Northwest Axis on Electrocardiogram: Decoding an Unusual Cardiac Axis in a Young Patient

We describe a patient with a "northwest" cardiac axis and electrocardiographic features of right ventricular (RV) pressure overload in the setting of Fontan circulation.

In atrioventricular canal defects with Fontan circulation, a northwest cardiac axis on electrocardiography reflects altered RV activation and remodeling, often persisting from childhood into adulthood and secondary to RV outflow tract obstruction.

A 28-year-old woman presented for routine medical follow-up. Medical history was notable for Fontan procedure, with the last operation performed 12 years earlier, followed by an unspecified percutaneous cardiac intervention. Electrocardiography demonstrated frontal QRS axis between -90° and ±180°, with RV pressure overload. Physical examination revealed a pansystolic murmur audible over the tricuspid and mitral areas, digital clubbing, and an oxygen saturation of 85%. Laboratory evaluation showed a hemoglobin level of 19 g/dL and hematocrit of 62%.