Electrolyte abnormalities underlying lethal and ventricular arrhythmias.

It is well known that changes in serum potassium cause ventricular arrhythmias as a result of clearly documented changes in the electrophysiological characteristics of single fibers. Hypopotassemia induced by thiazide and loop diuretics may contribute to the incidence of sudden cardiac death in patients with hypertension and those with congestive heart failure. In addition, hypopotassemia appears to be an independent risk factor for lethal ventricular arrhythmias occurring in the setting of acute myocardial infarction and contributes significantly to arrhythmias associated with starvation and alcoholism. The increase in myocardial extracellular potassium that occurs in the ischemic zone after coronary occlusion is clearly a major factor in the genesis of lethal ventricular arrhythmias that occur in this setting. A decrease in serum magnesium is also believed to be arrhythmogenic, and magnesium depletion is thought to play a role in many of the arrhythmias associated with hypopotassemia. Moreover, the administration of magnesium salts may be effective in the management of life-threatening ventricular arrhythmias. However, definite evidence establishing a causal relation between ventricular arrhythmias and hypomagnesemia or intracellular magnesium depletion is lacking. Changes in intracellular calcium contribute to the arrhythmias associated with acute ischemia and with reperfusion and may be important in the genesis of ventricular tachycardia induced by exercise and by digitalis. Thus, electrolyte and metabolic abnormalities clearly underlie lethal ventricular arrhythmias in a wide variety of clinical situations and should be routinely considered as potential etiologic factors in patients with life-threatening ventricular arrhythmias, particularly those with hypertension and congestive heart failure who are receiving thiazide and loop diuretics.