A. Arrhythmias
1. Tachyarrhythmias
The most malignant arrhythmia, ventricular fibrillation, is most common during the first four hours of infarction occurring in about 5% of patients and in about 0.4% of those admitted later. Ventricular fibrillation may occur without a warning arrhythmia and in the absence of heart failure or cardiogenic shock. This malignant arrhythmia may occur despite an adequate suppression of ventricular premature beats. Warning arrhythmias are seen frequently in those who have ventricular fibrillation as well as in those that who don’t. Thus, ventricular fibrillation cannot be accurately predicted.
It is possible that when ventricular fibrillation is precipitated by early occurring ventricular premature beats, R-on-T phenomenon, the ventricular fibrillation threshold at that time has been decreased by certain factors. These include myocardial ischemia, tachycardia, hypox-emia, alkalosis or acidosis, hypokalemia, or catecholamine release in the area of infarction that increases cyclic adenosine monophosphate activity, which is believed to facilitate the development of ventricular fibrillation.
The use of prophylactic lidocaine to suppress ventricular premature beats has been abandoned. The early adminis¬tration of beta-adrenergic blockers should suffice for most patients with ventricular premature beats. This strategy has been shown to reduce the incidence of ventricular fibrillation and death from acute infarction.

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