Evaluation of R-wave offset in the left chest leads for estimating the left ventricular activation delay: An evaluation based on coronary sinus electrograms and the 12-lead electrocardiogram

Abstract

Background: The QRS duration does not always reflect the left ventricular (LV) activation delay in patients with ventricular conduction disturbances. The R-wave offset in left chest leads may more closely reflect the LV activation delay than the QRS offset.

Methods: We evaluated 138 cases with left bundle branch block (LBBB, n=11), right BBB (RBBB, n=38), non-specific intraventricular conduction disturbance (n=11), narrow QRS (<120ms, n=56) and right ventricular pacing (n=22). Cases with right axis deviation (120 to 270 degrees) were excluded. The intervals from the QRS onset to the V-waves in coronary sinus bipolar electrograms (QCS) were measured, and the longest interval was defined as the QCSmax. In the 12-lead electrocardiogram, the interval from the QRS onset to the R-wave offset (QR) was measured and then averaged in leads I-aVL, II-III-aVF, V1-V2, V3-V4 and V5-V6.

Results: Significant correlations (p<0.05) were found between QCSmax and QR in I-aVL (r=0.83), II-III-aVF (r=0.51) and V5-V6 (r=0.86) in cases with a normal axis (0 to 90 degrees, n=64); and I-aVL (r=0.90), II-III-aVF (r=0.31) and V5-V6 (r=0.69) in cases with left axis deviation (-45 to -89 degrees, n=52). Overall, the QRS duration was also correlated with QCSmax (r=0.72, p<0.001); however, this correlation was weaker than the correlation between QCSmax and QR in I-aVL (r=0.89, p<0.001) due to disparities in RBBB (p<0.001).

Conclusions: The interval from the QRS onset to R-wave offset in the left chest leads reflects the degree of LV activation delay regardless of differences in QRS duration and morphology.

Keywords: 12-Lead ECG; Bundle branch block; Conduction disturbance; QRS duration.