Current research on the relevance of electrocardiography in cardiac resynchronization therapy

Even among those with true left bundle branch block (LBBB), about a third do not have a favourable response to cardiac resynchronization therapy (CRT). Thus all LBBB are not created equal and the pattern may be due to factors beyond delayed electrical activation (hypertrophy, dilatation, scar, isolated fascicular block). While a more strict definition of LBBB has been recently proposed [1], others have not found it correlatingwith electrical delay in the lateral wall. Risum et al. [2], investigated in a prospective observation study whether combining ECG criteria of LBBB with classical findings of electrical delay in lateral wall on 2D speckle tracking strain echocardiography (LBBB contraction pattern) improved the prediction of outcomes after CRT implantation. Only 30% of thosewith LBBB andQRSd between 120 and 150mshad typical LBBB contraction pattern, while 65% had this pattern above QRSd of 150ms. LBBB contraction patternwas an independent marker for future events, and had predictive power incremental to QRS duration and underlying cause of cardiomyopathy. Analysis in relation to strict LBBB criteria and conventional echocardiographic indices of dyssynchrony did not yield any further benefit. Thus it appears that investigating LBBB contraction pattern in those with QRSd 120-150 might help in choosing those whomight not benefit fromCRT. However the parameters used are semi-objective and might