Modern 4D flow MRI complements traditional imaging methods in the assessment of ascending aortic dilatation, according to the doctoral dissertation of Petteri Kauhanen, Bachelor of Medicine.
Ascending aortic (AA) dilatation can lead to serious, potentially fatal complications – aortic dissection or rupture. Aortic diseases are the 13th most common cause of death in the Western countries. AA dilatation can be viewed as a silent killer because the dilatation rarely causes any symptoms before the appearance of its complications. Most of the cases of AA dilatation are detected by chance during some imaging of the chest performed for other purposes. Well-known risk factors for AA dilatation are certain genetic syndromes, bicuspid aortic valve, hypertension, smoking and positive family history. According to the European Society of Cardiology guidelines, AA dilatation is present if the aortic diameter exceeds 40 mm. Patients with AA dilatation are followed-up regularly (after every 1–2 years) by either computed tomography (CT), magnetic resonance imaging (MRI) or ultrasound after the diagnosis. Recently, 4D flow MRI has been used to study the flow patterns in AA dilatation.
The purpose of prospective clinical study I was to investigate the flow characteristics with 4D flow MRI in patients with AA dilatation and with a normal tricuspid aortic valve without significant valve dysfunction and to compare the results to values in patients with normal AA. Twenty patients with dilated AA, being followed-up in the Department of Cardiothoracic Surgery in Kuopio University Hospital during 7/2017–3/2018, were recruited for the study as well as 20 volunteers with normal AA. The aim of retrospective study II was to determine the prevalence and the risk factors for AA dilatation in consecutive 1000 coronary artery CT angiography patients imaged in Kuopio University Hospital during 1/2012–3/2018. The purpose of retrospective study III was to determine whether the angle between the AA and the midline of the heart (heart-aorta-angle, HAA) would associate with AA dilatation in the same patient population imaged by coronary artery CT angiography. Furthermore, the aim was to find out whether a smaller HAA could induce shear stress in the AA wall as assessed with 4D flow MRI.
The result of the prospective study indicated that flow was displaced from the centerline of AA in the patients with a dilated AA as compared to the controls. The displacement of the flow significantly increased wall shear stress (WSS) on the displaced side of the AA wall. The ratios of circumferential WSS and total WSS in the inner curve of the AA were increased in patients with AA dilatation. In study II, the prevalence of AA dilatation was found to be high (23%) in a coronary CT angiography patient population when using the European Society of Cardiology guidelines. The prevalence remained high (15%) even in the subgroup of patients with no cardiovascular risk factors. Conventional risk factors for AA dilatation (hypertension, smoking and bicuspid aortic valve) were also detected in this study. Study III showed that a smaller HAA strongly associated with AA dilatation and a smaller angle also seemed to increase WSS in the proximal AA.
The present study helps to better understand the flow characteristics in the dilated AA in patients without a significant aortic valve dysfunction. According to current clinical guidelines, the prevalence of AA dilatation in coronary CT angiography patients is high. A smaller HAA associates with AA dilatation and this relationship should be taken into account when evaluating the risk of progression of AA dilatation.
The doctoral dissertation of Petteri Kauhanen, Bachelor of Medicine, entitled Dilatation of the ascending aorta: imaging, prevalence and associated factors, will be examined at the Faculty of Health Sciences on 12 June 2020. The Opponent in the public examination will be Docent Miia Holmström of the University of Helsinki, and the Custos will be Professor Marja Hedman of the University of Eastern Finland. The public examination will be held in Finnish.
Kauhanen, Petteri. Dilatation of the ascending aorta: imaging, prevalence and associated factors