Wednesday, December 31, 2008

2D Area-Length LV Mass Calculator

I much prefer the 'ellipse tool' to the default method of tracing borders with the trackball. Plus, it is quick, pretty, and is more consistent with the principle behind the calculation.



  • Measure at end diastole (End diastole can be defined at the onset of the QRS, but is preferably defined as the frame after mitral valve closure or the frame in the cardiac cycle in which the cardiac dimension is largest.)
  • Measure areas at the midventricular short axis view, at the level of the papillary muscle tips- generally the widest short axis diameter.
  • Measure the LV length from apex to plane of MV annulus, in A4C or A2C (largest) It is recommended that the basal border of the LV cavity area be delineated by a straight line connecting the mitral valve insertions.
  • Z-Scores are 'off label' (source article used M-Mode derived LV mass)

Recommendations for Chamber Quantification, JASE, December 2005
Recommendations for Quantification of the Left Ventricle by Two-Dimensional Echocardiography, JASE, 1989
A novel method of expressing left ventricular mass relative to body size in children.
Foster BJ, Mackie AS, Mitsnefes M, Ali H, Mamber S, Colan SD.
Circulation. 2008 May 27;117(21):2769-75.

Sunday, December 14, 2008

New Coronary Artery Z-Score Calculator

The folks over at Children's National Medical Center, Washington, D.C. (CNMC) have fired up their digital echo database: in a four month period, they sorted through over 400 eligible normal echos, and served up the largest analysis of normal coronary artery dimensions to date.

Their approach to the data analysis included explorations of the independent variables of BSA and height (and height, raised to the 2.7 power). Analysis of the varying independent measures and relationships demonstrated that the "best fit" model was the exponential model using BSA, or what is also known as the allometric model. Landing on this manner of analysis is not just fortuitous happenstance- numerous other investigations have come to the same conclusion regarding the scaling of cardiovascular structures. It is interesting to note that other recently published z-score data landed on a unique and quite different model (nonlinear polynomial fit).

Considering their allometric model, the scaling exponents of each of the coronary arteries calculated in this analysis are quite similar, but are not identical. Also, the scaling exponents are all very near 0.4-- not 0.5 as might be predicted by the theory of dimensional consistency (linear measurement of the coronary artery scaled to body surface area, i.e., cm vs. cm2). Actually, this comes as no surprise, given that the true nature of the relationship is (probably) a complex cascade between lean body mass, cardiac output, wall tension, and LV mass. Imperfect estimations of BSA are only peripherally related to some of these factors. It makes me wonder what the relationship would look like if we scaled/standardized the coronary artery diameters to LV mass instead of BSA.

Comparing this data to prior work, the authors note a very close correlation with the data from Boston, and they very politely admit some similarities to the data from Singapore (although, to be fair to the Singapore analysis it should be noted that they sought to make an internally standardized reference- indexing to the aorta- and thus their treatment of the relationship to BSA is not very robust). The authors have already done their own "smackdown" and their graphic comparison of the CNMC and Boston data is unsurprising. Moreover, the models and scaling exponents are remarkably similar. Here are the two LMCA prediction equations:






* note: the CNMC equation is the alternate/equivalent form of their published equation: ln(M) = beta1 + beta2 x  ln(BSA)

If we discount the Boston y-intercept of -0.02887, as being so small as to be very nearly zero ( or, "not significantly different from zero"), the equations become all the more similar. We are then left with the primary difference between the z-score predictions being: the manner in which they deal with variance. The Boston group attempts to predict the standard deviation by a second regression equation, and the CNMC group takes the approach, now currently in vogue, of substituting the regression RMSE as the SD. The validity of either approach could(should?) probably be debated…

In the words of the authors:

Having a readily available Z-score calculator will be invaluable

Give it a go at

I admit to taking a few liberties with this calculator: I convert the measurements to mm; I use the Haycock BSA formula rather than DuBois & DuBois (can't we just agree to do this already?); I use the 5th and 95th percentiles (± 1.65 SD's) for the limits on the range of normal values.

Coronary Artery Z Score Regression Equations and Calculators Derived From a Large Heterogeneous Population of Children Undergoing Echocardiography.
Laura Olivieri, Bob Arling, Mark Friberg, Craig Sable. Journal of the American Society of Echocardiography December 2008 (Article in Press DOI: 10.1016/j.echo.2008.11.003)
Theoretical and empirical derivation of cardiovascular allometric relationships in children.
Sluysmans T, Colan SD. J Appl Physiol. 2005 Aug;99(2):445-57. Epub 2004 Nov 19.
Allometric analysis of the association between cardiac dimensions and body size variables in 464 junior athletes.
George K, Sharma S, Batterham A, Whyte G, McKenna W. Clin Sci (Lond). 2001 Jan;100(1):47-54.
Derivation of a size-independent variable for scaling of cardiac dimensions in a normal adult population.
Neilan TG, Pradhan AD, Weyman AE. J Am Soc Echocardiogr. 2008 Jul;21(7):779-85. Epub 2008 Mar 10.
Does size matter? Clinical applications of scaling cardiac size and function for body size.
Dewey FE, Rosenthal D, Murphy DJ Jr, Froelicher VF, Ashley EA. Circulation. 2008 Apr 29;117(17):2279-87. Review.
Regression Equations for Calculation of Z Scores of Cardiac Structures in a Large Cohort of Healthy Infants, Children, and Adolescents: An Echocardiographic Study.
Pettersen MD, Du W, Skeens ME, Humes RA. J Am Soc Echocardiogr. 2008 Aug;21(8):922-34. Epub 2008 Apr 11.
A Novel Method of Expressing Left Ventricular Mass Relative to Body Size in Children.
Foster BJ, Mackie AS, Mitsnefes M, Ali H, Mamber S, Colan SD. Circulation. 2008 May 27;117(21):2769-75. Epub 2008 May 19.
Coronary artery involvement in children with Kawasaki disease: risk factors from analysis of serial normalized measurements.
McCrindle BW, Li JS, Minich LL, Colan SD, Atz AM, Takahashi M, Vetter VL, Gersony WM, Mitchell PD, Newburger JW; Pediatric Heart Network Investigators.
Circulation. 2007 Jul 10;116(2):174-9. Epub 2007 Jun 18.
Coronary normograms and the coronary-aorta index: objective determinants of coronary artery dilatation.
Tan TH, Wong KY, Cheng TK, Heng JT. Pediatr Cardiol. 2003 Jul-Aug;24(4):328-35. Epub 2002 Sep 25.

Sunday, December 7, 2008

Ascending Aorta Z-Score Calculator

A z-score calculator for the ascending aorta (AAO), based on this article, is now available at ParameterZ.

The source article is relatively recent (2006) and confirms my own experience: z-score data for the ascending aorta are hard to find.

We provide for the first time a published regression equation for calculation based on BSA of the expected size of the ascending aorta in children, which allows calculation of z scores.

Their data is based on a sample of 88 normal patients- the sample size was chosen to match their group of patients with bicuspid aortic valve. Technically speaking, this sample size is too small to be used to construct reference values. The demographic data describing the reference population is not provided.

The manner of z-score prediction was modeled after Daubeney et al., for "consistency with the prediction equations... used for other structures in our echocardiographic laboratory". Personally, I think that the "transform both sides" technique (regressing the log of both the BSA and the AAO measurements) is perfectly reasonable for modeling this relationship. However, I continue to have misgivings about the patent substitution of the regression root mean square error for the sample standard deviation- particularly for the purpose of calculating a z-score.

In the absence of any other AAO z-score equations, I used the following two manners to cross-check the Halifax data:

  1. The "internally standardized" approach of Sheil et al., using the observed consistent ratio between the size of the AAO and the aortic annulus: 1.16. I used the Boston aortic valve z-score data in combination with their ratiometric approach- I call these the Derived AAO values.
  2. Data from UCLA was used to generate z-scores for an exploration of dilated aortic root in children with bicuspid aortic valves. Their published data provide us with a formula for predicting a height-based mean value for the AAO.
MethodAOV MeanAAO MeanRangeAAO/AOV
Halifax :
Derived :

Dilatation of the ascending aorta in paediatric patients with bicuspid aortic valve: frequency, rate of progression and risk factors.
Warren AE, Boyd ML, O'Connell C, Dodds L. Heart. 2006 Oct;92(10):1496-500. Epub 2006Mar 17.
Echocardiographic assessment of aortic root dimensions in normal children based on measurement of a new ratio of aortic size independent of growth.
Sheil ML, Jenkins O, Sholler GF. Am J Cardiol. 1995 Apr 1;75(10):711-5.
Validation and re-evaluation of a discriminant model predicting anatomic suitability for biventricular repair in neonates with aortic stenosis.
Colan SD, McElhinney DB, Crawford EC, Keane JF, Lock JE. J Am Coll Cardiol. 2006 May2;47(9):1858-65. Epub 2006 Apr 17.
Frequency of aortic root dilation in children with a bicuspid aortic valve.
Gurvitz M, Chang RK, Drant S, Allada V. Am J Cardiol. 2004 Nov15;94(10):1337-40.
Two-dimensional echocardiographic aortic root dimensions in normal children and adults.
Roman MJ, Devereux RB, Kramer-Fox R, O'Loughlin J. Am J Cardiol. 1989 Sep1;64(8):507-12.
Interpretation of echocardiographic measurements: a call for standardization.
Vasan RS, Levy D, Larson MG, Benjamin EJ. Am Heart J. 2000 Mar;139(3):412-22.
Relationship of the dimension of cardiac structures to body size: an echocardiographic study in normal infants and children.
Daubeney PE, Blackstone EH, Weintraub RG, Slavik Z, Scanlon J, Webber SA. CardiolYoung. 1999 Jul;9(4):402-10.