Unipolar voltage mapping criteria for right ventricular septum: Influence of the aortic root

Unipolar voltage mapping through its wider "field of view" can identify substrate deeper to the endocardium on the right ventricular (RV) free wall and left ventricle. The reference value(s) for normal endocardial (ENDO) unipolar voltage (UNI) for the septal aspect of the right ventricle (RV) and the effect of the aortic root that is directly opposed to the posterior septal plane of the RV outflow tract (RVOT) have not been established.

We performed detailed (185 ± 70, range 127-342 points) RV ENDO UNI maps in 9 patients without structural heart disease; 6 had magnetic resonance (MR) imaging; 5 were males; the mean age was 49 ± 11 years. For MR analysis, the location of the aortic root was defined and its effect on unipolar voltage determined. The UNI voltage on posterior RVOT was lower (mean 6.56 ± 2.33 mV, 95% CI 6.08-7.05), compared to the rest of the septal aspect of RV (mean 8.33 ± 2.34 mV, P < 0.001, 95% CI 7.84-8.84). MR analysis confirmed that the lowest voltage region was opposite to MR-defined aortic root. Using a cutoff for UNI abnormality of 6.0 mV for the posterior aspect of the RVOT opposite to the aortic root and 7.5 mV for the rest of the septal aspect of the RV, there was no confluent area of unipolar abnormality in any patient.

We defined normal ENDO UNI cutoffs as 7.5 mV for the septal aspect of the RV with adjustment to 6.0 mV over the posterior RVOT opposite to the aortic root.