Screening for QTc prolongation during acute exercise in childhood acute lymphoblastic leukemia survivors

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Institute of Cancer Research (ICR) of the Canadian Institutes ofHealth Research (CIHR), C17 Council

Background

Anthracycline-related cardiotoxicity is a major cause of mortality and morbidity in childhood acute lymphoblastic leukaemia (ALL) survivors. Electrophysiologic complications and cardiac autonomic dysfunction are both known to be developed by childhood ALL survivors. Current methods for detection of cardiotoxicity have limitations, particularly due to their lack of sensitivity for early detection of subclinical cardiac dysfunction. Early detection of cardiac dysfunction remains a cardiologist’s challenge and is essential to allow optimal therapeutic intervention.

Purpose

This study aimed to observe ventricular repolarization during a maximal cardiopulmonary exercise test (CPET) in childhood ALL survivors. We hypothesized that cancer treatments lead to changes in ventricular repolarization that persist over time, and that the use of CPET allows the unmasking of electrophysiological abnormalities.

Methods

A total of 250 childhood ALL survivors underwent a maximal CPET on an ergocycle, and their direct oxygen uptake was measured. All survivors were monitored continuously during the test using a 12-lead electrocardiogram. Measurements of the QT interval were completed at rest, at the end of each stage of the CPET, and during recovery. The QT interval was defined as the period from the onset of the Q-wave to the end of the T-wave, measured linearly. Values were corrected (QTc) using a specific group equation. To compare the effect of cardiorespiratory fitness on QTc during CPET, participants were divided in two groups according to the median of survivors’ cardiorespiratory fitness (group A: <32.0 mL.kg-1.min-1; group B: ≥32.0 mL.kg-1.min-1).

Results

All survivors (median age: 21 years, 51.5% male) included in the final analysis (n=200) performed a validated maximal CPET. At rest, the QTc interval was 379.1±32.2ms. None of the participants had a prolonged QTc during exercise (371.5±16.1ms, range 310.7-416.1ms). The mean QTc interval during CPET was not different between groups A and B (370.1±17.6ms and 373.0±14.4ms, p=0.218). Group A had a longer QT interval at low to moderate exercise intensities. During recovery, the QTc interval was 373.4.1±16.2ms.

Conclusions

Cancer and anthracycline treatments have an impact on the cardiorespiratory system. Low cardiorespiratory fitness in childhood ALL survivors is associated with longer ventricular repolarization during exercise. These differences may be an indicator of altered cardiac function. This shows the importance of studying the response to exercise to improve early cardiac dysfunction detection, as well as documenting the autonomic nervous system response to exercise between survivors with lower and higher physical fitness.

Genetic factors in congenital heart malformation

Congenital heart disease is the commonest malformation in humans and contributes greatly to the burden of disease in infancy. Increasingly, developmental origins are also implicated in heart disease in adults. Significant advances have been made over the past decade in elucidating morphogenetic events of heart formation and their underlying molecular cascades, mostly in animal models. Clinical studies are increasingly successful in quantifying and unraveling genetic factors. This review focuses on recent progress made in understanding the genetic underpinnings of normal and abnormal heart formation and highlights the importance of understanding these mechanisms to improve patient management.

Detailed four-way comparative mapping and gene order analysis of the canine ctvm locus reveals evolutionary chromosome rearrangements

Canine tricuspid valve malformation (CTVM) maps to canine chromosome 9 (CFA9), in a region syntenic with gene-dense human chromosome 17q. To define synteny blocks, we analyzed 148 markers on CFA9 using radiation hybrid mapping and established a four-way comparative map for human, mouse, rat, and dog. We identified a large number of rearrangements, allowing us to reconstruct the evolutionary history of individual synteny blocks and large chromosomal segments. A most parsimonious rearrangement scenario for all four species reveals that human chromosome 17q differs from CFA9 and the syntenic rodent chromosomes through two macroreversals of 9.2 and 23 Mb. Compared to a recovered ancestral gene order, CFA9 has undergone 11 reversals of <3 Mb and 2 reversals of >3 Mb. Interspecies reuse of breakpoints for micro- and macrorearrangements was observed. Gene order and content of the ctvm interval are best extrapolated from murine data, showing that multispecies genome rearrangement scenarios contribute to identifying gene content in canine mapping studies.

Canine tricuspid valve malformation, a model of human Ebstein anomaly, maps to dog chromosome 9

BACKGROUND

Ebstein anomaly of the tricuspid valve is a congenital cardiac malformation characterised by downward displacement of the attachment of the septal and posterior leaflets of the tricuspid valve. Canine tricuspid valve malformation (CTVM) is morphologically similar to Ebstein anomaly; familial occurrence of CTVM has been described. Several observations suggest a genetic cause but most cases appear to be sporadic.

METHODS

Three purebred Labrador Retriever kindreds enriched for CTVM underwent clinical examination and echocardiography. DNA was extracted from whole blood. Genotyping was carried out using polymorphic repeat markers with an average spacing of 15 cM and polymorphic information content of 0.74.

RESULTS

Pedigree analysis identified CTVM segregating as an autosomal dominant trait with reduced penetrance. Genome wide linkage analysis in one kindred identified a CTVM susceptibility locus on dog chromosome 9 (CFA9) with a maximum multipoint lod score of 3.33. The two additional kindreds showed a conserved disease haplotype.

CONCLUSIONS

This study identifies a CTVM susceptibility locus on CFA9 and a founder effect in apparently unrelated Labrador Retriever kindreds. These results provide the basis for a positional candidate cloning effort to identify the CTVM disease gene. Identification of the CTVM gene will permit mutation screening of patients with Ebstein anomaly, which should provide additional insights into the genetic programmes of valve development.

Functional pulmonary atresia in neonatal Marfan's syndrome: successful treatment with inhaled nitric oxide

Functional pulmonary atresia is characterized by a structurally normal pulmonary valve not opening during right ventricular ejection. We report this rare condition in a premature newborn of a twin pregnancy, in which fetal echocardiography findings were consistent with critical pulmonary stenosis. After birth, features of neonatal Marfan's syndrome were noted. Echocardiography showed a morphologically normal but immobile pulmonary valve with continuous regurgitation. Right ventricular pressure was subsystemic. In this case, initial treatment with nitric oxide, followed by pharmacological duct closure, was successful. Differentiating between anatomic and functional pulmonary valve atresia may be difficult. The echocardiographic criteria are discussed.

Characterization of PGE2 receptors in fetal and newborn lamb ductus arteriosus

Although the role of PGE2 in maintaining ductus arteriosus (DA) patency is well established, the specific PGE2 receptor subtype(s) (EP) involved have not been clearly identified. We used late gestation fetal and neonatal lambs to study developmental regulation of EP receptors. In the fetal DA, radioligand binding and RT-PCR assays virtually failed to detect EP1 but detected EP2, EP3D, and EP4 receptors in equivalent proportions. In the newborn lamb, DA total density was one-third of that found in the fetus and only EP2 was detected. Stimulation of EP2 and EP4 increased cAMP formation and was associated with DA relaxation. Though stimulation of EP3 inhibited cAMP formation, it surprisingly relaxed the fetal DA both in vitro and in vivo. This EP3-induced relaxation was specifically diminished by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide. In conclusion, PGE2 dilates the late gestation fetal DA through pathways that involve either cAMP (EP2 and EP4) or K(ATP) channels (EP3). The loss of EP3 and EP4 receptors in the newborn DA is consistent with its decreased responsiveness to PGE2.

Late effects of anthracycline therapy in childhood in relation to the function of the heart at rest and under physical stress

To evaluate the long-term effects of anthracyclines on the myocardium of the young child we examined 34 patients who had been treated with anthracyclines in childhood. In addition to anthracycline, the patients were treated with other potentially cardiotoxic substances within the framework of different protocols. The mean cumulative anthracycline dose was 128.6 mg/m2, the average age at onset of chemotherapy 4.2 years, and the time interval after discontinuation of treatment 9.0 years. The cardiological examination consisted of a physical examination, electrocardiography and echocardiography, including Doppler and bio-impedance cardiography. The patients were studied at rest and after physical exercise with a cycle ergometer test in a supine position. The results of the physical examination, the electrocardiogram at rest and the 24 h Holter monitoring were normal. The left ventricular enddiastolic diameter, shortening fraction, velocity of fibre shortening (VCF), the diastolic flow profile at the mitral valve level and the cardiac stroke volume at rest were also normal. However, the shortening fraction (SF) was below the margin of 2 standard deviations in two patients and the VCF in three patients. There was a significant reduction in septal thickness, (-1.4 SD, P < 0.0004), in the width of left ventricular posterior wall (-1.5 SD, P > 0.0002) and in the left ventricular myocardial mass (-0.76 SD, P = 0.0042). Physical working capacity was normal. Immediately after physical stress the expected rise of SF and VCF did not occur and the SF fell below the values at rest. In comparison to a healthy control group the SF and the VCF were markedly decreased (P > 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)