A 36-year-old male with a history of dextrocardia, atrial septal defect, and ccTGA underwent atrial septal defect repair and morphological tricuspid valvuloplasty in 2014. However, several months later, he experienced a drug-refractory persistent atrial flutter and progressive deterioration of morphological right ventricle (mRV) function. The ejection fraction of mRV ranged from 47 to 54% during sinus rhythm and decreased to 28–42% during atrial flutter. Intermittently administration of amiodarone was used to treat atrial flutter. Electrocardiogram showed an atrial flutter at 130 beats/min with 2:1 atrioventricular conduction (Fig. 1a). A chest X-ray showed dextrocardia, left-sided hepatic contour, right-sided magenblase, and an enlarged cardio-thoracic ratio (Fig. 1b). Echocardiogram showed severe morphological tricuspid regurgitation with mRV ejection fraction of 35%. The diameters of right atrium (RA), left atrium (LA) and mRV end-diastolic diameter are 51, 54 and 73 mm, respectively.
Before electrophysiological study (EPS), contrast-enhanced computed tomography was performed to demonstrate the anatomical structure of the abnormal heart. Reconstructed geometric structure of LA revealed an unusually huge LAA (Fig. 1c, d). We also used CARTOSYNC™ to reconstruct the 3-dimensional imaging of atriums and ventricles and conform the spatial relationship between them (Fig. 1e, f), which would be a useful guidance for atrial septal puncture and EPS.
A decapolar steerable electrode catheter was positioned within coronary sinus and a hexapolar electrode catheter was placed in morphologically left ventricular (mLV) separately. The intracardial ECG revealed an atrial flutter with a cycle length (CL) of 257 ms. A PentaRay catheter (Biosense Webster, Inc., Diamond Bar, CA, USA) was used to perform high-density mapping of the RA under the guidance of the Carto 3 system (Biosense Webster, Inc., Diamond Bar, CA, USA). The activation mapping revealed a passive activation pattern from LA to RA, the postpacing interval (PPI) after entrainment at coronary sinus (CS) ostium and free atrial wall were 245 ms and 423 ms, respectively, which means the reentrant circuit comes from LA rather than the RA.
Therefore, we performed high-density mapping of the LA after interatrial septal puncture through the surgical patch [7]. As vividly showed in activation mapping (Fig. 2a, b), two reentry circuit loops were located around the morphological tricuspid annulus (functional mitral annulus) and local area behind aberrant LAA, respectively. Propagation mapping and RIPPLE mapping show the activation sequence of two reentry circuit loops vividly (Additional files 1, 2, 3, 4). The two reentry circuit loops were overlapped in inferior area behind LAA (close to 6’ clock of tricuspid annulus). The major tachycardia circuit consecutively rotated around the tricuspid annulus in a counterclockwise direction and had a proximal to distal activation pattern in the coronary sinus. The PPI after entrainment at the 6’ clock, 12’ clock of morphological tricuspid annulus and posterior wall were 271 ms, 255 ms and 275 ms, respectively.
Since the aberrant LAA almost occupied the entire atrial free wall in this patient, it is difficult to perform conventional mitral isthmus line to connect the morphological tricuspid annulus and the ostium of the right inferior pulmonary vein. The first ablation line we performed was from 12’ clock of morphological tricuspid annulus to right superior pulmonary vein (RSPV). During ablation of this line, CL of atrial flutter prolonged from 260 to 275 ms, and when this ablation line accomplished, CL increased to 290 ms but tachycardia did not stop (Fig. 3a, b). Entrainment mapping at a pacing cycle length of 270 ms demonstrated a PPI of 351 ms in anterior wall (close to 1’ clock of tricuspid annulus) and 282 ms in posterior wall (close to 6’ clock of tricuspid annulus), respectively. Entrainment from posterior wall also demonstrates a good stimulus-to-p wave interval (99 ms, S-P/AFLCL = 0.34) with concealed fusion, confirming this as the critical isthmus of the atrial flutter. Therefore, we performed second ablation line carefully from right inferior pulmonary vein to 6’ clock of morphological tricuspid annulus, which was also the overlapped area of two reentry circuit loops, and terminated the tachycardia (Fig. 4a). Two ablation lines were illustrated in Fig. 4b/c and sinus rhythm was shown in ECG after ablation (Fig. 5). We confirmed the complete conduction block by activation map along the TA and by differential pacing from each end of the ablation lines.
The patient reported no tachycardia episodes during the 8-month follow-up after the procedure. Echocardiogram showed functional left ventricular ejection fraction increased to 49% and functional left ventricular end-diastolic diameter decreased to 60 mm at the 8-month follow-up visit.