A thirty-five-year-old male was referred for evaluation of recurrent hemodynamically tolerated sustained monomorphic ventricular tachycardia of 200 bpm, which had right bundle branch block (RBBB) morphology with leftward axis deviation (Figure 1). He suffered from non-syncopal palpitations in the past 3 months. He was in functional class NYHA I and had no symptoms suggestive of ischemic heart disease. His medical history was unremarkable. There was no family history of cardiomyopathies or sudden unexplained death. His 12-lead ECG in sinus rhythm was clearly abnormal with borderline Q-waves in the inferior leads, mid-QRS notching and slurring of narrow QRS complexes (QRSd of 98 ms) in limb and right precordial leads, respectively, and flattened biphasic or negative T waves in the inferolateral leads (Figure 1). Echocardiography detected slight LV dilatation (end-diastolic diameter of 63 mm) with mild global hypokinesia (ejection fraction of 42%). CT coronary angiography excluded coronary artery disease. Cardiac magnetic resonance imaging (CMR) showed late gadolinium enhancement (LGE), which was distributed circumferentially in the epicardial layer of the LV free wall myocardium (approximately one-third of the LV wall thickness) including the rightward portion of the interventricular septum (IVS) (Figure 2). The LGE spread also to a small adjacent region of the mid-anterior free wall of right ventricle (RV). Moreover, T1-weighted and SPIR magnetic resonance sequences visualised adipose infiltration of myocardium in the anterior right IVS and an adjacent portion of the anterior RV free wall in the zone of positive LGE. The LV was slightly dilated (end-diastolic diameter of 62 mm, end-diastolic volume of 287 mL) with mild global hypokinesia (ejection fraction of 50%). There were no wall motion abnormalities of the RV. The typical scar distribution together with ECG abnormalities and VT of RBBB morphology suggested the diagnosis of LDAC. Treatment with bisoprolol 2.5 mg and trandolapril 4 mg daily was initiated.

Because of recurrent VT despite medical therapy, an electrophysiological study, 3D electroanatomical mapping, and ablation were indicated. The procedure was performed under local anesthesia and mild conscious sedation with midazolam and alfentanyl. At the beginning of the procedure, clinical VT of 191 bpm and RBBB morphology (Figure 1, VT #1) was induced by programmed LV stimulation. This was unexpectedly poorly tolerated, so the procedure was continued with substrate mapping in sinus rhythm (3.5 mm irrigated-tip catheter, NaviStar Thermocool, D-curve and CARTO 3, Biosense Webster Inc., Diamond Bar, CA, USA). The procedure was guided by intracardiac echocardiography (AcuNav Diagnostic Ultrasound Catheter, Acuson – Siemens, Mountain View, CA, USA). The LV was accessed by a transseptal approach using a steerable sheath (Agilis, St. Jude Medical Inc., St. Paul, MN, USA) in order to enable subsequent endomyocardial biopsy. As expected, endocardial LV bipolar mapping did not reveal low-voltage areas <1.5 mV. There were a limited number of sites with abnormal electrograms, which were located only at the apicoseptal LV region (Figure 3). Stimulus-to-QRS (S-QRS) delay did not exceed 20 ms in any of them. The best, but far from optimum, pacemap (Figure 1) for the clinical VT was achieved in the mid-inferior LV septum where the morphology of bipolar electrograms was fairly normal. Despite this finding, RF energy (Stockert EP Shuttle, Biosense Webster Inc., Diamond Bar, CA, USA; setting: 30 W, <40°C, 30 ml/min) was delivered at this site and its close vicinity. After the initial ablation, we were unable to re-induce the VT of clinical morphology. However, three other non-clinical VTs (of 206, 125 and 220 bpm), all of left bundle branch block (LBBB) pattern, were observed (Figure 1, VT #2 - #4). They were inducible by programmed stimulation from the RV/LV or by catheter manipulation and were either non-sustained or non-tolerated. The pacemapping for VT morphology #2 and #3 suggested an exit site at the mid-to-apical RV septum. VT morphology #4 had an inferior axis and its exit site was located at the anteroseptal portion of the right ventricular outflow tract (RVOT). Electroanatomical mapping of the RV identified dispersed regions of abnormal electrograms, predominantly at the septum and the anterior/septum portions of the RVOT, while the RV free wall including the inferolateral peritricuspid annulus region was generally not affected. Maximum scar involvement was found at the RV aspect of the IVS, where sites with discrete late potentials and slow conduction zones (maximum S-QRS of 50 ms) were identified (Figure 3). Substrate-based ablation was performed rather extensively at the RV aspect of the midseptum from the inferior to middle segments up to the proximity of right bundle branch (contralateral to the exit of clinical VT #1 and close to the suspected exits of VT #2 and #3) as well as at the anterior portion of the RVOT (site of origin of VT #4).

An endomyocardial biopsy was performed prior to ablation, with an attempt to guide the catheter bioptome (7-F/104 cm biopsy forceps, Cordis, Bridgewater, NJ, USA) into affected regions according to electroanatomical mapping. Histological examination confirmed the presence of abnormal fibrous and adipose tissue with myocyte reduction in endomyocardial samples taken from both left and right aspects of the IVS (Figure 2). Mutation screening for desmosomal genes was not performed.

A cardioverter-defibrillator (ICD) was implanted and the patient was discharged on the same dosage of bisoprolol and trandolapril medication. No class I or III antiarrhythmic drugs were given. During the 18-month follow-up, the patient experienced only a single episode of monomorphic VT (243 bpm) when bisoprolol medication was discontinued by mistake. LV dilatation and mild dysfunction remained stable at regular check-ups.

Written informed consent was obtained from the patient to the publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor of this journal.