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QUARTERLY FOCUS ISSUE: HEART RHYTHM DISORDER: CLINICAL RESEARCH: VENTRICULAR TACHYCARDIA

Characterization of the Arrhythmogenic Substrate in Ischemic and Nonischemic Cardiomyopathy

Implications for Catheter Ablation of Hemodynamically Unstable Ventricular Tachycardia

University of California, Los Angeles, Cardiac Arrhythmia Center, David Geffen School of Medicine, Los Angeles, California

Manuscript received October 19, 2009; revised manuscript received January 5, 2010, accepted January 11, 2010.

^_* Reprint requests and correspondence: Dr. Kalyanam Shivkumar, UCLA Cardiac Arrhythmia Center, A2-237 CHS, 10833 Le Conte Avenue, Los Angeles, California 90095-1679 (Email: kshivkumar{at}mednet.ucla.edu).

Objectives: The purpose of this study was to compare the characteristics and prevalence of late potentials (LP) in patients with nonischemic cardiomyopathy (NICM) and ischemic cardiomyopathy (ICM) etiologies and evaluate their value as targets for catheter ablation.

Background: LP are frequently found in post-myocardial infarction scars and are useful ablation targets. The relative prevalence and characteristics of LP in patients with NICM is not well understood.

Methods: Thirty-three patients with structural heart disease (NICM, n = 16; ICM, n = 17) referred for catheter ablation of ventricular tachycardia were studied. Electroanatomic mapping was performed endocardially (n = 33) and epicardially (n = 19). The LP were defined as low voltage electrograms (<1.5 mV) with onset after the QRS interval. Very late potentials (vLP) were defined as electrograms with onset >100 ms after the QRS.

Results: We sampled an average of 564 ± 449 points and 726 ± 483 points in the left ventricle endocardium and epicardium, respectively. Mean total low voltage area in patients with ICM was 101 ± 55 cm² and 56 ± 33 cm², endocardial and epicardial, respectively, compared with NICM of 55 ± 41 cm² and 53 ± 28 cm², respectively. Within the total low voltage area, vLP were observed more frequently in ICM than in NICM in endocardium (4.1% vs. 1.3%; p = 0.0003) and epicardium (4.3% vs. 2.1%, p = 0.035). An LP-targeted ablation strategy was effective in ICM patients (82% nonrecurrence at 12 ± 10 months of follow-up), whereas NICM patients had less favorable outcomes (50% at 15 ± 13 months of follow-up).

Conclusions: The contribution of scar to the electrophysiological abnormalities targeted for ablation of unstable ventricular tachycardia differs between ICM and NICM. An approach incorporating LP ablation and pace-mapping had limited success in patients with NICM compared with ICM, and alternative ablation strategies should be considered.

Key Words: catheter ablation • ventricular tachycardia • myocardial infarct scars • late potentials

Abbreviations and Acronyms   BZ = border zone   DS = dense scar   ICM = ischemic cardiomyopathy   LP = late potentials   mLP = moderate late potentials   NICM = nonischemic cardiomyopathy   TCL = tachycardia cycle length   TLV = total low voltage   vLP = very late potentials   VT = ventricular tachycardia

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