LETTERS TO THE EDITOR
Cardiac rehabilitation, excercise training, and psychosocial risk factors:REPLY
Philippe Pibarot, DVM, PhD, FACC* and
Jean G. Dumesnil, MD, FACC
* Research Group in Valvular Heart Diseases, Research Center of Laval Hospital, Quebec Heart Institute, Laval University, 2725 Chemin Sainte-Foy, Sainte-Foy G1V-4G5, Quebec, Canada (Email: philippe.pibarot{at}med.ulaval.ca).
We thank Dr. Shanmugam for his interest in our study (1). Most of the limitations he raises have
been discussed in detail in our report. We have never suggested that a cutoff of 40 mm Hg was
equivalent to severe pulmonary hypertension. Nonetheless, as we have also alluded to in our
study, such levels of pulmonary pressures, equivalent to mild/moderate pulmonary hypertension,
have been associated with significantly worse outcomes. Moreover, the fact that such levels of
pressure would persist in patients with prosthesis-patient mismatch (PPM), whereas they would
regress in most patients without PPM, indeed confirms that levels above 40 mm Hg are clearly
abnormal.
The indexed effective orifice area (EOA) is a physiological parameter that relates to the intrinsic hemodynamic
performance of the prosthesis and has nothing to do with valve annular diameters. The
threshold value of 1.2 cm2/m2 was chosen to identify PPM because it was the most discriminative
value to identify patients with persisting pulmonary artery hypertension after mitral valve replacement (MVR), and it is consistent with
previous in vitro and in vivo studies on mitral PPM. As we have emphasized, the pressure
gradient is a much less appropriate parameter with which to assess the consequences of PPM, especially in the
mitral position, because it is highly influenced by chronotropic conditions and because mitral flow
tends to decrease when pulmonary resistances are increased.
The statement that "the minimum absolute valve EOA of any size-23
prosthesis is 2.54 cm2" denotes a gross misunderstanding of valve prosthesis physiology and is
equivalent to saying that all prostheses of a given labeled size would have similar hemodynamic
performance. Indeed, it is well known that labeled sizes have no relevance to valve
hemodynamics and that they grossly overestimate the actual EOA, which may vary from one type
of prosthesis to another. In this context, it is interesting to note that the normal reference values of
EOA for 27-mm mitral prostheses range from 1.6 to 2.2 cm2 (2). Hence, it is not surprising that
PPM defined as an indexed EOA 
1.2 cm2/m2 can be a frequent occurrence in patients
undergoing MVR.
We agree with Dr. Shanmugam that the prevention of PPM in the mitral position is a particularly
demanding challenge for the surgeon and that there are not as many options as in the aortic
position. Nonetheless, and as we have shown, it is not a rare occurrence and definitely warrants
further documentation. Our results also provide impetus for the development of better performing
mitral prostheses.
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References
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- Li M, Dumesnil JG, Mathieu P, Pibarot P. Impact of valve prosthesis–patient mismatch on pulmonary arterial pressure after mitral valve replacement J Am Coll Cardiol 2005;45:1034-1040.[Abstract/Free Full Text]
- Rosenhek R, Binder T, Maurer G, et al. Normal values for Doppler echocardiographic assessment of heart valve prostheses J Am Soc Echocardiogr 2003;16:1116-1127.[CrossRef][Medline]
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References