QRS 3D voltage-time integral in narrow QRS complex - Establishing the normal reference range.

Background: Vectorcardiographic 3D QRS voltage-time integral (VTI) is a novel marker of ventricular dyssynchrony pertinent for cardiac resynchronization therapy. It may have additional clinical utility but its normal reference ranges have not been established. We sought to define reference ranges for VTI in healthy individuals.

Methods: We retrospectively analyzed 12‑lead ECGs of healthy adults (2010-2014) and compared them to patients with cardiomyopathy with reduced ejection fraction (EF) <50 %. Using the Kors matrix, 12‑lead ECGs with QRS duration ≤120 ms were converted to vectorcardiographic X, Y, and Z leads. VTI was calculated as the instantaneous root-mean-square (3D) voltage integrated over the QRS duration. Reference range limits were defined as the 2.5th to 97.5th percentiles respectively for healthy females and males in age groups 18-34, 35-54 and ≥ 55 years.

Results: The study included 468 healthy adults (age 44.6 ± 17.0 years; 63.9 % female) and 314 patients with cardiomyopathy (age 62.1 ± 14.0 years; 34.4 % female). VTI was significantly larger in the cardiomyopathy patients compared to the healthy population (48.2 ± 21.4 vs. 38.1 ± 9.3 μVs, p < 0.0001). Increased age and female sex were significant predictors of lower VTI in the healthy population (both p < 0.0001). VTI reference ranges for respective age groups for healthy females were 23.2-55.0, 23.9-56.4 and 19.6-50.9 μVs, and for healthy males were 29.9-57.2, 28.2-56.7 and 21.4-55.9 μVs.

Conclusion: VTI is higher in younger individuals and males within healthy adult population but is overall higher in patients with cardiomyopathy with reduced EF. Age and sex need to be accounted for using VTI as a marker for cardiac disease.