Hypokalemia and cardiac disease

In health, serum potassium concentration is maintained within the approximate range of 3.5-5.2 mmol/L. Disturbance of potassium homeostasis is a common electrolyte disorder that is clinically manifest through its adverse effect on both skeletal and cardiac muscle cell function. 

Although often asymptomatic, both reduced serum potassium (hypokalemia) and increased serum potassium (hyperkalemia) can cause muscle weakness/paralysis and cardiac arrhythmias. A recently published short review focuses on hypokalemia occurring in patients with cardiovascular disease, in particular the contribution that hypokalemia can make to sudden cardiac death in this patient group. 

The article includes a brief consideration of the physiological mechanisms involved in maintaining normal serum potassium, and the prevalence of hypokalemia among patients with cardiovascular disease (7-17 %). Also included is a summary of the accumulating epidemiological evidence that hypokalemia increases the risk of cardiac arrhythmias and reduces survival among patients suffering myocardial infarction and heart failure. 

Common causes of hypokalemia in patients with cardiovascular disease are highlighted; these include the use of non-potassium-sparing diuretics that can result in increased loss of potassium in urine and consequent potassium depletion.

Hypokalemia can also occur not from depletion but from shift of potassium into cells due to increased activity of the Na/K pump. Insulin, catecholamines and beta-adrenoceptor agonist drugs (used to treat heart disease) all increase the activity of the Na/K pump and thereby cause hypokalemia. 

The author argues that since many patients with cardiac disease are also diabetic, the hypokalemic potential of exogenous insulin is significant. Additionally, he observes, catecholamines are frequently raised in patients with heart disease. 

In conclusion, the author implies that despite the associated increased risk of fatal cardiac arrhythmia (sudden cardiac death), hypokalemia is often ignored in patients with heart disease. He suggests that it may be beneficial for these patients to maintain serum potassium at the high end of the normal range.