Taylor Chung

Evaluation of Regional Differences in Right Ventricular Systolic Function by Acoustic Quantification Echocardiography and Cine Magnetic Resonance Imaging

BACKGROUND Accurate quantitative evaluation of right ventricular (RV) function has been limited by its complex structural geometry. Although embryological and anatomic observations suggest that the RV is composed of 2 distinct components, the RV sinus and infundibulum, most studies on RV dimensions and function viewed it as a single chamber. This study was designed to determine the volumes, relative contribution to global systolic function, and temporal course of contraction and relaxation of the RV sinus and infundibulum. METHODS AND RESULTS Thirty-one individuals without heart disease (aged 1 month to 17 years, 16 boys and 15 girls) participated in this study. Instantaneous area over time, its derivatives, and the temporal course of contraction and relaxation were studied by acoustic quantification echocardiography and phonocardiography in 20 individuals. Global and regional RV volumes and ejection fraction were determined by cine MRI in 11 individuals. The RV sinus made up 81+/-6% of the combined RV end-diastolic volume and 87+/-4% of the combined stroke volume. The infundibulum accounted for the remaining 19+/-6% and 13+/-4%, respectively (P<0.0001). Compared with the infundibulum, the extent of RV sinus fiber shortening was significantly greater: for ejection fraction (56+/-11% versus 38+/-13%, P<0.001), fractional area change (42+/-14% versus 28+/-9%, P<0.0001), and dA/dt (27+/-17% versus 13+/-6%, P<0.0001). Analysis of temporal course of contraction and relaxation (expressed as percentage of the cardiac cycle to adjust for differences in heart rate) showed that the infundibulum follows the RV sinus: onset of contraction 53%+/-14 versus 19+/-11% of systole, time to peak systole 115+/-16% versus 97+/-19% (P< or =0.01), indicating a peristalsis-like pattern of contraction and relaxation. CONCLUSIONS The results of this study demonstrate significant regional differences between the sinus and infundibulum components of the RV with regard to contribution to stroke volume, extent of fiber shortening, and sequence of mechanical activation. These data from normal individuals can be used in future research on RV function in pathological conditions.

Phase-Velocity Cine Magnetic Resonance Imaging Measurement of Pulsatile Blood Flow in Children and Young Adults: In Vitro and In Vivo Validation

Abstract. Quantification of blood flow in vessels provides valuable information that aids management decisions in a variety of cardiac conditions. Current flow measurement techniques are often limited by accuracy, time resolution, convenience, or anatomic localization. This study examined the accuracy of a commercially available phase-velocity cine magnetic resonance imaging (PVC MRI) technique to quantify flow rate in a pulsatile flow phantom. In addition, the equivalence of PVC MRI measurements of pulmonary and systemic flow was evaluated in children and adults without any pathologic shunt. Using a pulsatile flow phantom, volume flow rates measured by PVC MRI were compared to those by a transit-time ultrasound flowmeter over a range of flow rates (1.25–3.5 L/min, 13 trials). Close agreement was found between these techniques (y= 1.02x− 0.02, r= 0.99, Bland–Altman bias =−0.045 L/min, 95% limits of agreement =−0.19–0.10 L/min). Twenty subjects (median age 12.8 years, range 0.7–49 years) with no pathologic shunt underwent PVC MRI measurement of blood flow in the main pulmonary artery (Qp) and the ascending aorta (Qs). Data processing time for each location was 20 minutes. The Qp/Qs ratio closely approximated unity (mean = 0.99, SD = 0.10, range 0.85–1.19). Interobserver agreement was excellent (Bland–Altman bias = 0.09 L/min, 95% limits of agreement = 0.15–0.33 L/min). PVC MRI is an accurate technique to quantify pulsatile blood flow at a specific location. It can be used to noninvasively calculate Qp and Qs under normal flow conditions.

Guidelines and protocols for cardiovascular magnetic resonance in children and adults with congenital heart disease: SCMR expert consensus group on congenital heart disease.

Cardiovascular magnetic resonance (CMR) has taken on an increasingly important role in the diagnostic evaluation and pre-procedural planning for patients with congenital heart disease. This article provides guidelines for the performance of CMR in children and adults with congenital heart disease. The first portion addresses preparation for the examination and safety issues, the second describes the primary techniques used in an examination, and the third provides disease-specific protocols. Variations in practice are highlighted and expert consensus recommendations are provided. Indications and appropriate use criteria for CMR examination are not specifically addressed.

In Vivo Evaluation of Fontan Pathway Flow Dynamics by Multidimensional Phase-Velocity Magnetic Resonance Imaging

BACKGROUND Hemodynamic efficiency of Fontan circulation is believed to be a major determinant of outcome. Prior research on flow dynamics in different modifications of Fontan circulation used in vitro models and computer-based simulation. This study was designed to compare in vivo flow dynamics in the systemic venous pathway between patients with atriopulmonary anastomosis (APA) and those with total cavopulmonary connection (TCPC). METHODS AND RESULTS Multidimensional phase-velocity magnetic resonance imaging (PV-MRI) studies were performed on 10 patients who had undergone a modified Fontan operation (5 with TCPC and 5 with APA) and were free of symptoms. The groups were comparable in terms of age and body surface area. The interval since surgery was longer for APA than for TCPC subjects. In each subject, the phase-velocity data sets were used to generate dynamic velocity-vector maps and to calculate quantitative flow indices describing the 3-dimensional blood-flow patterns throughout the cardiac cycle at the widest diameter of the Fontan pathway. Mean flow rate was comparable between groups. Velocity-vector maps showed areas of flow reversal, flow stagnation, and circular flow within APA but not TCPC pathways. Analysis of quantitative flow indices showed that compared with the APA group, flow velocities in the TCPC patients were significantly higher (mean velocity, 14+/-6 cm/s versus 5+/-3 cm/s; P=0.02), less variable (coefficient of variation, 19+/-2% versus 37+/-3.5%; P<0.0001), and more unidirectional (degree of unidirectionality, 89+/-7% versus 71+/-12%; P=0.03). APA pathways were significantly more dilated than were TCPC pathways (P<0.01) and showed a trend toward larger diameter with increased interval since surgery (R2=0.6, P=0.09). Fontan pathway dilatation correlated with flow velocity variability (R2=0.57, P=0.01) and inversely with flow unidirectionality (R2=0.75, P=0.001). CONCLUSIONS Blood flow patterns are more organized and uniform in TCPC than in APA pathways and are significantly influenced by pathway diameter. We speculate that TCPC may result in a more hemodynamically efficient circulation than APA because of differences in pathway dimension and uniformity.

Assessment of cardiovascular anatomy in patients with congenital heart disease by magnetic resonance imaging.

Abstract. The following discussion addresses the assessment of cardiovascular anatomy in patients with congenital heart disease by magnetic resonance (MR). The focus of this review is on the techniques of performing the MR examination. In particular, individual pulse sequences are described and illustrated with their strengths and weaknesses. Imaging strategies using the described pulse sequences are proposed. The pulse sequences described are widely available on most MR scanners. Therefore, the proposed imaging strategies are clinically proven to be simple and effective ways to perform cardiac MR examination for the assessment of cardiovascular anatomy in patients with congenital heart disease. Functional imaging, such as flow analysis and ventricular function assessment, are discussed elsewhere in this issue.

The use of oral pentobarbital sodium (Nembutal) versus oral chloral hydrate in infants undergoing CT and MR imaging--a pilot study.

Background. Chloral hydrate, a commonly used oral sedative for infants undergoing imaging examinations, has a bitter taste and requires relatively large volume, provoking unpleasant reactions from the infants. Experience with an alternative sedative, oral pentobarbital (Nembutal), has not been reported for infants Objective. To compare patient acceptance of oral Nembutal and oral chloral hydrate for sedation of infants up to 12 months of age. Methods and materials. Fifty-four infants (mean age: 7 months) were prospectively enrolled. Parents chose Nembutal, chloral hydrate, or no preference. Thirty-eight infants received Nembutal (4–6 mg/kg) mixed with cherry syrup and 16 received chloral hydrate (50–100 mg/kg). We recorded infants acceptance of sedative, parental impression of infants acceptance, time to sedation, time to discharge, adverse effects, parental preference of future sedative. Results. Infant acceptance and parental impression were better for Nembutal (P < 0.0001). Fewer parents in the Nembutal group preferred another sedative (P = 0.05). There was a trend toward shorter time to discharge with Nembutal (P = 0.03). There were no adverse effects in either group. One infant failed to sedate with Nembutal. Conclusions. Compared with chloral hydrate, oral Nembutal has significantly better acceptance by infants and parents, equal effectiveness, and may result in a shorter time to discharge.

Time-resolved contrast-enhanced magnetic resonance angiography in pediatric patients using sensitivity encoding

To evaluate the role of time‐resolved contrast‐enhanced magnetic resonance angiography (CE‐MRA) using sensitivity encoding in imaging the thoraco‐abdominal vessels in pediatric patients.

Multimodality Imaging of Tracheobronchial Disorders in Children

The trachea and bronchial airways in children are subject to compromise by a number of extrinsic and intrinsic conditions, including congenital, inflammatory, infectious, traumatic, and neoplastic processes. Stridor, wheezing, and respiratory distress are the most common indications for imaging of the airway in children. Frontal and lateral chest and/or neck radiography constitute the initial investigations of choice in most cases. Options for additional imaging include airway fluoroscopy, contrast esophagography, computed tomography (CT), and magnetic resonance (MR) imaging. Advanced imaging techniques such as dynamic airway CT, CT angiography, MR angiography, and cine MR imaging are valuable for providing relevant vascular and functional information in certain settings. Postprocessing techniques such as multiplanar reformatting, volume rendering, and virtual bronchoscopy assist in surgical planning by providing a better representation of three-dimensional anatomy. A systematic approach to imaging the airway based on clinical symptoms and signs is essential for the prompt, safe, and accurate diagnosis of tracheobronchial disorders in children.

Accuracy of MRI evaluation of pulmonary blood supply in patients with complex pulmonary stenosis or atresia.

Detailed imaging of pulmonary artery (PA) anatomy and significant aorto-pulmonary collaterals (APCs) is crucial for surgical planning and follow-up in patients with complex congenital heart disease (CHD) and pulmonary stenosis or atresia. Because examination by echocardiography is often technically limited and catheterization is invasive, this study evaluated the diagnostic accuracy of magnetic resonance imaging (MRI) as an alternate non-invasive tool. Thirteen patients (median age 28 years, range: 1–44 years) underwent both cardiac catheterization and MRI within a median of two months (range 0.1–8 months). Diagnoses included tetralogy of Fallot (TOF) with pulmonary atresia (n = 8), TOF with pulmonary stenosis (n = 2), single left ventricle with pulmonary stenosis (n = 2), and complex heterotaxy with pulmonary stenosis (n = 1). The MRI sequences used in this study were ECG-gated spin echo and gradient echo sequences acquired in multiple planes. Compared to catheterization, MRI had 100% sensitivity and specificity for the diagnosis of main PA (n = 6) and branch PA (n = 13) hypoplasia or stenosis, as well as discontinuous (n = 4) or absent (n = 10) branch PAs. There was complete agreement between catheterization and MRI identification of significant APCs (n = 18). Main PA atresia was noted by MRI in four patients but was not definitively seen by catheterization in any. MRI but not catheterization precisely defined the distance between discontinuous PAs and their relationship to other mediastinal structures. In conclusion, cardiac MRI is a reliable non-invasive imaging modality to define PA and APC anatomy in patients with complex pulmonary stenosis or atresia.

Transrectal drainage of deep pelvic abscesses in children using a combined transrectal sonographic and fluoroscopic guidance.

The authors review their experience with transrectal drainage of pelvic abscesses in seven children and adolescents (6–16 years old). Initial access was guided by transrectal ultrasound with an endovaginal transducer followed by fluoroscopy for placement of self-retaining catheters (8.5–10 F) using the Seldinger technique. All abscesses were successfully drained without complications. A transrectal catheter was well tolerated by most patients without spontaneous dislodgment. Catheters were removed after an average of 4 days (range 3–7 days). Transrectal drainage of pelvic abscess with transrectal sonographic and fluoroscopic guidance seems to be a safe and effective procedure in children.