Animals of 50 kg were sedated, intubated, and coupled to a ventilator. In six animals, standard “midline sternotomy” was performed, heparin administered, cannulas placed in the ascending aorta and right atrium, and cardiopulmonary bypass established. The aorta was clamped and cardioplegia administered into the aortic root. In a minimally invasive group of six animals, a small neck incision was used to allow cannulation in the right carotid artery and external jugular vein. Heparin was administered, cardiopulmonary bypass was established, and a small left thoracotomy was made in the fourth intercostal space (Fig. 3). In both groups, a left atriotomy was done, and a prototype of the Medtentia double helix annuloplasty ring implanted by rotating it into place with one helix arm above and one below the posterior mitral valve annulus. The sewing ring was fixated to the mitral annulus with 6 to 8 sutures. The atriotomy was closed and after 30 minutes of reperfusion animals were weaned from cardiopulmonary bypass and cannulas removed. Protamine sulfate was administered, hemostasis secured, and drains placed. Steel wires were used to close the sternal bone in midline sternotomy animals, and in the minimally invasive animals, the thoracotomy was closed with sutures. When hemodynamic stabilization was obtained and bleeding was less than 50 mL/h, animals were awakened, extubated, and returned to the farming facilities. Ten weeks later, transthoracic echocardiography was performed, and animals were subsequently killed to allow gross anatomic examination.
Operating time was defined as time from skin incision to skin closure. Recovery time was defined as to time from skin closure to extubation. Cardiopulmonary bypass time was recorded. Ten weeks postoperatively, mitral valve function and morphology were assessed using 2D transthoracic echocardiography. Ex vivo hearts were inspected to assess annuloplasty ring placement, mitral leaflet morphology, and signs of infection.
The significance level was 5%. Data are presented as mean ± SD. Normally distributed data in the minimally invasive and midline sternotomy groups were compared using Student t test, and nonnormally distributed data were compared using the Mann–Whitney rank-sum test.
All animals survived surgery and 10 weeks follow-up. Midline sternotomy animals had a statistically significant 4-fold increase in recovery time. There was, however, a nonstatistically significant tendency of longer operating and cardiopulmonary bypass times in the minimally invasive group (Table 1).
In all animals 10 weeks postoperatively, transthoracic echocardiography revealed bileaflet mitral valve function without regurgitation, morphologic signs of tissue deterioration, or endocarditis.
In all animals, the Medtentia annuloplasty ring was imbedded in scar tissue in the mitral annulus. There were no signs of ring dehiscence, thickened or damaged leaflets, or endocarditis.
In this study, we conducted preclinical testing of a prototype of the Medtentia double helix mitral annuloplasty ring in 12 healthy pigs. Animals were allocated to either conventional sternotomy or a minimally invasive thoracotomy for surgical access. All animals survived surgery and 10 weeks follow-up. In both groups, the annuloplasty rings were embedded in scar tissue without signs of mitral regurgitation, leaflet damage, or infection. This indicates that the implantation technique of the Medtentia annuloplasty ring in mitral annulus and leaflets using the key-ring concept is not harmful to the mitral valve apparatus in the porcine experimental model. Accordingly, we also conclude that, compared with conventional midline sternotomy, the minimally invasive approach did not negatively affect mitral valve function and morphology 10 weeks after implantation. Whether this is also the case in the clinical setting will be addressed in a clinical safety study currently being performed.
A tendency, although not statistically significant, was observed in the minimally invasive animals toward longer operating and cardiopulmonary bypass times. This is in concordance with clinical experience where introducing minimally invasive procedures, i.e., robotic surgery and port access surgery, has shown to be more time consuming because of a limited surgical operating field, use of endoscopic type equipment, and more complex setups in the operating theater.1 It should be noted, however, that the Medtentia double helix mitral annuloplasty ring system used in this model has the potential for sutureless implantation, which could theoretically shorten implantation time. Furthermore, significantly reduced recovery time was observed in the minimally invasive group compared with midline sternotomy animals as a result of shorter time to obtain hemodynamic stability and cessation of bleeding. This indicates that the extra time used in the operating theater could be well spent in terms of reducing patient distress and potentially obtaining a faster recovery.
Caution must always be observed when addressing the external validity from animal experimental testing. Furthermore, minimally invasive mitral valve surgery is most often performed in patients with myxomatous degeneration of the mitral valve leaflets and chordae tendineae. Because no animal model of this disease has been established, this study was done using healthy animals, which might further limit the external validity. The animals were observed for 10 weeks postoperatively, which may not be sufficient to conclude long-term durability of the Medtentia annuloplasty ring. The potential for sutureless implantation of the Medtentia ring was not addressed.
By using a both minimally invasive and conventional midline sternotomy approach in a porcine experimental model, the Medtentia double helix annuloplasty ring showed no sign of mitral valve dysfunction or tissue damage 10 weeks postoperatively.
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This experimental study evaluates a novel annuloplasty system that would be easier to implant than traditional rings and may potentially facilitate a minimally invasive approach. It joins a growing number of innovations designed to permit minimally invasive approaches to mitral valve pathology. Using both a left thoracotomy and a conventional sternotomy approach in this porcine model, the Medtentia Double Helix Mitral Annuloplasty ring showed no sign of impairing mitral valve function or damaging surrounding tissue 10 weeks following surgery. There are a number of limitations to this study. The experiments were done on healthy animals without mitral valve disease. Therefore, whether or not this ring would correct actual mitral pathology remains to be addressed in future studies. The short followup also does not address whether this ring would have long-term durability. Finally, the experiments did not address whether or not sutureless implantation is possible.
Keywords:© 2010 Lippincott Williams & Wilkins, Inc.
Minimally invasive surgery; Mitral valve ring annuloplasty; Porcine experimental model