The Journal of Thoracic and Cardiovascular Surgery
Volume 139, Issue 5 , Pages 1356-1357, May 2010

Hydrodynamic performance of heart valve prostheses: Open discussion on European Committee for Standardization International Organization for Standardization standard 5840

  • Francesca Maria Susin, PhD

      Affiliations

    • Department of Hydraulic, Maritime, Environmental, and Geotechnical Engineering, University of Padua, Padua, Italy
    • ,
  • Andrea Bagno, PhD

      Affiliations

    • Department of Chemical Process Engineering, University of Padua, Padua, Italy
    • ,
  • Gino Gerosa, MD

      Affiliations

    • Department of Cardiovascular Surgery, University of Padua Medical School, University of Padua, Padua, Italy

Article Outline

CTSNet classification: 35.3.7

 

To the Editor:

In response to the publication of the European Committee for Standardization International Organization for Standardization (EN ISO) standard 5840 on May 2009,1 which replaces the previous release of March 2006, we would like to open a discussion on the criteria used to assess the performance of cardiac valve prostheses. This EN ISO standard gives the minimum performance requirements that have to be matched by heart valve substitutes in terms of “effective orifice area AEO” for a number of given valve sizes for both aortic and mitral positions (see Table 2 in EN ISO standard 58401).

AEO depends on the pressure drop through the valve. The following formula (which derives from the Bernoulli equation) has been adopted in the EN ISO standard to calculate AEO1:

where qVRMS is the root mean square forward flow (in milliliters per second), Δp is the mean pressure difference measured over the positive pressure period of the forward flow phase (in millimeters of mercury), and ρ is the density of the test fluid (in grams per cubic centimeter). The constant (51.6) is not dimensional; thus the equation is only valid with the specified units.

First, we point out that for pulsatile-flow tests, the norm details neither the geometry of the pulse duplicator in the proximity of pressure measuring sites nor the location of these sites with respect to the midplane of the heart valve substitute sewing ring. Indeed, the geometry of the device in the vicinity of the valve housing affects the geometry of the jet through the open valve. Moreover, according to conservation of mass, jet velocity varies along flow axis as a function of jet cross-sectional area.2 According to the Bernoulli equation, the pressure (that is Δp itself) thus varies along the jet.2

Furthermore, the norm states, “The minimum performance requirements correspond to the following pulsatile-flow conditions: …mean aortic pressure = 100 mm Hg….”1 Pulsatile flow conditions are usually reproduced in a pulse duplicator, as reported for previous work from our laboratory3, 4 in which the Sheffield pulse duplicator was used. We found that different prostheses tested in the Sheffield pulse duplicator may present comparable values of mean aortic pressure but quite different aortic pressure waveforms (data not published; Figure 1). We therefore wonder whether the mean value alone can be considered a reliable parameter for assessing prosthesis performance.

From a clinical viewpoint, any uncertainty in the assessment of prosthetic heart valve devices due to a lack of confidence in pressure measurement could result in an ambiguous characterization of their hemodynamic performance. Actually, the norm cannot prevent misestimation of the AEO. As a consequence, Doppler evaluation of patients after valve replacement could estimate values of AEO lower than expected (or, equivalently, pressure gradients higher than expected). Misleading quantification of the degree of obstruction to flow caused by the prosthetic device is thus possible.

For these reasons, we suggest an open discussion to improve the assessment of cardiac valve prostheses.

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References 

  1. Cardiovascular implants—cardiac valve prostheses. EN ISO 5840:2009. ICS: 11.040.40. 2009. Available from: http://webstore.uni.com/unistore/public/productdetails?productId=UNINI584000-2009!EEN.
  2. Yoganathan AP, Travis BR. Fluid dynamics of prosthetic valves. In:  Otto CM editors. Practice of clinical echocardiography. 3rd ed. Philadelphia: WB Saunders; 2007;p. 552–576
  3. Bottio T, Caprili L, Casarotto D, Gerosa G. Small aortic annulus: the hydrodynamic performances of 5 commercially available bileaflet mechanical valves. J Thorac Cardiovasc Surg. 2004;128:457–462
  4. Gerosa G, Tarzia V, Rizzoli G, Bottio T. Small aortic annulus: the hydrodynamic performances of 5 commercially available tissue valves. J Thorac Cardiovasc Surg. 2006;131:1058–1064

PII: S0022-5223(10)00060-7

doi:10.1016/j.jtcvs.2010.01.025

The Journal of Thoracic and Cardiovascular Surgery
Volume 139, Issue 5 , Pages 1356-1357, May 2010

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