Retrograde aortic blood flow as a mechanism of stroke: MR evaluation of the prevalence in a population-based study.

OBJECTIVES: Retrograde blood flow from complex atheroma in the descending aorta (DAo) has only recently been described as a potential mechanism of stroke. However, prevalence of this mechanism in the general population and the exact factors influencing stroke risk are unclear. METHODS: One hundred twenty-six consecutively recruited inhabitants of Freiburg, Germany, between 20 and 80 years of age prospectively underwent 3-T MRI. Aortic plaque location and thickness were determined by 3D T1 MRI (1 mm3). 4D flow MRI (spatial/temporal resolution 2 mm3/20 ms) and dedicated software were used to determine prevalence and extent of flow reversal and potential embolization from DAo plaques. Flow was correlated with baseline characteristics and echocardiographic and MRI parameters (aortic diameter, wall thickness, and pulse wave velocity). RESULTS: The maximum length of retrograde blood flow connecting the DAo with the left subclavian artery (LSA) increased from 16.1 ± 8.3 mm in 20-29-year-old to 24.7 ± 11.7 mm in 70-80-year-old subjects, correlated with age (r = 0.37; p < 0.001), and was lower in females (p = 0.003). Age was the only independent predictor of increased flow reversal. Complex DAo plaques ≥ 4-mm thickness were found in eight subjects (6.3%) and were connected with the LSA, left common carotid artery, and brachiocephalic trunk in 8 (100%), 1 (12.5%), and 0 (0%) cases, respectively. CONCLUSIONS: Retrograde blood flow from the DAo was very frequent. However, potential retrograde embolization was rare due to the low incidence of complex DAo plaques. The magnitude of flow reversal and prevalence of complex atheroma increased with age. Thus, older patients with aortic atherosclerosis are especially vulnerable to this stroke mechanism. KEY POINTS: • 4D flow MRI allows in vivo visualization and quantification of individual and three-dimensional blood flow patterns within the thoracic aorta including retrograde components. • This population-based study showed that blood flow reversal from the proximal descending aorta to the brain-supplying great arteries is very frequent and able to reach all brain territories. The extent of such flow reversal increases with age and with the extent of aortic atherosclerosis. • The combination of blood flow reversal with plaque rupture in the proximal descending aorta constitutes a potential stroke mechanism that should be considered in future trials and in the management of stroke patients in clinical routine.

Determination of aortic stiffness using 4D flow cardiovascular magnetic resonance - a population-based study.

BACKGROUND: Increased aortic stiffness is an independent predictor of cardiovascular disease. Optimal measurement is highly beneficial for the detection of atherosclerosis and the management of patients at risk. Thus, it was our purpose to selectively measure aortic stiffness using a novel imaging method and to provide reference values from a population-based study. METHODS: One hundred twenty six inhabitants of Freiburg, Germany, between 20 and 80 years prospectively underwent 3 Tesla cardiovascular magnetic resonance (CMR) of the thoracic aorta. 4D flow CMR (spatial/temporal resolution 2mm3/20ms) was executed to calculate aortic pulse wave velocity (PWV) in m/s using dedicated software. In addition, we calculated distensibility coefficients (DC) using 2D CINE CMR imaging of the ascending (AAo) and descending aorta (DAo). Segmental aortic diameter and thickness of aortic plaques were determined by 3D T1 weighted CMR (spatial resolution 1mm3). RESULTS: PWV increased from 4.93 ± 0.54 m/s in 20-30 year-old to 8.06 ± 1.03 m/s in 70-80 year-old subjects. PWV was significantly lower in women compared to men (p < 0.0001). Increased blood pressure (systolic r = 0.36, p < 0.0001; diastolic r = 0.33, p = 0.0001; mean arterial pressure r = 0.37, p < 0.0001) correlated with PWV after adjustment for age and gender. Finally, PWV increased with increasing diameter of the aorta (ascending aorta r = 0.20, p = 0.026; aortic arch r = 0.24, p = 0.009; descending aorta r = 0.26, p = 0.004). Correlation of PWV and DC of the AAo and DAo or the mean of both was high (r = 0.69, r = 0.68, r = 0.73; p < 0.001). CONCLUSIONS: 4D flow CMR was successfully applied to calculate aortic PWV and thus aortic stiffness. Findings showed a high correlation with distensibility coefficients representing local compliance of the aorta. Our novel method and reference data for PWV may provide a reliable biomarker for the identification of patients with underlying cardiovascular disease and optimal guidance of future treatment in studies or clinical routine.

Age-related changes of right atrial morphology and inflow pattern assessed using 4D flow cardiovascular magnetic resonance: results of a population-based study.

BACKGROUND: To assess age-related changes of blood flow and geometry of the caval veins and right atrium (RA) using 4D flow cardiovascular magnetic resonance (CMR) data obtained in a population-based study. METHODS: An age-stratified sample (n = 126) of the population of the city of Freiburg, Germany, underwent transthoracic echocardiography and electrocardiogram-triggered and navigator-gated 4D flow CMR at 3 Tesla covering the caval veins and right heart. Study participants were divided into three age groups (1:20-39; 2:40-59; and 3:60-80 years of age). Analysis planes were placed in the superior and inferior caval vein. Subsequently, RA morphology and three-dimensional blood inflow pattern was assessed. RESULTS: Blood flow of the RA showed a clockwise rotating helix without signs of turbulence in younger subjects. By contrast, such rotation was absent in 12 subjects of group 3 and turbulences were significantly more frequent (p < 0.001). We observed an age-related shift of the caval vein axis. While the outlets of the superior and inferior caval veins were facing each other in group 1, lateralization occurred in older subjects (p < 0.001). A convergence of axes was observed from lateral view with facing axes in older subjects (p = 0.004). Finally, mean and peak systolic blood flow in the caval veins decreased with age (group 3 < 2 < 1). CONCLUSIONS: We have provided reference values of 4D CMR blood flow for different age groups and demonstrated the significant impact of age on hemodynamics of the RA inflow tract. This effect of aging should be taken into account when assessing pathologic conditions of the heart in the future.

Age dependence of pulmonary artery blood flow measured by 4D flow cardiovascular magnetic resonance: results of a population-based study.

BACKGROUND: It was our aim to systematically analyze pulmonary artery blood flow within different age-groups in the general population using 4D flow cardiovascular magnetic resonance (CMR) in order to provide a context for interpreting results of future studies (e.g., in pulmonary hypertension) using this technique. METHODS: An age-stratified sample (n = 126) of the population of the city of Freiburg, Germany, underwent ECG-triggered and navigator-gated 4D flow CMR at 3 T of the pulmonary arteries and the thoracic aorta. Analysis planes were placed in the main, left, and right pulmonary artery using dedicated software. Study participants were divided into three groups (1:20-39; 2:40-59; and 3:60-80 years of age). Subsequently, pulmonary blood flow was visualized, quantified and compared between groups. RESULTS: Time-to-peak of systolic antegrade flow was shorter, peak and average velocities and flow volumes were lower in older subjects. At the end of systole, retrograde flow in the main pulmonary artery was observed in all but one subject. Subsequently, a second antegrade flow peak occurred in diastole which was lower in older subjects. Age was an independent predictor of hemodynamic change after adjustment for cardiovascular risk factors and body-mass-index. During systole, abnormal vortices occurred in the main pulmonary artery in four male subjects. CONCLUSIONS: Comprehensive analysis of pulmonary blood flow was feasible in all subjects. We were able to detect an independent effect of ageing on pulmonary hemodynamics reflecting increased vessel stiffness and reduced pulmonary circulation. Findings of this study may be helpful for discriminating physiological from pathological flow in patients with pulmonary diseases in the future.