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Sunday, January 27, 2019

Left bundle branch block -a really big deal part 2

Left bundle branch block (LBBB) is associated with a contraction pattern(s), that are dyssynchronous in regard to the pattern of left venricular (LV) relaxation and contraction.

The first "big deal " I commented on was the observation that the ventricular dyssynchrony associated with LBBB per se can lead to heart failure. See here.

The next big deal is that the pattern of ventricular dyssynchrony typical of "true" LBBB is determinative of a favorable clinical response to CRT and the presence of a LBBB EKG pattern does not necessary indicate a underlying LBBB dyssynchronous pattern.


Risum et al (1) list 3 criteria for the typical contraction pattern of a "true"LBBB
(these apply to description of a longitudinal stain curve in a 4 chamber 2-D strain echocardiogram)

1)early shortening of one or more segment in the ventricular septal wall and early stretching in one or more segments in the lateral wall
2)early septal peak shortening
3)lateral wall peak shortening after aortic valve closure

The early shortening of the septum is recognizable on standard echocardiography and referred to as "septal flash". "Apical rocking" is another echo finding in which there is a rocking motion  of the LV apical  myocardium perpendicular to the long axis. These two findings seem to be the findings on routine echo exams that correspond at least to some degree  (possibly large degree) to the Risum's criteria from strain echocardiography and  perhaps share to some degree the predictive power as regards outcomes of cardiac resynchronization therapy (CRT).

Those patients with a ekg pattern of LBBB and these findings on strain echo are much more likely to have a favorable clinical response to CRT.

Not all patients with a typical LBBB EkG pattern have what Risum refers to as the typical LBBB contraction pattern which is predictive of likelihood of favorable response. to CRT.This seems to hold true in regard to both the standard criteria for LBBB and the newer Strauss criteria .


Quoting Risum : "It seems reasonable to believe that the main mechanism underlying the differential effect from CRT according to QRS morphology is whether a significant activation delay in present in the LV". ( my underlining)

Question: Does the presence of septal flash and apical rocking predict likelihood of success with CRT as good or better than Risum's criteria? Have the two set of criteria been directly compared? While I could find no direct comparison ,Stankovic et al (2) published data that indicated apical rock and septal flash could predict reverse remodeling with a sensitivity of 84 and 79% absence of both was associated with unfavorable long term survival.

Bottom line from Risum's work is that a patient may have EKG criteria for LBBB  (either the standard criteria or the new criteria proposed by Strauss) and not have the mechanical dyssynchrony pattern described by Risum do not respond well to RCT.

So is the evidence strong enough to recommend pre-implantation 2d strain echo and not proceed with Bi-V pacing if the Risum criteria are not met? Is the absence of apical rock and septal flash reason to not proceed with Bi-v (or His Bundle) implantation?



1) Risum , N Identification of typical left bundle branch block contraction by strain echocardiography is additive electrocariography in prediction of long-term outcome after cardiac resynchronization
J Amer Coll of cardiology, 2015, vol 66, no. 631-641

2)Stankovic, I Relationship of visually assessed apical rocking and septal flah and long term survival following cardiac resynchronization therapy (PREDICT-CRT) Eur Heart J Cardiovasc Imaging. 2016,Mar 17 (3)262-9

addendum 1/30/19 reference to the Stankovic paper added
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