The narrowing of the aortic valve comes with aging and open heart surgery is often the conventional method to treat this. But for elderly patients and those with debilitating diseases, the surgical risk for open heart surgery is high. Dr Paul Chiam shares a minimally invasive method termed TAVI and the efficacy and safety of this method.
The aortic valve allows blood to be pumped out of the heart to the rest of the body. With aging, the aortic valve may become narrowed (aortic valve stenosis [AS]). When the stenosis becomes severe, patients develop breathlessness, fainting spells and chest discomfort. Left untreated, the death rate is high, with up to 50 per cent of patients dying from the condition within two years.
Open heart surgery to replace the aortic valve is the conventional method of treating this disease, relieving patients of their symptoms and prolonging their life span. For many elderly patients and for patients with other debilitating diseases (for example those with very poor heart function, severe lung disease, end stage renal failure on dialysis etc), the surgical risk for open heart surgery is high, and some patients are even considered inoperable.
In 2002, a percutaneous option “replacing” this aortic valve was first performed in a human as an alternative to open heart aortic valve replacement (AVR) in a “no surgical option” patient. A small incision was made in the patient’s groin and a new valve was delivered via a catheter (tube) into the heart and implanted within the patient’s native aortic valve. This technique has been termed “Transcatheter Aortic Valve Implantation” (TAVI) or” Transcatheter Aortic Valve Replacement” (TAVR) (Fig. 1).
This minimally invasive method is mostly performed via a small puncture in the groin, although in a very small number of patients, other access sites are required (through the subclavian artery in the chest, through the aorta directly via a right lateral thoracotomy, or through the left ventricular apex via a five to six cm incision in the left chest wall). The groin approach (true percutaneous) is the least invasive and thus preferred.
Unlike open heart surgery to replace the aortic valve, with TAVI/TAVR, the patient does not need the chest cracked open, the heart is not stopped and the transcatheter heart valve is implanted on a beating heart, the native aortic valve is not removed and the newly implanted transcatheter heart valve is not sutured in place. The procedure can also be done under local anesthesia for the groin approach.
There are several transcatheter heart valves in commercial use but 2 of these – the Sapien valve made by Edwards Lifesciences (Fig. 2) and the CoreValve made by Medtronic (Fig. 3) – have been used most widely and have the most robust scientific evidence. There are now over 150,000 implants worldwide using these 2 valves alone.
Several large randomized studies have shown the efficacy and safety of this technology. The PARTNER trial (using the Sapien valve) showed that TAVR was superior to (better than) medical therapy (including balloon aortic valvuloplasty – “aortic valve ballooning") in patients with severe aortic valve stenosis (AS) who were inoperable and was non-inferior (equal) to open heart AVR in patients at high surgical risk.
Similarly, the CoreValve trial demonstrated that TAVR using the CoreValve was not only non-inferior (equal) to, but superior to (better than) open heart AVR in high risk patients. From these data, TAVI or TAVR established itself as the treatment of choice for inoperable patients and may be a safer (better) treatment option in patients at high surgical-risk.
However, inoperable and high surgical-risk patients constitute a minority of patients with severe AS who require valve replacement as most patients belong to a moderate or a low surgical-risk category.
Two major randomized trials have very recently addressed the moderate risk group of patients. In the Partner 2A trial that randomized moderate surgical-risk patients with severe AS, TAVI using the Sapien valve was non-inferior (equal) to open AVR with regards to the composite end-point of all-cause mortality and disabling stroke at 2 years. In a sub-analysis of patients who underwent the transfemoral (groin) approach (the majority of patients), TAVI had a lower rate of disabling stroke or death and was thus superior to (better than) open AVR.
Similarly, the SURTAVI trial randomizing moderate risk patients showed that TAVI using the CoreValve prosthesis was non-inferior to open AVR for the combined endpoint of all-cause death or stroke at 2 years. The robust evidence provided by these 2 randomized trials (over 3500 patients studied) suggest that TAVI has become an attractive less invasive treatment option in patients at moderate surgical-risk.
Although the risk of stroke associated with TAVI has been shown in the randomized trials to be either similar to, or numerically lower as compared to open AVR, the absolute risk of stroke is still not insignificant at between two to five per cent. This will take on even more importance as TAVI becomes increasingly applied in lower risk and younger patients.
Several devices have been developed to try to “filter” out debris before these reach the brain or “deflect” them away from the cerebral circulation towards the peripheral organs.
One device in particular, has demonstrated efficacy in reducing the risk of stroke and cerebral embolic burden in a randomized trial. In this trial, the Claret Sentinel device (Fig. 4) – that places two net-like filters into the innominate artery and left carotid artery – has been shown to reduce the risk of peri-procedural stroke by approximately 50 per cent. Based on these promising results, the U.S. FDA has therefore approved this cerebral protection device for use during TAVI (this is the first such device approved by the FDA for this specific purpose).
Up till a couple of years ago, the transcatheter heart valves though safe and effective, could not be repositioned or recaptured if they were implanted in a suboptimal position. In effect, the team had “one chance” to optimally deploy the valve. In January 2015, two repositionable and recapturable valves became available in Asia – the Medtronic CoreValve Evolut R (Fig. 5) and the Boston Lotus (Fig. 6) valves. These new generation transcatheter heart valves could be recaptured and repositioned if the initial implant position is deemed suboptimal, and could even be removed from the body if a smaller or larger sized valve is required. These features increase the accuracy and safety of the procedure.
Other improvements to the technology include the addition of an “external skirt” on the valves (CoreValve Evolut Pro (Fig 5), Lotus valve (Fig. 6), Sapien 3 valve (Fig. 7)) that improves “sealing” of the transcatheter heart valve against the native tissue, thereby significantly reducing the problem of paravalvular leaks (regurgitation between the newly implanted valve and the native tissue due to tiny “gaps”).
Mount Elizabeth Hospital was the first hospital in Asia to perform TAVR/TAVI with these recapturable and repositionable valves and recently was also the first hospital in the South East Asia region to use the Claret Sentinel cerebral protection device during TAVI procedures. The cases were successfully performed under local anesthesia and sedation, via an access in the groin.
These new generation valves are indeed a game changer, with remarkable improvements made over a short span of time, and the recent addition of the cerebral protection device will offer many patients with severe aortic valve stenosis not only an attractive and viable treatment option with TAVR/TAVI, but also a more accurate and safer TAVR/TAVI procedure.
About the Author
Dr Paul TL Chiam
Senior Consultant Cardiologist
The Heart & Vascular Centre, Mount Elizabeth Hospital
Adjunct Associate Professor, National University of Singapore
Dr Chiam is an Interventional Cardiologist at the Mount Elizabeth Hospital. He is also an Adjunct Associate Professor at National University of Singapore. He is trained in complex coronary angioplasty, peripheral artery angioplasty, carotid angioplasty and structural (heart valve) interventions.
He performed the first TAVR in Asia in 2009 and serves as a consultant and proctor to Medtronic CoreValve, helping to train and proctor new centres in Asia that are beginning their TAVR/TAVI programs.