Tall P-waves in inferior leads: A case of coexisting ectopic rhythm and atrial fibrillation arising from the superior vena cava.

Suppression of atrial fibrillation (AF) arising within the superior vena cava (SVC) requires SVC electric isolation (SVCI) without sinus node (SN) injury. If an ectopic rhythm and AF trigger coexist within the SVC, the intra-SVC ectopic rhythm complicates the pre-SVCI search for the SN. This coexistence is without precedent; however, it is important to carefully locate the SN to prevent injury during SVCI. This case shows a paroxysmal AF with both phenomena coexisting in the SVC. Moreover, outpatient electrocardiographic assessment for tall P-waves in inferior leads before catheter ablation could predict these phenomena and enable safer SVCI.