Myocardial Fiber Mapping of Rat Hearts,Using Apparent Backscatter,with Histologic Validation

Myocardial fiber architecture is a physiologically important regulator of ejection fraction, strain and pressure development. Apparent ultrasonic backscatter has been shown to be a useful method for recreating the myocardial fiber architecture in human-sized sheep hearts because of the dependence of its amplitude on the relative orientation of a myofiber to the angle of ultrasonic insonification. Thus, the anisotropy of the backscatter signal is linked to and provides information about the fiber orientation. In this study, we sought to determine whether apparent backscatter could be used to measure myofiber orientation in rodent hearts. Fixed adult-rat hearts were imaged intact, and both a transmural cylindrical core and transmural wedge of the left ventricular free wall were imaged. Cylindrical core samples confirmed that backscatter anisotropy could be measured in rat hearts. Ultrasound and histologic analysis of transmural myocardial wedge samples confirmed that the apparent backscatter could be reproducibly mapped to fiber orientation (angle of the fiber relative to the direction of insonification). These data provided a quantitative relationship between the apparent backscatter and fiber angle that was applied to whole-heart images. Myocardial fiber architecture was successfully measured in rat hearts. Quantifying myocardial fiber architecture, using apparent backscatter, provides a number of advantages, including its scalable use from rodents to man, its rapid low-cost acquisition and minimal contraindications. The method outlined in this study provides a method for investigators to begin detailed assessments of how the myocardial fiber architecture changes in preclinical disease models, which can be immediately translated into the clinic.     

Anisotropy of high-frequency integrated backscatter from aortic valve cusps

The biaxial anisotropy of integrated backscatter from aortic valve cusps was characterized ex vivo as an initial assessment of the suitability of high-frequency ultrasound for nondestructive evaluation of fiber alignment in tissue-engineered heart valves. Apparent integrated backscatter (AIB) from eight fresh, intact porcine cusps was measured over an 80 degrees range of insonification angles using a 40-MHz ultrasound system. Angular dependence of backscatter was characterized by fitting a sinusoid to plots of AIB versus insonification angle for data acquired while rotating the transducer about the cusps in the circumferential and radial directions. Angular variations in backscatter were detected along both directions in individual specimens, although the mean amplitude of the fitted sinusoid was significantly greater for the circumferential data (12.1 +/- 2.6 dB) than the radial data (3.5 +/- 3.1 dB, p = 0.002). The higher angular variation of backscatter in the circumferential direction implies that collagen fibers in the fibrosa layer are the most prominent source of high-frequency scattering from porcine aortic valve cusps. The ability to characterize anisotropic backscattering from individual specimens demonstrates that high-frequency ultrasound can be used for nondestructive evaluation of fiber alignment in heart valve biomaterials. (E-mail: jlacefield@eng.uwo.ca).     

Anisotropy of apparent backscatter in the short-axis view of mouse hearts

The goals of this investigation were to measure the anisotropy of backscattered ultrasound observed in the short-axis view of mouse hearts in systole and diastole and to compare these measurements with predictions from a computer simulation. Measurements of midmyocardial apparent backscatter were obtained from analyses of the hearts of seven wild-type mice using a clinical imaging system utilizing a linear array with a nominal center frequency of 13 MHz. A computer model simulating the short-axis view was implemented based on previous measurements of the angle of insonification dependence of myocardial backscatter and attenuation. Results demonstrate that the measured backscatter was largest for those myocardial regions corresponding to approximately perpendicular insonification relative to the myofibers and the smallest for regions of approximately parallel insonification, with the minimum to maximum values of apparent backscatter differing by approximately 10 dB. The measured anisotropy of backscatter was similar for end-systole and end-diastole and was in good agreement with the predicted anisotropy obtained from the computer simulations. (E-mail: mrh@wuphys.wustl.edu)     

Measurements of ultrasonic attenuation properties of midgestational fetal pig hearts

The objectives of this study were to measure the relative attenuation properties of the left and right ventricles in fetal pig hearts and to compare the spatial variation in attenuation measurements with those observed in previously published backscatter measurements. Approximately 1.0-mm-thick, short-axis slices of excised, formalin-fixed heart were examined from 15 midgestational fetal pigs using a 50-MHz single-element transducer. Measurements of the attenuation properties demonstrate regional differences in the left and right ventricular myocardium that appear consistent with the previously reported regional differences in apparent integrated backscatter measurements of the same fetal pig hearts. For regions of perpendicular insonification relative to the myofiber orientation, the right ventricular free wall showed larger values for the slope of the attenuation coefficient from 30-60 MHz (1.48 +/- 0.22 dB/(cm x MHz) (mean +/- SD) and attenuation coefficient at 45 MHz (46.3 +/- 7.3 dB/cm [mean +/- SD]) than the left ventricular free wall (1.18 +/- 0.24 dB/(cm x MHz) and 37.0 +/- 7.9 dB/cm (mean +/- SD) for slope of attenuation coefficient and attenuation coefficient at 45 MHz, respectively). This attenuation study supports the hypothesis that intrinsic differences in the myocardium of the left and right ventricles exist in fetal pig hearts at midgestation.     

Analysis of transmural trends in myocardial integrated backscatter in patients with progressive systemic sclerosis.

Cardiac involvement in progressive systemic sclerosis (PSS) is common and has a strong negative impact on the prognosis, especially when autoantibodies are present. To determine whether ultrasonic tissue characterization can detect early ultrastructural changes in the sclerodermal myocardium, we analyzed the transmural heterogeneity in myocardial integrated backscatter (THIB). "A-THIB" was defined as the absolute difference in integrated backscatter between the left (subendocardial) and right (subepicardial) ventricular halves of the myocardium in the septum and posterior wall, and was measured in 11 patients with PSS and 10 age- and sex-matched healthy participants. A-THIB in patients with PSS was higher than that in healthy participants (1.3 +/- 1.3 vs 4.0 +/- 1.4 dB for the septum and 1.1 +/- 0.7 dB vs 2.8 +/- 0.4 dB for the posterior wall; mean +/- SD, respectively, P <.0005). Septal A-THIB was higher in patients with PSS with than without anti-Scl70 or antinucleolar antibodies (3.2 +/- 1.1 vs 5.0 +/- 1.0 dB, P =.0165). Early changes in the myocardium of patients with PSS, possibly related to increased interstitial collagen deposition, can be detected by quantitative analysis of THIB.     

Detection of remote myocardial infarction with quantitative real-time ultrasonic characterization

We have previously shown that the intrinsic properties of myocardium can be characterized quantitatively by the assessment of ultrasonic integrated backscatter. In this study we utilized a novel, real-time, two-dimensional system capable of quantitative integrated backscatter imaging to determine whether zones of remote myocardial infarction in dogs could be delineated definitively by ultrasonic tissue characterization. Detection of such zones in patients is needed as a basis for management decisions related to thrombolysis, angioplasty, and coronary surgery. Integrated backscatter was measured through the closed chest from 25 myocardial sites. Zones of infarction exhibited time-averaged integrated backscatter values approximately 10 dB (9.5 +/- 0.5 dB, standard error of the mean) greater than those in normal regions (p less than 0.001). In addition, the physiologic cardiac cycle--dependent variation of integrated backscatter was blunted significantly in zones of infarction [0.8 dB +/- 0.3 vs. 3.8 +/- 0.6 (p less than 0.01) for normal regions]. Ultrasonic results matched the histopathologic features assessed directly. Thus quantitative ultrasonic tissue characterization can differentiate infarcted tissue from normal myocardium and offers promise for quantitative detection of histopathology in vivo.     

Characterization of anisotropic myocardial backscatter using spectral slope, intercept and midband fit parameters

The specific myocardial structural components that contribute to the observed level of backscatter from the heart and its dependence on the angle of insonification have not been completely identified: The objectives of this study were to measure the anisotropy of backscatter from myocardium using the approach first introduced by Lizzi et al. [J Acoust Soc Am 73, 1366-1373 (1983)] and to use the extracted spectral parameters (spectral slope, intercept and midband fit) to characterize changes in the apparent scatterer size, spatial concentration and acoustic impedance properties as functions of the angle of insonification. Backscatter measurements were performed in vitro on eight cylindrical formalin-fixed lamb myocardial specimens using a 5 MHz focused transducer. The backscattered spectral data as a function of angle of insonification relative to the myocardial fiber direction were analyzed over the frequency range of 4 to 6 MHz. The spectral parameters describing features of backscatter were determined by applying a linear fit to attenuation-compensated normalized spectra. Results show that values of the spectral slope do not exhibit a significant dependence on the angle of insonification within uncertainties; however, the zero-frequency intercept showed clear anisotropy and was found to be a maximum for insonification perpendicular to the predominant myofiber orientation and a minimum for parallel insonification. A comparison of midband fit values at 5 MHz with attenuation-compensated integrated backscatter values showed excellent agreement for all angles of insonification. These data suggest that measurements of spectral slope, intercept, and midband fit can provide insights regarding aspects of tissue microstructure underlying the observed anisotropy of myocardial scattering properties. Measurements of the slope parameter suggest a very modest change in effective scatterer size with angle of insonification. However, the observed anisotropy in intercept and midband fit and apparent absence of anisotropy in the spectral slope suggests an angle of insonification dependence of acoustic concentration, the combination of effective spatial scatterer concentration and acoustic impedance properties, without a significant contribution from changes in effective scatterer size.     

Backscatter tensor imaging and 3D speckle tracking for simultaneous ex vivo structure and deformation measurement of myocardium

Objective: Biaxial mechanical testing is a common method for elucidation of mechanical properties of excised ventricular myocardium, especially in the context of structural remodeling that accompanies heart disease. Current imaging strategies in biaxial testing are based on optical camera imaging of the tissue surface, thus providing no information about the tissue microstructure and limiting strain measurements to two dimensions. Here, these limitations are overcome by replacing the camera with ultrasound imaging in order to measure both transmural fiber orientation and 3D tissue deformation during biaxial testing. Methods: Quasi-static biaxial mechanical testing is applied to four samples of excised porcine ventricular myocardium (two left- and two right-ventricular tissues). During testing, a rotational scan of an ultrasound linear array provides data for both backscatter tensor imaging and 3D speckle tracking, from which transmural fiber orientation and tissue deformation are computed, respectively. Ultrasound-derived fiber orientation and tissue strain are validated against histology and camera surface imaging, respectively. Discussion: Ultrasound-derived fiber angle and tissue strain exhibit good accuracy, with root-mean-square errors of 9.9° and 1.2% strain, respectively. Further investigation into the optimization of backscatter tensor imaging is warranted. Replacing the rotational scan of a linear array with volume imaging with a matrix array will improve the technique. Conclusion: Ultrasound imaging can replace the optical camera measurement during biaxial mechanical testing of ventricular myocardium in order to accurately provide measurements of transmural fiber orientation and tissue strain. In situ knowledge of transmural fiber structure and tissue deformation can enhance the inverse problem used to determine tissue mechanical properties from biaxial testing.     

应用背向散射积分技术评价糖尿病心肌病变的临床研究

目的　应用背向散射积分技术研究糖尿病患者的心肌超声组织特征 ,旨在探讨背向散射积分 (integrated backscatter,IBS)参数测定在评价糖尿病患者心肌病变方面的临床应用价值。方法　采用 HP Sonos5 5 0 0型超声诊断仪 ,该机配置声学密度定量 -背向散射积分 (AD- IBS)联机采样分析软件 ,检测了 17例无微血管并发症的 2型糖尿病患者 (I组 )和 17例有微血管并发症的糖尿病患者 (II组 )以及 16例正常人 (对照组 )心肌的心动周期时间平均背向散射积分 (IBS)、背向散射积分标化值 (IBS% )、背向散射积分周期变异幅度 (CVIB)、背向散射积分跨壁梯度 (TGIB)等超声背向散射积分参数 ,采样部位为胸骨旁左室长轴切面室间隔及左室后壁心肌的中间段。同时测定糖尿病患者的糖化血红蛋白 (Hb A1c)水平。运用 t检验进行 3组受检者心肌超声背向散射积分参数的显著性检验 ,对糖尿病患者的 TGIB与Hb A1c进行相关性分析 ,P<0 .0 5定义为有统计学意义。结果　 (1)糖尿病 I组、II组室间隔及左室后壁心肌的 IBS%均明显高于对照组 ;(2 )糖尿病 I组、II组室间隔及左室后壁心肌的 CVIB均明显低于对照组 ;(3)糖尿病 I组、II组室间隔及左室后壁心肌的 TGIB均显著高于对照组 ;(4 )糖尿病 II组室间隔及左室后壁心肌的 IBS%均明显高于糖     

Ultrasonic myocardial integrated backscatter and myocardial wall thickness in animal experiments

The purpose of this study was to distinguish between normal and ischemic myocardium using ultrasonic integrated backscatter (IB) measurements and to relate IB with myocardial wall thickness. IB was measured in 9 open-chested Yorkshire pigs (24-30 kg) before, after 30 minutes of partial occlusion of the proximal left anterior descending coronary artery (LADCA), and after 60 minutes of subsequent reperfusion. The ultrasound transducer (4 MHz) was sutured onto the epicardial surface perfused by the LADCA. IB measurements were made with a repetition rate of 50 times per heart rate simultaneously with a left ventricular pressure signal. Myocardial wall thickness was measured off-line. The measurements of integrated backscatter, left ventricular pressure and wall thickness were based on mean values of ten subsequent cardiac cycles. End-systolic IB measurements were 5.3 dB higher during occlusion as compared to the reference measurements (7.1 +/- 3.2 dB versus 1.8 +/- 2.6 dB; p = 0.002). No statistically significant differences were found in end-systolic IB measurements. End-systolic wall thickness was 5 mm smaller during occlusion as compared to the reference measurements (7.2 +/- 1.4 mm versus 12.2 +/- 1.2 mm; p less than 0.001). Simple linear regression analysis showed a statistically significant inverse relationship between IB measurements and wall thickness in 21 out of the 23 sequences in which wall thickness could be measured. End-systolic IB measurements are favourable to distinguish acute ischemic myocardium from normal myocardium. There is a distinct inverse relationship between IB and myocardial wall thickness.     

Extracting three-dimensional orientation and tractography of myofibers using optical coherence tomography

Abnormal changes in orientation of myofibers are associated with various cardiac diseases such as arrhythmia, irregular contraction, and cardiomyopathy. To extract fiber information, we present a method of quantifying fiber orientation and reconstructing three-dimensional tractography of myofibers using optical coherence tomography (OCT). A gradient based algorithm was developed to quantify fiber orientation in three dimensions and particle filtering technique was employed to track myofibers. Prior to image processing, three-dimensional image data set were acquired from all cardiac chambers and ventricular septum of swine hearts using OCT system without optical clearing. The algorithm was validated through rotation test and comparison with manual measurements. The experimental results demonstrate that we are able to visualize three-dimensional fiber tractography in myocardium tissues.OCIS codes: (110.4500) Optical coherence tomography, (100.0100) Image processing, (170.6935) Tissue characterization     

Ultrasonic integrated backscatter two-dimensional imaging: evaluation of M-mode guided acquisition and immediate analysis in 55 consecutive patients

We have shown previously that cardiac cycle-dependent integrated backscatter characterizes the physical state of myocardium in patients with ischemic heart disease and cardiomyopathy. In the present study the clinical applicability of M-mode guided two-dimensional integrated backscatter imaging was defined in evaluation of 55 nonselected patients. The mean amplitude of cyclic variation of integrated backscatter in normal segments (long-axis view) was as follows: basal septum, 4.2 +/- 1.3 dB (mean +/- SD; n = 27), mid-septum, 4.5 +/- 1.0 dB (n = 26), basal posterior, 4.8 +/- 1.0 dB (n = 30), and mid-posterior, 4.8 +/- 1.2 decibels (n = 27). The respective mean delay values (R wave to nadir) were as follows: 0.89 +/- 0.09, 0.84 +/- 0.09, 0.86 +/- 0.09, and 0.85 +/- 0.12. At least one cardiac cycle could be analyzed fully in 62% of patients. Limitations included technically difficult two-dimensional echocardiography, inadequate M-line orientation, technically remediable errors, or poor quality integrated backscatter images. In abnormal segments (n = 13) cyclic variation was reduced and delay was prolonged (1.2 +/- 1.1 dB and 1.21 +/- 1.1, respectively). Intraobserver and interobserver variability for amplitude measurements were modest, with respective correlation coefficients of r = 0.93; r = 0.72. The findings demonstrate that M-mode--assisted integrated backscatter is a practical approach for characterization of regional myocardial properties promptly and at the bedside in a large portion of patients with cardiac disease.     

Distribution of cardiac myosin isozymes in human conduction system. Immunohistochemical study using monoclonal antibodies.

To determine the presence and distribution of cardiac myosin isozymes in the human conduction system, we performed an immunohistochemical study using monoclonal antibodies CMA19 and HMC14, which are specific for myosin heavy chains of human atrial type (alpha-type) and ventricular type (beta-type), respectively. Serial frozen sections of human hearts were obtained from autopsy samples and examined by indirect immunofluorescence. Alpha-type was found in all myofibers of sinus node and atrio-ventricular node, and in 55.2 +/- 10.2% (mean +/- SD, n = 5) of the myofibers of ventricular conduction tissue, which consists of the bundle of His, bundle branches, and the Purkinje network. In contrast, beta-type was found in all myofibers of the atrio-ventricular node and ventricular conduction tissue, whereas almost all myofibers of the sinus node were unlabeled by HMC14. Although the number of ventricular myofibers labeled by CMA19 was small, the labeled myofibers were more numerous in the subepicardial region than in the subendocardial region. These findings show that the gene coding for alpha-type is expressed predominantly in specialized myocardium compared with the adjacent ordinary working myocardium.     

Feasibility of catheter cryoablation in normal ventricular myocardium and healed myocardial infarction

Although novel cryoablation systems have recently been introduced into clinical practice for catheter ablation of supraventricular tachycardia, the feasibility of catheter cryoablation of VT is unknown. Thus, the present study evaluates catheter cryoablation of the ventricular myocardium (1) in healthy sheep and (2) of VT in chronic myocardial infarction (MI). In three healthy sheep, 21 ventricular lesions (12 left and 9 right ventricle) were created with a catheter cryoablation system. Different freeze/thaw characteristics were used for lesion creation. The mean nadir temperature was -84.1 degrees C +/- 0.9 degrees C, mean lesion volume was 175.8 +/- 170.3 mm3, and 5 of 21 lesions were transmural. Lesion dimensions were 7.5 +/- 3.1 mm (width) and 4.2 +/- 2.5 mm (depth). Left ventricular lesions were significantly larger than right ventricular lesions (262 +/- 166 vs 60.5 +/- 91.6 mm3, P=0.0025). There was no difference in lesion volume with respect to different freeze/thaw characteristics. Anatomically (n=3) or electrophysiologically (n=3) guided catheter cryoablation was attempted in six sheep 105 +/- 56 days after MI, three of six animals had reproducibly inducible VT with a mean cycle length of 215 +/- 34 ms prior to ablation. In these animals, five VTs were targeted for ablation. A mean of 6 +/- 3 applications for nine left ventricular lesions were applied, six of nine lesions were transmural. The mean lesion volume was 501 +/- 424 mm3. No VT was inducible in two of three animals after cryoablation using an identical stimulation protocol. Therefore, catheter cryoablation of VT in healed MI is feasible, and no acute complications were observed.     

Cyclic variation of ultrasound backscatter in normal myocardium is view dependent: clinical studies with a real-time backscatter imaging system

Real-time ultrasound backscatter imaging is a new method of evaluating relative integrated backscatter in a clinically applicable manner. The potential clinical utility of real-time backscatter imaging of diseased tissue depends on recognition of normal variations in cyclic backscatter when measured from different echocardiographic image orientations. The view dependence of cyclic backscatter variation was studied in normal human volunteers. In twenty normal male subjects (mean age 28 +/- 5 years) cyclic variation in integrated backscatter (diastolic minus systolic backscatter) was assessed in multiple left ventricular regions with four standard two-dimensional echocardiographic views (parasternal long-axis and short-axis views, and apical two-chamber and four-chamber views). M-mode backscatter imaging was performed from the standard parasternal long-axis view. Cyclic variation in backscatter was present in the septum only when imaged from the parasternal long-axis view (2.7 +/- 3.1 [standard deviation] decibels [dB], p less than 0.01 for diastole versus systole). The posterior wall of the left ventricle demonstrated cyclic variation of integrated backscatter when imaged from both the parasternal long-axis (4.6 +/- 1.6 dB, p less than 0.01) and short-axis views (2.8 +/- 2.2 dB, p less than 0.01). Cyclic variation in integrated backscatter was not demonstrated in inferoseptal, septal, or lateral wall regions when imaged from the parasternal short-axis view. The apical views did not demonstrate cyclic variation in integrated backscatter in any of the segments studied.(ABSTRACT TRUNCATED AT 250 WORDS)     

背向散射积分技术评价PTCA术前后左室肌回声与收缩功能

目的：用超声背向散射积分(IBS)评价经皮冠状动脉成形术(PTCA)前后左室肌回声及收缩功能变化。方法：对33例择期行PTCA 支架术的冠心病患者用HP 5500型超声诊断仪，于PTCA术前及术后3天、1～3个月对胸骨旁乳头肌短轴切面的前间壁、下壁、后壁、侧壁行二维超声心动图(2DE)检测各节段的室壁运动情况、声学密度一背向散射积分(AD-IBS)检测心肌背向散射积分平均值及其标化值，心肌整层及心内外膜下心肌层的周期变化幅度并计算跨壁梯度指数。结果：左室存活心肌背向散射积分参数值于术后3天就有了改善，与术前相比有统计学意义；术后1～3个月检测，左室存活心肌回声及收缩功能均有明显改善。结论：PTCA能够有效地挽救存活心肌，背向散射积分技术能够为早期检测存活心肌及早期评价或预测PTCA疗效提供敏感指标。     

Noncircumferential myofiber function: impact on early diastolic filling in children.

Circumferential and noncircumferential myofiber contraction may have varying impact on systolic and diastolic function. The purpose of this study was to determine the relation of circumferential, longitudinal, and oblique fiber shortening to early diastolic filling in children. Twenty-five patients (8.1 +/- 5.6 years of age; 12 boys and 13 girls) with normal echocardiograms and no heart disease had prospective echocardiographic evaluation of circumferential (shortening fraction, fractional area change), longitudinal (left ventricular axial shortening), combined circumferential and longitudinal (left ventricular ejection fraction), oblique (left ventricular systolic twist [LVST]) shortening, and early diastolic filling. Mean LVST was 16 +/- 8 degrees. There was no relation between early diastolic filling indexes and indexes of circumferential or longitudinal shortening. However, there was a significant inverse relation between heart rate-corrected E-wave acceleration time and LVST (r = 0.63, P <.001). Oblique fiber shortening affects early diastolic filling in children. Describing the functional role of noncircumferential left ventricular myofibers may improve our understanding of global left ventricular function.     

慢性缺血性功能异常心肌血管重建术后跨壁收缩的背向散射研究

目的利用超声背向散射（IBS）技术研究慢性缺血性功能异常心肌在血管成功再灌注后跨壁收缩的变化特征。方法分别在血管重建术前、术后3d、术后6～8周，检测58例慢性冠心病伴有左室壁节段性功能障碍患者（共88个异常心肌节段，43个正常心肌节段）相关心肌节段心内膜下层心肌及心外膜下层心肌的IBS周期变化幅度（cycle variation of IBS，CVlB），并在常规超声下测量相应心肌节段的室壁增厚率（WT）。结果正常心肌节段心内膜下心肌CVIB明显高于心外膜下心肌CVIB（P〈0．001）。血管重建术前，慢性缺血性功能异常心肌节段心内膜下和心外膜下心肌的CVIB均减低，以前者为著，二者间无显著性差异（P=0．067）。成功再灌注后，心内膜下心肌CVIB恢复较心外膜下慢，出现“心内膜下顿抑”。术后WT的恢复与心内膜下心肌层CVIB的恢复相平行（r=0．816，P〈0．0001），而与心外膜下心肌CVIB的恢复无明显相关性（r=0．125，P=0．056）。结论CVIB可以无创检测心肌的跨壁收缩性。在慢性缺血心肌的再灌注恢复过程中，心内膜下心肌跨壁收缩性的变化与心脏收缩功能的恢复密切相关。     

Regional variation in the measured apparent ultrasonic backscatter of mid-gestational fetal pig hearts

The goal of this study was to characterize and compare regional backscatter properties of fetal hearts through measurements of the apparent integrated backscatter. Sixteen excised, formalin-fixed fetal pig hearts, representing an estimated 53 to 63 days of gestation, were investigated. Spatially localized measurements of integrated backscatter from these specimens were acquired using a 50 MHz single-element transducer. The apparent integrated backscatter measurements demonstrate different patterns of backscatter from the myocardium of the right ventricle compared with that of the left ventricle. These backscatter measurements appear to be consistent with the anisotropy of the fiber orientation observed in histologic assessment of the same specimens. For each of the 16 hearts, the apparent integrated backscatter from the right ventricular myocardium was larger than that from the left ventricular myocardium, exhibiting mean apparent backscatter values of –35.9 ± 2.0 dB and –40.1 ± 1.9 dB (mean ± standard deviation; n = 16; p < 0.001), respectively. This study suggests that the intrinsic ultrasonic properties of the left and right ventricular myocardium are distinct in fetal pig hearts at mid-gestation. (E-mail: mrh@wuphys.wustl.edu)     

Systolic heterogeneity of transmural myocardial function in normal subjects: physiological functional heterogeneity

Because of the lack of a clinical method for assessing the transmural myocardial function, few studies on the heterogeneity during the myocardial contraction/relaxation sequence inside the human ventricular wall have been reported, despite the fact that the importance of the pathophysiology in the transmural heterogeneity has been stressed in previous experimental studies. We studied the transmyocardial functional heterogeneity of the basal anteroseptal segment in normal subjects (n = 8, 40.0 +/- 12.8 year, male), adopting the novel high resolution Doppler measurement "Phased Tracking Method". Each transmural layer of 0.75 mm thickness showed functional heterogeneity (physiological transmural functional heterogeneity), namely larger thickening occurred in the left ventricular endocardial side (right side 1/3: 26.1 +/- 5.2% of the total wall thickness, middle 1/3: 31.9 +/- 2.7%, left side 1/3: 42.1 +/- 6.4%) and the peak thickening shifted smoothly in time from the middle layers to the left subendocardial side during the contraction period. We concluded that transmural functional heterogeneity does exist in normal subjects as well as in the experimental animals of previous reports. Smooth and coordinate myocardial layer contraction across the ventricular wall (physiological transmural functional heterogeneity) is fundamental to maintain the normal ventricular function.