BARCELONA – A serum potassium level of at least 5.0 mmol/L or 3.5 mmol/L or less at admission for suspected acute coronary syndrome is a red flag for increased risk of in-hospital mortality and cardiac arrest, according to a Swedish study of nearly 33,000 consecutive patients.
That’s true even if, as so often ultimately proves to be the case, the patient turns out not to have ACS, Jonas Faxén, MD, of the Karolinska Institute, Stockholm, reported at the annual congress of the European Society of Cardiology.
“This study highlights that, if you have a patient in the emergency department with a possible ACS and potassium imbalance, you should really be cautious,” Dr. Faxén said.
He reported on 32,955 consecutive patients admitted to Stockholm County hospitals for suspected ACS during 2006-2011 and thereby enrolled in the SWEDEHEART (Swedish Web System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies) registry.
Overall in-hospital mortality was 2.7%. In-hospital cardiac arrest occurred in 1.5% of patients. New-onset atrial fibrillation occurred in 2.4% of patients. These key outcomes were compared between the reference group – defined as patients with an admission serum potassium of 3.5 to less than 4.0 mmol/L – and patients with an admission serum potassium above or below those cutoffs.
In a multivariate logistic regression analysis adjusted for 24 potential confounders, including demographics, presentation characteristics, main diagnosis, comorbid conditions, medications on admission, and estimated glomerular filtration rate, patients with a serum potassium of 5.0 to less than 5.5 mmol/L were at 1.8-fold increased risk of in-hospital mortality. Those with a potassium of 5.5 mmol/L or greater were at 2.3-fold increased risk.
In contrast, a low rather than a high serum potassium was an independent risk factor cardiac arrest. An admission potassium of 3.0 to less than 3.5 mmol/L carried a 1.8-fold increased risk of in-hospital cardiac arrest, while a potassium of less than 3.0 was associated with a 2.7-fold increased risk.
A serum potassium below 3.0 mmol/L at admission also was associated with a 1.7-fold increased risk of new-onset atrial fibrillation.
These elevated risks of bad outcomes didn’t differ significantly between patients with ST-elevation MI, non-STEMI ACS, and those whose final diagnosis was not ACS, Dr. Faxén noted.
Session cochair David W. Walker, MD, medical director of the East Sussex (England) Healthcare NHS Trust, observed, “When I was a junior doctor I was always taught that when patients came onto coronary care we had to get their potassium to 4.5-5.0 mmol/L. I think you might want to change that advice now.”
“The implication would be that, if you intervene quickly in a patient with an abnormal potassium level, you might make a difference. Clearly, a potassium that’s too high is much worse than too low, since patients with in-hospital cardiac arrest can often be resuscitated,” Dr. Walker commented.
Dr. Faxén reported having no financial conflicts regarding his study, which was funded by the Swedish Heart and Lung Foundation and the Stockholm County Council.