High-density mapping-based ablation strategy in a 30-year-old patient with a history of myocarditis

A 30-year-old man with a history of myocarditis and recurrent ventricular tachycardia (VT) underwent epicardial ablation guided by ultra-high density mapping. The patient had been implanted a subcutaneous cardioverter defibrillator 1 year previously following sudden cardiac arrest. Endocardial bipolar voltage in sinus rhythm using a 64-pole multielectrode mapping catheter (OrionTM, Boston Scientific, Marlborough, MA, USA) did not indicate any abnormal local voltage. Epicardial origin of the critical VT isthmus site was indicated by signal characteristics and timing. Epicardial ultra-high density mapping identified the site of critical isthmus on the posterolateral left ventricle (Figure 1A; note the conduction zone represented in purple) confirmed by entrainment and pace mapping. Propagation of the activating wavefront formed a ‘figure of eight’ with fast propagation in the protected critical isthmus and slow propagation at the entry and exit site (Figure 1A; indicated by circular broken lines converging in the common isthmus). Focused activation mapping of a second VT with opposite axis (Figure 1B; note change to caudocranial propagation in the critical isthmus) revealed mid-diastolic potentials on the identified isthmus site, highlighted using LUMIPOINTTM software (Figure 1B; note highly fractionated signals preceding the QRS-complex) and confirmed by the near-field electrograms from the mini-electrodes incorporated in the ablation catheter (IntellaNav MIFI OITM, Boston Scientific). Radiofrequency ablation was monitored by local impedance drop (Direct SenseTM software, (Figure 1C) and resulted in specific VT termination [Figure 1C; VT termination at local impedance (LI) drop of 9.1Ω]. In line with late enhancement documented by cardiac magnetic resonance imaging, epicardial voltage mapping during sinus rhythm identified a low-voltage area, and local abnormal ventricular activation (Figure 1D; extended LAVA following the QRS-complex). Consecutive substrate modification was performed. Non-inducibility of ventricular arrhythmia was confirmed at the end of the procedure, and the patient is now free from arrhythmia recurrence during 5-months follow-up. Epicardial ventricular tachycardia (VT) ablation and substrate modification following myocarditis. (A) Twelve-lead electrocardiogram (ECG) of the initially induced VT and epicardial activation map showing the critical isthmus. Ventricular tachycardia-re-entry forms a figure of eight (indicated by circular broken lines). Isochronal lines visualize local propagation velocity. Narrow spaced isochronal lines (set at 10 ms) at entry and exit site indicate slower propagation velocity compared to propagation velocity in the isthmus with wider spaced isochronal lines. (B) Twelve-lead-ECG morphology of a second VT. Focused activation mapping during VT identifies critical isthmus with inversely directed propagation (broken arrow). Roving probe, implemented for rapid review of local signals, indicates site where signals were recorded. Mid-diastolic potentials (MDP) during VT are highlighted after reannotation with LUMIPOINT™ software by using an additional window of interest. The ‘complex activation’ feature highlights regions of the map that both activate within the time-of-interest period and exhibit multiple components of activation. The Skyline, reflecting the size of the depolarizing region throughout the mapping window, indicates presence of local signals with near-field MDP are identified during the ‘valley’ of the Skyline as a surrogate for the limited amount of activated myocardium at this given point of time. (C) Upper panel: Local impedance (LI) as visualized to the operator (white: raw data, yellow: mean values) during the procedure. Baseline LI is indicated in blue, LI drop is indicated in orange. Lower panel: Electrograms during ablation and VT termination (turquoise: V5 and V6; pink: right ventricular apex; white: ablation catheter; purple: mini-electrodes). (D) Substrate modification in sinus rhythm is guided by voltage mapping (>1 mV corresponding to normal voltage, ≤0.1 mV corresponding to low-voltage areas) and electrogram timing. LUMIPOINT™ software highlights local abnormal ventricular activation (LAVA) as indicated by late potentials and fractionated potentials. This case demonstrates the usefulness of automated ultra-high density electroanatomical mapping to identify distinctive characteristics of near-field electrograms which can guide successful VT termination and substrate modification. Specific propagation patterns can be detected and detailed VT characteristics visualized.1 Targeted radiofrequency ablation can be monitored by local impedance.2,3 This young patient was successfully treated for electrical storm adopting advanced signal-processing integrating near-field electrograms and local impedance in conjunction with classical entrainment and pace mapping. Supplementary material is available at Europace online. This paper was published as part of a supplement supported by a grant by Boston Scientific Italy. Conflict of interest: P.M.: received travel grant from Medtronic. S.W.: compensation for participation on speaker’s bureau and consultant or on advisory board for: Boehringer Ingelheim, Bayer, Daiichi-Sankyo, BMS, Abbott. C.M.: compensation for participation as consultant for Biotronik, Biosense Webster and on speaker’s bureau for Abbott, Boston Scientific, Medtronic.