Comparing substrate mapping techniques for ventricular tachycardia

Different substrate mapping techniques are available to identify myocardial sites for catheter ablation in ventricular tachycardia (VT) patients. A recent study has for the first time looked at how well they work compared with one another.

Published in the journal Heart Rhythm, the study, “Comparison of Combined Substrate-based Mapping Techniques to Identify Critical Sites for Ventricular Tachycardia Ablation¹,” compared voltage mapping, isochronal late activation mapping (ILAM), and fractionation mapping from fractionated electrograms (fEGM).

“Identifying critical sites for maintenance of VT with extensive substrate mapping leads to favorable clinical outcomes compared with a more limited approach,” said Hassan Khan, M.D., Ph.D., a Norton Heart & Vascular Institute electrophysiologist and lead author of the study. “At the same time, extensive ablation strategies can result in unnecessary ablation, which can cause complications such as prolonged anesthesia, volume overload and hemodynamic compromise.”

VT ablation uses cold or heat energy to create tiny ablation lesions in the heart to block faulty signals that cause VT’s rapid, erratic heart rhythm.

Substrate-based approaches look for local abnormal ventricular electrograms that represent diseased areas, potential targets for VT ablation. The study compared three substrate mapping techniques:

• Voltage mapping, a commonly used technique to identify low-voltage regions for catheter ablation
• ILAM, a functional substrate mapping technique that identifies “isochronal crowding,” signifying delayed activation. The “isochronal crowding” correlates with the slowing of conduction and has been shown to relate with critical sites for catheter ablation of VT.
• Fractionation, an automated, real-time mapping algorithm using fEGM, which measures muscle response to electrical stimulation

In the study, electroanatomic substrate maps of 27 patients with 33 VT critical sites identified were retrospectively analyzed. Electroanatomic maps were reanalyzed using an EnSite X workstation, from Abbott Medical. Traditional bipolar electroanatomic maps, from clinical procedures, and post-processed omnipolar maps, created from saved case files, were used in the analysis.

Patients were monitored during routine clinical follow-up including outpatient visits, hospitalizations and implantable cardioverter defibrillator (ICD) interrogation. VT recurrences were defined as documented sustained monomorphic ventricular tachycardia more than 30 seconds in duration or any appropriate ICD therapy with anti-tachycardia pacing or shock. Patients lost to follow-up were censored, and mortality was confirmed with electronic medical records.

Following the analysis, the study concluded that ILAM and fractionation each identified distinct critical sites and provided a smaller area of interest than did voltage mapping alone. A primary limitation of voltage mapping is the lack of specificity in identifying critical sites for VT ablation.

1. Heart Rhythm. 2023 Jun;20(6):808-814. doi: 10.1016/j.hrthm.2023.02.023. Epub 2023 Feb 28. PMID: 36863636