Successful Catheter Ablation of Two Macro-reentrant Atrial Tachycardias in a Patient with Congenitally Corrected Transposition of the Great Arteries: A Case Report

Figure 1:. Patient anatomy: cardiac chambers and great vessels. Both AV and VA discordance are present in cc-TGA. Thus, a morphologic RA drains into a morphologic LV through a mitral valve, then ejects into the main PA. Similarly, a morphologic left atrium drains into a morphologic RV through a tricuspid valve, ejecting into the ascending aorta. Note the LV-to-PA conduit that was surgically constructed to palliate obstruction of the RV outflow tract. PA: pulmonary artery; RVOT: right ventricular outflow tract.

Figure 2:. Presenting SVT. The standard 12 leads were recorded simultaneously. The lead II rhythm strip is a continuous recording.

Figure 3:. SVT1. SVT1 was noted to be a long-R–P tachycardia with 2:1 AV conduction, excluding orthodromic AV reentrant tachycardia and making AV-nodal reentrant tachycardia less likely, although 2:1 AV-nodal reentrant tachycardia with a lower common pathway block is not definitively excluded on this tracing. HRA: high right atrium (located in the RA appendage); RVa: right ventricular apex. CS 9,10 is located at the coronary sinus ostium. The His catheter is positioned in the basal right ventricle, inferior to the expected His bundle position.

Figure 4:. Activation map of SVT1. The image shows a left anterior oblique projection of the RA. The endocardial activation sequence is consistent with counterclockwise reentry around the mitral valve. Because of the presence of cc-TGA, the subeustachian isthmus is a cavomitral rather than cavotricuspid isthmus. Yellow tags: His recording locations; white, blue, and pink tags: locations of other attempts at entrainment.

Figure 5:. Entrainment of SVT1. Entrainment is performed with the pacing catheter positioned in the cavomitral isthmus. Note the downstream/upstream effect evident in this tracing as there is orthodromic capture of the high RA electrogram, identifying reentry as the tachycardia mechanism. The postpacing interval of the tachycardia cycle length was 0 ms in this location. CS: coronary sinus; HRA: high right atrium; RVa: right ventricular apex. The His catheter was located in the basal RV, inferior to the His recording location.

Figure 6:. SVT2. Note the slightly different activation sequence in the CS recordings relative to that of SVT1. A halo catheter was placed prior to tachycardia mapping to further delineate the RA activation sequence.

Figure 7:. Electroanatomic mapping of SVT2. A: Activation map of SVT2, which used a zone of slow conduction in the posterolateral RA free wall. B: Voltage map of SVT2. Note that the voltage calipers have been adjusted with the lower limit set to less than 0.02 mV. With these settings, several conducting channels are identified coursing through the slow conduction zone indicated in the activation map. Red tags: ablation lesions; blue tag: the entrainment location, where the postpacing interval of the tachycardia cycle length was 21 ms. The RA is presented in a posteroanterior arrangement.