Clinically indicated 12-lead ECGs prior to ICD implantation were acquired using a GE-Marquette system. ECG median beats were analyzed by two investigators using calipers and 2× magnification. At the time of analysis, investigators were blinded to all patient data (including cardiomyopathy etiology, CMR imaging results and electrophysiologic evaluation) except age, gender and race. ECGs were first analyzed for the presence of conduction defects and hypertrophy, according to the following pre-specified definitions:23 , 24
Left inferior (posterior) fascicular block (LPFB) does not affect the scoring system and if signs of right ventricular hypertrophy (RVH) are present then certain points in V1 and V2 cannot be counted (see Appendix).23 , 24 See the recent review for detailed explanations of the minor differences between these and the World Health Organization criteria.23
QRS-score criteria were then applied for the specific underlying conduction type present (see Appendix for complete scores and instructions). There are 32 possible total points and each point represents 3% of the LV mass. QRS scores for RBBB, LAFB, LAFB+RBBB and LVH have relatively minor differences from the no confounder QRS-score, however the LBBB score is fundamentally different because the electrical activation wavefront has to proceed through the ventricular septum before activating the LV (Figure 1 ).
For localization of scar by QRS-scoring, because the ECG is registered anatomically relative to the thorax, the LV walls, papillary muscles and fascicles are labeled accordingly (see Appendix). We subdivided the ECG scar locations into anteroseptal and/or anterior-superior versus inferior and/or posterolateral for comparison with the CMR-LGE locations.
By a trained observer, the QRS-scores take less than 5 minutes to complete per patient.
Left inferior (posterior) fascicular block (LPFB) does not affect the scoring system and if signs of right ventricular hypertrophy (RVH) are present then certain points in V1 and V2 cannot be counted (see Appendix).23 , 24 See the recent review for detailed explanations of the minor differences between these and the World Health Organization criteria.23
QRS-score criteria were then applied for the specific underlying conduction type present (see Appendix for complete scores and instructions). There are 32 possible total points and each point represents 3% of the LV mass. QRS scores for RBBB, LAFB, LAFB+RBBB and LVH have relatively minor differences from the no confounder QRS-score, however the LBBB score is fundamentally different because the electrical activation wavefront has to proceed through the ventricular septum before activating the LV (
For localization of scar by QRS-scoring, because the ECG is registered anatomically relative to the thorax, the LV walls, papillary muscles and fascicles are labeled accordingly (see Appendix). We subdivided the ECG scar locations into anteroseptal and/or anterior-superior versus inferior and/or posterolateral for comparison with the CMR-LGE locations.
By a trained observer, the QRS-scores take less than 5 minutes to complete per patient.
