Third-degree atrioventricular block associated with severe acute hyponatraemia.

Area of Science:

• Cardiology
• Nephrology
• Electrophysiology

Background:

• Severe acute hyponatraemia (serum sodium <120 mEq/L) primarily causes neurological symptoms.
• Arrhythmogenic effects of hyponatraemia are rare, with few reported cases of atrioventricular (AV) block.

Observation:

• A patient with subdural hematoma developed refractory bradycardia.
• Diagnostic workup revealed severe acute hypo-osmolar hyponatraemia as the likely cause.
• The patient presented with third-degree AV block at a sodium level of 115 mEq/L.

Findings:

• The presented case is one of the few documented instances of third-degree AV block directly induced by severe hyponatraemia.
• The patient had no other identifiable risk factors for cardiac conduction abnormalities.
• Complete resolution of third-degree AV block occurred following successful correction of serum sodium levels.

Implications:

• Highlights the critical need to consider electrolyte disturbances, particularly hyponatraemia, in the differential diagnosis of new-onset third-degree AV block.
• Underscores the importance of comprehensive metabolic panel assessment in patients with unexplained bradycardia or heart block.
• Suggests that prompt electrolyte correction can reverse severe cardiac conduction abnormalities in select cases.