Page 43 - Simplicity is Key in CRT

ABSTRACT
Background Left bundle branch block (LBBB) morphology is associated with improved outcome of cardiac resynchronization therapy (CRT) and is an important criterion for patient selection in the current CRT guidelines. There are, however, multiple definitions for LBBB. Moreover, applying these definitions requires careful examination of the ECG and seems subjective. We investigated the intra- and inter-observer variability in the determination of LBBB and the agreement between the various definitions and their correspondence to clinical judgement of the presence of LBBB.
Methods Observers were provided with 12-lead ECGs of 100 randomly selected CRT patients. Four observers judged the ECGs based on different LBBB-definitions (ESC, AHA/ACC/HRS, MADIT, and Strauss). Additionally, four implanting cardiologists scored the same 100 ECGs for the presence of LBBB based on their clinical judgement.
Results The probability of classifying an ECG as LBBB by available definitions varied considerably (range 0.20-0.76). Relative intra-observer agreement (Kappa) with LBBB definitions is moderate (k ranging from 0.47 to 0.74). Intra- observer agreement in clinical judgement of LBBB as well was moderate (k=0.76 (0.14)). Relative inter-observer agreement for LBBB definitions was minimal to weak (k ranging from 0.19 to 0.44). Clinical judgement showed weak relative agreement as well (k=0.35 (0.20)). The agreement between different definitions of LBBB ranged from good (P=0.95 (0.07)) to weak (P=0.40 (0.22)). AHA/ACC/HRS LBBB definition showed the poorest agreement with other definitions. Furthermore, correlation between clinical judgement and the LBBB definitions was poor (0.33- 0.55), with poorest correlation with AHA/ACC/HRS definition.
Conclusion Overall significant variation in the probability of classifying a patient as showing LBBB is present in using different LBBB definitions or clinical judgement. Considerable intra- and inter-observer variability in classification using both LBBB criteria or clinical judgement by experienced implanting physicians, adds to this variation. Inter- definition agreement varies significantly and correlation of clinical judgement and LBBB classification by definitions is modest at best.
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