Purpose: Sinus rhythm (SR) electrocardiogram (ECG) features in patients with nonischemic cardiomyopathy (NICM) and ventricular tachycardia (VT) have been described. ECG characteristics that distinguish nonischemic VT substrate from prior myocardial infarction (MI) have yet to be determined. We aimed to identify ECG differences between patients with basal-inferolateral scar due to NICM versus prior MI.
Methods: SR/atrial-paced ECGs from patients who underwent VT ablation with endocardial/epicardial basal-inferolateral nonischemic scar (n = 25) were compared to patients with inferior/inferolateral MI (n = 30). Surface QRS complexes in each lead were analyzed. Patients with bundle branch block or ventricular pacing were excluded. The best diagnostic algorithm was determined by multivariate analysis then validated prospectively.
Results: The NICM group had smaller R amplitude in leads I, II, and III (p ≤ 0.05 for all), greater S amplitude in leads II, III, and V6 (p ≤ 0.001 for all) and S/R ratio in lead V6 (p = 0.001). Inferior Q waves were uncommon in NICM (24 % vs. 87 %, p < 0.001). Lateral QRS fragmentation was uncommon (20 %) but only found in NICM. A three-step algorithm was derived with 100 % sensitivity and 77 % specificity for NICM. In the validation cohort (n = 51), ICM was appropriately excluded in 93 % of the cases of NICM (91 % interobserver agreement) by the algorithm.
Conclusions: Lateral lead QRS fragmentation, absence of inferior Q waves, and lead V6 S/R ratio ≥0.25 on the SR ECG distinguishes patients with basal-lateral scar due to NICM from those with prior MI. These findings demonstrate the value of the surface ECG in identifying unique scar-based VT substrate.