(Circulation. 1999;100:2153.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
Opening and Closing Characteristics of the Aortic Valve After Different Types of Valve-Preserving Surgery
From the Departments of Cardiac Surgery, Medical University of Lübeck, Lübeck, Germany (R.G.L., C.S., H.-H.S.), and the National Heart and Lung Institute at the Imperial College of Science, Technology, and Medicine, London, UK (M.H.Y.).
Correspondence to Prof H.H. Sievers, Klinik für Herzchirurgie, Medizinische Universität zu Lübeck, Ratzeburger Allee 160, D-23538 Lübeck, Germany. E-mail herzchir{at}medinf.mu-luebeck.de
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Abstract |
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Background—The surgical approach to aortic root aneurysm and/or dissection remains controversial. The use of valve-sparing operations, which are thought to have many advantages, is increasing. We hypothesized that the particular technique and type of surgery could influence valve motion characteristics and function. Therefore, we studied the instantaneous opening and closing characteristics of the aortic valve after the main 2 types of valve-sparing surgery.
Methods and Results—In 20 patients (10 with tube replacement of the aortic root, group A; and 10 with separate replacement of the sinuses of Valsalva, group B) and 10 controls (group C), transthoracic and transesophageal studies on aortic valve dynamics were performed. Three distinct phases of aortic valve motion were identified. They were as follows: (1) a rapid opening, with a velocity of 20.9±4.2 cm/s in group C, 27.1±10.9 cm/s in group B (P=NS), and 58.3±18.4 cm/s in group A (group A versus group C, P<0.001; group A versus group B, P=0.001); (2) a slow systolic closure, with 12.5±6.6% and 10.8±2.2% of maximal opening in groups C and B, respectively (P=NS), and 3.8±1.6% in group A (group A versus group C, P=0.001; group A versus group B, P<0.001); and (3) a rapid closing movement, with a velocity of 26.3±5.6 cm/s in group C, 32.4±11.4 cm/s in group B (P=NS), and 21.8±3.5 cm/s in group A (group A versus group C, P=NS; group A versus group B, P=0.008). The pressure strain of the elastic modulus was different in groups C and B only at the commissures (682±145 g/cm2 versus 1896±726 g/cm2, respectively; P<0.001). At all root levels, the distensibility was reduced in group A (P<0.001). Systolic contact of aortic cusps and wall occurred only in group A.
Conclusions—Near-normal opening and closing characteristics can be achieved by a technique that preserves the shape and independent mobility of the sinuses of Valsalva.
Key Words: aorta • valves • surgery • echocardiography
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The surgical approach to aortic root aneurysm and/or dissection is still controversial. Replacing the diseased aortic root with a composite graft including a mechanical valve is commonly performed; with this procedure, patients must accept the disadvantages of lifelong anticoagulation and risks of thromboembolism, hemorrhage, endocarditis, and restricted hemodynamics in favor of defined, long-term function of the prosthesis.1 2 3 4 5 Because aortic disease leaves the aortic valve cusps largely unaffected, valve-preserving operations, with excision of all diseased tissue, have been developed and used in several series.6 7 8 9 10 11 12 13 The main 2 techniques used either replace the diseased sinuses of Valsalva by 3 separate, tongue-shaped extensions of the Dacron tube, thus maintaining the independent mobility of each sinus,6 7 13 or suture the mobilized aortic valve inside the cylindrical Dacron tube.8 The influence of the particular technique used on the opening and closing characteristics of the aortic valve, including the pattern of instantaneous movements of the cusps and aortic wall during the different parts of the cardiac cycle, has not been studied before. These movements could have important implications on the durability of the repair and, possibly, on coronary flow and left ventricular function and, thus, long-term results. The purpose of this study was to evaluate echocardiographically the opening and closing characteristics of the aortic valve after the 2 main types of valve-preserving surgery.
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Methods |
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Patients
Between November 1992 and September 1997, 20 patients with aortic root disease underwent 2 different types of aortic valve-sparing operations. During the initial period, the David technique (group A; n=10) was performed8 ; subsequently, the Yacoub technique (group B; n=10) was used.7 13 The inclusion criteria for both groups were identical and consisted of the absence of gross organic changes in the valve cusps, regardless of the size of the aneurysm, the duration of aortic insufficiency, ventricular function, or age. Patients with severe neurological abnormalities before the operation were excluded. The control group (group C) consisted of 10 healthy individuals in whom no abnormalities of the aortic valve, aortic root, or left ventricle were detected by medical history, standard clinical examination, and transesophageal echocardiography. The clinical characteristics of all groups are shown in Table 1
. Informed written consent was obtained
before echocardiography. The investigative
procedures were performed in accordance with institutional guidelines.
All patients were clinically evaluated at regular intervals at our
hospital.
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Operative Technique
Standard cardiopulmonary bypass with a membrane
oxygenator (Hollow Fiber Oxygenator, Spiral Gold) at moderate
hypothermia (28°C nasopharyngeal temperature) or deep hypothermic
circulatory arrest (18°C nasopharyngeal temperature) was used, and
cold crystalloid cardioplegia (St. Thomas’ Hospital solution) was
used for myocardial protection. The operative techniques are described
in detail elsewhere.7 8 11 12 In brief, the David
technique is performed as follows: after excision of the sinuses, the
aortic valve is implanted inside a straight (not tailored) Dacron tube
(Hemashield Gold, Meadox Medicals) in a manner similar to the
implantation of an aortic valve homograft; this is followed by
reimplantation of the coronary ostia (Figure 1). The Yacoub technique, in brief, is as
follows: after excision of the diseased sinuses, the end of the sized
Dacron tube is trimmed to produce 3 separate, tongue-shaped extensions,
which are fixed to the aortic annulus at the line of attachment of the
cusps; this is followed by reimplantation of the coronary ostia
(Figure 1). No reduction annuloplasties were performed, except
for 1 in a patient with Marfan syndrome who needed plication of the
intervalvular trigone between the noncoronary and left
coronary sinus.
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Echocardiographic Data Acquisition and
Measurements
Echocardiograms were performed on a Hewlett Packard Sonos 2500
system with 2.5- and 5.0-MHz ultrasound transducers during routine
follow-up investigations. All patients underwent
transthoracic and transesophageal
echocardiography at rest. Examinations were
performed with the patients in the left lateral decubitus position. A
modified ECG lead I was continuously recorded. Blood pressure was
measured by cuff sphygmomanometry (Dinamap, Siemens).
Echocardiographic measurements were performed while
blood pressure was constant.
Root dimensions and valve-motion parameters were determined by 2 independent observers from video-recorded studies, and the average value of 5 consecutive beats in sinus rhythm was taken.
To evaluate the reproducibility of the echocardiographically determined aortic root diameters at base, sinus, and commissural levels, 3 patients were studied twice using transesophageal echocardiography within a period of 10 days. The range of variation of the sequentially measured diameters was 0% to 2.9%.
Two-Dimensional Echocardiography
First, the morphology of all 3 aortic cusps was examined in
standard longitudinal and cross-sectional views. Then, the diameters of
the aortic root at the level of the annulus, the sinuses of Valsalva,
and the commissures were determined transesophageally
by using the leading edge method, as described by Roman et
al.15
By definition, the annulus level was circumscribed by the nadir hinge points of the aortic cusps, the sinus level was the largest root diameter between the annulus and the supraaortic ridge, and the commissural diameter was measured at the distal rim of the sinuses of Valsalva.
Measurements of diameters were made perpendicular to the long axis of the aorta in views showing the largest and smallest dimensions during 1 cardiac cycle. Left ventricular end-systolic and end-diastolic volumes were obtained from standard apical 4-chamber views. Diastole was defined as the beginning of the QRS complex on the simultaneous ECG recording. Left ventricular outflow tract diameter was obtained by freeze frame at maximum aortic valve leaflet opening in systole.
M-Mode Echocardiography
Tracings were recorded from transesophageal
views at 100 mm/s paper speed on a strip chart and magnified. The
purpose of these recordings was to analyze the
intermittent systolic contact of an aortic cusp and the aortic
wall, as well as the opening and closing movements of the aortic
leaflets, as defined in Figure 2. Only
views with the leaflet coaptation at the midline of the aortic root and
a symmetrical configuration of the echocardiographic
appearance of the valve motion pattern were analyzed.
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Continuous-Wave and Pulsed-Wave Doppler
Maximum velocities across the aortic valve were obtained by
continuous-wave Doppler using the apical 5-chamber view showing the
aorta and left ventricular outflow tract. With pulsed-wave
Doppler, the sample volume was placed just below the aortic
leaflets and recorded at 0.5-cm intervals to the
midventricular level, where the drop-off of aortic
velocities occurred, to measure velocities and velocity time integrals
in the left ventricular outflow tract. Pulsed-wave
Doppler was also used for mapping the left ventricular
outflow tract to assess aortic regurgitation.
Resting coronary artery blood flow velocity was determined by pulsed-wave Doppler exploration of the anterior descending coronary artery.16 The resting systolic and diastolic coronary flow velocity time integrals, defined as the area under the curve during systole and diastole, were measured. The ratio of resting systolic to diastolic velocity time integrals was then calculated.
Color-Flow Doppler
Aortic regurgitation was assessed by color-flow
Doppler techniques in the standard transthoracic and
transesophageal views and graded as follows using the
ratio of jet height/left ventricular outflow tract
height17 : ratio of 1% to 24%, Grade I; 25% to 46%,
Grade II; 47% to 64%, Grade III; and 
65%, Grade IV.
Calculations
The following items were calculated with the indicated
formulas.
Cardiac output (CO) was calculated using:
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Ejection fraction (EF) was calculated as follows:
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Peak systolic pressure gradient across the aortic valve (
p)
was calculated as follows:
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Percent change in radius (PCR) was calculated using the following:
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R indicates the difference between the
largest and smallest diameter, and R, the average
diameter.18
Pressure strain elastic modulus (PSEM) was calculated as follows:
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P is the difference between systolic
and diastolic blood pressures.18
Slow closing displacement (SCD) of leaflets was calculated using the
following:
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).
Statistical Analysis
Data are given as mean±SD. To compare the continuous data of
different groups, the H test according to Kruskal-Wallis was used. If
significantly different, a Mann-Whitney ranked sum test (U-test) was
applied. According to Bonferroni’s method for multiple pairwise tests,
a 2-tailed P
0.016 (0.05/3) was considered significant.
Relative frequencies were analyzed using the
2 test. Statistics were performed using
statistical software (SPSS for Windows 6.0, SPSS Inc).
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Results |
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No early or late deaths occurred in this series during the follow-up period of 2 to 42 months (mean, 13.7±11.6 months). No endocarditis or thromboembolic events occurred. No patient was on oral anticoagulants or antiplatelets. All patients were in New York Heart Association Class I at the latest follow-up. Clinically, all patients were judged to have good valve function throughout the follow-up period.
Heart rate, stroke volume, cardiac output, ejection fraction, blood
pressure, and the transvalvular aortic pressure gradient were
comparable in the 3 groups (Table 2).
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A total of 50% of patients in group A (David procedure) and 70% of patients in group B (Yacoub procedure) had no aortic regurgitation. None of the patients had more than grade I aortic regurgitation. No calcifications, vegetation, or areas of thickening were observed on any leaflet.
Valve Opening and Closing Characteristics
Three distinct phases of aortic valve movement were observed: a
rapid valve opening, a slow systolic closure, and a rapid valve
closing movement (Figures 2 and 3
and Table 3). Valve opening and closing
characteristics were largely similar in groups B and C (Figure 3, Table 3). The rapid opening of the valve in these
groups was smooth, with a similar average speed of 27.1 cm/s in group B
and 20.9 cm/s in controls. Maximal opening of the valve was achieved
14.5 ms later, on average, in controls compared with group B patients.
Valve displacement was 21.1 mm smaller in group B than in group C
(23.1 mm).
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In contrast, the valves in group A opened faster, with an essentially
increased speed of 58.3 cm/s and a shorter time (23.0 ms) for maximal
opening. Valve displacement (Table 3) was largest (26.0 mm)
in this group of patients.
The duration of valve opening as expressed as ejection time was
shortest in group B. The decrease of valve displacement during the slow
closing movement (Table 3, Figure 3) was less apparent in
group A (only 3.8% of maximal opening) than in groups B and C (>10%
for both). The valves in group A took longer for rapid closing (Table 3, Figure 3), with a decreased speed (21.8 cm/s) when
compared with groups B and C (32.4 and 26.3 cm/s, respectively).
Intermittent systolic contact of 1 aortic cusp with the
aortic wall was a constant finding in all patients in group A but no
patients in groups B and C (Figure 4).
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Aortic Root Distensibility
Cyclic changes in the radius and pressure strain elastic modulus,
as parameters of the distensibility of the aortic root, are
listed in Table 4 and illustrated in
Figure 5. Aortic root distensibility in
group A was significantly reduced; it did not exceed a 2.2% change in
radius with a high pressure strain elastic modulus of >1900
g/cm2 at any measured level. In contrast,
near-normal values for percent change in radius at the sinus and
annulus level of 9.6% and 10.1% were observed for group B; at the
commissural level, the root was relatively stiff, with only a 2.7%
change in radius and a pressure strain elastic modulus, on average, of
1896±726 g/cm2.
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Coronary Artery Blood Flow Velocity
A biphasic pattern of coronary blood flow velocity in the
left anterior descending coronary artery at rest with a greater
diastolic component (9.02 cm in group B, 8.63 cm in group
A, and 9.98 cm in group C) and a smaller systolic component
(3.1 cm in group A, 3.48 cm in group B, and 3.98 cm in group C) was
recorded (Table 5). No significant
differences in coronary artery flow velocity were observed in
the 3 groups.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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This study defines, for the first time, the pattern of instantaneous valve opening and closing after valve-sparing operations compared with normal subjects. In addition, we showed that valve opening and closing characteristics varied with the particular technique used. These findings could have implications on the durability of the repair and, possibly, on cardiac performance.
The concept of valve repair is extremely appealing in patients with aortic root malformation in whom the disease process is largely confined to the aortic wall, leaving the aortic cusps capable of functioning normally for varying periods of time, despite the presence of histological abnormalities, particularly in Marfan syndrome.19
The success of this operation depends on preserving the extremely sophisticated dynamic function of the valve, which is best suited for its hemodynamic performance to maintain optimal left ventricular function, coronary blood flow, and cardiac output under widely different physiological and pathological conditions while minimizing mechanical stress on the leaflets.
Previous studies in animal models using high-speed cineradiography20 or electromagnetic induction techniques21 have shown changes in root dimension during the cardiac cycle that are thought to be important for the smooth functioning of the aortic valve. These changes have 3 distinct phases: a rapid valve opening, a slow systolic closure, and a rapid valve closing movement.
Using transesophageal echocardiography in control subjects, we found a pattern of movement of the cusps and the aortic root similar to that observed by Thubrikar et al20 22 and Higashidate et al21 in animal models.
After root replacement with separate reconstruction of the sinuses (group B), we measured an opening velocity of 27.1±10.9 cm/s, which was similar to that of the controls (group C; 20.9±42 cm/s). The aortic root distensibility in group B was also comparable to controls, except for a distensibility of a 2.7% change in radius at the upper part of the sinuses. This restricted distensibility, however, did not affect valve opening and closing characteristics, which were largely normal in this group of patients. In contrast, the distensibility of the aortic root was reduced in group A, with a maximal change in the radius of 2.2% at all levels; in this group, the velocity of valve opening was significantly faster (57.3 cm/s). This might be explained by the fact that the aortic root cannot change its shape during the cardiac cycle, as was suggested by the work of Higashidate et al,21 Thubrikar et al,20 22 and Sievers et al.23 These authors observed that the semilunar valves start to open, without any forward flow, only because of root expansion during the beginning of systole in animal models. This interaction between the root and the leaflets leads to a stellate orifice of the valve that becomes circular with increasing blood flow velocity.22 Thus, a gradual, smooth opening movement of the valve is achieved, which reduces stresses on the leaflets.24 25
Also, left ventricular ejection parameters
might have influenced valve-opening velocities.21 In our
series, the ejection time was lower in group B compared to group
A and group C. In conjunction with an equal stroke volume, this would
lead to more abrupt changes in the valve-opening motion, which is
contrary to what we observed. This emphasizes the importance of repair
techniques on cusp movement. Furthermore, we observed contact of the
leaflets with the aortic wall only in group A patients. This could be
due to the rapid leaflet displacement during opening or due to the lack
of sinuses in group A; this is supported by the
echocardiographic appearance of 3 separate sinuses in
controls and in patients in group B (Figure 6). In this context, Bellhouse et
al.26 reported that the fully opened cusps are normally
accurately positioned between the sinus wall and the bloodstream, with
the sinus vortex adjusting the sinus pressure to balance that on the
aortic side of the cusps. The lack of sinuses in group A probably
prevents this mechanism from operating and, consequently, contributes
to leaflet contact. Another reason for this phenomenon could be the
lack of space in the Dacron tube, leading to a redundancy of cusp
tissue.
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Bellhouse and Bellhouse27 reported, in an in-vitro study, that a valve in a straight tube without the closing forces of the sinus vortices would increase regurgitation considerably during closure. We were, however, not able to confirm these results; only grade I regurgitation, without significant differences between groups A and B, occurred.
In the second phase of valve movement, the degree of slow closing motion was 10.8±2.2% of maximal opening in group B, which is comparable to that of controls (12.5±6.6%). In group A, we measured a slow closing motion of only 3.8±1.6%. Again, the missing sinus vortices impair the ability of leaflets to begin to close before the onset of flow deceleration in these patients.27 Furthermore, the lack of internal forces, which are stored by the displacement of the cusps after root distension and which initiate valve closure during flow deceleration (as described for normal valves by Thubrikar et al20 ), could have contributed to the reduced slow systolic valve closure with reduced root distensibility in group A.
During the third phase of valve movement, we observed differences in the valve closing velocity between groups A (21.8±3.5 cm/s) and B (32.4±11.4 cm/s), although both values are not different from that of controls (26.3±5.6 cm/s). This rapid valve closure is determined by the radial thrust of the sinus vortices on the sinus surface of the leaflets during the deceleration phase of aortic blood flow,27 and it is then completed by the reversal of aortic flow. The lower speed for this movement in group A patients is probably also related to the lack of sinus configuration and, thus, the closing forces of sinus vortices to push the leaflets to the midline.
In addition, Bellhouse et al26 reported that sinus vortices not only initiate valve closure but also promote coronary artery blood flow. In our series, differences between groups in coronary artery blood flow at rest could not be detected during systole or diastole. Whether this holds true for exercise conditions remains to be established.
Limitations
This study has several limitations. (1) It could be argued that
the resolution of the ultrasound technique is not sufficient to define
accurate instantaneous movements of the aortic root and the leaflets.
However, possibly more accurate techniques, such as high speed
cineradiography20 or electromagnetic
induction,21 are not applicable to humans and could
interfere with valve movement. The ultrasound technique used in this
study operates at a 900-Hz sampling frequency, providing an interval
between 2 consecutive signals of 1.1 ms, which we believe is adequate
to define aortic root motion. In addition, the technique produced
reproducible results. (2) The fact that the aortic root moves during
measurement could induce errors. However, these errors would apply to
all groups and, therefore, should not affect comparative results. (3)
Another limitation relates to the significantly longer period of
follow-up in group A than in group B (23.2±8.5 versus 4.1±1.8 months)
and the fact that this was not a randomized study. However, the 2
groups were well matched with regard to patient demographics and the
size of the Dacron tube used.
In conclusion, we demonstrated important differences in valve opening and closing characteristics after valve-sparing operations, depending on the particular technique used. The near-normal pattern of valve movement and the preserved distensibility after the Yacoub technique could reduce stress on the valve. This is supported by the study of Reis et al,28 who showed that increased flexibility of a stented semilunar valve results in marked reduction of the measured stress on the cusps. Whether the observed differences in valve movement and distensibility between the 2 groups will affect long-term valve durability, cardiac performance, and patient survival remains to be evaluated.
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Acknowledgments |
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We thank Bettina Hansen for her assistance in the preparation of the manuscript.
Received March 11, 1999; revision received July 16, 1999; accepted July 20, 1999.
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A. Rama, S. Rubin, N. Bonnet, and I. Gandjbakhch New Technique of Aortic Root Reconstruction With Aortic Valve Annuloplasty in Ascending Aortic Aneurysm Ann. Thorac. Surg., May 1, 2007; 83(5): 1908 - 1910. [Abstract] [Full Text] [PDF]
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A. Moritz, P. Risteski, S. Dogan, H. Macit, B. Akbulut, A. Zierer, and T. Aybek Six stitches to create a neosinus in David-type aortic root resuspension J. Thorac. Cardiovasc. Surg., February 1, 2007; 133(2): 560 - 562. [Full Text] [PDF]
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D. C. Miller Valve-Sparing Aortic Root Replacement: Current State of the Art and Where Are We Headed? Ann. Thorac. Surg., February 1, 2007; 83(2): S736 - S739. [Full Text] [PDF]
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A. W. Erasmi, H.-H. Sievers, J.F. M. Bechtel, T. Hanke, U. Stierle, and M. Misfeld Remodeling or Reimplantation for Valve-Sparing Aortic Root Surgery? Ann. Thorac. Surg., February 1, 2007; 83(2): S752 - S756. [Abstract] [Full Text] [PDF]
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G. Gerosa, S. Pontarollo, S. Iliceto, and F. di Marco An alternative technique for aortic root remodeling in patients with bicuspid aortic valve J. Thorac. Cardiovasc. Surg., January 1, 2007; 133(1): 249 - 250. [Full Text] [PDF]
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D. Pacini, F. Settepani, R. De Paulis, A. Loforte, S. Nardella, D. Ornaghi, R. Gallotti, L. Chiariello, and R. Di Bartolomeo Early results of valve-sparing reimplantation procedure using the Valsalva conduit: a multicenter study. Ann. Thorac. Surg., September 1, 2006; 82(3): 865 - 871. [Abstract] [Full Text] [PDF]
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N. D. Patel, J. A. Williams, C. J. Barreiro, B. T. Bethea, T. P. Fitton, H. C. Dietz, J. A.C. Lima, P. J. Spevak, V. L. Gott, L. A. Vricella, et al. Valve-Sparing Aortic Root Replacement: Early Experience With the De Paulis Valsalva Graft in 51 Patients Ann. Thorac. Surg., August 1, 2006; 82(2): 548 - 553. [Abstract] [Full Text] [PDF]
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R. Fries, T. Graeter, D. Aicher, H. Reul, C. Schmitz, M. Bohm, and H.-J. Schafers In vitro comparison of aortic valve movement after valve-preserving aortic replacement J. Thorac. Cardiovasc. Surg., July 1, 2006; 132(1): 32 - 37. [Abstract] [Full Text] [PDF]
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L. A. Vricella, J. A. Williams, W. J. Ravekes, K. W. Holmes, H. C. Dietz, V. L. Gott, and D. E. Cameron Early Experience With Valve-Sparing Aortic Root Replacement in Children Ann. Thorac. Surg., November 1, 2005; 80(5): 1622 - 1627. [Abstract] [Full Text] [PDF]
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J. M. Albes, U. A. Stock, and M. Hartrumpf Restitution of the Aortic Valve: What is New, What is Proven, and What is Obsolete? Ann. Thorac. Surg., October 1, 2005; 80(4): 1540 - 1549. [Abstract] [Full Text] [PDF]
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A. Erasmi, H.-H. Sievers, M. Scharfschwerdt, T. Eckel, and M. Misfeld In vitro hydrodynamics, cusp-bending deformation, and root distensibility for different types of aortic valve-sparing operations: Remodeling, sinus prosthesis, and reimplantation J. Thorac. Cardiovasc. Surg., October 1, 2005; 130(4): 1044 - 1049. [Abstract] [Full Text] [PDF]
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