Retrospective Analysis of ECG Changes and Arrhythmias in Patients With Profound Hyponatremia

Hyponatremia is the most common electrolyte disorder in hospitalized patients. It is associated with high morbidity and mortality. Acute profound hyponatremia is defined by a drop in sodium level to < 125 mEq/L within ≤ 48 h. As the cation with the highest extracellular concentration, sodium is the main determinant of serum osmolality. Thus, profound hyponatremia can lead to hypoosmolality of the serum (< 275 mosmol/kg) and a resulting osmotic gradient to a variably pronounced cerebral edema with neurological and/or psychiatric symptoms such as confusion, nausea, psychosis, vigilance disorder up to coma or seizures.

While the effects of hyponatremia on the central nervous system (CNS) are well characterized, its effects on cardiac function, particularly excitation and conduction system, are poorly understood. Thus, it is unclear whether osmotically induced swelling of human cardiomyocytes is a possible pathophysiological mechanism for cardiac dysfunction. In animal studies with isolated ventricular cardiomyocytes from rabbit hearts, significant swelling of cardiomyocytes was shown under osmotic stress in both ischemic preconditioned and non-preconditioned cells. In another experimental study, Yanagi et al. systematically investigated the effects of decreasing extracellular sodium concentration on the mechanical and electrophysiological properties of pig hearts in the Langendorff perfusion model. Electrocardiographic changes in the PQ interval and QT duration were demonstrated with decreasing sodium concentration as an expression of impaired atrioventricular and intraventricular conduction.

In contrast, there are no clinical cohort studies in which the frequency and prognostic relevance of electrocardiographic changes and arrhythmias in profound hyponatremia have been investigated. The majority of publications comprise case reports and small case series describing variable and mostly reversible electrocardiographic changes and arrhythmias associated with profound hyponatremia.

The electrocardiogram (ECG) as a primary basic diagnostic tool plays a central role in cardiology and emergency medicine in particular for clarifying chest pain, shortness of breath, palpitations and dizziness/syncope. In addition, it can also provide indications of pathologies outside the cardiovascular system such as intoxication or electrolyte disorders or be used to monitor drug therapy.

The extent to which the ECG can be used in the diagnosis and risk stratification of profound hyponatremia cannot be answered today, but the aforementioned case reports suggest that hyponatremia might have an influence on the electrophysiological processes of the heart and thus the ECG.