Ablation of Unmappable Scar-Related Ventricular Tachycardia in Patient With Mixed Cardiomyopathy

Background Ablation of scar-related ventricular tachycardia (VT) remains challenging, particularly when the arrhythmia is hemodynamically unstable and could not be mapped. Functional substrate mapping techniques such as isochronal late activation mapping (ILAM) and decrement-evoked potential (DeEP) mapping allow identification of critical slow-conduction zones without the need for sustained VT. Case Illustration A 54-year-old man with prior ICD implantation presented with recurrent VT storm. Device interrogation showed frequent VT/VF episodes requiring therapy. MRI showed mixed of ischemic and hypertrophic cardiomyopathy. Programmed ventricular stimulation induced VT with several different morphologies and unstable hemodynamic, making activation and entrainment VT mapping not feasible. Electroanatomical mapping was performed using EnSite Precision system and HD grid multipolar catheter. Endocardial mapping demonstrated a low-voltage scar at LV apical anterolateral area, while isochronal crowding was not clearly seen during ILAM. Epicardial mapping was required due to findings of subendocardial late enhancement on MRI and VT MDI > 0.55 on ECG. Epicardial voltage mapping showed scar at LV apicolateral area, while ILAM and DeEP mapping with S2 pacing confirmed late potentials and critical slow conduction site at the same area, adjacent to the endocardial area of interest. Targeted ablation was delivered by epicardial and endocardial approach via transseptal access. Following ablation, aggressive ventricular pacing could no longer induce VT. Conclusion Functional substrate mapping including ILAM and DeEP mapping is a practical strategy for identifying critical sites of VT circuit, enabling effective targeted ablation of unmappable scar VT in cases such as mixed cardiomyopathy.Figure 1.Inducible multifocal VT by ventricular pacing during mapping (A); Endocardial DeEP mapping with S2 pacing showed area of interest at apicolateral LV (B); ILAM mapping during S1 pacing showed isochronal crowding area representing slow conduction area at apicolateral LV (C); Endocardial and epicardial targeted site were adjacent to each other (D); Epicardial ablation site at safe range from the coronary arteries (E); Endocardial ablation site with transseptal approach (F)