Case report
A 54-year-old man was referred to our hospital because of palpitation attacks. He had a history of mitral annuloplasty with a superior transseptal (STS) approach for mitral valve prolapse at the age of 49 years. Atrial flutter was recognized by 12-lead echocardiography (ECG); thus, catheter ablation was performed. When both atria were mapped using the CARTO3 system (Biosense Webster, Diamond Bar, CA) during tachycardia, double potentials, indicating an incision line connecting the right atrial free wall to the septum and then to the left atrial roof, were observed (Figure 1A ). The typical counterclockwise atrial flutter with a cycle length of 260 ms was mapped and terminated during cavotricuspid isthmus (CTI) ablation. Subsequently, atrial tachycardia (AT) with a cycle length of 272 ms was induced. The entrainment and activation mapping revealed a macroreentrant circuit associated with the right atrial part of the incision line from the STS approach. The activation wavefront circulated clockwise around the incision with two penetration points along the surgical incision in right atrium (Figure 1B ). AT was rapidly terminated after 2 seconds of the first radiofrequency application (30 W, 60 seconds in total) at the conduction site across the incision of the right atrial free wall. AT was not induced thereafter. Another conduction point across the incision was also ablated. In addition, a linear ablation connecting the incisional scar with the inferior vena cava (IVC) was created. Then, pacing from the low lateral right atrium (anterior side of the incision line) showed residual conduction beyond surgical incision at 10 O’clock and 11 O’clock positions viewing the annulus as a clockface (Figure 2, A and B ). Radiofrequency application at these sites was performed, and complete conduction block was verified (Figure 2, C ). The excitation of sinus rhythm propagates behind the incision, then turns to the tricuspid annulus (anterior side of the incision) and ascends in a counterclockwise manner to the free wall. The two block lines (incision to IVC and CTI) make the posterolateral wall of the tricuspid annulus the most delayed site of propagation during sinus rhythm in the right atrium. The patient has been free of recurrence of tachycardia for three years after ablation.