Correspondence

Atrial Arrhythmias after Cardiac Surgery

N Engl J Med 1997; 337:860-861September 18, 1997

Article

To the Editor:

In the review of atrial arrhythmias after cardiac surgery by Ommen et al. (May 15 issue),1 no mention is made of the use of parenteral magnesium sulfate. Hypomagnesemia is frequent after diuresis in patients who have undergone cardiopulmonary bypass, and it is a risk factor for atrial and ventricular arrhythmias. Intravenous magnesium therapy has much to recommend it, because it avoids the proarrhythmic effects associated with most of the drugs cited in the article. Given on its own, magnesium reduces ventricular rates rapidly.2 This effect is thought to be due both to direct action on the atrioventricular node and to a reduction in the sympathetic input to that node. Similar effects are noted in patients with hypomagnesemia and those without it, which suggests that magnesium has a pharmacologic action.3 Magnesium used alone has been shown to be better than digoxin in controlling the ventricular response rate in atrial fibrillation, and the two agents control the rate better than either in isolation.3 Magnesium has an efficacy similar to that of intravenous amiodarone in controlling the ventricular rate, and it may be superior with respect to cardioversion in atrial tachyarrhythmias.4 Indeed, cardioversion of atrial arrhythmias after parenteral magnesium therapy has been reported in several small studies.2-4

There is also evidence for the prophylactic use of magnesium in preventing atrial arrhythmias after bypass surgery. Fanning et al. reported a double-blind, placebo-controlled trial in 99 patients that showed a reduction in atrial fibrillation from 42 episodes in 14 patients in the control group to 12 episodes in 7 patients in the magnesium group (P<0.02).5

When patients have new atrial fibrillation after bypass surgery, it is our practice to seek reversible causes of atrial arrhythmias actively and then use an intravenous bolus of 12 mmol of magnesium over a period of 1 hour, followed by an infusion of 60 mmol over a 24-hour period, before using other antiarrhythmic agents.

William J.C. Hobbs, M.B., Ch.B.
Alan Fitchet, M.R.C.P.
Lawrence Cotter, M.B., Ch.B.
Manchester Heart Centre, Manchester MI 9WL, United Kingdom

5 References

1. 1

   Ommen SR, Odell JA, Stanton MS. Atrial arrhythmias after cardiothoracic surgery. N Engl J Med 1997;336:1429-1434
   Full Text | Web of Science | Medline

2. 2

   McLean RM. Magnesium and its therapeutic uses: a review. Am J Med 1994;96:63-76
   CrossRef | Web of Science | Medline

3. 3

   Brodsky MA, Orlov MV, Capparelli EV, et al. Magnesium therapy in new-onset atrial fibrillation. Am J Cardiol 1994;73:1227-1229[Erratum, J Cardiol 1994;74:639.]
   CrossRef | Web of Science | Medline

4. 4

   Moran JL, Gallagher J, Peake SL, Cunningham DN, Salagaras M, Leppard P. Parenteral magnesium sulfate versus amiodarone in the therapy of atrial tachyarrhythmias: a prospective, randomized study. Crit Care Med 1995;23:1816-1824
   CrossRef | Web of Science | Medline

5. 5

   Fanning WJ, Thomas CS Jr, Roach A, Tomichek R, Alford WC, Stoney WS Jr. Prophylaxis of atrial fibrillation with magnesium sulfate after coronary artery bypass grafting. Ann Thorac Surg 1991;52:529-533
   CrossRef | Web of Science | Medline

To the Editor:

I was astonished that Ommen et al. concluded that patients with transient atrial fibrillation in the postoperative period should be treated with heparin. Heparin therapy is associated with a distinct incidence of life-threatening complications, related primarily to bleeding and the occurrence of heparin-induced thrombocytopenia with thrombosis. It is not at all clear that a putative small increase in the postoperative stroke rate caused by atrial fibrillation would in any way be more important than the known complications of prolonged heparin therapy.

William E. Walker, M.D.
2831 Sackett, Houston, TX 77098

Author/Editor Response

The authors reply:

To the Editor: We strongly agree with Hobbs and colleagues that reversible causes of arrhythmia should be investigated and corrected, and we consider this standard care. Possible causes include such factors as hypoxia, infection, ischemia, and electrolyte abnormalities. Hobbs et al. provide impressive evidence for using magnesium postoperatively. However, there are conflicting data. Another randomized, placebo-controlled study of 140 patients who had continuous electrocardiographic monitoring for 4 days after the operation and 12-lead electrocardiography to detect symptomatic palpitations for up to 10 days found that routine magnesium administration had no benefit. In addition, the patients who had atrial arrhythmias had higher serum magnesium levels than those who remained in sinus rhythm.1

As Walker points out, heparin therapy is not without risk. Heparin-induced thrombocytopenia has been reported in up to 5 percent of patients. A small percentage of these patients also have a tendency to thrombosis. Walker's comments underscore the importance of monitoring the complete blood count frequently while patients are receiving heparin. We recommend discontinuing heparin completely if the platelet count falls by 30 percent from base line, or below 100,000 per cubic millimeter. We should point out that we did not recommend heparin for every patient with transient atrial fibrillation. Our recommendation is that anticoagulation be considered when arrhythmia persists for more than 24 hours in patients who have no contraindication to heparin therapy. As we acknowledged, the risk–benefit ratio of anticoagulant therapy in this setting is not known.

Steve R. Ommen, M.D.
Marshall S. Stanton, M.D.
John A. Odell, M.D.
Mayo Clinic, Rochester, MN 55905

1 References

1. 1

   Parikka H, Toivonen L, Pellinen T, Verkkala K, Jarvinen A, Nieminen MS. The influence of intravenous magnesium sulphate on the occurrence of atrial fibrillation after coronary artery by-pass operation. Eur Heart J 1993;14:251-258
   CrossRef | Web of Science | Medline

Citing Articles (2)

Citing Articles

1. 1

   E. Victor Tselentakis, Edward Woodford, Joby Chandy, Glenn R. Gaudette, Adam E. Saltman. (2006) Inflammation Effects on the Electrical Properties of Atrial Tissue and Inducibility of Postoperative Atrial Fibrillation. Journal of Surgical Research 135:1, 68-75
   CrossRef

2. 2

   Andre Gries, Christoph Bode, Stefanie Gross, Karlheinz Peter, Hubert Bohrer, Eike Martin. (1999) The Effect of Intravenously Administered Magnesium on Platelet Function in Patients After Cardiac Surgery. Anesthesia & Analgesia 88:6, 1213-1219
   CrossRef