Letter Regarding Article by Koch et al, “Impact of Prothesis–Patient Size on Functional Recovery After Aortic Valve Replacement”
To the Editor:
We have read with interest the article by Koch et al.1 The conclusion is that “prothesis–patient size does not influence functional recovery after aortic valve replacement ….” As appropriately pointed out by the authors, this result is at odds with many previous studies showing that patient-prosthesis mismatch (PPM) has an impact on perioperative and postoperative outcomes and that the discrepancy could be related to the parameter chosen to characterize PPM. Hence, these authors use the internal geometric area (IGA), whereas many other studies2 have used the effective orifice area (EOA), and it thus becomes important to clearly understand the intrinsic differences between these two parameters.
The IGA is derived from the static measurement of the diameter of the prosthesis. It should be noted that the criteria used for this measurement are different for each type of prosthesis and that the indexed IGA has never been shown to have any relevance to postoperative hemodynamics. This observation is indeed corroborated by the results of the present study, whereby, compared with allografts, pericardial valves have very similar values for indexed IGA but approximately 2-fold values for peak and mean gradients (see Figure 2 and Table 1 of the article). In contrast, the indexed EOA is a hemodynamic parameter, which has consistently been shown to correlate with postoperative gradients.
Given these fundamental differences, we would therefore submit that the terminology used should be without ambiguity and in particular, that the term “indexed orifice area” should not be used without specifying whether it is indexed IGA or EOA, as was done in Figure 2. Also, given that the term PPM stems from a hemodynamic concept, its use should be reserved for data relating to hemodynamics (eg, indexed EOAs and gradients), whereas it would seem more appropriate to describe the results of the present study exclusively in terms of patient-prosthesis size, without using the term mismatch, thus avoiding much confusion. The use of proper terminology is important because, as further demonstrated by this study, patient-prosthesis size is seldom related to outcomes, whereas it is the opposite for PPM.2 Moreover, PPM can largely be avoided by using a preventive strategy at the time of operation.2
Koch CG, Khandwala F, Estafanous FG, Loop FD, Blackstone EH. Impact of prothesis–patient size on functional recovery after aortic valve replacement. Circulation. 2005; 111: 3221–3229.
Blais C, Dumesnil JG, Baillot R, Simard S, Doyle D, Pibarot P. Impact of prothesis–patient mismatch on short-term mortality after aortic valve replacement. Circulation. 2003; 108: 983–988.
Over the years, Dr Pibarot and colleagues have contributed enormously to our understanding of prosthesis–patient mismatch. We agree that the term prosthesis–patient size should be reserved for expressing the continuous relation of prosthesis dimensions, however expressed, to body size, as proposed previously.1,2 We disagree that prosthesis–patient mismatch is fundamentally a hemodynamic concept; originally, it referred to a clinical syndrome.3 Semantics aside, readers need to understand our long-standing differences in perspective about the clinical importance of prosthesis size.
1, A few patients manifest a clinical syndrome after aortic valve replacement (AVR) that is relieved by inserting a larger prosthesis.3 This is true prosthesis–patient mismatch syndrome, not an arbitrary dichotomous characterization of hemodynamics.
2, Within the constraints of prudent AVR, it is difficult to demonstrate a relationship between long-term survival and physical prosthesis dimensions.1
3, Life expectancy after AVR does not return to normal, except in the elderly, who tend to receive small prostheses.1 This suggests a complex relationship between prosthesis size and clinical outcome, including genetic factors,4 secondary cardiomyopathy, afterload reduction by AVR, post-AVR left ventricular outflow tract (LVOT) dynamics, aorta, and intrinsic properties of the prosthesis.
4, Calculated effective orifice area (EOA) and pressure gradient are of necessity well correlated because they are derived from the same primary echocardiographic velocity measurements.
5, EOA is time-varying and depends on many factors besides intrinsic properties of the prosthesis. Attributing complex LVOT energy losses solely to the prosthesis leads to the unproven hypothesis that simply inserting a large-size prosthesis will improve clinical outcome. Understanding the implications of this attribution is important when considering percutaneous AVR.
In our view, with so little evidence that prosthesis size makes a substantial impact on long-term mortality and quality of life, it is time to identify other factors that might be more important in improving outcomes after AVR.