Author + information
- Received February 22, 2011
- Revision received June 14, 2011
- Accepted June 15, 2011
- Published online September 13, 2011.
- Alban Redheuil, MD, PhD⁎∥,
- Wen-Chung Yu, MD¶,
- Elie Mousseaux, MD, PhD∥,
- Ahmed A. Harouni, PhD†,
- Nadjia Kachenoura, PhD∥,
- Colin O. Wu, PhD‡,
- David Bluemke, MD, PhD§ and
- Joao A.C. Lima, MD⁎,⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Joao A. C. Lima, Cardiovascular Imaging, Division of Cardiology, Johns Hopkins University School of Medicine, 600 Wolfe Street, Blalock 524, Baltimore, Maryland 21287
Objectives We sought to define age-related geometric changes of the aortic arch and determine their relationship to central aortic stiffness and left ventricular (LV) remodeling.
Background The proximal aorta has been shown to thicken, enlarge in diameter, and lengthen with aging in humans. However, no systematic study has described age-related longitudinal and transversal remodeling of the aortic arch and their relationship with LV mass and remodeling.
Methods We studied 100 subjects (55 women, 45 men, average age 46 ± 16 years) free of overt cardiovascular disease using magnetic resonance imaging to determine aortic arch geometry (length, diameters, height, width, and curvature), aortic arch function (local aortic distensibility and arch pulse wave velocity [PWV]), and LV volumes and mass. Radial tonometry was used to calculate central blood pressure.
Results Aortic diameters and arch length increased significantly with age. The ascending aorta length increased most, with age leading to aortic arch widening and decreased curvature. These geometric changes of the aortic arch were significantly related to decreased ascending aortic distensibility, increased aortic arch PWV (p < 0.001), and increased central blood pressures (p < 0.001). Increased ascending aortic diameter, lengthening, and decreased curvature of the aortic arch (unfolding) were all significantly associated with increased LV mass and concentric remodeling independently of age, sex, body size, and central blood pressure (p < 0.01).
Conclusions Age-related unfolding of the aortic arch is related to increased proximal aortic stiffness in individuals without cardiovascular disease and associated with increased LV mass and mass-to-volume ratio independent of age, body size, central pressure, and cardiovascular risk factors.
Aging, in a complex interplay with associated and aggravating factors such as disease, genetics, and environmental factors, contributes to metabolic, structural, and functional alterations of both large conduit arteries and microvessels (1,2). Arterial stiffness is now recognized as an independent measure of cardiovascular risk beyond traditional risk factors (3–5). Stiffening of the proximal aorta has been shown to be strongly related to aging and to be one of the earliest manifestations of vascular aging in otherwise healthy humans (6). Alterations of the proximal aorta with age include structural and functional changes of the aortic wall and aortic pressure changes potentially leading to geometric and functional changes of the aortic arch. Ascending aortic diameter enlargement and lengthening have been described with advancing age (7) and correlated with increased global arterial stiffening measured as carotid to femoral pulse wave velocity by tonometry (8,9). More recently, measures of proximal aortic function by magnetic resonance imaging (MRI) have been proposed and validated (6,10,11). MRI allows direct measurement of regional stiffness in the aortic arch (pulse wave velocity [PWV]) in addition to local function such as distensibility in the ascending and descending aorta. Prior studies have shown the relationship between altered aortic arch geometry, increased aortic stiffness, and sustained high blood pressure in adult patients with aortic coarctation (12). However, the comprehensive age-related changes in aortic arch geometry in a healthy population have not been described, except for a recent study that demonstrated age-related overall lengthening of the aorta without investigation of alterations in aortic diameters or aortic arch geometry (9). In this regard, alterations in aortic arch morphology may play an important role in explaining the age-related increase in aortic arch stiffness and central pulse pressure (PP) seen in asymptomatic older individuals (13).
Changes in left ventricular (LV) mass and concentric remodeling have also been related to aging and are associated with poor cardiovascular outcome in large, multiethnic general population studies (14), but the relationship between aortic and ventricular morphology in relation to age has not yet been described. MRI together with central pressures calculated with arterial tonometry can provide a comprehensive analysis of both aortic and ventricular morphology and function noninvasively.
In this prospective cross-sectional study, we sought to investigate the interaction between age and aortic arch geometry, including lengthening, widening, and altered curvature, measures of aortic arch stiffness, and LV mass and geometry.
We studied 108 consecutive subjects. All subjects were informed about the study protocol and provided written consent. The procedures followed were in accordance with institutional guidelines and the Declaration of Helsinki, and the study was approved by the Johns Hopkins University Ethics Review Board. This was a general population study sample from the Baltimore community. Subjects enrolled in the study were asked questions from a standardized questionnaire, including medication regimen. Inclusion criteria were in the absence of contraindications to MRI: age >18 years, absence of acute or chronic disease including diabetes, no personal history or symptoms of cardiac disease, normal physical examination, and normal electrocardiogram. Hypertension was defined as diastolic blood pressure ≥90 mm Hg, systolic blood pressure ≥140 mm Hg, or receiving treatment for hypertension. Hyperlipidemic patients were defined as either participants with known abnormal lipid levels or receiving lipid-lowering therapy. None of the screened subjects presented a family history of aortic disease, sudden death, Marfan syndrome, or connective tissue disease. Height and weight were measured and body mass index (BMI) was used as a measure of global adiposity.
Image acquisition and analysis
All images were acquired on a 3.0-T scanner (Trio Tim, Siemens, Munich, Germany) using electrocardiogram (ECG) gating and breath-holding with a 6-element thoracic coil for radiofrequency signal detection.
Assessment of LV Function and Mass by MRI
To measure end-diastolic and end-systolic LV volumes and end-diastolic LV mass, endocardial and epicardial borders were traced semiautomatically on 8 to 10 short-axis cine MRI slices covering the entire LV using QMass (MEDIS, Leiden, the Netherlands). End-diastolic LV mass-to-volume ratio (M/V) was calculated and used as a measure of concentric remodeling.
Aortic Geometry and Function Measurements
To visualize the aorta, we acquired 4 sagittal oblique views of the aortic arch using a black blood spin echo sequence (slice thickness: 6 mm, no gap, matrix: 256 × 256). A gradient echo pulse sequence with through-plane velocity encoding, simultaneously providing the velocities in the ascending and descending aorta, was applied perpendicular to the aorta at the level of the pulmonary artery bifurcation. Maximal velocity encoding was 150 cm/s, slice thickness: 6 mm, matrix: 192 × 192, and temporal resolution: 20 ms. The same slice location was used to acquire an aortic cine using a fast retrospectively gated gradient echo sequence (slice thickness: 6 mm, matrix: 256 × 256, temporal resolution: 20 ms) followed by an acquisition perpendicular to the diaphragmatic descending thoracic aorta.
The contours of the ascending, proximal, and distal (diaphragmatic) descending aorta were automatically traced for all phases of the cardiac cycle on both the modulus images of the phase contrast acquisition for flow analysis and on the cine images for aortic area analysis using the ARTFUN software (INSERM U678) (15,16).
The maximal (Amax) and minimal (Amin) aortic lumen areas were used to calculate average aortic diameters of the ascending and the proximal and distal descending aorta. Relative change in area (aortic strain) defined as AS = (Amax − Amin)/Amin was used to calculate aortic distensibility in each subject as follows: distensibility = AS/cPP, where cPP is the central pulse pressure obtained by tonometry. Aortic arch PWV was calculated by using the transit time of the flow curves and the distance between the ascending and proximal descending aortic locations of the phase contrast acquisition as previously described (6).
The length of the aortic arch traveled by the flow wave (L1) was measured as the centerline of the aorta. Eight to 10 control points were manually placed on the central black blood views of the aortic arch in the center of the vessel and their 3-dimensional (3D) coordinates recorded (Fig. 1). The first and last points were placed at the center of the ascending and descending aorta, respectively, and in the plane used for the velocity acquisition. We then performed a spline interpolation to our manual points to construct a 3D vessel centerline curve and calculated the following parameters: 1) aortic arch width (W): given by the distance between the center of the ascending and descending aorta; 2) aortic arch height (H): defined as the length of the orthogonal projection of the curve's inflection point at the top of the arch on the width of the aortic arch; 3) the H/W ratio for the aortic arch defined as the height (H) divided by the width (W); and 4) curvature: following Wood et al. (17), we calculated the average aortic arch curvature expressed in mm−1, which is an estimate of the global tortuosity of the aortic arch. See the Appendix for details. In addition, we measured the centerline vascular distance (L2) between the proximal and distal descending aortic acquisition planes (Fig. 1).
Tonometry Data Acquisition and Analysis
Tonometry was performed immediately after MRI at rest in the supine position in a quiet, temperature-controlled room. We used a commercially available device (VP-2000, Colin Corporation, Komaki, Japan) customized to output all physiological signals, including ECG, phonocardiogram, oscillometric signals, and tonometric signals. Brachial systolic and diastolic pressures were the averages of 4 oscillometric measurements (2 on each side) and were used to calculate mean brachial pressure. All signals were digitized simultaneously at a sampling frequency of 250 Hz for offline analysis. Right radial artery waveforms were recorded for 30 s. Then, central aortic pressure waveforms were reconstructed for each subject from the radial waveforms using a generalized transfer function as in (18).
Baseline characteristics are provided as mean ± SD for continuous variables and percentages ± SD for discrete variables. To present an exploratory analysis for the trends of the different arterial parameters over age, we grouped the subjects into 6 age strata of 10 years, and calculated the conditional mean ± SD of the arterial parameters given each age group. Age group sample size: 20 to 29 years: n = 20, 30 to 39 years: n = 16, 40 to 49 years: n = 26, 50 to 59 years: n = 15, 60 to 69 years: n = 13, >70 years: n = 10. The general distribution of values of the arterial parameters across age groups and quartiles of aortic stiffness were evaluated using the ANOVA F-test at 5% significance level.
Potential covariates with clinical relevance, such as sex and BMI, were selected by examining their significance in univariate and multivariate models and the stepwise variable selection procedures. Univariate correlations between arterial measures were reported using Pearson correlation coefficients. When LV mass and M/V are taken separately as continuous random variables, the relationships between age, body size, blood pressure, and other cardiovascular risk factors and the arterial parameters were studied using multivariate regression models. All reported p values are 2-sided, and a p value <0.05 is used to indicate statistical significance. Analysis was done with STATA 10 IC (StataCorp LP, College Station, Texas).
Of the 108 participants enrolled, 6 did not complete an MRI due to claustrophobia, and 2 failed to complete the protocol, leaving 100 studies (55 women, 45 men, mean age 46 ± 16 years, range 20 to 84 years) for analysis. Fifty-seven subjects free of cardiovascular risk factors and 43 subjects having at least 1 cardiovascular risk factor at the exclusion of diabetes were studied, of which 33 had hypertension, 8 were current smokers, and 18 had hypercholesterolemia. Of the hypertensive subjects, 24 (73%) had antihypertensive medication, of whom 16 (67%) received diuretics, 13 (54%) an angiotensin-converting enzyme inhibitor or angiotensin receptor blocker, and 8 (33%) a beta-blocker.
Subject characteristics are summarized in Table 1. Men were, on average, significantly taller than women and had an increased aortic arch height, width, and length and a lower average arch curvature as well as slightly higher descending aortic diameters and length compared with women. However, peripheral and central blood pressures and aortic stiffness (local aortic distensibilities and aortic arch PWV) were similar in both sexes. None of the significant unadjusted differences between men and women persisted after adjustment of aortic geometry measures for body surface area and BMI except for aortic arch curvature adjusted for body surface area (p = 0.001), indicating that body proportions play a significant role in explaining the apparent differences by sex.
Age, Body Size, and Aortic Arch Geometry
Relative adult lifetime changes of aortic dimensions are summarized in Table 2 and Figure 2. Average aortic diameters increased with age (p < 0.0001) but with important regional differences. Indeed, the magnitude of diameter increase of the ascending aorta was slightly greater than that of the proximal and distal descending aorta (Fig. 2A) with respective increases of 21% (27.5 to 33.2 mm), 19% (20.5 to 24.3 mm), and 17% (18.3 to 21.5 mm) from the second to seventh decade. On average, the diameter of the ascending aorta increased by 0.11 mm/year. Moreover, the length of the aortic arch (L1) increased significantly with age in our study (Fig. 2B), with an average increase of 30% (100.4 to 130.9 mm) from the second to seventh decade and an increase of 6 mm per 10 years (p < 0.0001). In contrast, descending aortic length (L2) did not change significantly (p = 0.27). The overall proportions of the arch changed with aging because the increase in arch width: +34% (59 ± 5 mm to 79 ± 9 mm) significantly exceeded the increase in arch height: +21% (34 ± 3 mm to 42 ± 5 mm) from the second to the seventh decade (Fig. 2C). Consequently, the H/W ratio decreased with age. Furthermore, the observed widening of the aortic arch was not symmetrical, with a notably greater increase of the anterior compared with the posterior portion of the arch (Fig. 2C). Hence, most of the age-associated widening of the arch was related to an elongation of the anterior portion of the arch. The average curvature of the arch decreased progressively with aging up to the sixth decade (Fig. 2D). Importantly, there were no significant associations between measures of aortic arch geometry and body height. Conversely, increased body weight was associated with increased aortic arch width (r = 0.34, p < 0.001) and increased aortic diameters (ascending aorta: r = 0.24, p = 0.01) as well as decreased aortic arch curvature (r = −0.29, p = 0.003). Overall, these correlations were not very strong, although the negative correlation between the H/W ratio and body weight was relatively strong (r = −0.41, p < 0.001).
Relationships Between Aortic Arch Geometry and Blood Pressure
We found significant correlations between measures of aortic arch geometry and both brachial and central blood pressures. More specifically, increased ascending aortic diameter and increased aortic arch length and width as well as decreased aortic arch curvature were highly correlated with increased central and brachial systolic, diastolic, mean, and pulse pressures (p < 0.001). Overall, the strongest correlations were found between increased ascending aortic diameter, increased aortic arch length, decreased curvature, and systolic blood pressures (respectively: r = 0.61, r = 0.64, r = −0.71, p < 0.001 for brachial systolic blood pressure [SBP] and r = 0.62, r = 0.65, r = −0.70, p < 0.001 for central SBP). After adjustment for age, sex, and body height and weight, average ascending aortic diameter (R2 = 0.53, p = 0.003), arch length (R2 = 0.56, p < 0.001), and arch curvature (R2 = 0.57, p < 0.001) were all independent associates of central SBP. Similar independent associations were obtained between aortic geometry measures and brachial SBP. These relationships remained significant after further adjustment for other risk factors such as hypertension, antihypertension medication, hypercholesterolemia, and smoking. When both the brachial and central SBP were added to the multivariate regression models, the 2 pressures were not independent, and age remained the strongest associate of all aortic geometry measures.
Relationships Between Aortic Arch Geometry and Stiffness
As shown in Figure 3, increased ascending aorta diameter was significantly associated with increased regional stiffness of the proximal aorta, that is, increased aortic arch PWV (r = 0.56, p < 0.001). Furthermore, increased length and width and decreased curvature of the aortic arch were strongly associated with increased local and regional aortic stiffness. In particular, decreased aortic arch curvature was related to decreased aortic distensibility (r = 0.65, p < 0.001) and increased aortic arch PWV (r = −0.61, p < 0.001), respectively (Fig. 3). In multivariate analysis, after adjustment for age, sex, body height, weight, and central SBP, we observed a significant association between increased arch PWV, decreased aortic arch curvature (p = 0.01), and increased aortic arch length (p = 0.03). These relationships remained significant after further adjustment for other risk factors such as hypertension, antihypertensive medication, hypercholesterolemia, and smoking.
Relationship Between Aortic Geometry and LV Mass and M/V
Univariate analysis showed significant correlations between increased aortic arch width, decreased aortic arch curvature, and increased LV mass and M/V. The aortic arch geometry parameter that most strongly correlated with LV mass and M/V was aortic arch curvature. Decreased arch curvature was significantly associated with increased LV mass (r = 0.46, p < 0.001) and M/V (r = 0.41, p < 0.001). The interrelationship between LV mass, aortic geometry, and age is illustrated in Figure 4. Across age groups, we found a significant trend for subjects in the higher quartiles of LV mass to have significantly increased aortic arch length and decreased curvature, beyond the effect of age. Multivariate analysis (Table 3) showed that increased ascending and descending aortic diameter, increased aortic arch length, height, and width, and decreased arch curvature are related to increased LV mass independent of age, sex, body size, and central SBP. The strongest aortic geometry associates of LV mass were ascending aortic diameter and aortic arch length and curvature. Furthermore, increased ascending aortic diameter, increased aortic arch length, and decreased arch curvature were independently related to increased LV M/V, although significance levels were lower than in LV mass models. These results were obtained after adjustment for the presence of other cardiovascular risk factors such as hypertension, antihypertensive medication, smoking, and hypercholesterolemia. The addition of antihypertensive medication as a dichotomous variable or the addition of all individual antihypertensive medications did not change the strength of the results concerning the relationship between aortic geometry, aortic stiffness, and LV mass/remodeling. However, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers were independently associated with increased aortic diameter, arch length, and aortic unfolding, whereas no significant impact of other drugs was found. Furthermore, when both the brachial and central SBP were added to the multivariate regression models exploring relationships between aortic geometry and LV mass, the 2 pressures were not independent.
Our study demonstrates a close relationship between alterations in proximal aortic geometry, namely aortic unfolding (elongation and widening of the aortic arch) and increased LV mass and concentric remodeling. Although mainly related to aging, this vascular–ventricular relationship remains significant after adjustment for age, sex, body size, central blood pressure, and traditional cardiovascular risk factors. Second, we demonstrate a strong relationship between aortic unfolding and increased central and brachial blood pressures and altered local and regional aortic function (increased stiffness).
Age-related arterial function change is considered to be an important independent determinant of cardiovascular morbidity and mortality (3–5). The aorta is subject to constant pulsatile stress, so that the elastic components of the aortic media fragment and eventually break down to be partially replaced by mostly fibrotic nonelastic tissue (19). These histological processes lead to stiffening of the aortic wall and increased mean aortic blood pressure, and finally to transverse dilation of the aorta. This mechanism of increased central arterial volume may initially compensate for stress-induced alteration of aortic function and elasticity but may also progressively lead over time to chronically increased LV afterload and promote LV hypertrophy and concentric remodeling (20). The increase in aortic diameter with age is well known and described (21), and has been classically related to prominent aortic knuckle and aortic unfolding on chest radiography. However, the longitudinal alterations have been much less studied, largely because of difficult access to detailed imaging of the proximal aorta. A recent study showed a preferential age-related elongation of the ascending aorta using MRI in apparently healthy subjects and demonstrated the importance of measuring the central vascular distances when calculating the PWV (9). Our study demonstrates that the age-related longitudinal elongation of the aortic arch exceeds the transversal dilation process, whereas the opposite is true for the descending aorta. This may be partially secondary to the relative fixation of the descending aorta to the spine by intercostal arteries and the horizontal portion of the aortic arch by the neck arteries in contrast to the free mediastinal space occupied by the ascending aorta from its anterior LV attachment up to the horizontal portion of the arch. We found a diameter increase in the ascending aorta of 1.1 mm/decade, which is consistent with the value of 0.96 mm/decade reported by Hickson et al. (8). The length and diameter increases of the ascending aorta reported here were also predominant over changes in the descending aorta in their study. Taken together, these findings indeed suggest that the age-related dilation and lengthening, hence augmentation of proximal aortic volume, may help to offset wall stiffening and loss of distensibility by augmenting the storage capacity of systolic blood volume.
This study shows a close relationship between alterations in aortic geometry and decreased proximal aortic function, thus defining an age-related vascular phenotype. Furthermore, we demonstrate an association between changes in aortic arch geometry and an increase in all components of central and brachial blood pressure, particularly systolic, mean, and pulse pressures independently of age, sex, and body size. This altered aortic phenotype combines transversal and longitudinal enlargement of the vessel, loss of the harmonious arch morphology and unfolding (decrease in average curvature), loss of arterial elasticity, and elevation of regional PWV. It is noteworthy that aortic arch width could be used as a surrogate and more simple measure of aortic unfolding and geometry alteration. We postulate that these structural aortic alterations are integrated markers summarizing, at the time they are measured, large artery damage but also ventricular remodeling over one's past lifetime. Although age is considered to be an important determinant of these arterial changes, its effects are clearly modulated by disease and exposure to traditional cardiovascular risk factors, explaining, along with genetic and other constitutional factors, the heterogeneity of measures of aortic stiffness in younger individuals.
LV hypertrophy has been shown to be a predictor of cardiovascular events and sudden death in large population studies (22,23). More recently, increased LV mass and concentric remodeling measured by MRI have further been shown to be predictors of incident cardiovascular events (24). The prognostic role of concentric remodeling without hypertrophy has also been discussed (25–27). A recent study found increased M/V to be the most representative feature of age-related LV changes because of differential changes in LV volumes and mass during the aging process in a large multiethnic cohort. M/V was a stronger predictor of all cardiovascular events in younger individuals (age <65 years), suggesting that subclinical concentric remodeling in younger subjects could indicate a higher risk (14). We have previously shown that alterations of aortic function began early in life before significant changes in aortic diameter in the absence of blood pressure modifications and in the absence of significant LV hypertrophy or remodeling (6). However, direct relationships between aortic stiffness and LV dysfunction have been reported, suggesting that an early increase in arterial stiffness may lead to subclinical LV dysfunction (14,28,29). Since aortic diameter, arch length, and curvature independently predicted LV mass and M/V in our study, they might be sensitive markers of coupled subclinical vascular–ventricular alterations.
Aortic morphology alterations may be among causal factors in the pathway leading to LV hypertrophy and concentric remodeling. However, the cross-sectional design of our study does not allow us to prove time or causal relationships. Nevertheless, our results show that proximal aortic and LV remodeling are strongly coupled, independently from central and brachial blood pressure levels, and are more strongly related to vascular age than calendar age.
Limitations of our study also include the time difference, albeit short, between central pressure measurements and MRI acquisition, because we could not perform the measurements inside the magnet. However, we tried to minimize this bias by numerous pressure acquisitions immediately after MRI in a similar environment. We estimate global tortuosity of the aortic arch defined as an average of local curvatures from 3D centerline points. Future works could measure local or segmental tortuosity of the thoracic aorta, requiring very detailed centerline measurement using automated methods on 3D aortic acquisitions. Furthermore, the study sample does not allow one to generalize results to define normal aortic arch values for an individual. Further studies with longitudinal design are necessary to determine the chain of causality in defining patterns of vascular–ventricular coupling during aging.
Management strategy of aneurysms of the thoracic aorta mainly rely on diameters. However, we know that aortic dissection may occur in only moderately dilated aortas, below commonly used diameter thresholds warranting surgical treatment. Our study shows an average increase of aortic diameter of 7 mm over 5 decades of life, whereas arch length increased an average of 20 mm during the same period. However, we do not know clearly what the predictive value of aortic length or tortuosity could be for adverse aortic events. In this regard, a better understanding of the biomechanics of the aorta in vivo in humans using a noninvasive imaging technique is a prerequisite to determine valuable new markers (morphology and function) of age- and disease-related subclinical alterations that may be more sensitive to identify in future studies aortic phenotypes at high risk for potentially lethal aortic complications. Furthermore, novel measures of aortic morphology such as volume could help to determine potentially reversible aortic alterations early and prevent evolution toward LV hypertrophic remodeling and dysfunction.
Age-related alterations of aortic arch geometry, in particular aortic unfolding, are related to functional aortic alterations such as decreased aortic distensibility and augmented aortic arch PWV in individuals without overt cardiovascular disease. Furthermore, increased aortic arch length and decreased curvature are associated with increased LV mass beyond calendar age, body size, central pressure, and cardiovascular risk factors.
The authors wish to thank Elzbieta Chamera, Rosalie Cosgriff, and Alain DeCesare for their important contribution to data collection and participant management.
For supplemental methods, please see the online version of this article.
Dr. Redheuil received partial grant support from Fédération and Société Française de Cardiologie and Société Française de Radiologie. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Michael O'Rourke, MD, served as Guest Editor for this paper.
- Abbreviations and Acronyms
- body mass index
- left ventricle/ventricular
- magnetic resonance imaging
- left ventricular end-diastolic mass-to-volume ratio
- pulse pressure
- pulse wave velocity
- systolic blood pressure
- Received February 22, 2011.
- Revision received June 14, 2011.
- Accepted June 15, 2011.
- American College of Cardiology Foundation
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