Focal mechanism of ventricular tachycardia in coronary artery disease

Background: Re-entry is the most common mechanism of sustained monomorphic ventricular tachycardia (VT) in patients with coronary artery disease and prior myocardial infarction (MI). Objective: This study sought to report the electrophysiological properties of a series of patients with prior MI who underwent radiofrequency ablation (RFA) for VT originating instead from a focal source. Methods: The electrophysiological properties of 46 patients with prior MI (male 89%, age 64.8 ± 10.2 years) who underwent RFA for sustained VT were studied. A total of 101 VTs were induced (92 [91%] macro-re-entrant VT and 9 [9%] focal VT). Results: One patient had adenosine-sensitive idiopathic focal VT. The focal VT group had a significantly shorter pre-systolic interval (electrogram to QRS) during VT compared with the macro-re-entrant VT group (36 ± 17 ms vs. 117 ± 67 ms, P = .001). The successful ablation sites in the focal VT group also had a significantly lower ratio (in percentage) of electrogram-QRS interval to diastolic interval (VT cycle length - QRS duration) during VT (14 ± 8%) as compared with macro-re-entrant VTs (48 ± 30%, P <.001). Focal VTs demonstrated an apparent point source of endocardial activation and could not be entrained, whereas 77% of macro-re-entrant VTs were entrained. Successful ablation sites for focal VT (success rate 100%) were predominantly in the basal half of the left ventricle (75%), whereas only 60% of macro-re-entrant VTs (success rate 90.7%) were basal (P = .01). However, the procedure time, VT cycle length, number of RFA applications required for success, and acute success results were not significantly different in these 2 groups. Conclusion: A focal mechanism is present in up to 9% of VTs in patients with CAD and prior MI that are induced during electrophysiology study for RF ablation. Mechanistic distinction from more typical macro-re-entrant VT in this population is important because ablation site characteristics are very different.