Our heart contains valves which allow blood to flow in a single direction. This is very important for the function of the heart. The aortic valve is the first valve that controls the exit of blood from the left heart chamber to enable the supply of oxygen and nutrients to the rest of the body. When this heart valve is damaged, leading to valve stiffening and an inability to open adequately, we term this aortic valve stenosis.This condition is progressive and the valve narrows more, leading to higher difficulty for the left heart to eject blood out of the heart. This results in increased thickening of the left heart muscle and eventually heart failure. We grade the severity of aortic stenosis into mild, moderate and severe.
This occurs most commonly from wear and tear, fibrous tissue and calcium accumulation over time. This is termed degenerative calcific aortic valve stenosis which presents itself in the 7th decade of life. Other causes include degeneration of a bicuspid aortic valve, which is a congenital heart condition, as well as rheumatic heart valve disease (when patients had suffered from rheumatic fever in the past).
A physician would be able to perform a physical examination to diagnose this condition. Often times, this may be suspected when a murmur (abnormal sound) is heard with the stethoscope.This can then be confirmed by an echocardiographic examination.
When this is diagnosed, first consult a cardiologist to discuss the condition. Severe symptomatic aortic valve stenosis is a serious condition, which leads to death if left untreated. This should not be neglected or ignored as successful treatment can lead to significant improvement of the condition.
It is important to note that some patients may not be overtly symptomatic (if they lead relatively sedentary lives) and may only be detected to have this condition by his/her physician or after tests are done.
There are a variety of methods to treat this condition.
This includes conventional open heart surgery where the diseased valve is removed and replaced with a new artificial heart valve. Open heart surgery has improved significantly over the years and now minimally invasive techniques are also available.
This is a catheter based treatment where a stent based valve is delivered through a tube (catheter) often through the thigh arteries and delivered to the diseased heart valve. In this treatment, the diseased valve is not removed but the tissues are pushed aside by the stent and the internally sewn valve tissue starts to function immediately.
Transcatheter Aortic Valve Implantation (TAVI) is used to treat severe aortic stenosis, a condition in which the aortic valve becomes narrowed, obstructing the outflow of blood from the heart and thereby requiring the heart to work harder to pump blood around the body.
TAVI is a procedure performed using the Edwards Sapien Transcatheter Heart Valve (THV), an artificial heart valve designed to be inserted into your heart so that it holds open and replaces your diseased aortic valve. It consists of a metal stent (made of steel or cobalt-chromium) which secures the device in its intended position inside your own valve, and valve leaflets (made of biological material derived from cows) to direct the flow of blood out of your heart.
TAVI now offers effective treatment to patients who are at high risk for conventional open heart surgery. It is also intended to prevent further damage to the heart from aortic stenosis and to prolong life, which medical therapy cannot do.
Before the procedure, you will undergo routine investigations to evaluate whether TAVI is possible and which of the two techniques for TAVI (Transfemoral or Transapical route) is most appropriate for you. The investigations will also identify any other considerations that need to be addressed for your treatment.
Whether you are selected to undergo the transfemoral or the transapical approach, this procedure will be performed under general anesthesia. As the heart is not opened to expose the aortic valve, fluoroscopy (X-rays) and transesophageal echocardiography (ultrasound) are used to visualise the heart and THV, and to guide the insertion of the THV. The duration of X-ray exposure that you will receive will normally be less than 30 minutes, the normal length of time it takes for a coronary artery procedure in the cardiac catheterisation laboratory.
1.3.1. Transfemoral TAVI
The transfemoral device is designed to be implanted through the blood vessel (femoral artery) in your leg. Due to the size of the catheter (hollow tube) being placed in your artery for this approach, your doctors will evaluate the angiograms and/or CT scans to ensure your blood vessels are big enough for this device. Prior to implantation, the THV is “crimped” (carefully compressed to a size that fits inside your femoral artery) using a specifically designed crimping device. The crimped THV is mounted onto a balloon delivery catheter, a special device which is used to carry the THV up to the heart and directly into your aortic valve. The valve is then expanded using a balloon to fit inside your stenotic aortic valve, holding your own valve open permanently. Once the valve is in position and the delivery system is removed from your femoral artery, the artery is closed using a special suture device designed for this purpose. After the procedure, you will be transferred to the Coronary Care Unit (CCU).
1.3.2. Transapical TAVI
The transapical approach is used for patients whose arteries are too small or too diseased for the transfemoral approach.
The delivery system for this approach is designed for THV implantation through the tip (apex) of your heart, which is reached through a small incision made between the ribs just below the left nipple. The crimped THV and delivery system is inserted through the apex of your heart directly into your stenotic aortic valve. The valve is then expanded using a balloon to fit across your stenotic aortic valve, holding it open permanently. After the procedure you will be transferred to the Cardiothoracic Intensive Care Unit (CTICU).
After the TAVI procedure, you will be transferred to either the CCU ward or the CTICU ward for close monitoring. When you are first transferred, you may be under sedation and on ventilatory support. Over the course of the next 24 hours, you will be awakened from the sedation and allowed to breathe on your own with the ventilation tube removed. You will remain in the CCU or CTICU ward until your doctor feels that you can be transferred to a regular hospital ward, where you will continue to be monitored until your discharge from the hospital, usually within 5 – 7 days.
You will be given blood thinning medications such as aspirin and clopidogrel (Plavix). You should continue taking these or other blood thinners for 6 months after the procedure and aspirin for life (as recommended for routine stenting of coronary blood vessels and any replacement heart valve).
The following routine checks will be completed while you are in hospital:
Thereafter, you will be required to see your doctor in the clinic after 30 days, 6 months, 12 months, and then once a year. Routine checks such as echocardiography are repeated at your first and subsequent outpatient follow-ups.
Like any other kind of operations, there are risks associated with this procedure. However, the long-term risk to your life and your quality of life may be higher if severe aortic stenosis is not treated.