Aortic Stenosis and Transcatheter Aortic Valve Implantation
Contents
- Introduction and background
- Diagnosis of aortic stenosis
- Treatment options
- Surgical aortic valve replacement
- Transcatheter Aortic Valve Implantation (TAVI)
- Balloon Aortic Valvuloplasty (BAV)
- Medical therapy
- Conclusion
Introduction and background
The healthy heart has a number of valves which prevent the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. from flowing backwards. Normally these delicate structures are made of thin flexible and durable tissueA group of cells with a similar structure and a specialised function. that works efficiently over the 2000 million heart beats that occur during the course of our lives. When you consider this statistic it is not surprising that on occasions the heart valves can begin to fail. This can occur in one of two ways. Firstly, and most commonly, the valve tissue can become narrowed or stenosed. Alternatively the valves can begin to leak. This is known as regurgitation or incompetence.
Narrowing of the aortic valve, which is known as aortic stenosis, is one of the most common forms of heart disease. It is caused by thickening, fusion and even calcificationCalcium deposited in tissues and organs. of the valve leaflets and is common in the elderly affecting over 4% of people over 80 years of age. It affects both men and woman equally. Aortic stenosis can be tolerated quite well with few symptoms for many years. However, eventually symptoms of breathlessness on walking, anginaA central chest pain caused by insufficient oxygen supply to the heart. or collapse may develop. When this happens it is important to get treatment quickly as untreated symptomatic aortic stenosis is progressiveContinuously increasing in extent or severity. and often fatal.
Diagnosis of aortic stenosis
Aortic stenosis typically causes a loud heart murmurA sound produced by the turbulent blood flow within the heart or arteries, heard with a stethoscope. that your doctor can hear using a stethoscope on your chest. This heart murmur is produced by the turbulent flow of blood being squeezed through the narrow heart valve. The diagnosis is confirmed by a heart ultrasoundA diagnostic method in which very high frequency sound waves are passed into the body and the reflective echoes analysed to build a picture of the internal organs – or of the foetus in the uterus. or echocardiogramAn ultrasound examination of the heart as it is pumping. Also known as an 'echo'.. This test uses sound waves to visualise the heart muscleTissue made up of cells that can contract to bring about movement. and valve and determine the severity of the narrowing. Other tests that might be needed include an ECGThe abbreviation for electrocardiogram, a tracing of the electrical activity of the heart to help in the diagnosis of heart disease. and coronary angiogramAn X-ray image of the coronary arteries, which is taken after introducing a catheter through a blood vessel and threading it towards the heart, then injecting a contrast medium to improve visibility. to assess whether there is any narrowing in your coronaryRelating to the arteries supplying the heart itself. arteries as well. Once you have had these tests your cardiologist can advise you on the most appropriate treatment for you.
Treatment options
Unfortunately aortic stenosis cannot be treated with medicines and in the majority of cases it is better to relieve the narrowing of the valve. Traditionally this has been exclusively by open heart surgery to remove the narrowed valve and replace it with a new man-made valve. Recently, however, a new minimally invasive technique has been developed that allows a new valve to be implanted in the heart through a tube, known as a catheter, inserted through a blood vessel. This treatment is known as Transcatheter Aortic Valve Implantation or TAVI for short. It has the advantage of avoiding opening the chest and the use of a heart-lung bypass machine and therefore has a quicker recovery and return to normal activities time. The recommendation of which treatment is best for you is usually determined by a ‘multidisciplinaryRelating to a group of healthcare professionals with different areas of specialisation.’ heart team which may include many doctors including cardiologists, cardiacRelating to the heart surgeons and anaesthetists. The heart team will consider, amongst other things, the severity of your symptoms and aortic stenosis and other illnesses you may have that would increase the risk or reduce the benefit of one or other treatments. Occasionally, the narrowed heart valve can be simply stretched using a balloon (balloon aortic valvoplasty or BAV) or no intervention may be recommended. Below we describe, in more detail, the various options for treating aortic stenosis and outline the pros and cons of each treatment option.
Surgical aortic valve replacement
Aortic valve replacement by open heart surgery is the standard way of replacing a diseased aortic valve. This involves opening the chest wall through the breast bone to get access to the heart. The heart is stopped using a special solution which protects the heart and the diseased valve removed and a new man-made valve sewn in its place. While the heart is stopped the circulation is supported by a heart-lung bypass machine. There are two main categories of valves, namelyy, biological and mechanical. The optimal choice is dependent on many factors including age, life style and the presence of other medical conditions. Biological valves are usually made from pig valve tissue (porcine) or cow pericardial tissue (bovine). These valves are easy to implant, durable (lasting from 15 to 20 years), and may allow patients to avoid lifetime use of anticoagulants (blood thinning medications). However, in younger patients (aged below 60), these valves are likely to wear out and will need replacing at some stage. Mechanical valves are very durable and may last for many years but do require the patient to take anticoagulants for life. After surgery most patients will stay in hospital for one week and then continue their recovery over a 2-3 month period.
Advantages
Surgery is very effective at replacing the diseased aortic valve with excellent results. There are many different types of valve than can be chosen to suit the individual patient. In many cases, patients may have other heart conditions like coronary disease or disease of other heart valves and surgical aortic valve replacement can be combined with coronary arteryA blood vessel that carries blood away from the heart. Apart from the pulmonary artery and umbilical artery, all arteries carry oxygenated blood. bypass grafting or other valve surgery if necessary.
Disadvantages
In healthy patients isolated surgical AVR is a relatively low risk operation. Other factors such as the patient’s age and presence of lung or kidneyOne of two bean-shaped organs that are located on either side of the body, below the ribcage. The main role of the kidneys is to filter out waste products from the blood. disease can considerably increase the risk and length of recovery time after surgical AVR. Repeat heart surgery or combined surgical AVR and other operations can also increase the risk. If the risk is high then other forms of treatment may be considered (see below). The recommended treatment option should be based on a multidisciplinary team (cardiac surgeon, cardiologist, anaesthetist and others) decision taking in to account all factors including patient's preference.
Transcatheter Aortic Valve Implantation (TAVI)
In TAVI a new aortic valve is implanted in your heart via a tube or catheter. This tube is normally introduced through the artery at the top of your leg (transfemoral approach) and then advanced up to the heart through the blood vessels. If these blood vessels are narrowed or diseased then the catheter can be introduced via the blood vessel under your collar bone (subclavian approach) or directly into the aortaThe body's main artery, which arises out of the heart and supplies blood to all other parts of the body. by making a small incision in your chest wall (direct aortic approach). The final option is to introduce the catheter directly into the heart from the left side of the chest. This is known as a transapical approach. While the transfemoral approach can be performed without the need for surgery the other approaches require progressively more surgical intervention although they all avoid the need for cardiopulmonary bypass or fully opening the chest cavity. With advances in the technology we have found that the majority of patients can be treated by the transfemoral approach without the need for any surgery. Once the catheter has been introduced into the body a guide-wire is fed across the narrowed valve and the valve is stretched open as an initial step. The new valve is mounted within in a metal frame that can be fed through the catheter and positioned inside your own narrowed valve. Depending on the type of valve your doctor chooses, it is then deployed by either using a balloon to expand it or a spring like frame that expands itself when it is released from the catheter. In both cases your heart continues to beat and pump blood throughout the procedure. Once the valve has been deployed the catheter and guide-wires are withdrawn and the arterial puncture repaired.
Advantages
The main advantage of TAVI is that it avoids the need for open heart surgery and cardiopulmonary bypass. This means a more rapid recovery and return to normal activities. Patients on average stay in hospital for about 5 days. To date more than 40,000 TAVI procedures have been performed worldwide with overall excellent results compared to surgery and, so far, excellent valve durability.
Disadvantages
The main disadvantage of TAVI is that it is relatively new technology and therefore it is difficult to know for sure how long the valves will last. With some valves leakage may occur around the outside of the new valve and in a small number of patients this can be significant and require either a second TAVI procedure or even open surgery. The risk of strokeAny sudden neurological problem caused by a bleed or a clot in a blood vessel. following TAVI may be higher than following open heart surgery. Other complications include the need for a permanent pacemakerA small electrical device that functions to maintain a normal heart rate., and the possibility of heart attackThe death of a section of heart muscle caused by an interruption in its blood supply. Also called a myocardial infarction. or damage to the blood vessel during introduction of the catheter. Fortunately, major complications are now rare and further improvements in the technology should reduce some of the risks further.
Balloon Aortic Valvuloplasty (BAV)
In this treatment the narrowed valve is stretched open by a balloon, but no new valve is implanted. It is usually part of the TAVI procedure but occasionally can be used as a treatment in its own right. BAV can be performed through a smaller catheter than TAVI and this is its main advantage. In younger patients with congenitalAny condition present since birth. aortic stenosis the BAV can relieve the narrowing for several years but in many patients its effect is short lived and repeat treatment is necessary.
Medical therapy
This means either doing nothing or treating the symptoms with medication. As such it is reserved only for those patients who have mild aortic stenosis and no symptoms or patients who are too high risk for other interventions described above. Medication itself cannot treat the narrowed valve but it can make patients feel less symptomatic
Conclusion
Aortic stenosis is the most common form of valvular heart disease and if untreated is often fatal. Timely intervention to replace the valve can both improve symptoms and increase lifespan and therefore, in general, should not be delayed once symptoms develop. There are many treatment options for patients including open heart surgery and transcatheter aortic valve implantation (TAVI). A multidisciplinary heart team is essential to consider the most appropriate treatment for each patient.
Dr Michael Mullen
Mr John Yap
