Evaluation of aortic distensibility with transesophageal echocardiography

A clinically applicable stochastic approach for noninvasive estimation of aortic stiffness using computed tomography data

The degeneration of the vascular wall tissue induces a change of the arterial stiffness, i.e., the capability of the vessel to distend under the pulsatile hemodynamic load. In the literature, the aortic stiffness is usually computed following a simple deterministic approach, in which only the maximum and the minimum values of arterial diameter and blood pressure over the cardiac cycle are considered. In this paper, we propose a stochastic approach to assess the stiffness, and its spatial variation, of a given aortic region exploiting patient-specific geometrical data derived from computed tomography angiography (CTA). In particular, the arterial stiffness is computed linking the aortic kinematic information derived from CTA with pressure waveforms, generated using a lumped parameter model of the arterial circulation. The proposed method is able to include the uncertainty of the input variables as well as to use the entire diameter and blood pressure waveforms over the cardiac cycle rather than only their maximum and minimum values. Although the efficiency and accuracy of the proposed method are tested on a single patient-specific case, the proposed approach is powerful and already possesses the ability to evaluate regional changes of stiffness in human aorta using noninvasive data. The final objective of our paper is to support the adoption of techniques such as CTA as a standard tool for diagnosis and treatment planning of aortic diseases.

Validity of the Water Hammer Formula for Determining Regional Aortic Pulse Wave Velocity: Comparison of One-Point and Two-Point (Foot-to-Foot) Measurements Using a Multisensor Catheter in Human

BACKGROUND

Lack of high-fidelity simultaneous measurements of pressure and flow velocity in the aorta has impeded the direct validation of the water-hammer formula for estimating regional aortic pulse wave velocity (AO-PWV1) and has restricted the study of the change of beat-to-beat AO-PWV1 under varying physiological conditions in man.

METHODS

Aortic pulse wave velocity was derived using two methods in 15 normotensive subjects: 1) the conventional two-point (foot-to-foot) method (AO-PWV2) and 2) a one-point method (AO-PWV1) in which the pressure velocity-loop (PV-loop) was analyzed based on the water hammer formula using simultaneous measurements of flow velocity (Vm) and pressure (Pm) at the same site in the proximal aorta using a multisensor catheter. AO-PWV1 was calculated from the slope of the linear regression line between Pm and Vm where wave reflection (Pb) was at a minimum in early systole in the PV-loop using the water hammer formula, PWV1 = (Pm/Vm)/ρ, where ρ is the blood density. AO-PWV2 was calculated using the conventional two-point measurement method as the distance/traveling time of the wave between 2 sites for measuring P in the proximal aorta. Beat-to-beat alterations of AO-PWV1 in relationship to aortic pressure and linearity of the initial part of the PV-loop during a Valsalva maneuver were also assessed in one subject.

RESULTS

The initial part of the loop became steeper in association with the beat-to-beat increase in diastolic pressure in phase 4 during the Valsalva maneuver. The linearity of the initial part of the PV-loop was maintained consistently during the maneuver. Flow velocity vs. pressure in the proximal aorta was highly linear during early systole, with Pearson's coefficients ranging from 0.9954 to 0.9998. The average values of AO-PWV1 and AO-PWV2 were 6.3 ± 1.2 and 6.7 ± 1.3 m/s, respectively. The regression line of AO-PWV1 on AO-PWV2 was y = 0.95x + 0.68 (r = 0.93, p <0.001).

CONCLUSION

This study concluded that the water-hammer formula (one-point method) provides a reliable and conventional estimate of beat-to-beat aortic regional pulse wave velocity consistently regardless of the changes in physiological states in human clinically. (English Translation of J Jpn Coll Angiol 2011; 51: 215-221).

A comparison of echocardiographic techniques in determination of arterial elasticity in the pediatric population

BACKGROUND

Many methods are used to measure arterial elasticity in children using echocardiography. There is no data to support the equivalence of the different techniques. The goal of this study was to evaluate the reproducibility of several techniques used to measure arterial elasticity using echocardiography.

METHODS

Aortic distension in two different sites (arterial distension) through the cardiac cycle was measured by (four) two-dimensional (2D) and M-mode echocardiographic techniques in 20 children without significant structural heart disease. These measurements combined with noninvasive blood pressure measurements were used to calculate arterial elastic indices. Arterial elasticity was expressed in terms of distensibility and stiffness. Data were collected by two sonographers and interpreted by two reviewers. Paired Student's t-test and Pitman's test for equality of variance for correlated observations were used to detect differences between different sonographers, different reviewers, and different techniques.

RESULTS

No significant difference in the measured elasticity between sonographers or reviewers was observed. There was a somewhat increased variance in two of the four techniques evaluated. There was no significant difference in elasticity measured using different techniques to evaluate the same arterial site, although a significantly decreased elasticity was noted from measurements taken in the proximal ascending aorta as compared with the distal ascending aorta.

CONCLUSIONS

Many echocardiographic techniques produce reproducible measurements of arterial elasticity. There may be intrinsic differences in arterial elasticity between different segments of the ascending aorta, which have not been previously described in children with normal cardiac anatomy. Comparisons of data from separate studies must take these differences into account.

Preserved Windkessel Function in Patients Following Reduction Aortoplasty of the Ascending Aorta

OBJECTIVE

Reduction ascending aortoplasty (RAA) is a controversial procedure. Agreement has not yet been made regarding the indication for surgery and surgical technique. The goal of this study was to examine the long-term outcome of RAA without external support, and to compare the accuracy of transthoracic echocardiographic with computed tomographic (CT) measurements. Of particular interest was whether the important elastic properties of the aorta, the Windkessel function, is preserved following reduction aortoplasty of the ascending aorta without external wrapping.

METHODS

Ninety-eight patients with dilation of the ascending aorta underwent reduction aortoplasty with concomitant cardiac procedures. Fifty-four patients were available for follow-up. Measurement of the ascending aortic diameter was performed prior to and directly following surgery, and 37 months postoperatively (range: 10-96 months). Both echocardiography and CT imaging were performed. The elastic properties of the ascending aorta were determined by measuring the distension of the ascending aorta during diastole and systole by means of transthoracic echocardiography. Fifteen patients with graft replacement of the ascending aorta were examined, and the control group contained 11 healthy volunteers.

RESULTS

The diameter of the ascending aorta was significantly reduced in all patients who had undergone RAA. The change in diameter between diastole and systole was 3 mm in patients with reduction aortoplasty. Patients with graft replacement had a change of only 0.07 cm. There was no relevant increase (2 mm) in diameter at follow-up. Echocardiographic and CT measurements of the aortic diameter did not differ.

CONCLUSIONS

RAA without external wrapping shows good long-term results in patients with a dilated ascending aorta who underwent concomitant cardiac procedures. Echocardiography is very accurate in measuring the ascending aortic diameter, which makes it a cost-effective diagnostic tool. Moreover, ascending aortoplasty without external wrapping preserves the important elastic properties, namely the Windkessel function. Follow-up of the cardiac function and aortic diameter can be performed easily and precisely in the outpatient setting.

Abnormal left ventricular mass and aortic distensibility in pediatric dialysis patients

There is ample evidence that the same pathophysiological processes that affect cardiovascular function in adults with end-stage renal disease (ESRD) also operate in children with ESRD. In adults undergoing hemodialysis (HD), a good correlation has been established between left ventricular mass (LVM) and aortic distensibility (AD) as markers of cardiovascular disease progression; however, this correlation has not been established in children. Therefore, in this retrospective study we investigated some aspects of cardiovascular damage (i.e., LVM, LVMI, and AD) in children with ESRD undergoing HD (n=9) or peritoneal dialysis (PD, n=9), and analyzed the relationship between AD, LVM, LVMI, pre-dialysis, post-dialysis blood pressure (BP), and demographic factors in children and adolescents with ESRD. Both LVM and AD were significantly greater in the dialysis population than in a control population derived from our institutional files (P=0.015, P=0.001). LVM and LVMI in children undergoing HD (92.9+/-83.7 g, 80.1+/-31.1 g/cm) were not statistically different from the values in children on PD (130.0+/-89.2 g, 89.6+/-35.9 g/cm), (P=0.3, P=0.5). AD in children on HD (2.2+/-0.55 cm2* dynes(-1*(10-6)) was significantly lower than in children on PD (2.7+/-0.54 cm2* dynes(-1*(10-6)), (P=0.01). The findings in this study confirm earlier studies that demonstrated that LVMI is greater in children on dialysis. This study also demonstrates that abnormal vascular stiffness, as defined by AD, is present in these children. The degree of vascular stiffness in children receiving HD is greater than in children receiving PD. However, further study is needed to address how control of BP, uremia, and other factors may affect these abnormalities in children with ESRD.

Evolution of healthy thoracic aortic segment diameter during follow-up of patients with aortic aneurysm or dissection: a magnetic resonance imaging study

We studied the normal evolution over time of the diameter of the healthy descending aorta in patients suffering from aneurysm or dissection of the ascending aorta, in order to anticipate potential complications of endoprosthetic treatment in this aortic segment. During their follow-up (average 35.9 months), 52 patients suffering from aneurysm or dissection of the ascending aorta had 168 aortic MRI examinations (2-7; average 3). Measurements were taken according to conventional reference landmarks making it possible to study the evolution of the diameter of the supposed healthy descending thoracic aorta. The variations in diameter with time were on average 5 mm, and there was no significant variation in this diameter, either for early controls or for the controls carried out after more than 1 year or 3 years, whatever the age group. Thus according to our series it seems that patients with a descending aorta endoprosthesis are not exposed to graft endoleak due to inadequate contact of the prosthesis and aorta within the 5 years following its implantation.

Analysis of the regional pulse wave velocity by Doppler: methodology and reproducibility

Increased arterial stiffness is observed in a number of cases. The analysis of the regional functional arterial properties is of interest to determine the role of a given risk factor on the vascular wall and in some diseases such as atherosclerosis. We analysed the pulse wave velocity (PWV) measured by the Doppler method with 2D guidance and its reproducibility in different arterial segments in 15 men with coronary artery disease. Regional Doppler PWV was defined as the distance between the extremities of a given segment divided by the transit time calculated by Doppler. Intra- and interobserver reproducibilities of the Doppler measurements were studied in all of the subjects. The variation coefficients were low, maximum at the level of ascending aorta and minimal at the level of iliac segment. This good reproducibility was validated by the Bland-Altman method. Moreover, using this Doppler technique, we found a progressive increase in PWV from the ascending aorta to the iliac segment. These data demonstrate that noninvasive Doppler analysis is a feasible and reproducible method to determine regional PWV.

Arterial elastic properties and cardiovascular risk/event

Cardiovascular disease is a major cause of morbidity and mortality in the western world. There is convincing evidence that the elastic properties, particularly of large arteries, are impaired in the presence of cardiovascular disease and risk factors such as cigarette smoking, hypertension, diabetes and ageing. Evidence is also emerging that treatment of these risk factors is associated with an improvement in the elastic properties, mirrored by a reduction in the cardiovascular risk and events. The main problems associated with arterial elasticity are the multiple definitions and methods of measurement and the problem of obtaining reliable nearby blood pressure measurement. Nevertheless, duplex estimation appears to be a non-invasive, accurate and reliable method of defining these properties. This method is broadly used as a research tool, but there is a good case for its use in clinical practice, particularly in the screening of patients at risk of cardiovascular events.

Clinical applications of arterial stiffness; definitions and reference values

Arterial stiffening is the most important cause of increasing systolic and pulse pressure, and for decreasing diastolic pressure beyond 40 years of age. Stiffening affects predominantly the aorta and proximal elastic arteries, and to a lesser degree the peripheral muscular arteries. While conceptually a Windkessel model is the simplest way to visualize the cushioning function of arteries, this is not useful clinically under changing conditions when effects of wave reflection become prominent. Many measures have been applied to quantify stiffness, but all are approximations only, on account of the nonhomogeneous structure of the arterial wall, its variability in different locations, at different levels of distending pressure, and with changes in smooth muscle tone. This article summarizes the methods and indices used to estimate arterial stiffness, and provides values from a survey of the literature, followed by recommendations of an international group of workers in the field who attended the First Consensus Conference on Arterial Stiffness, which was held in Paris during 2000, under the chairmanship of M.E. Safar and E.D. Frohlich.

Assessment of effect of angiotensin II receptor antagonist losartan on aortic distensibility in patients with essential hypertension by echocardiography

The effects of angiotensin II receptor antagonist losartan on elastic properties of aorta in patients with mild to moderate essential hypertension were assessed. The ascending aortic distensibility in 26 patients (48 +/- 3 years) with mild to moderate essential hypertension before and after 12 weeks of treatment with losartan (50 mg/day) was evaluated by using two-dimensional echocardiography. M-mode measurements of aortic systolic (Ds) and diastolic diameter (Dd) were taken at a level approximately 3 cm above the aortic valve. Simultaneously, cuff brachial artery systolic (SBP) and diastolic (DBP) pressures were measured. Aortic pressure-strain elastic modulus (Ep) was calculated as Dd x (SBP-DBP)/(Ds-Dd) x 1333 and stiffness index beta (beta) was defined as Dd x Ln (SBP/DBP)/(Ds-Dd). Blood pressure significantly decreased from 148 +/- 13/95 +/- 9 mmHg to 138 +/- 12/88 +/- 8 mmHg (systolic blood pressure, P = 0.001; diastolic blood pressure, P = 0.003). There was no significant difference in pulse pressure before and after treatment with losartan (53 +/- 10 mmHg vs 50 +/- 7 mmHg). The distensibility of ascending aorta increased significantly as showed by the significant decrease in pressure-strain elastic modulus from 4.42 +/- 5.79 x 10(6) dynes/cm2 to 1.99 +/- 1.49 x 10(6) dynes/cm2 (P = 0.02) and stiffness index beta from 27.4 +/- 32.9 to 13.3 +/- 9.9 (P = 0.02). Although there was a weak correlation between the percent changes in pressure-strain elastic modulus and stiffness index beta and that in diastolic blood pressure after losartan treatment (r = 0.40, P = 0.04 and r = 0.55, P = 0.004, respectively), no correlation was found between the percent changes in pressure-strain elastic modulus and stiffness index beta and that in systolic blood pressure (r = 0.04, P = 0.8 and r = 0.24, P = 0.2, respectively). Our study demonstrated that angiotensin II receptor antagonist losartan has a beneficial effect on aortic distensibility in patients with mild to moderate essential hypertension and this effect is partly independent of blood pressure reduction.

Risk Factors for Stiffness of the Wall of the Thoracic Aorta in Patients With Mild Atherosis

Previous studies have suggested that aging is associated with progressive arterial stiffness and widening of the pulse pressure, and pulse pressure has been found to be a risk factor of cardiovascular diseases. However, the effects of age, blood pressure (including pulse pressure) or atherogenic factors on thoracic aortic wall stiffness in patients with mild atherosis are unclear, so the present study used transesophageal echocardiography to examine 103 consecutive patients with various cardiovascular diseases. The extent of atherosis was evaluated in terms of intima-medial thickness (IMT), and 2 indices of wall stiffness in the aorta were calculated: elastic modulus and stiffness parameter (beta). In subjects with mild atherosis (IMT <1.0mm), age, body mass index, systolic blood pressure, pulse pressure, triglyceride level, and hypertension were factors significantly associated with high wall stiffness, and multiple logistic stepwise analysis revealed that age, pulse pressure, and triglyceride level were particularly significant.

Aortic distensibility is closely related to the progression of left ventricular hypertrophy in patients receiving hemodialysis

Aortic stiffening and left ventricular hypertrophy are believed to be major determinants for the prognosis of patients with end-stage renal disease. However, the relationship between left ventricular hypertrophy and aortic stiffness remains to be determined. Echocardiographically determined parameters and aortic distensibility determined with cine magnetic resonance were evaluated in 21 patients undergoing chronic hemodialysis. Hemodynamic variables measured at the beginning of the study were compared with those measured after 28 months. Aortic distensibility determined at the descending aorta was markedly lower in patients undergoing hemodialysis than in healthy control subjects. During the follow-up period, blood pressure and hemodynamic variables, including left ventricular mass index, remained unchanged. However, multiple regression analysis indicated that aortic distensibility independently contributed to the left ventricular mass index and to the change in left ventricular mass index between baseline and after 28 months. Baseline left ventricular mass index negatively correlated to aortic distensibility (r = -0.74, p < 0.0001), and the changes in left ventricular mass index positively correlated to aortic distensibility (r = 0.52, p < 0.05). Our study demonstrates that aortic distensibility at the descending aorta is a predictable marker for the development or regression of left ventricular hypertrophy. Therefore, patients with end-stage renal disease must be treated with appropriate drugs to improve aortic distensibility.

Measurement of aortic arch distension wave with the echo-track technique

The aim of this study was to use the echo-track method for measuring aortic arch diameter, distension waveform and elastic parameters. Data were obtained from 50 healthy volunteers of 32 +/- 15 y (mean +/- 1 SD). The aortic arch was interrogated from the suprasternal position with M-mode ultrasonography using a 3.5-MHz transducer; diameter and distension waves were determined by means of an echo-track algorithm (WTS, Pie Medical); arterial blood pressure was measured in the arm with sphygmomanometry. Aortic arch diameter, distension, distensibility and compliance were 24.55 +/- 2.99 mm, 2199 +/- 726 micrometer, 3.9 +/- 1.4. 10(-3) mmHg(-1) and 1.86 +/- 0.61 mm(2). mmHg(-1), respectively. Intrasession, interobserver and intersession variability was less than 10%, 10% and 18%, respectively. It is concluded that aortic arch distension wave can be recorded noninvasively with acceptable reproducibility, allowing assessment of aortic elastic parameters, and yielding insight into pressure wave reflection within the arterial system.

Transesophageal echocardiography in the diagnosis of diseases of the thoracic aorta: part II-atherosclerotic and traumatic diseases of the aorta

Transesophageal echocardiography (TEE) has provided an accurate new window for the evaluation of diseases of the thoracic aorta. Experience with TEE has led to an increased recognition of atherosclerosis of the thoracic aorta as a source of cerebral and systemic embolism. Certain features of aortic plaque morphology detected by TEE may prove to have prognostic and therapeutic significance. The intraoperative assessment of thoracic aortic atherosclerosis by TEE may guide modifications in surgical techniques and aortic manipulations that reduce the incidence of perioperative neurologic complications. TEE has also become a valuable tool for the diagnostic evaluation of patients with blunt chest trauma. The precise role of TEE in the management of these disorders is currently under investigation.

Vascular compliance as a measure of biological age

OBJECTIVES

To determine the measure of vascular compliance most closely related to age.

DESIGN

A review of 22 studies relating aortic compliance to age and a discussion of other factors related to vascular compliance.

MEASUREMENTS

Aortic compliance, elastic modulus, postmortem aortic changes, pulse wave velocity in the aorta, common carotid, lower limb and upper limb.

RESULTS

1. Aortic compliance and carotid artery compliance is closely related to age; 2. Compliance in the peripheral arteries, in 16 reports, appears less closely related to age; 3. There is evidence that aortic compliance is related to hypertension, cardiac function, and left ventricular hypertrophy and can be increased by exercise, hormonal therapy, antioxidant and antihypertensive treatment; and 4. Vascular compliance is more closely related to chronological age than other measures such as skin inelasticity, greying of hair, baldness etc.

CONCLUSIONS

Because of the close relationship between aortic and carotid compliance and chronological age, deviation from the age-predicted norm (biological age) may prove to be a good predictor of cardiovascular pathology.

Comparison of thickness and distensibility in the carotid artery and descending thoracic aorta: in vivo ultrasound assessment

Early atherosclerotic changes in the carotid artery and thoracic aorta have been examined by high-frequency ultrasound measuring of intimal-medial thickness and stiffness. Whether changes in stiffness and thickness occur in parallel and whether the determinants of stiffness and thickness in the two vessels are similar is unknown. To examine the relation between ultrasonographic measures of atherosclerosis in the carotid and the thoracic aorta, 146 patients aged 20 to 84 years (mean 54 years) were studied by both transesophageal echocardiography (TEE) and carotid duplex scanning. From two-dimensionally derived M-mode recordings of the thoracic aorta and high-frequency B-mode imaging of the common carotid, the intimal-medial thickness was measured along with diastolic and systolic diameters for calculation of stiffness. Interobserver and intraobserver variability of carotid and aortic intimal-medial thickness and diameter were low. There was a good relation between carotid and aortic intimal-medial thickness (r = 0.69; p=0.0001). Age was the major independent determinant of thickness in both vessels. Carotid and aortic stiffness, as measured by Peterson's elastic modulus, were less closely related (r=0.51; p=0.0001). Age was the only independent predictor of stiffness in both vessels. In conclusion, structural ultrasonographic manifestations of early atherosclerosis in the carotid artery and thoracic aorta are closely related. Large population studies measuring only carotid intimal-medial two-thickness may reflect atherosclerotic changes occurring throughout the vascular bed.

Detection of abnormal aortic elastic properties in asymptomatic patients with Marfan syndrome by combined transoesophageal echocardiography and acoustic quantification

OBJECTIVE

To evaluate the potential value of transoesophageal echocardiography combined with automated border detection and acoustic quantification for the assessment of elastic properties of the thoracic aorta in patients with Marfan syndrome.

SUBJECTS

16 patients with Marfan syndrome and 12 age matched normal controls.

METHODS

Transoesophageal echocardiography was performed in all subjects. Minimum and maximum diameters of the descending thoracic aorta were obtained from M mode images and acoustic quantification was used for the on-line evaluation of cross sectional aortic area and peak positive area changes over time. Compliance, distensibility, and stiffness index were calculated using M mode data and non-invasively measured blood pressure and were compared with the indices derived from acoustic quantification.

RESULTS

Aortic dimensions normalised for body surface area were not statistically different between patients and normal controls, but there were significant differences for all elasticity indices except compliance. Marfan patients had a lower distensibility [4.2 (SD 1.8) v 5.8 (2.1) cm2/dyn, P < 0.05] and a higher stiffness index [9.7 (3.0) v 7.1 (1.8), P < 0.05]. The dynamic indices derived from the acoustic quantification were significantly smaller in Marfan patients [peak positive area change: 5.1 (1.0) v 7.7 (1.7) cm2/s; P < 0.001; and normalised peak positive area change: 2.5 (1.2) v 4.0 (0.8) cm2/s respectively, P < 0.001] and were suitable to discriminate between normal and abnormal elastic properties.

CONCLUSIONS

In Marfan syndrome elastic properties of the descending aorta are significantly different from normal controls, even in the absence of vessel dilatation. In addition to established static indices, indices derived from acoustic quantification reflect dynamic changes of the cross sectional area for the evaluation of regional vessel mechanics. The on-line assessment of peak positive area change allows differentiation from normal individuals and may be more accurate than standard M mode measurements.

Pressure-diameter relation of the human aorta. A new method of determination by the application of a special ultrasonic dimension catheter

BACKGROUND

Pressure-diameter relation of the aorta provides important information about the elastic properties of the vessel. However, owing to methodological limitations, data regarding this relation are limited in conscious humans. In the present study, we assessed a new method for the direct estimation of the elastic properties of the aorta in conscious humans by simultaneous acquisition of instantaneous aortic pressure and diameter.

METHODS AND RESULTS

With this method, instantaneous diameter of the thoracic aorta was acquired by a newly designed intravascular catheter developed in our institution that incorporates an ultrasonic displacement meter at its distal end. Instantaneous aortic pressure was acquired simultaneously at the same aortic level with a catheter-tip micromanometer. Aortic pressure-diameter loops were derived from computer analysis of data. After in vitro and animal testing, elastic properties of the aorta were investigated in coronary artery disease (CAD) patients (n = 15) and compared with those of control subjects (n = 10). Aortic distensibility was less in the CAD group than in the control group (1.73 +/- 0.33 versus 3.95 +/- 1.09 x 10(-6) x cm2 x dyne-1, P < .001). Compared with control subjects, the mean value of the slope of the pressure-diameter loops was significantly greater in the CAD group (38.89 +/- 8.75 versus 19.62 +/- 5.46 mm Hg.mm-1, P < .001), whereas the mean value of the intercept was lower in this latter group of patients (-785.60 +/- 177.55 versus -313.43 +/- 126.41 mm Hg, P < .001). An excellent correlation was found between the slope of pressure-diameter loop and age in the group of control subjects (r = .827). Ninety-three percent of the patients with CAD had values above the upper 95% confidence limits of the control subjects (P < .001). In a third group of patients (n = 16) in whom assessment of pulse wave velocity was also included in the study of the elastic properties of the aorta, pulse wave velocity had a strong inverse correlation with aortic distensibility (r = -.95) and a strong positive correlation with the slope of the pressure-diameter loop (r = .97).

CONCLUSIONS

This new method of determination of pressure-diameter of the aorta enables an accurate and reliable evaluation of the elastic properties of the aorta in conscious humans and may be useful for a profound study of human aorta mechanics.

Measurement of regional elastic properties of the human aorta. A new application of transesophageal echocardiography with automated border detection and calibrated subclavian pulse tracings

BACKGROUND

Evaluation of regional aortic elastic properties in humans has been hampered by the need for invasive techniques to access instantaneous aortic pressure, wall thickness, and cross-sectional area or diameter. In this study, a new noninvasive method is presented for quantification of regional aortic elastic properties.

METHODS AND RESULTS

Twenty-five patients were studied during transesophageal echocardiographic procedures. Measurements of instantaneous aortic cross-sectional area were obtained with an automated border detection algorithm applied to short-axis transesophageal two-dimensional echocardiographic images of the proximal descending thoracic aorta. Instantaneous aortic wall thickness was derived from combined two-dimensional targeted M-mode end-diastolic wall thickness and instantaneous aortic area measurements. Instantaneous aortic pressures were estimated from calibrated subclavian pulse tracings recorded simultaneously. Data were digitized to generate aortic area-pressure loops. Regional aortic mechanical properties were quantified in terms of compliance per unit length (C is the slope of the area-pressure regression), aortic midwall radius (Rm), and incremental elastic modulus of the aortic wall (Einc). To assess the independent effect of age, Rm and Einc values were compared at a common level of aortic midwall stress (0.666 x 10(6) dynes/cm2). Mean values (+/- SD) for C, Rm, and Einc were 0.01 +/- 0.004 cm2/mm Hg, 1.14 +/- 0.17 cm, and 7.059 +/- 4.091 x 10(6) dynes/cm2, respectively. An inverse linear correlation was found between aortic compliance per unit length and age (r = -.68, P < .0007). Incremental elastic modulus was related to age (r = +.80, P < .00003) in a nonlinear fashion such that it increased sharply after the age of 60 years. Finally, midwall radius was less tightly correlated with age (r = +.45, P < .05). Values for C, Rm, and Einc as well as the age dependency of these properties are similar to those reported previously when invasive techniques were used.

CONCLUSIONS

This methodology constitutes a new tool to improve the clinical evaluation of regional aortic elastic properties in multiple disease states.

Utility of transesophageal echocardiography in the diagnosis of disease of the thoracic aorta

PURPOSE

Transesophageal echocardiography (TEE) offers a rapid, minimally invasive method for diagnosing thoracic aortic disease. High-resolution images are possible because of the close proximity of the esophagus and vascular structures within the chest. Lung and chest wall components have little influence on the image quality and a virtually unobstructed view of the heart, thoracic aorta, and pulmonary vasculature is seen. The role of TEE in diagnosing diseases of the thoracic aorta is rapidly developing. The purpose of this study is to define the role of TEE in the diagnosis of thoracic aortic disease.

METHODS

Between July 1, 1989 and December 31, 1992, 1005 TEEs were performed at our center. Of these, 199 (125 men, 74 women) were entered into our aortic disease registry. Indications for the studies included 37 referrals to rule out aortic dissection, 18 to assess aortic aneurysm, 55 to assess for an intraaortic source of embolus, 9 to rule out intraaortic thrombus, and 13 with familial hyperlipidemia being followed to mark response to low-density lipoprotein apheresis. In 67 cases, subclinical aortic plaquing was found incidentally. No complications from the TEE procedure were encountered.

RESULTS

In cases of suspected aortic dissection, TEE was equal to computed tomography (CT) scanning in identifying the type (DeBakey) and extent of thoracic aortic dissection. In addition, TEE provided information regarding functional status of the aortic valve, identified interluminal communications, and assessed blood flow and thrombus burden in the false lumen. TEE correctly identified true aneurysms, intraluminal thrombus, and plaques as possible sources of emboli. One false-positive CT scan result for aortic dissection was seen and was ruled out both by TEE and angiography.

CONCLUSION

Biplane TEE can be considered the method of choice in diagnosing disease of the thoracic aorta. Information from TEE can be obtained at the patient's bedside or in the operating suite, to assess surgical results before procedure termination and afterward for follow-up. Adjunctive magnetic resonance imaging, CT scanning, or aortography may be needed to assess extension of the disease process into the abdomen or pelvis or to plan surgical intervention.

Transesophageal echocardiographic assessment of the effects of age, gender, and hypertension on thoracic aortic wall size, thickness, and stiffness

Aging is associated with progressive arterial stiffening and widening of the pulse pressure, resulting in a high prevalence of systolic hypertension. The contribution of increased aortic thickness to this process and to essential hypertension has been poorly characterized. With transesophageal echocardiography, aortic thickness and diameter can be measured. Thus, the influence of aging, gender, and hypertension on the geometry and stiffness of the descending thoracic aorta in humans can be determined in vivo. In 83 patients undergoing transesophageal echocardiography for clinical indications, recordings of the descending thoracic aorta were made. There were 53 normotensive subjects (33 men and 20 women, mean age 46 years, range 14 to 79 years) and 25 hypertensive subjects (8 men and 17 women, mean age 67 years, range 50 to 80 years). Measurements of diastolic and systolic aortic thickness and aortic diameter were made, and three measures of the elastic properties of the aorta were calculated: (1) Peterson's elastic modulus, (2) Young's modulus, and (3) the stiffness index (beta). Aortic thickness averaged 1.1 +/- 0.1 mm in both normotensive men and women. Normotensive women had a significantly greater thickness/diameter ratio than men (0.06 +/- 0.01 vs 0.05 +/- 0.01, p < 0.01), but there were no differences in stiffness between men and women. Age was highly positively correlated with thickness (r = 0.74, p < 0.001), diameter (r = 0.67, p < 0.001), beta (r = 0.79, p < 0.001), Peterson's modulus (r = 0.78, p < 0.001), and Young's modulus (r = 0.81, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of thoracic aortic atherosclerosis by transesophageal echocardiography

Transesophageal echocardiography (TEE) provides excellent images of the thoracic aorta, which cannot be visualized by transthoracic echocardiography. The purpose of this study was to assess atherosis and sclerosis of the thoracic aorta by TEE, to evaluate the risk factors for atherosis and sclerosis, and to assess the relationship between the two components of atherosclerosis. The mean value of the maximum thickness of the intima-media complex in the six segments of the thoracic aorta (MIMC) was used as an index of atherosis, and the stiffness parameter beta was used as an index of sclerosis. The study population consisted of 88 Japanese patients. Multivariate analysis showed that age, low-density lipoprotein cholesterol (or apolipoprotein B), and diabetes mellitus were significantly and independently related to MIMC, whereas age and hypertension were related to the stiffness parameter beta. Both components of atherosclerosis demonstrated a significant although weak relationship. The risk factors for atherosis appear to differ from those for sclerosis in the thoracic aorta, so we should evaluate these two components of atherosclerosis separately. TEE is a useful method of assessing thoracic aortic atherosclerosis because both atherosis and sclerosis can be examined simultaneously.

Transesophageal echocardiography in the diagnosis of aortic disease

Transesophageal echocardiography (TEE) has recently become a major diagnostic tool in aortic disease. By far the most important role of TEE is in the rapid diagnosis of acute aortic dissection. In this disease the sensitivity and specificity of TEE are both well more than 90%, patient risk is minimal, and the test can (and should) be done in the emergency department. Limitations of TEE include, in some cases, difficulty delineating involvement of the proximal arch, major branch vessels, and abdominal aorta. Another emergency department application of TEE is the assessment of patients suspected of traumatic aortic rupture. TEE also is being applied to the diagnosis of aortic protruding atheromas, thought to have significant embolic potential.