Correlation between surface and intracardiac electrocardiogram in a patient with inappropriate defibrillation shocks due to hyperkalemia.

A 39-year-old man received implantable cardioverter defibrillator (ICD) shocks during sinus rhythm, triggered by an increase in amplitude and oversensing of intracardiac T waves, caused by hyperkalemia. After treatment of hyperkalemia, the T wave morphology normalized, and oversensing and inappropriate ICD shocks were eliminated. Alteration of the intracardiac electrogram was well correlated to the surface electrocardiogram (ECG) changes. Intracardiac T waves can be altered by hyperkalemia and it seems that this alteration can be estimated by surface ECG analysis.