The
first successful valve surgery of any kind, a mitral valve repair (blind mitral
commissurotomy) was performed at Peter Bent Brigham Hospital (now Brigham and
Women’s Hospital) in Massachusetts, USA by Dr Elliot C. Cutler in a young girl
comatose from low cardiac output with rheumatic mitral stenosis in 1923 [1,2].
In 1925, Sir Henry S. Souttar performed the first finger fracture of mitral
stenosis. After the Second World War, Dr. Dwight E. Harken (famous for removing
shell fragments lodged in soldiers’ hearts) at the Peter Bent Brigham Hospital,
performed a large series of closed mitral valvuloplasties for mitral stenosis.
He worked very closely with Dr. Laurence B. Ellis, a cardiologist there. This
exemplifies the concept that mitral valve problems are best treated by a team
involving cardiac surgeons, cardiologists and cardiac anesthesiologists working
together [3]. The first open mitral valve repair for mitral insufficiency was
performed by Dr. C W Lillehei at the University of Minnesota in 1957 [4]. Dr.
Dwight C. McGoon of the Mayo Clinic reported the nouvelle techniques of valve
repair to repair a ruptured cord in the posterior leaflet in a 1960 issue of
Journal of Thoracic and Cardiovascular surgery [5]. The first artificial mitral
valve was implanted by Dr. Nina Starr Braunwald in 1960 at the National
Institute of Health that was a homemade device and never produced commercially.
The first commercially successful valve was revolutionized by Dr. Albert Starr
and his collaborator M. Lowell Edwards at the University of Oregon in the early
1960s. The misconceptions of deleterious effect of valve surgery on left
ventricle of the 1970s was changed by the demonstration of the importance of
the mitral apparatus in maintaining good left ventricular function after mitral
valve surgery by Dr. Miller and colleagues at Stanford University[6,7]. In
1980s, there was an increased incidence of mitral valve repair and Dr. Alain F.
Carpentier of the University of Paris outlined the pathophysiological
classification of mitral valve lesions and provided the tools for collaborative
work of cardiologists, cardiac surgeons and cardiac anesthetists. But, the
recurrence of regurgitation was a problem and Dr. Carlos M. G. Duran pioneered
flexible ring as a solution. Patients with regurgitant myxomatous mitral valves
that underwent repair with ring had a recurrence rate of 3.6% (Figures 1 and
2).But repair without ring had a recurrence rate of 15%.
The development of treatment for mitral valvular disease behind the iron
curtain during 60 covers another interesting chapter. Until recently many of
these stories were not known to the Western world d ue to censorship and
language barrier. The first valvular prosthesis in USSR was implanted by a
Ukrainian surgeon Nikolai Mikhailovich Amosov. In 1965 he also developed a
valve made of antithrombotic materials. He was also famous for his writings.
His famous novel Mysli i serdce (Thoughts and heart) is actually based on the
story of the first valve implantation. This amazing book has been translated in
more than 30 different languages. It’s a must read for any cardiac surgeon.
Anticoagulation has always been an issue with the mechanical valves. Daily
intake of anticoagulants and regular checking of prothrombin time made life
difficult for the valve recipients. One solution of this problem was implanting
biological valves. Various bioprosthetic devices were designed and marketed for
implantation in the mitral position incorporating porcine, bovine, equine
tissue. These valves had excellent hemodynamic properties and didn’t require
anticoagulation, but the long term durability has been a major concern. These
valves tend to degenerate and a difficult second redo surgery for replacing the
degenerated valve is often warranted.
Minimal access mitral
surgery
Since the first mitral valve repair procedure for
mitral stenosis, mitral valve surgery has been evolving rapidly. Prosthetic
mitral valves have been developed for mitral valve replacement, which can be
performed using transcatheter access. Similarly, mitral valve repair has
progressed form closed commissurotomies to open complex mitral valve repairs
using artificial cordaes and rings. Access to the mitral valve is achieved
through small incisions with the use of endoscopes and robotic systems, thus
avoiding sternotomy.
Endoscopic minimal
access mitral surgery
Endoscopic minimal access mitral surgery was
introduced in 1996. It incorporates the use of endoscope and instruments
specially designed to minimize surgical trauma caused by the conventional
access to the mitral valve through the median sternotomy as much as possible.
In a typical setting, the patient is connected with the cardiopulmonary bypass
circuit through the peripheral vessels. For venous drainage, internal jugular
and femoral veins are used, and for arterial access the femoral artery is
typically cannulated. The aorta is then clamped with the use of either a
cross-clamp or an endoballoon, which acts as an occlusion device. Cardioplegic
solution is then instilled into the coronary arteries and the heart is arrested
in a similar manner to conventional procedures. The mitral valve is access from
a right lateral minithoracotomy (4-6cm) or even a right peri-areolar incision.
Visualization and exposure of the mitral valve is optimized with the use of endoscopes,
which can provide two-dimensional (2D) or three-dimensional (3D) images. With
the use of thoracoscopic instrumentation, the mitral valve is assessed and
repaired with contemporary techniques, which include ring implantation,
artificial chordal replacement, leaflet resection etc. From the same minimal
access, mitral valve can be replaced with a mechanical or a biological
prosthesis. Many concomitant procedures can also be performed using the above
set-up, including tricuspid valve surgery, atrial septal defect closure, relief
of hypertrophic obstructive cardiomyopathy, excision of masses such as myxomas,
atrial fibrillation surgery and closure of left atrial appendage [8]. From the
description above, one can understand why the phrase “minimal access mitral
surgery” is better suited to these techniques, as opposed to the term “minimal
invasive mitral surgery”. Despite the fact that access is minimal, the
procedure to the heart itself has a similar degree of “invasiveness” to
conventional mitral surgery performed through a median sternotomy.
Robotic mitral surgery
Robotic systems mainly consist of a console and a
robotic cart. Through small incisions, robotic instruments and endoscopes are
introduced to the chest cavity and the operation is performed by the operating
surgeon unscrubbed, controlling the robotic instruments from a distance. The
main advantages of robotic implementation include superior 3D visualization,
elimination of tremor, seven angles of freedom for the instruments (compared to
four in endoscopic access). However, it involves a loss of tactile feedback for
the surgeon and higher cost when compared to endoscope or traditional access
mitral surgery [9]. Establishment of cardiopulmonary bypass and cardiac arrest
is similar between endoscopic and robotic mitral surgery, with similar
incisions and identical possibilities for concomitant procedures. Therefore,
robotic mitral surgery can also be classified as “minimal access”. The robotic
system that has been used most in cardiac surgery worldwide is the da Vinci
family from Intuitive Surgical (Sunnyvale, CA, USA). First applications for
mitral operations started in 1998 and since then there has been a gradual
adaptation in many centres in Europe and the USA. Currently, over 100
robot-assisted mitral procedures per year are taking place in Europe and over
1700 in the USA. The main limitation of further expansion is the increased cost
and steeper learning curve of robotic training compared to endoscopic
[10].
Contraindications of
minimal access mitral surgery
Minimal access mitral surgery, despite being
technically more demanding and having a learning curve, offers the complete
range of surgical options for the treatment of mitral valve disease. There are
however, a few contraindications and limitations to minimal access approaches.
Pleural adhesions and history of extensive radiation to the chest could
complicate the entrance to the chest cavity and access to the heart. As single
lung ventilation is required until cardiopulmonary bypass is stablished,
patient with poor lung function or inability to tolerate single lung
ventilation should be excluded from these techniques. Patients with peripheral
vascular disease and aortic regurgitation should also be excluded, and chest
deformities such as pectus excavatum can make access very difficult. Minimal
access robotic mitral surgery is also associated with increased operation times
compared to conventional sternotomy approach, leading some surgeons to avoid
minimal access surgery in patients with many comorbidities or reduced left
ventricular function who may benefit from a quicker operation.
Outcomes of minimal
access mitral surgery
The short and long term data for conventional mitral
valve surgery, and more specifically mitral valve repair through sternotomy
approach, demonstrate excellent results. The STS database revealed a 1.2%
mortality for isolated mitral valve repairs, which is further reduced to 0.6%
when the patients are asymptomatic. Reports of long-term outcomes show freedom
from reoperation which reaches 95% in 15 years and survival similar to a
control population when the procedure is carried out early and the patient is
in NYHA class I or II. These excellent results serve as a bench mark to which
minimal access mitral procedures should be compared. Reports and meta-analysis
that compare traditional and minimal access endoscopic techniques demonstrate
less pain, improved cosmesis, reduced blood transfusions, reduced wound
infections, less incidence of atrial fibrillation, and reduced ventilation
time, intensive care length of stay and hospital length of stay for minimal
access surgery. In a large series, the mortality rate remained low (1.1%) and
in 95% mitral valve repair was feasible with a 94% freedom from reoperation at
15 years. Robotic mitral surgery has demonstrated similar excellent outcomes
with mortality rates of <1% despite the fact that cross-clamp and
cardiopulmonary bypass times were slightly longer [9]. In hospital morbidity
for endoscopic minimal access mitral surgery procedures has been low.
Conversion to sternotomy has been reported to be as low as 2%, incidence of
stroke 0.3%, myocardial infarction 0.6%, new-onset atrial fibrillation 17%,
need for permanent pacemaker implantation 2.3%, renal insufficiency 2.6% and
wound infection 0% [11]. The above results show excellent perioperative
mortality, morbidity, and long-term outcomes of minimal access mitral surgery.
However, there are currently no randomized control trials with enough power to
demonstrate significant superiority of these techniques when compared to
conventional sternotomy mitral surgery.
Other minimal invasive
mitral valve procedure
Technological advances in transcatheter aortic valve
replacement (TAVR) have also been implemented to the mitral valve. Transcatheter
mitral valve replacement procedures have been introduced, which are performed
in centres experienced in TAVR. These procedures aim to replace the mitral
valve using a catheter delivery system without the need for cardiopulmonary
bypass or cardiac arrest. Four different systems have currently been
implemented into humans; they are all still under clinical investigation and
are not available commercially. These are the CardioAQ (Edwards Lifesciences,
Irvine, CA, USA), TendyneTM (Tendyne Inc. [now Abbott], Roseville, MN, USA),
TiaraTM (Neovasc Inc., Richmond, BC, Canada) and the Twelve valve (Medtronic,
Minneapolis, MN, USA). All these valves are delivered through the apex of the
heart following a small left anterior thoracotomy, with the exception of the
CardioAQ valve which is designed also to be delivered trans-femorally and
trans-septally. There are anatomical and morphological limitations which make
transcatheter mitral valve replacement more complex compared to TAVR. There is
however, increased interest from the industry as more devices are currently
under development [12]. Minimal invasive chordal replacement techniques have
recently become commercially available. The Neocord (Neocord, Inc., St. Louis
Park, MN, USA) is a device which introduces artificial chordae’s from the
cardiac apex and secures them at the edge of the posterior mitral leaflet. The
other end is then tied at the epicardial surface of the left ventricle, with
chordal length adjustment happening in real time with a beating heart under
echocardiographic guidance. Long-term results are awaited from this exciting
new technique. Finally, interventional cardiologists have an armamentarium of
innovative therapies for the treatment of mitral regurgitation. These
techniques are the Mitraclip (Abbott Vascular, Santa Clara, CA, USA), mitral
annular remodeling devices and ventricular remodeling devices. The MitraClip is
by far the one that has been most extensively implanted and investigated. First
implantations took place in 2003, and CE mark and FDA approval was granted in
2008 and 2013, respectively. This device, inspired by the surgical edge-to-edge
repair initially described by Alfieri, is a clip which is introduced through a
femoral vein and advanced to the mitral valve through the atrial septum. Under
echocardiographic and fluoroscopic imaging, the clip is deployed to grasp
anterior and posterior mitral valve leaflets, which results in increased
coaptation and reduced regurgitation. The procedure is performed typically by
interventional cardiologists without any use of cardiac arrest or
cardiopulmonary bypass and is effective in high and prohibitive risk patients
suffering from primary and secondary mitral regurgitation. Results from the
randomized control trial EVEREST II were promising, despite the fact that a
recurrence in mitral regurgitation was observed in 25% of the patients in one
year. Furthermore, the randomized COAPT trial recently published results that
demonstrate reduced rates of hospitalizations and death, as well as improved
quality of life and functional capacity for symptomatic patients suffering from
secondary mitral regurgitation and heart failure. These patients were receiving
maximum tolerated optimum medical therapy and were also treated with MitraClip.
As other studies, such as the MITRA-FR, found no benefit for patients suffering
from secondary mitral regurgitation treated with MitraClip, we can therefore
assume that there is need for further evidence with regards to indications of
MitraClip implantation [13].