Arrhythmia

Arrhythmia is common in acute myocardial infarction. Early randomized trials showed the benefit of routine intravenous lidocaine (lignocaine) in the prevention of ventricular fibrillation. However, a later meta-analysis showed an excess mortality in those allocated lidocaine, owing to an excess of asystole! Lidocaine is now reserved for symptomatic sustained ventricular tachycardia or resuscitated ventricular fibrillation. At the same time an alternative antiarrhythmic should be considered. The safest and best proven is a cardioselective b-blocker such as atenolol or metoprolol. Since this is not always effective or tolerated, many physicians go immediately to intravenous amiodarone, about 600 mg/day, followed by oral amiodarone, reducing rapidly to 400 mg orally or less. Once the first few days are over this can usually be stopped, unless ventricular tachycardia or ventricular fibrillation recurs. In this case the drug is continued orally at the lowest effective dose, often 100 to 200 mg/day, since side-effects are common (photosensitivity, bradycardia, thyroid dysfunction) or rare but often fatal (liver and lung toxicity).

Recent randomized trials (GEMICA, CAMIAT, EMIAT) have addressed the question of routine prophylaxis with amiodarone. Unfortunately, although there is clearly some benefit, this is almost outweighed by toxicity, and so it cannot be recommended in low-risk individuals. In addition, these trials were not mutually consistent; it is probable that the doses of amiodarone were too high and continued for too long. Nevertheless, clinical and anecdotal experience with the drug (at the lower doses given above) is reassuring. The drug is presently the most effective for established life-threatening arrhythmia, and it is remarkably well tolerated for short-term use in the coronary care unit, even in patients with overt left ventricular dysfunction.

Other antiarrhythmic agents, for example flecainide, encainide, sotalol (a b-blocker with class IV long-QT action) have generally been discarded because of adverse trial data in ischemic patients.

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