Download Prosthesis patient mismatch in aortic valve replacement: possible

Current opinion
European Heart Journal (2006) 27, 644–646
doi:10.1093/eurheartj/ehi757
Prosthesis patient mismatch in aortic valve
replacement: possible but pertinent?
David P. Taggart
Professor of Cardiovascular Surgery, University of Oxford, Oxford, UK
Received 4 October 2005; revised 6 January 2006; accepted 12 January 2006; online publish-ahead-of-print 1 February 2006
Aortic valve replacement (AVR) is now the second most commonly performed cardiac operation and with an increasingly
elderly population, the number of such procedures will
inevitably continue to grow.1 In 1978, Rahimtoola2 defined
the term prosthesis patient mismatch (PPM) to describe
the situation in which the effective orifice area (EOA) of a
prosthetic valve, after implantation, is smaller than that
of the native valve. Although described nearly three
decades ago, there are several reasons why PPM has only
more recently become much more openly debated. First,
PPM was initially overshadowed by the more immediate
issues of operative mortality and major morbidity. Second,
by definition, all prosthetic valves must therefore have at
least some degree of PPM; over 90% of AVR still use prostheses with a sewing ring, or have struts, hinge mechanisms,
and rigid carbon or relatively stiff bioprosthetic leaflets.
Third, and most importantly, as moderate aortic stenosis
can be tolerated over long periods with excellent functional
status and well-preserved ventricular function, the clinical
relevance of all but the most severe PPM has remained
uncertain.
In the last decade, however, as Pibarot and colleagues
sub-classified PPM more precisely according to the effective
orifice index area (EOIA) of a prosthetic valve as mild
(.0.85 cm2/m2), moderate (0.65–0.85 cm2/m2), or severe
(,0.65 cm2/m2),3–5 several studies have debated whether
PPM affects short and long-term survival as well as functional status.4–11 On the other hand, surgical procedures
designed to avoid PPM, by enlarging the aortic root, increase
the complexity of the operation and its operative mortality
even in the best centres.12 So is there appropriately compelling evidence that the potential detrimental effects of PPM
merit the performance of more complex and higher risk
operations?
Four crucial considerations regarding
PPM and outcome
Intuitively, PPM should impact adversely on clinical
outcome, but establishing this beyond reasonable doubt is
The opinions expressed in this article are not necessarily those of the
Editors of the European Heart Journal or of the European Society of
Cardiology.
* Corresponding author.
E-mail address: [email protected]
bedeviled by several facts. First, and most significantly,
patients at the highest risk of PPM are those who are
already at the highest risk from surgery. PPM is most
common in patients with small aortic roots and this occurs
most frequently in the elderly (especially females) who
are also more likely to have severe coronary artery disease
and poorer cardiac function and are therefore already at a
higher risk from surgery. Accordingly, PPM could almost
be considered as a ‘surrogate’ variable for other risk
factors and as such even multivariate analysis can only
partially, at best, discriminate between patient-related
and prosthesis-size confounding factors.
Second, the EOIA is a functional measurement (derived
echocardiographically from the continuity equation),
which is dependent not only on the characteristics of the
prosthesis but also on the properties of the left ventricular
and aortic outflow tract. EOIA cannot therefore be established before prosthesis insertion and as there are few
large cohort studies with serial measurements of EOIA,
rigorously performed at rest and exercise, for different
valve models and sizes, there is wide variability of published
EOA data. This seriously questions the relevance of several
studies, not only composed of numerous valve types (mechanical and bioprosthetic, stented and stentless, old and
new, etc.) but which have used published fixed-reference
EOA values to calculate EOIA.
A third confounding factor is the difference between EOIA
and the indexed internal geometric orifice area (GOA) of the
prosthesis. Although both are related to the internal
diameter of the prosthesis, in contrast to the EOA, the
GOA is a non-functional, ex vivo, static measurement of
the internal diameter. Whereas the EOA has been shown to
consistently correlate with post-operative gradients and
haemodynamics that relationship with the GOA is less
obvious. Because of the square relationship between
gradient and EOA and that a decreasing EOIA correlates
exponentially with the prosthesis gradient, a marked
increase in gradient only occurs when the EOIA falls below
0.85 cm2/m2.4 Blackstone et al.10 have calculated that the
equivalent point for an indexed GOA is 1.2 cm2/m2, and
this may explain the less obvious relationship with pressure
gradients and haemodynamics in the few studies which have
used indexed GOA.
The fourth complicating factor is increasing recognition of
marked discrepancies between the manufacturer labelled
and actual diameter of the valve prosthesis.13–17 Failure to
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PPM in AVR
account for this has almost certainly contributed to a frequent inability in the literature to relate labelled size of
valves to haemodynamic performance.
PPM and short-term survival following AVR
The effect of PPM on short-term mortality following AVR is
conflicting with four studies reporting a positive association5,6,8,10 and two studies reporting no association.7,11
The strongest evidence that PPM increases operative
mortality after AVR is by Pibarot and coworkers.5 In 1266
consecutive AVR patients, the 30-day mortality was 4.6% in
the 62% of patients without PPM, but was doubled with moderate PPM and increased 11-fold with severe PPM. Although
patients with moderate and severe PPM had significantly
more risk factors including impaired left ventricular function, older age, female gender, coronary artery disease,
and emergent/salvage surgery, the authors nevertheless
concluded that PPM was a strong and independent predictor
of short-term mortality. Likewise, Rao et al.6 also noted an
increased operative mortality (8 vs. 5%) in the 8% of their
2891 AVR patients with PPM, but who similarly had a
higher incidence of other risk factors. Finally, Blackstone
et al.,10 using multivariable hazard domain analysis with
balancing score and risk factor adjustment in over 13 000
AVR patients from nine centres, reported that PPM increased
the operative mortality by 1–2%. In contrast, two other
studies correcting for differing baseline factors and involving
8927 and 156311 patients, respectively, found no increase in
short-term mortality with PPM.
A possible explanation for these apparently conflicting
results might be an interaction of PPM with pre-existing
impairment of left ventricular function. In a multivariate
analysis of 52 patients undergoing AVR with a left ventricular
ejection fraction below 35%, the only predictor of surgical
mortality was smaller prosthesis size.18 In an observational
study of 1103 patients undergoing AVR with a stentless
bioprosthesis, baseline left ventricular mass index and
PPM were the strongest predictors of the extent of postoperative LV mass regression, implying a more powerful
effect of PPM in the impaired ventricle.19
PPM and cardiac failure following AVR
Four studies have addressed the relationship of PPM and nonPPM to cardiac failure after AVR. Three studies reported an
association between PPM and subsequent heart failure but
also noted, somewhat counter-intuitively, that this did not
contribute to long-term mortality.4,6,11 In one of these
reports, Ruel et al. 11 reported that PPM defined as an EOIA
,0.80 cm2/m2 was an independent predictor of postoperative congestive heart failure, but not if PPM was
defined as an EOIA ,0.85 cm2/m2. In contrast to these
three studies, Hanayama et al. 8 found no association
between PPM and heart failure in their series of 1129 patients.
PPM and long-term survival following AVR
Seven studies, including those which reported an adverse
effect of PPM on short-term survival or an increased incidence of cardiac failure have also addressed the effect of
PPM on long-term survival in more than 20 000 patients followed for 5–15 years.4,6–11 The consistent observation in
645
these studies is the absence of any adverse effect of PPM
on long-term survival. Individually, the most definitive
study is that of Blackstone et al.,10 who followed over
13 000 AVR patients for a mean of 5 years and up to 15
years. After adjustment for other pre-operative risk
factors, the authors could identify no adverse effect of
PPM on long-term survival.
PPM and functional recovery after AVR
This question was recently addressed in a study from the
Cleveland Clinic in 1108 patients undergoing AVR and
whose functional post-operative recovery was assessed by
the Duke Activity Status Index (DASI) 8 months after
surgery.20 Overall, there was a significant improvement
in post-operative functional recovery in all AVR patients,
but no measure of valve orifice area could be correlated
with functional recovery. On the other hand, female sex,
increasing age, and pre-operative renal impairment were
associated with a poor functional recovery.
Surgical options and risks for avoiding PPM
The potential risk of PPM has led some surgeons to recommend manoeuvres to enlarge the aortic annulus or root.
Although these procedures may be technically successful in
permitting implantation of a larger-sized prosthesis, they
also increase the complexity of the procedure and, more
importantly, the operative risk. Although some authors
have reported excellent results,21 Sommers and David12
described an increase in operative mortality from 3.5 to
7.1% in 98 of 530 patients who underwent patch enlargement or the aortic annulus to avoid the risk of PPM.
Thankfully, there are now newer generation mechanical
and bioprosthetic valves with significantly superior haemodynamics, which should allow avoidance of root enlargement in all but the most potentially severe cases of PPM.
Summary and conclusions
Most patients undergoing prosthetic AVR will ‘technically’
have some degree of PPM, but this is rarely severe and
patients at the highest risk of significant PPM are those who
are already at the highest risk from surgery. Although it is
possible that severe PPM may result in a slight increase in
operative mortality, and especially in the setting of pre-existing impaired ventricular function, there is general agreement
that PPM, even when severe, does not adversely affect longterm survival. Use of newer generation aortic prosthesis with
superior haemodynamics may avoid the need for enlargement
of the aortic root/annulus where significant PPM is likely.
Conflict of interest: none declared.
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