Right ventricular outflow tract ventricular tachycardia ablation post-Rastelli repair

We present a case of right ventricular outflow tract (RVOT) ventricular tachycardia (VT) ablation following remote Rastelli repair. The patient was born with a double-outlet right ventricle (RV), D-transposition of the great arteries (D-TGA), a perimembranous sub-aortic ventricular septal defect (VSD), and valvular and sub-valvular pulmonary stenosis. A Blalock–Taussig shunt was created in the neonatal period, followed by a Rastelli-type repair at the age of 7 years. The latter consisted of tunnelling left ventricular flow along the patch-repaired VSD to the aorta and directing RV flow to the pulmonary artery by means of a valved homograft. The native RVOT had not been over-sewn. At the age of 21 years, the patient presented with a haemodynamically tolerated VT consistent with RVOT origin. Despite treatment with Sotalol the patient experienced a second episode with pre-syncope. Investigations included echocardiography and cardiac magnetic resonance imaging. An electrophysiology study was undertaken of all medication under minimal sedation. A decapolar catheter was inserted into the coronary sinus and quadrapolar catheters were placed at the His bundle region and at the RV apex. Atrio-ventricular Wenkebach occurred at 340 ms with no aberrant conduction. No supraventricular tachycardia was inducible with atrial programmed electrical stimulation (PES; incremental pacing, single extra stimulation testing down to atrial effective refractory period, and burst pacing). Ventricular PES revealed no ventriculo-atrial conduction at a drive cycle of 700 ms. Ventricular extra stimulation testing with two drive cycles (600 and 400 ms) and upto two extra stimuli was performed from the RV apex and native RVOT. The clinical tachycardia was not inducible despite isoprenaline and only infrequent single RVOT PVCs were observed. However, a poorly tolerated VT from the RV apex (morphology similar to RV apical pacing) was induced (cycle length 270 ms), which was pace terminated. Electroanatomical mapping was undertaken using CARTO-3 (Biosense Webster, CA, USA) guidance (Figure 1). Extensive pace mapping was undertaken around the Rastelli conduit, patch-repaired VSD, tricuspid annulus (TA), and RVOT at a pacing cycle length of 500 ms at an output just above the diastolic threshold. The RVOT PVCs and clinical tachycardia was pace mapped to the native mid-septal RVOT. Radiofrequency energy was delivered at this site with a 7 Fr 4 mm irrigated tip catheter (Navi-Star, Biosense Webster) limited to 40 W for 60 s. Additional applications were performed around this site (total six ablations) for a total duration of 337 s (Figure 1). (A) Transthoracic echocardiogram—modified parasternal short axis angled through the native right ventricular outflow tract (RVOT) (thin arrow) and conduit (thick arrow). The left ventricular (LV) was of normal size and function. (B) Cardiac magnetic resonance imaging—short axis scar imaging showing right ventrical (RV) to pulmonary artery (PA) conduit anteriorly (long arrow) and native right ventricular outflow tract posteriorly (short arrow). Delayed gadolinium enhancement demonstrated a thin scar in the right ventrical free wall and basal interventricular septum consistent with surgical engraftment of the Rastelli conduit to the right ventrical free wall and the ventricular septal defect (VSD) repair, respectively. The right ventrical was moderately dilated with normal global systolic function but with focal akinesia at the surgical insertion of the Rastelli conduit. (C) Electro-anatomical mapping using CARTO-3 (Biosense Webster, CA, USA) guidance; voltage map of the right ventricle and conduit integrated with 3D cardiac magnetic resonance imaging showing normal voltage (>2 mV in pink and low voltage in red). No low-voltage areas other than the ventricular septal defect patch and conduit were detected. (D) Volume rendered 3D scar enhanced myocardial imaging using a 3T cardiac magnetic resonance scanner (showing the scar associated with the conduit in white-arrow). (E) The clinical right ventricular outflow tract VT 12 lead electrocardiogram. (F) The infrequent right ventricular outflow tract premature ventricular contractions that was observed (asterix) during the electrophysiology study and the best pace map. White stars, ideal pace map sites where radiofrequency ablation was delivered. Given the presence of ventriculotomy incisions/scars, pre-syncope with the clinical VT, and an inducible unstable VT, an implantable cardioverter-defibrillator (ICD) was implanted. At 3 months of follow-up, the patient remained free from VT. The only prior report of VT ablation following Rastelli repair consisted of attempts to target a scar-based substrate.1 Electroanatomical mapping had revealed an anterolateral scar extending from the TA to the lateral border of the Rastelli conduit insertion. Although procedural success was suspected, the patient had multiple VT recurrences and succumbed to disseminated sepsis. In patients with tetralogy of Fallot (ToF), inducible sustained VT is associated with approximately five-fold risk of sudden cardiac death or clinical sustained VT.2 Patients with Rastelli repairs have potential substrates for the development of macro-reentrant VT as per repaired ToF, including VSD patches and RV suture lines. The approach to VT ablation in patients with congenital heart disease is founded on review of all imaging studies, original surgical/interventional reports, and documented tachyarrhythmias. In the current case, identified anatomical and electrical barriers to conduction around which circuits may propagate included the Rastelli conduit, patch-repaired VSD, TA, and RVOT. When activation and entrainment mapping cannot be performed due to non-inducibility or haemodynamic instability, pace-mapping and/or non-contact mapping can be utilized. In our patient due to the presence of a scar around and in proximity to the outflow tract extensive pace mapping of potential macro re-entry isthmi was also undertaken to exclude an exit site from a potential macro re-entry circuit. Interestingly, the suspected site was located within the native remnant RVOT, where ablation was performed in sinus rhythm. High rates of appropriate ICD shocks occur in primary and secondary prevention patients with repaired ToF.3 The only predictor of appropriate ICD shocks was a prior ventriculotomy incision. For such patients, VT ablation is not a stand-alone therapy for the prevention of sudden cardiac death. Ventricular tachycardia appears to be infrequent following Rastelli repair, but have been poorly characterized. This case demonstrates the feasibility, safety, and potential efficacy of RVOT VT ablation in the setting of Rastelli repair. Conflict of interest: none declared.

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