Download Long-Term Outcomes After Valve Replacement for Low

Long-Term Outcomes After Valve Replacement for
Low-Gradient Aortic Stenosis
Impact of Prosthesis-Patient Mismatch
Alexander Kulik, MD; Ian G. Burwash, MD; Varun Kapila, BSc;
Thierry G. Mesana, MD, PhD; Marc Ruel, MD, MPH
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Background—The long-term outcomes of patients with low-gradient aortic stenosis (LGAS) after aortic valve replacement
(AVR) are poorly defined. The purpose of this study was to define the long-term outcomes of LGAS patients after AVR
and to evaluate the potential impact of prosthesis–patient mismatch (PPM) in these patients.
Methods and Results—A cohort of 664 patients undergoing AVR for aortic stenosis after 1990 were followed-up
prospectively with annual clinical assessment and echocardiography (total follow-up 3447 patient-years; mean
follow-up 5.2⫾3.3 years). LGAS was defined as an aortic valve area ⬍1.2 cm2, a mean transvalvular pressure gradient
⬍40 mm Hg, and a left ventricular (LV) ejection fraction ⬍50%, and was present in 79 patients. Rates and correlates
of survival, freedom from congestive heart failure (CHF), and LV mass regression after AVR were determined using
multivariate regression methods. Ten-year survival and freedom from CHF after AVR were 72.7⫾7.5% and
68.2⫾9.5%, respectively, for patients with LGAS, compared with 89.6⫾1.8% and 84.1⫾4.2% for patients without
LGAS (hazard ratio [HR] for death and postoperative CHF, 3.1⫾1.1 and 2.7⫾0.9, respectively; P⬍0.01). In LGAS
patients, PPM, defined as an indexed effective orifice area ⱕ0.85 cm2/m2, was independently associated with increased
rates of CHF (HR, 3.6⫾2.2; P⫽0.039), impaired LV mass regression (P⫽0.037), and a trend toward increased late
mortality (HR, 3.0⫾1.9; P⫽0.084).
Conclusions—Patients with LGAS have worse long-term outcomes after AVR compared with patients without LGAS.
PPM adversely affects the long-term outcomes of LGAS patients and should be avoided in this population. (Circulation.
2006;114[suppl I]:I-553–I-558.)
Key Words: aortic stenosis 䡲 aortic valve replacement 䡲 prosthesis–patient mismatch
A
ortic valve replacement (AVR) relieves symptoms and
improves survival in patients with symptomatic aortic
stenosis (AS).1 However, a subset of patients with AS have a
low transvalvular pressure gradient as a result of left ventricular (LV) systolic dysfunction and reduced transvalvular
flow, a condition known as low-gradient aortic stenosis
(LGAS). The ventricular dysfunction in patients with LGAS
may result from excessive afterload of long-standing AS, or
alternatively relate to concomitant coronary artery disease or
a cardiomyopathy.2 Importantly, patients with LGAS undergoing AVR have higher operative mortality rates and reduced
medium-term survival compared with patients with high
gradient AS.3– 8 However, little is known regarding the
long-term outcomes of LGAS patients after AVR and
whether they are affected by the presence of prosthesis–
patient mismatch (PPM).9 Therefore, the purpose of this
study was to compare the long-term results of AVR in
patients with and without LGAS with respect to all-cause
mortality, freedom from congestive heart failure (CHF), and
LV mass regression, and to identify potential factors that
affect long-term outcomes.
Methods
Patient Population and Follow-Up
Patients aged 18 years or older were prospectively followed-up after
first-time AVR for AS between 1990 and 2002 at the University of
Ottawa Heart Institute. Patients were excluded from the study
population if they had more than mild (1⫹) aortic insufficiency at the
time of operation, another concomitant valve procedure, did not
survive the operation, or received a prosthesis that is no longer
commercially available. After AVR, patients were assessed 6 months
postoperatively and thereafter on an annual basis by a physician in a
dedicated valve clinic. At each visit, patients underwent a medical
history focused on the determination of functional status and the
occurrence of valve-related complications, a physical examination,
ECG, chest radiograph, complete blood count, serum chemistries,
and international normalized ratio determinations when applicable.
The methods of data collection and analysis of the valve clinic
From the Division of Cardiac Surgery (A.K., V.K., T.G.M., M.R.), the Division of Cardiology (I.G.B.), and the Department of Epidemiology (M.R.),
University of Ottawa, Ottawa, Ontario, Canada.
Presented at the American Heart Association Scientific Sessions, Dallas, Tex, November 13–16, 2005.
Correspondence to Marc Ruel, University of Ottawa Heart Institute, 40 Ruskin St, Suite 3403, Ottawa, Ontario, Canada K1Y 4W7. E-mail
[email protected]
© 2006 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/CIRCULATIONAHA.105.001180
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Circulation
July 4, 2006
database have been reviewed and approved by the University of
Ottawa Heart Institute Human Research Ethics Board. All patients
(N⫽664) were followed-up for at least 1 outpatient visit. The total
follow-up was 3447 patient-years (mean 5.2⫾3.3 years; maximum
14.0 years). Patients were defined as having LGAS if they fulfilled
all of 3 previously published criteria: preoperative aortic valve area
⬍1.2 cm2,5 mean transvalvular pressure gradient ⬍40 mm Hg,8,10
and left ventricular ejection fraction ⬍50%.3,6,11 Of the 664 patients
in the study cohort, 79 patients had LGAS.
Prostheses
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Prosthesis type and size were recorded in all patients. Prostheses
were implanted and oriented according to the manufacturer’s recommendations. The effective orifice area (EOA) for each prosthesis
type and size was obtained from the literature of patients with
normally functioning prostheses,9,12 and averaged if ⬎1 published
value was available. This was supplemented with phase I regulatory
data provided by the valve manufacturer if published data were
insufficient with respect to a specific prosthesis size. The indexed
EOA was obtained by dividing the EOA by the patient’s body
surface area at the time of operation, which was available for all
patients. PPM was defined a priori as an indexed EOA ⱕ0.85
cm2/m2, because this definition constitutes the most commonly
reported description of PPM in the literature.9,13,14
Echocardiograms
Patients underwent a complete M-mode, 2-dimensional, and Doppler
transthoracic echocardiogram at our institution before AVR. All
patients underwent a postoperative echocardiogram, and thereafter as
clinically indicated. LV mass was calculated from M-mode recordings as per the recommendations of the American Society of
Echocardiography.15
TABLE 1.
Characteristics of Patients With and Without LGAS
LGAS
(N⫽79)
No LGAS
(N⫽585)
Female
17 (21.5%)*
212 (36.2%)
Age at operation (years)
67.2⫾11.5
65.2⫾13.7
Body mass index (kg/m2)
26.7⫾3.3
27.5⫾4.6
Cigarette smoking
14 (17.7%)
91 (15.6%)
Cerebrovascular accident
0 (0%)
4 (0.7%)
8 (10.1%)*
28 (4.8%)
3 (3.8%)
12 (2.0%)
1
19 (24.3%)
171 (29.3%)
2
18 (22.9%)
181 (30.9%)
3
23 (28.6%)
145 (24.8%)
4
19 (24.3%)
88 (15.1%)
1
0 (0%)*
451 (77.1%)
2
22 (27.8%)*
75 (12.8%)
3
28 (35.4%)*
40 (6.7%)
4
29 (36.7%)*
20 (3.4%)
Preoperative mean transvalvular
pressure gradient (mm Hg)
29.1⫾7.7*
50.4⫾19.8
Preoperative aortic valve area (cm2)
Diabetes mellitus
Chronic atrial fibrillation
NYHA class
LV grade
†
0.81⫾0.19
0.72⫾0.45
Preoperative LV end-diastolic diameter (cm)
6.0⫾0.9*
5.3⫾0.9
Preoperative LV end-systolic diameter (cm)
4.5⫾1.0*
3.3⫾1.0
Statistical Analyses
Preoperative mitral regurgitation grade
1.2⫾0.8*
0.9⫾0.8
Clinical Outcomes
*P⬍0.05 vs patients without LGAS.
Grade 1⫽LV ejection fraction ⱖ50%; grade 2⫽LV ejection fraction of
40%0 – 49%; grade 3⫽ejection fraction of 30%–39%; grade 4⫽ejection
fraction ⬍30%.
LGAS indicates low-gradient aortic stenosis; LV, left ventricle; NYHA, New
York Heart Association.
Data were analyzed in Intercooled Stata 8.0 (Stata, College Station,
Tex). Non-parametric estimates of freedom from all-cause death and
freedom from the composite CHF end-point were determined using
the Kaplan-Meier method. For the CHF analysis, a composite CHF
end-point was a priori defined as: (1) New York Heart Association
(NYHA) functional class 3 or 4 for ⬎4 consecutive weeks; or (2)
death in which the primary or main contributing diagnosis was
CHF.9 Clinical impressions were corroborated with physical examination, chest radiograph, ECG, and echocardiographic findings.
Deaths from an unknown cause were not considered to result from
CHF and were treated as a censored event if the patient had not
previously experienced NYHA class 3 or 4 symptoms. Survival and
freedom from CHF rates after AVR were reported as mean⫾standard
error.
Multivariate Analyses
Possible predictors of death or the CHF composite end-point were
individually tested for equality with a log-rank test. Cox proportional
hazards models were developed: (1) by forcing into the model risk
factors for decreased survival and freedom from CHF after AVR (LV
function, age, atrial fibrillation, preoperative heart failure functional
class, coronary artery disease, smoking, and insulin-dependent diabetes mellitus) that have been previously identified;9 and (2) by
incorporating any other variable that had Pⱕ0.20 on univariate
log-rank testing. To account for confounding, no automated model
selection procedure was used, and all covariates were used simultaneously unless found to be collinear as determined by a Spearman
rank correlation coefficient ⱖ0.30 and P⬍0.005. For all other tests,
statistical significance was set at P⬍0.05.
Statement of Responsibility
The authors had full access to the data and take full responsibility for
their integrity. All authors have read and agree to the manuscript as
written.
†
Results
Patient Characteristics
Preoperative characteristics of patients with and without
LGAS are presented in Table 1. Patients with LGAS were
more often male, had a higher prevalence of diabetes, and had
worse preoperative LV function (all P⬍0.05). The operative
procedure and valve prosthesis characteristics are summarized in Table 2. LGAS patients underwent concomitant
coronary artery bypass grafting (CABG) more frequently
than those without LGAS (P⬍0.05). There was no difference
in the types of valves implanted between groups.
Survival
During the study period, the perioperative mortality of all
patients who underwent AVR was 3.5%, whereas that of
patients with LGAS was significantly higher at 7.5%
(P⫽0.02). Survival (excluding operative mortalities) at 1, 5,
and 10 years after AVR for patients with LGAS was
97.3⫾1.9%, 83.8⫾5.1%, and 72.7⫾7.5%, respectively. In
contrast, patients without LGAS had 1-year, 5-year, and
10-year survival rates of 98.8⫾0.5%, 93.1⫾1.2%, and
89.6⫾1.8%, respectively, significantly higher than those
observed for LGAS patients (HR, 3.1; 95% confidence
Kulik et al
TABLE 2.
Low-Gradient Aortic Stenosis
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Operative and Valve Prosthesis Characteristics
LGAS
(N⫽79)
No LGAS
(N⫽585)
Concomitant CABG
49 (62.0%)*
198 (33.8%)
Cardiopulmonary bypass duration (minutes)
125.8⫾34.8
117.6⫾41.0
Aortic cross-clamp duration (minutes)
85.3⫾22.0
79.7⫾27.1
Mechanical valves
39 (49.4%)
272 (46.5%)
Medtronic Hall
4 (5.0%)
45 (7.7%)
St. Jude
20 (25.3%)
139 (23.8%)
Carbomedics
14 (17.7%)
82 (14.0%)
1 (1.3%)
6 (1.0%)
40 (50.6%)
313 (53.5%)
MCRI On-X
Bioprosthetic valves
Homograft
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2 (2.5%)
42 (7.2%)
Medtronic Hancock
35 (44.3%)
230 (39.3%)
Edwards Pericardial
3 (3.8%)
32 (5.5%)
Edwards Porcine
—
4 (0.7%)
Stentless Porcine†
—
5 (0.9%)
*P⬍0.05 vs patients without LGAS.
†
Denotes either a St. Jude Toronto Stentless or Medtronic Freestyle
prosthesis.
CABG indicates coronary artery bypass grafting; LGAS, low-gradient aortic
stenosis.
interval [CI], 1.5, 6.1; P⫽0.001; Figure 1A). Furthermore,
LGAS patients had decreased long-term survival when compared with patients without LGAS who had LV dysfunction
(HR, 3.0; 95% CI, 1.1, 8.0; P⫽0.027). After adjusting for
known confounders,9 late mortality among LGAS patients
was independently predicted by a history of atrial fibrillation
(HR, 5.1; 95% CI, 1.1, 24.4; P⫽0.04). There was a trend
toward increased late mortality among LGAS patients with
PPM (HR, 3.0; 95% CI, 0.9, 10.1; P⫽0.084; Figure 2A).
Moreover, using indexed EOA as a continuous variable, there
was a trend to better long-term survival among LGAS
patients with a larger indexed EOA (HR, 0.08 per unit m2/cm2
change; 95% CI, 0.01, 4.3; P⫽0.213).
Heart Failure
NYHA class improved from the preoperative to postoperative
period in patients with LGAS (2.5⫾1.1 to 1.3⫾0.6;
P⬍0.001) and patients without LGAS (2.3⫾1.0 to 1.2⫾0.5,
P⬍0.001). However, patients with LGAS were more likely to
have persistent or recurrent CHF after AVR, with lower
freedom from the composite CHF outcome of NYHA 3 to 4
symptoms or CHF-related death (Figure 1B). Freedom from
the composite CHF outcome for LGAS patients at 1, 5, and
10 years was 97.2⫾2.0%, 84.4⫾5.3%, and 68.2⫾9.5%,
respectively, and significantly worse compared with
99.5⫾0.3%, 94.5⫾1.2%, and 84.1⫾4.2% for patients without
LGAS (HR, 2.7; 95% CI, 1.4, 5.2; P⫽0.003). Furthermore,
LGAS patients had a significantly lower freedom from the
composite CHF outcome when compared with patients without LGAS who had LV dysfunction (HR, 2.6; 95% CI, 1.1,
6.4; P⫽0.028). After adjustment for known confounders,9 the
presence of PPM (ⱕ0.85 cm2/m2) was an independent predictor of persistent or recurrent CHF after AVR among
LGAS patients (HR, 3.6; 95% CI, 1.1, 11.9; P⫽0.039; Figure
Figure 1. Survival (A) and the incidence of persistent or recurrent CHF (B) in patients with and without LGAS after AVR. *Hazard ratio adjusted for left ventricular function, age, atrial fibrillation, preoperative NYHA functional class, coronary artery
disease, smoking, and insulin-dependent diabetes mellitus. AVR
indicates, aortic valve replacement; CHF, congestive heart failure; CI, confidence interval; LGAS, low-gradient aortic stenosis.
2B). Moreover, using indexed EOA as a continuous variable,
a larger indexed EOA was associated with better freedom
from CHF among LGAS patients (HR 0.02 per unit m2/cm2
change; 95% CI 0.01, 0.69; P⫽0.03).
Postoperative LV Remodeling
Patients with LGAS and postoperative PPM had significantly
less LV mass regression compared with patients with LGAS
and no PPM (PPM 9⫾14 versus no PPM 79⫾31 grams;
P⫽0.037) (Figure 3). Similarly, patients with LGAS and
PPM had less LV mass regression when indexed for body
surface area compared with LGAS patients without PPM
(PPM 5⫾7 versus no PPM 45⫾19 g/m2, P⫽0.05). Furthermore, the coefficient for PPM was significantly reduced in a
multivariate linear model for LV mass regression that included patient characteristics and the presence of persistent
hypertension during postoperative follow-up (coefficient 32;
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Figure 2. Impact of PPM on survival (A) and the incidence of
persistent or recurrent CHF (B) after AVR in patients with LGAS.
*Hazard ratio adjusted for LV function, age, atrial fibrillation, preoperative heart failure functional class, coronary artery disease,
smoking, and insulin-dependent diabetes mellitus. IEOA indicate
indexed effective orifice area; PPM, prosthesis–patient
mismatch.
95% CI: 4, 59; P⫽0.02). A detrimental effect of PPM on LV
mass regression was also observed in patients without LGAS
but was not as pronounced (PPM 44⫾6 versus no PPM 59⫾7
grams; P⫽0.1).
Discussion
The natural history of patients with LV systolic dysfunction
and LGAS is poor with medical management. AVR has the
Figure 3. Impact of PPM on LV mass regression after AVR
among patients with and without LGAS. LV indicates left
ventricle.*P⫽0.037 refers to the comparison of PPM vs no PPM
in LGAS patients. †P⫽0.1 refers to the comparison of PPM vs
no PPM in no LGAS patients.
potential to improve LV function and survival by removing
the excessive afterload caused by a severely stenotic aortic
valve. However, LV function may not improve after AVR if
concomitant coronary artery disease or a cardiomyopathy is
responsible for the LV dysfunction.2 Furthermore, high perioperative mortality rates have been observed in LGAS
patients undergoing AVR,3– 8 and the long-term outcomes of
LGAS patients surviving surgery is unclear. The purpose of
this study was to define the long-term outcomes after AVR in
LGAS patients and determine whether the presence of PPM
impacts on patient outcome. In this cohort followed-up
annually after AVR, we observed that: (1) patients with
LGAS have worse survival and freedom from CHF after
AVR compared with patients without LGAS; (2) PPM is an
independent risk factor for CHF and a trend to late mortality
in patients with LGAS; and (3) LGAS patients with PPM
have less LV mass regression following AVR. Thus, patients
with LGAS have a worse long-term prognosis after AVR and
tolerate PPM poorly.
Patients with LGAS are at substantial risk during AVR,
with reported surgical mortality rates ranging from 8% to
33%.3–7 However, the short-term and intermediate-term outcomes with medical management appear worse.7,8 In a
propensity matched study, the 1-year and 4-year survival
rates of 39 patients with LGAS undergoing AVR were 82%
and 78%, respectively, compared with 41% and 15% observed in 56 medically treated patients (P⬍0.0001).7 In our
larger cohort of LGAS patients undergoing AVR, we observed a similar 84% 5-year survival rate, and we extended
these observations with a 10-year survival rate of 73%. In
addition, we have demonstrated that the majority of LGAS
patients obtain benefit through the improvement of symptoms
following surgery.
The principal finding of our study relates to the profoundly
negative impact of PPM on the long-term outcomes of LGAS
patients undergoing AVR. The concept of PPM was first
introduced by Rahimtoola in 1978 to describe the condition in
which the prosthetic valve orifice area is less than that of the
native human valve.16 Subsequent studies examining the
physiological sequelae of PPM have fostered the recommendation that the indexed EOA of an aortic prosthesis should
ideally be greater than 0.85 cm2/m2 to minimize postoperative
gradients and improve clinical results.12,13 While there remains controversy in the literature as to the relevance of
PPM, previous work by our group9,17 and others18 has
demonstrated that PPM is a strong and independent predictor
of adverse outcomes after AVR, particularly in patients with
LV dysfunction.
The current study adds to our understanding of the optimal
management of LGAS patients. Along with defining the
expected long-term survival of LGAS patients undergoing
AVR, we have identified a threshold in prosthesis size related
to the patient’s body surface area, beyond which survival and
cardiac recovery may not reach their maximum potential after
valve replacement. No published study to date has described
the detrimental effect of PPM (defined as a threshold of
ⱕ0.85 cm2/m2) after AVR on the long-term clinical outcomes
in LGAS patients. PPM significantly impaired long-term
survival, freedom from heart failure, and LV mass regression
Kulik et al
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in this patient population. Therefore, PPM at or beyond this
threshold should be avoided in patients with LGAS undergoing AVR. Strategies to predict12 and avoid PPM at the time of
surgery may lead to improved LGAS outcomes, such as aortic
root enlargement.
Previous studies in patients with LGAS have demonstrated
a negative impact of small prosthesis size on surgical mortality, signifying that failure to effectively reduce afterload
can lead to detrimental outcomes.5,19 In contrast, we used the
indexed EOA derived from normally functioning valves
because this methodology has the advantage of accounting
for the large variation in body size in AVR patients, which is
an important determinant of the adequacy of a given prosthesis size to relieve outflow obstruction.12 The EOA derived by
Doppler-echo continuity equation from individual patients
after implantation of the prosthesis may have betterquantified the degree of PPM. However, this methodology
has several significant limitations related to difficulties in
accurately measuring the LV outflow diameter because of
prosthetic valve reverberations, and the presence of large
localized transprosthetic gradients or nonuniform transprosthetic spatial velocity profiles, which frequently result in
large discrepancies between Doppler-echo and “actual” EOA
measurements.20,21 Importantly, EOAs derived from individual patients are not available at the time of surgical decisionmaking. The EOA can only be determined once the prosthesis
has been inserted, the patient has been weaned from cardiopulmonary bypass, and the preload, afterload, and contractility have normalized. Therefore, the EOA of an individual
patient has little or no role in predicting whether PPM will be
avoided or not by a given prosthesis type and size, whether
another prosthesis type or size should be selected, or whether
aortic root enlargement should be performed before
implantation.
In patients with severe AS and preoperative LV dysfunction, AVR induces a favorable remodeling of the LV,
characterized by normalization of wall stress indices, regression of chamber dilatation, reduction of LV hypertrophy, and
an improvement in cardiac performance.22 Similarly, we
observed LV mass regression in our patients with and without
LGAS after AVR. However, there was a significant impairment in LV mass regression in LGAS patients with PPM after
AVR compared with LGAS patients without PPM, and this
was associated with a decrease in long-term survival and
freedom from CHF. This illustrates the concept that patients
with LV dysfunction and LGAS are particularly sensitive to
increases in afterload and incomplete relief of LV outflow
tract obstruction after AVR.
The definition of LGAS used in this study included the
previously published criteria of preoperative aortic valve area
⬍1.2 cm2, mean transvalvular pressure gradient ⬍40 mm Hg,
and left ventricular ejection fraction ⬍50%.3,5,6,8,10,11 In this
regard, some investigators have used even lower gradients
and/or ejection fraction criteria; however, a consensus definition of LGAS has not yet been agreed on in the literature.2– 8
The LGAS definition used in this article was decided on for
2 reasons before performing the statistical analyses. First, if
PPM was found to have a detrimental effect at our chosen
LGAS definition, then it would likely result in at least
Low-Gradient Aortic Stenosis
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equivalent impact among LGAS patients with even lower
transvalvular gradients and more severe LV dysfunction.17
Second, our chosen definition allowed for sufficient sample
size to explore the impact of PPM in this relatively rare
clinical condition.
Potential Limitations
All patients in the study cohort had AS and underwent AVR.
However, many patients had concomitant coronary artery
disease, and it is therefore difficult to determine with certainty the foremost indication for surgery. Nevertheless, both
LGAS and no LGAS patient groups had mean preoperative
aortic valve areas within the severe range, indicating that
hemodynamically severe AS was present in these patients.
Preoperative dobutamine challenge during echocardiography
or cardiac catheterization was performed in a minority of our
patients and thus could not be incorporated in our outcome
models. Unsuspected demographic and selection factors
unique to this study cohort may have resulted in overfitted
statistical associations.
We examined the long-term outcomes of LGAS patients
who survived AVR to evaluate the impact of surgery and
PPM on heart failure symptoms and LV mass regression.
Perioperative outcomes were not examined because surgical
decision-making and confounding by indication may particularly bias operative mortality rates in patients with PPM.
Furthermore, a threshold of ⱕ0.85 cm2/m2 was chosen a priori as the definition of PPM. Lower thresholds have occasionally been used to quantify the severity of PPM (ie, severe
PPM defined as ⱕ0.65 cm2/m2) and higher 30-day mortality
rates have been reported in AS patients with severe PPM after
AVR.18
Conclusions
Patients with LGAS represent a small subset (⬇12%) of AS
patients requiring AVR. LGAS patients have a worse longterm survival and decreased freedom from CHF after AVR
compared with patients without LGAS. PPM in patients with
LGAS results in less LV mass regression after AVR and is an
important and potentially preventable independent risk factor
for both late mortality and CHF in this challenging subset of
AS patients.
Disclosures
None.
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of Prosthesis-Patient Mismatch
Alexander Kulik, Ian G. Burwash, Varun Kapila, Thierry G. Mesana and Marc Ruel
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Circulation. 2006;114:I-553-I-558
doi: 10.1161/CIRCULATIONAHA.105.001180
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