LV Mass Reference Values: Smackdown

I am starting to think I should change the tagline for this blog to:

more questions than answers

I am in the midst of building another smackdown calculator:



I hope that it use is self-explanatory and that it requires no introduction- because I am now out of time (heading out to the ASE meeting!).
This is still a 'work in progress' (I seem to have lots of these). Upon my return from the nation's capitol, I plan to add additional functionality:

• tips on measurement technique
• input validation
• automatically detecting discrepancies between references
• allowing users the opportunity to provide feedback in the cases where there are discrepancies

I think this is going to be very interesting ...

Critical Aortic Stenosis: Echo Calculations

Calculators for Critical Aortic Stenosis: Rhodes Score, Discriminant Score, and CHSS Survival Benefit

In a previous post I presented my first version of the Discriminant Score calculator. Since then, we (sonographers) still get asked to calculate a Rhodes Score (this score has achieved virtual Brand Name recognition at this point) for patients with what appear to be borderline anatomy- even though the Discriminant Score now updates and improves upon the older score. In the process of developing the calculator for the Rhodes Score I was also clued-in to the Congenital Heart Surgeons Society (CHSS) Survival Benefit score. So, I thought I could present calculators based on each of these manuscripts (references included):

• Discriminant Score
• Rhodes Score
• CHSS Survival Benefit Score

A few procedural notes related to the actual calculations are probably worth mentioning:

• Rhodes Score
  • an erratum was published in 1995 (the original article was published in 1991). This is not to be missed, as is corrects the misprinted formula for the area of an ellipse used to calculate the MV (annulus) area, thus the indexed MV area, and thus the overall score
  • I omit the calculation of LV mass as the authors note the technical difficulty of the measurement (particularly, I might add, in patients where the LV is misshaped)
• CHSS Survival Benefit Score
  • this is not the CHSS's current survival benefit calculator (I still can't figure that one out); they prefer you not play "what if..." with theirs  :)
  • necessary calculations of the z-scores use the only published data available at the the time: the Wessex z-score data (discussed previously here)
  • swapping the aortic root z-score equations for the competition (i.e., the Boston data) can have a pronounced effect (try it yourself)

It is this last point that I find both fascinating and more than a little disturbing: the CHSS survival benefit score, the way it is published- referring to the Wessex z-score data- appears to have a built in bias against biventricular repair. That is to say, in my experience (see for yourself) the Wessex data has a small standard deviation, and thus, less tolerance for deviations from the mean, and calls "abnormal" too soon. Way, way too soon. So, if the choice to go down the single ventricle pathway is (somewhat) dependent upon the relative size of the measured structures, and the relative size is gauged by the z-score, and the z-scores are biased...

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If the choice of z-score equations perches neonates on the balance of biventricular vs. univentricular repair, we should probably be thinking pretty hard about how and where we want to derive our reference values.

A consensus *cough* Z-Score Writing Project *cough* can't come soon enough.

Pediatric Echo Z-Score Graphs

I have been working on different visualizations of the data we see and use every day in the pediatric echo lab.

Consider the following hypothetical patient data:

	t0	t1	t2	t3
Height(cm):	55	58	65	75
Weight(kg):	3.5	3.9	4.5	7
LMCA (mm):	2.9	2.95	3.2	3.5

A simple graph of these individual measurements over time- particularly for pediatric patients- is potentially a bit misleading:

While the graph clearly conveys the information that the coronary artery size changes over time, unless you also happen to know what the normal values are for each point in time, there is no way to know if the change in size is pathologic, or simply due to somatic growth.

This is the entire reason we use z-scores.

So, maybe more to the point- at least for the purpose of trending- would be to graph the z-scores over time:

(This simple LMCA graphing routine can be found here.)

However, neither graph is entirely satisfactory for me.
I want to see both the absolute values and their relationship to normal values… more like this:

Using the coronary artery z-score data published from Boston and the enormously cool JavaScript plotting library, flot,  I built a few more z-score graphing routines:

• left main coronary artery charting utility 
• LAD coronary artery charting utility 
• right coronary artery charting utility

They're not perfect (I'd like the z-score to show as a 'tooltip' when hovering over individual data points, and the axes need labels...), but they are a lot more fun. If they seem useful, I may release more of them into the wild.

I'd love to know what anyone else thinks about graphing their pediatric echo data.

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(special thanks to the authors of "Normal values for aortic diameters in children and adolescents – assessment in vivo by contrast-enhanced CMR-angiography" for the inspiration)

3D Lament (a haiku)

"...now give back the green" 
billing is not collecting
elevation plane

Digital Imaging Protocols for Pediatric Echo

"Because."

This was the explanation I was given, very early in my introduction to "digital echo", about why we record These Views in This Order. At the time, I was coming from a lab that did things proper: starting with the subcostal views. The only sense this new "parasternal images 1st" protocol made was that it supposedly made reading the studies easier.
How convenient.

For you.

Who is this protocol for anyhow?

I insist that the marriage of the image acquisition protocol with the ordered reviewing of said images is a potential liability. Always starting with the parasternal view is fine for most hearts— most hearts are nearly normal. The problem, in my opinion, with starting with the parasternal view is: it presumes that things are normal, or are nearly normal, or that I can at least make something up to look passably normal.

If things are not normal (this is what we're supposed to be particularly good with in Peds, isn't it?) this type of protocol presumes too much: that I already know enough about the heart to make some sense of the parasternal views. Try this on: what is the PLAX view for a patient with dextrocardia, DORV, and pulmonary atresia supposed to look like? How about HLHS? In order to record meaningful parasternal long axis views of these types of abnormal hearts, the sonographer has to either:

• immediately recognize the pathology from this one clip
• spend time scanning from subcostals and apicals first (in order to sort it out) then return to the "starting point"- the parasternal views.

The first option is not a fair predicament for most sonographers (including physicians), and the second- grossly inefficient.

The Images are for Physicians

Certainly, I appreciate that in order to report the anatomy, arrangement, size, and function of the examined heart some considerable structure is required. There must be images that support and document our conclusions. And, as we are increasingly moving towards structured reporting, the structure of the underlying, supporting images must also evolve. I have no problem with this, in fact, I embrace it. It's the "absence of evidence is not evidence of absence" philosophy, taken to it's logical conclusion. We don't want anyone to report anything that our images can't substantiate. The fact that physicians will determine and require a certain, precise collection of images is undisputed. They may choose and prefer to review them in any particular order. Bully for them.
Our obligation is to provide these images.

I simply prefer to do it in a manner that is most efficient for me.

The Protocol is for Sonographers

What is really needed to improve our exam consistency is a system that allows for the flexible acquisition of any prescribed (minimum) set of images. On a small scale, we are already doing this with stress echo, particularly with exercise stress echo: you grab what you can, when you can, and sort it out later. The order of collection is irrelevant, but the presentation of the images, in order, is everything. I can't tell you how many fetal echos I have done that would have been greatly improved by the ability to collect the images as I saw them, and then sort them into a logical arrangement later. Not to mention every "new blue" dextrocardia-aortic-atresia-single-ventricle-goat-wreck (Goat Rodeo + Train Wreck, contracted form), I have done since the inception of the current "parasternals 1st" protocol.

I am eager to see what the new Philips iE33's SmartExams are all about.

• Philips' SmartExams announcement
• SmartExams introduced to cardiology by way of new iE33
• Philips appearing to work harder on this front than anyone else

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Lately, I have been tinkering about with a collection of image acquisition protocols suitable for pediatric echo.
In addition to providing a basis for building our own structured, protocol-driven exams, I believe these could also turn into a fairly useful teaching tool (I still need more descriptions/images though).