Management of atrial fibrillation after cardiac surgery-part II: prevention and treatment

Continuous Magnesium Infusion to Prevent Atrial Fibrillation After Cardiac Surgery: A Sequential Matched Case-Controlled Pilot Study

OBJECTIVE

The authors aimed to test whether a bolus of magnesium followed by continuous intravenous infusion might prevent the development of atrial fibrillation (AF) after cardiac surgery.

DESIGN

Sequential, matched, case-controlled pilot study.

SETTING

Tertiary university hospital.

PARTICIPANTS

Matched cohort of 99 patients before and intervention cohort of 99 consecutive patients after the introduction of a continuous magnesium infusion protocol.

INTERVENTIONS

The magnesium infusion protocol consisted of a 10 mmol loading dose of magnesium sulphate followed by a continuous infusion of 3 mmol/h over a maximum duration of 96 hours or until intensive care unit discharge.

MEASUREMENTS AND MAIN RESULTS

The study groups were balanced except for a lower cardiac index in the intervention cohort. The mean duration of magnesium infusion was 27.93 hours (95% confidence interval [CI]: 24.10-31.76 hours). The intervention group had greater serum peak magnesium levels: 1.72 mmol/L ± 0.34 on day 1, 1.32 ± 0.36 on day 2 versus 1.01 ± 1.14 and 0.97 ± 0.13, respectively, in the control group (p < 0.01). Atrial fibrillation occurred in 25 patients (25.3%) in the intervention group and 40 patients (40.4%) in the control group (odds ratio 0.49, 95% CI, 0.27-0.92; p = 0.023). On a multivariate Cox proportional hazards model, the hazard ratio for the development of AF was significantly less in the intervention group (hazard ratio 0.45, 95% CI, 0.26-0.77; p = 0.004).

CONCLUSION

The magnesium delivery strategy was associated with a decreased incidence of postoperative AF in cardiac surgery patients. These findings provide a rationale and preliminary data for the design of future randomized controlled trials.

Magnesium sulphate replacement therapy in cardiac surgery patients: A systematic review

OBJECTIVE

The objective of this review was to identify evidence to inform clinical practice guidelines for magnesium sulphate (MgSO₄) replacement therapy for postoperative cardiac surgery patients.

DATA SOURCES

Three databases were systematically searched: CINAHL Complete, MEDLINE Complete, and EmBase.

REVIEW METHOD USED

A systematic literature review method was used to locate, appraise, and synthesise available evidence for each step of the medication management cycle (indication, prescription, preparation, administration, and monitoring) for MgSO₄ replacement therapy. Database searches used combinations of synonyms for postoperation or surgery, cardiac, heart, arrhythmia, atrial fibrillation, and magnesium sulphate. Search results were independently screened for inclusion by two researchers at title, abstract, and full-text stages with good statistical agreement (kappa scores of 0.99, 0.87, and 1.00, respectively).

RESULTS

Twenty-four included studies reported varying methodologies, data collected, and medication management practices. Of these, 23 studies (95.8%) excluded patients with comorbidities commonly observed in clinical practice. This review identified low-level evidence for two practice recommendations: (i) concurrent administration of MgSO₄ with medications recommended as the best practice for prevention of postoperative atrial fibrillation and (ii) clinical and laboratory monitoring of magnesium blood serum levels, vital signs, and electrocardiography should be performed during MgSO₄ replacement therapy. Evidence to inform MgSO₄ replacement therapy for each medication management cycle step was limited; therefore, a guideline could not be developed.

CONCLUSIONS

Although MgSO₄ is routinely administered to prevent hypomagnesaemia in postoperative cardiac surgery patients, there was insufficient evidence to guide critical care nurses in each medication management cycle step for MgSO₄ replacement therapy. These findings precluded the development of comprehensive recommendations to standardise this practice. Poor standardisation can increase the risk for patient harm related to variation in clinical processes and procedural errors. In light of this evidence gap, consensus of expert opinion should be used as a strategy to guide MgSO₄ medication management.

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.

The Clinical Noncompliance of Oral Sotalol/Magnesium for Prophylactic Treatment of Atrial Fibrillation After Coronary Artery Bypass Grafting

BACKGROUND

Postoperative atrial fibrillation has been refractory to many attempted pharmacologic prevention methods and, when effective, side effects have been described. The present aim was to study the clinical compliance of a suggested prophylactic treatment, oral sotalol, and magnesium.

METHODS

Coronary-bypass patients without clinical contraindications to receive oral sotalol (80 mg twice daily) and magnesium supplementation were enrolled (n = 49) with an intention-to-treat strategy and being compared with a matched control group (n = 844). A protocol listed exclusion criteria of clinical compliance that was postoperatively evaluated prior to and during treatment.

RESULTS

Twenty-seven of the 49 enrolled patients (55%) were compliant to sustain the treatment according to the protocol. The remaining patients were postoperatively excluded, mainly because of hemodynamic reasons, of whom 14 were noncompliant to initiate any treatment. The AF occurrence in the compliant group was 7% versus 36% in noncompliant patients (p = 0.035), and 24% in the control group (p = 0.076). However, with an intention-to-treat policy the overall AF incidence became 18%. The subgroups of enrolled patients demonstrated skewing phenomena. The noncompliant group had higher requirement for inotropic support (p = 0.029) and longer aortic cross-clamp time (p = 0.048) compared to compliant patients. Further, the body weight of noncompliant patients was markedly lower than in the compliant counterpart (p = 0.015).

CONCLUSIONS

The tested treatment protocol showed limited compliance among routine cardiac-surgery patients, and further, introduced a biased selection of patients that skewed the results and may have partly explained the treatment effect.

Atrial Fibrillation After Aortic Arch Repair Requiring Deep Hypothermic Circulatory Arrest: Incidence, Clinical Outcome, and Clinical Predictors

OBJECTIVE

To delineate the incidence, outcome impact, and clinical predictors of atrial fibrillation (AF) after adult aortic arch repair requiring deep hypothermic circulatory arrest (AAR-DHCA) AIMS: To determine the incidence of AF after AAR-DHCA, to determine whether AF after AAR-DHCA affects mortality or stay in the intensive care unit (ICU), to determine multivariate predictors for AF after AAR-DHCA, and to determine whether aprotinin protects against AF after AAR-DHCA.

STUDY DESIGN

Retrospective and observational.

STUDY SETTING

Single large university hospital.

PARTICIPANTS

All adults undergoing AAR-DHCA in 2000 and 2001.

MAIN RESULTS

The cohort size was 144. Antifibrinolytic exposure was 100%, aprotinin 66% and aminocaproic acid 34%. The incidence of AF was 34.0%. AF was not significantly associated with increased mortality or prolonged ICU stay. Advanced age was a multivariate risk factor for AF. Lower temperature nadir during DHCA was protective against postoperative AF. Aprotinin had no demonstrable effect on AF after AAR-DHCA.

CONCLUSIONS

AF after AAR-DHCA is common but does not independently increase mortality or ICU stay. The risk of AF after AAR-DHCA increases with age but decreases with the degree of hypothermia during DHCA. Aprotinin does not appear to affect the risk of AF after AAR-DHCA.

Predictors of atrial fibrillation after off-pump coronary artery bypass graft surgery

BACKGROUND

Postoperative atrial fibrillation (AF) is one of the most common complications after cardiothoracic surgery and is associated with an increased risk of stroke, and longer hospital stay. The pathophysiology of postoperative AF is uncertain, and its prevention remains unsatisfactory. Many previous studies have examined the predictors of AF after on-pump coronary artery bypass graft surgery (CABG), but there are few reports after off-pump CABG.

METHODS

The aim of the present prospective observational study, in which 296 consecutive patients were enrolled, was to elucidate the predictors of AF after off-pump CABG. The association of perioperative factors with AF was investigated using univariate analysis. Significant variables were included into a stepwise logistic regression model to ascertain their independent influence on the occurrence of AF.

RESULTS

The incidence of AF was 32%. AF prolonged the time until patients were fit for discharge by 3 days (P<0.01). Stepwise multivariate analysis identified increasing age [odds ratio (OR) 1.44 per 10-yr increase; 95% confidence interval (CI) 1.06-1.95], intraoperative average core temperature (OR 1.64; 95% CI 1.05-2.56), the average cardiac index in the intensive care unit (OR 0.37; 95% CI 0.19-0.71), and intraoperative fluid balance (OR 0.96 per 100-ml increase; 95% CI 0.93-0.99) as independent predictors of postoperative AF.

CONCLUSION

Our present findings indicate that ageing, the intraoperative fluid balance, and postoperative cardiac index are associated with the onset of AF after off-pump CABG.

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.

Epicardial atrial defibrillation: successful treatment of postoperative atrial fibrillation

BACKGROUND

Atrial fibrillation is the most common complication after cardiac surgery. Current medical treatment using antiarrhythmics and anticoagulants has a significant morbidity. The goal of this study was to determine if epicardial atrial defibrillation can be safely performed and return patients to sinus rhythm.

METHODS

A prospective analysis of patients undergoing cardiac surgery was performed. Patients with a prior pacemaker/defibrillator, history of arrhythmia, preoperative antiarrhythmic, age greater than 85 years, history of stroke, or intraaortic balloon pump were excluded. Temporary epicardial atrial cardioversion wires were placed on the right and left atrium. Bipolar atrial and ventricular pacing wires were also placed. The wires were tested in the operating room. Patients who went into postoperative arial fibrillation were cardioverted with 3 J, 6 J, or 9 J.

RESULTS

There were 45 patients enrolled. Sixteen patients (35%) went into postoperative arial fibrillation during their hospital stay. Mean time to onset of arial fibrillation was 2.6 +/- 1.4 days after surgery. Fifteen patients were successfully cardioverted to sinus rhythm on the primary cardioversion, with mean of 5.7 +/- 2.4 J. One patient was cardioverted at 6 hours after onset of arial fibrillation, at 6 J. Recurrent arial fibrillation occurred in 4 patients during their hospital stay. All 4 of these patients were cardioverted with a mean of 6.4 +/- 2.6 J. All wires were removed the day before patients were discharged. There were no complications with wire insertion or removal. There were no adverse neurologic events. The mean hospital stay was 5.1 +/- 2.2 days. All patients were in sinus rhythm at 1 month follow-up.

CONCLUSIONS

The use of a temporary atrial defibrillator to resynchronize patients in postoperative arial fibrillation is safe and effective.

Atrial fibrillation and cardiac surgery

PURPOSE OF REVIEW

To discuss the pathophysiology, risk factors, and treatments for atrial fibrillation occurring after cardiac surgery.

RECENT FINDINGS

Atrial fibrillation occurs frequently after cardiac surgery and it may lead to patient morbidity. Many variables have been suggested to be associated with this arrhythmia, but only advanced patient age can consistently identify risk for this complication. Immediate electrical cardioversion is indicated when the arrhythmia leads to hemodynamic instability or myocardial ischemia. Otherwise treatment is aimed at heart rate control, elective cardioversion with drugs or electrical means, and anticoagulation when the arrhythmia persists. Multiple investigations have evaluated methods for preventing postoperative atrial fibrillation, but only beta-adrenergic receptor blocking drugs have been consistently shown to be effective, and then not in all patients. Surgical treatments are increasingly being considered as a therapeutic means for ameliorating chronic atrial fibrillation. The use of these procedures has been simplified with the development of devices that can generate linear scars in the atrium and around the pulmonary vein orifices. These simplifications will allow for broader application of these techniques to patients undergoing other cardiac surgery (e.g. mitral valvular surgery).

SUMMARY

Atrial fibrillation is one of the most common complications of cardiac surgery. There are three major aims for treating atrial fibrillation: conversion to sinus rhythm, heart rate control, and anticoagulation. Only beta-blockers can be recommended for prophylaxis against postoperative atrial fibrillation. Further refinements in surgical treatments for atrial fibrillation may allow for wider applications of this therapy with lower rates of complications.