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Changes in aortic distensibility and pulse wave velocity assessed with magnetic resonance imaging following beta-blocker therapy in the marfan syndrome

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Abstract

It has been shown that β-adrenergic blocking agents may reduce the rate of aortic root dilation and the development of aortic complications in patients with the Marfan syndrome. This may be due to β–blocker-induced changes in aortic stiffness, of which distensibility and pulse wave velocity are in vivo measurable derivatives. We studied changes in distensibility at 4 levels of the aorta and pulse wave velocity along the entire aorta after 2 weeks of β-blocker therapy in 6 Marfan syndrome patients and in 6 healthy volunteers, using magnetic resonance imaging (MRI) combined with brachial artery blood pressure measurements. In both groups, mean blood pressure decreased significantly (Marfan: 86 ± 6 vs 78 ± 5 mm Hg, p <0.05; control: 80 ± 8 vs 73 ± 3 mm Hg, p <0.05) (all data expressed as mean ± 1 SD). At baseline, the Marfan syndrome patients exhibited decreased distensibility at the level of the ascending aorta (2 ± 1 vs 6 ± 2 10−3mm Hg−1, p <0.01) and increased pulse wave velocity (6.2 ± 0.4 vs 3.9 ± 0.4 ms−1, p <0.01) compared with control subjects. Only the Marfan syndrome patients had a significant increase in aortic distensibility at multiple levels and a significant decrease in pulse wave velocity after β-blocker therapy (ascending aorta distensibility: 2 ± 1 vs 4 ± 1 10−3mm Hg−1, p <0.05; abdominal aorta distensibility: 5 ± 2 vs 8 ± 3 10−3mm Hg−1, p <0.05; pulse wave velocity: 6.2 ± 0.4 vs 5.0 ± 1.0 ms−1, p <0.05). Thus, aortic stiffness in Marfan syndrome, together with mean blood pressure, is reduced by β-blocker therapy, and MRI is well suited to detect these changes by measuring distensibility and pulse wave velocity.

Section snippets

Study subjects and protocol

Six subjects who met the criteria of the diagnosis “the Marfan syndrome” according to the revised Berlin criteria15 and 6 healthy volunteers were studied. None of the study subjects took β-blocking agents or had undergone surgery. Body surface area was calculated from length and height using the formula of Du Bois and Du Bois.16 The study population characteristics are listed in Table I. After MRI without medication, all 12 subjects received 200 mg of metoprolol or 100 mg of atenolol daily for

Reproducibility of measurements

Figure 5 shows reproducibility of all areas measured (n = 3,257) in this study. A clear linear correlation between the results of 2 observers was found (R2 = 0.98, p <0.001). Interobserver variability was 5%.

Blood pressure and heart rate during MRI examination

No significant changes in mean blood pressure, pulse pressure, or heart rate occurred during the imaging protocol. Mean systolic and diastolic values were used per study subject.

Differences between and within groups

Differences in distensibility and pulse wave velocity between and within groups are shown in Table II.

In vivo examination of aortic stiffness with MRI

Our study extends the findings of previous studies that MRI enables the in vivo examination of aortic stiffness.3., 7., 14. Together with its excellent sensitivity and specificity in visualization of aortic disease, MRI offers the combination of morphologic and functional examination of the entire aorta. With MRI, it is always possible to acquire short-axis images of any part of the aorta, in which aortic area changes can reliably be assessed. Although T1-weighted spin-echo MRI offers the

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