Download Impact of impaired myocardial deformations on exercise tolerance

European Journal of Echocardiography (2009) 10, 414–419
doi:10.1093/ejechocard/jen299
Impact of impaired myocardial deformations
on exercise tolerance and prognosis in patients
with asymptomatic aortic stenosis
Stéphane Lafitte1*, Matthieu Perlant1, Patricia Reant1, Karim Serri2, Herve Douard1,
Anthony DeMaria3, and Raymond Roudaut1
1
Cardiologic Hospital, Pessac and Bordeaux 2 University, France; 2Sacre Coeur Hospital, University of Montreal,
Montreal, Canada; and 3Division of Cardiology, University of California at San Diego, USA
Received 16 July 2008; accepted after revision 10 October 2008; online publish-ahead-of-print 7 November 2008
KEYWORDS
Aortic valvular stenosis;
Myocardial contractility;
Strain echocardiography;
Prognosis
Aims As assessed by tissue Doppler velocities, longitudinal contraction is commonly altered at an earlier
stage than radial contraction in patients with severe aortic stenosis (AS). However, its relationship to
exercise tolerance or to prognosis has not been clearly established. By using two-dimensional (2D) echocardiographic strain, we sought to evaluate values of deformation components in the setting of severe
AS and to correlate these values with exercise tolerance and with patients’ outcome.
Methods and results Sixty-five asymptomatic patients with severe AS (aortic valve area ,1 cm2) were
studied by echocardiography and exercise treadmill and were compared with controls. Conventional
echographic parameters as well as longitudinal, radial, and circumferential deformations by 2D strain
were measured at rest. During exercise treadmill, maximum tolerated workload, maximum heart
rate, blood pressure, and EKG ST variations were recorded. Patients were then followed during
12 months. Compared with controls, despite similar ejection fractions, AS patients presented with a
significantly lower global longitudinal strain (GLS) (217.8 + 3.5 vs. 221.1 + 1.8%, P , 0.05) more pronounced in the basal segments (BLS) (212.4 + 2.9 vs. 218.4 + 2.5%, P , 0.05). No difference was
observed in terms of radial or circumferential strains. In a subgroup of AS patients with abnormal
response to exercise, GLS and BLS were significantly lower (214.7 + 5.1 vs. 219.3 + 4.0% and
210.7 + 2.5 vs. 214.4 + 2.1%, P , 0.05). With cut-offs of 218 and 213%, GLS and BLS were able to
determine an inadequate exercise response with a sensitivity and specificity of 68 and 75% (AUC
0.77), and 77 and 83% (AUC 0.81), respectively. Finally, patients with a basal strain below 213% presented with more cardiac events in the follow-up.
Conclusion In asymptomatic patients with severe AS, impaired longitudinal contraction assessed by 2D
strain is associated with abnormal exercise response and with an increased risk of cardiac events during
follow-up.
Introduction
In patients with severe valvular aortic stenosis (AS), chronically increased afterload generates left ventricular (LV)
myocardial hypertrophy and interstitial fibrosis.1,2 Before
the appearance of symptoms, LV systolic function, as assessed
by ejection fraction (EF), seems to be preserved. However,
despite normal left ventricular ejection fraction (LVEF) and
* Corresponding author: Service des Echocardiographies, Hôpital Cardiologique Haut-Lévêque, Avenue Magellan, Pessac 33600, France.
Tel: þ33 5 57656565 ext. 56430.
E-mail address: [email protected]
fractional shortening with compensatory concentric hypertrophy, significant myocyte dysfunction may be present.3,4
The first demonstration of LV contraction component
dichotomy was observed by Dumesnil et al. 5 by using dedicated M-mode tracing analysis. Although EF, mainly dependent on radial contraction, was preserved in patients with
AS, a significant decrease in longitudinal contraction was
observed compared with controls. More recently, studies
based on tissue Doppler or strain techniques have confirmed
the opposite time course of different contraction components
again illustrating that consequences of pressure overload in
AS affect longitudinal deformation earlier than radial contraction.6–8 Moreover, these abnormalities in longitudinal
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2008.
For permissions please email: [email protected].
Myocardial strain and prognosis in aortic stenosis
contraction can be reversed after aortic valve replacement9
and have been shown to predict exercise tolerance in heart
failure10 and more recently in AS patients.11
Management of asymptomatic AS patients has benefited
from exercise testing which is now recommended in these
cases allowing the identification of signs of subclinical LV
dysfunction.12 However, exercise testing may not be feasible
in certain situations, particularly in elderly patients.
Using ‘speckle tracking’ strain for the analysis of myocardial deformation, we hypothesized that (i) longitudinal
impairment obtained by this technique could be correlated
to exercise capacity in AS patients and (ii) early alteration
of longitudinal deformation could be a marker of AS
evolution.
Methods
A total of 65 consecutive patients with asymptomatic AS referred for
exercise testing according to ACC/AHA practice guidelines12 were
prospectively included in our study. The mean age was 70 + 12
years. The following were the inclusion criteria: severe aortic
valve stenosis with an effective orifice area (EOA) ,1 cm2, normal
LV systolic function (defined by an EF .55% and no regional wall
motion abnormality), no more than mild aortic regurgitation, and
no other significant valve disease. Patients with known pulmonary
disease and coronary artery disease were excluded as well as
those with poor ultrasound windows. Patients were screened for
the presence of the following symptoms: dyspnoea on exertion,
syncope, discomfort, angina, dizziness, or palpitation. If any one
of these was present, patients were excluded so that only true
asymptomatic patients were selected.
The control group consisted of 60 normal subjects.
Echocardiographic measurements
Standard echocardiographic examinations were performed in all
patients totally blinded by a single experienced operator to the
results of the exercise treadmill and controls using a Vivid Seven
digital ultrasound system (GE Medical Systems). Three cardiac
cycles were stored in cineloop format for offline analysis. LV and
left atrial dimensions were measured according to ASE recommendations. LV mass was calculated using Devereux’s formula and
indexed for body-surface area and for height. LVEF was measured
using Simpson’s method. Diastolic function was evaluated by analysis of mitral Doppler inflow and tissue Doppler imaging (TDI) at the
lateral mitral annulus. Mitral regurgitation was evaluated according
to ASE recommendations.
Pulsed Doppler recordings were performed in the apical five- or
three-chamber view with the sample volume moved axially from
the level of the aortic annulus until a clear non-aliased signal was
obtained, usually 0.5–1 cm below the valve. The signal was traced
to obtain peak velocity, velocity time integral, and mean pressure
difference using the online software. Continuous wave recordings
were made from the apex and right intercostal positions, and the
optimal signal was traced to obtain peak velocity, velocity time
integral, and mean pressure difference using the online software.
Pulsed and continuous wave Doppler tracings were analysed
offline. The average of three signals was taken. EOA (in square
centimetres) was calculated by the continuity equation.
Strain measurements
The LV was divided into 16 segments and each segment individually
analysed. Using a dedicated software package (EchoPac PC, GE),
two-dimensional (2D) strain was measured as described previously.13
2D strain is a non-Doppler-based method to evaluate systolic strain
from standard bidimensional acquisitions. By tracing the endocardial contour on an end-systolic frame, the software automatically
415
tracks the contour on subsequent frames. Adequate tracking can
be verified in real-time and corrected, by adjusting the region of
interest or manually correcting the contour, to ensure optimal
tracking.
Two-dimensional longitudinal and transverse strains were
assessed in apical views, and circumferential and radial strain in
short-axis view at the basal level. Transverse and radial strains
both represent radial deformation during systole; however, being
obtained from different echocardiographic views, they were analysed separately. Average longitudinal and transverse strains were
calculated for the 16 segments, and average circumferential and
radial strains for the 6 mid-LV segments. Global longitudinal strain
(GLS) was the average of longitudinal strains from the three apical
views.
For longitudinal and transverse strains, analysis was also performed according to LV segments (six basal, six mid-LV, and four
apical). The basal ventricular septum was analysed separately and
compared with other basal LV segments.
Two-dimensional longitudinal strain was measured on three consecutive cycles by analysing bidimensional acquisitions.
Comparison between TDI and speckle strains was not performed in
this study since such analysis has been published previously.13
Exercise testing
Exercise testing was performed with standard treadmill device
(Quinton, WA, USA) using a Bruce protocol modified by two
warm-up stages. Subjects were questioned for symptoms every
2 min and the heart rate, blood pressure, and a 12-lead electrocardiogram were recorded at baseline, at the end of each stage, and at
peak exercise.
The test was defined as positive if it was stopped prematurely
because of limiting breathlessness/chest discomfort or dizziness.
Other predetermined criteria for cessation were ST segment
depression of .2 mm measured 80 ms after the J point, more
than three consecutive ventricular premature beats, and hypotension (defined as a fall in systolic blood pressure of .20 mmHg
from baseline).14 Otherwise, the test was continued to the
maximum tolerated workload.
Total exercise time in seconds and maximum ST depression in
millimetres in a single lead at 80 ms after the J point during the
test were recorded. ST depression 2 mm in at least one lead was
considered significant. Abnormal blood pressure response was
defined as a systolic blood pressure at peak exercise either the
same as or below the baseline level.
Follow-up
Independently of the protocol, patients were managed based on
echo and exercise EKG findings. They were reassessed for symptoms
at 12 months. The following data were collected: re-hospitalization
for any cardiac cause, aortic valve surgery, cardiovascular death
within 12 months and were associated for a unique composite
criteria.
Reproducibility
The studies were analysed offline by a second blinded observer for
10 patients, corresponding to 160 (longitudinal and transverse
strains) and 60 segments analysed (radial and circumferential
strains). Intra-observer variability was calculated by the average
difference between the 10 measurements realized. Inter-observer
variability was calculated as the absolute difference divided by
the average of the two observations for all parameters.
Statistical analysis
Results are shown as mean + SD. Data were analysed with Stat-EL
software. The two-sided paired t-test and ANOVA tests were used
to compare patients and controls. After testing the Gaussian
416
repartition of our data set, normal range of strain values and cut-off
were defined by the average minus two SDs in a global and segmental analysis. This allowed identification of two different profiles of
AS patients.
ROC analysis was also performed in order to determine strain
cut-off values in predicting abnormal response on exercise testing.
Individual echocardiographic variables were tested for the ability
to predict symptom onset within 12 months by univariate analysis.
After separating patients based on strain cut-off values, event-free
survival was demonstrated using the Kaplan–Meier life table and
compared with the log-rank test. A significance level of 0.05 was
used for comparison.
Results
Patient’s characteristics
Five patients were excluded due to inadequate ultrasound
windows. Characteristics for all remaining 60 patients and
60 controls are shown in Table 1. Despite the presence of
severe stenosis (mean gradient .54 mmHg), EF in AS patients
was comparable to controls. LV mass and LV thickness were
significantly higher in AS patients. As previously observed,
S’ TDI was lower in AS patients compared with controls.
All patients completed a satisfactory treadmill exercise
test. There were no severe adverse events during exercise
testing. Forty-six per cent of the patients reached the
target heart rate. Exercise heart rate, systolic, and diastolic
blood pressures were 117 + 20, 176 + 25 mmHg, 83 +
16 mmHg, respectively. Thirty-seven per cent of the
patients stopped because of limiting symptoms, 35% had
an abnormal blood pressure response, and 13% presented
significant EKG ST depressions. Finally, 65% of our patients
presented with an abnormal exercise profile.
Strain analysis
Inter- and intra-observer variabilities in strain measurements are shown in Table 2. Values of global strains in AS
patients were 217.8 + 3.5, 222 + 4.9, and þ36.5 +
16.3% for longitudinal, circumferential, and radial components, respectively. For longitudinal strain, a significant
difference was observed between apical and basal strains
(223.9 + 4.9 vs. 212.4 + 2.9%, P , 0.001) (Figure 1). Compared with controls, longitudinal strain was significantly lower
in AS patients (217.8 + 3.5 vs. 221.1 + 1.8%, P , 0.05),
whereas no difference was observed for the circumferential
and radial components. Segmental analysis revealed that
only basal segments had decreased longitudinal strain
compared with controls (212.4 + 2.9 vs. 218.4 + 2.5%,
P , 0.05). Neither apical nor mid segments were significantly different in terms of strain.
No significant relation was observed between any strain
component and morphological measurements of left ventricle (i.e. LV thickness, LV mass, EF, etc.) or AS severity.
From the Gaussian repartition of the normal population,
cut-off values of 218 and 213% were calculated for
global and basal strains. Based on these values, 57 and
64% of the AS patients were classified with an abnormal
strain pattern, respectively. Basal strain below j213j% was
associated with more severe AS (0.59 + 0.18 vs. 0.73 +
0.18 cm2, 0.31 + 0.09 vs. 0.43 + 0.17 cm2/m2, P , 0.05).
Stroke volume was also significantly lower in this subgroup,
when compared with AS patients with normal basal strain
(57.3 + 33 vs. 74 + 16 mL, P , 0.05). However, no
S. Lafitte et al.
Table 1 Global and echocardiographic characteristics of AS
patients and controls
Age (years)
Sex (M/F)
Body-surface area (m2)
Systolic blood pressure
(mmHg)
Diastolic blood pressure
(mmHg)
Heart rate (beats/min)
Medical treatment
Beta-blockers
Diuretic
Calcium inhibitor
ACE
Angiotensin antagonist
Echocardiography
LV EDD (mm)
LV ESD (mm)
IVST (mm)
PWT (mm)
LVFS (%)
Mass index (g/m2)
LV diastolic volume
LV systolic volume
Ejection fraction (%)
Pulmonary pressure
(mmHg)
ERO (PISA) (mm2)
Left atrial area
(cm2)
LVOT VTI (cm)
LVOT diameter (mm)
E/A
Dec. Time (ms)
E/E0
S0 (TDI)
Max aortic velocity
(cm/s)
Mean aortic gradient
(mm/Hg)
EOA (cm2)
Indexed EOA (cm2/m2)
BNP (pg/mL)
AS patients
Controls
70 + 12
49/11
1.85 + 0.18
142 + 22
66 + 15
45/15
1.81 + 0.15
139 + 16
ns
71 + 12
78 + 19
ns
66 + 9
70 + 12
ns
43 + 5
27 + 4
13 + 3
12 + 2
35 + 8
117 + 28
90 + 11
31 + 8
64 + 7
38 + 8
41 + 6
26 + 4
10 + 2
9+3
36 + 7
91 + 15
95 + 13
32 + 10
66 + 5
25 + 6
ns
ns
ns
ns
ns
P , 0.05
ns
ns
ns
P , 0.05
0.04 + 0.02
23 + 6
0.02 + 0.01
18 + 4
ns
P , 0.05
23 + 6
19 + 2
0.80 + 0.25
282 + 93
10 + 2
9+3
4.4 + 0.6
21 + 4
21 + 3
0.98 + 0.13
210 + 59
8+3
12 + 3
1.2 + 0.2
ns
ns
P , 0.05
P , 0.05
ns
P , 0.05
P , 0.05
54 + 15
9+2
P , 0.05
0.7 + 0.2
0.4 + 0.2
381 + 559
3.4 + 0.5
2.1 + 0.2
P , 0.05
P , 0.05
ns
ns
15%
31%
20%
61%
28%
LV EDD, left ventricular end-diastolic diameter; ESD, end-systolic diameter; IVST, inter-ventricular septal thickness; PWT, posterior wall thickness; FS, fractional shortening; LVOT, left ventricular outflow track; EOA,
effective orifice area.
significant difference was observed between AS patients
with basal strain values below and above cut-offs for EF,
LV mass, and wall thickness.
Strain and exercise treadmill
Comparing patients with and without symptoms-limited
exercise, we found a significant difference in terms of GLS
and BLS (214.2 + 4.1 vs. 219.6 + 3.1% and 211.0 + 2.0
vs. 214.1 + 2.4%). In patients with an abnormal blood
pressure elevation, GLS and BLS were also significantly
lower than in patients with a normal haemodynamic
profile (215.1 + 5.6 vs. 219.0 + 4.2% and 210.1 + 2.2
Myocardial strain and prognosis in aortic stenosis
417
Table 2 Values of inter- and intra-observer variabilities
Variabilities
Intra-observer
Inter-observer
Longitudinal strain (%)
Radial strain (%)
Circonferential strain (%)
7.9
14.1
10.4
8.5
16.0
11.9
Figure 2 ROC curves showing relation between global and basal
longitudinal strains and exercise tolerance during treadmill test.
Values of 218 and 213% for global and basal longitudinal strains
were associated with high level of sensitivity and specificity to
predict abnormal profile during exercise in patients with AS.
GLS and BLS values of 218 and 213% were associated
with a sensitivity and specificity of 68 and 75%, and 77 and
83%, respectively, in predicting an abnormal exercise
response (Figure 2).
Strain and clinical outcome
Figure 1 Top panel: Global longitudinal, radial, and circumferential strain values as well as apical and basal longitudinal strains
for AS patients and controls (long global, global longitudinal
strain; long basal, basal longitudinal strain; long apex, apical longitudinal strain; circumf, circumferential). Bottom panel: Values of
segmental longitudinal strains (SA, septo-apical; LA, latero-apical;
ISM, inferosepto median; ALM, anterolatero media; ISB, inferosepto
basal; ALB, anterolatero basal). Only basal segments were different
between patients and controls.
vs. 214.9 + 2.0%). No significant difference was observed
for other strain components. When assessing patients with
positive EKGs, only basal strain was lower in patients with
an abnormal pattern (211.1 + 2.3 vs. 214.2 + 1.9%).
By combining all positive exercise criteria, significant
differences were observed for both GLS and BLS but not
for other components (214.7 + 5.1 vs. 219.3 + 4.0% and
210.7 + 2.5 vs. 214.4 + 2.1%).
When focusing on patient subgroups with normal or abnormal strain values, contingence tables demonstrated significant relations between these subgroups and patients with
abnormal exercise response (P , 0.01).
Finally, an ROC analysis was performed in order to determine best strain values for predicting exercise tolerance.
All 60 patients were assessed in terms of clinical outcome at
12 months. Forty-two patients (70%) had aortic valve replacement during the follow-up period. In the remaining 18
patients (30%), 2 cardiovascular deaths and 5 non-lethal cardiovascular events were reported (3 heart failures and 2
atrial fibrillations). Subgroup analysis of non-operated
patients demonstrated a significant relation between basal
strain and cardiac events without any event in patients
with basal strain above 213% (P , 0.05).
Figure 3 depicts Kaplan–Meier curves of outcome in subgroups of patients with basal strain above and below
213%, illustrating significantly better outcome of patients
with basal strain above j213j% (P , 0.01), showing the
impact of strain on prognosis. When using GLS, differentiation between the two subgroups was less significant
than with basal strain parameter.
Discussion
Our results demonstrate that (i) despite normal EF, contractility is altered in AS as measured by 2D strain, (ii) impaired
contractility is associated with an abnormal exercise profile
in asymptomatic AS patients (Figure 4), and (iii) reduced
longitudinal strain is a marker of cardiovascular event in
this population.
418
Figure 3 Kaplan–Meier curves of event-free survival in AS patients
with basal strains below and above 213%.
S. Lafitte et al.
the identification of abnormal longitudinal contractility.
Interestingly, the normal values reported in this first study
are similar to those we obtained with the 2D strain technique. However, longitudinal strain in those original patients
with AS was lower than in our population (213 vs. 218%)
probably due to more severe stenoses as suggested by
higher transvalvular gradients. More recently, subclinical
LV systolic dysfunction was demonstrated by TDI in patients
with AS despite normal EF. Displacement and deformation of
some LV segments were significantly decreased as well.15,16
The progressive accumulation of interstitial collagen in the
hypertrophied LV, in parallel with an increase in heart
weight, contributes to a spectrum of regional ventricular
dysfunction involving either diastole or systole. Longitudinal
abnormalities were also observed by Poulsen et al.4 As we
found, no relation was found between mean longitudinal
strain and aortic peak gradient, mean gradient, or systolic
blood pressure. The pressure overload itself does not
appear to directly influence longitudinal systolic function
in AS. As expected, a significant relation was found
between strain and measures of LV global systolic function
such as LVEF and LV end-systolic volume.
More specifically, our study described longitudinal strain
in different segments identifying significantly decreased
strain in the basal segments compared with the apex.
Beyond the hypothesis of altered perfusion in subendocardial layers generating impaired longitudinal deformation,
the impact of myocyte architecture and timing of contraction in the long axis could play a role. It has been recently
shown that longitudinal contraction occurs earlier at the
apex than in the basal part of the heart, which ends its longitudinal contraction later, after aortic valve closure.17
Because of the progressive rise in intraventricular pressure
during isovolumic contraction in AS, one hypothesis is that
this dynamic increase in afterload becomes deleterious by
increasing wall stress in the basal segments more than at
the apex. Preserved radial and circumferential strains are
mainly explained by the fact that these deformation components stem from circumferential fibres localized in the
mid-wall. One could hypothesize that these fibres are less
sensitive to micro-ischaemia and can adapt to the afterload
increase by hypertrophy as a compensatory mechanism.
Finally, the reason why radial strain is not significantly
higher than controls in our study is probably due to the
lack of robustness of radial strain measurements combined
to the insufficient number of patients compared with
radial strain variability.
Two-dimensional strain and exercise
tolerance/prognosis
Figure 4 Two examples of AS patients, one (top) with high values
of strains and normal exercise profile, and one (bottom) with low
values of strains and drop in systolic blood pressure at 50 W stage.
Contractility in aortic stenosis patients
Alteration of LV performance due to increased afterload was
described three decades ago, particularly in the setting of
AS.5 Using M-mode recordings combined with a complex
mathematical model, dissociation between function in the
transverse and longitudinal planes was demonstrated with
The relationship between longitudinal shortening and symptoms has been described by Tongue et al.6 showing that
longitudinal shortening is more closely associated with
changes in symptomatic status than other indices of systolic
function, even in patients with normal EFs. Exercise
capacity tests have shown that abnormal responses to exercise in asymptomatic AS patients are mediated by a larger
increase in mean transaortic pressure gradient and/or a
limited contractile reserve characterized by an inadequate
increase in EF during exercise.18,19 This was also observed
by Marechaux et al.20 It is now acknowledged that exercise
tolerance is an important risk predictor for asymptomatic AS
Myocardial strain and prognosis in aortic stenosis
patients.21 Our study demonstrates that basal strain is
closely related to exercise tolerance in these patients. As
expected, we also observed a relation between basal
strain and global cardiac events at 12 months, showing the
inadequacy of EF in identifying patients at risk at an early
stage. We based our analysis on a speckle tracking method
which was validated several times in our institution.13 2D
strain is more accurate and reproducible than TDI strain
and can be applied with a high level of feasibility in AS
patients.
Limitations
The relatively limited number of patients is one of the limitations of our study. However, differences between patients
and controls appeared to be highly significant, as well as
in subgroup analysis.
A second limitation is the high level of abnormal exercise
responses in our population (.70%) probably reflecting the
fact that our institution is a reference centre for the management of such patients. Subsequently, we observed a
higher rate of events, including aortic valve surgery,
during follow-up compared with other studies. However,
this issue does not decrease the impact of our findings
since exercise and prognosis in AS patients are closely
related and, based on our results, with longitudinal strain
as well.
The last limitation concerns the technical approach used
in this study. As suggested by the reproducibility analysis,
it is likely that circumferential and radial strains present a
variability .10% which could limit routine clinical use.
This is likely explained by the fact that speckle tracking
analysis is not ideal for short-axis acquisitions. However,
our main results are based on longitudinal strains, which
are much more reliable than other strains components.
Conclusion
Identification of high-risk patients with AS is possible by
‘speckle tracking’ strain analysis, whereas no evidence of
LV dysfunction is observed by conventional measures.
Although classified as asymptomatic, these patients
present with an impaired exercise capacity and require surgical management more frequently than patients with
normal strain measurements. Although requiring confirmatory studies on a larger patient population, our findings
can already be applied in asymptomatic patients with AS
for whom exercise testing is not achievable.
Conflict of interest: none declared.
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