Macquarie research addresses keyhole heart surgery limitations

Aortic stenosis — the narrowing of the valve that controls blood flow from the heart — is one of the most common heart valve diseases, affecting one in eight older Australians. Without surgery, about half of all people with severe aortic stenosis will die within two years.

One of the greatest advances in the treatment of heart disease this century has been the development of transcatheter aortic valve implantation, or TAVI, to treat aortic stenosis, according to Macquarie University.

Instead of performing open heart surgery, a cardiologist introduces a new valve usually through an artery in the groin and then moves it to the heart. Once the new valve is in place, it is expanded.

Professor Martin Ng, an interventional cardiologist at RPA and Macquarie University Hospital, has led a research program to significantly improve the transcatheter aortic valve implantation (TAVI) treatment by addressing its key limitations.

One of the greatest advances in the treatment of heart disease this century has been the development of TAVI to treat aortic stenosis.

Instead of performing open heart surgery, a cardiologist introduces a new valve usually through an artery in the groin and then moves it to the heart. Once the new valve is in place, it is expanded.

The perfect fit

“TAVI has changed millions of people’s lives, because instead of having major surgery and taking weeks to recover, you can have this minimally invasive procedure and go home one or two days later,” Professor Ng said.

“Unfortunately, there are limits. The replacement valve needs to fit exactly once expanded.

“If the new valve is not expanded enough, the patient ends up with paravalvular leak, which is the biggest contributor to long-term mortality following TAVI. If the valve is expanded too much, it ruptures the aorta, and if that happens, the patient dies on the table. There is nothing we can do to save them.

“Until now, nobody knew how to determine the correct pressure to achieve that perfect fit.”

Building on the research of the late Professor Geoffrey White, the founding professor of vascular surgery at Macquarie University Hospital, Professor Ng worked with colleagues including Dr Afik Snir, who has a background in biomedical engineering, heart valve imaging specialist Dr Chris Naoum and engineers at the University of Sydney to determine the ‘sweet spot’ for inflating the valve.

They used the Law of Laplace, which governs tension in the walls of containers — such as heart valves — to work out the correct thresholds.

“These findings represent five years of work and are the first time anyone has been able to determine the correct pressure to deploy the valves every time,” Professor Ng said.

“Once the cardiologist choses the size of the replacement valve, we can reliably tell them the right pressure to expand it to minimise the chance of paravalvular leak while also protecting the aorta from rupture.

High-risk patients

“Using this threshold, we have performed TAVI procedures successfully and safely on 330 consecutive patients, most of whom had their surgery at Macquarie University Hospital.

“TAVI can now be safely performed even for the highest-risk patients such as those with a build-up of calcium that has hardened the aorta.

“We stood on the shoulders of giants to reach this point. Professor Geoffrey White was there when we first began doing TAVI procedures, and he was the first person to recognise that over-inflation of the valve would injure the patient.”

The paper describing the development has been published in the November edition of the world’s premier cardiology journal, the Journal of the American College of Cardiology: Cardiovascular Interventions, with an editorial discussing the significance of the findings from Canadian TAVI pioneer Professor John Webb.

Image caption: Professor Martin Ng from MQ Health is an interventional cardiologist with interests in clinical, scientific and technological innovation in cardiology. He founded the Structural Heart program at MQ Health. Image credit: Sydney Heart Team.