1 INTRODUCTION
Aortic Valve Replacement
(AVR) is by far the most effective
approach to treat aortic stenosis
(AS).
Since the implementation of
minimally invasive aortic valve
replacement (MIAVR) by right
thoracotomy in 1993, a variety of surgical methods including partial
midline sternotomy, reverse sternotomy, parasternal approaches, and
port-access via thoracoscopy have been developed.1-3Compared with conventional AVR, MIAVR has several advantages, including
reduced blood transfusion, less pain, excellent postoperative outcome,
quicker recovery, and better cosmesis.4-5 Despite
differences in surgical approach, the basic operative procedure has
remained similar. Following aortotomy, the diseased valve leaflets are
excised and the annulus is debrided. Then the prosthetic valve is
anchored in the aortic annulus by sutures under
cardiopulmonary
bypass (CPB) and cross-clamping of
the aorta. Removal of the severely
calcified aortic valve and annulus is the most challenging step.
The conventional technique in MIAVR has several limitations. It
mechanically pulverizes the calcified tissue on the valve and annulus,
which requires prolonged cross-clamping time and CPB time. The residual
tissue generated during annular debridement may cause perioperative
myocardial infarction and cerebral infarction. Incomplete removal of
calcification also prohibits
implantation of a prosthetic valve
of proper size and may cause perivalvular leakage. Recently, ultrasonic
aspirator has been applied during MIAVR.6 However, in
our practice, this method generates large amount of debris, is not
effective in crushing calcified tissue deeply wrapped by the intimal
tissue, and causes damage to the local normal tissues by ultrasonic
energy.7
Aortic valve leaflet is composed of 4 clearly defined tissue layers: the
endothelium, fibrosa, spongiosa and ventricularis. The valve leaflets
are attached to aortic valve annulus
which is a dense collagenous network.8 The aortic
valve annulus is covered by fibrosa, which continues to cover the
adjacent valve tissue.9 The calcific nodules and
lesions tend to occur primarily in the fibrosa layer and extend to the
aortic side of the valve.10 Therefore, calcified
tissue is formed not only on the valve, but also on the annulus. As long
as the fibrosa layer is peeled off, the purpose of removing
calcification can be achieved. Histologically, the spongiosa layer is
located below the fibrosa layer. The spongiosa layer, which has a high
proteoglycan content, is a layer of loose
connective,11 so it is easy to separate the fibrosa
layer from the spongiosa layer. Taking advantage of the above
pathological characteristics of calcified tissue, we have developed a
new surgical technique, which we coined a term as
fibrosa layer stripping
(FLS), to peel off the fibrosa layer
at the calcified tissue of aortic annular.
In order to evaluate the potential benefits of using FLS technique in
removing the calcified tissue in MIAVR, we designed a prospective and
randomized clinical trial and assessd its short- and long-term outcomes
compared to conventional technique in present study.