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An Uncommon Block of a Common Circuit HUSSAM ALI, M.D., ANTONIO SORGENTE, M.D., Ph.D., GIANLUCA EPICOCO, M.D., and RICCARDO CAPPATO, M.D. From the Arrhythmia & Electrophysiology Center, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy

atrial flutter, cardiac surgery, catheter ablation, electrical anatomic mapping A 55-year-old man with a prior history of surgical mitral valve repair and documented episodes of common atrial flutter was referred to our center for catheter ablation of the cavotricuspid isthmus (CTI). At admission, his ECG showed sinus rhythm and his echocardiogram revealed correct functioning of the mitral valve and mild biatrial dilatation. At electrophysiological study multipolar diagnostic catheters were introduced and positioned at the His bundle level, coronary sinus (CS), and peri-tricuspid region (Orbiter catheter). CTI ablation was performed during proximal CS pacing and using a conventional fluoroscopic approach. During ablation there was a sudden loss of atrial electrograms recorded at the lateral wall of the right atrium (RA; Fig.1, panel A). CS pacing was interrupted promptly to check out preserved propagation of sinus rhythm throughout the AV node. Several possible mechanisms might cause this electrophysiological phenomenon: a displacement of the Orbiter catheter around the tricuspid valve was excluded by

J Cardiovasc Electrophysiol, Vol. 26, pp. 809-810, July 2015. No disclosures. Address for correspondence: Hussam Ali, M.D., Arrhythmia and Electrophysiology Center, IRCCS Policlinico San Donato, Via Morandi 30, 20097 San Donato Milanese, Milan, Italy. Fax: 39-02-5560-3125; E-mail: [email protected] doi: 10.1111/jce.12633

fluoroscopy. Another intriguing hypothesis was the appearance of a CTI block (double solid lines; Fig. 1, panel A) in addition to a pre-existent line of conduction block (double dotted lines; Fig. 1, panel A) at the lateral wall, probably consequent to the prior cardiac surgery. The CTI block caused complete electrical isolation of a wide area of the lateral RA wall, creating regional electrical silence. Interestingly, pacing from within that lateral “atrial island” demonstrated local atrial capture (the arrows; Fig. 1, panel B) dissociated from sinus rhythm, confirming both the bidirectional feature of both lines of conduction block and finally our hypothesis. After ablation, sinus rhythm showed complete atrial silence at the lateral RA wall presenting as an atrial scar (Fig. 1, panel C). We suggest in patients with a prior cardiac surgery or ablation it is prudent to use an electroanatomical mapping system, even when performing standard CTI ablation, in order to recognize and localize pre-existing areas of conduction block/scar. In our case, if the pre-existent lateral line had been located more septal, CTI ablation would have caused isolation of the sinus node region and probably impaired total AV conduction. Second, what is commonly defined as a scar during substrate mapping in sinus rhythm could be alternatively an excitable area protected by conduction blocks. Therefore, it is advisable to attempt pacing from these silent areas in order to confirm their real nature as unexcitable scars or alternatively to discover excitable zones protected by lines of conduction block that might be unidirectional and proarrhythmic.

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Journal of Cardiovascular Electrophysiology

Vol. 26, No. 7, July 2015

Figure 1. A: RA wall isolation during CTI ablation. B: Pacing from the lateral RA wall at pacing cycle length of 700 milliseconds after CTI block. C: Recordings during sinus rhythm after CTI ablation. A1→A18 = Orbiter catheter recordings around the tricuspid valve (lateral→ septal); ABL = ablation catheter; CS1→10 = coronary sinus (distal→proxymal); SAN = sino-atrial node; SVC = superior vena cava; IVC = inferior vena cava; CT = crista terminalis; CSos = CS ostium; p = proximal; d = distal.

An Uncommon Block of a Common Circuit.

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