Heart surgery

Macquarie’s research addresses the limits of keyhole heart surgery

Macquarie's research addresses the limits of keyhole heart surgery

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

One of the biggest 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 widened.

Professor Martin Ng, Interventional Cardiologist at RPA and Macquarie University Hospital, has led a research program to dramatically improve catheter aortic valve implantation (TAVI) treatment by addressing its main 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 widened.

The perfect fit

“TAVI has changed the lives of millions of people because instead of having major surgery and taking weeks to recover, you can undergo this minimally invasive procedure and go home a day or two later,” said the professor Ng.

“Unfortunately, there are limits. The replacement valve should fit exactly when deployed.

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

“Until now, no one knew how to determine the correct pressure to achieve that perfect fit.”

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

They used Laplace’s Law, which governs the voltage in the walls of containers – such as heart valves – to determine the correct thresholds.

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

“Once the cardiologist chooses the size of the replacement valve, we can reliably tell them the right pressure to expand it to minimize the risk of paravalvular leakage while protecting the aorta from rupturing.

High risk patients

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

“TAVI can now be performed safely, even in patients at greatest risk, 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 present when we began to perform the TAVI procedures, and he was the first person to recognize that excessive valve inflation would injure the patient.

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

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


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