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Minimally invasive aortic valve replacement


23 June, 2011  

Dr Konstantinos 
Zannis, MD

Cardiac Surgeon, Cardiac Pathology Department, Institut Mutualiste Montsouris, Paris, France

Dr François Laborde, MD

Professor of Cardiac Surgery, Institut Mutualiste Montsouris, Paris, France

Aortic stenosis (AS) is the most frequent heart valve disease in western countries and its prevalence increases with age. Aortic valve replacement (AVR) is advised in patients with severe, symptomatic AS. AVR is done through median sternotomy with cardiopulmonary bypass and cardioplegic cardiac arrest. In-hospital mortality ranges from 3% up to 8% in high-risk patients.1,2

Despite the good results of this classical approach, the medical community still seeks further improvement. Could new medical or surgical techniques and/or technologies be applied to reduce patients’ trauma while preserving the quality and safety of the conventional approach? Could these advances benefit patients that until now were considered too ill for AVR?

In the last few years, trans-catheter aortic valve implantation has gained interest in clinical practice, especially in elderly and/or in critically ill patients considered at too high risk for conventional aortic valve replacement. By introducing such technology, it was hypothesized that this elderly and frail population would run a lower procedural risk.

However, available data demonstrate that even in experienced centres, percutaneous valve implantation remains a risky procedure.3 This therapeutic option is not feasible in patients with small peripheral vessels, heavily diseased aorta, or low implantation of coronary arteries. Furthermore, paravalvular leaks are still frequent due to lack of decalcification. Finally, concern has been raised regarding the longevity of trans-catheter aortic valves due to damage inflicted to its pericardial structure after crimping on the delivery catheter.

On the other hand, surgical ‘aggression’ has a double aspect: one aspect being the trauma caused by surgical incision and sternotomy, the other being cardio-pulmonary bypass (CPB).

Pros and cons of keyhole surgery
Minimally invasive aortic valve surgery was introduced in the mid ’90s as an alternative to the full sternotomy approach, and has gained acceptance during the last decade.4,5 A variety of less invasive approaches have been developed.

Parasternal approaches were rapidly abandoned due to resection of right costal cartilages resection, which caused lung herniation in many cases. Actually, most surgeons use either 3rd right (Figure 1) intercostal acess or partial upper sternotomy: this last access is probably the most frequently used.

The theoretical basis of less invasive approaches could be explained by the quantum sufficit concept (as much as suffices): skin incision and sternal division should be just large enough to offer an adequate working space. Exposure of the aortic valve is good using partial upper sternotomy, leaving space for aortic and venous cannulation if the surgeon prefers central to peripheral cannulation, without compromising security, since this access can very rapidly be transformed into full sternotomy in case of emergency.

Partial sternotomy should allow less blood loss and less postoperative pain, thus allowing a more rapid recovery of pulmonary function. It should furthermore result in better sternal stability.6 
Finally, cosmetic advantage with this minimally invasive approach is obvious.

Some technical caveats
Some technical points however require caution. Tying of aortic sutures, dearing of the heart after aortotomy and epicardial leads placement can be cumbersome and require special attention. A knot-pusher is necessary for aortic annulus suture tying; continuous carbon dioxide flooding field must be maintained throughout the whole procedure, and epicardial leads should be placed before aortic cross clamping is ended, because access to the heart is limited. These additional specificities require longer CPB and cross-clamp times and could make some surgeons uncomfortable with this technique.

Tabata et al,7 in one of the largest series published, demonstrated excellent results in patients treated for AVR with a minimally invasive approach. Operative mortality rate was 2.1%, whereas predicted mortality was 4.2%. More interestingly, in the subgroup of patients aged more than 80 years, operative mortality rate was 1.9%, whereas predicted mortality was 7.5%. The results clearly show that the greatest benefit was obtained in the older and more fragile patients.

These excellent results where sustained over time with an actuarial survival rate of 91% at five years and 88% at ten years. These results have to be born to mind when compared with a 30% mortality rate at 30 days after percutaneous valve implantation and a 22% major complication rate. Furthermore, the recently published Parteners study showed mortality at one year was 30.7%.8

The sutureless valve
DeveIopment of new devices could further facilitate mitral and aortic valve replacement (MAVR). Since 2006, we have been evaluating in our department a sutureless biological valve (Figure 2), the Perceval S valve (Sorin Salugia, Italy), which facilitates AVR by avoiding suture tying.

After cross-clamping of the aorta, transverse aortotomy is made higher than usual, 1cm distal to the sinotubular junction, leaving a free edge for closure of the aortotomy after implantation of the device. The diseased, native aortic valve is removed and the aortic annulus decalcified.

Three guiding threads are placed at the nadir level of each resected cusp. These threads are used as reference for accurate alignment of the inflow section of the prosthesis with the insertion plane of the native leaflets. These threads are positioned in the lowest part of the native leaflet insertion line for each valve sinus. At the prosthesis level, each thread is passed into a slot corresponding to the median part of the prosthetic sinus.

The release device is inserted into the aorta to the point where it is blocked by pulling the previously positioned thread guides. The valve prosthesis, loaded into the delivery device, is released in two phases: first, the inflow section is opened, then the outflow part is opened. Full release of the prosthesis is obtained only after the latter procedure. When the prosthesis has been completely deployed, the thread guides are removed.

In order to optimize the area of contact between the prosthesis and the aortic annulus, post-dilation is performed using a balloon catheter at a pressure of 4 atmospheres. Aortotomy is then closed by the means of a running 5-0 polypropylene suture.

Comparison with percutaneous valves
Early results with this new valve are very good. This new kind of implant not only reduces CPB time but also offers some other interesting advantages when compared to percutaneous valves:

  • 
Sutureless valves are implanted on an arrested motionless heart, avoiding potential interference with the patient’s hemodynamics and allowing very precise positioning in the ventricular outflow tract
  • 
Migration during implantation is impossible
  • 
The hemodynamic profile of this sutureless bioprosthesis compares favourably with classical bioprosthesis, allowing very low transvalvular gradients.9

All the above-mentioned advantages could further stimulate interest in MAVR.

Cardiopulmonary bypass circuit evolution  
Since the beginning in the early ‘50s, CPB has revolutionized cardiac surgery and became a standardized tool used in everyday practice. However, CPB is responsible for some of the morbidity associated with AVR. During CPB, the blood is diverted into an extracorporeal circulation circuit. Contact with perfusion circuit exerts an inflammatory and procoagulant action, provoking increased capillary permeability with fluid shift to the extra vascular compartment and organ impairment. These impairments of normal physiology could have a clinical reflex patients could require longer ventilatory support, diuresis support and, in more rare cases, hemodialysis.10

Air-blood interaction in the cardiotomy reservoir of the CPB circuit is also a source of platelet activation, with consecutive platelet dysfunction and accentuation of postoperative bleeding.

Modern CPB circuits coated with heparin and phosphorylcholine, together with Mini-extra corporeal circulation (MECC), were some of the responses developed to attenuate the inflammatory response (IR), stimulating the widespread use of this technique. MECC uses a shorter heparin-coated circuit, which allows for a shorter blood-circuit interface of activation and a low priming volume that decreases hemodilution. There is no venous reservoir leading to no air-blood contact. Beneficial effect on hemostasis and decreased inflammatory markers in patients operated using MECC have been confirmed.11

As the medical community keeps seeking the Holy Grail of minimally aortic valve replacement, this new old friend can be a solid proposition to nearly every patient suffering from symptomatic AS, until the percutaneous approach reaches 
maturity.

References

  1. 
The Society of Thoracic Surgeons 2008 Cardiac Surgery Risk Models: Part 2 – Isolated Valve surgery. Ann Thorac Surg. 2009 July;88(1 Suppl):S23-S42
  2. 
Leontyev S et al. Ann Thorac Surg 2009;87:1440-5
  3. 
Safety of percutaneous aortic valve insertion. A systematic review. www.biomedcentral.com/1471-2261/9/45
  4. 
Cosgrove DM 3rd & Sabik JF. Ann Thorac Surg 1996;62:596-7.
  5. 
Cohn LH et at. Ann Surg 1997;226:421-8.
  6. 
Tabata M et al. Eur J Cardiothorac Surg 2008;33:537-541
  7. 
Karimov JH et al. Interact CardioVasc ThoracSurg 2009;9:1021-2
  8. 
Leon MB et al. N Engl J Med 2010;363:1597-1607
  9. 
Shrestha M et al. J Heart Valve Dis 2009;18:698-702
  10. 
Modine T et al. Interact Cardio Vasc Thorac Surg 2010;11:406-10
  11. Minimally invasive closed circuit for aortic valve replacement. Ann Thorac Surg 2007;84:586-587