Saturday, December 15, 2007

Ebstein's Anomaly: Measuring the Spectrum

Ebstein's anomaly is a malformation of the tricuspid valve and right ventricle. The classic description is something along the lines of: a tethered and displaced septal (and posterior) leaflet, a "sail-like" anterior leaflet, and a variable "atrialized" portion of the right ventricle. Echocardiographically, it is important to understand the measurable parameters that help describe the spectrum of disease, and thus help guide the management.

At one end of the spectrum is a tricuspid valve that is apically displaced just slightly more than normal:

Tricuspid Valve Offset Calculator:

At the other end of the spectrum are the critically ill neonates whose biventricular circulation— and very survival— are not certain:

Great Ormond Street Ebstein Index Calculator:

Ultimately, it is the actual leaflet and right ventricle morphology which dictates just how much and what kind of repair can be attempted, and 3D echo seems best suited to describing these.

Source: Ebstein's Anomaly
Attenhofer Jost et al. Circulation.2007; 115: 277-285

Saturday, December 8, 2007

Fetal Echo Z-Scores: the SGA conundrum

actual size! The fetal echo z-score calculator was initially a proof-of-concept project (as were all of the calculators at It has since proven itself to be quite useful, and I refer to it for nearly all fetal echos now.

However, a shortcoming of the current calculator is highlighted by this common referral:

  • SGA (Small for Gestational Age)
  • RV > LV
  • LV measures lower limits of normal for EGA

The real difficulty here of course, is the SGA baby. Based purely on dates, the baby is known to be small- and all measures of her cardiac structures are sure to be small as well.

But can't her heart still be relatively normal

In the article Development of Z-scores for fetal cardiac dimensions from echocardiography, regressions are presented based on three independent variables: femur length, biparietal diameter, and EGA. According to the authors, "femur length gave the better correlation coefficient with fetal cardiac dimensions" though admittedly, all the independent variable gave good correlations. And a good discussion is made over EGA as a surrogate for fetal size, the importance of considering fetal size, fetal growth and fetal size, fetal size, fetal size, ...

So why don't I build the calculator based on the femur length- ergo the fetal size?

Because: I have now become an advocate of measuring the fetus:

  • measuring the BPD
  • measuring the head circumference
  • measuring the abdominal circumference
  • measuring the femur length

Now, I measure the fetal size and, taking advantage of the OB calculation package on the ultrasound machine, use the size-determined EGA- rather than the date-determined EGA.


The new and improved fetal echo worksheet allows you to edit the EGA and automatically update all of the z-scores based on your measurements. And, just for fun, makes estimations of the EDC and LMP.


Users of the Pediatric Cardiac Valve Z-Score calculator might be interested to know about an erratum to the reference article:

The tricuspid valve nomograms have been re-published.

In the process of refining the calculator on, it was noted that tricuspid valve z-scores calculated by the supplied formula differed considerably from the result when using the nomogram. I contacted the lead author, he contacted their statistician, and it was discovered that the original nomograms were in error.

Fortunately, the error involved only the nomograms themselves- the formulae are (still) correct and thus, none of our calculations were affected.

Sunday, August 12, 2007

Relatively Normal: pediatric echo z-scores

Big people have big hearts. Little people have little hearts- and mitral valves, aortas, and pulmonary arteries. As a student sonographer, one of the few things I excelled at was committing things to memory. I was all about flashcards. I had flashcards for everything, but particularly for normal dimensions. Normal left atrium? 19-40mm. Normal IVS? 6-11. LV? 37-56. In the adult echo arena this knowledge served me well as part of a routine:
  • Perform study
  • Obtain standardized measurements
  • Compare measurements to established criteria
Executing these simple steps allowed me to declare some exams within normal limits and others, unequivocally abnormal. I basked in the power and the glory. But pediatric echo brings a whole new set of flashcards. There are all the same adult values, and then again several times over: for kids with BSA up to 0.5 m2, 0.5 to 1.0 m2, 1-1.5, and the babies, and preemies, and what about the transverse arch... Yikes. Too many flashcards.
The problem of relating normal values over a wide variety of body sizes is at least as old as pediatric cardiology itself. Knowing if a newborn's tricuspid valve is too small or a two year-old's coronary artery is too big, is essential to the modern practice of pediatric echo.Enter the nomogram: Found in the backs of textbooks and throughout the literature, nomograms soon became the staple that replaced my flashcards. Now, all I needed was a copy machine and notebook. Nomograms aren't perfect, however. If the nomogram is printed too small (as I have deviously done with the above sample) it is quite difficult to resolve small differences between our measurement and the printed reference- and almost all of them require some interpolation on our part. Still, for the most part, the power and the glory had returned. Soon however, the absurdity of sitting in front of a computer/echo reading station, while interpolating hash-marks in a notebook caught up with me. This is the Age of Information? Besides- what if an unscrupulous cardiology fellow absconded with our Precious Notebook of Nomograms? What if?
Underlying each nomogram is the theory that a predictable relationship exists between the independent measure (age, weight, BSA, etc.) and a dependent variable (coronary artery diameter, annulus dimension, etc.). Further underlying each of these relationships, is the assumption that these variables have a normal distribution in our population.When we perform an echocardiogram and measure, for instance, the left coronary artery, and then ask "is it normal?"-- what we are really asking is: "how does our measurement compare to the mean of the population of other (normal) humans of this size?" The answer is best given with one number: the z-score. The z-score tells us in one simple, elegant number how our measure relates to the population.
  • Exactly normal: z = 0
  • pretty much normal: ± 1
  • too small: -3
  • gigantic: +7
Provided the authors of all these nomograms have actually published the predictions equations themselves (and not just the nomograms), we can now extract the information, leverage it to construct the predicted mean and standard deviation for our measure, and report a z-score. No more flashcards. No more notebooks. Power. Glory.

Saturday, July 21, 2007

Coronary Artery Z-Score Calculator

Coronary Artery Involvement in Children With Kawasaki Disease, just published in this month's Circulation, contains a Z-Score gem: updated prediction equations for coronary arteries. These new prediction equations provide one major advantage over the equations of de Zorzi et al.: they account for the tendency towards non-constant variance, i.e. heteroscedasticity. It is interesting to note that, based on prior work in 2005, one might have expected the prediction equations to be linear regressions based upon the square root of body surface area (BSA raised to the 0.5 power). Instead, the prediction equations are nonlinear and relate to the BSA raised to the 0.3xxx power...
Perhaps the coronary artery system is different enough in structure and function that it does not obey the same rules for parent/daughter vessels in the remainder of the arterial tree. On a more practical note, the authors excluded the left main coronary artery from their analysis, noting:

normal anatomic variations make its interpretation less reliable

The normal variation of the coronary arteries includes such arrangements as left-dominant and right-dominant systems, long and short main coronary artery segments, and even separate origins of the circumflex and anterior descending coronary arteries, to the exclusion of the left main altogether. I doubt that this point gives us a hall pass to abandon measuring the left main coronary artery in our Kawasaki patients, but it is certainly an important observation.

Check out the new and improved Kawasaki Disease Coronary Artery Z-Score calculator here:

Friday, July 13, 2007

How To Image Patients With Dextrocardia

Based upon: ASE Sonographer Core Curriculum Understanding the cardinal directions that are expected in each of the imaging planes will greatly simplify the sonographer's work when evaluating patients with complex congenital heart disease- particularly those patients with dextrocardia. Dextrocardia: heart is positioned in the right chest, apex pointing rightward (as opposed to Dextroposition: heart is positioned in the right chest, apex pointing leftward {or toward midline})

Parasternal Long Axis:

  • "base" on the right side of screen
  • apex of heart on left side of screen
  • image is then an anterior-posterior section along the cardiac long axis- regardless of cardiac position
  • if patient has dextrocardia, image should be labeled "DEXTRO" or "RSB" (for Right Sternal Border)
Parasternal Short Axis:
  • 90 degrees CLOCKWISE from long axis
  • patient left is on right side of screen
Apical 4-Chamber:
  • patient left is on right side of screen
Subcostal Transverse:
  • patient left is on right side of screen
Subcostal Short Axis:
  • 90 degrees CLOCKWISE from transverse
Suprasternal Notch Short Axis:
  • patient left is on right side of screen
Suprasternal Notch Long Axis:
  • ascending aorta on left side of screen, descending aorta on right (regardless of laterality)
When confronted with a patient with known (or suspected) cardiac malposition, begin scanning from the subcostal transverse imaging plane. The transducer index mark and image (screen) index mark should both be oriented to the patient's LEFT:
  • subcostal transverse: define absolute and relative positions of AO, IVC, and spine
  • sweep (tilt) up to demonstrate the position of the heart in the chest and the direction the apex is pointing
  • sweep (continue tilting) anterior to determine the AV and VA connections and positions of the great vessels
Allow yourself a few minutes at the outset of the exam to determine the cardiac position, situs, AV/VA connections- before recording an echo "officially". It is far easier to record an echo, adhering to the imaging protocol, when you already know what to expect (because you spent the time to figure it out). Lastly, it is worth mentioning that positioning- of both the patient and the sonographer- can impact the performance of the exam. Patients with dextrocardia should be optimally positioned in the right lateral decubitus position, and the sonographer should be positioned such that scanning can be comfortably performed with the patient in that position.

Friday, June 1, 2007


Who am I? My name is Dan Dyar.

Natural Habitat? San Diego, CA.

What makes me qualified to make anything other than passing remarks about pediatric echocardiography? I am RDCS certified in AE/PE/FE; over 15 years experience "scanning".

A 'Fortuitous Concatenation of Shadows'- What is that about? I first heard this from one of my mentors, who picked it up from Baylor. Since then, innumerous others of their progeny have confirmed that the phrase was coined there- as a somewhat pejorative remark about the ambiguity of interpreting ultrasound images.