Tuesday, July 29, 2014

LBBB on Cardiac Ultrasound: do not be fooled into diagnosing a wall motion abnormality!

The last case on the blog of LBBB with very high voltage was actually first identified as LBBB by ED bedside echo, which was done PRIOR to the ECG.

The images were captured on one of our new ultrasound machines, with Speckle Tracking, which uses software to outline the movement of the myocardium, making it easier to see the wall motion.


The sonographers acquiring the image stated "there is a wall motion abnormality."


Question:

Is there a wall motion abnormality?  Better question: the wall motion is abnormal, but why?

Here is the Apical view:


apical from HQMedEd on Vimeo.

Here is a still picture with annotation:
White oval: Right Ventricle.  Blue Arrow is Septum.  Yellow Arrow is LV free wall.
The graph on the right show that different walls (see color coding of graph lines which correspond to the line colors of the speckle tracking on the image) have movement at different times, with the LV free wall (light blue) both contracting (positive deflection) and relaxing (negative deflection) later than the septum (lavender color)

Answer:  the wall motion is abnormal because of an abnormal sequence of activation: the RV and septum move before the LV free wall.

I was looking at this image when the MDs doing the exam claimed there was a wall motion abnormality.  I could see that this was due to an abnormal sequence of activation.


My response was: "The ECG will show Left Bundle Branch Block."


LBBB activates the septum and RV first, through the intact right bundle.  Next, the impulse travels through myocardium (not through the high speed purkinje system) to activate the rest of the LV, including the LV free wall.


Here is the Parasternal Short Axis View:


short from HQMedEd on Vimeo.

As on the previous video, the septum (left side of outlined LV is activated before the LV free wall.

Here is the ECG:


Comment:

Diagnosing a wall motion abnormality on bedside echo is very difficult and requires a high degree of expertise, and even then is difficult without having contrast material such as Definity (R).


False negatives are very common.


But there are also false positives: a common false positive is due to bundle branch block.  BBB causes an abnormality in the sequence of activation and thus causes wall motion to appear abnormal.  However, the wall motion is not abnormal because of decreased motion; it is abnormal only because it is activating in an abnormal sequence compared to the remainder of the heart.


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