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Nawwar Al-Attar
Bichat–Claude Bernard Hospital
Paris, France
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What we know so far...
Aortic valve replacement (AVR) is the gold standard treatment for symptomatic aortic stenosis, shown to improve outcome and survival. The indications for intervention have been revised often, to be performed earlier before severe myocardial damage. As an isolated procedure, AVR carries an average 30-day mortality of 3%.
High risk AVR
AVR can be fraught with risk and higher mortality in the presence of certain factors. The five most important predictors of mortality in a multivariate analysis of almost 6000 AVR patients were age >80 years, NYHA class >III, EF 30% associated with previous MI, emergent AVR and concomitant CABG surgery. In addition, certain surgical conditions make AVR challenging to perform and increase operative risk. These include:
- redone surgery with patent coronary artery bypass grafts
- a heavily calcified, atheromatous or porcelain ascending aorta
- mediastinal radiotherapy and radiation damage to the myocardium
Unlike co-morbidities, not all technical difficulties are taken into account in the calculation of the preoperative risk with traditional risk-scoring systems. Thus, risk assessment should be performed individually for each patient by a multidisciplinary team, with clinical judgement priming over score calculation.
Patient profile has changed, with patients now presenting with several co-morbidities, particularly coronary artery disease, concomitant CABG and a greater incidence of left heart failure. Thus, transcatheter aortic valve implantation (TAVI) techniques offer a minimally invasive approach by avoiding sternotomy and extracorporeal circulation, thereby providing an alternative therapeutic approach to patients previously denied AVR on the basis of a high operative risk.
Technology and techniques of TAVI
Currently two devices have been commercialised:
- The Edwards SAPIEN valve consists of three bovine pericardial leaflets mounted within a tubular stainless steel stent. It exists in 23 and 26mm sizes, and a 29 mm size is nearing commercialisation. It is available for both ante- and retro-grade implantation. The valve is deployed by balloon expansion under rapid pacing of the heart.
- The CoreValve ReValving system consists of three porcine pericardial leaflets mounted in a selfexpanding nitinol stent. It exists in 26 and 29 mm sizes and is available for retrograde implantation.
TAVI is performed under fluoroscopic and echocardiographic guidance, ideally in a dedicated hybrid operating room offering both catheter-based and surgical facilities. A multidisciplinary approach involving cardiac surgeons, cardiologists and anesthesiologists is crucial for the success of the procedure.
Choice of approach
- The retrograde transfemoral/subclavian (TF) approach is performed using the Seldinger technique through the common femoral or subclavian/axillary artery either prepared surgically or approached percutaneously.
- The antegrade transapical (TA) approach concerns only the balloon-expandable prosthesis. It is performed through a left antero-lateral minithoracotomy under general anesthesia.
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Transcatheter aortic valve protheses:
left Edwards SAPIEN valve and right Medtronic CoreValve
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Each approach has its advantages. Although there are no direct comparative studies for the two approaches, we described outcomes according to an inclusion strategy that favours the TF approach, leaving the TA approach for patients refused all other options. The mean predicted mortality rate was 28% by the EuroSCORE and 16% by the STS score for the study population, but co-morbidities were more frequent in TA patients. Successful implantation was 85.7% and 100% in the TF and TA group respectively, with satisfactory gradients and valve orifice area in all surviving patients. Greater procedural safety and success with the TA approach may be explained by the fact that it is more direct, allowing surgical control of the site of puncture and introduction of the necessary instruments.
The most frequent complications were major vascular observed in the TF group. However, this is expected to decrease with reduction of the diameters of the introduction systems. Stroke was observed in the TF group (6%) only. The absence of stroke in the TA group is probably related to the antegrade positioning and manipulation of the delivery system and valve, a consistent advantage of this approach. On the other hand in-hospital mortality rate was 8% in the TF and 27% in the TA group. This correlated with the higher risk and greater prevalence of major co-morbidities in TA patients, which negatively influenced survival. The results in each approach were thus strongly influenced by the selection strategy. The respective places of both approaches need to be clarified for each approach by a randomised study.
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Gerhard C Schuler
Heart Centre University of Leipzig
Leipzig, Germany
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... and the everyday practicalities
In many centres transcatheter aortic valve replacement has been established as an integral part of daily routine. Implantation success and survival rates have increased remarkably as a result of improved implantation procedures, refinement of device design and selection of appropriate patients. A team approach between cardiologists, cardiac surgeons and anaesthesiologists has demonstrated its efficacy in addressing most of the issues relevant to a successful procedure.
Patients considered for transcatheter valve replacement are evaluated jointly in order to select the implantation route – transfemoral, transsubclavian, or transapical; careful risk assessment and selection of the appropriate device is part of the discussion. As the mean age of patients undergoing this procedure is well above 80 years, a number of comorbidities must be taken into account: frailty, a term unknown in younger patient groups, plays a predominant role. Measurement of iliac vessel size, annular dimension and distance between valvular plane and coronary ostia must be done in a reproducible and highly precise fashion. Significant CAD should be treated by PCI prior to valve replacement.
A hybrid operating room equipped with a full size digital angiographic and hemodynamic monitoring system is the appropriate environment for performing these complex procedures. The importance of high quality imaging cannot be overemphasised. Transesophageal echocardiography, operated by the anaesthesiologist, is extremely helpful in providing additional information for correct positioning of the device. It is able to distinguish between central and paravalvular aortic regurgitation following implantation of the device, and recognises complications - for example, pericardial tamponade - before it causes hemodynamic problems. Although used quite rarely, cardiopulmonary bypass should be kept on stand-by for unforeseen complications (occlusion of a coronary ostium, acute left ventricular failure). Material required for handling of complications, such as covered stents for repair of pelvic vessels, coronary balloon and stents, and equipment for pericardiocentesis should be at close reach.
The implantation procedure itself has become very safe and predictable thanks to careful orchestration and synchronisation between the individual players: each step is pre-assigned, and precise timing of rapid pacing during balloon angioplasty and device deployment is essential, with corrective manoeuvres defined beforehand for immediate execution.
However, deployment of a self-expanding CoreValve prosthesis can be performed without haste, allowing ample time for adjustment of position because blood flow is impaired only very briefly during the process. For a balloon expandable frame the position must be selected with great precision, anticipating movements during deployment which are unique for each model; deployment is usually straightforward and does not allow correction of the final position. We have found it quite useful to have two operators handle the crucial moments of balloon expansion: one operator responsible for stepwise inflation of the balloon, the other concentrating on maintaining position and applying corrections during the last moments of deployment before the final position is reached.
Closure of the femoral artery is routinely achieved by a suture device with a high degree of success. In the near future reduction of device size will benefit handling characteristics even further.
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Transcatheter aortic valve implantation,
Monday 31 August 14:00-15:30, Madrid - Zone 6, FPN 2852-2855