Doctoral Defense in Medical Sciences – Hildur Margrét Ægisdóttir

On Friday, 12 December 2025, Hildur Margrét Ægisdóttir will defend her doctoral thesis in Medical Sciences at the Faculty of Medicine, University of Iceland. The thesis is titled: Erfðir hjartsláttartruflana, raflífeðlisfræði hjartans og yfirliðs. Genetics of heart rhythm disorders, cardiac electrophysiology and syncope.

The opponents are Dr. Arthur A.M. Wilde, Professor at Amsterdam University Medical Center, and Dr. Eiríkur Steingrímsson, Professor at the Faculty of Medicine, University of Iceland.

The supervisor was Professor Davíð O. Arnar, and the co-supervisor was Hilma Hólm, specialist. Other members of the doctoral committee were Ingibjörg Jóna Guðmundsdóttir, specialist, Rósa Björk Þórólfsdóttir, specialist, and Daníel F. Guðbjartsson, head of the Statistics Department at deCODE genetics.

Sædís Sævarsdóttir, Professor and Dean of the Faculty of Medicine, will chair the ceremony, which takes place in the Ceremonial Hall of the University of Iceland and begins at 9:00.

Abstract
The genetic background of cardiac paroxysmal supraventricular tachycardias (PSVTs), conduction disorders (CDs), and syncope is poorly understood. The aim of this doctoral project was to provide insights into the pathophysiology of PSVTs, CDs and syncope through a genome-wide approach, and through adjunct methods such as genetic scores and Mendelian randomization. In the first part of the project, we identified ten associations with PSVTs which support that activity of sodium ion channels, potassium ion channels and the autonomic nervous system, among others, have a role in the risk of PSVTs. In the second, we found 162 associations with CDs, of which many also associated with atrial fibrillation and cardiomyopathies. Mendelian randomization validated a causal role for atrial fibrillation in sinus node dysfunction risk but did not support a straightforward causal relationship between cardiomyopathies and CDs. Among the CD variants, there was enrichment at binding sites for GATA-4 and ESRRG, both of which are transcription factors involved in myocardial hypertrophy. In the third and final part, we found 18 associations between sequence variants and syncope, but neither the variants nor a genetic score based on their effects associated with other diseases. Enrichment in neural-specific regulatory regions and effects of the variants on heart rate regulation pointing to a role of central processing and the autonomic nervous system in the pathophysiology of syncope. These studies provide novel insights into the genetics of diseases of the cardiac conduction system and syncope, and their relationship with other heart disease and the autonomic nervous system.

About the doctoral candidate
Hildur Margrét Ægisdóttir was born in 1990 in Reykjavík. She completed her cand.med. degree in medicine at the University of Iceland in 2015 and worked in clinical departments at Landspítali – The National University Hospital of Iceland, until she joined the cardiovascular division of deCODE genetics in 2018. In 2020, she began her doctoral studies in medical sciences with a focus on the genetics of heart rhythm disorders and syncope. Hildur also currently works as a physician at the Hlíðar Health Clinic and will begin her residency in family medicine at the beginning of 2026.
Hildur’s parents are Sigríður Anný Gunnlaugsdóttir and Ægir Breiðfjörð Sigurgeirsson. Her partner is Ólafur Freyr Birkisson, and they have two daughters, Sigríður Kristín (7 years old) and Bergþóra Margrét (4 years old).