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

• QRS waveforms in patients with non-left bundle branch block (non-LBBB) are variable. It may be useful if the degree of left ventricular (LV) activation delay can be estimated from the 12-lead electrocardiogram (ECG).
• The intervals from the QRS onset to the V-waves in coronary sinus electrograms (QCS) was measured, and QCSmax was defined as the longest QCS interval found. In the 12-lead ECG, the interval from the QRS onset to R-wave offset (QR) was measured.
• QR in left chest leads (especially in leads I and aVL) was closely associated with the QCSmax regardless of differences in QRS duration and morphology.
• QRS duration was correlated with QCSmax, but the correlation was weak due to disparities in right BBB patients.

BackgroundThe 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.MethodsWe 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 (< 120 ms, 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.ResultsSignificant 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).ConclusionsThe 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.