Backscatter evaluation of myocardial functional and textural findings in children with right ventricular pressure and/or volume overload

Diagnosis and Pathophysiological Mechanisms of Group 3 Hypoxia-Induced Pulmonary Hypertension

PURPOSE OF REVIEW

Group 3 hypoxia-induced pulmonary hypertension (PH) is an important and increasingly diagnosed condition in both the pediatric and adult population. The majority of pulmonary hypertension studies to date and all three classes of drug therapies were designed to focus on group 1 PH. There is a clear unmet medical need for understanding the molecular mechanisms of group 3 PH and a need for novel non-invasive methods of assessing PH in neonates.

RECENT FINDINGS

Several growth factors are expressed in patients and in animal models of group 3 PH and are thought to contribute to the pathophysiology of this disease. Here, we review some of the findings on the roles of vascular endothelial growth factor A (VEGFA), platelet-derived growth factor B (PDGFB), transforming growth factor-beta (TGFB1), and fibroblast growth factors (FGF) in PH. Additionally, we discuss novel uses of echocardiographic parameters in assessing right ventricular form and function. FGF2, TGFB, PDGFB, and VEGFA may serve as biomarkers in group 3 PH along with echocardiographic methods to diagnose and follow right ventricle function. FGFs and VEGFs may also function in the pathophysiology of group 3 PH.

Evaluation of right and left ventricular diastolic filling

A conceptual fluid-dynamics framework for diastolic filling is developed. The convective deceleration load (CDL) is identified as an important determinant of ventricular inflow during the E wave (A wave) upstroke. Convective deceleration occurs as blood moves from the inflow anulus through larger-area cross-sections toward the expanding walls. Chamber dilatation underlies previously unrecognized alterations in intraventricular flow dynamics. The larger the chamber, the larger becomes the endocardial surface and the CDL. CDL magnitude affects strongly the attainable E wave (A wave) peak. This underlies the concept of diastolic ventriculoannular disproportion. Large vortices, whose strength decreases with chamber dilatation, ensue after the E wave peak and impound inflow kinetic energy, averting an inflow-impeding, convective Bernoulli pressure rise. This reduces the CDL by a variable extent depending on vortical intensity. Accordingly, the filling vortex facilitates filling to varying degrees, depending on chamber volume. The new framework provides stimulus for functional genomics research, aimed at new insights into ventricular remodeling.

Novel methods for assessment of right heart structure and function in pulmonary hypertension

Long-term increases in pulmonary vascular resistance and pulmonary arterial pressure resulting from structural alterations and abnormal vasoreactivity of the pulmonary vasculature may lead to right ventricular (RV) remodeling. Conventional methods of assessment of RV structure and function do not provide sensitive markers of RV remodeling for prognostic information. Advances in cardiac imaging have provided the capability to obtain quantitative information on the RV structure and function. This article reviews the clinical conditions that result in PH and discusses the novel and emerging methods for the assessment of right heart structure and function in PH in infants and children.

Relationship between integrated backscatter and atrial fibrosis in patients with and without atrial fibrillation who are undergoing coronary bypass surgery

OBJECTIVE

The purpose of this study was to investigate the relationship between the integrated backscatter (IBS) and atrial fibrosis, with and without atrial fibrillation (AF), in patients who are undergoing coronary bypass grafting (CABG).

METHODS

A total of 74 patients (18 preoperative AF, 56 sinus rhythm [SR]) with coronary artery disease undergoing CABG were included. The IBS of the left atrium (LA) posterior wall was acquired from transthoracic echocardiographic examination before surgery. Samples from the LA appendage were collected after opening the pericardium and quantitative assessment of atrial fibrosis was performed with collagen volume fraction (CVF). Postoperative AF was monitored with electrocardiographic telemetry in-hospital.

RESULTS

There was a positive relationship between age, IBS of the left atrial posterior wall indexed by pericardium (IBS%), and CVF by multivariate linear regression analysis (r = 0.612, p = 0.034; r = 0.887, p < 0.001 respectively). The value of IBS%, LA dimension (LAD), and CVF values were higher in patients with preoperative AF than in patients with preoperative SR (p < 0.001, p < 0.01, p < 0.001, respectively). The value of age, IBS%, and CVF in patients with postoperative AF were higher than in patients without postoperative AF (p = 0.029, p < 0.001, p = 0.001 respectively).

CONCLUSIONS

IBS of the LA posterior wall indexed by pericardium provides an objective quantitative measure of atrial fibrosis and correlates with postoperative AF in patients undergoing CABG surgery.

Analysis of the intensity of radio-frequency signals in intracranial ultrasonography of preterm infants

PURPOSE

The purpose of this study was to evaluate the usefulness of analysis of the intensity of radio-frequency (RF) signals in intracranial ultrasonography of preterm infants.

METHODS

Twenty neonatal infants admitted to the neonatal intensive care unit of our hospital were included in this study. Their gestational age was 33-35 weeks. The studies were performed with a System 5 ultrasound system with 3.0-and 5.0-MHz transducers. The transducer was placed on the anterior fontanel to obtain images. Regions of interest were determined based on B-mode images and were positioned at the thalamus, caudate nucleus, cerebral white matter, cerebellum, brain stem, and lateral ventricle. The software used for analysis of the RF signals was EchoMAT (Vingmed Ultrasound).

RESULTS

The RF signals of the ventricle and the choroid plexus showed the lowest and the highest intensities, respectively. The intensities of the brain stem and vermis signals were the same, and were higher than the intensity of the cerebellar hemisphere. The thalamus and caudate nucleus showed macroscopically identical brightness levels; however, the intensity of the thalamus was lower than that of the caudate nucleus. The intensity of subependymal hemorrhage was lower than that of the caudothalamic groove. The intensity of subependymal cyst was the same as that of the lateral ventricle. The RF signal frequencies and intensities were distinctive in each tissue.

CONCLUSION

The results of this study suggest that measurement of RF signal intensity may be useful to differentiate macroscopically similar lesions.

Relationship between myocardial ultrasonic integrated backscatter and mitochondria of the myocardium in dogs

OBJECTIVE

This study aimed to explore the relationship between integrated backscatter (IBS) and mitochondria in arrested myocardium.

METHODS

Twelve open-chest dogs were randomly divided into two groups: one group with cardiac arrest in systole and the other with cardiac arrest in diastole. IBS images at parasternal papillary muscle short-axis view were stored at different time frames (0, 30, and 60 min after cardiac arrest). The values of ultrasonic IBS were obtained using the acoustic densitometry technique. After ultrasound examination, tissue samples of corresponding times were harvested and observed under the transmission electron microscope. The microscopic images were analyzed using a computer imaging analysis system to obtain the stereological parameters of mitochondria. The correlation between IBS and the stereological parameters was analyzed.

RESULTS

After cardiac arrest, swollen mitochondria with electron-lucent matrix could be observed in some myofibers following the progression of time. The alteration of IBS correlated well with that of mitochondrial stereological parameters, such as volume density (Vv), surface density (Sv), average volume (v), average surface area (s), and specific surface (Rsv, ratio between surface and volume).

CONCLUSION

Mitochondria might be an important scatterer in the myocardium for IBS.

Similar cardiac remodelling after transcatheter atrial septal defect closure in children and young adults

OBJECTIVE

To study the cardiac geometric changes after transcatheter closure of large atrial septal defects (ASDs) according to patient age at the time of the procedure.

DESIGN

Prospective echocardiographic follow-up study.

SETTING

Tertiary referral centre.

PATIENTS AND INTERVENTION

25 asymptomatic patients younger than 16 years (median 8 years; group 1) and 21 asymptomatic adults (median 38 years; group 2) underwent percutaneous closure of large ASD with the Amplatzer septal occluder device (mean 25 (SD 7) mm).

MAIN OUTCOME MEASURES

Cardiac remodelling was assessed by M mode and two dimensional echocardiography one and six months after ASD closure.

RESULTS

By six months, right atrial volume decreased from 31 (15) to 19 (5) ml/m(2) (p < 0.001) and right ventricular (RV) transverse diameter decreased from 29.8 (8.6) to 23.2 (5.6) mm/m(2) (p < 0.001). Conversely, left atrial volume did not change significantly (from 18 (6) to 20 (6) ml/m(2), NS) and left ventricular (LV) transverse diameter increased from 27.8 (6.4) to 31.8 (7.3) mm/m(2) (p < 0.05). Ventricular remodelling resulted in an RV:LV diameter ratio decrease from 1.1 (0.2) to 0.7 (0.1) (p < 0.001). The magnitude and time course of cardiac remodelling did not differ significantly between the age groups. Indeed, right atrial volume decreased by 33 (26)% versus 37 (23)%, RV diameter decreased by 26 (10)% versus 20 (13)%, LV diameter increased by 17 (15)% versus 15 (10)%, and RV:LV diameter ratio decreased by 36 (8)% versus 27 (15)% in groups 1 and 2, respectively.

CONCLUSIONS

Cardiac remodelling after percutaneous ASD closure seems to be independent of the patient's age at the time of the procedure up to early adulthood. Thus, postponing ASD closure for a few years may be a reasonable option for potentially suitable asymptomatic children.

Update on pediatric echocardiography

PURPOSE OF REVIEW

The past year was dominated by developments in echocardiographic assessment of myocardial function in children, and this paper reviews some of these major advancements in pediatric echocardiography as a guide to those interested in imaging of the pediatric heart and vascular system.

RECENT FINDINGS

Characterization of myocardial function using Doppler tissue imaging, both in the normal child and in the child with congenital or acquired heart disease, was a primary focus of pediatric echocardiographic investigation. Other new technologies, including integrated backscatter analysis and three-dimensional echocardiography, appear to hold significant promise as tools to improve myocardial assessment echocardiographically. Three-dimensional echocardiography also is developing into a powerful technique in fetal echocardiography, allowing rapid data acquisition and extensive image postprocessing with opportunities for both anatomic and functional assessment. Childhood fitness and diseases have a significant impact on the heart and vascular bed, and descriptions of echocardiographic findings in obese children, children engaged in athletic activities, children with renal disease, children who have undergone cardiac transplantation, and those with aortic valve disease were better characterized by investigations published over the past year.

SUMMARY

Pediatric echocardiography has clearly expanded from a diagnostic tool used to describe anatomic abnormalities associated with congenital heart disease to a noninvasive myocardial monitoring tool that allows serial assessment of the pathologic effects of both cardiac and noncardiac disease.

Potential relationships among myocardial stiffness, the measured level of myocardial backscatter (“image brightness”), and the magnitude of the systematic variation of backscatter (cyclic variation) over the heart cycle

BACKGROUND

In a number of recently published studies comparing measurements from patients with those from control subjects, a decreased magnitude of the systematic variation of backscattered energy over the heart cycle (cyclic variation) is accompanied by an increased level of overall myocardial backscatter (calibrated myocardial image brightness) when measured at a specific phase of the heart cycle (eg, end systole or end diastole). The goal of this study was to investigate whether this observation is consistent with predictions based on a model of the mechanisms of cyclic variation incorporating changes in relative intracellular and extracellular acoustic impedance over the heart cycle.

METHODS

A previously described 3-component Maxwell-type model of muscle mechanics representing cardiac cell mechanical behavior was utilized to predict the systematic variation in the relative acoustic impedance differences between intracellular and extracellular elastic properties over the heart cycle and hence the observed magnitude of cyclic variation and overall myocardial scattering level. Predictions were obtained for a series of specific values of relative intracellular and extracellular acoustic impedance.

RESULTS

Results indicate that the predicted magnitude of cyclic variation can be directly related to the overall myocardial backscatter level. For example, specific changes in the acoustic impedance (stiffness properties) of the extracellular matrix without any change in the intracellular acoustic impedance result in predicted values of -43.5 dB, -38.5 dB, and -33.5 dB for end-diastolic myocardial backscatter levels with corresponding values of 5.0 dB, 2.5 dB, and 1.3 dB for the predicted magnitude of cyclic variation, respectively.

CONCLUSION

This study suggests that observed decreases in the magnitude of cyclic variation with concomitant increases in the measured overall myocardial backscatter level are consistent with predictions from a model based on the relative acoustic impedance differences between intracellular and extracellular elastic properties over the heart cycle. These results suggest that ultrasonic backscatter measurements may provide a noninvasive approach for assessing some relationships among myocardial stiffness, degree of fibrosis, and contractile performance.