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Background: Post-myocardial infarction (MI) remodeling contributes to increased electrophysiological and structural heterogeneity and arrhythmogenesis. Utilising the post-infarct ovine model our aim was to determine unipolar electrogram frequency characteristics consequent to this remodeling and the development of Ventricular Tachycardia (VT)., Methods and Results: Mapping studies were performed on 14 sheep at >1 month post-MI induction. Sheep were divided into VT inducible (n = 7) and non-inducible (n = 7) groups. Multielectrode needles (n = 20) were deployed within and surrounding ventricular scar for electrophysiological assessment of electrogram amplitude and width. Spectral analysis of electrograms was undertaken using wavelet and fast fourier transformations (WFFT) to calculate root mean square (RMS) power intervals spanning 0-300Hz in 20Hz intervals. Quantitative assessment between electrophysiological and histological parameters including collagen density, and structural organization of the myocardium was performed. Increasing myocardial scar density resulted in attenuation of electrogram amplitude and RMS values. (all p<0.01). Between groups there were no differences in electrogram amplitude (p = 0.37), however WFFT analysis revealed significantly higher RMS values in the VT group (p<0.05) in association with high frequency fractional components of the electrogram. As scar density increased, greater between-group differences in RMS were observed spanning this high frequency (200-280Hz) spectrum and which were proportionally dependent on the degree of structural disorganisation of the myocardium (p<0.001) and number of extrastimuli required to induce VT (p<0.05)., Conclusion: High frequency unipolar electrogram spectral characteristics were quantitatively co-influenced by the presence of fibrosis and degree of myocardial structural dissorganisation and were associated with the propensity for development of VT., Competing Interests: The authors have declared that no competing interests exist.

Background: Frequent ventricular premature depolarizations (VPDs) can cause cardiomyopathy (CMP). The mechanisms underlying its development remain unclear, with VPD burden being only a weak predictor of risk., Objective: To determine whether VPD QRS duration at the time of initial presentation could predict risk for the subsequent development of CMP in patients with normal left ventricular ejection fraction (LVEF)., Methods: From consecutive patients referred for ablation between January 1, 2006, and April 2, 2013, with ≥10% VPDs on 24-hour Holter monitoring, we identified 45 patients with normal LVEF and an electrocardiogram of the targeted VPD, who were then followed for at least 6 months (median 14 months; interquartile range [IQR] 8-32 months) before intervention. We excluded patients with structural or genetic heart disease., Results: Of the 45 patients, 28 (62%) maintained normal LVEF and 17(38%) developed VPD-induced CMP. VPD burden was similar (26.5% [IQR 19.3%-39.5%] vs 26.0% [IQR 16.4%-41.0%]; P = 0.4) between the 2 groups. Patients who developed VPD-induced CMP had significantly longer VPD QRS duration (159 ms vs 142 ms; P < .001) and a longer sinus QRS duration (97 ms vs 89 ms; P = .04). A VPD QRS duration of ≥153 ms best predicted development of VPD CMP (82% sensitivity and 75% specificity). Longer VPD QRS duration and a non-outflow tract site of VPD origin were independent risk factors for left ventricular dysfunction after multivariate analysis., Conclusion: VPD QRS duration longer than 153 ms and a non-outflow tract site of origin might be useful predictors of the subsequent development of VPD-induced CMP., (© 2013 Heart Rhythm Society Published by Heart Rhythm Society All rights reserved.)

Implantable cardioverter-defibrillator therapy in the form of high-energy shock (HES) is associated with adverse effects. This study evaluated an alternative therapy to HES, including antitachycardia pacing (ATP) for very fast ventricular tachycardia (VFVT) and low-energy shock (LES) ≤5 J for ventricular tachycardia (VT) of any cycle length (CL). This multicenter study recruited 602 patients with standard indications for an implantable cardioverter-defibrillator. Programming was standardized into 3 zones: (1) ventricular fibrillation (VF) CL of <200 ms treated with HES; (2) VFVT defined within the VF zone (CL, 200 to 250 ms) treated with 2 ATP bursts, LES, and HES; and (3) fast ventricular tachycardia (CL, 251 to 320 ms) and slow VT (CL, >320 ms) treated with 3 ATP bursts, LES, and HES. The primary end point was ATP and LES efficacy and safety. After a mean follow-up of 19 ± 8 months, 2,815 device activations were recorded in 152 patients. Of 67 VFVT episodes, 34 reverted with combined ATP and LES (success rate 50.7%) with first and second ATPs successful in 36% and 13.8%, respectively. LES was used in 39 fast ventricular tachycardia and 60 slow VT episodes with success rates of 53.8% and 73.3%, respectively. Syncope occurred in 19.4%, 16.2%, and 1% of episodes because of VFVT, VF, and VT CL >250 ms, respectively. In conclusion, tiered ATP and LES therapy terminates >50% of VFVT episodes (CL, 200 to 250 ms), which otherwise would fall within the VF zone and be treated exclusively with HES. LES is efficacious and safe in patients with VT CL >250 ms with extremely low syncope rates. Limitation of ATP to a single burst in VFVT is recommended to minimize syncope., (Copyright © 2013 Elsevier Inc. All rights reserved.)