Right Ventricular Structure and Function in Adolescent Athletes: A 3D Echocardiographic Study

The aim of this study was to characterize the right ventricular (RV) contraction pattern and its associations with exercise capacity in a large cohort of adolescent athletes using resting three-dimensional echocardiography (3DE). We enrolled 215 adolescent athletes (16±1 years, 169 males, 12±6 hours of training/week) and compared them to 38 age and sex-matched healthy, sedentary adolescents. We measured the 3DE-derived biventricular ejection fractions (EF). We also determined the relative contributions of longitudinal EF (LEF/RVEF) and radial EF (REF/RVEF) to the RVEF. Same-day cardiopulmonary exercise testing was performed to calculate VO2/kg. Both LV and RVEFs were significantly lower (athletes vs. controls; LVEF: 57±4 vs 61±3, RVEF: 55±5 vs 60±5%, p<0.001). Interestingly, while the relative contribution of radial shortening to the global RV EF was also reduced (REF/RVEF: 0.40±0.10 vs 0.49±0.06, p<0.001), the contribution of the longitudinal contraction was significantly higher in athletes (LEF/RVEF: 0.45±0.08 vs 0.40±0.07, p<0.01). The supernormal longitudinal shortening correlated weakly with a higher VO2/kg (r=0.138, P=0.044). Similarly to the adult athlete's heart, the cardiac adaptation of adolescent athletes comprises higher biventricular volumes and lower resting functional measures with supernormal RV longitudinal shortening. Characteristic exercise-induced structural and functional cardiac changes are already present in adolescence.

Get to the heart of pediatric kidney transplant recipients: Evaluation of left- and right ventricular mechanics by three-dimensional echocardiography

Background

Kidney transplantation (KTX) markedly improves prognosis in pediatric patients with end-stage kidney failure. Still, these patients have an increased risk of developing cardiovascular disease due to multiple risk factors. Three-dimensional (3D) echocardiography allows detailed assessment of the heart and may unveil distinct functional and morphological changes in this patient population that would be undetectable by conventional methods. Accordingly, our aim was to examine left- (LV) and right ventricular (RV) morphology and mechanics in pediatric KTX patients using 3D echocardiography.

Materials and methods

Pediatric KTX recipients (n = 74) with median age 20 (14–26) years at study enrollment (43% female), were compared to 74 age and gender-matched controls. Detailed patient history was obtained. After conventional echocardiographic protocol, 3D loops were acquired and measured using commercially available software and the ReVISION Method. We measured LV and RV end-diastolic volumes indexed to body surface area (EDVi), ejection fraction (EF), and 3D LV and RV global longitudinal (GLS) and circumferential strains (GCS).

Results

Both LVEDVi (67 ± 17 vs. 61 ± 9 ml/m2; p &lt; 0.01) and RVEDVi (68 ± 18 vs. 61 ± 11 ml/m2; p &lt; 0.01) were significantly higher in KTX patients. LVEF was comparable between the two groups (60 ± 6 vs. 61 ± 4%; p = NS), however, LVGLS was significantly lower (−20.5 ± 3.0 vs. −22.0 ± 1.7%; p &lt; 0.001), while LVGCS did not differ (−29.7 ± 4.3 vs. −28.6 ± 10.0%; p = NS). RVEF (59 ± 6 vs. 61 ± 4%; p &lt; 0.05) and RVGLS (−22.8 ± 3.7 vs. −24.1 ± 3.3%; p &lt; 0.05) were significantly lower, however, RVGCS was comparable between the two groups (−23.7 ± 4.5 vs. −24.8 ± 4.4%; p = NS). In patients requiring dialysis prior to KTX (n = 64, 86%) RVGCS showed correlation with the length of dialysis (r = 0.32, p &lt; 0.05).

Conclusion

Pediatric KTX patients demonstrate changes in both LV and RV morphology and mechanics. Moreover, the length of dialysis correlated with the contraction pattern of the right ventricle.

Evaluation of Left Ventricular Structure and Function using 3D Echocardiography

Three-dimensional (3D) quantification of the left ventricle (LV) provides significant added value in terms of diagnostic accuracy and precise risk stratification in various cardiac disorders. Recently, 3D echocardiography became available in routine cardiology practice; however, high-quality image acquisition and subsequent analysis have a steep learning curve. The present article aims to guide the reader through a detailed 3D protocol by presenting tips and tricks and also by highlighting the potential pitfalls to facilitate the widespread but technically sound use of this important technique concerning the LV. First and foremost, we show the acquisition of a high-quality 3D dataset with optimal spatial and temporal resolution. Then, we present the analytical steps toward a detailed quantification of the LV by using one of the most widely applied built-in software. We will quantify LV volumes, sphericity, mass and also systolic function by measuring ejection fraction and myocardial deformation (longitudinal and circumferential strain). We will discuss and provide clinical examples about the essential scenarios where the transition from a conventional echocardiographic approach to a 3D-based quantification is highly recommended.

Importance of Nonlongitudinal Motion Components in Right Ventricular Function: Three-Dimensional Echocardiographic Study in Healthy Volunteers

BACKGROUND

Global right ventricular (RV) function is determined by the interplay of different motion components related to the myofiber architecture, and the relative importance of these components is still not thoroughly characterized. The aims of this study were to quantify the relative contributions of longitudinal, radial, and anteroposterior motion components to global RV function and to examine their determining factors in a large cohort of healthy volunteers using three-dimensional echocardiography.

METHODS

Three hundred healthy adults with a balanced age range and an equal sex distribution were investigated at two centers. A three-dimensional mesh model of the right ventricle was generated, and its motion was decomposed along the three anatomically relevant axes. Multiplicative relative contributions were measured by dividing the ejection fraction (EF) values generated by shortening in the longitudinal, radial, and anteroposterior directions by global RV EF (longitudinal EF index [LEFi], radial EF index [REFi], and anteroposterior EF index, respectively). The circumferential contribution was defined as shortening in the radial and anteroposterior directions, omitting only longitudinal shortening.

RESULTS

Circumferential EF index was markedly higher compared with LEFi (79 ± 7% vs 47 ± 9%, P < .001). LEFi (47 ± 9%) and anteroposterior EF index (49 ± 7%) were found to be similar in the pooled population, whereas REFi (44 ± 10%) was lower (P < .001). In younger individuals (20-39 years of age), the relative contribution of longitudinal shortening was significantly higher compared with the radial component; however, in the older age groups, LEFi and REFi were comparable. Age, body surface area, heart rate, and RV end-diastolic volume were independent predictors of LEFi and REFi, but all with opposite effects on the two motion directions.

CONCLUSIONS

In contrast to the traditional viewpoint, the contributions of the radial and anteroposterior motion directions may be of comparable significance with that of longitudinal shortening in determining global RV function. Standard parameters referring only to longitudinal shortening of the right ventricle may be inadequate to characterize RV function thoroughly.

Evidence for DNA bending at the T7 RNA polymerase promoter

Phage T7 RNA polymerase is the only DNA-dependent RNA polymerase for which we have a high-resolution structure of the promoter-bound complex. Recent studies with the more complex RNA polymerases have suggested a role for DNA wrapping in the initiation of transcription. Here, circular permutation gel retardation assays provide evidence that the polymerase does indeed bend its promoter DNA. A complementary set of experiments employing differential phasing from an array of phased A-tracts provides further evidence for both intrinsic and polymerase-induced bends in the T7 RNA polymerase promoter DNA. The bend in the complex is predicted to be about 40-60 degrees and to be centered around positions -2 to +1, at the start site for transcription, while the intrinsic bend is much smaller (about 10 degrees ). These results, viewed in the light of a recent crystal structure for the complex, suggest a mechanism by which binding leads directly to bending. Bending at the start site would then facilitate the melting necessary to initiate transcription.

Identification of a minimal binding element within the T7 RNA polymerase promoter

The T7 RNA polymerase promoter has been proposed to contain two domains: the binding region upstream of position -5 is recognized through apparently traditional duplex contacts, while the catalytic domain downstream of position -5 is bound in a melted configuration. This model is tested by following polymerase binding to a series of synthetic oligonucleotides representing truncations of the consensus promoter sequence. The increase in the fluorescence anisotropy of a rhodamine dye linked to the upstream end of the promoter provides a very sensitive measure of enzyme binding in simple thermodynamic titrations, and allows the determination of both increases and decreases in the dissociation constant. The best fit value of Kd=4.0 nM for the native promoter is in good agreement with previous fluorescence and steady state measurements. Deletion of the downstream DNA up to position -1 or to position -5 leads to a fivefold increase in binding, while further sequential single-base deletions upstream result in 20 and 500-fold decreases in binding. These results indicate that the (duplex) region of the promoter upstream of and including position -5 is both necessary and sufficient for tight binding, and represents the core binding element of the promoter. We propose a model in which part of the upstream binding energy is used by T7 RNA polymerase to melt the downstream initiation region of the promoter. We also show that the presence of magnesium is necessary for optimal binding, but not for specific enzyme-promoter complex formation, and we propose that magnesium is not required for melting of the promoter.

Thermodynamic and kinetic measurements of promoter binding by T7 RNA polymerase

Previous steady state kinetic studies of the initiation of transcription by T7 RNA polymerase have shown that melting of the DNA helix near the transcription start site is not rate limiting [Maslak, M., & Martin, C. T. (1993) Biochemistry 32, 4281-4285]. In the current work, fluorescence changes in a nucleotide analog incorporated within the promoter are used to monitor changes in the DNA helix associated with polymerase binding. The fluorescence of 2-aminopurine has been previously shown to depend on the environment of the base, with fluorescence increasing in the transition from a double-stranded to a single-stranded environment [Xu, D., Evans, K.O., & Nordlund, T. M.(1994) Biochemistry 33, 9592-9599]. Fluorescence changes associated with polymerase binding to promoters incorporating 2-aminopurine at positions -4 through -1 support a model which includes melting, in the statically bound complex, of the region of the promoter near the start site. Equilibrium titrations at 25 degrees C with label at position -2 provide a thermodynamic measure of the dissociation constant (Kd = 4.8 nM) for promoter binding, while stopped-flow kinetic assays measure the apparent association (k1 = 5.6 x 10(7) M-1 s-1) and dissociation (k-1 = 0.20 s-1) rate constants for simple promoter binding (the ratio k-1/k1 = 3.6 nM, in good agreement with the thermodynamic measurement of Kd). These results suggest that binding is close to the diffusion-controlled limit and helix melting is extremely rapid. In studies of structurally altered promoters, a base functional group substitution at position -10 is shown to significantly decrease k1, with little effect on k-1. In contrast, removal of the nontemplate strand from position +1 downstream results in a large decrease in k-1, with no significant effect on k1.