Christopher Hart

Normal values of aortic dimensions, distensibility, and pulse wave velocity in children and young adults: a cross-sectional study

BackgroundAortic enlargement and impaired bioelasticity are of interest in several cardiac and non-cardiac diseases as they can lead to cardiovascular complications. Cardiovascular magnetic resonance (CMR) is increasingly accepted as a noninvasive tool in cardiovascular evaluation. Assessment of aortic anatomy and bioelasticity, namely aortic distensibility and pulse wave velocity (PWV), by CMR is accurate and reproducible and could help to identify anatomical and bioelastic abnormalities of the aorta. However, normal CMR values for healthy children and young adults are lacking.MethodsSeventy-one heart-healthy subjects (age 16.4 ± 7.6 years, range 2.3 - 28.3 years) were examined using a 3.0 Tesla CMR scanner. Aortic cross-sectional areas and aortic distensibility were measured at four positions of the ascending and descending thoracic aorta. PWV was assessed from aortic blood flow velocity measurements in a aortic segment between the ascending aorta and the proximal descending aorta. The Lambda-Mu-Sigma (LMS) method was used to obtain percentile curves for aortic cross-sectional areas, aortic distensibility and PWV according to age.ResultsAortic areas, PWV and aortic distensibility (aortic cross-sectional areas: r = 0.8 to 0.9, p < 0.001; PWV: r = 0.25 to 0.32, p = 0.047 to 0.009; aortic distensibility r = -0.43 to -0.62, p < 0.001) correlated with height, weight, body surface area, and age. There were no significant sex differences.ConclusionsThis study provides percentile curves for cross-sectional areas, distensibility and pulse wave velocity of the thoracic aorta in children and young adolescents between their 3rd and 29th year of life. These data may serve as a reference for the detection of pathological changes of the aorta in cardiovascular disease.

Maladaptive Aortic Properties in Children After Palliation of Hypoplastic Left Heart Syndrome Assessed by Cardiovascular Magnetic Resonance Imaging

Background— The status of the reconstructed aorta in hypoplastic left heart syndrome is considered an important determinant of long-term prognosis. Therefore, we assessed the anatomy, elastic properties, and viability of the aorta and right ventricular function in patients with hypoplastic left heart syndrome by cardiovascular magnetic resonance imaging. Methods and Results— Cardiovascular magnetic resonance imaging was performed in 40 patients with hypoplastic left heart syndrome (age, 6.0±2.2 years) and 13 control subjects (age, 6.6±2.2 years). Aortic dimensions and distensibility were calculated at different locations of the aorta using gradient-echo cine imaging at 3.0 T. Additionally, pulse-wave velocity, right ventricular ejection fraction, and aortic late gadolinium enhancement for viability assessment were measured. Compared with control subjects, patients with hypoplastic left heart syndrome had increased axial diameters of the aortic root (36.0±5.5 versus 24.1±2.7 mm/m2; P<0.01), ascending aorta (32.0±5.0 versus 21.3±1.5 mm/m2; P<0.01), and transverse aortic arch (22.7±5.2 versus 18.7±2.5 mm/m2; P<0.01). Wall distensibility was reduced in the ascending aorta (4.1±2.4 versus 13.5±7.2 10−3 mm Hg−1; P<0.01) and transverse aortic arch (5.4±3.6 versus 10.3±3.5 10−3 mm Hg−1; P<0.01). Pulse-wave velocity trended higher in patients (P=0.06). Reduced distensibility in the ascending aorta correlated with the amount of late gadolinium enhancement in a volume that included the aortic root and the ascending aorta (r=−0.72, P<0.01), and both parameters correlated with decreased right ventricular ejection fraction. Conclusions— Adverse aortic properties post palliation of hypoplastic left heart syndrome manifest themselves by aortic dilatation, decreased distensibility, and increased volume of nonviable aortic wall tissue. The negative association between aortic late gadolinium enhancement and right ventricular ejection fraction suggests unfavorable aortic-ventricular coupling. The potential impact of these findings on long-term right ventricular function should be evaluated in future studies.

Adverse results of a decellularized tissue-engineered pulmonary valve in humans assessed with magnetic resonance imaging.

OBJECTIVES Matrix P® and Matrix P plus® tissue-engineered pulmonary valves (TEPV) were offered as an improvement for pulmonary valve replacement (PVR) because of recellularization by host cells. The high frequency of graft failure gave reason to evaluate the underlying morphological substrate using magnetic resonance imaging (MRI) and histology. METHODS Between June 2006 and August 2008, 17 Matrix P® and 10 Matrix P plus® TEPVs were implanted in 26 patients with a median age of 12.4 (range: 0.8-38.7, interquartile range: 6.1-18.1) years. The grafts were studied by MRI, and underwent histological examination when explantation was required. RESULTS Surgical (n = 13) or transcatheter (n = 1) TEPV replacement because of graft failure was needed in 14 cases (52%) 19 (0.5-53) months after implantation. MRI detected significant TEPV stenosis with mild insufficiency (V(max) = 3.7 ± (standard deviation) 0.5 m/s, regurgitant fraction (RGF) = 10 ± 3%) and stenosis with moderate-to-severe insufficiency (V(max) = 3.5 ± 0.8 m/s, RGF = 38 ± 10%) in 6 patients, respectively, and severe insufficiency (RGF = 40%) in 1 patient. In patients with graft failure, MRI showed hyperenhancement and TEPV wall thickening. Histology revealed severe inflammation, increased fibrous tissue and foreign-body reaction against valve leaflets and fascial tissue, while TEPV endothelialization was not detected in any case. CONCLUSIONS The high frequency of Matrix P® and Matrix P plus® graft failure can be related to inflammation and fibrosis revealed by MRI and histology. Our results do not support the use of these valves for PVR and suggest careful follow-up examinations, including MRI for early detection of graft inflammation and fibrosis.

Two-Dimensional Global Longitudinal Strain Rate Is a Preload Independent Index of Systemic Right Ventricular Contractility in Hypoplastic Left Heart Syndrome Patients After Fontan Operation

Background—Assessment of systemic right ventricular (RV) function in patients with hypoplastic left heart syndrome is important during long-term follow-up after Fontan repair. Traditional echocardiographic parameters to evaluate systolic ventricular function are affected by loading conditions. The only generally accepted load-independent parameter of systolic function, end systolic elastance (Ees), requires invasive catheterization. Therefore, we sought to determine if parameters obtained by 2-dimensional speckle tracking (2DST) were affected by acute changes in preload and correlated with catheterization-derived indices of RV contractility in hypoplastic left heart syndrome patients after Fontan palliation. Methods and Results—Fifty-two patients with hypoplastic left heart syndrome (median age, 6.6; range 2.9–22.2 years) were prospectively enrolled to have echocardiography and conductance catheter studies performed simultaneously. We compared traditional echo, 2-dimensional speckle tracking and catheterization-derived parameters during different states of preload at baseline and during dobutamine infusion. Global longitudinal strain (S) showed a tendency to decrease with preload reduction, whereas global longitudinal strain rate (SR) did not change (S: −17.7±3.4% versus −16.9±3.8%, P=0.08; SR: −1.30±0.29 versus −1.34±0.34 s−1, P=0.3). S did not change with dobutamine infusion (−17.7±3.4% versus −18.4±3.9%, P=0.24), whereas SR increased significantly (−1.30±0.29 versus −2.26±0.49 s−1, P<0.001). RV Ees correlated with SR (rs= −0.47, P<0.001), but not with S (rs=0.07, P=0.5) or other echocardiographic parameters. Conclusions—In contrast to S, SR was not affected by preload and correlated with Ees of the systemic RV. SR may be a useful noninvasive surrogate of RV contractility and suitable for follow-up of patients with hypoplastic left heart syndrome after Fontan palliation.

Implications of early aortic stiffening in patients with transposition of the great arteries after arterial switch operation.

Background— The elastic function of the aorta in patients with transposition of the great arteries after arterial switch operation (ASO) is suspected to be important for long-term prognosis. Methods and Results— Fifty-one patients and 34 controls were studied at 3.0 Tesla with MRI. Forty-three patients (12.8±6.9 years) underwent 1-stage ASO, 8 patients (23.8±6.9 years) had prior pulmonary artery banding (2-stage ASO). Aortic dimensions, distensibility, pulse wave velocity, aortic arch angle, left ventricular (LV) mass, LV systolic function and left atrial (LA) volumes, and LA passive emptying function as marker of LV diastolic function were assessed. Compared with controls, patients had increased aortic root areas (602.6±240.5 versus 356.8±113.4 mm2/m; P<0.01) and reduced distensibility of the thoracic aorta most pronounced at the aortic root (3.2±2.0 versus 9.1±4.7×10−3 mm Hg−1; P<0.01). Aortic distensibility correlated negatively with the aortic areas (P<0.01). Pulse wave velocity was higher in adults after ASO (5.0±1.0 versus 3.8±1.3 m/s; P<0.01). In contrast to controls pulse wave velocity and distensibility correlated with age in patients (P=0.04 to <0.01), LV mass was higher in patients (P=0.02). LA volumes correlated negatively with aortic root and ascending aortic distensibility and positively with pulse wave velocity (P<0.05). In patients, LA passive emptying function was lower (27.3±8.9 versus 41.1±6.0; P<0.01) and correlated with aortic root distensibility (P=0.004). Conclusions— Reduced aortic bioelasticity and aortic root dilatation are present in transposition of the great artery patients post ASO and are likely to contribute to LV diastolic dysfunction. Impaired aortic bioelasticity was strongly associated with age, suggesting the usefulness of follow-up studies for early onset of degenerative cardiovascular disease.

New insights in the Fontan circulation: 4-dimensional respiratory- and ECG-triggered phase contrast magnetic resonance imaging

Background Evaluation of blood flow characteristics in total cavo-pulmonary connection (TCPC) with CMR remains difficult due to its strong modulation by respiration, and is not yet entirely understood. New approaches using 4D phase contrast magnetic resonance imaging (4D PC MRI) are promising and can contribute to the understanding of hemodynamics in the Fontan Circulation. Our objective was to compare flow, velocities, wall shear stress (WSS) and circulation in the TCPC using respiratory- and ECG triggered 4D PC MRI. Methods 10 children with hypoplastic left heart syndrome were evaluated after surgical completion of the Fontan circulation (TCPC with lateral intra-atrial tunnel) in a single center. In all patients one respiratory- (80 -100 phases) and one ECG-triggered (30 phases) 4D PC MRI covering the whole thorax, voxel size ranging from isotropic 1.5 to 2.0 mm were acquired during a single CMR examination with a custom-made electronic respiratory triggering compatible with our scanner. Dedicated commercial and custom software was used for further analysis of flow, velocity, WSS and circulation. Results

Does left ventricular size impact on intrinsic right ventricular function in hypoplastic left heart syndrome

BACKGROUND The size of the remnant left ventricle (LV) may influence right ventricular function and thus long-term outcome in palliated hypoplastic left heart syndrome (HLHS). We therefore sought to assess the impact of the size of the hypoplastic LV on intrinsic RV function in HLHS patients after Fontan surgery. METHODS Fifty-seven HLHS patients were studied 2.5 (range: 0.8-12.6) years after Fontan-type palliation with the pressure-volume conductance system. The patient cohort was divided into two groups according to the median LV area index (group 1: LV area index ≤ 1.33 cm(2)/m(2), n=29; group 2: LV area index>1.33 cm(2)/m(2), n=28). RESULTS The slopes of the end systolic elastance (Ees) and the preload recruitable stroke work relation (Mw) were not different between group 1 and 2 (Ees: 2.70 ± 1.92 vs. 3.68 ± 2.68 mmHg/ml; Mw: 52.75 ± 14.98 vs. 51.09 ± 16.63 mmHg x ml; P=NS for all). Furthermore, the systolic responses to dobutamine were not statistically different between groups. However, the slope of the end diastolic stiffness (Eed) was higher in group 2 and catecholaminergic stimulation resulted in a decrease in Eed in group 2 (group 1: 0.40 ± 0.26 vs. 0.52 ± 0.45; group 2: 0.68 ± 0.44 vs. 0.47 ± 0.38 mmHg/ml, P<0.01). Furthermore Eed was lowest in patients with mitral atresia/aortic atresia, the anatomic subgroup with the smallest LV remnant. CONCLUSIONS Intrinsic systolic RV function is not affected by the size of the hypoplastic LV in survivors of surgical palliation of HLHS. Diastolic stiffness, however, was higher in patients with a larger LV remnant.

Anatomical and functional assessment of the intra-atrial lateral tunnel in the Fontan circulation

OBJECTIVES In patients after completion of the total cavopulmonary connection (TCPC) with an intra-atrial lateral tunnel, deviations of the tunnel from an ideal straight tubular shape were observed. However, little is known about frequency and adverse effects of such shape deviations. We sought to analyse tunnel anatomy, dimensions and blood flow using cardiac magnetic resonance imaging (CMR). METHODS Fifty-four patients with hypoplastic left heart syndrome (HLHS; mean age 6.0 ± 2.4 years) underwent CMR with gradient-echo cine sequences, 2D- and 3D-phase-contrast imaging. We analysed anatomy, diameters, cross-sectional areas, volumes and blood flow of the tunnel. RESULTS Twenty-five patients had a tubular tunnel. In 29 patients, bulging and/or narrowing of the tunnel were present. Cross-sectional areas and volumes of the tunnel were not significantly different between the two groups. There were also no differences for the mean blood flow and the mean and maximal flow velocity (P = 0.05-0.6). In all the patients, the normalized tunnel volume was related to age (r = 0.44; P = 0.002) and body surface area (BSA; r = 0.42; P = 0.005). The mean tunnel blood flow correlated with age (r = 0.73; P = 0.001) and BSA (r = 0.83; P < 0.0001). CONCLUSIONS A considerable percentage of patients with an intra-atrial lateral tunnel develop mild deviations of the tunnel from ideal tubular shape. The correlation between tunnel volume and mean blood flow with age and BSA suggests that the capacity of the tunnel adjusts to body growth, independent of tunnel shapes that deviate from a fluid-dynamically favourable shape. Follow-up CMRs are needed to detect long-term effects of irregular tunnel shapes on flow dynamics.

Frequent Dilatation of the Descending Aorta in Children With Hypoplastic Left Heart Syndrome Relates to Decreased Aortic Arch Elasticity.

Background Patients with hypoplastic left heart syndrome after a Norwood operation show dilatation and reduced distensibility of the reconstructed proximal aorta. Cardiac magnetic resonance imaging (CMR) and angiographic examinations indicate that the native descending aorta (DAo) is also dilated, but this has not been studied in detail. Methods and Results Seventy‐nine children with hypoplastic left heart syndrome in Fontan circulation (aged 6.3±3.2 years) and 18 control participants (aged 6.8±2.4 years) underwent 3.0‐tesla CMR. Gradient‐echo cine and phase‐contrast imaging was applied to measure cross‐sectional areas (CSAs), distensibility, pulse wave velocity, and the incremental elastic modulus of the thoracic aorta. CSA of the DAo in patients was also compared with published percentiles for aortic CSA. Patients had significantly larger CSA of the DAo at the level of pulmonary artery bifurcation (229.1±97.2 versus 175.7±24.3 mm/m2, P=0.04) and the diaphragm (196.2±66.0 versus 142.6±16.7 mm/m2, P<0.01). In 41 patients (52%), CSA of the DAo was >95th percentile level for control participants, and the incremental elastic modulus of the aortic arch and the DAo was higher than in patients with normal CSAs (arch: 90.1±64.3 versus 45.6±38.9 m/s; DAo: 86.3±53.7 versus 47.1±47.6 m/s; P<0.01). Incremental elastic modulus of the aortic arch and the DAo correlated with the CSA of the DAo (arch: r=0.5; DAo: r=0.49; P<0.01). Conclusions Children with hypoplastic left heart syndrome frequently show dilatation of their DAo associated with increased stiffness of the aortic arch. Higher aortic impedance increases the afterload of the systemic circulation and likely contributes to the burden of the systemic right ventricle.

Normal Values of Aortic Dimensions, Distensibility and Pulse Wave Velocity in Children and Young Adults

Background Aortic enlargement and impaired bioelasticity is a focus of interest in several cardiac and non-cardiac diseases as it can lead to severe cardiovascular complications. Assessment of aortic anatomy and bioelasticity, namely aortic distensibility and pulse wave velocity (PWV), by cardiovascular magnetic resonance imaging (CMR) is accurate and reproducible and can help to identify anatomical and functional abnormalities of the aorta. However, normal CMR values for healthy children and young adults are lacking. Methods Seventy-one heart-healthy subjects (mean age 16.4 ± 7.6 y, range 2.3 - 28.3 y) were examined using a 3.0-T CMR scanner. Aortic cross-sectional areas and aortic distensibility were measured at four positions of the thoracic aorta. PWV was assessed from aortic phase-contrast flow measurements in a segment which includes the aorta between the ascending aorta and the proximal descending aorta. Reference percentile curves for aortic cross-sectional areas, aortic distensibility and PWV were computed with the Lambda-Mu-Sigma method by Cole. Results Aortic areas, aortic distensibility and PWV (aortic crosssectional areas: r= 0.8 to 0.9, p<0.001; aortic distensibility r= -0.43 to -0.62, p<0.001; PWV: r= 0.25 to 0.32, p= 0.047 to 0.009) correlated with height, weight, body surface area, and age. There were no significant sex differences. Percentile curves for aortic cross-sectional areas, aortic distensibility and PWV according to age are presented (Figure: Example of reference percentiles for PWV in the aortic arch). Conclusions This study provides percentile curves for cross-sectional areas, distensibility and PWV of the thoracic aorta in children and young adolescents between their 3rd and 29th year of life. These data may serve as a reference for the early detection of pathological changes of the aorta in various cardiovascular diseases. Funding None.