Normal ultrasonic myocardial reflectivity in hypertensive patients. A tissue characterization study

Review: New approaches to the assessment of left ventricular hypertrophy

In hypertension, Left ventricular hypertrophy is initially a useful compensatory process that represents an adaptation to increased ventricular wall stress; however, it is also the first step toward the development of overt clinical disease. For this reason most international guidelines recommend the assessment of cardiac target organ damage in hypertensive patients for cardiovascular risk stratification. It is therefore of great importance to keep in mind the strengths and weakness of the different available methods for LVH assessment.

Several methods are currently available for the assessment of LVH; however the various techniques differ in cost, availability, sensitivity and specificity. Due to its wide availability and its low cost, eLectrocardiography should be part of all routine assessment of subjects with high blood pressure; however, despite its good specificity, the sensitivity for LVH detection is low. Several other methods have been proposed for LVH detection. Cardiac magnetic resonance imaging allows 3D reconstruction of the heart with high spatial resolution; however its main limitation is represented by the relatively low availability and by its costs. Echocardiography certainly represents a valuable method for the detection of LVH in hypertensive patients, due to its wide availability and its relatively low cost. The main limitations of the technique are represented by the lower spatial resolution and reproducibility in comparison with magnetic resonance. The development of new matrix-array transducers and new software for 3D reconstruction with echocardiography make this approach particularly promising for the future; in the meantime, standard echocardiography, widely available and with low cost, will probably remain the most used tool for the evaluation of left ventricular structure and function in hypertension.

Changes in cardiac tissue characterization in carriers with gene mutations associated with hypertrophic cardiomyopathy

BACKGROUND

Early detection in patients with hypertrophic cardiomyopathy (HCM) is very important. Integrated backscatter (IB) provides a useful noninvasive measure of the acoustic properties of the myocardium, and may detect early myocardial changes.

METHODS

Thirty-four carriers who had gene mutations causing HCM were studied. The patients were divided into three groups as follows: (1) 21 patients with wall hypertrophy (Group A), (2) 7 patients with ECG abnormalities but without wall hypertrophy (Group B), and (3) 6 carriers with neither ECG abnormalities nor wall hypertrophy (Group C). All subjects underwent ECG, conventional echocardiography and acoustic densitometry. In addition, we studied subjects < or =20 years old from Groups B and C (Group B-2 and Group C-2, respectively), and compared them with control subjects with no cardiac disorders who were < or =20 years old.

RESULTS

In Group A, cyclic variations of integrated backscatter (CV-IB) in the interventricular septum and left ventricular posterior wall were significantly smaller than in Group C. The amplitude of IB in the interventricular septum and left ventricular posterior wall in Group A was significantly higher than those in Group C. Even in Group B, CV-IB in the interventricular septum was significantly smaller than those in Group C. Among patients < or =20 years old, CV-IB in the interventricular septum was significantly smaller in Group B-2 than in control subjects, while that in Group C-2 did not differ from that in control subjects.

CONCLUSIONS

Changes in tissue characterization were found in the hearts of HCM gene carriers even in the absence of wall hypertrophy. These results suggest that tissue changes detectable by the acoustic densitometry methods may occur in the hearts of HCM gene carriers without wall hypertrophy, and that they may be detectable at the time of appearance of ECG abnormalities.

Cyclic variation of the myocardial integrated backscatter signal in hypertensive cardiopathy: a preliminary study

BACKGROUND

Ultrasound tissue characterization studies realized through integrated backscatter analysis with end-diastolic sampling in hypertensive cardiopathy have demonstrated that abnormalities in the left ventricular myocardial ultrasonic texture are present in extreme forms of left ventricular hypertrophy (LVH). Such abnormalities are not evident in the athlete's heart. The aim of the present study was to analyze the ultrasonic backscatter myocardial indexes both as peak end-diastolic signal intensity and as cardiac-cyclic variation in two models of LVH: hypertensive cardiopathy and athlete's heart.

METHODS

Three groups of 10 subjects each, all men of mean age (31.6+/-3.5 years), and of comparable weight and height, were analyzed. Group A comprised 10 cyclists of good professional level, while hypertensive patients were grouped in Group H. Both groups presented a comparable left ventricular mass (LVM). Group C included 10 healthy subjects acting as controls. The men with hypertension were selected on the basis of the results of ambulatory monitoring of the blood pressure according to ISH-World Health Organization guidelines (International Society of Hypertension). A 2D-color Doppler echocardiography with a digital echograph Sonos 5500 (Agilent Technologies, Andover, Massachusetts, USA), was carried out on all the subjects in the study for conventional analysis of the LVM and function. The ultrasonic myocardial integrated backscatter signal (IBS) was analyzed with an 'acoustic densitometry' module implemented on a AT echograph. The signal was also sampled with a region of interest (ROI) placed at interventricular septum and at posterior left ventricular wall level. The systo-diastolic variation of the backscatter was also considered, as cyclic variation index (CVIibs).

RESULTS

According to the inclusion criteria, the LVM was comparable in groups A and H, but it was significantly higher than group C (left ventricular mass (body surface) (LVMbs)=154.5+/-18.7 (A), 146.8+/-25.5 (H), 101.4+/-12.4 (C), p < 0.001). The end-diastolic IBS did not show significant statistical differences among the three groups. The CVI(IBS) both at septum (30.5+/-5.3 (A), 13.2+/-13.1 (H), 27.2+/-7.3(C), p < 0.002) and posterior wall level (43.7+/-9.1 (A), 16.5+/-12.1 (H), 40.7+/-9.1 (C), p < 0.001) though, was significantly lower in the hypertensive patients than in both the athletes and the control group, where the results were comparable.

CONCLUSION

A significant alteration of the myocardial CVIibs (both for septum and posterior wall) was found in the hypertensive model. This was probably the expression of an alteration in the intramural myocardial function.

Echocardiographic patterns of myocardial fibrosis in hypertensive patients: endomyocardial biopsy versus ultrasonic tissue characterization

Echocardiographic image texture has been demonstrated to reflect the physical properties of the tissue under examination. To evaluate the role of collagen in determining the echo pattern of the left ventricular wall, we studied nine hypertensive patients with left ventricular hypertrophy (left ventricular mass index > 125 gm/m2) and biopsy-proven different degrees of myocardial fibrosis by analyzing the echocardiographic examinations performed before the biopsy. Myocardial tissue was sampled under fluoroscopy and two-dimensional echo guidance in the interventricular septum. Collagen volume fraction (CVF; normal range up to 2%) was taken as an index of fibrosis. The echo patterns were assessed by analyzing standard two-dimensional parasternal long-axis echocardiograms recorded on videotape. Images were color-coded at 256 levels (0 = yellow, 256 = black) and digitized off-line onto a personal computer. The region of analysis was set using a selection tool (20 x 10 mm) in the general area of septum where the specimen was taken. For each selection a color-level histogram, representing the frequency distribution, was derived with estimates of the average pixel intensity (mCS), skewness (SK), kurtosis (K), and the broad band (Bb) of the echoes about the distribution. Echo-derived parameters in each patient were compared with corresponding CVF values. CVF was out of range in all patients, ranging from 2.6% to 7.6% (mean 4.3% +/- 1.6%). No correlation was found between CVF and mCS, whereas a significant correlation was found at end diastole between CVF and the parameters describing histogram morphology, respectively, SK (r = 0.73), K (r = 0.69), Bb (r = 0.72). These findings for the first time demonstrate in vivo in hypertensive patients with left ventricular hypertrophy an agreement between echo amplitude and histologically assessed collagen volume. Thus in our studied patients collagen content appears to be the major determinant of regional echo intensity, its increase resulting in a significant and progressive wider asymmetrical left shift (yellow) of the color histogram.

Myocardial ultrasonic tissue characterization in patients with different types of left ventricular hypertrophy: a videodensitometric approach

Although analysis of the radio frequency signal is the most accurate approach to myocardial tissue characterization, clinical diffusion has been limited because of the complex technology required. Much easier to perform, videodensitometric analysis could represent a valuable alternative. Previous works carried out on radio frequency data have shown that the absolute value of ultrasonic back scatter increases while its diastole-to-systole variation decreases in the hypertrophied myocardium. This study was aimed at clarifying whether alterations in characterization indexes of ultrasonic tissue can be detected by means of a videodensitometric approach, whether a specific type of left ventricular (LV) hypertrophy can be identified with this method, and finally what possible relationships exist between parameters of contractile function and tissue characterization indexes. Myocardial echo intensity (MEI), its cyclic variation (CV), and the dynamic relationship between myocardial signal and wall thickness variations during the cardiac cycle were assessed in 20 healthy subjects, 11 patients with essential hypertension and LV hypertrophy, 15 patients with hypertrophic cardiomyopathy, and 4 patients with primary amyloidosis. The CV was lower in the interventricular septum of patients with cardiac hypertrophy as a group, compared with that of control subjects (13.0% +/- 5.6% versus 18.8% +/- 5.5%, p < 0.001), but it was similar among patients with different types of hypertrophy. In control subjects, a significant inverse correlation was found between the progressive decrease of the myocardial signal and the parallel increase in wall thickness during systole; this correlation was lost in 60% of patients with hypertrophic cardiomyopathy and 50% of those with amyloidosis, but only in 9% of patients with essential hypertension (chi square analysis 12.68, p < 0.01). The CV was associated with systolic wall thickening (r = 0.53, p = 0.0001) and fractional shortening (r = 0.44, p = 0.0014). MEI and its CV per se cannot distinguish among different types of LV hypertrophy; however, the loss of an inverse relationship between the myocardial signal and wall thickness may suggest abnormal myocardial conditions in individual patients with the same disease or comparable wall thickness.

Increased echodensity of myocardial wall in the diabetic heart: an ultrasound tissue characterization study

OBJECTIVES

We sought to characterize myocardial echodensity in asymptomatic patients with insulin-dependent diabetes and normal conventional two-dimensional echocardiographic findings to determine whether ultrasound tissue characterization can detect ultrastructural changes in myocardium, such as an increase in collagen content.

BACKGROUND

Fibrosis alters the acoustic properties of the heart in animals and humans, and these changes are detectable by cardiac tissue characterization with ultrasound. Early changes detected in the diabetic heart include increased interstitial collagen deposition.

METHODS

Using two-dimensional echocardiography, we evaluated 26 asymptomatic patients with insulin-dependent diabetes with normal regional and global rest function, and 17 age- and gender-matched control subjects. By selection, all diabetic patients were normotensive and had negative maximal exercise stress test results to avoid the confounding effects of hypertension and coronary artery disease. Using an echocardiographic instrument implemented at the Institute of Clinical Physiology, we performed an on-line radiofrequency analysis to obtain quantitative operator-independent measurements of the integrated back-scatter signal of the ventricular septum and posterior wall. The integrated values of the radiofrequency signal from the myocardial wall were normalized for those from the pericardial interface and were expressed as percentages (integrated backscatter index).

RESULTS

Diabetic patients showed a significant increase in myocardial echodensity both in the septum ([mean +/- SD] 36.6 +/- 8.1 vs. 23.6 +/- 4.4, p < 0.0001) and posterior wall (21.2 +/- 5.3 vs. 18.4 +/- 3.7, p < 0.001). By individual patient analysis, 17 patients exceeded the 95% confidence limits for normal myocardial echocardiographic reflectivity found in normal subjects, and only 3 had a relatively abnormal transmitral Doppler filling pattern (E/A ratio), mainly consisting of an abnormally increased late peak flow velocity (65% vs. 11%, p < 0.001). The increased myocardial intensity was similar in patients with (n = 16) and without (n = 10) noncardiac complications, such as retinopathy or nephropathy (37.5 +/- 7.9% vs. 35.0 +/- 8.3%, p = 0.35).

CONCLUSIONS

Abnormally increased myocardial echodensity, possibly related to collagen deposition, can be detected in asymptomatic diabetic patients with normal rest function. Theoretically, this finding might be considered a very early preclinical alteration potentially related to subsequent development of diabetic cardiomyopathy.