Cardiac resynchronization therapy (CRT) is a cornerstone therapeutic opportunity for
selected patients with heart failure. For optimal patient selection, no other method
has been proven to be more effective than the 12-lead ECG, and hence ECG characteristics
are extensively researched. The evaluation of particular ECG signs before the implantation
may improve selection and, consequently, clinical outcomes. The definition of a true
left bundle branch block (LBBB) seems to be the best starting point with which to
select patients for CRT. Although there are no universally accepted definitions of
LBBB, using the classical LBBB criteria, some ECG parameters are associated with CRT
response. In patients with non-true LBBB or non-LBBB, further ECG predictors of response
and non-response could be analyzed, such as QRS fractionation, signs of residual left
bundle branch conduction, S-waves in V6, intrinsicoid deflection, or non-invasive
estimates of Q-LV which are described in newer publications. The most important and
recent study results of the topic are summarized and discussed in this current review.
