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* From the From the Heart Institute (Drs. Schwammenthal, Vered, Rabinowitz, and Feinberg) and the Department of Cardiac Surgery (Drs. Moshkowitz, Ziskind, and Smolinski), Chaim Sheba Medical Center, Tel Hashomer, Israel, and the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
Correspondence to: Ehud Schwammenthal, MD, Heart Institute, Sheba Medical Center, Tel Hashomer 52621, Israel; e-mail: sehud{at}post.tau.ac.il
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Patients and measurements: Twenty-four patients with aortic stenosis and LV dysfunction (mean ejection fraction, 28%; New York Heart Association class, II to IV) were studied by dobutamine echocardiography assessing mean pressure gradient, aortic valve area, and aortic valve resistance. Patients were prospectively divided into severe and nonsevere aortic stenosis groups according to the response of the valve area to the augmentation of systolic flow. The clinical decision was considered to be concordant with the results of dobutamine echocardiography, when patients with severe aortic stenosis and preserved contractile function were referred by a specialist for aortic valve replacement and when patients with nonsevere aortic stenosis were not. Patients were observed for up to 3 years.
Results: All eight patients with severe
aortic stenosis who were referred for surgery survived and had good
cardiovascular outcomes, and six of eight patients who were not
initially referred for surgery had poor outcomes, including heart
failure and sudden cardiac death. The eight patients with nonsevere
aortic stenosis did comparatively well without valve replacement.
Cardiac death or pulmonary edema occurred in 4 of 16 patients (25%)
when the clinical decision was concordant with the results of the
dobutamine echocardiogram and occurred in 6 of 8 patients (75%) when
the clinical decision was discordant (p = 0.019 [
2
test]).
Conclusion: Patients with aortic stenosis, LV dysfunction, and relatively low gradients have better outcomes when management decisions are based on the results of dobutamine echocardiograms. Those patients identified as having severe aortic stenosis and preserved contractile reserve by dobutamine echocardiography should undergo surgery, while patients identified as having nonsevere aortic stenosis can be managed conservatively.
Key Words: aortic stenosis • dobutamine echocardiography • left ventricular dysfunction
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Therefore, we prospectively addressed the question of whether the assessment of valvular hemodynamics and myocardial function during low-dose dobutamine infusion can guide decision making about patients with aortic stenosis and LV dysfunction, and whether it can predict outcome as a function of management strategy. In particular, we hypothesized that patients with relatively low transvalvular gradients who have been identified as having severe aortic stenosis and preserved contractile reserve by dobutamine echocardiography would have better outcomes when undergoing surgery and that patients identified as having nonsevere aortic stenosis by dobutamine echocardiography could be managed conservatively. In addition, we sought to identify whether a hemodynamic parameter exists that can distinguish between severe and nonsevere aortic stenosis in patients with LV dysfunction at baseline.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Measurements
Stroke volume was calculated as the LV outflow tract area
multiplied by the time-velocity integral of the outflow tract velocity
(pulsed-wave Doppler). For the assessment of the LV outflow tract area,
outflow tract diameter (D) was measured from a zoomed systolic
freeze-frame in the parasternal long-axis view as the distance between
the insertion points of the aortic cusps. Outflow tract area then was
calculated as D2
/4. Systolic flow was
calculated as aortic stroke volume divided by systolic ejection time.
The mean pressure gradient was determined from the continuous-wave
Doppler signal using the modified Bernoulli equation. Aortic valve area
was calculated by the continuity equation as outflow tract area times
the ratio of the time-velocity integrals of outflow tract and stenotic
orifice Doppler signals.18
19
Aortic valve resistance was
calculated from the ratio of mean gradient and systolic flow (times
1.33 to convert millimeters of mercury to dynes per second per
square centimeter).15
20
21
22
23
The measurements were repeated during dobutamine infusion. Because the LV outflow tract area has been shown to remain constant during flow changes both in normal subjects 24 25 and in patients with valve disease,26 the resting value of LV outflow tract area was used to calculate stroke volume both at rest and during dobutamine infusion. Thus, changes in stroke volume, systolic flow, and aortic valve area could be assessed as intraindividual changes of the ratio of time-velocity integrals, eliminating the confounding influence of two different outflow tract measurements (squared in the calculation) on the comparison of rest and peak dobutamine values.
Definitions
Aortic Stenosis Severity:
Aortic stenosis was defined as
severe when the augmentation of systolic flow caused by the dobutamine
infusion was paralleled by an increase in the maximal orifice velocity
on the continuous-wave Doppler signal, so that the calculated aortic
valve area did not increase by > 0.29
cm216
27
and remained < 1.0
cm2.15
27
Aortic stenosis was defined as
nonsevere when systolic flow increased more than the maximal orifice
velocity, because the effective aortic valve area had increased by at
least 0.3 cm216
27
to at least 1.0
cm2.15
27
Contractile Reserve:
Contractile reserve was defined
as being preserved when the systolic flow could be increased by
> 20% of the baseline values (requiring at least the preservation of
stroke volume as the ejection time decreases during dobutamine
infusion).
Concordant and Discordant Clinical Decision:
Applying the
above-mentioned criteria, dobutamine echocardiography identified 16 of
the 24 patients as having severe aortic stenosis and 8 of the patients
as having nonsevere aortic stenosis (Fig 1 ). The clinical decision of the referring physician (who would
have knowledge of the test results) was defined as being concordant
with the result of the dobutamine echocardiogram in patients with
severe aortic stenosis who were referred for aortic valve replacement
and in patients with nonsevere aortic stenosis who were not referred
for aortic valve replacement. The clinical decision of the referring
physician was defined as discordant with the test result in patients
who were initially not referred for surgery despite severe aortic
stenosis or in patients who were referred for surgery despite having
nonsevere aortic stenosis. In all patients who were reported as
having nonsevere aortic stenosis, the treating cardiologist decided
against aortic valve replacement (including one patient who underwent
coronary artery bypass grafting). Half of the patients who were
reported to have severe aortic stenosis were directly referred for
aortic valve replacement (in three cases, this was combined with
coronary artery bypass grafting), whereas half of the patients were
initially managed conservatively because the comorbidity was
considered to be prohibitive by the referring physician. Thus, the
clinical decision was concordant with the result of the dobutamine
echocardiography in 16 patients and was discordant in 8 patients.
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Statistical Analysis
Results were expressed as the mean ± SD. Comparisons of
proportions between groups were made using the
2 test, and a p value of < 0.05 was
considered to be significant. Differences between groups in hemodynamic
parameters were explored by unpaired two-way comparisons (Student’s
t test), and changes of hemodynamic parameters during
dobutamine infusion were tested for significance by a paired two-tailed
Student’s t test. In order to account for multiple
comparisons applying the same type of test, the p value indicating
statistical significance was conservatively set at p < 0.01
(Bonferroni correction).
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Valvular Hemodynamics
Systolic flow at baseline was similar in patients with severe and
nonsevere aortic stenosis (164 ± 26 mL/s vs 178 ± 33 mL/s,
respectively; not significant [NS]) (Fig 2
and 3
, Table 2
). During dobutamine infusion, systolic flow increased
significantly (p < 0.000001 and p < 0.0001, respectively)
in both groups (248 ± 58 vs 285 mL/s, respectively; NS). The mean
pressure gradient at baseline was 31 ± 10 mm Hg in patients with
severe aortic stenosis (27 ± 4 mm Hg without the two patients with
resting pressure gradients of > 35 mm Hg who were referred for
assessment of contractile reserve) and 24 ± 6 mm Hg in patients with
nonsevere aortic stenosis (p = 0.09; NS). The mean pressure
gradient increased significantly to 46 ± 12 mm Hg in patients with
severe aortic stenosis (p < 0.000002) and to 33 ± 9 mm Hg
in patients with nonsevere aortic stenosis (p < 0.005). The
difference between the mean gradients during dobutamine infusion in
both groups (p = 0.011; NS) was of marginal significance at the
conservatively set threshold. The mean aortic valve area at baseline
was 0.65 ± 0.1 cm2 in patients with severe
aortic stenosis (0.69 ± 0.1 cm2 without the
two patients with gradients of > 35 mm Hg) and 0.76 ± 0.1
cm2 in patients with nonsevere aortic stenosis
(p = 0.047; NS). The aortic valve area increased significantly to
1.11 ± 0.08 cm2 in patients with nonsevere
aortic stenosis (p < 0.00001), and to 0.75 ± 0.15
cm2 in patients with severe aortic stenosis
(p < 0.000001).
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Outcome
Follow-up was completed in all patients during an observational
period of up to 36 months (mean, 17 ± 10 months). The individual
courses of the patients during follow-up are detailed in Table 1
.
All patients with severe aortic stenosis who were referred for aortic valve replacement survived surgery and virtually all of them experienced symptomatic benefits. One patient had a minor perioperative stroke from which he completely recovered; the same patient had transient pulmonary edema after inadvertently stopping treatment with his heart failure medication. Two patients died during follow-up. One patient who had mild pancytopenia preoperatively developed leukopenia and sepsis without clinical or echocardiographic evidence of endocarditis after a follow-up period of 17 months and died. One physically active 87-year-old patient with a low-grade lymphoma who became asymptomatic following aortic valve replacement and continued to work in the store he owned died from pneumonia after a follow-up period of 30 months.
Patients with severe aortic stenosis who were initially not referred to aortic valve replacement had poor outcomes. Two patients died from heart failure after 3 months and 7 months, and one died suddenly after 9 months. Three patients had recurrent episodes of pulmonary edema and worsening of heart failure; two of them ultimately were referred for aortic valve replacement (both patients survived surgery and improved clinically). Only two patients remained in fairly stable condition.
Patients with nonsevere aortic stenosis were treated conservatively except for one patient who underwent coronary artery bypass grafting (without concomitant aortic valve replacement). One patient with diffuse coronary artery disease (which was not suitable for revascularization) died while under local anesthesia for a minor surgical procedure after a follow-up period of 6 months, and one patient was admitted to the hospital for severe unstable angina with cardiogenic shock after 3 months, underwent unsuccessful emergency angioplasty of a left anterior descending artery stenosis, and died. One patient was admitted to the hospital for pulmonary edema during an episode of paroxysmal atrial fibrillation with rapid ventricular response.
In the 10 patients who ultimately underwent aortic valve replacement,
the mean pressure gradient across the aortic prosthesis was 17 ± 9
mm Hg (median, 13 mm Hg) at the first follow-up and 16 ± 8 mm Hg
(median, 15 mm Hg) at the second follow-up. This represents a decrease
in the pressure gradient of 50% (mean, 32 ± 17 mm Hg; median, 28 mm
Hg) despite the postoperative increase in the LV ejection fraction
(Table 1)
. During the first year of follow-up, both the first combined
end point (ie, cardiac death or pulmonary edema) and the
second combined end point (ie, all-cause death or pulmonary
edema) occurred in 3 of the 16 patients (19%) in whom the clinical
decision was concordant with the result of the dobutamine
echocardiography, and in 6 of 8 patients (75%) when it was discordant
(p = 0.0073 [2]). In the group of patients
for whom the clinical decision was discordant with the dobutamine
study, all end points occurred during the first year (average, 7 ± 2
months; range, 3 to 11 months), and all deaths were cardiovascular in
origin.
During the complete study period, the first combined end point
(ie, cardiac death or pulmonary edema) occurred in 4 of 16
patients (25%) in whom the clinical decision was concordant with the
result of the dobutamine echocardiography, and in 6 of 8 patients
(75%) when it was discordant (p = 0.019
[2]). The second combined end point
(ie, all-cause death or pulmonary edema) occurred in 6 of 16
patients (37%) in whom the clinical decision was concordant with the
result of the dobutamine echocardiography and in 6 of 8 patients (75%)
when it was discordant (p = 0.083 [2]).
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The present study demonstrates that dobutamine echocardiography can answer the following two fundamental questions for decision making in these patients: (1) is there severe aortic stenosis with a low gradient resulting from low cardiac output across a severely stenotic valve, or is there nonsevere aortic stenosis with a small calculated aortic valve area reflecting low cardiac output in LV dysfunction unrelated to valvular disease?; and (2) is there sufficient myocardial (contractile) reserve to indicate a potential benefit and a reasonable perioperative risk that justify surgery? Therefore, the assessment of valvular hemodynamics and myocardial function during a low-dose dobutamine infusion lasting 9 to 12 min can predict the outcomes of these patients with different management strategies.
Outcome
To our knowledge, this is the first study of patients with aortic
stenosis, LV dysfunction, and relatively low pressure gradients that
demonstrates a better outcome when management decisions are based on
the result of a dobutamine echocardiogram. In contrast to previous
data,16
17
the present study prospectively followed three
arms of management decisions, as follows: surgery for patients
identified as having severe aortic stenosis; medical therapy in
patients identified as having severe stenosis, but not referred to
surgery; and medical therapy in patients identified as having nonsevere
aortic stenosis and LV dysfunction that is unrelated to valvular
disease. Patients with severe aortic stenosis did extraordinarily well
when undergoing surgery (despite the fact that almost all of them had
previously experienced myocardial infarctions), particularly
considering the poor outcome of patients with severe congestive heart
failure without correctable cause. In the long run, these patients then
were limited by comorbidity. Not less important is the fact that
patients with severe aortic stenosis who were not considered to be
surgical candidates because of significant comorbidity had a low
event-free survival rate with a prognosis limited by their cardiac
disease and not by the comorbid factors. Two of these patients, one of
them with severe lung disease and morbid obesity, ultimately underwent
aortic valve replacement for severe progressive symptoms and are alive
and well (the patient with morbid obesity, who previously was severely
limited, was able to increase his physical activity, to reduce his
weight significantly, and thus also to improve his respiratory
condition). In the 10 patients who ultimately underwent aortic valve
replacement, the mean pressure gradient across the aortic prosthesis
was 16 ± 8 mm Hg (median, 15 mm Hg), which represents a decrease in
the pressure gradient of 50% (from 32 ± 17 mm Hg; median, 28 mm Hg)
despite the postoperative increase in LV ejection fraction (Table 1)
.
This further corroborates the hemodynamic benefit of aortic valve
replacement in this patient group and the validity of the selection
criteria. Considering their low ejection fractions, patients identified
as having nonsevere aortic stenosis did comparably well without
undergoing aortic valve replacement. This includes one patient who
underwent coronary artery bypass surgery without valvular intervention
as a result of the findings on the dobutamine echocardiography
test. This patient group seemed to be limited mainly by coronary events
(Table 1) . It must be emphasized that all of the patients studied in
this series, both the surgical candidates as well the conservatively
treated patients, had preserved contractile reserves. The results of
the study therefore cannot be applied to patients lacking improvement
of LV function during low-dose dobutamine infusion.16
Criteria
Contractile reserve was defined as the ability to increase
transvalvular flow and was not defined by an improvement in wall motion
score or measured ejection fraction. This has both theoretical and
practical advantages. In contrast to measuring the ejection fraction,
the accuracy of assessing systolic flow is not influenced by the degree
of geometric distortion of the LV shape following myocardial
infarction. In contrast to wall motion score, improvement in systolic
flow does not necessarily require the improvement of segments with
abnormal wall motion at rest (ie, evidence of regional
viability). Thus, patients who can improve their global LV function,
even if this is achieved primarily by an increase in the
contractility of normal segments, are still correctly categorized as
having the ability to hemodynamically adapt to increased stress. For
practical purposes, the assessment of systolic flow does not require
any additional measurement, so that all relevant parameters
(ie, mean gradient, systolic flow, aortic valve area, and
resistance) can be obtained from the three following recordings: a
pulsed-wave Doppler signal of the outflow tract velocity; a
continuous-wave Doppler signal of the maximal stenotic orifice
velocity; and a two-dimensional systolic frame for the assessment of
the outflow tract diameter.
Aortic Stenosis Severity: The following two criteria have been
proposed to distinguish between patients with severe and nonsevere
aortic stenosis who have LV dysfunction: the presence or absence of
significant flow variations during dobutamine infusion16
;
and the achievement of an absolute cutoff value for the aortic valve
area during pharmacologic intervention.15
We used a
combination of both criteria to determine the severity of aortic
stenosis. Only when both criteria were concordant was the
categorization of patients as severe and nonsevere considered to be
conclusive for suggesting a management recommendation, which was the
case for all patients.
Mechanism and Physiology
The following three possible mechanisms have been proposed to
explain the observed variation of the calculated aortic valve area: (1)
variation of the coefficient of contraction with flow leading to a
decrease in the effective valve area at low flow states despite an
essentially unchanged anatomic valve area8
9
14
28
29
; (2)
variation of the anatomic valve area itself29
30
31
; and (3)
variation of the velocity flow profile across the orifice with flow,
changing from flat to parabolic as the flow rate decreases due to
viscous effects at the edges of the vena contracta.32
Therefore, continuous-wave Doppler echocardiographic measurements
of the peak flow velocity (the central velocity vector in the
parabolic profile) may overestimate the average velocity across the
orifice and, thus, underestimate the valve area at low flow rates.
The present study does not answer the question of which of the three proposed explanations for the flow variation of the aortic valve area is true, but it provides a solution for each case. No matter what the cause for the small orifice area at a low flow rate, the recalculation of the orifice area at an augmented flow rate during dobutamine infusion will definitely clarify whether aortic stenosis is severe or not and at the same time will provide information about the contractile reserve of the LV. Correspondingly, no matter what the cause for the larger orifice area during dobutamine infusion, it can explain why these patients do comparatively well when treated conservatively. If an observed increase in the calculated aortic valve area represents a true increase in the effective valve area, then such patients are likely to increase their effective valve area also during normal daily physical activity,33 preventing the excessive increase in LV afterload that may occur in patients with a fixed aortic valve area during exercise. Of interest, in a prospective study33 of outcomes in individuals with asymptomatic aortic stenosis, patients with an end point (death or aortic valve surgery) showed smaller increases in valve area during exercise while undergoing the initial stress echocardiogram. However, if the observed increase results from the underestimation of valve area at baseline, then valve area calculated at a higher flow rate will simply reflect more accurately the lesser severity of the stenosis.
Baseline Parameters
Figure 3
demonstrates the complete overlap of values for the mean
gradient in patients with severe and nonsevere aortic stenosis.
Substantial overlap is also present for the values of the aortic valve
area. All patients with an aortic valve area of < 0.65
cm2 had severe aortic stenosis; however, given
the flow dependence of the aortic valve area in patients from both
groups (Fig 2
, Table 2
), this cutoff value must be a function of the
severity of LV dysfunction in the examined patient group and,
therefore, cannot be constant for different groups of patients. In
fact, Carabello et al34
reported the presence of nonsevere
stenosis or "pseudostenosis" of the aortic valve in a patient with
a baseline aortic valve area as low as 0.6 cm2.
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Limitations and Comparisons With Other Studies
The present study prospectively examined the course of 24 patients
with aortic stenosis and LV dysfunction, of whom 10 ultimately
underwent aortic valve replacement, over a follow-up period of up to 3
years. The size of the study group necessarily reflects the limitations
of a single-center experience. In a feasibility and safety survey
published in 1998,35
it took 6 years to accumulate the
experience of 27 dobutamine studies in this patient group. Only seven
patients underwent surgery, and no attempt was made to define the
criteria of distinction between severe and nonsevere aortic stenosis in
order to correlate test results with follow-up data.35
In
fact, the recommendation to consider pharmacologic testing in patients
with low gradient stenosis and LV dysfunction in order to identify true
anatomically severe aortic stenosis, as published in 1998 in the
American College of Cardiology/American Heart Association practice
guidelines for the management of patients with valvular heart
disease,37
is (to the best of our knowledge) based on only
two published reports providing data on outcome: one retrospective
study15
that used nitroprusside administration during
cardiac catheterization in 7 patients, 3 of whom underwent surgery; and
one report16
on 18 patients studied by dobutamine
echocardiography, only 4 of whom underwent aortic valve replacement.
The paucity of published data reflects the difficulty in conducting a
controlled study in a group of patients with considerable cardiac
and noncardiac morbidity and different comorbid factors influencing
therapeutic considerations. The variation in comorbid factors and
clinical profiles remains a limitation when comparing the clinical
course of different subgroups. Nevertheless, the present study confirms
the pathophysiologic concept outlined in the two cited studies in a
prospective manner, further supporting the recommendations of the
American College of Cardiology/American Heart Association practice
guidelines.
Referring physicians were not blinded to the test result because withholding this information would have been unethical, particularly in light of the current recommendations.37 However, defining the criteria for management recommendations according to the result of the dobutamine echocardiography beforehand enabled us to compare the outcome of such decisions prospectively as a function of concordance or discordance with the test results.
Coronary artery disease has been identified as the sole independent predictor of 30-day mortality in patients with aortic stenosis and severe LV dysfunction who are undergoing aortic valve replacement,38 and another retrospective study17 found an excess of surgical mortality in patients with aortic stenosis and poor LV function who had a history of myocardial infarction. In view of these data, it is important to emphasize that > 70% of the patients in our study had experienced a myocardial infarction (in the study by DeFillipi et al,16 only 44% of the patients had coronary artery disease). Thus, surgery seems to be justified in this patient group, as long as the contractile reserve is retained.
Conclusion
The assessment of valvular hemodynamics and myocardial function
during low-dose dobutamine infusion can guide decision making in
patients with aortic stenosis and LV dysfunction and can predict
outcome as a function of the management strategy. Such patients have a
better outcome when management decisions are based on the result of a
dobutamine echocardiogram. Patients with relatively low transvalvular
gradients, who have been identified as having severe aortic stenosis
and preserved contractile reserve by dobutamine echocardiography, have
a better outcome when undergoing surgery, while patients identified as
having nonsevere aortic stenosis by dobutamine echocardiography can be
managed conservatively. Although aortic valve resistance is
relatively flow-independent and showed a trend toward better
discrimination between severe and nonsevere aortic stenosis at rest,
definite assessment of lesion severity requires dobutamine
echocardiography.
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Acknowledgements |
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Footnotes |
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Supported by a grant from the Israel Science Foundation, Jerusalem, Israel.
Received for publication July 21, 2000. Accepted for publication December 5, 2000.
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