Frequency Content of Unipolar Electrograms May Predict Deep Intramural Excitable Substrate: Insights From Intramural Needle Catheter Ablation of Ventricular Tachycardia

Objectives: This study sought to identify midmyocardial arrhythmogenic substrates by examining the frequency content of unipolar endocardial surface electrograms, comparing sites with transmural scar versus sites with intramural excitable substrate (IES) as identified during needle catheter ablation for ventricular tachycardia (VT). Background: Midmyocardial arrhythmogenic substrates are a common reason catheter ablation for VT may fail. Methods: A total of 659 intramural needle sites were studied in 26 patients (age 61 ± 9 years, 85% male, 69% nonischemic cardiomyopathy) who underwent intramural needle catheter ablation for VT. Among 136 sites where endocardial pacing did not capture (threshold >10 mA), needle pacing captured at 29 indicating IES, and did not capture at 107 indicating transmural scar. Intramural needle ablation was performed at 21 of 29 IES sites. Analysis of voltage amplitude, duration, and power spectra of endocardial and intramural needle electrograms was performed. Results: IES sites compared with transmural scar had higher endocardial unipolar electrogram voltage, 0.99 (interquartile range [IQR]: 0.69 to 1.62) mV versus 0.78 (IQR: 0.61 to 1.09) mV; p = 0.038; higher unipolar intramural needle electrogram voltage, 1.16 (0.80 to 1.69) mV versus 0.76 (0.6 to 1.12) mV; p = 0.003; higher endocardial unipolar frequency power particularly in the 5- to 20-Hz band, 1.97 (IQR: 0.93 to 3.89) mV²/s versus 1.03 (IQR: 0.63 to 2.22) mV²/s; p = 0.002; and higher unipolar intramural electrogram frequency particularly in the 0 to 10 Hz range, 3.02 (IQR: 0.98 to 6.95) mV²/s versus 1.33 (IQR: 0.70 to 3.13) mV²/s; p = 0.018. Endocardial unipolar frequency in the 5- to 20-Hz band identified sites with IES, area under the curve of 0.676; p = 0.002; power frequency integral of >0.77 mV²/s provided a 90% sensitivity and 41% specificity. Conclusions: The frequency content of unipolar electrograms may complement voltage in the detection of deep intramural substrates to facilitate VT catheter ablation. (Intramural Needle Ablation for Ablation of Recurrent Ventricular Tachycardia; NCT01791543)