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Percutaneous valve replacement: an alternative to open chest surgery in aortic stenosis patients

Transcatheter aortic valve implantation is a less invasive procedure that avoids many of the risks associated with conventional open heart surgery, enabling elderly patients to be treated

Jan Kovac
Cardiology Division,
University Hospital
of Leicester

Aortic stenosis is the most common valvular disease in adults in the Western world and, when severe and symptomatic, carries a poor prognosis. Among the elderly, however, up to 30-40% of cases are considered too high risk or inappropriate for conventional open heart surgery and therefore remain unreferred and untreated. These factors played a role when in 2005 our team joined the effort of French inventor Professor Jacques Seguin and worked on the concept of transcatheter aortic valve implantation (TAVI). The idea behind it was that, like any other catheter laboratory procedure, if there was a good design of valve this would be much less invasive for the patient than conventional surgery and would avoid all the risks related to conventional open chest surgery in an ageing patient.
In Leicester, we have one of the largest centres for heart disease in the UK and long-term experience in various structural interventions, with a tradition of pioneering various percutaneous treatments for cardiac diseases.  All the complementary specialties needed for optimal care and starting these procedures were already in place in Leicester – a good and spacious catheter laboratory with up-to-date angiographic imaging modalities and echocardiography machines. In addition, there were good personnel resources: a cardiac surgeon with keen innovative interest, an imaging specialist, an echocardiographer, a cardiac anaesthetist who specialised in high-risk anaesthesia for cardiac intervention, and a care of the elderly specialist to look after general aspects of those polymorbid and sometimes frail patients.
This multi-specialty group, which we now call the ‘Valve Team’, was quite a novel concept in 2006 when we negotiated with the regulatory authorities in the UK to join the efforts of German colleagues who had also started these procedures with first-generation devices. Our effort culminated in 2007 when, following all regulatory approvals, we successfully initiated a
programme of TAVI in the UK. Results of a pivotal study performed during 2007 were very successful and encouraging, and the device received the CE mark based on these in 2008. We were pleased when our very first female patient – who was a housebound 89-year old before treatment – was well enough to turn out for our annual patient ballroom dancing event two years later. We have had a steady stream of patients for this procedure from the UK and overseas ever since, and we are involved in a broad range of studies with further improved devices as well as in studies comparing these directly with conventional surgery and looking at possibly moving to lower-risk groups of patients. Because of the less invasive nature of the procedure, it promises to be the preferred method of treatment for patients in the future.
Encouraging results have since been confirmed by other centres around the globe and the method is now spreading rapidly,
providing new hope for many patients in whom the risk from conventional surgery was prohibitively high, if possible at all. We now perform these procedures on a weekly or fortnightly basis. In the process, we learned the value of multidisciplinary teamwork and multidisciplinary clinic, which is challenging
to organise, but extremely rewarding when we see the quality of life in our patients changing tremendously in a relatively short period of time after implant. It is a concerted team effort
in selection of patient and precise diagnostics, culminating in the minute details of precision during the implant itself.
The procedure is performed in a catheter laboratory either under sedation or general anaesthesia, the purpose of which is to monitor valve deployment by transoesophageal echocardiography. Recent developments in echocardiography with miniaturisation of the probes might obviate the need for general anaesthesia altogether. It is usually accomplished in around 45 minutes with the patient back on the ward and woken up and mobilised within a day and discharged home a few days later. This compares favourably with conventional surgery (if at all possible in such patient), which is an operation lasting a few hours followed by a stay of some days on an intensive care unit and then on a surgical ward, with a need for rehabilitation afterwards. TAVI has become a rapidly evolving technique with potential to create a paradigm shift similar to the introduction of PTCA in early 1980s. Two ‘first-generation’ devices are currently marketed in Europe and around the world: the Edwards Sapien balloon expandable bioprosthesis (Edwards Lifesciences, Irwine, California) and the Medtronic-Corevalve self-expanding bioprosthesis (Medtronic Inc, Minneapolis, Minnesota) and several further devices are being assessed in first-in-man (FIM) trials (Lotus-Sadra, Direct Flow, Jena).
The number of prostheses implanted is growing rapidly in Europe. So far worldwide, there have been about 9,000 devices implanted. Acute and long-term results suggest that the 30
days mortality with this procedure is around 10%, with one-year survival around 70%, reflecting the high group of patients in whom these valves are implanted. Late mortality
is almost exclusively related to non-cardiac comorbidity of these patients.
While evidence for the position of these devices in relation to conventional surgery and conservative management is being sought via ongoing or planned randomised trials, this
therapy is currently provided to many elderly or severely polymorbid patients around the world as an alternative to surgical aortic valve replacement (AVR), if the risk of surgical AVR is considered too high. Selection criteria for TAVI are clinical and anatomical. Clinical risk assessment is complex. There are very few absolute contraindications to surgical AVR (such as porcelain aorta), and there is no current valve-specific surgical risk score to apply. Euroscore and STS can be used as supportive documentation, but validation of risk and suitability for TAVI should be by a multidisciplinary team, which should review each case. Assessment of anatomical variables is detailed – the aortic annulus and adjacent structures, the relationship and distance to coronary arteries and the cardiac septum size.
Currently available CE marked devices cover a range of anatomies for annular sizes between 18mm and 27 mm, with substantial sizing overlap in the middle for both designs
(Edwards 18-25mm, Medtronic Corevalve 20-27mm). Attention needs to be paid to precise measurement of the annular dimensions (using TTE, TOE, angiography and CT, if necessary), especially at either end of the spectrum or with borderline measurements between the different sizes of the prostheses.
While these designs are fundamentally different, many patients can be treated successfully with either device. Furthermore,
due to the size of prostheses, there are additional minimal diameter requirements for the size of the femoral artery access (6mm for current Medtronic Corevalve and 7-8mm for current Edwards Sapien). Multislice CT and aortography enable femoral measurement, as well as qualitative assessment of the whole
femoro-ileo-aortic path. Alternative access (transapical or transaxillary) may be more appropriate in some patients with excessive calcific tortuosity of the vessel, even if their femoral diameters are sufficient.
Short- and mid-term results of this therapy are very encouraging and promising. Provided that these results are confirmed with durability matching currently implanted surgical
bioprostheses, we can expect gradual expansion into lower risks groups in years to come. Another appealing concept here is to use this method to treat failed surgically implanted aortic valve prosthesis. This is now also being tested in ongoing trials around Europe. At present, the cost of the procedure is driven by the cost of the prosthesis. But apart from that, all other costs are significantly less – inclusive of shortening of hospital stay as well as much earlier patient mobilisation and
discharge home.
My prediction for the future is that with novel designs developed by leading companies resulting in miniaturisation of devices as well as in simplification and increased safety of implant procedure, and with increasing experience of physicians, TAVI will evolve into the main therapy for aortic valve disease in the general population over the next few years.