Doctoral Defense in Medical Sciences - Maríanna Garðarsdóttir

On Thursday, May 21, Maríanna Garðarsdóttir will defend her doctoral dissertation in Medical Sciences at the Faculty of Medicine of the University of Iceland. The dissertation is titled: Þáttur gáttatifs og ósæðarstífleika í formgerð og starfsemi heilans. The role of atrial fibrillation and aortic stiffness in brain structure and function.

The opponents are Dr. Jens Cosedis Nielsen, Chief Physician and Professor at Aarhus University, and Dr. David Fällmar, Associate Professor at Uppsala University Hospital.

The supervisor and advisor was Professor Davíð O. Arnar, and the co-supervisor was Sigurður Sigurðsson, Managing Director. In addition to them, the doctoral committee included Professor Thor Aspelund and Professor Vilmundur Guðnason.

Sædís Sævarsdóttir, Professor and Dean of the Faculty of Medicine, will preside over the ceremony, which will take place in Veröld – House of Vigdís, Auðarsalur, and will begin at 9:00 a.m.

Abstract
Atrial fibrillation is the most common long-lasting heart rhythm disorder and becomes more frequent with increasing age. It is well known that atrial fibrillation increases the risk of stroke and in recent years researchers have also found that people with atrial fibrillation are more likely to experience memory problems and changes in brain structure, even without stroke, but the cause is not fully understood. This thesis explored whether changes in blood flow between the heart and the brain might help explain this connection.
The brain does depend on a steady supply of blood flow to receive oxygen and nutrients. In atrial fibrillation, the heartbeat becomes irregular and less efficient, and this may affect how blood is delivered to the brain. In the first study, older individuals with long-lasting atrial fibrillation had lower blood flow to the brain compared with those who were in normal sinus heart rhythm. They also had smaller brain volumes but differences in cognitive function were, however, not observed.
In a second study, people with atrial fibrillation were examined before and after electrical cardioversion, which may restore normal sinus heart rhythm. Individuals who successfully returned to normal rhythm showed an improvement in brain blood flow, but those who remained in atrial fibrillation did not. This suggests that reduced blood flow in atrial fibrillation may not be permanent and can improve when normal rhythm is restored.
The thesis also examined a related condition called aortic stiffness. As people age, the large artery leaving the heart, the aorta, can become stiffer. This changes how blood pressure waves travel through the body and may increase stress on small blood vessels, including in the brain. The results showed that individuals with stiffer arteries had lower blood flow to the brain and more signs of degenerative changes in the brain, as well as smaller brain volume. Cognitive performance was not affected.
Together, these findings suggest that both irregular heart rhythm and stiffened aorta may affect the brain through changes in blood flow to the brain. While aging remains the most important factor influencing brain structure and brain health, heart rhythm and vascular health appear to play an early role in structural and functional changes in the brain. Understanding how cardiac and vascular conditions influence brain health may help guide future strategies to protect cognitive function as people grow older.

About the doctoral candidate
Maríanna Garðarsdóttir was born in Reykjavík in 1969. She graduated from the modern languages department of Menntaskólinn í Reykjavík in 1989 and received her medical degree from the Faculty of Medicine at the University of Iceland in 1999. After completing her internship year, Maríanna worked in the ophthalmology and radiology departments at Landspítali University Hospital before moving abroad for specialist training at Sahlgrenska University Hospital and Queen Silvia Children’s Hospital in Gothenburg.

Maríanna completed her specialist training in diagnostic imaging in 2007 and then returned to Iceland to work as a consultant physician at Landspítali University Hospital. Since 2024, she has served as Director of Imaging Services at Landspítali.

Maríanna’s parents are Maia Sigurðardóttir, psychologist (deceased in 2012), and Garðar Gíslason, Supreme Court Justice. Her spouse is Sveinbjörn Jóhannesson, carpenter and business graduate, and her daughters are Maia and Arna Snorradætur.