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Bristol: The operations
Some people have likened paediatric heart surgery to plumbing - and in principle, they are similar.
Congenital heart defects leave the heart pumping the blood the wrong way - tubes are connected to the wrong point, or valves do not work as intended.
Here, however, the similarities between these trades ends.
Most plumbers carry a large selection of spare parts, don't have to work on a boiler the size of a small plum - and turn off the entire system before they start.
There are perhaps fewer than two dozen heart surgeons in the UK who are skilled in operating on babies.
It is a remarkable science, with the difference between success and failure a matter of millimetres.
The Bristol heart babies affair focused on just a few, highly complex operations.
BBC News Online spoke to Martin Elliott, an experienced surgeon from the Great Ormond Street Hospital for Sick Children in London, who explained how they developed, and how they are done today.
How the heart should work
The heart is a pump which drives blood around the body in two different ways.
The heart is split in two, with each side having one chambers whose job it is to pump out blood - the ventricles.
The right ventricle of the heart pushes blood out to the lungs through the pulmonary artery, where it receives oxygen.
When it returns from the lungs via the pulmonary vein, it falls into the left atrium, then through a valve into the powerful left ventricle, which forces it out through a blood vessel called the aorta to supply the rest of the body.
Here it loses its oxygen - and its bright red colour, turning back to a dull blue.
This "blue blood" returning through a blood vessel called the vena cava arrives back in the right atrium, and falls into the right ventricle - where the whole process starts again.
In babies with congenital heart defects, there is some fault in the structure of these chambers, the walls which divide them, or the vessels which feed blood to and from them.
These faults mean blood doesn't circulate efficiently - and the baby's body is starved of oxygen it needs.
The wall of muscle which divides the left side of the heart from the right must be kept intact.
This keeps the oxygenated blood returning from the lungs separate from the de-oxygenated, or blue blood coming back from the rest of the body.
Some babies are born with holes in this central divider, mixing the two types of blood and preventing the heart from directing them efficiently.
Simple versions of this involve a hole perhaps between the two ventricles (ventricular septal defect or VSD), or between the two atria (atrial septal defect, ASD).
This involves a much bigger hole - really two holes, one between the two atria, and one between the ventricles, which have joined in the middle.
Because the hole is so big, it stops two heart valves forming properly, so the end result is one inefficient valve.
The net result is that blood is "shunted" from the left side into the right, and is pumped to and from the lungs at greater pressure than normal.
Over time, this can lead to permanent damage to the lungs - so the operation to patch the hole shut and rebuild the valves is normally carried out within the first few months of life, so that the damage can be minimised.
Transposition of the great arteries
This is a major plumbing problem - essentially the major blood vessels taking blood away from the heart to the lungs and the body are "plugged in the wrong way".
Instead of oxygenated blood from the lungs being sent off around the body, it simply gets forced back through the lungs again.
And de-oxygenated blood is sent on an endless and useless cycle around the body.
Normally that duct closes naturally in the days after birth - but doctors use a drug to fool the body into keeping it open, and keeping the baby alive.
Unfortunately, correcting the problem is not simply a question of unplugging both these vessels and plugging them back in the right way.
Other, smaller, but vital arteries supplying blood to the heart muscles themselves branch off one of the vessels only a tiny distance from the heart.
These tiny vessels have to be successfully moved too - and this was beyond the skills of the surgeon and his team in the 1960s and 1970s.
Some tried this "switch" procedure then - but all the patients died.
Instead, the Senning procedure was developed.
A technically simpler operation, it involved reshaping the heart so that the left and right ventricles effectively swapped roles.
The weaker right ventricle took on the tough job of pumping blood around the body instead of only getting it up to the lungs and back.
Initial survival rates were good - but the disadvantages soon became clear.
Because the right ventricle is doing a job for which it is not designed, it weakens - and doesn't last.
Early death, and poorer quality of life, are very likely.
So surgeons, as skills improved, started to consider the switch again. As it left the heart working as nature intended, it should give a better quality of life, and a longer one. Was it now possible?
By the late 1970s, in the top centres in the world, it was. By the early 1980s, the technique was finding favour elsewhere - and early mortality rates started to drop.
When Janardan Dhasmana, the surgeon at Bristol, tried to start doing switches in the late 1980s, he was already lagging behind many surgeons elsewhere, whose survival rates were improving fast.
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