Malignant arrhythmias in acute myocardial infarction. Relationship to serum potassium and effect of selective and non-selective beta-blockade.

The risk of malignant arrhythmias during myocardial infarction is greatly increased in patients with diuretic-induced hypokalaemia. In our study an increased risk was seen also in hypokalaemic patients not treated with diuretics. This indicates that hypokalaemia as such could trigger malignant arrhythmias. The frequency of hypokalaemia was much higher (22.5%) in diuretic-treated infarct patients than in those not treated with diuretics (12.9%). Thus, hypokalaemia should be avoided in diuretic-treated patients with increased risk of myocardial infarction. The incidence of malignant arrhythmias in hypokalaemic patients was 13.2% in those treated with non-selective beta-blockers on admission versus 26.1% in those treated with selective beta-blockers; corresponding figures in infarctions with serum potassium concentrations above 3.6 mmol/L were 9.4% and 10.4%, respectively. Non-selective beta-blockers reduced the frequency of malignant arrhythmias in hypokalaemic infarctions. This was in contrast to selective beta-blockers, which had no favourable effect on the frequency of malignant arrhythmias in hypokalaemic infarctions. Non-selective beta-blockers did not completely counteract the hypokalaemia. Still, the risk of malignant arrhythmias decreased. Thus, our study indicates that apart from hypokalaemia, some additional mechanism specifically linked to adrenaline stimulation in important for the development of malignant arrhythmias in acute myocardial infarction.