An implant the size of a watch that zaps the heart with electric pulses could help thousands of people with heart failure – by cleverly changing the organ’s source of fuel.
Healthy hearts mostly burn fat to keep working normally and pump oxygen-rich blood round the body, as it’s the most efficient source of fuel and produces the strongest heartbeats.
But in people with heart failure, where the organ becomes weak and floppy from damage done by heart attacks, high blood pressure or faulty valves, it switches to using glucose or blood sugar.
This is because much less oxygen is needed to turn glucose into energy (and levels of the gas are usually severely depleted in patients with heart failure).
Cardiac cells have a built-in switch for swapping between the two fuel sources as needed – when exercising, for example.
The problem is glucose does not produce as strong a heartbeat, which means the heart has to work harder to force blood round the body, gradually tiring it out.
Now research by the University of Oxford, funded by the British Heart Foundation (BHF), shows that when some heart failure patients are fitted with the implant – called a cardiac resynchronisation therapy (CRT) pacemaker – their hearts switch back almost instantly to burning fat.
More importantly, findings just published in the European Heart Journal show that the size of the left ventricle – the main pumping chamber of the heart, which can become very enlarged in heart failure patients because of being overworked – reduced by half after six months of CRT treatment.
In many heart failure patients, the ventricles don’t contract at the same time so blood tends to pool inside the heart. CRT pacemakers control the heartbeat, but they also send electrical signals to jolt the heart’s lower chambers back to contracting in unison
Pumping function, or the heart’s ability to squeeze blood out to the rest of the body, also improved by more than a third.
Scientists think this dramatic improvement may be because of the implant turning on the fat-burning mechanism in cardiac cells, at the same time turning off the instructions to burn glucose, although just how it does this isn’t clear.
Neil Herring, a professor of cardiovascular medicine who led the study, said the results were ‘remarkable’.
He told the Mail: ‘We were really surprised by the extent of improvement in these patients. You sometimes see that kind of improvement with medication (such as ACE inhibitors to lower blood pressure, or SGLT2 inhibitors to improve pumping capacity) – but the patients in our study were already taking these drugs without major benefit.’
He added that ‘within two minutes of turning on the pacemaker the heart had changed back to burning fat as it normally would’.
More than a million people in the UK have heart failure, with 200,000 new cases diagnosed each year, according to the BHF.
Neil Herring, a professor of cardiovascular medicine, led the study into the new implants. He is pictured fundraising for the British Heart Foundation by running a half-marathon
Numbers are expected to double by 2040. Symptoms include breathlessness, extreme fatigue and swollen ankles (because of fluid pooling there as the heart is too weak to pump blood all the way round the body).
It’s not curable but with the right medication and regular exercise, doctors can prolong patients’ survival and improve their quality of life.
CRT pacemakers are also sometimes used. In many heart failure patients, the left and right ventricles don’t contract at the same time so blood tends to pool inside the heart.
These devices control the heartbeat (as a normal pacemaker does), but they also send electrical signals to jolt the heart’s lower chambers back to contracting in unison.
Many patients respond well to the treatment, which has been shown to reduce their risk of premature death and improves quality of life.
The latest study set out to discover whether the secret to the success of a CRT pacemaker in synchronising heart contractions was linked with the type of fuel the heart burns.
Researchers recruited 14 patients with heart failure who were due to have a CRT pacemaker fitted. Each one underwent an MRI scan of their heart after being injected with either glucose or fat, to see which one the cardiac muscle cells used to produce energy.
The scans showed that within minutes of their CRT device being switched on, patients whose hearts had been burning glucose switched to using fat.
Over the following months, their hearts grew stronger, shrank to a more normal size and were able to pump more oxygen-rich blood – reducing symptoms such as breathlessness.
Professor Herring is now carrying out a study involving up to 100 heart failure patients to see if ordinary pacemakers – which regulate heart rate but don’t synchronise contractions between the heart’s chambers, as CRT does – may actually be stopping heart muscle cells from switching to burning fat.
If they do, it could lead to CRT pacemakers being much more widely used. At the moment, about 12,000 of the devices, which sit just under the skin near the collarbone and are connected by leads to the heart, are implanted each year.
Commenting on the findings, Professor Francisco Leyva-Leon, a consultant cardiologist at Queen Elizabeth Hospital, Birmingham, said: ‘This is promising research and early findings suggest CRT is able to switch the heart’s fuel consumption back to fat – which may make it beat stronger and more efficiently.
‘It may also partly explain why resynchronisation seems to be so effective at improving survival and reducing symptoms in heart failure patients.’
However, Dr Lisa Anderson, a consultant cardiologist at St George’s University Hospitals NHS Foundation Trust in London, said the study was rather technical – and was unlikely to change the way heart failure is treated.
