Rather than looking overseas, more heart patients are turning to heart valves donated by fellow Singaporeans, thanks to a national facility set up three years ago, reports LEE HUI CHIEH
Patients here are now getting more heart valve transplants from donors in Singapore than donors from other countries – since a national facility to collect and preserve grafts of heart tissue was set up three years ago. The number of those who received a heart valve donated here grew from two in 2008 – when the National Cardiovascular Homograft Bank was started – to 17 last year. The 30 recipients of donated heart valves in the last three years were aged between three and 60 years old. The 30 donors, both living and deceased, were aged between 18 and 63. The living donors no longer needed their own heart valves after receiving a whole heart transplant.
Last year, the grafts came from nine cadaveric and three living donors, up from three cadaveric donors and three living in 2008. The bank also stores other types of grafts, such as the windpipe and arteries like the aorta. Only one of these has been used. The donated aorta was used in 2009 to repair a patient’s heart artery that had been badly damaged by an infection. Though donations of tissue grafts are up, it is not directly because of recent changes to organ transplant laws, said Ms Tracy Seck, the bank’s clinical coordinator, who counsels donors and their families on tissue donation.
The Human Organ Transplant Act was expanded in 2004 to include corneas, hearts and livers, in addition to kidneys. Under the Act, these organs in Singaporeans who suffer brain death can be used for transplant, unless they had opted out. As heart valves, windpipes and arteries are not included under the Act, donors or their next-of-kin had to have pledged to donate these parts.
But the publicity over the legislative changes and organ donation in the last few years has resulted in greater awareness and acceptance of organ donation, said Ms Seck. Previously, hospitals here had to request all donated heart valves from overseas agencies, said Dr Lim Yeong Phang, the bank’s medical director.
Last year, the National Heart Centre Singapore and KK Women’s and Children’s Hospital used 17 valves donated here, but still had to import five from Britain. The National University Heart Centre, Singapore has performed about 50 heart homografts in the last 10 years and has obtained most of the tissue from Britain. Higher fees for overseas valves Patients have to pay a higher processing and transportation fee of $7,800 for a valve from Britain, compared to $5,000 for a valve from Singapore, said Dr Lim.
Donated heart valves are usually needed by patients with congenital heart disease. They often have a missing or malfunctioning pulmonary valve, which controls the flow of oxygen-rich blood from the heart to the lungs. Some patients may have an aortic valve – it allows the flow of oxygen-rich blood from the heart into the aorta and the rest of the body – which is problematic. When such patients were babies, they were too small for any type of replacement valve to be implanted, said Dr Lim, who is also a senior consultant at the department of cardiothoracic surgery in the National Heart Centre Singapore.
Typically, a shunt is inserted to connect the heart to the lungs, but this is too small to function as the patient grows in size and a valve is then needed, he said.
About 30 to 40 years ago, a mechanical valve was sometimes used as a replacement, but doctors now try to avoid implanting such valves, especially in children, as blood clots can form on the devices and raise the risk of strokes and heart attacks, said Dr Lim. Patients have to be on blood-thinning medication for life to prevent blood clots from forming and that then adds a risk of bleeding, he added. Instead, bioprosthetic heart valves, taken from pigs or cows and treated, can be used.
Donated heart valves are preferable as they tend to last 10 to 15 years, compared with the eight to 10 years for bioprosthetic valves, said Dr Lim. The body does not usually reject either of these types of valves and the patient does not need to take immunosuppressants or blood-thinning medication.
One patient, delivery van driver Quek Siow Kiak, 44, who was born with a hole in his heart and no pulmonary valve, had a shunt inserted in infancy. At the age of 12, he had the hole repaired and a mechanical valve inserted to function as the pulmonary valve. Thinking he felt fine three years ago, he stopped taking his blood-thinner as well as seeing his cardiologist. An unrelated toothache landed him back at the National Heart Centre Singapore last year, when his dentist realised that he had stopped taking his medication. Luckily, his arteries had not become clogged.
In July last year, he had an operation to replace the mechanical valve, which had become calcified and faulty, using a valve from the bank. A couple of months after that, he resumed cycling and playing football weekly. He also started working out at the gym four to five times a week. He said: “The difference before and after the operation is huge. Previously, I had to stop after 10 to 15 minutes of playing football because I would be too breathless, but now I can last the whole 45-minute half of the game.”
How heart tissue is banked
In the operating theatre, the surgeons cut free a block of tissue containing the heart valves, the windpipe or the aorta. The National Cardiovascular Homograft Bank’s scientific officer, Ms Heng Wee Ling, packs the tissue in a cold saline solution of 1 to 10 deg C.
Back in the bank’s
laboratory, located in the Singapore General Hospital
she separates the donated tissue if it contains two
She also removes excess
tissue. All this is done under
a laminar flow hood, a
special cover over a work
bench designed to prevent
contamination of the tissue
by creating a flow of air
towards the user.
The valves are soaked in an antibiotic solution for 24 hours to clean them. The windpipe is soaked for 48 hours because it has more contact with air and hence a higher risk of contamination.
After that, Ms Heng collects samples of tissue from the valves to test for the presence of bacteria and fungus. A sample of blood from the donor is also tested for infectious diseases. These tests take up to a month to complete. The bank’s medical director, Dr Lim Yeong Phang, assesses these results, the donor’s medical records and whether the heart valves leak. If any bacteria or fungus is found or the donor or valve is unsuitable, the tissue will be discarded. In the last three years, the bank has discarded 17 of 53 donated tissues for such reasons.
Each piece of donated tissue is packed in a double layer of special freezing bags. The inner bag is filled with a cryoprotectant solution, a special chemical to protect cells from dying after being frozen.
The bags of tissue are placed in a special cooler, which uses liquid nitrogen to lower their temperature gradually by 1 deg C per minute, until about -50 deg C.
The bags of frozen tissue are transferred into a portable column of metal drawers, which is then submerged in a tank of liquid nitrogen at -180 deg C, which is labeled a quarantine tank.
When a sample clears all the tests, it will then be transferred to the actual storage tank of liquid nitrogen. It remains viable for up to five years in storage.