Dr Chiam Toon Lim Paul
The aortic valve is like a one-way gate that regulates blood flow from the heart to the rest of the body. The valve opens to allow the heart to pump blood to other organs, and closes to prevent blood from flowing backward into the heart.
With ageing, the aortic valve may become narrowed, in a condition known as aortic valve stenosis. When the narrowing becomes severe, patients develop breathlessness, fainting spells and chest discomfort due to a lack of oxygen-rich blood. If left untreated, the disease can be deadly, with up to 50% of patients dying within 2 years.
Dr Paul Chiam, cardiologist at Mount Elizabeth Hospital, explains how transcatheter aortic valve implantation (TAVI) features in the treatment of this condition and how TAVI is a game changer in heart surgery.
Open heart surgery has been the conventional method to treat aortic valve stenosis. Replacing the aortic valve relieves patients of their symptoms and prolongs their life span. However, the surgical risk for open heart surgery is high for many elderly patients and for patients with debilitating diseases, such as poor heart function, severe lung disease and end-stage kidney failure. In fact, some of these patients are even considered inoperable.
As an alternative to open heart aortic valve replacement, the transcatheter aortic valve implantation (TAVI) was first performed on a 'no surgical option' patient in 2002. In this minimally invasive method, a small incision is first made in the patient's groin. Thereafter, a new valve is delivered through a catheter (or a tube) into the heart and implanted within the patient's native aortic valve.
Although TAVI is mostly performed via a small puncture in the groin, other access sites may be required in a very small number of patients, such as through the chest artery or the left ventricular apex of the heart. The groin approach, also known as 'true percutaneous' (via skin), is the least invasive and thus preferred.
Unlike open heart surgery, the patient undergoing TAVI does not need the chest cracked open, the heart is not stopped when implanting the transcatheter heart valve onto the beating heart, the native aortic valve is not removed and the newly implanted transcatheter valve does not need to be stitched in place. The groin approach procedure can also be done under local anaesthesia.
Several large randomised studies have shown the efficacy and safety of the TAVI technology. For instance, the PARTNER trial showed that TAVI was better than aortic valve ballooning, which uses a balloon to widen the narrowed heart valve, in inoperable patients. The trial also found that TAVI was as effective as open heart surgery. In addition, the CoreValve trial demonstrated that TAVI was better than open heart surgery in high-risk patients. From these data, TAVI has established itself as the treatment of choice for inoperable patients, and may be a better and safer treatment option for patients with high surgical risk.
For patients with moderate surgical risk, TAVI has also become a less invasive option. In a sub-analysis of patients who underwent the groin approach TAVI treatment, TAVI had a lower rate of consequent disabling stroke or death, and was thus better than open heart surgery.
Nonetheless, Dr Chiam qualifies that although the risk of stroke associated with TAVI is similar or lower than open heart surgery, there remains significant absolute risk of stroke at 2 – 5%, as with any heart surgery. This is an important consideration as low-risk and younger patients increasingly undergo TAVI.
Nonetheless, Dr Chiam adds that several devices have been developed to reduce the risk of stroke associated with heart treatments by filtering debris before it reaches the brain or deflect debris away from the brain's blood supply.
In addition, new generation transcatheter heart valves can now be repositioned if the initial implant position is deemed suboptimal, and can even be removed if a smaller or larger sized valve is required. This increases the accuracy and safety of the procedure. Some valves also improve 'sealing' of the transcatheter heart valve against the native tissue, thereby reducing the problem of leakage due to tiny gaps between the new implanted valve and the native tissue.
These new generation valves have indeed been a game changer, with improvements made over a short span of time. The recent addition of the cerebral protection device in TAVI also offers many patients with severe aortic valve stenosis a safer and viable treatment option.