Right Ventricular Electrogram Characteristics in a T1 Mapping-Validated Normal Population: Implications for Unipolar Voltage Mapping

Abstract

Objectives: The aim of this study was to define normal ventricular electrographic characteristics in T1 mapping-validated normal patients using a contemporary contact force catheter.

Background: Reference values for human endocardial ventricular electrographic characteristics have not been defined using contemporary mapping equipment in patients without heart disease or ventricular arrhythmias.

Methods: Fourteen patients undergoing SVT ablation underwent mapping of the right ventricle and cardiac magnetic resonance imaging with T1 mapping. Electrograms (EGMs) from sites with >10 g of contact force from the right ventricular free wall (RVFW) and right ventricular septum (RVS) were analyzed. Values <5th percentile or >95th percentile were defined as abnormal.

Results: The median age was 27 years, 64% of patients were men, and the mean left ventricular ejection fraction was 60%. Native T1 values (mean 979 ms) of the study population were comparable with that of a normal volunteer population. Ninety-five percent of bipolar EGMs had <6 (RVFW) or <7 (RVS) deflections and duration <37 ms. Ninety-five percent of unipolar EGMs had a maximum dV/dt >0.23 mV/ms (RVFW) or >0.24 mV/ms (RVS). Ninety-five percent of unipolar EGMs had a peak-to-peak voltage >3.8 mV (RVFW) or >4.5 mV (RVS).

Conclusions: In structurally normal hearts, the threshold for abnormal endocardial unipolar voltage in the RVFW (3.8 mV) is lower than that of the current standard (5.5 mV). The unipolar voltage characteristics of the RVS is distinct from that of the RVFW and left ventricle. This has implications for the detection of intramural or epicardial and especially midseptal scar.

Keywords: cardiac MRI; electrograms; substrate mapping; unipolar mapping.