(Circulation. 1999;100:II-78.)
© 1999 American Heart Association, Inc.
Surgery for Valvular Heart Disease |
Early Clinical Results After Stentless Mitral Valve Implantation and Comparison With Conventional Valve Repair or Replacement
From University Leipzig, Heartcenter, Departments of Cardiac Surgery and Cardiology (C.W.), Leipzig, Germany.
Correspondence to Dr Thomas Walther, Universität Leipzig, Herzzentrum, Klinik für Herzchirurgie, Russenstrasse 19, 04289 Leipzig, Germany. E-mail walt{at}medizin.uni-leipzig.de
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Abstract |
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Background—A new quadricusp stentless mitral bioprosthetic valve (QMV) is evaluated and compared with current standards.
Methods and Results—Since August 1997, 67 patients were prospectively evaluated: 23 patients received a QMV, 23 had mitral valve repair (MVR), and 21 received conventional mitral valve replacement (MVP). Patient age was 69±8, 64±10, and 62±9 years for QMV, MVR, and MVP treatment, respectively. The underlying pathology was mitral stenosis, incompetence, and mixed disease in a corresponding 8, 9, and 6 patients for QMV, 1, 22, and 0 patients for MVR, and 2, 12, and 7 patients for MVP. The papillary muscles were sufficient in all QMV cases to suspend the valve. Cross-clamp time was 59±19 minutes for QMV implantation. In-hospital mortality for QMV, MVR, and MVP was 1, 0, and 0 patients, respectively, and thoracotomy had to be performed again in 1, 1, and 2 patients, respectively (these outcomes were not valve related). At baseline transthoracic echocardiography, respective maximum flow velocities were 1.6, 1.4, and 1.7 m/s, and valve orifice area was 2.6, 3.5, and 3.4 cm2. Mild transvalvular reflux was seen in 8, 7, and 2 patients; moderate reflux, in 1, 1, and 1 patients. Left ventricular ejection fraction was 52%, 54%, and 51% in the respective treatment groups. At follow-up, hemodynamic parameters had further improved in all groups.
Conclusions—One year after clinical implantation, the QMV appears to function well and has no additional risks compared with MVR or MVP. The subvalvular apparatus is preserved by suspending the QMV at the papillary muscles; this arrangement is hemodynamically advantageous. Echocardiography reveals an excellent valve performance that resembles native mitral valve morphology and hemodynamic function. The QMV is a promising alternative for biological mitral valve replacement.
Key Words: mitral valve • surgery • echocardiography • prosthesis
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Introduction |
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Mitral valve surgery is characterized by improved methods of valve repair in selected patients. Mitral valve replacement (MVP) is indicated mainly for advanced disease with severe destruction or calcification. Although a routine operation, valve selection is still controversial, since no ideal artificial heart valve is available at the moment.1 2 Bioprostheses are usually indicated in patients older than 70 years.3 Nevertheless, complications such as structural valve failure, calcification, thrombosis, and anticoagulation-related hemorrhage are associated with artificial heart valves.4 5 6 In the mitral position, freedom from these complications is
70% at 10 years and 35% at 15
years for porcine bioprostheses and 77% at 10 years for pericardial
bioprostheses.7 8 9 Currently, no standard for valve
selection exists; the best option would be a durable, flexible
biological prosthesis resembling the native mitral valve. Anatomically, the mitral valve is a complex structure, like the individual fingerprint. Perfect function is guaranteed through the interaction of valve leaflets, chordae, papillary muscles, and the left ventricle together as a functional unit. Conventional MVP is associated with a nonphysiological inflexible annulus due to the stent. Furthermore, the annuloventricular continuity to support left ventricular function is partially or completely lost by resection of the chordae. This loss of continuity results in nonphysiological hemodynamics and impairment of left ventricular function.
To overcome this dilemma, a chordally supported stentless mitral valve (Quadricusp mitral valve [QMV], Glycar Inc) has been developed. The present study was performed to evaluate the initial 1-year clinical outcome after implantation of the QMV and to compare the results with those from a group of patients undergoing conventional mitral valve repair (MVR) or MVP.
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Methods |
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From August 1997 onward, 67 elective patients with nonischemic mitral valve disease were prospectively evaluated. Implantation of the QMV was approved by the International Freiburger Ethical committee, by the federal "Regierungspräsidium," and by the local ethical committee for a clinical trial. All patients gave informed consent after the study protocol had been outlined in detail. Patients suitable for bioprosthetic mitral valve replacement were informed that valve reconstruction would be attempted if possible; otherwise, the QMV would be implanted. Thus, one control group consisted of patients in whom MVR was performed, and the other group consisted of patients subjected to conventional MVP (because of their younger age) during the same time period. All operations were performed by one surgeon (F.W.M.) using median sternotomy or lateral minithoracotomy with the port-access technique.10 Extracorporeal circulation was initiated, and cold crystalloid cardioplegia (Bretschneider HTK solution, Köhler Chemie) and moderate hypothermia were applied. In all patients, follow-up was performed at our outpatient clinic after 6 and 12 months and annually thereafter. No patient was lost to follow-up. Data are available for 100% of patients at a mean interval of 9.1±4.4 months. At all visits, the patients were assessed for functional state, the specific activity questionnaire (SAQ)11 was applied, and clinical examination and routine transthoracic echocardiography were performed.
Quadricusp Mitral Valve
The QMV is a stentless mitral valve made of bovine pericardium
only. This material is selected for strength, thickness, and fiber
direction to fulfill in excess the function of the natural valve. The
pericardium is tanned by glutaraldehyde for collagen
cross-linking and for removal of immunogenicity. Residual aldehydes
known to be responsible for tissue calcification are being capped by
additional polyol treatment. This anticalcification treatment has
proven effective in weanling rat subcutaneous implants and in weanling
sheep whole-valve implants.12 13 The QMV is designed to
have one large anterior and one posterior leaflet consisting of 3
scallops. All pieces are aligned by non–load-bearing sutures. The
sewing ring consists of 3 layers of pericardium and thus can function
as an annuloplasty ring. There are 2 joint papillary flaps at the
anterolateral and posteromedial sides; each papillary flap supports the
anterior as well as the posterior leaflet. The annulus is D-shaped, and
during valve closure, the anterior leaflet meets the other 3 scallops.
A QMV is shown in panel A of the Figure
. Accelerated wear testing
proved valve durability up to 800 000 000 cycles, exceeding the FDA
requirements.14
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Surgery
QMV implantation is performed according to standard techniques
after 3 minutes of rinsing. The diseased mitral valve is completely
excised by using a straight-line cut from immediately in front of the
lateral to the medial commissure. The posterior leaflet is completely
excised, leaving a small rim of native valve. A stump of anterior
leaflet chordae should be temporarily left on each papillary muscle for
traction during implantation. Appropriate sizing is performed by
matching the sizer (small, medium, or large) to the cut subaortic
curtain between the commissures. A special sizer is used to measure the
exact distance to the papillary muscles. The papillary flaps are
implanted by use of 2
polytetrafluoroethylene-armed Tevdek II 3/0
sutures (Deknatel) each; for knot tying, a specially designed knot
pusher is used (Figure
, panel A.). At the annulus, 2 or 3
continuous 3–0 prolene sutures with 4 to 6 interruptions are used
(Figure, panel B.). The valve is competent if inserted in a
neutral position; furthermore, it is forgiving over a range of 1.5 cm
below or above this point because of its relatively large
coaptation area.
Echocardiography
Transthoracic echocardiography
(TTE) was performed before surgery to confirm mitral valve pathology,
after surgery before discharge, and at every follow-up visit. During
surgery, multiplane transesophageal
echocardiography (TEE) was used. System Five
(Sonotron Vingmed) was used by 2 experienced
echocardiographers. Standard views were chosen. At TTE,
cardiac morphology (chamber and wall sizes, wall motion, and valve
structure) and function (fractional shortening and ejection fraction)
as well as transvalvular hemodynamics
determined by Doppler ultrasound and color Doppler were
assessed. Intraoperative TEE was applied to confirm the underlying
pathology and to control postoperative valvular and
ventricular function. In addition, TEE was used for valve
sizing, measuring the exact distance from the annulus to the
papillary flaps under hemodynamically stable conditions
before surgery. Mitral valve incompetence was graded according to the
regurgitant jet area in relation to left atrial area as mild (<20%),
moderate (20% to 40%), or severe (>40%). Effective orifice area was
derived from transvalvular continuous-wave Doppler
recordings using the pressure half-time method.15
Mean transvalvular gradients were assessed from continuous-wave
Doppler examinations using the modified Bernoulli
equation.
Statistics
Absolute and relative frequencies were calculated. Results are
given as mean±SD. The Kolmogorov-Smirnov test was used to assess
normal distribution; Student’s t test for matched pairs was
then applied. A value of P<0.05 was considered significant.
Postoperative valve-related morbidity and mortality were evaluated
according to standard guidelines.16
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Results |
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Patient Population QMV
Twenty-three (17 female and 6 male) patients received the QMV (mean age, 69±7.8 years). Eight patients had predominant mitral stenosis, 9 had predominant incompetence, and 6 had combined disease. The preoperative NYHA functional class was 3.2±0.4, SAQ was 3.8±1, and body surface area was 1.74±0.2 m2. One patient had undergone previous MVR, and 3 patients had undergone previous balloon commissurotomy for mitral stenosis. Nine patients were in sinus rhythm, 9 had atrial fibrillation, and 5 had a permanent pacemaker. Left ventricular ejection fraction as assessed by cardiac angiography was 63±14% (patients having mitral incompetence were included); end-diastolic left ventricular volume, 122±41 mL; central venous oxygen saturation, 61±7%; left atrial pressure, 23±5 mm Hg; and cardiac index, 1.8±0.6 L · min-1 · m-2. In mitral stenosis, the mean valve orifice area was 0.9±0.4 cm2 at a mean pressure of 13±10.5 mm Hg. For mitral incompetence or combined lesions, reflux was graded as 2.5±1 according to standard criteria.17 Preoperative demographics for all groups are shown in Table 1
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Intraoperative Results
A 28-mm (medium) QMV was implanted in 15 patients, and a 30-mm
(large) QMV was implanted in 8 patients. All patients had uneventful
valve implantation at good exposure by use of a conventional (n=21) or
a minimally invasive (n=2) approach. The papillary muscles were
sufficient in all cases to suspend the papillary flaps. The
anterolateral and posteromedial annulopapillary distances were 32±4
and 33±5 mm, respectively, by intraoperative sizing and 36±5 and
34±3 mm, respectively, by echocardiographic
measurements. Four patients had additional single coronary
artery bypass grafting, and 2 patients had tricuspid reconstruction
according to DeVega’s technique. Most recently, in 2 patients with
concomitant atrial fibrillation, intraoperative radiofrequency ablation
in the left atrium was performed; both had persisting sinus rhythm
after surgery. Cross-clamp time was 59±19 minutes.
Perioperative results and valve disease etiology are
summarized in Table 2.
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Control Group
The control groups consisted of 23 patients subjected to MVR and
21 patients subjected to conventional MVP, both during the same time
interval. For the respective MVR and MVP treatments, 11 and 13 patients
were female, 1 and 2 patients had predominant mitral stenosis,
22 and 12 patients exhibited predominant incompetence, and 0 and 7 had
combined disease. SAQ measurements were 4.5±2.5 (MVR) and 4±0.8
(MVP). Annuloplasty ring size for MVR was 28.6±0.9 mm, and valve
size for MVP was 29±1.1 mm.
Perioperative results are
shown in Table 2; all MVR and MVP data
are compared with the QMV data.
Morbidity and Mortality
Surgery was uneventful in all 67 patients. Thoracotomy had to be
performed again in 2 QMV, 1 MVR, and 2 MVP patients because of
bleeding. One QMV patient, 0 MVR patients, and 1 MVP patient required
transient reintubation for respiratory failure. Severe
ventricular arrhythmia occurred in 1 QMV patient, 0
MVR patients, and 1 MVP patient; cardiopulmonary resuscitation
was required in the latter. There was one perioperative
death after QMV implantation due to a tear in the left internal
thoracic artery used as bypass graft; subsequent bleeding had required
further surgery, and finally, severe low cardiac output syndrome
occurred. Ten months after QMV implantation using a minimally invasive
approach, one patient presented with severe mitral incompetence
and required further surgery for paravalvular leakage. The
suture line had torn off at the middle of the previously calcified
posterior annulus. Electron microscopy revealed
endothelialization of the annulus as well as the tips
of the papillary flaps in this valve. Eight months after MVR, another
patient required further surgery and received a mechanical valve for
severe mitral incompetence due to new onset of chordal rupture at the
anterior leaflet. And another patient required cardiac transplantation
7 months after successful MVR because of progressive dilated
cardiomyopathy. After MVP, one patient was
diagnosed with anterior paravalvular leakage resulting in grade
2 mitral incompetence; thus far, he has been treated
conservatively.
Postoperative Hospital Stay and Follow-Up
All other patients were discharged from the hospital in time
according to the German standards. Wound healing was uneventful in all
patients. After QMV implantation, patients received continuous
anticoagulation therapy (warfarin) only if additional atrial
fibrillation was present. At follow-up, 12 patients were in sinus
rhythm. All patients had clinically improved and tolerated more
physical activities with no or only little dyspnea. NYHA functional
class at follow-up was 1.5±0.4 (QMV), 1.4±0.6 (MVR), and 1.3±0.6
(MVP); SAQ had improved in all patients and was 4.8±1.5 (QMV),
5.1±1.7 (MVR), and 4.6±1.6 (MVP).
Echocardiography
All patients had intraoperative transesophageal
echocardiography. Perfect valve function was seen
in all patients, and the trivial transvalvular refluxes
observed with most mechanical heart valve prostheses were accepted.
There typically is a laminar systolic transvalvular
flow profile after QMV implantation. TTE revealed normal mitral valve
function in all patients after surgery. Transmitral flow velocities
were comparable among the QMV, MVR, and MVP groups; mean
transvalvular gradients were slightly higher in the QMV group.
At follow-up, there was no relevant difference in mitral orifice area
index. First degree mitral valve incompetence was diagnosed in 8 (QMV),
7 (MVR), and 2 (MVP) patients after surgery, whereas second-degree
mitral incompetence was seen in 1 patient each. The average jet area
was 2.2±1 (QMV), 2.1±1.6 (MVR), and 2.6±1.7 (MVP)
cm2. At the 6-month follow-up, first-degree
mitral valve incompetence was diagnosed in 4 (QMV), 9 (MVR), and 2
(MVP) patients; second-degree mitral incompetence, in 1 (QMV), 0 (MVR),
and 1 (MVP) patient; and third-degree mitral incompetence in 1 patient
after MVR who later on underwent further surgery. The average jet area
was 2.1±1.7 (QMV), 3.3±1.7 (MVR), and 2.7±1.2 (MVP)
cm2. Comparative
echocardiographic results are summarized in Table 3.
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Discussion |
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The complex function of the mitral valve is achieved by interaction of the valve leaflets, annulus, chordae, papillary muscles, and the left ventricle. Mitral valve pathology can be divided into patients suitable for valve reconstruction and into those requiring valve replacement. In the latter, mechanical or stented biological valves have been implanted for years. Neither treatment is optimal; thus, new treatment options are required. Homografts or stentless mitral bioprostheses seem to be viable alternatives. Both resemble native mitral valve function, which might be of benefit for the patients. At the moment, there is growing enthusiasm for the use of stentless valves; in combination with effective anticalcification treatments, they might even be the first choice in the future.18 19
Options for Mitral Valve Surgery
Early attempts at mitral valve replacement in the 1960s involved
devices made of synthetic materials. Dissatisfaction at that time with
the imperfections of these first attempts led to experimental and
clinical use of biological tissues such as autologous pericardium and
fascia lata for partial and even complete mitral valve
replacements.20 21 22 23 24 These approaches were defeated by
excessive host response. Since then, aldehyde tanning of xenograft and
autograft tissue followed later by aldehyde treatments have
substantially improved the potential benefits of devices made from
pericardium in particular.25 Later, in the 1980s,
homograft mitral valve replacements were performed.26 27
Despite further research, the risk for tissue failure and the technical
problems of matching donor and host remain.28 29 30 31 32 33 The use
of mitral valve xenografts has been promising, but long-term follow-up
data are missing.34 35 Again, matching donor to host
remains a problem; thus, the procedure is technically complex. Failure
seen at intermediate follow-up may be related to these
factors.36 The use of an autologous pericardial valve was
accompanied by interindividual mistakes and failures as
well.37
Requirements for a Stentless Mitral Valve
An ideal mitral prosthesis should be as close as possible
to native valve, easy to implant at a low perioperative
risk, durable, nonthrombogenic, nonimmunogenic, and
endothelialized with a flexible annulus and chordal
support. Valve orifice area must be adequate, and central flow, low
gradients, low resistance to rapid opening or complete closure, and a
sufficient coaptation area should be achieved. These criteria can be
met only by a biological prosthesis. The QMV xenograft from 4
pieces of bovine pericardium12 13 fits the anatomic
structures, and sizing can be variable because of a large
coaptation area. In addition, an effective polyol anticalcification
treatment is applied.13 Standard sizes are available to
ease clinical implantation. The 3-layer annulus serves as flexible
annuloplasty as well. There has been sufficient experimental testing of
the QMV, and it fits all requirements of the FDA
guidelines.13 14
Evaluation of the Clinical Results
Technically, the QMV is relatively easy to implant when the
described technique is used. Exact sizing is crucial: the annulus
should not be oversized (excess tissue would restrict
transvalvular blood flow). For the adjustment of the papillary
flaps, a neutral position should be chosen. Besides mechanical sizing,
preoperative TEE measurements of the annulopapillary distance under
hemodynamically stable conditions are required.
Too-long chordae of the QMV will lead to bulking of the tissue, whereas
too-short chordae will straighten the valve, forcing more pressure on
annular sutures. Nevertheless, because of the large coaptation area,
risk of mitral incompetence is relatively low, even in postoperative
ventricular remodeling. One of the early patients who
required further surgery had tight papillary flaps; this might have
been the cause of the paravalvular leakage that developed. The
fact that host endothelium was growing on the explanted
valve proves that the polyol-treated tissue is relatively
biocompatible. Since there have been no thromboembolic complications
thus far, only patients with additional atrial fibrillation have
required warfarin for anticoagulation. Restoration of sinus rhythm by
radiofrequency ablation will be of additional benefit for future
patients.
The hemodynamic results shown in Table 3 were
satisfactory compared with conventional valve replacement.
Echocardiography revealed a laminar
transvalvular blood flow profile in most patients at acceptable
flow velocities and valve orifice areas. According to the
manufacturer’s instructions, the orifice area should be at the lower
edge of the normal range to achieve a perfectly competent valve. As far
as the early results are concerned, this goal has been reached.
Nevertheless, when using color Doppler, minimal
transvalvular reflux can be seen in some patients. This is most
likely from the 4 edges of the valve between the different pieces of
pericardium. Clinically, this is not relevant at all; it does not
exceed the "physiological transvalvular
reflux." All mechanical valves have an obligatory closing volume
followed in some designs by a continuing leak, which will be evident by
echo quantification as <10% of the atrial area. From an
echocardiographic perspective, the QMV resembles native
mitral function and perhaps can be considered to be close to an ideal
artificial heart valve.
Preservation of the annuloventricular integrity is important38 39 and can be achieved by QMV implantation. Thus, left ventricular function stabilizes and might even improve in the future. There were no clinically relevant differences when the overall outcome of the patients after QMV implantation was compared with that of the MVR and MVP patients. Before surgery, patients receiving MVR usually are in somewhat better condition and have less additional risk factors. This is well reflected by our patient population. Overall satisfactory clinical and functional results can be achieved by implanting the QMV instead of conventional stented mitral valves.
Limitations of the Present Study
The preliminary results after QMV implantation in a small subset
of patients are encouraging, but intermediate and long-term results are
warranted. Randomization would not be in accordance with ethical
guidelines at the moment. Durability as well as effectiveness of the
polyol anticalcification treatment can be evaluated only after several
years.
Summary/Perspective
This is the first clinical study of QMV implantation in a western
community where biological valve replacement is confined to older
patients only. The initial results are promising: the valve is
relatively easy to implant, and clinical as well as
hemodynamic results are satisfactory. The QMV meets
most criteria to become an ideal heart valve. As soon as long-term
performance is proven, it may become the bioprosthesis
of choice for mitral or even tricuspid valve replacement.
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