Do damaged hearts fight back?

"Patients who survive coronary disease develop stronger hearts which are more effective at fighting any further damage", the Daily Mirror said today.

The BBC, who also covered the story, reported that a study has found that the damage caused by heart disease may make the organ cope better with the dangers of surgery.

Researchers believe that by “understanding the exact chemical reaction they may be able to replicate this with drugs” and therefore boost the chances of success for heart patients, the BBC said.

The research behind these stories is a laboratory study in mice. It explored what effect a disease which resembles human coronary artery disease (CAD) has on the heart’s behaviour when blood is restored to the heart.

Any interpretation of this study's results should be tempered with the knowledge that there are vast differences in the physiology and anatomy of mice and humans, and only a small number of animals were analysed in this experiment.

It would be completely incorrect, not to mention potentially dangerous, to have the idea that people who survive coronary disease are protected against further damage. There is no benefit to having damaged heart tissue. One of the best ways to protect your heart is to avoid getting coronary artery disease in the first place, and if you already have CAD, to take the necessary precautions to protect yourself.

Where did the story come from?

Dr Anabelle Chase and colleagues from the Bristol Heart Institute, based in the Faculty of Medicine and Dentistry at the University of Bristol carried out this research. It was supported in part by a grant from the British Heart Foundation. The study was published in the peer-reviewed medical journal Critical Care Medicine.

What kind of scientific study was this?

This was a laboratory study conducted in mice who were predisposed to getting a fatty build-up in their arteries that was similar to coronary artery disease in humans. Some of the mice were fed a high fat diet, containing lard, while others were fed normal rodent food.

After about 24 weeks, the researchers extracted the mice hearts to determine how severe their artery disease was. Using a special blood-pumping machine, they restored the blood flow to some of the hearts and assessed how they behaved. They also assessed what happened when the hearts were starved of oxygen for 35 minutes before blood flow was restored for 45 minutes.

The reseachers were particularly interested in whether the hearts from the mice with artery disease behaved differently from the mice without it. To measure the effects of oxygen starvation and restoration of the blood flow on heart muscle, the researchers measured the release of a chemical that indicates heart injury.

What were the results of the study?

The researchers report that, when starved of oxygen, the diseased mice hearts took longer to stop beating than those that were not diseased. They also found that when the blood flow was restored to the hearts, the diseased ones were able to fully recover (in terms of how much work they did). This recovery was in spite of the fact that the diseased hearts went into “rigor” or strong contraction of the heart muscle.

The researchers found that after blood flow was restored to the heart, the concentration of an enzyme indicative of injury to the heart cells was lower in the diseased hearts. This suggested that the diseased hearts were more resistant to cell damage.

What interpretations did the researchers draw from these results?

The researchers conclude that oxygen starvation of heart cells as happens in coronary artery disease, may precondition heart cells and protect them against later heart damage.

What does the NHS Knowledge Service make of this study?

As with all laboratory studies, particularly those in mice, we should be cautious about extrapolating these findings directly to human health. The following points are especially relevant to this study:

• As usual with animal studies, these results are in mice, not humans. We can’t say for sure that human hearts will behave similarly.
• Only high-risk mice were included in this study, i.e. only genetically modified mice that were more likely to develop heart disease and have heart attacks.
• Though the authors state that they originally had 92 mice at the beginning of the study, it appears that very few of them were included in each laboratory analysis. Only about 9 hearts per group were compared in the oxygen starvation and reoxygenation part of the experiment. As such, smaller studies are less reliable than larger ones and so it is more likely that some significant results may have occurred by chance.

Although Professor Saadeh Suleiman is quoted as saying: "We believe that we could target these pathways to help people who are undergoing heart surgery.", He also stressed that it was still better to avoid surgery altogether by adopting healthy eating habits.

There are no benefits to having a damaged heart and the best way to protect it is to avoid damaging it in the first place.

Sir Muir Gray adds...

There is no evidence that having diseased heart muscle can be of any benefit to humans. In fact, the opposite of this is the case.