Abnormalities in serum biomarkers correlate with lower cardiac index in the Fontan population.

BACKGROUND: Fontan survivors have depressed cardiac index that worsens over time. Serum biomarker measurement is minimally invasive, rapid, widely available, and may be useful for serial monitoring. The purpose of this study was to identify biomarkers that correlate with lower cardiac index in Fontan patients. Methods and results This study was a multi-centre case series assessing the correlations between biomarkers and cardiac magnetic resonance-derived cardiac index in Fontan patients ⩾6 years of age with biochemical and haematopoietic biomarkers obtained ±12 months from cardiac magnetic resonance. Medical history and biomarker values were obtained by chart review. Spearman's Rank correlation assessed associations between biomarker z-scores and cardiac index. Biomarkers with significant correlations had receiver operating characteristic curves and area under the curve estimated. In total, 97 cardiac magnetic resonances in 87 patients met inclusion criteria: median age at cardiac magnetic resonance was 15 (6-33) years. Significant correlations were found between cardiac index and total alkaline phosphatase (-0.26, p=0.04), estimated creatinine clearance (0.26, p=0.02), and mean corpuscular volume (-0.32, p<0.01). Area under the curve for the three individual biomarkers was 0.63-0.69. Area under the curve for the three-biomarker panel was 0.75. Comparison of cardiac index above and below the receiver operating characteristic curve-identified cut-off points revealed significant differences for each biomarker (p<0.01) and for the composite panel [median cardiac index for higher-risk group=2.17 L/minute/m2 versus lower-risk group=2.96 L/minute/m2, (p<0.01)]. CONCLUSIONS: Higher total alkaline phosphatase and mean corpuscular volume as well as lower estimated creatinine clearance identify Fontan patients with lower cardiac index. Using biomarkers to monitor haemodynamics and organ-specific effects warrants prospective investigation.

Inability of a negative faecal occult blood test to rule out intussusception in children.

A short cut review was carried out to establish whether a negative faecal occult blood test was sufficiently sensitive to rule out a diagnosis of intussusception in children. 5 papers presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these papers are tabulated. It is concluded that a negative faecal occult blood test cannot reliably rule out the diagnosis of intussusception .

Ultrasonographic imaging of the cervical thoracic duct in children with congenital or acquired heart disease.

Conditions that increase central venous pressure lead to secondary dilation of the thoracic duct and impaired lymphatic circulation. We report the use of ultrasound to directly image the cervical part of the thoracic duct in children without the need for invasive techniques or contrast agents. Systematic evaluation of the thoracic duct may be useful in cardiovascular conditions with congestion of the lymphatic system such as single ventricle following Glenn or Fontan procedures.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D).

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a progressive genetic cardiomyopathy characterized by progressive fatty and fibrous replacement of ventricular myocardium. The clinical presentation is marked by ventricular arrhythmias, some fatal. The disease has evolved from a primary electrical/electrophysiological disorder (in the 1980s-1990s) to a diagnostic imaging conundrum (in the 2000s) to the current day understanding of a genetic cardiomyopathy caused by defects in cell-cell adhesion proteins or intracellular signaling components. The pathogenesis, clinical presentation, and the genetics of the disease are discussed in this review.

Disorders of left ventricular trabeculation/compaction or right ventricular wall formation.

Cardiomyopathies are remarkably variable in form. Although hearts may be dilated or hypertrophic, the spectrum of cardiomyopathies includes left ventricular noncompaction/hypertrabeculation and right ventricular wall disorders. These conditions have been increasingly recognized in patients given advances in clinical diagnostics. Here we present information on cardiac pathophysiology, from ventricular wall formation and trabeculae in model organisms to pediatric and adult disease. Many genes to affect the ventricular phenotype, and this has implications for deciphering developmental and disease pathways and for applying testing for clinical care.

Can proprioceptive training improve motor learning?

Recent work has investigated the link between motor learning and sensory function in arm movement control. A number of findings are consistent with the idea that motor learning is associated with systematic changes to proprioception (Haith A, Jackson C, Mial R, Vijayakumar S. Adv Neural Inf Process Syst 21: 593-600, 2008; Ostry DJ, Darainy M, Mattar AA, Wong J, Gribble PL. J Neurosci 30: 5384-5393, 2010; Vahdat S, Darainy M, Milner TE, Ostry DJ. J Neurosci 31: 16907-16915, 2011). Here, we tested whether motor learning could be improved by providing subjects with proprioceptive training on a desired hand trajectory. Subjects were instructed to reproduce both the time-varying position and velocity of novel, complex hand trajectories. Subjects underwent 3 days of training with 90 movement trials per day. Active movement trials were interleaved with demonstration trials. For control subjects, these interleaved demonstration trials consisted of visual demonstration alone. A second group of subjects received visual and proprioceptive demonstration simultaneously; this group was presented with the same visual stimulus, but, in addition, their limb was moved through the target trajectory by a robot using servo control. Subjects who experienced the additional proprioceptive demonstration of the desired trajectory showed greater improvements during training movements than control subjects who only received visual information. This benefit of adding proprioceptive training was seen in both movement speed and position error. Interestingly, additional control subjects who received proprioceptive guidance while actively moving their arm during demonstration trials did not show the same improvement in positional accuracy. These findings support the idea that the addition of proprioceptive training can augment motor learning, and that this benefit is greatest when the subject passively experiences the goal movement.

Integrating training, practice, and reflection within a new model for Canadian medical licensure: a concept paper prepared for the Medical Council of Canada.

In 2020 the Medical Council of Canada created a task force to make recommendations on the modernization of its practices for granting licensure to medical trainees. This task force solicited papers on this topic from subject matter experts. As outlined within this Concept Paper, our proposal would shift licensure away from the traditional focus on high-stakes summative exams in a way that integrates training, clinical practice, and reflection. Specifically, we propose a model of graduated licensure that would have three stages including: a trainee license for trainees that have demonstrated adequate medical knowledge to begin training as a closely supervised resident, a transition to practice license for trainees that have compiled a reflective educational portfolio demonstrating the clinical competence required to begin independent practice with limitations and support, and a fully independent license for unsupervised practice for attendings that have demonstrated competence through a reflective portfolio of clinical analytics. This proposal was reviewed by a diverse group of 30 trainees, practitioners, and administrators in medical education. Their feedback was analyzed and summarized to provide an overview of the likely reception that this proposal would receive from the medical education community.

En 2020, le Conseil médical du Canada a créé un groupe de travail chargé de formuler des recommandations sur la modernisation de ses pratiques d'octroi du titre de licencié aux stagiaires en médecine. À cette fin, le groupe de travail a sollicité la contribution d'auteurs experts en la matière. Dans le présent article conceptuel, nous proposons de réorienter l'approche traditionnelle axée sur l'évaluation sommative par des examens à enjeux élevés vers l'intégration de la formation, la pratique clinique et la réflexion. Plus précisément, nous proposons un modèle d'octroi progressif de la licence en trois étapes : un titre pour les stagiaires qui ont démontré qu'ils possèdent les connaissances nécessaires pour commencer leur formation en tant que résident étroitement supervisé, un titre de transition pour les stagiaires ayant un portfolio d'apprentissage réflexif qui démontre la compétence clinique requise pour entamer une pratique autonome avec du soutien et certaines limites, et un titre permettant la pratique pleinement autonome et non supervisée pour ceux dont le portfolio réflexif démontre une compétence en analyse clinique. Cette proposition a été examinée par un groupe diversifié de 30 stagiaires, praticiens et gestionnaires en éducation médicale. Leurs commentaires ont été analysés et résumés pour donner une idée de l'accueil que la proposition serait susceptible de recevoir de la part du milieu de l'éducation médicale.

Association of Digoxin With Preserved Echocardiographic Indices in the Interstage Period: A Possible Mechanism to Explain Improved Survival?

Background For patients with hypoplastic left heart syndrome, digoxin has been associated with reduced interstage mortality after the Norwood operation, but the mechanism of this benefit remains unclear. Preservation of right ventricular (RV) echocardiographic indices has been associated with better outcomes in hypoplastic left heart syndrome. Therefore, we sought to determine whether digoxin use is associated with preservation of the RV indices in the interstage period. Methods and Results We conducted a retrospective cohort study of prospectively collected data using the public use data set from the Pediatric Heart Network Single Ventricle Reconstruction trial, conducted in 15 North American centers between 2005 and 2008. We included all patients who survived the interstage period and had echocardiographic data post-Norwood and pre-Glenn operations. We used multivariable linear regression to compare changes in RV parameters, adjusting for relevant covariates. Of 289 patients, 94 received digoxin at discharge post-Norwood. There were no significant differences in baseline clinical characteristics or post-Norwood echocardiographic RV indices (RV end-diastolic volume indexed, RV end-systolic volume indexed, ejection fraction) in the digoxin versus no-digoxin groups. At the end of the interstage period and after adjustment for relevant covariates, patients on digoxin had better preserved RV indices compared with those not on digoxin for the ΔRV end-diastolic volume (11 versus 15 mL, P=0.026) and the ΔRV end-systolic volume (6 versus 9 mL, P=0.009) with the indexed ΔRV end-systolic volume (11 versus 20 mL/BSA1.3, P=0.034). The change in the RV ejection fraction during the interstage period between the 2 groups did not meet statistical significance (-2 versus -5, P=0.056); however, the trend continued to be favorable for the digoxin group. Conclusions Digoxin use during the interstage period is associated with better preservation of the RV volume and tricuspid valve measurements leading to less adverse remodeling of the single ventricle. These findings suggest a possible mechanism of action explaining digoxin's survival benefit during the interstage period.

The revised Approved Instructional Resources score: An improved quality evaluation tool for online educational resources.

BACKGROUND: Free Open-Access Medical education (FOAM) use among residents continues to rise. However, it often lacks quality assurance processes and residents receive little guidance on quality assessment. The Academic Life in Emergency Medicine Approved Instructional Resources tool (AAT) was created for FOAM appraisal by and for expert educators and has demonstrated validity in this context. It has yet to be evaluated in other populations. OBJECTIVES: We assessed the AAT's usability in a diverse population of practicing emergency medicine (EM) physicians, residents, and medical students; solicited feedback; and developed a revised tool. METHODS: As part of the Medical Education Translational Resources: Impact and Quality (METRIQ) study, we recruited medical students, EM residents, and EM attendings to evaluate five FOAM posts with the AAT and provide quantitative and qualitative feedback via an online survey. Two independent analysts performed a qualitative thematic analysis with discrepancies resolved through discussion and negotiated consensus. This analysis informed development of an initial revised AAT, which was then further refined after pilot testing among the author group. The final tool was reassessed for reliability. RESULTS: Of 330 recruited international participants, 309 completed all ratings. The Best Evidence in Emergency Medicine (BEEM) score was the component most frequently reported as difficult to use. Several themes emerged from the qualitative analysis: for ease of use-understandable, logically structured, concise, and aligned with educational value. Limitations include deviation from questionnaire best practices, validity concerns, and challenges assessing evidence-based medicine. Themes supporting its use include evaluative utility and usability. The author group pilot tested the initial revised AAT, revealing a total score average measure intraclass correlation coefficient (ICC) of moderate reliability (ICC = 0.68, 95% confidence interval [CI] = 0 to 0.962). The final AAT's average measure ICC was 0.88 (95% CI = 0.77 to 0.95). CONCLUSIONS: We developed the final revised AAT from usability feedback. The new score has significantly increased usability, but will need to be reassessed for reliability in a broad population.

Entrepreneurship and Innovation in Health Sciences Education: a Scoping Review.

BACKGROUND AND PURPOSE: This scoping review aimed to explore the connection between health education and entrepreneurship and to identify gaps in the current literature, educational models, and best practices regarding teaching medical professionals about entrepreneurship and innovation. METHODS: The methodology for this review was based on the principles of Arksey and O'Malley's (2005) model for scoping review design. Results from Embase, MEDLINE, PsycINFO, Emcare, AMED, PubMed, and Google Scholar were scanned, filtered, and mapped. RESULTS: Fifty-nine unique papers were found and mapped. The papers discussed common themes, including the entrepreneurial environment (n = 29), career planning and skill development (n = 3), and various skills crucial for the health entrepreneur. The satisfaction was high for most programs, but few reported more fulsome outcomes. The teaching techniques used to engage trainees or physicians in entrepreneurship were also fairly limited. CONCLUSION: Though some programs are described, few have demonstrated efficacy. More attention should be paid towards faculty-level recruitment, development and reward, so that they may in turn teach these approaches. Those involved with educational planning can help close this gap.

A Randomized Comparative Trial of the Knowledge Retention and Usage Conditions in Undergraduate Medical Students Using Podcasts and Blog Posts.

Introduction Podcasts and blog posts have gained popularity in Free Open Access Medical education (FOAM). Previous work suggests that podcasts may be useful for knowledge acquisition in undergraduate medical education. However, there remains a paucity of research comparing the two mediums. This study aims to investigate if there are differences in knowledge acquisition and usage conditions by medical students using podcasts and blog posts. Methods Medical students were randomized to either the podcast or blog post group. They completed an initial online assessment of their baseline knowledge on the subject matter. Participants then received access to learning materials and were given four weeks to complete the follow-up assessment on their own time. Independent t-test, paired samples t-test, and a mixed ANOVA (analysis of variance) were conducted to assess knowledge acquisition. An intention-to-teach analysis was used to impute missing data from students lost to follow-up. Simple descriptive statistical data was used to describe media usage conditions. Results Completion of at least one follow-up assessment was comparable (68% podcasts (n = 21/31), 73% blog posts (n = 22/30)). Both groups showed significant improvements in their test scores, with an average 22% improvement for the podcast group and 29% for the blog post group. There was no significant statistical difference in knowledge acquisition between educational modalities overall. Students in the blog post group that completed both post-intervention quizzes showed a larger improvement than the podcast group in the toxicology topic, with similar improvements in the asthma topic. The podcast group tended to engage in multiple activities while using the learning materials (e.g. at least two to three of the following: driving, eating, chores, taking notes, exercising/walking), while the blog readers tended to do fewer activities (e.g. only one of the following: note taking, eating). Conclusion This study suggests that podcasts and blog posts are useful for extracurricular knowledge acquisition by undergraduate medical students with no significant difference between the two modalities. The usage conditions for each type of media differ.

The effect of an infographic promotion on research dissemination and readership: A randomized controlled trial.

OBJECTIVE: Journals use social media to increase the awareness of their publications. Infographics show research findings in a concise and visually appealing manner, well suited for dissemination on social media platforms. We hypothesized that infographic abstracts promoted on social media would increase the dissemination and online readership of the parent research articles. METHODS: Twenty-four articles were chosen from the six issues of CJEM published between July 2016 and June 2017 and randomized to infographic or control groups. All articles were disseminated through the journal's social media accounts (Twitter and Facebook). Control articles were promoted using a screen capture image of each article's abstract on the journal's social media accounts. Infographic articles were promoted similarly using a visual infographic. Infographics were also published and promoted on the CanadiEM.org's website and social media channels. Abstract views, full-text views, and the change in Altmetric score were compared between groups using unpaired two-tailed t-tests. RESULTS: There were no significant differences in the groups at baseline. Abstract views (mean, 95% CI) were higher in the infographics (379, 287-471) than the control group (176, 136-215, p<0.001). Mean change in Altmetric scores was higher in the infographics (26, 18-34) than in the control group (3, 2-4, p<0.0001). There was no difference in full-text views between the infographics (50, 0-101) and control groups (25, 18-32). CONCLUSION: The promotion of CJEM articles using infographics on social media and the CanadiEM.org website increased Altmetric scores and abstract views. Infographics may have a role in increasing awareness of medical literature.

The impact of social media promotion with infographics and podcasts on research dissemination and readership.

OBJECTIVE: In 2015 and 2016, the Canadian Journal of Emergency Medicine (CJEM) Social Media (SoMe) Team collaborated with established medical websites to promote CJEM articles using podcasts and infographics while tracking dissemination and readership. METHODS: CJEM publications in the "Original Research" and "State of the Art" sections were selected by the SoMe Team for podcast and infographic promotion based on their perceived interest to emergency physicians. A control group was composed retrospectively of articles from the 2015 and 2016 issues with the highest Altmetric score that received standard Facebook and Twitter promotions. Studies on SoMe topics were excluded. Dissemination was quantified by January 1, 2017 Altmetric scores. Readership was measured by abstract and full-text views over a 3-month period. The number needed to view (NNV) was calculated by dividing abstract views by full-text views. RESULTS: Twenty-nine of 88 articles that met inclusion were included in the podcast (6), infographic (11), and control (12) groups. Descriptive statistics (mean, 95% confidence interval) were calculated for podcast (Altmetric: 61, 42-80; Abstract: 1795, 1135-2455; Full-text: 431, 0-1031), infographic (Altmetric: 31.5, 19-43; Abstract: 590, 361-819; Full-text: 65, 33-98), and control (Altmetric: 12, 8-15; Abstract: 257, 159-354; Full-Text: 73, 38-109) articles. The NNV was 4.2 for podcast, 9.0 for infographic, and 3.5 for control articles. Discussion Limitations included selection bias, the influence of SoMe promotion on the Altmetric scores, and a lack of generalizability to other journals. CONCLUSION: Collaboration with established SoMe websites using podcasts and infographics was associated with increased Altmetric scores and abstract views but not full-text article views.

Model-Based Comparison of the Normal and Fontan Circulatory Systems-Part III.

BACKGROUND: For patients with the Fontan circulatory arrangement, angiotensin-converting enzyme inhibition, guanylate cyclase activation, phosphodiesterase 5 inhibition, and endothelin receptor antagonism have so far resulted in little or no improvement in [Formula: see text] or peak cardiac index (CI), suggesting that our understanding of the factors that most impact the exercise hemodynamics is incomplete. METHODS: To facilitate comparisons with clinical reports of the exercise performance of preadolescent Fontan patients, we rescaled our previously reported computational models of a two-year-old normal child and similarly aged Fontan patient, extended our Fontan model to capture the nonlinear relationship between flow and resistance quantified from previous computational fluid dynamic analyses of the total cavopulmonary connection (TCPC), and added respiration as well as skeletal muscle contraction. RESULTS: (1) Without respiration, the computational model for both the normal and the Fontan cannot attain the values for CI at peak exercise reported in the clinical literature, (2) because flow through the TCPC is much greater during inspiration than during expiration, the effect on the CI of the dynamic (flow-related) TCPC resistance is much more dramatic during exercise than it is in breath-hold mode at rest, and (3) coupling breathing with skeletal muscle contraction leads to the highest augmentation of cardiac output, that is, the skeletal muscle pump is most effective when the intrathoracic pressure is at a minimum-at peak inspiration. CONCLUSIONS: Novel insights emerge when a Fontan model incorporating dynamic TCPC resistance, full respiration, and skeletal muscle contraction can be compared to the model of the normal.

Podcast Use in Undergraduate Medical Education.

Introduction Podcasts have become increasingly popular as a medium for free open access medical education (FOAM). However, little research has examined the use of these extracurricular audio podcasts as tools in undergraduate medical education. We aimed to examine knowledge retention, usage conditions, and preferences of undergraduate medical students at a Canadian university interacting with extracurricular podcasts. Methods Students enrolled in the undergraduate medical program at McMaster University volunteered to participate in this study. Two podcasts were created specifically for the purposes of this study, and online tests and surveys were sent to participants to gather data regarding user preferences of podcasts. In addition, we recorded changes in topic test scores before and after podcast exposure. Results Forty-two students were recruited to this study. Participants who completed the assessments demonstrated an effect of learning. Podcasts of 30 minutes or less were preferred in the majority of participants who had a preference in duration. The top three activities participants were engaged in while listening to the podcasts were driving (46%), completing chores (26%), and exercising (23%). A large number of participants who did not complete the study in its entirety cited a lack of time and podcast length to be the top two barriers to completion. Conclusion This is one of the first studies to examine extracurricular podcast-usage data and preferences in a Canadian undergraduate medical student population. This information may help educators and FOAM producers to optimize educational tools for medical education.

Enalapril to prevent cardiac function decline in long-term survivors of pediatric cancer exposed to anthracyclines.

PURPOSE: To determine whether an angiotensin-converting enzyme (ACE) inhibitor, enalapril, prevents cardiac function deterioration (defined using maximal cardiac index [MCI] on exercise testing or increase in left ventricular end-systolic wall stress [LVESWS]) in long-term survivors of pediatric cancer. PATIENTS AND METHODS: This was a randomized, double-blind, controlled clinical trial comparing enalapril to placebo in 135 long-term survivors of pediatric cancer who had at least one cardiac abnormality identified at any time after anthracycline exposure. RESULTS: There was no difference in the rate of change in MCI per year between enalapril and placebo groups (0.30 v 0.18 L/min/m(2); P =.55). However, during the first year of treatment, the rate of change in LVESWS was greater in the enalapril group than in the placebo group (-8.59 v 1.85 g/cm(2); P =.033) and this difference was maintained over the study period, resulting in a 9% reduction in estimated LVESWS by year 5 in the enalapril group. Six of seven patients removed from random assignment to treatment because of cardiac deterioration were initially treated with placebo (P =.11), and one has died as a result of heart failure. Side effects from enalapril included dizziness or hypotension (22% v 3% in the placebo group; P =.0003) and fatigue (10% v 0%; P =.013). CONCLUSION: Enalapril treatment did not influence exercise performance, but did reduce LVESWS in the first year; this reduction was maintained over the study period. Any theoretical benefits of LVESWS reduction in this anthracycline-exposed population must be weighed against potential side effects from ACE inhibitors when making treatment decisions.

Using health-related quality of life measures to predict cardiac function in survivors exposed to anthracyclines.

PURPOSE: As the number of pediatric cancer survivors increases, so does the number of survivors previously exposed to anthracyclines as part of their cancer therapy. Because screening is costly, some have suggested that health-related quality of life (HRQL) measures might be useful in focusing screening tests on those patients with cases most likely to display positive findings. This study reports on the predictive ability of HRQL measures to detect patients with abnormalities on serial cardiac testing. METHODS: Using 127 patients from the ACE-Inhibitor after Anthracycline (AAA) Trial, this study compared serial measures of the Short Form-36 (SF-36; for ages > 13 years) and Child Health Questionnaire-Child Form 87 (CHQ-CF87; for ages < or = 13 years) to serial cardiac performance tests including echocardiographic shortening fraction, left ventricular end systolic wall stress (LVESWS), LVESWS-index, and maximal cardiac index (MCI; a measure of cardiac output at peak exercise). RESULTS: Generally, there was no clinically or statistically significant correlation between any HRQL measure and any cardiac function measure except between MCI and vitality and physical functioning. For each of these measures, the correlation between MCI was statistically significant (P < .006), but each HRQL subscale could explain no more than 7% of the variation in MCI. HRQL measures were not predictive of any other cardiac function measure. CONCLUSION: HRQL measures should not be used in isolation as a screen for cardiac function abnormalities in patients exposed to anthracylines who already have a mild degree of ventricular dysfunction. Patient history appears to be no substitute for cardiac testing in this cohort.

Model-Based Comparison of the Normal and Fontan Circulatory Systems-Part II: Major Differences in Performance Characteristics.

BACKGROUND: In the absence of an accessible chronic animal model of the Fontan circulation, computational modeling can provide insights into this unique circulatory arrangement, especially how differently it behaves from the normal mammalian circulation. Many groups have focused on refining a single element of the entire Fontan circulation-the total cavopulmonary connection (TCPC). Yet, only modest improvements in transplant-free survival have resulted. From an engineering perspective, optimizing the performance of a complex, multiparameter system requires an understanding of how the performance is affected by the full set of system parameters. METHODS: We evaluated the hemodynamic impact of nine physiological perturbations in the two-year-old (yo) patient with hypoplastic left heart syndrome having a Fontan rearrangement (using our previously described lumped-parameter multicompartment model of both pulmonary and systemic circulations). In cases where comparison is appropriate, we evaluated the hemodynamic impact of analogous pathophysiologies in the normal two-year-olds. We operated the model in open-loop mode in order to expose the magnitude of the impact of uncompensated physiological perturbations. RESULTS: Without the benefit of compensatory mechanisms, a valvar regurgitant fraction of 50% is sufficient to drop the cardiac index (CI) to 2.0 L/min/m(2) or less. Aortopulmonary collateral flow of 0.6 L/min (1.1 L/min/m(2)) or 0.5 L/min (0.9 L/min/m(2)), sufficient to raise the ratio of pulmonary flow to systemic flow (Qp/Qs) to no higher than 1.2 or 1.5 (fenestration present or absent, respectively), is the maximum which could be tolerated (CI = 2.0 L/min/m(2)) without the help of compensatory mechanisms. Ventricular end-diastolic elastance (stiffness) changes have dramatic effects on CI in a Fontan circulatory arrangement. CONCLUSIONS: Several components of the Fontan circulation other than the TCPC actually have equal, or greater, impact on CI under certain conditions.

Cloning and characterization of zebrafish tbx1.

Tbx1 is one of the genes within the DiGeorge Critical Region (DGCR) and has been recently identified as the critical gene for the cardiovascular anomalies in the DiGeorge mouse models. We have cloned, sequenced and analyzed the zebrafish (Danio rerio) tbx1 cDNA. It encodes a protein of 460 amino acids that shares 64% identity and 67% similarity with the human TBX1 orthologue at the amino acid level. Although maternal expression was detected by RT-PCR, only zygotic expression could be detected by whole-mount in situ hybridization. Expression of zebrafish tbx1 by whole-mount in situ hybridization was first detected at 40% epiboly, 5.0 hours post fertilization (hpf) in the dorsal blastoderm margin. Through the stage of embryonic shield formation, tbx1 expression is restricted to the hypoblast, in the region of cells fated to become head and lateral plate mesoderm and pharyngeal endoderm. At 18 hpf, when the heart tube is beginning to assemble, three domains of tbx1 expression can be seen: cardiac precursors, pharyngeal arch precursors and otic vesicle. These three domains will remain the sites of tbx1 expression to varying degrees through at least 72 hpf. By 51 hpf, tbx1 expression can be seen in the cardiac outflow tract, the ventricle and the atrium, although by 72 hpf cardiac expression is strongest in the cardiac outflow tract. This newly identified tbx1 expression pattern in cardiac regions other than the cardiac outflow tract offers a new insight into the role of the tbx1 transcription factor in cardiac development.