Should electrocardiogram criteria for the diagnosis of left bundle-branch block be revised?

In this study, we consider the proposition that the criteria for the electrocardiographic (ECG) diagnosis of left bundle-branch block (LBBB) be revised, a proposition born from analysis of results of cardiac resynchronization therapy trials. The various ECG definitions for LBBB (or lack thereof) used in these trials are reviewed as are the results of the analysis of ECGs from patients with left ventricular conduction disturbances by Grant and Dodge (Am J Med. 1956;20:834-852) and the criteria for the ECG diagnosis of LBBB recommended by the World Health Organization and the International Society and Federation for Cardiology in 1985. These criteria stress that the QRS complex be notched or slurred, that the initial portion of the QRS complex (the "septal Q waves") be absent, and that the QRS duration be at least 120 milliseconds in duration. This is in contrast to the recent suggestion that the QRS complex has a minimum duration of 130 to 140 milliseconds. We conclude that the criteria for the ECG diagnosis of LBBB should be standardized to that recommended by the World Health Organization and International Society and Federation for Cardiology with retention of the minimum duration of 120 milliseconds and that the QRS prolongation should be not be gradual. However, we also conclude that in patients with LBBB being considered for cardiac resynchronization therapy, the duration of the QRS complex should be at least 130 milliseconds.