Circulation. 1999;100:II-36-II-41
(Circulation. 1999;100:II-36.)
© 1999 American Heart Association, Inc.
Surgery for Valvular Heart Disease |
Right Ventricular Function After Pulmonary Autograft Replacement of the Aortic Valve
Gerald S. Carr-White, MRCP;
Mark Kon, FRCS;
T. W. Koh, MRCP;
Sally Glennan;
Francis D. Ferdinand, MD;
Anthony C. De Souza, FRCS;
John R. Pepper, FRCS;
Dudley J. Pennell, FRCP;
Derek G. Gibson, FRCP;
Magdi H. Yacoub, FRS
From the Departments of Academic Surgery (G.S.C.-W., M.K., S.G., F.D.F.,
A.C.d.S., J.R.P., M.H.Y.), Cardiology (T.W.K., D.G.G.), and Diagnostic Imaging
(D.J.P.), National Heart and Lung Institute, Royal Brompton Hospital, London,
UK.
Correspondence to Professor Sir Magdi Yacoub, Professor of Cardiothoracic Surgery, National Heart and Lung Institute, Royal Brompton Hospital, Sydney Street, London SW3 6NP, United Kingdom. E-mail g.carr-white{at}rbh.nthames.nhs.uk
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Abstract
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Background—The pulmonary
autograft operation (the Ross
procedure) involves excision of a portion
of the right ventricular
(RV) outflow tract, prolonged
cross-clamp times, and insertion
of a pulmonary homograft.
There is concern about the effect
of such operations on right
ventricular function.
Methods and Results—Twenty-five patients undergoing either
pulmonary autograft or homograft replacement of the aortic
valve as part of a prospective randomized trial had
echocardiographic RV long-axis measurements performed
before surgery and 6 months (range 3 to 12 months) after surgery. In
all patients, systolic excursion (SE) and both shortening and
lengthening rates (SR and LR, respectively) were reduced
postoperatively (P<0.05) (homografts: SE 1.5±0.4
versus 2.3±0.6 cm, SR 6.8±2.1 versus 9.6±3.1 cm/s, LR 6.0±1.8
versus 8.9±3.0 cm/s; autografts: SE 1.4±0.4 versus 2.2±0.4 cm, SR
5.8±3.0 versus 8.2±3.0 cm/s, LR 5.7±1.9 versus 8.5±3.7 cm/s). There
were no differences between the 2 groups. Eighteen patients who had
undergone either aortic homograft or pulmonary autograft
surgery were studied between 6 and 35 months after surgery. RV volumes
were assessed with the use of MRI in addition to
echocardiographic RV long-axis measurements. Global
volumes were increased to a similar amount in both groups (homografts:
end-diastolic volume 145±34 mL, end-systolic
volume 78±23 mL; autografts: end-diastolic volume 157±33
mL, end-systolic volume 89±25 mL; P=NS),
whereas stroke volumes were maintained in both groups (homografts
67±15 mL, autografts 67±16 mL; P=NS). RV SE was
depressed in both groups to a similar degree to that seen with the
previous group (homografts 1.5±0.3 cm, autografts 1.4±0.2 cm).
Conclusions—Aortic valve replacement with either a
pulmonary autograft or an aortic homograft leads to a degree of
persistent RV longitudinal dysfunction that is not more pronounced in
those undergoing the Ross procedure. The mechanisms and long-term
effects of these changes must be further studied.
Key Words: aorta • valves • grafting • ventricles • magnetic resonance imaging • echocardiography
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Introduction
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The use of a pulmonary autograft as an aortic
valve substitute
1 has several potential
advantages,
2 including improved
hemodynamics,
durability, and the ability to
grow.
3 The operation itself,
however, involves 3 factors
that may adversely affect right
ventricular (RV) function:
excision of a portion of the RV outflow
tract, prolonged cross-clamp
times, and the insertion of a pulmonary
homograft. Although
many studies have examined the effect of
cardiac surgery, including
aortic valve replacement,
4 on RV
function, there is no
detailed information relating to the effect
of the Ross operation on RV
function. Given the increasing evidence
of the importance of RV
function in patient survival
5 and exercise
tolerance,
6 particularly in patients with left
ventricular (LV) impairment,
7 this question
may have important relevance for the long-term
efficacy of
pulmonary autografts.
Due to its complex geometry, the assessment of RV function has always
been difficult.8 Recently,
echocardiographic measurement of the longitudinal
movement of the tricuspid annulus (RV long-axis movement or tricuspid
annular plane systolic excursion [SE]) has been advocated as
a simple, objective measure of RV free wall function that has been
shown to correlate with both exercise tolerance9 and
ejection fraction10 in patients with ischemic
heart disease. This measure has additional importance due to the fact
that unlike LV ejection, longitudinal rather than short-axis movement
is the predominant mechanism for RV ejection.11 Although
echocardiography is effective for the measurement
of long-axis movement of the RV, it is acknowledged that other methods
are necessary for more detailed assessments of RV volumes. Currently,
MRI is accepted as the noninvasive gold standard for the measurement of
RV volumes.8
The aim of this study was to assess RV function after pulmonary
autograft surgery with a combination of
echocardiographic RV long-axis measurements and MRI
assessments of RV volumes. These measurements were repeated with a
similar cohort of patients who were undergoing aortic homograft
replacement as part of a prospective randomized trial, to allow a
comparison with a group who had a similar biological valve implanted
but in whom no surgical procedure was carried out on the right side of
the heart. The study involved 2 phases: (1) RV long-axis measurements
were obtained in patients before and after either pulmonary
autograft or aortic homograft surgery and (2) postoperative comparisons
were made of RV long-axis results and MRI RV volumes in a separate
cohort of patients who had undergone either pulmonary autograft
or aortic homograft surgery.
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Methods
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Patient Selection
Twenty-five patients in phase I were studied before surgery
and
at 6 months (range 3 to 12 months) after surgery. Eighteen
patients in
phase II were studied at 18 months after surgery
(range 6 to 35
months). Patient demographics and preoperative
variables are given
in Table 1
. Local ethical
committee approval
was obtained before the study was started, and full
informed
consent was obtained from each patient.
Operative Technique
All operations were performed by the same surgeon (M.Y.).
Cardiopulmonary bypass with moderate hypothermia (30°C) was
used. In both groups, myocardial protection was achieved with either
antegrade crystalloid or cold blood cardioplegia. All patients
underwent aortic root replacement with coronary reimplantation.
In the autograft group, the RV outflow tract was reconstructed with the
use of a large homovital or antibiotic-sterilized pulmonary
homograft conduit inserted with the use of continuous 4-0 sutures
without the inclusion of strips of prosthetic or autologous
tissue for support. These suture lines were performed before release of
the aortic clamp.
Echocardiographic Measurements
Transthoracic echocardiograms were performed with a
Hewlett Packard Sonos 500 or 2000 machine. An M-mode trace was obtained
through the tricuspid annulus from the apical 4-chamber view and
printed at a paper speed of 100 cm/s (Figure 1). This trace was then digitized offline
with customized software that allowed the calculation of SE,
lengthening rate (LR), and shortening rate (SR). In each case, 3
consecutive beats were analyzed and averaged.
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Figure 1. Echocardiographic method of
recording RV long-axis movement (right) and a normal M-mode RV
long-axis trace (left). PCG indicates phonocardiogram; RA, right
atrium; and LA, left atrium.
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MRI Measurements
Imaging was performed with a Picker 0.5-T whole-body system with
the use of prospective ECG gating and a jacket receiver coil.
Ventricular volume measurements were achieved by imaging
the heart from apex to base with the use of contiguous 10-mm slices in
the short-axis plane. A series of transthoracic
cross-sectional images allowed identification of the mitral valve and
the apex. The vertical long-axis plane was aligned from these images,
and the horizontal long-axis (HLA) plane was located perpendicular to
the vertical long-axis plane with maintenance of the LV axis
passing through the center of the mitral valve and the apex. The
short-axis plane was finally identified from the HLA plane, with the
most basal imaging slice located just below mitral and tricuspid valve
insertions (Figure 2). Subsequent slices
were parallel to the basal slice and repeatedly offset by 10 mm
toward the apex until the entire heart had been imaged, usually
involving 10 to 14 slices. Each slice of the volumetric study consisted
of a series of 12 to 16 frames throughout the cardiac cycle. The
end-diastolic and end-systolic frames could be
identified by running the frames in sequence as a cine loop (Figure 3). The endocardial borders were
identified for the LV and RV, and the enclosed areas were measured with
the use of online software. The total areas for diastole
and systole were summed and multiplied by the slice thickness (10
mm) to obtain left and right end-diastolic and
end-systolic volumes. Other MRI parameters include
field of view of 350 to 400 mm, slice thickness of 10 mm, 96
to 128 phase encoding lines, 2 signal averages, and repeat times of
45 ms to enable 12 to 16 images to be made per cardiac cycle.
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Figure 3. Short-axis cross sections of LV and RV, with
endocardial borders identified at end diastole and end
systole.
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Statistical Analysis
Statistical analysis was performed with a commercially
available software package (SPSS Inc). A comparison between groups of
demographic and preoperative or postoperative data was performed with
the use of an unpaired t test. A comparison of data over
time was made with the use of a 1-way ANOVA. A P value of
<0.05 was accepted as significant.
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Results
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At the time of their postoperative
echocardiographic or MRI
investigations, 37 (86%)
patients were in NYHA class I and 6
(14%) were in NYHA class II. No
patients were in class III or
IV. No patient had significant aortic or
pulmonary valve dysfunction
(defined as more than mild
valvular regurgitation or a peak
transvalvular
gradient of >30 mm Hg). Aortic cross-clamp
times were significantly
higher for the autograft group than for the
homograft group
(mean±SD, 110±20 versus 81±17 minutes,
P<0.001).
Both preoperative and postoperative indices of RV function were
analyzed according to whether the preoperative pathology was
aortic regurgitation or stenosis.
Analysis of patients with pure aortic stenosis or
regurgitation preoperatively demonstrated no
significant differences between the 2 groups (Table 2); therefore, the autograft and
homograft groups were not further subdivided according to preoperative
type of lesion.
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Table 2. RV SE (Measured With
Echocardiography) and Ejection Fraction (Measured
With MRI) in Patients With Either Lone Aortic Stenosis or
Regurgitation Before Surgery
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Although phase 1 patients were studied at a mean interval of 6 months
after surgery and phase 2 patients were studied at a mean interval of
18 months after surgery, the time period of analysis was wide
(3 to 12 months for phase 1 and 6 to 35 months for phase 2). Therefore,
in a subset of 7 patients for whom regular and extended follow-up was
available, RV SE was analyzed at 6 weeks and 6, 12, and 24
months after surgery (Table 3). The
postoperative depression in RV function did not alter according to time
since surgery over this period. Given that only 1 patient was studied
outside this time frame, this suggests that changes in postoperative RV
function over time should not bias the results, despite the wide time
range of analysis.
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Table 3. Changes in RV SE With Time Since Surgery in a Subset
of Patients for Whom Regular and Extended Follow-Up Was Available
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Phase I
In all patients studied, postoperative RV long-axis SE and both SR
and LR were reduced compared with preoperative values (Figure 4 and Table 4). There were no significant differences
between the autograft and homograft groups with regard to either
preoperative or postoperative values. All patients who were studied had
echocardiographic evidence of reversed
ventricular septal motion on an M-mode parasternal
long-axis recording.
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Figure 4. Preoperative and 6-month postoperative RV
long-axis traces, demonstrating typical and striking reduction in both
total amplitude and maximal velocities. PCG indicates
phonocardiogram.
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Phase II
The ventricular volumes and RV long-axis SE measured
for the 18 patients are summarized in Table 5. Stroke volume and ejection fraction as
a percentage of end-diastolic volume were calculated. All
parameters were similar for the 2 groups of patients. For
RV volumes, end-diastolic volume ranged from 80 to 202 mL,
end-systolic volume ranged from 38 to 116 mL, and ejection
fraction ranged from 0.37 to 0.55. In patients with no regurgitant
valves, LV and RV stroke volumes must be identical and therefore
provide additional validation of volumetric analysis. LV and RV
stroke volume correlation curves and Bland-Altman plots are given in
Figures 5 and 6.
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Figure 5. Correlation of MRI-calculated LV and RV stroke
volumes for both groups. Close correlation validates assessment of RV
volumes.
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Figure 6. Bland-Altman analysis comparing LV and RV
stroke volumes (SV) by volumetric analysis. Mean values and
95% confidence limits are indicated.
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Discussion
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The use of a pulmonary autograft as an aortic valve
substitute
has many potential advantages,
12 including
improved hemodynamics
and durability, resistance to
infection, and the ability to
grow. Conversely, it is a longer and more
technically demanding
operation, and concern still exists over the
effect of such
surgery on RV function.
13 The results of
this study demonstrate
that patients undergoing aortic valve
replacement with either
a homograft or an autograft valve substitute
have evidence of
persistent RV dysfunction after aortic valve
replacement; however,
the dysfunction is not more pronounced in those
undergoing the
Ross operation. A comparison of the RV volumes obtained
in this
study with other published "normal
values"
14 15 obtained with
MRI shows that the
end-diastolic and end-systolic values are
increased
by a factor of 10% to 30%, whereas the stroke volumes
appear to be
similar to other normal published values. Although
the numbers involved
are too small for statistically significant
comparisons, there does not
appear to be any difference in either
MRI or
echocardiographic values according to the underlying
disease
process and reason for surgery. This 2-phase study appears to
show
that patients undergoing aortic valve replacement with biological
valves
have mild long-standing postoperative RV dysfunction, which
preferentially
affects the long-axis movement of the RV, given that the
longitudinal
movement falls to at least as great a degree as the
absolute
volumes. The mechanism of preservation of stroke volumes and,
to
a lesser degree, global volumes is unclear, but it seems likely
that
both increased short-axis movement of the RV and reversed
ventricular
septal motion play a
role.
16 17
Although altered cardiac geometry and movement of the heart in space
may affect long-axis measurements immediately after surgery, such
problems should not exist with transthoracic
echocardiographic measurements from a fixed apical
window 6 to 18 months after surgery, especially when they are backed up
by similar changes in absolute volumes. Similar RV long-axis results,
with preservation and improvement of LV indices, have been described in
patients undergoing CABG.15 It therefore seems likely that
the RV dysfunction is secondary to a common feature of both types of
operation; possible factors include (1) pericardectomy and the loss of
a lubricating surface between the anterior surface of the heart and the
chest wall, (2) ischemic damage secondary to
cardiopulmonary bypass and poor RV preservation,18
and (3) right atrial and pectinate muscle damage secondary to placement
of the bypass cannulae. Further studies in patients undergoing beating
heart coronary surgery and with different methods of myocardial
protection should help to identify the underlying etiological factors.
Thus, although persistent RV long-axis dysfunction should be recognized
as an important entity after biological aortic valve replacement,
patients undergoing pulmonary autograft surgery are similar in
this regard to those undergoing simple homograft aortic valve
replacement. Given that patients undergoing pulmonary autograft
surgery have excision of part of the RV outflow tract, this implies
that intact infundibular function is not a major contributor to RV
function as assessed according to the methods in this study. Given the
number of patients who were studied, it is possible that the degree of
postoperative dysfunction seen in both groups may mask more subtle
changes in RV function in the autograft group. However, any such
changes appear to be less significant than the persistent longitudinal
dysfunction seen in both groups. A similar group of patients undergoing
mechanical valve replacement were not studied because the original goal
was to examine the effect of pulmonary autograft surgery on RV
function, and for this purpose, aortic homografts provide the best
comparison. Further studies, including those in patients undergoing
mechanical valve replacement and minimally invasive aortic valve
replacement, are required to define the exact mechanisms involved in
producing the RV dysfunction and the possible effects of our findings
in terms of functional capacity and longevity. All of our patients had
reversed septal motion, which almost certainly is an important
interrelated physiological or anatomic
postoperative effect that merits further study. It is hoped that these
studies will stimulate the search for better methods of myocardial
protection, focusing particularly on the RV and
interventricular septum.
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Acknowledgments
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This work was supported by the Royal Brompton Hospital Special
Cardiac
Fund. Dr Carr-White is a British Heart Foundation Junior
Research
Fellow. Dr Yacoub is a British Heart Foundation Professor of
Cardiac
Surgery.
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Top
Abstract
Introduction