New perspectives in the assessment of cardiac chamber dimensions during development and adulthood

Indexing left ventricular mass to account for differences in body size in children and adolescents without cardiovascular disease

Left ventricular (LV) mass has been established as an independent risk factor for cardiovascular disease morbidity and mortality. To account for differences in body size, a variety of factors have been proposed for indexing LV mass. Dual energy x-ray absorptiometry provides a measure of lean body mass which can be used as a comparison with other more clinically applicable methods of standardization. The study included 192 subjects (100 male, 103 white) aged 6 to 17 years. Lean body mass was determined by dual energy x-ray absorptiometry and LV mass was calculated from M-mode echocardiographic measurements. There were significant differences by gender (males 98.7 g, females 80.3g, p < 0.001), but not race, for unindexed LV mass. Indexing LV mass by lean body mass eliminated the difference by gender. Log-log regression analysis revealed that the optimal height exponent for indexing LV mass was height3 (95% confidence interval, 2.8 to 3.1). LV mass/height3 provided the most consistently high intraclass correlation with LV mass/lean body mass versus indexing with body surface area, height, height2, and height2.7 across the 4 race/gender groups. LV mass indexed by height3 eliminated differences in LV mass by gender (males 26.1 +/- 4.72 g/m3, females 25.5 +/- 4.8 g/m3, p = NS). The proposed method for indexing LV mass by height3 should be useful in the clinical setting. The 90th and 95th percentiles of LV mass/height3 provide cutpoints for determining the presence of LV hypertrophy in children and adolescents.

Gender-specific reference M-mode values in adults: population-derived values with consideration of the impact of height

OBJECTIVES

The purpose of this investigation was to derive population-based reference values for M-mode echocardiographic dimensions that can be applied in epidemiologic studies, clinical trials and clinical practice and to determine optimal methods for adjusting these dimensions for body size.

BACKGROUND

M-mode echocardiography remains an important modality for studying cardiovascular disease; this is especially true with regard to detecting target organ damage in systemic hypertension. Most previously published reference values were derived from hospital-based series or relatively small samples and were not gender specific.

METHODS

Using a sample of 288 men and 524 women who were between 20 and 45 years of age and who were free of cardiovascular disease, reference values were derived for end-diastolic and end-systolic left ventricular internal dimensions, left ventricular wall thickness and left atrial dimension. The relations between these dimensions and height, a measure of body size relatively independent of obesity, were investigated using various regression models.

RESULTS

Nomograms for mean and 95th percentile values in men and women were constructed on the basis of linear regression models relating echocardiographic dimensions to height. Adjustment for body surface area greatly attenuated associations between obesity and cardiac dimensions in a separate healthy but less restricted sample of 411 men and 503 women.

CONCLUSIONS

Gender-specific M-mode reference values and nomograms, with mean and 95th percentile values for echocardiographic dimensions as a function of height, are reported. The use of body surface area as means of body size adjustment is called into question.

Influence of blood pressure on left atrial size. The Framingham Heart Study

Increased left atrial size has been identified as a precursor of atrial fibrillation and of stroke once atrial fibrillation is manifest. Conflicting data exist regarding the effect of high blood pressure on left atrial size. Our objective was to evaluate the association of contemporary and long-term measures of blood pressure with echocardiographically determined left atrial size in a large, population-based cohort. The study sample consisted of 1849 male and 2152 female participants of the Framingham Heart Study and Framingham Offspring Study. All analyses were sex specific. In correlation analyses, systolic and pulse pressures were identified as statistically significant determinants of left atrial size after adjustment for age and body mass index, although the magnitudes of these relations were very modest (partial r < or = .10). Multivariable linear regression models showed the relative contributions of the pressure variables to the prediction of left atrial size to be substantially less than those of age and, in particular, body mass index. Furthermore, inclusion of left ventricular mass in these multivariable models eliminated or attenuated the associations of the pressure variables with left atrial size. In logistic analyses, increasing levels of the pressure variables were significantly predictive of left atrial enlargement. Subjects with 8-year average systolic pressure of 140 mm Hg or higher were twice as likely to have left atrial enlargement as those with values of 110 mm Hg or lower. Overall, in this population-based study sample, increased levels of systolic and pulse pressures (but not diastolic or mean arterial pressures) were significantly associated with increased left atrial size.(ABSTRACT TRUNCATED AT 250 WORDS)

Echocardiographic assessment of aortic root dimensions in normal children based on measurement of a new ratio of aortic size independent of growth

Two-dimensional echocardiography is commonly used as a method of monitoring aortic root dimensions in children with connective tissue disease. Measurements are usually standardized to body surface area (BSA) to account for growth. However, there are several theoretical and practical disadvantages to adopting this approach, and there has been little investigation of alternative methods of standardization. This study of 48 normal children and adolescents (age range 2 weeks to 23 years) was performed to determine the relation of 2-dimensional echocardiographic aortic root dimensions to indexes of body size and growth, and to examine a simple means of internally standardizing aortic root measurements to create an index of aortic root size independent of growth. Maximal diameters in the parasternal long-axis view were recorded at 4 levels: annulus, sinuses of Valsalva (SOV), supraaortic ridge (SAR), and ascending aorta (AAO). Ratios of aortic root size were created by internally standardizing aortic root diameters to aortic annular size. All diameters correlated closely with age, height, weight, and BSA (all r > 0.87). Linear regression in each case showed a significant positive slope (all p < 0.0001). The best predictor of aortic dimensions was height, with r values of 0.93 for annulus, SOV, and AAO, and 0.95 for SAR. Ratios of SOV/annulus, SAR/annulus, and AAO/annulus remained constant, with no correlation with age or any growth parameters. Mean values and 95% confidence limits were: SOV/annulus 1.37 (1.18-1.56); SAR/annulus 1.11 (0.95-1.28); and AAO/annulus 1.16 (0.97-1.35). Standardization to height, or the use of internally standardized aortic root ratios, provides a simple and accurate alternative to standardization to BSA for assessing aortic root dimensions in normal growing children.

Cardiac index quantification by Doppler ultrasound in patients without left ventricular outflow tract abnormalities

OBJECTIVES

We attempted to ascertain whether cardiac index can be directly estimated from Doppler mean velocity.

BACKGROUND

Although diverse Doppler echocardiographic methods have been described for cardiac output quantification, they are not widely used in clinical practice. Cross-sectional area measurement has been identified as the main source of error in flow volume quantification.

METHODS

A three-phase study by Doppler echocardiography was conducted in 306 patients. In phase I, the normal mean velocity ratio of the left and right ventricular outflow tracts was established in 170 normal subjects. In phase II, cardiac index, calculated as the product of aortic annular area index by mean velocity (conventional method), and mean velocity determined in the left ventricular outflow tract and ascending aorta by pulsed and continuous wave Doppler, respectively, were correlated with thermodilution cardiac index in 66 patients. In phase III, the accuracy of the regression equations obtained was prospectively assessed in an additional 70 patients.

RESULTS

The normal left/right ventricular outflow tract mean velocity ratio by pulsed wave Doppler was 1.1 +/- 0.1. Cardiac index (CI) calculated by the conventional method and thermodilution (TD) showed acceptable correlation (r = 0.90, CITD = 1.20 CIPWD + 357; r = 0.86, CITD = 0.90 CICWD + 262) for pulsed (PWD) and continuous wave (CWD) Doppler, respectively, but with systematic underestimation (-28 +/- 13%, p < 0.01) by pulsed wave Doppler. Mean velocity (MV) showed excellent correlation with the thermodilution cardiac index (r = 0.97, CITD = 172 MVPWD - 172; r = 0.93, CITD = 129 MVCWD - 255). When these regression equations were prospectively applied, better agreement with the thermodilution cardiac index was obtained by pulsed wave Doppler directly from mean velocity (SD 240 ml/min per m2) than when aortic annular area was considered in the calculation (SD 428 ml/min per m2). Similar results were obtained by continuous wave Doppler (SD 433 vs. 599 ml/min per m2) but with less accuracy.

CONCLUSIONS

Left ventricular outflow tract mean velocity determined by pulsed wave Doppler permits easy, accurate cardiac index quantification in the absence of left ventricular outflow abnormalities. The simplicity of this method enhances its clinical applicability in noninvasive monitoring of cardiac index.

Determinants of echocardiographic aortic root size. The Framingham Heart Study

BACKGROUND

Previous studies that evaluated the determinants of aortic root size have not yielded uniform results. We examined the relations of age, height, weight, body surface area, sex, and blood pressure to echocardiographically determined aortic root size in a population-based cohort.

METHODS AND RESULTS

The study sample consisted of 1849 men and 2152 women in the Framingham Heart Study and Framingham Offspring Study who were free of clinically apparent cardiac disease when echocardiography was performed. Aortic root measurements were made by M-mode echocardiography using a leading-edge-to-leading-edge technique. The relations of age, height, weight, body surface area, and blood pressure variables (contemporary and those obtained 8 years before) to aortic root dimension were examined by use of sex-specific correlations and linear regression analyses. Age, height, weight, and sex emerged as the principal determinants of aortic root dimensions in adults (cumulative R2 = .2085 in men and .2327 in women). The additional effect of contemporary or previous blood pressure measures was small and revealed direct associations of aortic root dimension with mean arterial and diastolic blood pressures and inverse associations with pulse and systolic blood pressures. Previous blood pressure measurements did not contribute significantly to prediction of aortic root size once contemporary blood pressure variable entered the models. Results of regression analyses using a sex-pooled data set showed that on average, the aortic root measurement in women was 2.4 mm smaller than that of men of comparable age, height, and weight. Logistic regression was used to assess the likelihood of aortic root enlargement according to blood pressure levels. After adjustment for age, height, and weight, the odds ratio of aortic dilation for a 1-SD increment in systolic pressure was 0.70 (95% CI, 0.52 to 0.95) in men and 0.79 (95% CI, 0.60 to 1.04) in women; the odds ratio for a 1-SD increment in diastolic pressure was 1.22 (95% CI, 0.91 to 1.63) in men and 1.33 (95% CI, 1.01 to 1.73) in women.

CONCLUSIONS

Age, height, weight, and sex emerged as the principal determinants of aortic root dimensions. The additional influences of blood pressure measurements were small; direct associations of aortic root dimensions with mean arterial and diastolic blood pressures and inverse associations with pulse and systolic blood pressures were observed. Additional prospective studies are needed to confirm these observations and to assess the impact of aortic root dimensions on the incidence of hypertension.

A new method for indexing left ventricular mass for differences in body size

Left ventricular (LV) mass is determined to a large extent by body size. This has created controversy regarding the optimal method of defining normal values in the clinical setting. Previous groups have advocated indexing LV mass for body surface area, lean body mass, or height, which is an obesity-independent measure of body size. This study describes a new approach that involves dividing LV mass by height raised to a noninteger power. In a sample of 387 men and 714 women who were between 20 and 45 years of age and who were free of cardiovascular disease, the height exponent was determined by logarithmic regression models to be 2.12 in men and 1.91 in women; in a pooled analysis, the height exponent was 1.97. This approach reduced male versus female differences in the mean and 95th percentile values for LV mass; mean value differences who reduced from 52% among raw values to 29% among adjusted values. Compared with height or body surface area indexation, it was found to slightly increase the correlation between LV mass and systolic blood pressure. In contrast, body surface area indexation reduced the association between LV mass and obesity. The current method of indexation is independent of obesity, reduces LV mass variability associated with body size and gender, and may therefore be a useful method for defining normal and abnormal values of LV mass in the clinical setting. The findings of this study also suggest that indexation of LV mass for body surface area is inappropriate.

Relation between age, arterial distensibility, and aortic dilatation in the Marfan syndrome

This study examined the relations between age, arterial distensibility, and systemic hemodynamics in patients with the Marfan syndrome. The study group included 170 patients referred to a specialist clinic, of whom 55 (age 26 +/- 12 years) were diagnosed as having Marfan syndrome. The remaining 115 patients (age 25 +/- 14 years) formed a control group. Each patient underwent echocardiographic examination, with measurement of ascending aorta diameter at end-diastole and end-systole, and aortic flow velocities. The elastic properties of the aorta were indexed by calculation of aortic distensibility, wall stiffness, and systemic pulse wave velocity. Mean end-diastolic aortic diameter in the Marfan group (38 +/- 9 mm) was greater than that in the controls (26 +/- 4 mm, p < 0.01). Resting heart rate and aortic flow velocities were similar in the 2 groups, but systemic arterial pulse pressure was greater in the Marfan group (50 +/- 12 mm Hg) than in the controls (41 +/- 8 mm Hg, p < 0.01). Aortic diameter increased with age in both groups, but at all ages the Marfan group exhibited greater aortic diameters (p < 0.05). Aortic distensibility was less in the Marfan group (2.6 +/- 1.3 cm2.dynes-1 x10(-6)) than in the controls (6.2 +/- 2.1 cm2.dynes-1 x 10(-6), p < 0.01), and the aortic wall stiffness index was greater in the Marfan group (7.9 +/- 3.4) than in the controls (2.8 +/- 0.6, p < 0.01). Aortic wall stiffness increased with age and aortic diameter, but at all ages the Marfan group exhibited a stiffer aorta for a given diameter than did the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Left ventricular mass and cardiovascular reactivity in young men

The relation between left ventricular wall thickness and mass, arterial plasma catecholamines, and blood pressure at rest and during a mental arithmetic challenge and a cold pressor test was examined in 69 healthy men 19 years of age. The subjects were recruited from the 1st (n = 21), 50th (n = 26), and 99th (n = 22) percentiles in mean blood pressure. All underwent echocardiography to determine mean wall thickness and left ventricular mass. Continuous intra-arterial blood pressure, electrocardiogram, and arterial sampling of plasma catecholamines were performed after 30 minutes of supine rest, during a 5-minute mental arithmetic challenge, and during a 1-minute cold pressor test. Stepwise multiple-regression analyses considering mean wall thickness and left ventricular mass as the dependent variables were applied. Intra-arterial systolic blood pressure (r = .54, P < .0001) and arterial plasma epinephrine (r = .31, P = .009) after 30 minutes of supine rest were the only independent explanatory variables of mean wall thickness (multiple R2 = .33, P < .0001). Blood pressure at screening and during mental stress and cold pressor tests were not independent explanatory variables. The present study suggests that resting arterial blood pressure and plasma epinephrine may be of importance for development of left ventricular hypertrophy.

Estimation of left ventricular filling pressures using two-dimensional and Doppler echocardiography in adult patients with cardiac disease. Additional value of analyzing left atrial size, left atrial ejection fraction and the difference in duration of pulmonary venous and mitral flow velocity at atrial contraction

OBJECTIVES

The purpose of this study was to determine whether left atrial size and ejection fraction are related to left ventricular filling pressures in patients with coronary artery disease.

BACKGROUND

In patients with coronary artery disease, left ventricular filling pressures can be estimated by using Doppler mitral and pulmonary venous flow velocity variables. However, because these flow velocities are age dependent, additional variables that indicate elevated left ventricular filling pressures are needed to increase diagnostic accuracy.

METHODS

Echocardiographic left atrial and Doppler mitral and pulmonary venous flow velocity variables were correlated with left ventricular filling pressures in 70 patients undergoing cardiac catheterization.

RESULTS

Left atrial size and volumes were larger and left atrial ejection fractions were lower in patients with elevated left ventricular filling pressures. Mean pulmonary wedge pressure was related to mitral E/A wave velocity ratio (r = 0.72), left atrial minimal volume (r = 0.70), left atrial ejection fraction (r = -0.66) and atrial filling fraction (r = -0.66). Left ventricular end-diastolic and A wave pressures were related to the difference in pulmonary venous and mitral A wave duration (both r = 0.77). By stepwise multilinear regression analysis, the ratio of mitral E to A wave velocity was the most important determinant of pulmonary wedge (r = 0.63) and left ventricular pre-A wave (r = 0.75) pressures, whereas the difference in pulmonary venous and mitral A wave duration was the most important variable for both left ventricular A wave (r = 0.75) and left ventricular end-diastolic (r = 0.80) pressures. The sensitivity of a left atrial minimal volume > 40 cm3 for identifying a mean pulmonary wedge pressure > 12 mm Hg was 82%, with a specificity of 98%.

CONCLUSIONS

Left atrial size, left atrial ejection fraction and the difference between mitral and pulmonary venous flow duration at atrial contraction are independent determinants of left ventricular filling pressures in patients with coronary artery disease. The additive value of left atrial size and Doppler variables in estimating filling pressures and the possibility that left atrial size may be less age dependent than other mitral and pulmonary venous flow velocity variables merit further investigation.

The natural history of aortic dilatation in Marfan syndrome

OBJECTIVES

To determine the relationship between age and aortic dilatation in patients with Marfan syndrome and to define the rate of progression of aortic dilatation in these patients.

DESIGN

All patients were evaluated in a multidisciplinary clinic to establish a firm diagnosis of Marfan syndrome. Aortic dimensions were measured by echocardiography and patients with Marfan syndrome were followed up with annual physical and echocardiographic examinations to detect any change in aortic diameter over the subsequent four years.

PATIENTS

One hundred and fifty-seven patients were referred to the clinic for assessment, of whom 40 exhibited diagnostic features of Marfan syndrome. Only 24 of these patients had previously been diagnosed with Marfan syndrome, while 17 other patients, previously diagnosed with Marfan syndrome, had insufficient clinical features to justify the diagnosis.

RESULTS

Among the 40 patients (19 male, 21 female) with Marfan syndrome (mean age, 28 +/- 15 years), the prevalence of cardiovascular abnormalities was 90%. Aortic root dilatation was present in 78% of patients, aortic regurgitation in 28%, mitral valve prolapse in 65% and mitral regurgitation in 35%. Mean aortic root diameter in the Marfan patients (21.4 +/- 4.0 mm/m2 body surface area) markedly exceeded that of age and sex matched controls without Marfan syndrome (14.9 +/- 2.2 mm/m2) and that of first-degree relatives without Marfan syndrome (15.3 +/- 2.9 mm/m2). The occurrence of aortic dilatation in Marfan syndrome was variable, with patients as young as 20 years exhibiting severe dilatation. All patients with Marfan syndrome exhibiting aortic dilatation were advised to take beta-adrenergic blocking drugs, unless contraindicated, in an effort to retard the rate of aortic dilatation. Among 33 patients followed up for at least one year, 14 (42%) exhibited an increase in aortic diameter of at least 2 mm, while 16 of 23 patients (70%) followed up for at least three years exhibited similar progression of aortic dilatation. The overall mean rate of dilatation in the Marfan patients was 1.9 mm per year. Nine patients developed aortic dilatation of more than 50 mm diameter during four years' follow-up and required surgical repair of the aorta. Each of these patients is well at between three months' and four years' follow-up.

CONCLUSIONS

Aneurysmal dilatation of the aorta is a common complication of Marfan syndrome and may become manifest at an early age. Furthermore, aortic dilatation can progress rapidly, even in the absence of symptoms. Individuals with Marfan syndrome should have annual echocardiographic examinations to monitor aortic root dimensions, and those exhibiting rapid progression of aortic dilatation or an aortic root diameter in excess of 50 mm, should be considered for elective composite graft repair of the aorta.