Effect of beta blockade on ventricular fibrillation- and ventricular tachycardia-induced circulatory arrest in acute myocardial infarction.

The risk of developing circulatory arrest secondary to ventricular fibrillation or tachycardia in acute myocardial infarction (AMI) is greatly increased in patients with hypokalemia, whether diuretic induced or not. In a retrospective study of 5,877 infarctions during an 8-year period, hypokalemia was more common (22.5%) in diuretic-treated AMI patients than in those not treated with diuretics (12.9%). Thus, hypokalemia should be avoided in diuretic-treated patients with increased risk of myocardial infarction. Circulatory arrest occurred in 13% of hypokalemic patients treated with nonselective beta blockers on admission compared with 26% in those treated with selective beta blockers. No difference was found in normokalemic patients. The mean serum potassium value was 4.07 mM/liter in the patients treated with nonselective beta blockers compared with 4.0 and 4.01 in those treated with selective and no beta blockade, respectively. In a separate study, adrenaline infusion in healthy volunteers produced a decrease not only in serum potassium but also in serum magnesium, although the latter occurred later. Pretreatment with verapamil exaggerated the decrease in serum potassium. When starting beta-blocker treatment in patients at risk of developing AMI, consideration should be given to commencing with a nonselective instead of a selective beta blocker.