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Background Interpretation of ECGs in athletes is complicated by physiological changes related to training. The purpose of this study was to determine the accuracy of ECG interpretation in athletes among different physician specialties, with and without use of a standised ECG criteria tool. Methods Physicians were asked to interpret 40 ECGs (28 normal ECGs from college athletes randomised with 12 abnormal ECGs from individuals with known ciovascular pathology) and classify each ECG as (1) 'normal or variant - no further evaluation and testing needed' or (2) 'abnormal - further evaluation and testing needed.' After reading the ECGs, participants received a two-page ECG criteria tool to guide interpretation of the ECGs again. Results A total of 60 physicians participated: 22 primary care (PC) residents, 16 PC attending physicians, 12 sports medicine (SM) physicians and 10 ciologists. At baseline, the total number of ECGs correctly interpreted was PC residents 73%, PC attendings 73%, SM physicians 78% and ciologists 85%. With use of the ECG criteria tool, all physician groups significantly improved their accuracy (p<0.0001): PC residents 92%, PC attendings 90%, SM physicians 91% and ciologists 96%. With use of the ECG criteria tool, specificity improved from 70% to 91%, sensitivity improved from 89% to 94% and there was no difference comparing ciologists versus all other physicians (p=0.053). Conclusions Providing standised criteria to assist ECG interpretation in athletes significantly improves the ability to accurately distinguish normal from abnormal findings across physician specialties, even in physicians with little or no experience. [ABSTRACT FROM AUTHOR]

Sudden cardiac death (SCD) is the leading cause of death in athletes during sport. Whether obtained for screening or diagnostic purposes, an ECG increases the ability to detect underlying cardiovascular conditions that may increase the risk for SCD. In most countries, there is a shortage of physician expertise in the interpretation of an athlete's ECG. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from abnormal findings suggestive of pathology. On 13-14 February 2012, an international group of experts in sports cardiology and sports medicine convened in Seattle, Washington, to define contemporary standards for ECG interpretation in athletes. The objective of the meeting was to develop a comprehensive training resource to help physicians distinguish normal ECG alterations in athletes from abnormal ECG findings that require additional evaluation for conditions associated with SCD. [ABSTRACT FROM AUTHOR]

This American Heart Association/American College of Cardiology scientific statement on clinical considerations for competitive sports participation for athletes with cardiovascular abnormalities or diseases is organized into 11 distinct sections focused on sports-specific topics or disease processes that are relevant when considering the potential risks of adverse cardiovascular events, including sudden cardiac arrest, during competitive sports participation. Task forces comprising international experts in sports cardiology and the respective topics covered were assigned to each section and prepared specific clinical considerations tables for practitioners to reference. Comprehensive literature review and an emphasis on shared decision-making were integral in the writing of all clinical considerations presented., (Copyright © 2025 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Youth and adult participation in sports continues to increase, and athletes may be diagnosed with potentially arrhythmogenic cardiac conditions. This international multidisciplinary document is intended to guide electrophysiologists, sports cardiologists, and associated health care team members in the diagnosis, treatment, and management of arrhythmic conditions in the athlete with the goal of facilitating return to sport and avoiding the harm caused by restriction. Expert, disease-specific risk assessment in the context of athlete symptoms and diagnoses is emphasized throughout the document. After appropriate risk assessment, management of arrhythmias geared toward return to play when possible is addressed. Other topics include shared decision-making and emergency action planning. The goal of this document is to provide evidence-based recommendations impacting all areas in the care of athletes with arrhythmic conditions. Areas in need of further study are also discussed., (Copyright © 2024 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Pediatric ECG standards have been defined without echocardiographic confirmation of normal anatomy. The Pediatric Heart Network Normal Echocardiogram Z-score Project provides a racially diverse group of healthy children with normal echocardiograms. We hypothesized that ECG and echocardiographic measures of left ventricular (LV) dimensions are sufficiently correlated in healthy children to imply a clinically meaningful relationship. This was a secondary analysis of a previously described cohort including 2170 digital ECGs. The relationship between 6 ECG measures associated with LV size were analyzed with LV Mass (LVMass-z) and left ventricular end-diastolic volume (LVEDV-z) along with 11 additional parameters. Pearson or Spearman correlations were calculated for the 78 ECG-echocardiographic pairs with regression analyses assessing the variance in ECG measures explained by variation in LV dimensions and demographic variables. ECG/echocardiographic measurement correlations were significant and concordant in 41/78 (53%), though many were significant and discordant (13/78). Of the 6 ECG parameters, 5 correlated in the clinically predicted direction for LV Mass-z and LVEDV-z. Even when statistically significant, correlations were weak (0.05-0.24). R 2 was higher for demographic variables than for echocardiographic measures or body surface area in all pairs, but remained weak (R 2  ≤ 0.17). In a large cohort of healthy children, there was a positive association between echocardiographic measures of LV size and ECG measures of LVH. These correlations were weak and dependent on factors other than echocardiographic or patient derived variables. Thus, our data support deemphasizing the use of solitary, traditional measurement-based ECG markers traditionally thought to be characteristic of LVH as standalone indications for further cardiac evaluation of LVH in children and adolescents., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Nitric oxide synthase 3 (NOS3) is a major vasoprotective enzyme that catalyzes the conversion of l-arginine to nitric oxide (NO) in response to a significant number of signaling pathways. Here, we provide evidence that NOS3 interactions with MAP kinases have physiological relevance. Binding interactions of NOS3 with c-Jun N-terminal kinase (JNK1 α1 ), p38α, and ERK2 were characterized using optical biosensing with full-length NOS3 and NOS3 specific peptides and phosphopeptides. Like p38α and ERK2, JNK1 α1 exhibited high-affinity binding to full-length NOS3 (K D 15 nm). Rate constants exhibited fast-on, slow-off binding (k on  = 4106 m -1 s -1 ; k off  = 6.2 × 10 -5  s -1 ). Further analysis using synthetic NOS3 peptides revealed two MAP kinase binding sites unique to NOS3. p38α evinced similar affinity with both NOS3 binding sites. For ERK2 and JNK1 α1, the affinity at the two sites differed. However, NOS3 peptides with a phosphate at either S114 or S633 did not meaningfully interact with the kinases. Immunoblotting revealed that each kinase phosphorylated NOS3 with a unique pattern. JNK1 α1 predominantly phosphorylated NOS3 at S114, ERK2 at S600, and p38α phosphorylated both residues. In vitro production of NO was unchanged by phosphorylation at these sites. In human microvascular endothelial cells, endogenous interactions of all the MAP kinases with NOS3 were captured using proximity ligation assay in resting cells. Our results underscore the importance of MAP kinase interactions, identifying two unique NOS3 interaction sites with potential for modulation by MAP kinase phosphorylation (S114) and other signaling inputs, like protein kinase A (S633)., (© 2022 The Authors. FEBS Open Bio published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

Objectives: We assessed whether the presence and character of a cardiac murmur in adolescents were associated with structural heart disease that confers risk of sudden cardiac death (SCD)., Methods: We performed a retrospective analysis of 15 141 adolescents age 12-19 who underwent a heart screen with history, physical examination and ECG. Participants with any screening abnormality underwent an echocardiogram for the assessment of structural heart disease. Murmurs were classified as physiological or pathological according to standard clinical criteria, and participants with murmurs were compared with a comparison group without murmurs. The primary outcome was echocardiogram-detected structural heart disease associated with SCD., Results: 905 participants with a cardiac murmur (mean age 15.8; 58% male) and 4333 participants without a murmur (comparison group; mean age 15.8; 55% male) had an echocardiogram to detect structural heart disease. 743 (82%) murmurs were described as physiological and 162 (18%) as pathological. Twenty-five (2.8%) participants with murmurs and 61 (1.4%) participants without murmurs had structural heart disease. Three (0.3%) participants in the murmur group were diagnosed with hypertrophic cardiomyopathy (HCM) which was the only identified condition associated with SCD. Two participants with HCM had physiological murmurs, one had a pathological murmur, and all three had an abnormal ECG. The most common minor structural heart disease was bicuspid aortic valve in both the murmur (7; 0.8%) and comparison (20; 0.5%) groups. The positive predictive value of physiological versus pathological murmurs for identifying any structural heart disease was 2.4% versus 4.3% (p=0.21), respectively. The positive predictive value of having any murmur versus no murmur for identifying structural heart disease was 2.8% versus 1.4% (p=0.003), respectively., Conclusions: In adolescents, the traditional classification of cardiac murmurs as 'physiologic' or 'pathologic' does not differentiate for structural heart disease that puts individuals at risk for SCD. We recommend ECG evaluation in all patients with a cardiac murmur found during preparticipation screening to increase detection of HCM., Competing Interests: Competing interests: JAD is Deputy Editor of BJSM., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

There are multiple conditions that can make children prone to having a sudden cardiac arrest (SCA) or sudden cardiac death (SCD). Efforts have been made by multiple organizations to screen children for cardiac conditions, but the emphasis has been on screening before athletic competition. This article is an update of the previous American Academy of Pediatrics policy statement of 2012 that addresses prevention of SCA and SCD. This update includes a comprehensive review of conditions that should prompt more attention and cardiology evaluation. The role of the primary care provider is of paramount importance in the evaluation of children, particularly as they enter middle school or junior high. There is discussion about whether screening should find any cardiac condition or just those that are associated with SCA and SCD. This update reviews the 4 main screening questions that are recommended, not just for athletes, but for all children. There is also discussion about how to handle post-SCA and SCD situations as well as discussion about genetic testing. It is the goal of this policy statement update to provide the primary care provider more assistance in how to screen for life-threatening conditions, regardless of athletic status., Competing Interests: POTENTIAL CONFLICT OF INTEREST: The authors have no potential conflicts of interest relevant to this article to disclose., (Copyright © 2021 by the American Academy of Pediatrics.)

Background Preparticipation cardiovascular screening in athletes is fully endorsed by major medical societies, yet the most effective screening protocol remains debated. We prospectively compared the performance of the American Heart Association ( AHA ) 14-point screening evaluation and a resting ECG for cardiovascular screening of high school athletes. Methods and Results Competitive athletes participating in organized high school or premier/select level sports underwent cardiovascular screening using the AHA 14-point history and physical examination, and an ECG interpreted with the Seattle Criteria. A limited echocardiogram was performed for all screening abnormalities. The primary outcome measure was identification of a cardiovascular disorder associated with sudden cardiac death. From October 2014 to June 2017, 3620 high school athletes (median age, 16 years; range 13-19; 46.2% female; 78.6% white, 8.0% black) were screened. One or more positive responses to the AHA 14-point questionnaire were present in 814 (22.5%) athletes. The most common history responses included chest pain (8.1%), family history of inheritable conditions (7.3%), and shortness of breath (6.4%). Abnormal physical examination was present in 356 (9.8%) athletes, and 103 (2.8%) athletes had an abnormal ECG . Sixteen (0.4%) athletes had conditions associated with sudden cardiac death. The sensitivity (18.8%), specificity (68.0%), and positive predictive value (0.3%) of the AHA 14-point evaluation was substantially lower than the sensitivity (87.5%), specificity (97.5%), and positive predictive value (13.6%) of ECG . Conclusions The AHA 14-point evaluation performs poorly compared with ECG for cardiovascular screening of high school athletes. The use of consensus-derived history questionnaires as the primary tool for cardiovascular screening in athletes should be reevaluated.

NADH-quinone oxidoreductase (complex I) is the largest and most complicated enzyme complex of the mitochondrial respiratory chain. It is the entry site into the respiratory chain for most of the reducing equivalents generated during metabolism, coupling electron transfer from NADH to quinone to proton translocation, which in turn drives ATP synthesis. Dysfunction of complex I is associated with neurodegenerative diseases such as Parkinson's and Alzheimer's, and it is proposed to be involved in aging. Complex I has one non-covalently bound FMN, eight to 10 iron-sulfur clusters, and protein-associated quinone molecules as electron transport components. Electron paramagnetic resonance (EPR) has previously been the most informative technique, especially in membrane in situ analysis. The structure of complex 1 has now been resolved from a number of species, but the mechanisms by which electron transfer is coupled to transmembrane proton pumping remains unresolved. Ubiquinone-10, the terminal electron acceptor of complex I, is detectable by EPR in its one electron reduced, semiquinone (SQ) state. In the aerobic steady state of respiration the semi-ubiquinone anion has been observed and studied in detail. Two distinct protein-associated fast and slow relaxing, SQ signals have been resolved which were designated SQNf and SQNs. This review covers a five decade personal journey through the field leading to a focus on the unresolved questions of the role of the SQ radicals and their possible part in proton pumping.

Background: Interpretation of pediatric ECGs is limited by lack of accurate sex- and race-specific normal reference values obtained with modern technology for all ages. We sought to obtain contemporary digital ECG measurements in healthy children from North America, to evaluate the effects of sex and race, and to compare our results to commonly used published datasets., Methods: Digital ECGs (12-lead) were retrospectively collected for children ≤18 years old with normal echocardiograms at 19 centers in the Pediatric Heart Network. Patients were classified into 36 groups: 6 age, 2 sex, and 3 race (white, black, and other/mixed) categories. Standard intervals and amplitudes were measured; mean±SD and 2nd/98th percentiles were determined by age group, sex, and race. For each parameter, multivariable analysis, stratified by age, was conducted using sex and race as predictors. Parameters were compared with 2 large pediatric ECG data sets., Results: Among ECGs from 2400 children, significant differences were found by sex and race categories. The corrected QT interval in lead II was greater for girls compared with boys for age groups ≥3 years ( P ≤0.03) and for whites compared with blacks for age groups ≥12 years ( P <0.05). The R wave amplitude in V6 was greater for boys compared with girls for age groups ≥12 years ( P <0.001), for blacks compared with white or other race categories for age groups ≥3 years ( P ≤0.006), and greater compared with a commonly used public data set for age groups ≥12 years ( P <0.0001)., Conclusions: In this large, diverse cohort of healthy children, most ECG intervals and amplitudes varied by sex and race. These differences have important implications for interpreting pediatric ECGs in the modern era when used for diagnosis or screening, including thresholds for left ventricular hypertrophy., (© 2018 American Heart Association, Inc.)

Heparin is used to decrease the risk of thromboembolic complications during electrophysiology studies (EPS); however, there is wide practice variation and minimal evidence to guide heparin dosing, particularly in pediatric patients. This study retrospectively analyzed heparin dosing and response, measured via activated clotting time (ACT), in patients undergoing EPS and used these data (pre-protocol cohort, n = 40), as well as guidance from available literature to implement a standardized heparin protocol (phase 1, n = 43). We utilized quality improvement methodology to refine this protocol (phase 2, n = 40) to improve therapeutic heparin response. Prior to the protocol, patients achieved therapeutic ACT levels (250-350 s) only 35% of the time which improved to 60% during phase 1 (p < 0.05) and to 73% during phase 2 (p < 0.001 compared to pre-protocol). There were no thromboses or significant adverse events in any group. These results demonstrate the effectiveness of a standardized heparin protocol in achieving effective antithrombotic therapy during left-sided pediatric EPS.

Sudden cardiac death (SCD) is the leading cause of mortality in athletes during sport. A variety of mostly hereditary, structural, or electrical cardiac disorders are associated with SCD in young athletes, the majority of which can be identified or suggested by abnormalities on a resting 12-lead electrocardiogram (ECG). Whether used for diagnostic or screening purposes, physicians responsible for the cardiovascular care of athletes should be knowledgeable and competent in ECG interpretation in athletes. However, in most countries a shortage of physician expertise limits wider application of the ECG in the care of the athlete. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology. Since the original 2010 European Society of Cardiology recommendations for ECG interpretation in athletes, ECG standards have evolved quickly over the last decade; pushed by a growing body of scientific data that both tests proposed criteria sets and establishes new evidence to guide refinements. On 26-27 February 2015, an international group of experts in sports cardiology, inherited cardiac disease, and sports medicine convened in Seattle, Washington, to update contemporary standards for ECG interpretation in athletes. The objective of the meeting was to define and revise ECG interpretation standards based on new and emerging research and to develop a clear guide to the proper evaluation of ECG abnormalities in athletes. This statement represents an international consensus for ECG interpretation in athletes and provides expert opinion-based recommendations linking specific ECG abnormalities and the secondary evaluation for conditions associated with SCD.

Aims: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an ion channelopathy characterized by ventricular arrhythmia during exertion or stress. Mutations in RYR2-coded Ryanodine Receptor-2 (RyR2) and CASQ2-coded Calsequestrin-2 (CASQ2) genes underlie CPVT1 and CPVT2, respectively. However, prognostic markers are scarce. We sought to better characterize the phenotypic and genotypic spectrum of CPVT, and utilize molecular modelling to help account for clinical phenotypes., Methods and Results: This is a Pediatric and Congenital Electrophysiology Society multicentre, retrospective cohort study of CPVT patients diagnosed at <19 years of age and their first-degree relatives. Genetic testing was undertaken in 194 of 236 subjects (82%) during 3.5 (1.4-5.3) years of follow-up. The majority (60%) had RyR2-associated CPVT1. Variant locations were predicted based on a 3D structural model of RyR2. Specific residues appear to have key structural importance, supported by an association between cardiac arrest and mutations in the intersubunit interface of the N-terminus, and the S4-S5 linker and helices S5 and S6 of the RyR2 C-terminus. In approximately one quarter of symptomatic patients, cardiac events were precipitated by only normal wakeful activities., Conclusion: This large, multicentre study identifies contemporary challenges related to the diagnosis and prognostication of CPVT patients. Structural modelling of RyR2 can improve our understanding severe CPVT phenotypes. Wakeful rest, rather than exertion, often precipitated life-threatening cardiac events., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2017. For Permissions, please email: journals.permissions@oup.com.)

Sudden cardiac death (SCD) is the leading cause of mortality in athletes during sport. A variety of mostly hereditary, structural or electrical cardiac disorders are associated with SCD in young athletes, the majority of which can be identified or suggested by abnormalities on a resting 12-lead electrocardiogram (ECG). Whether used for diagnostic or screening purposes, physicians responsible for the cardiovascular care of athletes should be knowledgeable and competent in ECG interpretation in athletes. However, in most countries a shortage of physician expertise limits wider application of the ECG in the care of the athlete. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology. Since the original 2010 European Society of Cardiology recommendations for ECG interpretation in athletes, ECG standards have evolved quickly, advanced by a growing body of scientific data and investigations that both examine proposed criteria sets and establish new evidence to guide refinements. On 26-27 February 2015, an international group of experts in sports cardiology, inherited cardiac disease, and sports medicine convened in Seattle, Washington (USA), to update contemporary standards for ECG interpretation in athletes. The objective of the meeting was to define and revise ECG interpretation standards based on new and emerging research and to develop a clear guide to the proper evaluation of ECG abnormalities in athletes. This statement represents an international consensus for ECG interpretation in athletes and provides expert opinion-based recommendations linking specific ECG abnormalities and the secondary evaluation for conditions associated with SCD., Competing Interests: Competing interests: None declared., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Sudden cardiac death (SCD) is the leading cause of mortality in athletes during sport. A variety of mostly hereditary, structural, or electrical cardiac disorders are associated with SCD in young athletes, the majority of which can be identified or suggested by abnormalities on a resting 12-lead electrocardiogram (ECG). Whether used for diagnostic or screening purposes, physicians responsible for the cardiovascular care of athletes should be knowledgeable and competent in ECG interpretation in athletes. However, in most countries a shortage of physician expertise limits wider application of the ECG in the care of the athlete. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology. Since the original 2010 European Society of Cardiology recommendations for ECG interpretation in athletes, ECG standards have evolved quickly over the last decade; pushed by a growing body of scientific data that both tests proposed criteria sets and establishes new evidence to guide refinements. On February 26-27, 2015, an international group of experts in sports cardiology, inherited cardiac disease, and sports medicine convened in Seattle, Washington, to update contemporary standards for ECG interpretation in athletes. The objective of the meeting was to define and revise ECG interpretation standards based on new and emerging research and to develop a clear guide to the proper evaluation of ECG abnormalities in athletes. This statement represents an international consensus for ECG interpretation in athletes and provides expert opinion-based recommendations linking specific ECG abnormalities and the secondary evaluation for conditions associated with SCD., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

Nitric oxide (NO) is a gaseous compound that serves as a signaling molecule in cellular interactions. In the vasculature, NO is synthesized from endogenous agents by endothelial nitric oxide synthase (eNOS) where it plays key roles in several functions related to homeostasis, adaptation, and development. Recent experimental studies have revealed cycles of increasing and decreasing NO production when eNOS is stimulated by factors such as glucose or insulin. We offer a mathematical model of a generic amino acid receptor site on eNOS wherein this species is subject to activation/deactivation by a pair of interactive kinase and phosphatase species. The enzyme kinetic model is presented as a system of ordinary differential equations including time delay to allow for various intermediate, unspecified complexes. We show that under conditions on the model parameters, varying the delay time may give rise to a Hopf bifurcation. Properties of the bifurcating solutions are explored via a center manifold reduction, and a numerical illustration is provided., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Objective: To determine the incidence and etiology of sudden cardiac arrest and death (SCA/D) in US high school athletes., Patients and Methods: A prospective media database of SCA/D was queried for cases aged 14 to 18 years from 7 states over 6 school years (September 1, 2007, to August 30, 2013). Event details were investigated to determine participation on a high school athletic team, sex, sport, and occurrence during school-sponsored activity or exertion. National sports participation numbers were used and a conversion factor was applied to account for multisport athletes. Autopsy reports were reviewed and cause of death was adjudicated by an expert panel., Results: A total of 16,390,409 million athlete-seasons representing 6,974,640 athlete-years (AY) were examined, encompassing 36% of the total US high school athlete population. A total of 104 cases of SCA/D were identified (35 SCA with survival and 69 sudden cardiac deaths [SCDs]). The rate of SCD was 1:101,082 AY and of SCA/D 1:67,064 AY. Eighty-eight percent (92) of events occurred in male athletes. The rate of SCA/D in male athletes was 1:44,832 AY and in female athletes 1:237,510 AY (incidence rate ratio, 5.3; 95% CI, 2.9-10.6; P<.001). Men's basketball was the highest risk sport with an SCA/D incidence of 1:37,087 AY followed by men's football at 1:86,494 AY. Men's basketball and football athletes accounted for 57% (39) of deaths. Eighty percent of SCDs (55 of 69) were exertional and 55% (38 of 69) occurred while playing for a school-sponsored team. Autopsy reports were obtained in 73% (50) of cases. The most common findings of autopsy were idiopathic left ventricular hypertrophy or possible cardiomyopathy (13 of 50 [26%]), autopsy-negative sudden unexplained death (9 of 50 [18%]), hypertrophic cardiomyopathy (7 of 50 [14%]), and myocarditis (7 of 50 [14%])., Conclusion: The rate of SCA/D in male high school athletes was 1:44,832 AY, with almost half due to possible or confirmed cardiomyopathy disease. It is likely that many cases were not identified because of reliance on media reports, and these numbers represent a minimum estimate., (Copyright © 2016 Mayo Foundation for Medical Education and Research. Published by Elsevier Inc. All rights reserved.)

Tachycardia-induced cardiomyopathy (TIC) is a treatable cause of heart failure in children, but there is little information as to which clinical variables best discriminate TIC from other forms of cardiomyopathy. TIC cases with dilated cardiomyopathy (DC) from 16 participating centers were identified and compared with controls with other forms of DC. Presenting clinical, echocardiographic, and electrocardiographic characteristics were collected. Heart rate (HR) percentile was defined as HR/median HR for age, and PR index as the PR/RR interval. P-wave morphology (PWM) was defined as possible sinus or nonsinus based on a predefined algorithm. Eighty TIC cases and 135 controls were identified. Cases demonstrated lower LV end-diastolic diameter and LV end-systolic diameter than DC controls (4.3 vs 6.5, p <0.001; 7.4 vs 10.9, p <0.001) and were less likely to receive inotropic medication at presentation (p <0.001 for both). Multivariable logistic regression identified HR percentile (OR 2.1 per 10% increase, CI 1.3 to 4.6; p = 0.014), PR index (OR 1.2, CI 1.1 to 1.4; p = 0.004), and nonsinus PWM (OR 104.9, CI 15.2 to 1,659.8; p <0.001) as predictive of TIC status. A risk score using HR percentile >130%, PR index >30%, and nonsinus PWM was associated with a sensitivity of 100% and specificity of 87% for the diagnosis of TIC. Model training and validation area under the curves were similar at 0.97 and 0.94, respectively. In conclusion, pediatric TIC may be accurately discriminated from other forms of DC using simple electrocardiographic parameters. This may allow for rapid diagnosis and early treatment of this condition., (Published by Elsevier Inc.)

The most effective protocol for cardiovascular screening of competitive athletes remains highly controversial. This study was a prospective, multicenter trial of cardiovascular screening at 35 National Collegiate Athletic Association institutions. Screening included a standardized history and physical examination (PE) as recommended by the American Heart Association and a 12-lead electrocardiogram (ECG) at rest. Centralized electrocardiographic interpretation was provided using the Seattle criteria. Athletes with screening abnormalities underwent additional evaluation directed by the host institution medical team. Primary outcomes included the proportion of total and false-positive screens; the sensitivity, specificity, and positive predictive value of history, PE, and ECG; and the prevalence of serious cardiovascular disorders associated with severe morbidity or sudden cardiac death. From August 2012 to June 2014, 5,258 athletes from 17 intercollegiate sports were screened: 55% men (mean age 20.1 years), 73% Caucasian, 16% African-American, and 11% other/mixed race. At least 1 positive cardiac symptom or family history response was reported by 1,750 athletes (33.3%). PE was abnormal in 108 athletes (2.1%), and electrocardiographic abnormalities were present in 192 athletes (3.7%). Thirteen athletes (0.25%) were identified with serious cardiac conditions including hypertrophic cardiomyopathy (1), large atrial septal defect with right ventricular dilation (1), and ventricular pre-excitation (11). The false-positive rate for history was 33.3%, PE 2.0%, and ECG 3.4%. The sensitivity/specificity/positive predictive value for history was 15.4%/66.9%/0.1%, PE 7.7%/98.2%/0.9%, and ECG 100%/96.6%/6.8%. In conclusion, electrocardiographic screening in National Collegiate Athletic Association athletes has a low false-positive rate and provides superior accuracy compared with a standardized history and PE to detect athletes with potentially dangerous cardiovascular conditions., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Objective: To determine the psychological impact of electrocardiogram (ECG) screening in young competitive athletes based on age, race, and gender., Design: Prospective multisite cross-sectional investigation., Setting: Young competitive athletes., Patients: One thousand five hundred six high school athletes (59.3% male with a mean age of 15.5 years, 56.2% white, 24.5% African American)., Independent Variables: Athletes underwent screening with a standardized American Heart Association-based history, physical examination, and ECG., Main Outcome Measures: Prescreen and postscreen validated assessments for health attitudes, anxiety, and impact of screening on sport., Results: Of the athletes participated, 76.3% had normal screens, 22.7% false-positive (FP) results (12.9% history, 4.2% examination, 3.1% ECG), and 0.9% were diagnosed with serious cardiac disorders. There were no differences in anxiety levels among athletes screening normal versus FP (P = 0.69). There was no difference in anxiety based on the reason for a FP result (history, physical examination, or ECG) both during (P = 0.95) and after (P = 0.40) screening. Analysis by age, race, and gender demonstrated that before screening, females were more likely to prefer knowing about underlying cardiac conditions compared with males (P < 0.001), and males were less concerned about having cardiac disease (P < 0.001) compared with females. African Americans were less concerned about underlying disease (P < 0.001) and less interested (P < 0.001) in cardiac screening compared with whites. Athletes diagnosed with a cardiac disease described anxiety after screening, but still believe that all athletes should receive an ECG before competition., Conclusions: Electrocardiogram screening does not cause excessive anxiety in US high school athletes across spectrums of age, race, and gender. Recognition of age, race, and gender-specific perspectives could improve physician-patient dialogue and support mechanisms for those diagnosed with potentially lethal cardiac disorders., Clinical Relevance: This article provides evidence that undue anxiety should not be used as an argument against the implementation of ECG screening during the preparticipation examinaton for young athletes. Although males and African Americans seem to be at highest risk for sudden cardiac death during exercise, they actually report being the least concerned and least worried about potentially harboring an underlying condition that might predispose them to such an event. Emotional support should readily be available for athletes who are diagnosed with cardiovascular conditions as these individuals report emotional distress after their diagnosis.

Background: The incidence and cause of sudden cardiac death (SCD) in athletes is debated with hypertrophic cardiomyopathy often reported as the most common cause., Methods and Results: A database of all National Collegiate Athletic Association deaths (2003-2013) was developed. Additional information and autopsy reports were obtained when possible. Cause of death was adjudicated by an expert panel. There were 4 242 519 athlete-years (AY) and 514 total student athlete deaths. Accidents were the most common cause of death (257, 50%, 1:16 508 AY) followed by medical causes (147, 29%, 1:28 861 AY). The most common medical cause of death was SCD (79, 15%, 1:53 703 AY). Males were at higher risk than females 1:37 790 AY versus 1:121 593 AY (incidence rate ratio, 3.2; 95% confidence interval, 1.9-5.5; P<0.00001), and black athletes were at higher risk than white athletes 1:21491 AY versus 1:68 354 AY (incidence rate ratio, 3.2; 95% confidence interval, 1.9-5.2; P<0.00001). The incidence of SCD in Division 1 male basketball athletes was 1:5200 AY. The most common findings at autopsy were autopsy-negative sudden unexplained death in 16 (25%), and definitive evidence for hypertrophic cardiomyopathy was seen in 5 (8%). Media reports identified more deaths in higher divisions (87%, 61%, and 44%), whereas the percentages from the internal database did not vary (87%, 83%, and 89%). Insurance claims identified only 11% of SCDs., Conclusions: The rate of SCD in National Collegiate Athletic Association athletes is high, with males, black athletes, and basketball players at substantially higher risk. The most common finding at autopsy is autopsy-negative sudden unexplained death. Media reports are more likely to capture high-profile deaths, and insurance claims are not a reliable method for case identification., (© 2015 American Heart Association, Inc.)

Background: Catecholaminergic polymorphic ventricular tachycardia is an uncommon, potentially lethal, ion channelopathy. Standard therapies have high failure rates and little is known about treatment in children. Newer options such as flecainide and left cardiac sympathetic denervation are not well validated. We sought to define treatment outcomes in children with catecholaminergic polymorphic ventricular tachycardia., Methods and Results: This is a Pediatric and Congenital Electrophysiology Society multicenter, retrospective cohort study of catecholaminergic polymorphic ventricular tachycardia patients diagnosed before 19 years of age. The cohort included 226 patients, including 170 probands and 56 relatives. Symptomatic presentation was reported in 176 (78%). Symptom onset occurred at 10.8 (interquartile range, 6.8-13.2) years with a delay to diagnosis of 0.5 (0-2.6) years. Syncope (P<0.001), cardiac arrest (P<0.001), and treatment failure (P=0.008) occurred more often in probands. β-Blockers were prescribed in 205 of 211 patients (97%) on medication, and 25% experienced at least 1 treatment failure event. Implantable cardioverter defibrillators were placed in 121 (54%) and was associated with electrical storm in 22 (18%). Flecainide was used in 24% and left cardiac sympathetic denervation in 8%. Six deaths (3%) occurred during a cumulative follow-up of 788 patient-years., Conclusions: This study demonstrates a malignant phenotype and lengthy delay to diagnosis in catecholaminergic polymorphic ventricular tachycardia. Probands were typically severely affected. β-Blockers were almost universally initiated; however, treatment failure, noncompliance and subtherapeutic dosing were often reported. Implantable cardioverter defibrillators were common despite numerous device-related complications. Treatment failure was rare in the quarter of patients on flecainide. Left cardiac sympathetic denervation was not uncommon although the indication was variable., (© 2015 American Heart Association, Inc.)

eNOS (endothelial nitric oxide synthase) contains a MAPK (mitogen-activated protein kinase)-binding site associated with a major eNOS control element. Purified ERK (extracellular-signal-regulated kinase) phosphorylates eNOS with a stoichiometry of 2-3 phosphates per eNOS monomer. Phosphorylation decreases NO synthesis and cytochrome c reductase activity. Three sites of phosphorylation were detected by MS. All sites matched the SP and TP MAPK (mitogen-activated protein kinase) phosphorylation motif. Ser602 lies at the N-terminal edge of the 42-residue eNOS AI (autoinhibitory) element. The pentabasic MAPK-binding site lies at the opposite end of the AI, and other critical regulatory features are between them. Thr46 and Ser58 are located in a flexible region associated with the N terminus of the oxygenase domain. In contrast with PKC (protein kinase C), phosphorylation by ERK did not significantly interfere with CaM (calmodulin) binding as analysed by optical biosensing. Instead, ERK phosphorylation favours a state in which FMN and FAD are in close association and prevents conformational changes that expose reduced FMN to acceptors. The close associations between control sites in a few regions of the molecule suggest that control of signal generation is modulated by multiple inputs interacting directly on the surface of eNOS via overlapping binding domains and tightly grouped targets.

Background: This study compares the accuracy of cardiovascular screening in active adolescents and young adults using a standardised history, physical examination and resting 12-lead ECG., Methods: Participants were prospectively screened using a standardised questionnaire based on the Pre-participation Physical Evaluation Monograph 4th Edition (PPE-4), physical examination and ECG interpreted using modern standards. Participants with abnormal findings had focused echocardiography and further evaluation. Primary outcomes included disorders associated with sudden cardiac arrest (SCA)., Results: From September 2010 to July 2011, 1339 participants underwent screening: age 13-24 (mean 16) years, 49% male, 68% Caucasian, 17% African-American and 1071 (80%) participating in organised sports. Abnormal history responses were reported on 916 (68%) questionnaires. After physician review, 495/916 (54%) participants with positive questionnaires were thought to have non-cardiac symptoms and/or a benign family history and did not warrant additional evaluation. Physical examination was abnormal in 124 (9.3%) participants, and 72 (5.4%) had ECG abnormalities. Echocardiograms were performed in 586 (44%) participants for abnormal history (31%), physical examination (8%) or ECG (5%). Five participants (0.4%) were identified with a disorder associated with SCA, all with ECG-detected Wolff-Parkinson-White. The false-positive rates for history, physical examination and ECG were 31.3%, 9.3% and 5%, respectively., Conclusions: A standardised history and physical examination using the PPE-4 yields a high false-positive rate in a young active population with limited sensitivity to identify those at risk for SCA. ECG screening has a low false-positive rate using modern interpretation standards and improves detection of primary electrical disease at risk of SCA., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Background: Published guidelines suggest that ECG screening in US athletes may cause excessive anxiety, especially in those with false-positive findings. However, this has never been formally evaluated., Methods and Study Design: Prospective, non-randomised controlled trial. High school athletes received a standardised history and physical examination (control) or a history and physical examination with an ECG (experimental). Prescreen and postscreen assessments for health attitudes, anxiety and impact of screening on sport were conducted., Results: 952 athletes (49.7% girls, mean age 15.5 years) participated (control=150; experimental=802). 4.4% worried about having an underlying cardiac condition, and 73% wanted to learn if they had a cardiac abnormality prior to competition. In the experimental group, 576 had normal screens, 220 had an abnormal screen (by history 15.8%, physical examination 6.2% or ECG 1.7%) but normal work up (false-positive) and 6 were identified with a serious cardiac condition (true-positive, 0.75%). Compared with the control group, those who received an ECG were more likely to: (1) be significantly more satisfied with their screening (p<0.001), (2) feel safer during competition (p<0.01), (3) support that all athletes should receive cardiac screening (p<0.001) and (4) state the ECG positively impacted their training (p<0.001). False-positive athletes did not report anxiety during or after screening. Distress levels did not differ based on reason for needing further evaluation (history, physical examination or ECG, p=0.311). Compared with control participants, individuals with false-positive results: (1) reported no difference in postscreen anxiety (p=0.775), (2) felt safer during competition (p<0.001), (3) would recommend ECG screening to others (p<0.001) and (4) expressed a positive impact on training (p<0.001)., Conclusions: Excessive anxiety should not be used as a reason to forego ECG screening in athletes., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.)

Background: Tachycardia-induced cardiomyopathy (TIC) carries significant risk of morbidity and mortality, although full recovery is possible. Little is known about the myocardial recovery pattern., Objective: The purpose of this study was to determine the time course and predictors of myocardial recovery in pediatric TIC., Methods: An international multicenter study of pediatric TIC was conducted. Children ≤18 years with incessant tachyarrhythmia, cardiac dysfunction (left ventricular ejection fraction [LVEF] <50%), and left ventricular (LV) dilation (left ventricular end-diastolic dimension [LVEDD] z-score ≥2) were included. Children with congenital heart disease or suspected primary cardiomyopathy were excluded. Primary end-points were time to LV systolic functional recovery (LVEF ≥55%) and normal LV size (LVEDD z-score <2)., Results: Eighty-one children from 17 centers met inclusion criteria: median age 4.0 years (range 0.0-17.5 years) and baseline LVEF 28% (interquartile range 19-39). The most common arrhythmias were ectopic atrial tachycardia (59%), permanent junctional reciprocating tachycardia (23%), and ventricular tachycardia (7%). Thirteen required extracorporeal membrane oxygenation (n = 11) or ventricular assist device (n = 2) support. Median time to recovery was 51 days for LVEF and 71 days for LVEDD. Two (4%) underwent heart transplantation, and 1 died (1%). Multivariate predictors of LV systolic functional recovery were age (hazard ratio [HR] 0.61, P = .040), standardized tachycardia rate (HR 1.16, P = .015), mechanical circulatory support (HR 2.61, P = .044), and LVEF (HR 1.33 per 10% increase, p=0.005). For normalization of LV size, only baseline LVEDD (HR 0.86, P = .008) was predictive., Conclusion: Pediatric TIC resolves in a predictable fashion. Factors associated with faster recovery include younger age, higher presenting heart rate, use of mechanical circulatory support, and higher LVEF, whereas only smaller baseline LV size predicts reverse remodeling. This knowledge may be useful for clinical evaluation and follow-up of affected children., (Published by Elsevier Inc.)

Context: Wolff-Parkinson-White (WPW) is a cardiac conduction system disorder characterized by abnormal accessory conduction pathways between the atria and the ventricles. Symptomatic patients classically present with palpitations, presyncope, or syncope that results from supraventricular tachycardia. While rare, sudden cardiac death may be the first manifestation of underlying disease and occurs more frequently in exercising individuals., Evidence Acquisition: Medline and PubMed databases were evaluated through 2012, with the following keywords: WPW, Wolff-Parkinson-White, pre-excitation, sudden cardiac death, risk stratification, and athletes. Selected articles identified through the primary search, along with relevant references from those articles, were reviewed for pertinent clinical information regarding the identification, evaluation, risk stratification, and management of WPW as they pertained to the care of athletes., Study Design: Systematic review., Level of Evidence: Level 1., Results: Diagnosis of WPW is confirmed by characteristic electrocardiogram changes, which include a delta wave, short PR interval, and widened QRS complex. Utilization of the electrocardiogram as part of the preparticipation physical evaluation may allow for early identification of asymptomatic individuals with a WPW pattern. Risk stratification techniques identify individuals at risk for malignant arrhythmias who may be candidates for curative therapy through transcatheter ablation., Conclusion: WPW accounts for at least 1% of sudden death in athletes and has a prevalence of at least 1 to 4.5 per 1000 children and adults. The risk of lethal arrhythmia appears to be higher in asymptomatic children than in adults, and sudden cardiac death is often the sentinel event. The athlete with WPW should be evaluated for symptoms and the presence of intermittent or persistent pre-excitation, which dictates further consultation, treatment, and monitoring strategies as well as return to play.

Objective: To evaluate current preparticipation physical evaluation (PPE) clinical practice behaviors., Design: Telephone and Web-based survey study with attention to utilization of the Fourth Edition PPE Monograph., Setting: We contacted the Washington State American Academy of Pediatrics (AAP) and American Academy of Family Physicians (AAFP) chapters, all Washington State high school athletic directors (ADs), and every state high school athletic association., Interventions: Data collection and analysis regarding clinical practice., Main Outcome Measures: Awareness and utilization of the Fourth Edition PPE Monograph., Results: The response rate was 72% (559/776) from the AAP, 56% (554/990) from the AAFP, 75% (317/424) from the ADs, and 100% (50/50) from the state athletic associations. Few physicians (37%) and ADs (6%) reported an awareness of the PPE Monograph. Knowledge of the Monograph did not vary by physician type, practice/school location, or experience (P > 0.05). Reported obstacles to the delivery of the PPE included time with patient (56%) and the lack of a standard form (52%). Physician awareness of the Monograph reduced the perception of obstacles (P < 0.01). Athletic directors reported financial limitations of the family as the primary obstacle (62%). Adoption of a single statewide PPE form was well supported (96% of physicians and 67% of ADs). Nationally, only 46% of state athletic associations mandate a single form, and only 16% use a form consistent with the Fourth Edition PPE Monograph., Conclusions: The medical community is largely unaware of national screening guidelines. New directions for education and policy are necessary to improve this implementation gap.

Acetoacetyl-CoA thiolase (EC 2.3.1.9), commonly named thiolase II, condenses two molecules of acetyl-CoA to give acetoacetyl-CoA and CoA. This enzyme acts in anabolic processes as the first step in the biosynthesis of isoprenoids and polyhydroxybutyrate in eukaryotes and bacteria, respectively. We have recently reported the evolutionary and functional equivalence of these enzymes, suggesting that thiolase II could be the rate limiting enzyme in these pathways and presented evidence indicating that this enzyme modulates the availability of reducing equivalents during abiotic stress adaptation in bacteria and plants. However, these results are not sufficient to clarify why thiolase II was evolutionary selected as a critical enzyme in the production of antioxidant compounds. Regarding this intriguing topic, we propose that thiolase II could sense changes in the acetyl-CoA/CoA ratio induced by the inhibition of the tricarboxylic acid cycle under abiotic stress. Thus, the high level of evolutionary and functional constraint of thiolase II may be due to the connection of this enzyme with an ancient and conserved metabolic route., (© 2013.)

Objective: In the USA, the preparticipation physical evaluation (PPE) is the standard of care for screening eight million high-school athletes for their risk of sudden cardiac death (SCD). Our aim was to evaluate both physician and school compliance with national guidelines for SCD screening., Methods: We conducted a confidential survey of the Washington Chapter of the American Academy of Pediatrics (AAP), the Washington Academy of Family Physicians (WAFP) and Washington State high-school athletic directors. Responses were evaluated for compliance with the American Heart Association (AHA) guidelines for SCD screening., Results: We received a response rate of 72% (559/776) from the AAP, 56% (554/990) from the WAFP and 78% (317/409) from the athletic directors. Only 6% of all providers and 0% of schools were in compliance with AHA guidelines. In addition, 47% of the physicians and 6% of athletic directors reported awareness of the guidelines. There was no difference in compliance between physician specialties (p=0.20). Physician location, years of experience and exposure to SCD were not significantly associated with compliance. Provider knowledge of the guidelines, number of PPE/month and frequency of referrals to cardiology were all positively associated with improved overall compliance (p<0.05)., Conclusions: Despite the unaltered presence of the AHA SCD screening guidelines for the past 15 years, compliance with the recommendations is poor. Lack of compliance does not reflect clinical experience, but rather lack of knowledge of the guidelines themselves. New directions for provider education and policy requirements are needed to improve this implementation gap.

Electrocardiographic changes in athletes are common and usually reflect benign structural and electrical remodelling of the heart as a physiological adaptation to regular and sustained physical training (athlete's heart). The ability to identify an abnormality on the 12-lead ECG, suggestive of underlying cardiac disease associated with sudden cardiac death (SCD), is based on a sound working knowledge of the normal ECG characteristics within the athletic population. This document will assist physicians in identifying normal ECG patterns commonly found in athletes. The ECG findings presented as normal in athletes were established by an international consensus panel of experts in sports cardiology and sports medicine.

This study aimed to examine practice patterns in the inpatient medical treatment of newborns and infants with supraventricular tachycardia (SVT) using the Pediatric Health Information System (PHIS) database, a large, multi-institutional administrative database. A retrospective examination of pediatric hospital discharge data was performed during the study period from January 2003 to September 2008. Data were extracted from the index hospitalization of all individuals younger than 1 year with the principal discharge diagnosis of SVT. Those with coexisting congenital or acquired structural heart disease were excluded from the study. The analysis included 171 patients. No deaths occurred, and 95 % of the infants were discharged to home. More than half (53 %) of the patients spent a portion of their hospital stay in an intensive care unit (ICU) setting. Multidrug therapy was common, with 45 % of the patients receiving two or more antiarrhythmic agents on the day of discharge. The five most commonly used antiarrhythmic drugs, in order of decreasing frequency of use, were propranolol, digoxin, amiodarone, flecainide, and sotalol. The median hospital stay for the group was 4 days, and this value increased as a function of the number of antiarrhythmic drugs used (median, 7 days for three or more agents) and the need for intensive care (median, 6 days). The information provided in this study helps to define common practice patterns and should allow caregivers to provide meaningful expectations to families regarding their potential treatment course and to anticipate the hospital length of stay.

Cardiac channelopathies are potentially lethal inherited arrhythmia syndromes and an important cause of sudden cardiac death (SCD) in young athletes. Other cardiac rhythm and conduction disturbances also may indicate the presence of an underlying cardiac disorder. The 12-lead ECG is utilised as both a screening and a diagnostic tool for detecting conditions associated with SCD. Fundamental to the appropriate evaluation of athletes undergoing ECG is an understanding of the ECG findings that may indicate the presence of a pathological cardiac disease. This article describes ECG findings present in primary electrical diseases afflicting young athletes and outlines appropriate steps for further evaluation of these ECG abnormalities. The ECG findings defined as abnormal in athletes were established by an international consensus panel of experts in sports cardiology and sports medicine.

Cardiomyopathies are a heterogeneous group of heart muscle diseases and collectively are the leading cause of sudden cardiac death (SCD) in young athletes. The 12-lead ECG is utilised as both a screening and diagnostic tool for detecting conditions associated with SCD. Fundamental to the appropriate evaluation of athletes undergoing ECG is an understanding of the ECG findings that may indicate the presence of an underlying pathological cardiac disorder. This article describes ECG findings present in cardiomyopathies afflicting young athletes and outlines appropriate steps for further evaluation of these ECG abnormalities. The ECG findings defined as abnormal in athletes were established by an international consensus panel of experts in sports cardiology and sports medicine.

We recently showed that inducible nitric oxide synthase conformational intermediates can be resolved via FMN fluorescence lifetimes. Here we show that neuronal NOS activation by calmodulin removes constraints favoring a closed 'input state', increasing occupation of other states and facilitating conformational transitions. The 90 ps FMN input state lifetime distinguishes it from ∼4 ns 'open' states in which FMN does not interact strongly with other groups, or 0.9 ns output states in which FMN interacts with ferriheme. Enablement of the conformational cycle is an important paradigm for control in nNOS and related enzymes, and may extend to other control modalities., (Copyright © 2012. Published by Elsevier B.V.)

Ceriporiopsis subvermispora oxalate oxidase (CsOxOx) is the first bicupin enzyme identified that catalyzes manganese-dependent oxidation of oxalate. In previous work, we have shown that the dominant contribution to catalysis comes from the monoprotonated form of oxalate binding to a form of the enzyme in which an active site carboxylic acid residue must be unprotonated. CsOxOx shares greatest sequence homology with bicupin microbial oxalate decarboxylases (OxDC) and the 241-244DASN region of the N-terminal Mn binding domain of CsOxOx is analogous to the lid region of OxDC that has been shown to determine reaction specificity. We have prepared a series of CsOxOx mutants to probe this region and to identify the carboxylate residue implicated in catalysis. The pH profile of the D241A CsOxOx mutant suggests that the protonation state of aspartic acid 241 is mechanistically significant and that catalysis takes place at the N-terminal Mn binding site. The observation that the D241S CsOxOx mutation eliminates Mn binding to both the N- and C- terminal Mn binding sites suggests that both sites must be intact for Mn incorporation into either site. The introduction of a proton donor into the N-terminal Mn binding site (CsOxOx A242E mutant) does not affect reaction specificity. Mutation of conserved arginine residues further support that catalysis takes place at the N-terminal Mn binding site and that both sites must be intact for Mn incorporation into either site.

Lead thrombosis is a recognized complication of permanent transvenous pacemaker (PM) implantation. We present the interesting case of an adolescent with a dual-chamber PM presenting with fatigue and hypoxemia. Due to limitations of various imaging modalities, the diagnosis was difficult. She was eventually diagnosed with intracardiac PM lead thrombi obstructing tricuspid valve inflow. The pediatric literature on PM lead thrombosis is also briefly reviewed.

Nitric oxide synthases (NOSs) produce NO as a molecular signal in the nervous and cardiovascular systems and as a cytotoxin in the immune response. NO production in the constitutive isoforms is controlled by calmodulin regulation of electron transfer. In the tethered shuttle model for NOS reductase function, the FMN domain moves between NADPH dehydrogenase and oxygenase catalytic centers. Crystal structures of neuronal NOS reductase domain and homologs correspond to an 'input state', with FMN in close contact with FAD. We recently produced two domain 'output state' (oxyFMN) constructs showing calmodulin dependent FMN domain association with the oxygenase domain. FMN fluorescence is sensitive to enzyme conformation and calmodulin binding. The inducible NOS (iNOS) oxyFMN construct is more fluorescent than iNOS holoenzyme. The difference in steady state fluorescence is rationalized by the observation of a series of characteristic states in the two constructs, which we assign to FMN in different environments. OxyFMN and holoenzyme share open conformations with an average lifetime of ~4.3 ns. The majority state in holoenzyme has a short lifetime of ~90 ps, probably because of FAD-FMN interactions. In oxyFMN about 25-30% of the FMN is in a state with a lifetime of 0.9 ns, which we attribute to quenching by heme in the output state. Occupancy of the output state together with our previous kinetic results yields a heme edge to FMN distance estimate of 12-15 Å. These results indicate that FMN fluorescence is a valuable tool to study conformational states involved in the NOS reductase catalytic cycle., (© 2012 The Authors Journal compilation © 2012 FEBS.)

Endothelial nitric oxide synthase (eNOS) contains a motif similar to recognition sequences in known MAPK binding partners. In optical biosensing experiments, eNOS bound p38 and ERK with ∼100 nM affinity and complex kinetics. Binding is diffusion-limited (k on ∼ .15 × 10(6) M(-1) s(-1)). Neuronal NOS also bound p38 but exhibited much slower and weaker binding. p38-eNOS binding was inhibited by calmodulin. Evidence for a ternary complex was found when eNOS bound p38 was exposed to CaM, increasing the apparent dissociation rate. These observations strongly suggest a direct role for MAPK in regulation of NOS with implications for signaling pathways including angiogenesis and control of vascular tone.

Using interferometry-based biosensors the binding and release of endothelial and neuronal nitric oxide synthase (eNOS and nNOS) from calmodulin (CaM) was measured. In both isoforms, binding to CaM is diffusion limited and within approximately three orders of magnitude of the Smoluchowski limit imposed by orientation-independent collisions. This suggests that the orientation of CaM is facilitated by the charge arrays on the CaM-binding site and the complementary surface on CaM. Protein kinase C phosphorylation of eNOS T495, adjacent to the CaM-binding site, abolishes or greatly slows CaM binding. Kinases which increase the activity of eNOS did not stimulate the binding of CaM, which is already diffusion limited. The coupling of Ca(2+) binding and CaM/NOS binding equilibria links the affinity of CaM for NOS to the Ca(2+) dependence of CaM binding. Hence, changes in the Ca(2+) sensitivity of CaM binding always imply changes in the NOS-CaM affinity. It is possible, however, that in some regimes binding and activation are not synonymous, so that Ca(2+) sensitivity need not be tightly linked to CaM sensitivity of activation. This study is being extended using mutants to probe the roles of individual structural elements in binding and release., (© 2011 The Authors Journal compilation © 2011 FEBS.)

The development of tachycardia-induced cardiomyopathy (TIC) is related to the rate and duration of supraventricular tachycardia (SVT). Infants may be more susceptible to TIC because early symptoms might be unrecognized. Extracorporeal membrane oxygenation (ECMO) may improve outcome in patients with SVT and TIC; however, clinical predictors of infants who require ECMO support have not been determined. The purpose of this study was to identify predictors of the need for ECMO in infants with SVT and TIC. Sixteen infants <6 months of age who experienced resolution of TIC following control of arrhythmia were identified. Three patients (19%) required ECMO support. Comparisons were made between patients who required ECMO and those who did not. The groups were similar with respect to age at presentation, type of SVT, rate of SVT, and degree of ventricular dysfunction. However, patients requiring ECMO had increased median M-mode-derived left ventricular end diastolic dimension (LVED) z-score when compared to the medically managed patents (+2.8 vs. 0.0, P = 0.009). No patient in the medically managed group had an LVED z-score >2.3. Infants presenting with SVT and TIC with LVED z-score >2 are at increased risk for requiring ECMO support and early use of ECMO should be considered.