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Look into your heart

Look into your heart : Computer technology could help us to understand the human heart better, says Sanjida O'Connell

Sanjida O'Connell

Thursday May 31, 2001

The problem with hearts is that they stop beating. They beat once a second until they stop and after four minutes you die.

Dramatic electric shock treatment, beloved of ER and Casualty, works for reasons of which we are unsure, but fewer than 5% of people who have a heart attack outside a hospital survive.

At the computational biology department at Leeds University, Professor Arun Holden is investigating how hearts die by creating a virtual heart.

It may soon be possible to hold a heart in its death throes and feel it quiver like a bag of jelly. He believes this technique will allow scientists to understand the heart better and could teach us how to keep a heart alive.

Normally, the pacemaker - a collection of cells which imposes the heartbeat - keeps the rest of the heart thumping in time by sending electrical signals to the cells, causing them to contract and relax.

During a heart attack, the cells beat and communicate with each other perfectly normally, but the system as a whole malfunctions. If the electrical signal hits an obstacle, for example, a part of the heart that has become damaged, the signal then acts as a wave flowing round the damaged section - rather like an ocean wave parting round a rock.

Some sections of the heart are thus stimulated more than others which means they don't have a chance to relax. This can create waves of contraction that spiral round the heart. The same wave constantly passing through the same piece of tissue is known as a re-entrant wave and makes the heart beat 10 times faster than normal, leaving it quivering or writhing as if coated with worms. Because the heart is no longer pumping properly, oxygenated blood is not forced round the body.

However, it is difficult to investigate what happens in a whole human heart. "You can't really do all that much in the way of experimental investigation on human hearts because if you think of going to the butcher's to buy a heart, it's a great lump of meat and you need to see what's happening inside it. As soon as you cut it you destroy its mechanical property," says Prof Holden.

He has been using computer programmes to model the heart beating arrythmically. The problem is that the heart needs to be modelled as an entire organ in 3D and this takes an enormous amount of computing time - 10 seconds of heart time could take six months of scientist time. But researchers need to know what happens during the whole four minutes from heart attack to heart death.

Prof Holden is about to buy a 100 gigaflop system which has the equivalent power of a military style supercomputer. This will allow him to continue modelling the heart, but much faster, and also ask qualitatively different questions, which would not normally be practical as they would take up so much computational time.

"It's like the difference between Lindbergh's transatlantic flight and a scheduled jumbo jet flight. It is the same basic science. Planes fly from A to B, but instead of doing it once, you can keep the tourism industry going," says Prof Holden.

In practical terms, the 3D heart could help surgeons. A patient with a heart problem would feed his or her own data - electrical readings from the heart - into the computer and watch the heart beating in 3D. Surgeons can then begin to work out the best treatment.

"You can say: 'here's a model of a person's heart and something is wrong with it. If I do this, what happens? Is it successful or not?' You use the computational model to guide you as to how you're going to intervene," says Prof Holden.

"At the moment, this is all done in the heads of cardiologists. The reason why this has to be a computational simulation rather than experience knowledge base is because everyone is slightly different. We are not textbook people and it's not a textbook disease."

It will also be possible to link the 3D heart to a virtual reality system so surgeons can feel the heart in their hands and plan how best to carry out operations. At the moment, surgeons often make clay or plastic models of the heart. "The model allows a more reliable prediction of the effects of intervention," says Prof Holden.

The 3D virtual heart could also be used to test the affects of drugs. One drug he has already looked at blocks the channels in heart cells through which sodium passes. This makes the cells less excitable and therefore less likely to be affected by arrhythmic waves. However, the virtual heart model showed that the tissue becomes more vulnerable to re-entrant waves so that taking the drug is risky.

The recent completion of the human genome map could help heart research too.

So far, 50 genes which code for the development of proteins in the heart have been discovered. One genetic heart disorder is known as LQT. Scientists now know which genes and which proteins are involved in this disease.

One variation of the disease affects the sodium channels in heart cells, while another affects potassium channels.

The former is five times more likely to be lethal because, during an arrythmic attack, the wave propagates round a small area and the heart cannot recover easily.

When the disorder affects potassium channels, the wave wanders round a large area and reaches the surface of the heart. This usually stops the wave, allowing the heart to resume a normal beat.

Now that the difference between the two forms of LQT has been discovered, it should be possible to develop a drug for people suffering from the sodium abnormality to make any arrythmias they have meander round a larger area and hopefully stop by themselves.

Every year, around 100,000 people die from heart disease, most of them unnecessarily and prematurely. Prof Holden's work may help reduce deaths in future. But as he points out, more than half of these fatalities could be prevented by a change in lifestyle.



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