2023-05-18 10:53:16
Sian Harding, you write in your latest book that the heart is our companion through good and bad days. The poets considered the heart to be the seat of all our feelings. Where does the special meaning of this organ come from?
I think our ancestors knew too little regarding the heart. They thought it kept us warm. The peculiarity of this organ is also that we feel it beating. When we are afraid, we find that its heartbeat quickens, just like when we meet someone we love. Another example: broken heart syndrome. The twists of fate within the family, for example, increase the risk of serious heart conditions linked to physical pain in the heart.
Conversely, can the heart also create emotions?
This happens, for example, when we perceive danger and the pulse quickens. In the heart, there is a kind of mini-brain, a nerve center that informs our brain that we are afraid. And this allows the brain to react to danger by triggering, for example, a flight reaction. In laboratory experiments, recordings of a very rapidly beating heart were played to people. If they were told that they heard their own heart, they were afraid and sometimes even panicked.
Why did you, as a young pharmacologist, become interested in the heart?
I was looking for a PhD subject when my father-in-law suffered from heart failure. This motivated me and I realized that we knew very little regarding the heart.
What surprised you the most?
We talk a lot regarding diseases. But really, the fascinating thing regarding the heart is how well it works and how evolution has shaped this organ. The big problem in medicine is that the heart works so well and it’s hard to fix anything in it. The researchers had a bunch of good ideas that ultimately came to nothing. The best-known example is the quest for an artificial heart. It began in the 1960s, around the same time as the conquest of the Moon. We wanted to create an artificial heart by the end of the decade. And we did. But it only worked for a few hours.
21% of women die of heart disease compared to 24% of men
Basically, how is the heart constructed? It seems that muscle cells form the building blocks?
Yes, the muscle cells of the heart, the cardiomyocytes, are like pieces of a puzzle. I was one of the first scientists to successfully isolate these cells from each other. It’s rather complicated because they have a lot of electrical connections to transfer energy. When these cells shorten, the result is a spiral-like movement of the heart muscle that pumps blood through the lungs and body. This movement of the ventricles, left and right, is perfectly coordinated. If the amounts of blood transported differed only by the volume of a teaspoon between one and the other, this would give a difference of 500 liters of blood per day.
The heart cells therefore have electrical connections to transfer the signal and mechanical connections for the force. Do nerve cells play no role?
There are neurons in the heart. But you can take the heart out of the body, fill the vessels with salt water and the heart will continue to beat, spontaneously and without you doing anything regarding it. In the body, the autonomic nervous system decides whether the heart should beat faster or slower, an unconscious mechanism.
Do cardiac muscle cells differ from skeletal muscle cells, for example from those of the arms?
The mechanism of muscle contraction is analogous. But there should be no cramping in the heart muscle cells. The arm can carry a weight, while the heart muscle must relax immediately following a contraction, otherwise the heart might no longer fill with blood.
The heart beats 100,000 times a day. If it doesn’t work for 240 beats, we die. It’s rather scary.
Yes, the heart must always function. This is also the reason why heart muscle cells rarely divide and regenerate. When we try to increase the rate of renewal of cardiac muscle cells by transferring stem cells into them, we find that the heart no longer works so well, because the new cells do not have the necessary electrical contact with other cells and it results in heart rhythm disturbances. This low capacity for renewal of heart cells explains why, even at an advanced age, 50% of our heart cells have been there since we were born.
What are the biggest risk factors for heart health?
The best known are high blood pressure, smoking, diabetes, obesity and lack of movement. And of course age! Heart ailments are diseases of age. But infections also play their part, as the Covid-19 pandemic has shown. Air pollution is also an important risk factor. Not to mention the side effects of certain medical therapies, especially cancer chemotherapy, and psychosocial factors: people at the bottom of the scale suffer more often than those at the top.
And being a man is also a risk factor?
Absolutely. The differences are significant especially among young people: 21% of women die of heart disease compared to 24% of men.
Even though women are apparently treated less well than men.
Studies indicate that women treated by a male cardiologist are twice as likely to die as those treated by a cardiologist. And that’s not because heart disease is a male ailment, as we often hear. Among women, heart disease is not rare enough that doctors cannot identify it. It’s like for a lot of other diseases: we believe less in the symptoms of women than in those of men. The more they suffer, the less they are taken seriously.
Can we describe in simple terms how a heart attack takes place?
A heart attack begins in what is called the sinus node of the heart which is located in the right atrium. It is here that heart cells create periodic electrical signals. The electrical potential increases and as soon as it crosses a certain threshold, the electrical signal continues to propagate, causing the heart muscle to contract. The atria react first, then the ventricles.
During physical exertion, does the heart only beat faster or also stronger?
When we have to exert more effort, the beats get shorter, which speeds up the pulse. But at the same time the amount of calcium flowing into the heart cells changes, so that the beats also get stronger.
What happens during a heart attack?
A heart attack occurs when blood vessels are blocked. The origin may be atherosclerosis, in other words, deposits on the inner wall of the arteries. Blockages can also be caused by lumps from elsewhere in the body that get stuck in a coronary artery. Then the oxygen supply is interrupted and the heart cells begin to die. It goes very fast. Cells die following half an hour already. We must react quickly and place a stent to reduce the blockage. We only have two hours to do it, and the faster we go, the better.
And what happens to dead cells?
This results in stiff scar tissue that no longer regenerates. And that is the problem. In the event of a heart attack, we lose around 2 billion cells out of a total of 5 billion. These heart cells do not grow back.
Is there a biological reason heart tissue doesn’t repair itself?
Cardiac muscle cells are embedded in tissue. It would have to be dissolved for the cells to divide. But there is a mechanism that prohibits cell division.
Can we compare it to neurons which, in the brain, renew themselves very little?
Yes exactly. In these two organs, there is little regeneration. It is quite different with the skin. Following an injury, new tissue grows and the injury heals. On the other hand, the brain adapts insofar as the cells modify themselves: they know how to undertake new connections. Cardiac cells can lengthen, they can create new muscle fibers and adapt to new conditions. The heart thus knows how to control a pregnancy during which the volume of blood increases by 50%.
How to differentiate sudden death of the heart from a heart attack?
There are overlaps between the two. Basically, sudden death of the heart is a consequence of heart rhythm disturbances. The heart then looks like a crawling bag of maggots. In such a case, a defibrillator is needed which restores synchronous heartbeats using an electrical impulse. It can also be achieved by a heart-lung massage or even by a solid punch on the chest. However, such mechanical impulses risk, on the contrary, triggering cardiac arrhythmias. Imagine the impact of a cricket ball.
In the event of a heart attack, approximately 2 billion cells are lost out of a total of 5 billion
And where is the overlap between unexpected heart death and myocardial infarction?
A heart attack can damage the heart to the point of triggering heart rhythm disturbances that eventually lead to the death of the heart.
An artificial heart would be useful. Why is it so difficult to develop?
One of the problems is the risk of infections. An artificial heart must be supplied with electricity from outside. However, connections always involve the risk of infection. To which is added that it is extremely difficult to achieve the balance between the pumping power of the left and right ventricles. Finally, the pump must be prevented from damaging the blood cells.
Will we ever be able to replace the heart with an artificial organ?
In any case, we are making progress. We are now integrating systems that help the heart to pump. This is done in particular for patients who are waiting for a heart transplant. In addition, there is also interesting research on the side of stem cells: we are trying to help the heart with the help of heart cells grown in the laboratory which are attached to the heart muscle like a kind of bandage.
You have practiced forty years of research in cardiac medicine. What are the biggest advances that have been made?
Our understanding of heart failures has greatly improved and so have the drugs to treat them. They prevent damage resulting from the body wanting to stimulate a weakened heart. Immense advances have also been made in pacemakers and implantable defibrillators. These are fantastic auxiliary means today. But I also want to insist on statins. It is completely wrong that these drugs have bad press. These cholesterol reducers are very effective and their side effects are much less than what the media say.
Journey
Sian E. Harding is Emeritus Professor of Cardiac Pharmacology at Imperial College London. She explored the role of heart muscle cells and was the scientific director of the first heart gene therapy study in Britain. Last year, she published with MIT Press Editions the popular work The Exquisite Machine.
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