The value of defibrillator far-field electrograms for ablation of idiopathic ventricular fibrillation

Abstract

We report a case of idiopathic ventricular fibrillation treated by catheter ablation of the monomorphic initiating premature beat. The initiating focus was identified using intacardiac defibrillator electrograms (EGMs).

Case report

A 61-year-old man with no prior cardiac history had ventricular fibrillation (VF) arrest for which he underwent implantation of a single-chamber implantable cardioverter defibrillator (ICD). During the 4 months following discharge, he experienced 46 appropriate ICD shocks for VF despite therapy with amiodarone. Device interrogation revealed a premature ventricular contraction (PVC) with uniform far-field electrogram (EGM) morphology as the initiating event for all recorded VF events.

In the electrophysiology laboratory, programmed double extra-stimuli delivered from the right ventricular (RV) apex (600/300/280 ms) reproducibly induced VF. A PVC with left bundle/inferior axis morphology was uniformly noted immediately after the programmed extra-stimuli and before initiation of VF. The ICD-EGM of the induced PVCs closely resembled the ICD-EGM of PVCs that preceded VF in spontaneous episodes (Figure 1A and B). Additionally, the timing of the near-field EGM relative to the peak of the PVC in the far-field EGM was similar in both induced and spontaneous episodes. Pace-mapping was performed in the RV outflow tract to identify sites with (a) similar far-field ICD-EGM to that of PVCs initiating spontaneous VF and (b) 12/12 electrocardiogram (ECG) morphology match to PVCs preceding induced VF in the laboratory (Figure 1C). These criteria were satisfied by pacing in the antero-lateral RV outflow tract (Figure 1D). Catheter manipulation in this region repeatedly induced VF during mapping. The region was targeted with irrigated radiofrequency lesions. After catheter ablation, no inducible PVCs or VF were noted despite RV burst pacing or extrastimuli delivered from the RV apex or outflow tract on/off isoproterenol. During initial follow-up, the patient did well with no VF recurrence during 10 months of follow-up. However, after 10 months, he presented with a single shock for VF with an initiating PVC morphology similar to those ablated at the prior session. Repeat mapping of the area with pace maps similar to the ICD-EGM template, revealed recovery of tissue with myocardial capture. The area was again ablated with 3.5 mm irrigated radiofrequency lesions (40 W). The patient has had no further recurrence during 8 months of follow-up.

Figure 1.

Illustrates the qualitative similarity of the far-field implantable cardioverter defibrillator-electrocardiogram of the ventricular fibrillation initiating clinical premature ventricular contraction (A) with the ventricular fibrillation initiating premature ventricular contraction induced by double extra-stimuli in the electrophysiology laboratory (B). Once taking into account the variable electrocardiogram amplitude between near and far-field implantable cardioverter defibrillator-electrocardiograms, the morphologies are similar. Additionally, the timing of the near-field electrocardiogram relative to the peak of the premature ventricular contraction in the far-field electrocardiogram was similar in panels A and B. (C) Shows the corresponding surface ECG for the induced event in panel B. (D) Shows the area targeted for catheter ablation on magnetic resonance angiography (red dots) and fluoroscopy images of the right ventricle in right anterior oblique and left anterior oblique projections. The magnetic resonance image was registered to right ventricle landmarks using CARTO XP (Biosense Webster, Diamond Bar, CA, USA) registration software.

Discussion

Catheter ablation of VF triggers from the myocardium of the RV outflow tract has previously been reported by Haissaguerre et al.¹ This report highlights the potential utility of the ICD far-field EGM as a valuable surrogate for localization of clinically significant but rare PVCs. Yoshida et al.² recently showed that stored ICD-EGMs can (a) serve as an accurate surrogate for 12-lead ECGs for differentiating clinical VTs from other VTs, and (b) serve as a template for pace-mapping of VT exit sites. Our case highlights the importance and applicability of Yoshida and colleagues’ findings to the case of idiopathic VF.

Conflict of interest: none declared.

Funding

Dr Nazarian is funded by a National Heart, Lung, and Blood Institute Career Development Award (K23HL089333).