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Innovations: Technology & Techniques in Cardiothoracic & Vascular Surgery:
doi: 10.1097/IMI.0b013e3181d84316
Original Article

Medtentia Double Helix Mitral Annuloplasty System Evaluated in a Porcine Experimental Model

Jensen, Henrik MD, PhD*; Simpanen, Jarmo MD†; Smerup, Morten MD, PhD*; Bjerre, Marianne MS*; Bramsen, Morten MS*; Werkkala, Kalervo MD, PhD†; Vainikka, Tiina MD, PhD†; Hasenkam, J. Michael MD, DMSc*; Wierup, Per MD, PhD*

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Author Information

From the *Department of Cardiothoracic and Vascular Surgery T and Institute of Clinical Medicine, Aarhus University Hospital-Skejby, Aarhus, Denmark; and †Department of Cardiothoracic Surgery, Helsinki University Central Hospital, Helsinki, Finland.

Accepted for publication February 1, 2010.

Supported by Heart Beat Medical Technology and also it supplied the Medtentia double helix annuloplasty rings.

Presented at the Annual Scientific Meeting of the International Society for Minimally Invasive Cardiothoracic Surgery, Boston, MA USA, June 11–14, 2008.

Address correspondence and reprint requests to Per Wierup, MD, PhD, Department of Cardiothoracic and Vascular Surgery T and Institute of Clinical Medicine, Aarhus University Hospital-Skejby, Aarhus, Denmark. E-mail: perwieru@rm.dk.

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Abstract

Objective: To further develop and improve minimally invasive surgical procedures, dedicated appropriate surgical devices are mandatory. In this study, the safety and feasibility of implanting the novel Medtentia double helix mitral annuloplasty ring, which uses the key-ring principle to potentially allow faster and sutureless implantation, was assessed using both minimally invasive and conventional surgical techniques. Because of ethical concerns, a human compatible porcine experimental model of mitral valve surgery was used.

Methods: Twelve 50-kg pigs were allocated to implantation of the Medtentia double helix annuloplasty ring using conventional midline sternotomy including cardioplegic arrest or a minimally invasive approach using peripheral cannulation and left ventricular fibrillation. Ten weeks after surgery, echocardiography was performed to assess mitral valve function. Animals were then killed, and gross mitral valve anatomy was examined ex vivo.

Results: All animals survived 10 weeks without developing mitral regurgitation, structural leaflet damage, ring dehiscence, or endocarditis. In the minimally invasive compared with the midline sternotomy group (mean ± SD), significantly reduced recovery time (80 ± 16 vs. 327 ± 23 minutes, P < 0.01) and a tendency toward increased operating time (199 ± 33 vs. 168 ± 15 minutes, P > 0.05) and cardiopulmonary bypass time (98 ± 12 vs. 91 ± 11 minutes, P > 0.05) were observed.

Conclusions: By using a both minimally invasive and conventional midline sternotomy implantation techniques, the Medtentia double helix annuloplasty ring showed no mitral valve dysfunction or tissue damage 10 weeks postoperatively.

The prevalence of heart valve disease is expected to increase in the next decades as the large 1950s generation pass into the phase of life prone to cardiovascular disease. This calls for continued reevaluation of surgical methods and dedicated devices to improve surgical outcome and relieve patient distress. Most cardiac surgical procedures require conventional midline sternotomy. However, despite a complication rate of only 1% to 2%, sternotomy is generally perceived with great apprehension by patients and referring physicians. This entails a significant psychologic barrier to the application of open-heart surgery even in severely symptomatic patients. A solution to this problem may be a more widespread use of minimally invasive procedures, which have been shown to decrease bleeding and transfusion rates, reduce pain, improve cosmetic results, and shorten hospital stay.1 In many adult cardiac surgery centers, minimally invasive techniques for aortic and mitral valve procedures have been a focus area in recent years. Minimally invasive port access mitral valve surgery using robotics2 and fiber endoscopic cameras have shown results comparable with those achieved with full sternotomy.3,4 Furthermore, minimally invasive mitral valve repair has been introduced in experimental studies using the Alfieri stitch,5 coronary sinus annuloplasty,6 and left ventricular remodeling,7 and clinical trials are being conducted. To further facilitate faster and easier mitral valve annuloplasty procedures, the novel Medtentia double helix mitral annuloplasty was developed. This ring consists of a double helix similar to a key ring and is implanted by rotating it around the mitral valve leaflets to place one helix arm in the left atrium and one arm in the left ventricle. The ring is, thereby, fixated by squeezing the mitral annulus, thus establishing a potential for sutureless implantation.

To test the safety and feasibility of implanting the Medtentia annuloplasty ring using both minimally invasive and conventional midline sternotomy implantation techniques, we used a human compatible large animal porcine model previously established at our institution.8

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METHODS

This study was conducted using 12 Danish landrace pigs. All animal experiments were conducted according to the guidelines given by the Danish Inspectorate for Animal Experimentation and after specific approval from this institution. Qualified animal caretaker personnel monitored the health status of animals at all times during the study period. Analgesics were administered whenever animals showed any sign of pain. In case of refractory pain or poor thriving, animals were killed.

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The Medtentia Double Helix Annuloplasty Ring

The Medtentia double helix annuloplasty ring consists of one titanium rod folded to form a spiral (double helix) similar to a key ring (Fig. 1). The ring is implanted by leading the free end of the spiral under the posterior leaflet at the posterior commissure. The ring is then rotated clockwise around the posterior and anterior mitral leaflet. This places one helix arm above and one below the mitral annulus, fixating the ring as it squeezes the mitral annulus between the two helix arms. The Medtentia prototype was, however, fitted with a cloth-sewing ring to allow suture placement if deemed necessary by the surgeon (Fig. 2).

Figure 1
Figure 1
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Figure 2
Figure 2
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Surgical Procedures

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.

Figure 3
Figure 3
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Data Acquisition

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.

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Statistical Analysis

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.

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RESULTS

Surgery Time

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).

Table 1
Table 1
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Echocardiography

In all animals 10 weeks postoperatively, transthoracic echocardiography revealed bileaflet mitral valve function without regurgitation, morphologic signs of tissue deterioration, or endocarditis.

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Gross Anatomy

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.

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DISCUSSION

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.

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Limitations

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.

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CONCLUSIONS

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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REFERENCES

1.Richardson L, Richardson M, Hunter S. Is a port-access mitral valve repair superior to the sternotomy approach in accelerating postoperative recovery? Interact Cardiovasc Thorac Surg. 2008;7:678–683.

2.Anderson CA, Kypson AP, Chitwood WR Jr. Robotic mitral surgery: current and future roles. Curr Opin Cardiol. 2008;23:117–120.

3.Chitwood WR Jr, Elbeery JR, Chapman WH, et al. Video-assisted minimally invasive mitral valve surgery: the “micro-mitral” operation. J Thorac Cardiovasc Surg. 1997;113:413–414.

4.Aybek T, Dogan S, Risteski PS, et al. Two hundred forty minimally invasive mitral operations through right minithoracotomy. Ann Thorac Surg. 2006;81:1618–1624.

5.St Goar FG, Fann JI, Komtebedde J, et al. Endovascular edge-to-edge mitral valve repair: short-term results in a porcine model. Circulation. 2003;108:1990–1993.

6.Maniu CV, Patel JB, Reuter DG, et al. Acute and chronic reduction of functional mitral regurgitation in experimental heart failure by percutaneous mitral annuloplasty. J Am Coll Cardiol. 2004;44:1652–1661.

7.Fukamachi K, Inoue M, Popovic ZB, et al. Off-pump mitral valve repair using the Coapsys device: a pilot study in a pacing-induced mitral regurgitation model. Ann Thorac Surg. 2004;77:688–692.

8.Smerup M, Pedersen TF, Nyboe C, et al. A long-term porcine model for evaluation of prosthetic heart valves. Heart Surg Forum. 2004;7:E259–E264.

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CLINICAL PERSPECTIVE

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:

Minimally invasive surgery; Mitral valve ring annuloplasty; Porcine experimental model

© 2010 Lippincott Williams & Wilkins, Inc.

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