Natural pacemaker discovery changes understanding of heart anatomy

Natural pacemaker discovery changes understanding of heart anatomy
© iStock-Paul Campbell

A team of researchers have discovered that there is a natural, backup pacemaker in the heart in a study that completely changes our understanding of the heart’s anatomy.

The team from the University of Manchester and Manchester University NHS Foundation Trust made the discovery, which has important implications for the work of both cardiologists and heart surgeons. The researchers found that this natural, backup pacemaker can generate a pulse and control the heart rate.

Lead author Dr Halina Dobrzynski, from The University of Manchester, said: “This study completely reshapes our understanding of the how the heart works and is tremendously exciting. It builds on our work on the human heart over many years and we hope will make an important contribution to future treatments.”

The study has been funded by the British Heart Foundation and appears in the journal Frontiers in Physiology.

The SA node

The study, which involved 15 goats, found that a ‘subsidiary atrial pacemaker’ (SAP) takes over from the primary way the heart generates electrical signals that make it beat when it fails – the nearby sinoatrial (SA node).  The SA node in human, goat, and other mammalian species is a group of cells located in the wall of the right atrium of the heart, which can spontaneously produce the electrical impulses to make our hearts beat.

The team is confident the discoveries are highly relevant to the human heart, as the organ in goats has similar anatomy and physiology, producing a similar heart rate.

When the SA node fails it can cause the heart rate to slow and cause breathlessness and blackouts. However, when the malfunctioning SA node is removed by cardiologists, in a procedure known as ablation, the new structure discovered by the team in the goats took over as the dominant pacemaker – driving the electrical activity of the heart.

Co-author, Dr Gwilym Morris, a clinical researcher at The University of Manchester and a Consultant Cardiologist at Manchester Royal Infirmary, part of Manchester University NHS Foundation Trust, (MFT), said: “Not only will this knowledge improve our understanding of the anatomy of the heart – which is crucial for clinicians – it will give patients the full facts so they can make a more informed choice about ablation.”

The study also explains why ablation of the SA node – sometimes performed by cardiologists to treat a fast heartbeat called inappropriate sinus tachycardia – is often unsuccessful, as the researchers found that the SA node is difficult to destroy it using the ablation procedure. The team demonstrated that even if a few cells of the SA node are left it will continue to function as the heart’s pacemaker.

Anatomy of the heart

Co-author Dr Luca Soattin, from The University of Manchester, highlighted that before the study was carried out, it was thought that the sinoatrial node was the primary activation site in the heart.

He said: “When that failed, the atrioventricular node nearer to the ventricle was thought to kick in. But now we know of another site, the subsidiary atrial pacemaker, which kicks in after the SA node fails. We believe this is a remarkable discovery.”

Professor Metin Avkiran, Associate Medical Director at the British Heart Foundation (BHF), said: “The heart is a wonderfully complex organ that contains many different types of specialist cells serving distinct functions. These include the cells in the heart’s own ‘pacemaker’, which generates the electrical signal triggering each heartbeat.

“This detailed study improves our understanding of how the heartbeat continues to be generated when the normal pacemaker is damaged. The findings will inform future work to better understand and treat human diseases associated with abnormal pacemaker activity.”

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