Periaortic Ventricular Tachycardias in Nonischemic Cardiomyopathy: Substrate and Electrocardiographic Correlations.

Background: Periaortic fibrotic ventricular tachycardia (VT) substrate is common in nonischemic cardiomyopathy (NICM), often intramural, and difficult to ablate. We sought to better characterize normal and abnormal periaortic voltage map parameters and NICM periaortic VTs.

Methods: In 15 patients without heart disease, the 5th percentile of endocardial voltage for increasing distance from the aortic valve ring was determined. In 53 consecutive patients with NICM (64±11 years; left ventricular ejection fraction 31±10%) undergoing ablation of recurrent VT, periaortic electrogram voltage and VT characteristics were analyzed.

Results: In healthy patients, the fifth percentile of the bipolar voltage increased proportional to the distance from the aortic valve ring, from 1.0 mV at 1 cm to 1.5 mV at 1.5 cm; the corresponding unipolar voltage cutoffs were 5.0 and 7.5 mV. A total of 160 VTs were induced in 53 patients with NICM, of which 28 VTs in 20 patients had periaortic origins. Periaortic VTs were associated with similar periaortic bipolar voltage, but lower UVs consistent with intramural fibrosis as an important substrate. Periaortic VTs could be divided into left and right bundle branch block forms with mapping showing right septal and lateral exits. Left bundle branch block VTs were more often acutely abolished with ablation (100% versus 69%; =0.034), but with a 23% incidence of heart block. Greater extent of low voltage was associated with more induced VTs and worse acute outcome.

Conclusions: Adjusting voltage parameters based on distance from the aortic valve may improve definition of left ventricular outflow tract arrhythmia substrate. Periaortic VTs are common in NICM, often associated with intramural substrate and can be divided into left bundle branch block and right bundle branch block types associated with different ablation outcomes and risks.