Permanent junctional reciprocating tachycardia due to an atypical retrograde slow conducting decremental left posterolateral accessory pathway and tachycardia-induced cardiomyopathy in a pregnant adolescent

Permanent junctional reciprocating tachycardia (PJRT) is a rare form of supraventricular tachycardia (SVT) due to a retrograde slow conducting decremental accessory pathway (AP) which is often incessant and can lead to tachycardia-induced cardiomyopathy (TIC). We report the challenging clinical course of a pregnant adolescent with PJRT due to an atypical retrograde slow conducting decremental left posterolateral AP. Pregnancy is known to exacerbate supraventricular arrhythmias and can lead to adverse maternal and fetal outcomes. To the best of our knowledge, there are no prior reports on the clinical course of rare incessant and difficult-to-treat arrhythmias such as PJRT in a pregnant adolescent patient.

Life-threatening pulmonary haemorrhage treated with coil embolisation followed by lobectomy in a patient with KCNT1 mutation

KCNT1 mutations are associated with childhood epilepsy, developmental delay, and vascular malformations. We report a child with a likely pathogenic KCNT1 mutation (c.1885A>C, p.Lys629Glu) with recurrent pulmonary haemorrhage due to aortopulmonary collaterals successfully managed with coil embolisation followed by right upper lobectomy.

Novel Phenotypic Effects of a Rare SCN5A (c.2482C>T) Mutation

In a familial cohort with 8 heterozygous carriers of a rare pathogenic SCN5A mutation (c.2482C>T), 4 female mutation carriers manifested with fetal ventricular tachycardia and 2:1 atrioventricular block. One presented with multifocal ectopic premature Purkinje-related complexes-like phenotype and atrial fibrillation later in life. These novel findings inform the need for robust fetal monitoring of mutation carriers.

Subcutaneous Implantable Cardioverter Defibrillators in Pediatrics and Congenital Heart Disease

Subcutaneous implantable cardioverter defibrillators (S-ICDs) are being used with increased frequency in children and patients with congenital heart disease. Vascular access complexities, intracardiac shunts, and specific anatomies make these devices particularly appealing for some of these patients. Alternative screening, implantation, and programming techniques should be considered based on patient size, body habitus, anatomy, procedural history, and preference. Appropriate and inappropriate shock rates are generally comparable to those seen with transvenous devices. Complications such as infection can occur, although their severity is likely to be less than that seen with transvenous devices. Technical advances are likely to further broaden S-ICD applicability.

Cardiovascular Phenotypic Spectrum of 1p36 Deletion Syndrome

Chromosome 1p36 deletion syndrome is a common genetic anomaly (prevalence: 1 in 5,000-1 in 10,000). Despite reports of cardiovascular involvement, the cardiovascular phenotypic spectrum of patients with 1p36 deletion syndrome is not well characterized. In this article, we reported the clinical course of a full-term African American boy with chromosome 1p36 deletion syndrome and neonatal onset of severe cardiac disease with moderate-to-severe biventricular dysfunction and severe pulmonary hypertension. Early neonatal onset presentation of 1p36 deletion syndrome is rare and might be associated with a more guarded prognosis. This case based study is supplemented by a comprehensive review of cardiovascular involvement in this relatively common genetic syndrome.

Dichorionic Diamniotic Twin Pairs with Complex Congenital Heart Disease

Complex congenital heart disease (CHD) in each of dichorionic diamniotic (DiDi) twin pairs is extremely rare and has not been well characterized. Four DiDi twin pairs were included in this multi-institutional case series. The congenital cardiac abnormalities noted included tetralogy of Fallot (ToF) with pulmonary atresia and collaterals (n = 1), ToF with absent pulmonary valve (n = 1), ToF (n = 2), discontinuous right pulmonary artery (RPA) (n = 1), tricuspid atresia (TA) with normally related great arteries and pulmonary valve stenosis or atresia (n = 2) and coarctation of aorta (CoA) with bicuspid aortic valve (BAV) and borderline left-sided structures (n = 1). Genetic testing was obtained on seven of the eight twins but did not reveal any causal abnormality. A comprehensive review of literature yielded another 8 DiDi twin pairs with complex CHD. The CHD noted in these twin pairs included ToF (n = 2), CoA (n = 4), corrected transposition of great arteries (ccTGA) (n = 2), truncus arteriosus (n = 2), complete common atrioventricular canal (CCAVC) (n = 2), hypoplastic left heart syndrome (HLHS) (n = 2), Shone's complex (n = 1), and hypoplastic right heart syndrome (HRHS) (n = 1). Limited genetic testing was obtained on 4 of these twins and revealed trisomy 21 in a twin pair. Conotruncal abnormalities (42%), CoA (21%), and abnormalities of the right ventricle, the right ventricular outflow tract and pulmonary arteries (17%) are more prevalent in DiDi twins with complex CHD. Clustering of these abnormalities suggests a possible genetic basis; however, genetic testing was obtained on eleven of the twins, and except for trisomy 21 in a twin pair both of whom had CCAVC, did not reveal any causal abnormality. A major direct genetic contribution is therefore unlikely and like other CHD, the underlying etiopathological basis is likely multifactorial.

Intra-Hisian Wenckebach after surgical closure of conoventricular ventricular septal defect

We report a 5-year-old girl with transient complete atrioventricular (AV) block following surgical closure of a symptomatic conoventricular ventricular septal defect (VSD) which recovered on post-operative day 9. She later presented with exertional dizziness and fatigue. While congenital cardiac defect repairs are occasionally complicated by complete heart block, this patient was found to have intra-Hisian Wenckebach which is rare in the pediatric population and can be very difficult to discern from surface electrocardiograms and by Holter monitoring. Mechanisms of post-surgical AV block, including intra-Hisian Wenckebach, are not well characterized in the pediatric population.

Brugada syndrome in infants (<12 months): A case report and literature review

While Brugada syndrome (BrS) is well described in adults and older children, presentation of BrS within the first 12 months of life is rare and therefore poorly characterized. We report a 7-year-old male with a malignant BrS phenotype with onset at 8 months of age, leading to multiple ventricular tachycardia (VT) and ventricular fibrillation (VF) related cardiac arrests and ultimately his death. The report is supplemented by a comprehensive review of existing literature on infantile-onset BrS and unique features in this population are discussed.

Outcomes Associated With Early vs. Delayed Invasive Strategy in NSTEMI Complicated by High Degree AV Block: A Nationwide Analysis

Background: High degree atrioventricular block (HDAVB) is an uncommon complication of non-ST-segment elevation myocardial infarction (NSTEMI) that frequently necessitates pacemaker implantation. This contemporary analysis compares need for pacemaker implantation based on the timing of intervention in acute NSTEMI complicated by HDAVB.Methods: We used 2016-2017 National Inpatient Sample database to identify admissions with NSTEMI and HDAVB. Time to coronary intervention from initial admission was used to segregate the admissions into two groups: early invasive strategy (EIS) (<24 hours) and delayed invasive strategy (DIS) (>24 hours). Multivariable linear and logistic regression analysis was performed to compare in-hospital outcomes among the two groups.Results: Out of 949,984 NSTEMI related admissions, coexistent HDAVB was present in 0.7% (n=6725) patients. Amongst those, 55.61% (n=3740) hospitalizations included invasive intervention (EIS=1320, DIS=2420). Patients treated with EIS were younger (69.95 years vs. 72.38 years, P<0.05) and had concomitant cardiogenic shock. Contrarily, prevalence of chronic kidney disease, heart failure, and pulmonary hypertension was higher in DIS group. EIS was associated with lower length of stay and total hospitalization cost. In-hospital mortality and pacemaker implantation rates were not significantly different between patients in the EIS and DIS groups.Conclusion: HDAVB is a rare complication of NSTEMI and often associated with right coronary artery disease. The timing of revascularization does not appear to influence the rate of pacemaker placement in NSTEMI complicated by HDAVB. Further studies are needed to assess if early invasive strategy can benefit all patients with NSTEMI and HDAVB.

Applying Practice Analysis to Develop a New Test Content Outline for the Pediatric Cardiology Certification Examination

The evolving breadth and complexity of the contemporary pediatric cardiology specialty requires regular, systematic analysis of the practice to ensure that training and certification requirements address the demands of real-world clinical experience. We report the process of the American Board of Pediatrics (ABP) for conducting such a practice analysis and revising the test content outline (TCO) for the pediatric cardiology subspecialty certification exam. A panel of 15 pediatric cardiologists conducted seven 2-h virtual meetings, during which they identified 37 unique tasks that represent the work a pediatric cardiologist may reasonably expect to perform within the first 5 years after training. These tasks were grouped into nine performance domains, similar to the entrustable professional activities (EPA), previously endorsed by the ABP in collaboration with the pediatric cardiology education community, and which represent the critical activities of the profession. The panel then enumerated the knowledge, skills, and abilities necessary to perform each task. These deliberations resulted in two work products: a practice analysis document (PAD) and subspecialty board TCO based on testable knowledge, skills, and abilities. Survey assessments of the panel's work were then distributed to pediatric cardiology fellowship program directors and to practicing pediatric cardiologists for their input, which largely aligned with the panel's recommendations. Survey responses were considered in the final revisions of the PAD and TCO. This approach to practice analysis proved to be an efficient process for describing the work performed by today's pediatric cardiologists and the knowledge, skills, and abilities needed to competently perform that work.

mRNA Coronavirus Disease 2019 Vaccine-Associated Myopericarditis in Adolescents: A Survey Study

In this survey study of institutions across the US, marked variability in evaluation, treatment, and follow-up of adolescents 12 through 18 years of age with mRNA coronavirus disease 2019 (COVID-19) vaccine-associated myopericarditis was noted. Only one adolescent with life-threatening complications was reported, with no deaths at any of the participating institutions.

Atrial Fibrillation Management: A Comprehensive Review with a Focus on Pharmacotherapy, Rate, and Rhythm Control Strategies

Atrial fibrillation (AF) is an increasingly common arrhythmia encountered in clinical practice that leads to a substantial increase in utilization of healthcare services and a decrease in the quality of life of patients. The prevalence of AF will continue to increase as the population ages and develops cardiac comorbidities; thus, prompt and effective treatment is important to help mitigate systemic resource utilization. Treatment of AF involves two tenets: prevention of stroke and systemic embolism and symptom control with either a rate or a rhythm control strategy. Historically, due to the safe nature of medications like beta-blockers and non-dihydropyridine calcium channel blockers, used in rate control, it has been the initial strategy used for symptom control in AF. Newer data suggest that a rhythm control strategy with antiarrhythmic medications with or without catheter ablation may lead to a reduction in major adverse cardiovascular events, particularly in patients newly diagnosed with AF. Modulation of factors that promote AF or its complications is another important aspect of the overall holistic management of AF. This review provides a comprehensive focus on the management of patients with AF and an in-depth review of pharmacotherapy of AF in the rate and rhythm control strategies.

Clinico-histopathological correlation of symptomatic left main coronary artery electrocardiographic ischemia pattern in a young child with hypertrophic cardiomyopathy

The specific electrocardiographic (ECG) pattern of left main coronary artery ischemia is exceptionally rare in children and under recognized. Occasional reports are bereft of a detailed mechanistic ECG description and limited to dissection, spasm, or anomalous origin of the left main coronary artery. An association with pediatric hypertrophic cardiomyopathy (HCM) is hitherto unreported. We furbish a detailed electrocardiographic description of this entity in the unusual setting of a 4-year-old child with HCM with a restrictive phenotype and exertional symptoms consistent with myocardial ischemia. Heart transplant was performed for this rare indication. Histopathology of the explanted heart in particular revealed left main coronary artery narrowing and provided us with a unique window of opportunity to correlate with clinical findings. The pathophysiology was also likely exacerbated by diffuse sub endocardial ischemia in the milieu of left ventricular hypertrophy with elevated end diastolic pressures. We anticipate that this illustrative case will help contextualize this as well as pediatric scenarios in which the 'left main ischemia' ECG pattern can be encountered and foster an accurate electrocardiographic recognition of this entity in children.

Myopericarditis after messenger RNA Coronavirus Disease 2019 Vaccination in Adolescents 12 to 18 Years of Age

OBJECTIVES

To characterize the clinical course and outcomes of children 12-18 years of age who developed probable myopericarditis after vaccination with the Pfizer-BioNTech (BNT162b2) coronavirus disease 2019 (COVID-19) messenger RNA (mRNA) vaccine.

STUDY DESIGN

A cross-sectional study of 25 children, aged 12-18 years, diagnosed with probable myopericarditis after COVID-19 mRNA vaccination as per the Centers for Disease Control and Prevention criteria for myopericarditis at 8 US centers between May 10, 2021, and June 20, 2021. We retrospectively collected the following data: demographics, severe acute respiratory syndrome coronavirus 2 virus detection or serologic testing, clinical manifestations, laboratory test results, imaging study results, treatment, and time to resolutions of symptoms.

RESULTS

Most (88%) cases followed the second dose of vaccine, and chest pain (100%) was the most common presenting symptom. Patients came to medical attention a median of 2 days (range, <1-20 days) after receipt of Pfizer mRNA COVID-19 vaccination. All adolescents had an elevated plasma troponin concentration. Echocardiographic abnormalities were infrequent, and 92% showed normal cardiac function at presentation. However, cardiac magnetic resonance imaging, obtained in 16 patients (64%), revealed that 15 (94%) had late gadolinium enhancement consistent with myopericarditis. Most were treated with ibuprofen or an equivalent nonsteroidal anti-inflammatory drug for symptomatic relief. One patient was given a corticosteroid orally after the initial administration of ibuprofen or an nonsteroidal anti-inflammatory drug; 2 patients also received intravenous immune globulin. Symptom resolution was observed within 7 days in all patients.

CONCLUSIONS

Our data suggest that symptoms owing to myopericarditis after the mRNA COVID-19 vaccination tend to be mild and transient. Approximately two-thirds of patients underwent cardiac magnetic resonance imaging, which revealed evidence of myocardial inflammation despite a lack of echocardiographic abnormalities.

Extreme hyperthermia-induced arrhythmogenesis

Hyperthermia is defined as an elevated body temperature above the normal range due to a failure of heat regulatory mechanisms. In addition to its effects on other organ systems, hyperthermia is associated with profound cardiovascular effects. We report the sentinel case of a 6-year-old girl with structurally and electrically normal heart, who presented with life-threatening hyperpyrexia-induced ventricular tachycardia, which was refractory to cardioversion and anti-arrhythmics but responded promptly to cooling. We emphasise the lifesaving role of immediate and aggressive cooling in such patients.

Temporal progression of P wave abnormality in a patient with classical or atriopulmonary Fontan

We present the electrocardiographic findings in a 36-year-old female with tricuspid atresia with double-outlet right ventricle and malposition of great arteries who underwent classical or "atriopulmonary" Fontan procedure in childhood. Her electrocardiograms have consistently shown marked intra-atrial delay with an initial positive P wave deflection and terminal negative P deflection in all leads with progressive increase in P wave duration with time. She has had frequent episodes of intra-atrial tachycardia, atrial fibrillation and sinus and post ectopic pauses over the past few years. The findings in our patient, which have not been reported before, illustrate the atrial pathology, which is unique to Fontan physiology, particularly those with classical or atriopulmonary Fontan. We hope that the specific electrocardiographic findings presented will allow for their recognition.

Atypical pathogens associated with cardiac implantable electronic device infections

BACKGROUND

Cardiovascular implantable electronic device (CIED) infections are associated with significant morbidity and mortality making the identification of the causative organism critical. The vast majority of CIED infections are caused by Staphylococcal species. CIED infections associated with atypical pathogens are rare and have not been systematically investigated. The objective of this study is to characterize the clinical course, management and outcome in patients with CIED infection secondary to atypical pathogens.

METHODS

Medical records of all patients who underwent CIED system extraction at the University of Chicago Medical Center between January 2010 and November 2020 were retrospectively reviewed to identify patients with CIED infection. Demographic, clinical, infection-related and outcome data were collected. CIED infections were divided into typical and atypical groups based on the pathogens isolated.

RESULTS

Among 356 CIED extraction procedures, 130 (37%) were performed for CIED infection. Atypical pathogens were found in 5.4% (n = 7) and included Pantoea species (n = 2), Kocuria species (n = 1), Cutibacterium acnes (n = 1), Corynebacterium tuberculostearicum (n = 1), Corynebacterium striatum (n = 1), Stenotrophomonas maltophilia (n = 1), and Pseudozyma ahidis (n = 1). All patients with atypical CIED infections were successfully treated with total system removal and tailored antibiotic therapy. There were no infection-related deaths.

CONCLUSIONS

CIED infections with atypical pathogens were rare and associated with good outcome if diagnosed early and treated with total system removal and tailored antimicrobial therapy. Atypical pathogens cultured from blood, tissue or hardware in patients with CIED infection should be considered pathogens and not contaminants.

PR interval prolongation is significantly associated with aortic root abscess: An age- and gender-matched study

BACKGROUND

Electrocardiographic abnormalities, such as PR interval prolongation, have been anecdotally reported in patients with aortic root abscess (ARA). An electrocardiographic marker may be useful in identifying those patients with aortic valve endocarditis who may progress to ARA. The objective of this study is to evaluate the change in the PR interval in patients with surgically confirmed ARA and compare it to age- and gender-matched controls with echocardiographically or surgically confirmed aortic valve endocarditis but without aortic root abscess and those hospitalized with diagnoses other than endocarditis.

METHODS

Patients were eligible for enrollment if they were 18 years or older and were hospitalized for either ARA, aortic valve endocarditis, or for unrelated reasons and had at least one 12-lead electrocardiogram (ECG) prior to or on the day of hospitalization and at least one ECG after hospitalization but prior to any cardiac surgical procedure. Delta PR interval, defined as the difference between the pre- and post-admission PR interval, was the primary outcome of interest. The patients in the ARA group were age- and gender-matched to patients with aortic valve endocarditis and to those without endocarditis. Comparisons of demographic variables and study outcomes were performed.

RESULTS

Eighteen patients with surgically confirmed ARA were enrolled. These patients were age- and gender-matched to 19 patients with aortic valve endocarditis and 18 patients with no past history or evidence of endocarditis during hospitalization. No difference was noted in the baseline PR interval between the groups. However, the PR interval following admission in the aortic root abscess group (201 ± 66 ms) was significantly longer than the PR interval in both the aortic valve endocarditis (162 ± 27 ms) (24%, p = .009) and no endocarditis (143 ± 24 ms) (40%, p < .001) groups. The primary outcome measure, delta PR interval, was significantly longer in the ARA group (35 ± 51 ms) than no endocarditis (-5 ± 17 ms) (p = .001) and aortic valve endocarditis groups (0.2 ± 18) (p = .003).

CONCLUSIONS

The findings of our study support the notion that the PR interval is more likely to be prolonged in patients with ARA. Since ARA is associated with a high morbidity and mortality, PR interval prolongation in a patient with aortic valve endocarditis should prompt a thorough evaluation for aortic root involvement.

A novel familial SCN5A exon 20 deletion is associated with a heterogeneous phenotype

The SCN5A gene, located on chromosome 3p21, has 28 exons and is a member of the human voltage-gated sodium channel gene family. Genetic variation in SCN5A is associated with a diverse range of phenotypes. Due to incomplete penetrance, delayed expression, inherent low signal-to-noise ratio, and marked phenotypic heterogeneity, rare novel variants in SCN5A could be misinterpreted. Hence, defining the phenotypic characteristics of these rare SCN5A variants in humans is of importance. We describe the phenotypic heterogeneity noted in 4 familial carriers of a rare, previously unreported, large deletion in exon 20 of SCN5A (c.3667-?_c.3840C +?del) and discuss the mechanisms that underlie this heterogeneity.

Resting electrocardiographic differences in ventricular repolarization between children and young adults with congenital heart disease and those with a structurally normal heart are diminished by exercise

OBJECTIVE

Exercise-induced repolarization changes have not been systematically evaluated in children and young adults with congenital heart disease (CHD). We carried out this study to assess the QTc responses during exercise in children and young adults (≤ 21 years) with CHD with comparison to those with structurally normal hearts.

METHODS

Baseline QRS duration, calculated baseline QTc, QTc at 4 min of recovery and delta QTc was measured in 360 exercise stress tests which were performed in 360 subjects (137 stress tests in patients with CHD [CHD group] and 223 stress tests in patients with structurally normal hearts). The effects of presence of CHD and potential confounders on primary outcome measure, change in QTc (delta QTc), and secondary outcome measures (QTc at baseline and QTc at 4 min of recovery) were determined using multiple linear regression analyses.

RESULTS

The baseline QTc and the QTc at 4 min of recovery in the CHD group was longer than patients with structurally normal hearts (respective p values = .00 and .001). No significant difference was noted in delta QTc between the CHD and structurally normal heart groups.

CONCLUSIONS

While patients with CHD had a longer QRS duration and QTc interval at baseline than those with structurally normal hearts, these differences did not persist or augment with exercise.

Isolated left bundle branch block in the young: case reports and review of literature

Isolated left bundle branch block (LBBB) aberrancy is exceedingly rare in the young and its clinical and genetic determinants remain poorly characterized. Furthermore, there is conflicting data on its natural history in the pediatric age group patients. We report the rare phenotype of isolated typical LBBB aberrancy in two healthy children, one of whom carried a likely pathogenic mutation in the coding exon 1 of NKX2-5 (p.Q22R, c.65A > G, rs201442000). Our findings suggest that isolated LBBB aberrancy could be non-progressive in some children, at least in the short term. However, given the paucity of data on this entity, we recommend continued long-term surveillance.

COVID-19 pneumonia in an infant with a hemodynamically significant ventricular septal defect

Reports thus far suggest a mild course for acute COVID-19 infection in children; however, its effects in vulnerable paediatric populations, including children with haemodynamically significant congenital heart disease, have rarely been reported. We therefore report on a 4-month-old Hispanic male with a moderate sized conoventricular ventricular septal defect and pulmonary overcirculation who presented with COVID-19-associated pneumonia.

Fulminant myocarditis and atrial fibrillation in child with acute COVID-19

COVID-19 has manifested with ventricular dysfunction and cardiac arrhythmias, most commonly atrial fibrillation (AFib), in adults. However, very few pediatric patients with acute COVID-19 have had cardiac involvement. AFib, an exceedingly rare arrhythmia in otherwise healthy children, has not been reported in children with COVID-19. We report a 15 year-old girl with acute COVID-19, fulminant myocarditis and AFib.

SIDS associated RYR2 p.Arg2267His variant may lack pathogenicity

Sudden infant death syndrome (SIDS) is the sudden death of an infant under 1 year of age that remains unexplained after death scene and medicolegal investigation, including a complete autopsy and clinical history review. The fatal event typically occurs during sleep and heart rhythm during the event is rarely documented. Large series which have utilized molecular autopsy show that long QT syndrome (LQTS) associated cardiac channel mutations contribute to between 5 and 10% of SIDS deaths. In addition, rare novel RYR2 variants have been identified in SIDS victims. Given the lack of a phenotype, the pathogenicity of these variants is inferred from in vitro studies. We report a family with 5 members (mother and 4 children) who are carriers of a rare RYR2 variant (c.6800G > A, p.Arg2267His [Exon: 45], heterozygous) which has previously been identified in a SIDS victim and shown to confer a gain-of-function CPVT phenotype in vitro. All of these 5 family members including the mother (age range 7 to 41 years) have had negative exercise stress tests, echocardiograms and Holter monitors. These findings suggest that caution should be exercised in inferring pathogenicity of rare RYR2 variants based on in vitro functional data which does not always translate to human phenotype.

Genetic variation in alpha2-adrenoreceptors and heart rate recovery after exercise

Heart rate recovery (HRR) after exercise is an independent predictor of adverse cardiovascular outcomes. HRR is mediated by both parasympathetic reactivation and sympathetic withdrawal and is highly heritable. We examined whether common genetic variants in adrenergic and cholinergic receptors and transporters affect HRR. In our study 126 healthy subjects (66 Caucasians, 56 African Americans) performed an 8 min step-wise bicycle exercise test with continuous computerized ECG recordings. We fitted an exponential curve to the postexercise R-R intervals for each subject to calculate the recovery constant (kr) as primary outcome. Secondary outcome was the root mean square residuals averaged over 1 min (RMS1min), a marker of parasympathetic tone. We used multiple linear regressions to determine the effect of functional candidate genetic variants in autonomic pathways (6 ADRA2A, 1 ADRA2B, 4 ADRA2C, 2 ADRB1, 3 ADRB2, 2 NET, 2 CHT, and 1 GRK5) on the outcomes before and after adjustment for potential confounders. Recovery constant was lower (indicating slower HRR) in ADRA2B 301-303 deletion carriers (n = 54, P = 0.01), explaining 3.6% of the interindividual variability in HRR. ADRA2A Asn251Lys, ADRA2C rs13118771, and ADRB1 Ser49Gly genotypes were associated with RMS1min. Genetic variability in adrenergic receptors may be associated with HRR after exercise. However, most of the interindividual variability in HRR remained unexplained by the variants examined. Noncandidate gene-driven approaches to study genetic contributions to HRR in larger cohorts will be of interest.

Blacks have a greater sensitivity to α1-adrenoceptor-mediated venoconstriction compared with whites

Blacks have increased hemodynamic responses to both physiological and pharmacological adrenergic stimulation compared with whites, and this may contribute to the greater prevalence of hypertension in this ethnic group. A small study suggested enhanced α1-adrenoreceptor-mediated arterial vasoconstriction in the forearm vasculature of blacks compared with whites, but it is unknown whether this reflects a generalized vascular phenomenon. The objective of this study was to examine the hypothesis that there are ethnic differences in venous α1-adrenoreceptor responsiveness. Using a linear variable differential transformer, we measured local dorsal hand vein responses to increasing doses of the selective α1-adrenoreceptor agonist, phenylephrine, in 106 subjects (64 whites and 42 blacks). There was wide interindividual variability in responses to phenylephrine. The dose that produced 50% of maximal constriction (ED50) ranged from 11 to 5442 ng/min, and maximal venoconstriction (Emax) ranged from 13.5% to 100%. Blacks (geometric mean ED50 =172 ng/min; 95% confidence interval, 115-256 ng/min) were more sensitive to phenylephrine than whites (310 ng/min; 95% confidence interval, 222-434 ng/min; unadjusted P=0.026; adjusted P=0.003). Median Emax was slightly higher in blacks (89%; interquartile range, 82% to 98%) compared with whites (85%; interquartile range, 75% to 95%; P=0.07). Taken together with previous findings in arterial vessels, our results suggest a generalized increased sensitivity to α1-adrenoreceptor-mediated vasoconstriction in blacks. Increased vascular α-adrenoreceptor sensitivity could predispose to hypertension, and future studies addressing the contribution of this mechanism to ethnic differences in the prevalence of hypertension will be of interest.

CYP2A6 genetic variation and dexmedetomidine disposition

PURPOSE

There is a large interindividual variability in dexmedetomidine dose requirements for sedation of patients in intensive care units (ICU). Cytochrome P450 2A6 (CYP2A6) mediates an important route of dexmedetomidine metabolism, and genetic variation in CYP2A6 affects the clearance of other substrate drugs. We examined whether CYP2A6 genotypes affect dexmedetomidine disposition.

METHODS

In 43 critically ill ICU patients receiving dexmedetomidine infusions adjusted to achieve the desired level of sedation, we determined a median of five plasma dexmedetomidine concentrations each. Forty subjects were genotyped for five common CYP2A6 alleles and grouped into normal (n = 33), intermediate (n = 5), and slow metabolizers (n = 2).

RESULTS

Using a Bayesian hierarchical nonlinear mixture model, estimated dexmedetomidine clearance was 49.1 L/h (posterior mean; 95% credible interval 41.4-57.6 L/h). There were no significant differences in dexmedetomidine clearance among normal, intermediate, and slow CYP2A6 metabolizer groups.

CONCLUSION

Genetic variation in CYP2A6 does not appear to be an important determinant of dexmedetomidine clearance in ICU patients.

A Bayesian hierarchical nonlinear mixture model in the presence of artifactual outliers in a population pharmacokinetic study

The purpose of this study is to develop a statistical methodology to handle a large proportion of artifactual outliers in a population pharmacokinetic (PK) modeling. The motivating PK data were obtained from a population PK study to examine associations between PK parameters such as clearance of dexmedetomidine (DEX) and cytochrome P450 2A6 phenotypes. The blood samples were sparsely sampled from patients in intensive care units (ICUs) while different doses of DEX were continuously infused. Conventional population PK analysis of these data revealed several challenges and intricacies. Especially, there was strong evidence that some plasma drug concentrations were artifactually high and likely contaminated with the infused drug due to blood sampling processes that are sometimes unavoidable in an ICU setting. If not addressed, or if arbitrarily excluded, these outlying values could lead to biased estimates of PK parameters and miss important relationships between PK parameters and covariates due to increased variability. We propose a novel population PK model, a Bayesian hierarchical nonlinear mixture model, to accommodate the artifactual outliers using a finite mixture as the residual error model. Our results showed that the proposed model handles the outliers well. We also conducted simulation studies with a varying proportion of the outliers. These simulation results showed that the proposed model can accommodate the outliers well so that the estimated PK parameters are less biased.

GRK5 Gln41Leu polymorphism is not associated with sensitivity to beta(1)-adrenergic blockade in humans

AIMS

A common, functionally significant polymorphism in GRK5 (Gln41Leu) encodes a gain-of-function enzyme that enhances desensitization of the beta(1)-adrenergic receptor. GRK5 Leu41 has been postulated to confer endogenous 'genetic beta-blockade' and contribute to an attenuated response to beta-blockers in black subjects. The effects of this GRK5 variant on sensitivity to a beta-blocker have not been studied in humans. We hypothesized that the GRK5 Gln41Leu variant contributes to interindividual variability in response to beta-blockade and to the ethnic difference in sensitivity between black and Caucasian individuals.

MATERIALS & METHODS

We measured the heart rate at rest and during a graded incremental exercise in 154 healthy subjects (85 white and 69 black) before and after an oral administration of 25 mg atenolol. We determined the genotypes of GRK5 (Gln41Leu), beta(1)-adrenergic receptor (ADRB1 Ser49Gly and Arg389Gly) genotypes and plasma atenolol concentrations. The effects of genotype and covariates on sensitivity to atenolol, measured as the reduction in exercise-induced tachycardia, were determined using multiple regression analyses.

RESULTS

The minor allele frequency of GRK5 Leu41 was 32.6% in blacks and 0% in whites. Black individuals were less sensitive to atenolol than white individuals (p < or = 0.011) but this was not explained by the GRK5 genotype. The GRK5 genotype had no effect on resting heart rate before (p = 0.61) and after adjustment for age, sex, ethnicity, atenolol concentrations, BMI and ADRB1 genotypes (p = 0.81). The decrease in heart rate after atenolol administration did not differ significantly according to the GRK5 genotype at rest or after exercise, before (all p > 0.14) and after statistical adjustment for covariates (all p > 0.17).

CONCLUSION

The GRK5 Gln41Leu polymorphism does not affect sensitivity to the beta(1)-adrenergic blocker, atenolol, during acute physiological adrenergic stimulation, nor does it contribute to the ethnic differences in sensitivity to atenolol among black and Caucasian individuals.

Change in mRNA Expression after Atenolol, a Beta-adrenergic Receptor Antagonist and Association with Pharmacological Response

AIMS: Genetic determinants of variability in response to beta-blockers are poorly characterized. We defined changes in mRNA expression after a beta-blocker to identify novel genes that could affect response and correlated these with inhibition of exercise-induced tachycardia, a measure of beta-blocker sensitivity. METHODS: Nine subjects exercised before and after a single oral dose of 25mg atenolol and mRNA gene expression was measured using an Affymetrix GeneChip Human Gene 1.0 ST Array. The area under the heart rate-exercise intensity curve (AUC) was calculated for each subject; the difference between post- and pre-atenolol AUCs (Delta AUC), a measure of beta-blocker response, was correlated with the fold-change in mRNA expression of the genes that changed more than 1.3-fold. RESULTS: Fifty genes showed more than 1.3-fold increase in expression; 9 of these reached statistical significance (P < 0.05). Thirty-six genes had more than 1.3-fold decrease in expression after atenolol; 6 of these reached statistical significance (P < 0.05). Change in mRNA expression of FGFBP2 and Probeset ID 8118979 was significantly correlated with atenolol response (P = 0.03 and 0.02, respectively). CONCLUSION: The expression of several genes not previously identified as part of the adrenergic signaling pathway changed in response to a single oral dose of atenolol. Variation in these genes could contribute to unexplained differences in response to beta-blockers.

Myocardial cell injury is common in children with septic shock

OBJECTIVE

To determine the prevalence of myocardial cell injury in children with septic shock by estimating the levels of biochemical markers of myocardial injury, troponin I (TnI) and creatine kinase MB (CK-MB).

PATIENTS

Children aged 3 months to 16 years were admitted to paediatric intensive care unit (PICU) with septic shock. Children with sepsis without shock and children with hypovolaemic shock were enrolled as controls.

MEASUREMENTS AND MAIN RESULTS

Serum TnI and CK-MB levels were measured at admission and serially at 24 h, 48 h and 96 h in children with septic shock, while baseline measurement of the same markers was taken from the controls. In total, 88% (15/18) of children with septic shock had elevated TnI levels compared with 25% (5/20) with sepsis and 6.7% (1/15) with hypovolaemic shock (p < 0.001). Serial TnI levels at admission, 24 h, 48 h and 96 h were higher in the nonsurvivors. There was a positive correlation between the baseline TnI levels and the predicted mortality using the paediatric index of mortality (PIM2) scores at admission (r = 0.51, p = 0.03).

CONCLUSION

A majority of children with septic shock have evidence of myocardial cell injury. The estimation of serum TnI levels may help in better prognostication of children with septic shock.

Prevalence of MTHFR C677T polymorphism in north Indian mothers having babies with Trisomy 21 Down syndrome

Recent studies have evaluated possible links between polymorphisms in maternal folate metabolism genes and Down syndrome. Some of these studies show a significantly increased prevalence of the C677T polymorphism of the 5,10-methylene tetrahydrofolate reductase (NADPH) gene (MTHFR) among mothers who have had babies with Down syndrome. This study examined the prevalence of the MTHFR C677T polymorphism among 104 north Indian mothers of babies with Down syndrome and 109 control mothers. The prevalence of MTHFR C677T polymorphism observed among mothers of babies with Down syndrome was 28% compared to 35% in controls (C677T/T677T). There was no significant difference between the two groups (p = 0.294). Mean homocysteine level in mothers of children with Down syndrome was lower than the level in the controls. Our data suggests that the MTHFR C677T polymorphism is not associated with an increased risk of Down syndrome in the north Indian population. Homocysteine levels in our study were higher when compared to other studies. Methylcobolamin and folate deficiency or use of random samples for homocysteine determination could possibly account for this observation.