Pathological S-wave in lead I in left bundle branch block is associated with MRI scar and reduced left ventricular function

The 2009 electrocardiographic Selvester QRS score for LBBB (2009 LBSS) is prognostic in CRT-patients. Previous studies show limited diagnostic performance in detecting and quantifying left ventricular (LV) scar determined by cardiovascular magnetic resonance imaging (CMR). We aimed to develop an improved method for ECG detection of scar using a large and broadly selected dataset of patients with LBBB. We retrospectively identified LBBB patients (n=325) with available ECG and late gadolinium enhancement (LGE) CMR exams from four centers (142 [44%] with>0% CMR scar). ECG metrics were measured digitally and semi-automatically, and were compared to CMR-determined scar presence and extent. The 2009 LBSS did not accurately detect or quantify CMR scar (R2=0.04, Area under the Receiver operating characteristic curve [AUC]: 0.60, [95% confidence interval: 0.54–0.66]). Multivariable stepwise logistic regression applied in 44 pre-determined ECG variables resulted in an improved 6-variable ECG model to detect CMR-scar (AUC 0.72 [0.66–0.77]). Furthermore, a single ECG variable (Lead I R/S amplitude ratio) was predictive of both scar presence (AUC 0.71 [0.65–0.77]) and of LV ejection fraction