Cardiac Surgical Patient

The subspecialty of interventional cardiology began in 1977. Since then, the discipline of interventional cardiology has matured rapidly, particularly with regards to ischemic heart disease. As a result, more patients are undergoing percutaneous catheter interventional therapy for ischemic heart disease and fewer patients are undergoing surgical myocardial revascularization. Those patients referred for surgical revascularization are generally older and have more complex problems. Furthermore, as the population ages more patients are referred to surgery for valvular heart disease. The result of these changes is a population of surgical patients older and sicker than previously treated.

Prevention of atrial fibrillation after cardiac surgery

Atrial fibrillation is the most common arrhythmia occurring after heart surgery. Its prevalence after coronary artery bypass surgery is 17-33%. Atrial fibrillation requires additional treatment, lengthens hospitalization and increases the overall expenses of cardiac surgery. Atrial fibrillation can cause hemodynamic problems, predispose to congestive heart failure and increase the risk of stroke. Beta-blockers have been shown to effectively prevent atrial fibrillation, and beta-blockers should be a part of the medication of every patient undergoing cardiac surgery, if there are no contraindications. Amiodarone therapy can also be considered for especially high-risk patients.

Perioperative Magnesium Supplementation to Prevent Atrial Fibrillation After Off-Pump Coronary Artery Surgery: A Randomized Controlled Study

OBJECTIVE

Atrial fibrillation is a common complication after cardiac surgery. Magnesium is an effective and safe antiarrhythmic agent for arrhythmias that develop after cardiac surgery. The authors performed a study to evaluate the role of perioperative magnesium for prophylaxis of atrial fibrillation after off-pump coronary artery surgery.

DESIGN

Randomized controlled study.

SETTING

University teaching hospital.

PARTICIPANTS

One hundred sixty consecutive patients undergoing elective, isolated, off-pump coronary artery bypass grafting were prospectively randomized into 2 groups.

INTERVENTIONS

Patients in the magnesium group (n = 80) received a 2.5-g (20 mEq) magnesium sulphate infusion intraoperatively over 30 minutes, and the placebo group (n = 80) received normal saline solution.

MEASUREMENTS AND MAIN RESULTS

Postoperative atrial fibrillation occurred in 16 of 80 patients (20%) in the magnesium group and in 18 of 80 (22.5%) in the placebo group (p = 0.9).

CONCLUSION

The use of 2.5 g of intraoperative magnesium showed no effect in preventing atrial fibrillation after off-pump coronary artery bypass.

Magnesium deficiency in critical illness

Magnesium (Mg) deficiency commonly occurs in critical illness and correlates with a higher mortality and worse clinical outcome in the intensive care unit (ICU). Magnesium has been directly implicated in hypokalemia, hypocalcemia, tetany, and dysrhythmia. Moreover, Mg may play a role in acute coronary syndromes, acute cerebral ischemia, and asthma. Magnesium regulates hundreds of enzyme systems. By regulating enzymes controlling intracellular calcium, Mg affects smooth muscle vasoconstriction, important to the underlying pathophysiology of several critical illnesses. The principle causes of Mg deficiency are gastrointestinal and renal losses; however, the diagnosis is difficult to make because of the limitations of serum Mg levels, the most common assessment of Mg status. Magnesium tolerance testing and ionized Mg2+ are alternative laboratory assessments; however, each has its own difficulties in the ICU setting. The use of Mg therapy is supported by clinical trials in the treatment of symptomatic hypomagnesemia and preeclampsia and is recommended for torsade de pointes. Magnesium therapy is not supported in the treatment of acute myocardial infarction and is presently undergoing evaluation for the treatment of severe asthma exacerbation, for the prevention of post-coronary bypass grafting dysrhythmias, and as a neuroprotective agent in acute cerebral ischemia.

Hypomagnesemia after Major Abdominal Operations in Cancer Patients: Clinical Implications

BACKGROUND

Serum magnesium levels are rarely measured in routine chemistry panels. The extent and impact of postoperative serum magnesium changes remain unclear.

METHODS

One hundred seventy-one cancer patients who had undergone celiotomy procedures during a 38-month period were evaluated retrospectively for postoperative electrolyte alterations, with special emphasis on serum magnesium. Clinicopathologic predictors and early postoperative outcome correlations were examined.

RESULTS

There were 151 major procedures and 20 minor operations. All postoperative electrolyte and hematocrit values were significantly different from preoperative values, except for serum phosphate. Preoperative total serum magnesium (normal range: 1.7-2.5 mg/dL {0.7-1.03 mmol/L}), obtained prior to any bowel cleansing, differed from postoperative levels (means +/- standard deviation: 2.0 +/- 0.46 vs. 1.53 +/- 0.33 mg/dL; p < 0.0001). A lowered postoperative serum magnesium was observed in those patients who had either undergone an operation with curative intent (p = 0.0035), a major resection (vs. no resection, p = 0.0259), or preoperative bowel cleansing with sodium phosphate (p = 0.024). Other laboratory serum parameters that correlated with the postoperative magnesium level included postoperative levels of phosphate (p = 0.009), potassium (p = 0.01), and total calcium (p = 0.012), as well as preoperative calcium (p = 0.017). The complication rate was 20%, with five postoperative deaths (2.9%). Postoperative morbidity was predicted by preoperative potassium (p = 0.004) and albumin levels (p = 0.016); deaths were predicted by postoperative infections (p = 0.0007) and correlated to postoperative hypokalemia (p = 0.03).

CONCLUSIONS

Major abdominal cancer operations lead to significant electrolyte alterations. The severity of these changes correlates with the resection extent, especially in procedures with curative intent. In addition, bowel cleansing with sodium phosphate may participate in lowering serum magnesium as well as other electrolytes. In light of our postoperative magnesium replacement policy, no untoward events could be linked to postoperative hypomagnesemia in this series. To evaluate the impact of postoperative hypomagnesemia or magnesium replacement on postoperative outcomes requires a prospective randomized trial.

Vitamins, Supplements, Herbal Medicines, and Arrhythmias

Nutritional and herbal supplements may have harmful or beneficial effects on arrhythmias. Potential supplements that may have antiarrhythmic activity include omega-3 polyunsaturated fatty acids (N-3 PUFA), coenzyme Q10, and carnitine. Clinical studies show that N-3 PUFA or fish oil supplementation appears to reduce mortality and sudden death. Coenzyme Q10, used in treatment of heart failure, and carnitine and its derivatives may have beneficial effects on arrhythmias, although clinical studies have been limited. Antioxidant supplements may be beneficial, but large studies with vitamin E have been disappointing in that it does not reduce mortality. Correction of electrolyte disturbances has been long advised and magnesium supplementation has been beneficial in the treatment of torsades de pointes and in some studies after cardiac surgery. However, routine electrolyte supplementation with empiric potassium or magnesium in non-deficient patients has not been convincingly beneficial. Several herbal supplements have also been promoted to have antiarrhythmic activity. However, clinical studies are lacking to support routine use of these herbal medications. In addition, some herbal supplements may cause serious proarrhythmia, and many supplements significantly interact with warfarin and digoxin.

Off-pump coronary artery bypass surgery: physiology and anaesthetic management †

Increasing interest is being shown in beating heart (off-pump) coronary artery surgery (OPCAB) because, compared with operations performed with cardiopulmonary bypass, OPCAB surgery may be associated with decreased postoperative morbidity and reduced total costs. Its appears to produce better results than conventional surgery in high-risk patient populations, elderly patients, and those with compromised cardiac function or coagulation disorders. Recent improvements in the technique have resulted in the possibility of multiple-vessel grafting in all coronary territories, with a graft patency comparable with conventional surgery. During beating-heart surgery, anaesthetists face two problems: first, the maintenance of haemodynamic stability during heart enucleation necessary for accessing each coronary artery; and second, the management of intraoperative myocardial ischaemia when coronary flow must be interrupted during grafting. The anaesthetic technique is less important than adequate management of these two major constraints. However, experimental and recent clinical data suggest that volatile anaesthetics have a marked cardioprotective effect against ischaemia, and might be specifically indicated. OPCAB surgery requires team work between anaesthetists and surgeons, who must be aware of each other's constraints. Some surgical aspects of the operation are reviewed along with physiological and anaesthetic data.

Intravenous magnesium sulfate prophylaxis for atrial fibrillation after coronary artery bypass surgery

OBJECTIVE

Atrial fibrillation is a rhythm disorder commonly seen early after coronary artery bypass grafting, and it increases morbidity.

METHODS

To investigate the effectiveness of magnesium sulfate in the prophylaxis of atrial fibrillation, we conducted a prospective, randomized, placebo-controlled clinical study on 200 consecutive patients in whom we performed elective and initial coronary artery bypass grafting operations. In each group 50% of patients underwent beating-heart operations. In the treatment group 100 patients (76 men and 24 women; mean age, 57.63 +/- 9.68 years) received 24.34 mEq (3 g) of magnesium sulfate in 100 mL of saline solution that was administered over 2 hours (50 mL/h) preoperatively, perioperatively, and at postoperative days 0, 1, 2, and 3. In the control group 100 patients (74 men and 26 women; mean age, 59.96 +/- 9.29 years) received only 100 mL of saline solution according to the same administration schedule as the treatment group.

RESULTS

Atrial fibrillation developed in 15 patients from the treatment group and in 16 patients from the control group. The arrhythmia developed after 37.87 +/- 12.76 and 45.26 +/- 15.27 hours in the treatment and control groups, respectively. Although a significant relationship was found between low magnesium sulfate levels and increased incidence of atrial fibrillation (P <.05), when the incidence of postoperative atrial fibrillation is concerned, no significant difference was found between the 2 groups (P >.05). Also, no significant difference was found between operations with cardiopulmonary bypass and beating-heart operations in terms of atrial fibrillation incidence (P >.05). However, atrial fibrillation extended the duration of hospital stay in both groups (P <.05).

CONCLUSION

Our findings indicate that magnesium sulfate infusion alone is not sufficient for the prophylaxis of atrial fibrillation.

Off-pump coronary artery bypass grafting: new developments but a better outcome?

Off-pump coronary artery surgery is now performed safely and effectively without cardiopulmonary bypass. This review includes indications, approaches, anaesthetic and haemodynamic management, and compares the occurrence of postoperative complications and multiorgan dysfunction with conventional cardiac surgery.