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.