This is when the heart cannot pump sufficient blood around the body, causing fatigue and breathlessness.
In a fifth of cases, patients have an abnormally long delay in the time it takes for natural electrical signals that tell the heart to contract to travel from the top to the bottom of the heart. This is known as PR prolongation.
But in a new trial, funded by the British Heart Foundation and led by Imperial College London, doctors are investigating whether inserting a pacemaker lead into the middle of the heart to target an area of cells there could help.
Known as the His-bundle, this small track of muscle fibres plays a key role in keeping the different parts of the heart beating in sync - but has never been targeted with a pacemaker before.
In normal hearts, a tiny area of tissue or cells, the sinus node, in the right upper chamber (atrium) generates electrical impulses that keep heart rate regular by stimulating all four heart chambers.
The impulses start in the right atrium and make the left atrium contract at the same time, then travel along special pathways and down a tiny track - the His-bundle - in the centre of the heart which branches into the left and right bottom chambers (ventricles). These contract a fraction of a second after the top chambers.
Heart failure can damage this mechanism, leading to an abnormal heart rhythm.
Where patients have a slow heartbeat or a significant delay in the heart’s natural electrical impulses, treatment is typically a pacemaker which sends electrical impulses to the heart via two leads, one in the right atrium and the other in the right ventricle.
However, these aren’t always effective for people with severe heart failure, partly because they don't improve the pumping function of the heart, but also because they can’t help if the heart isn't relaying electrical signals from the right to the left side, or from top to bottom, efficiently.
A relatively new development is cardiac resynchronisation therapy, a pacemaker with a third lead placed in the left ventricle, helping it to pump more efficiently as signals are sent to both the right and left sides of the heart.
Fifteen hospitals across the UK and 160 patients are now involved in the HOPE-HF trial, with results expected in October next year. - Daily Mail