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Background: Transcatheter tricuspid valve replacement (TTVR) abolishes tricuspid regurgitation (TR) and has emerged as a definitive treatment for TR., Objectives: The purpose of this multicenter, observational study was to determine the clinical characteristics and short-term outcomes of patients with TR screened for TTVR., Methods: Patients underwent TTVR screening at 7 centers on a compassionate-use basis. The primary endpoints were NYHA functional class and TR grade at 30-day follow-up. Secondary endpoints included all-cause mortality, heart failure hospitalization, technical success, and reasons for TTVR screening failure., Results: A total of 149 patients (median age 79 years [Q1-Q3: 72-84 years], 54% women) underwent TTVR screening. The TTVR screening failure rate was 74%, mainly related to large tricuspid annular diameter. Patients undergoing TTVR (n = 38) had significant functional improvements (NYHA functional class I or II from 21% to 68%; P < 0.001), with TR ≤1+ in 97% at 30-day follow-up (P < 0.001 from baseline). Technical success was achieved in 91%, with no intraprocedural mortality or conversion to surgery. At 30-day follow-up, mortality was 8%, heart failure hospitalization 5%, major bleeding 18%, and reintervention 9%. Patients who failed screening for TTVR and subsequently underwent "bailout" transcatheter edge-to-edge repair (n = 26) had favorable outcomes (NYHA functional class I or II from 27% to 58%; P < 0.001), with TR ≤1+ in 43% at 30-day follow-up (P < 0.001 from baseline)., Conclusions: This first real-world report of TTVR screening demonstrated a high screening failure rate, mainly related to large tricuspid annular diameter. Patients undergoing TTVR had superior TR reduction and symptom alleviation compared with bailout tricuspid transcatheter edge-to-edge repair, at the cost of greater procedural complications., Competing Interests: Funding Support and Author Disclosures Dr Taramasso has served as a consultant for Abbott Vascular, Boston Scientific, 4Tech, and CoreMedic; and has received speaker honoraria from Edwards Lifesciences. Dr Dumonteil has received consultancy and proctoring fees from Abbott Vascular, Ancora Heart, Boston Scientific, Edwards Lifesciences, and Medtronic. Dr Modine has been a consultant for Boston Scientific, Medtronic, Edwards Lifesciences, MicroPort, GE, and Abbott. Dr Latib has served on advisory boards for Medtronic, Abbott Vascular, Boston Scientific, Edwards Lifesciences, Shifamed, NeoChord, VDyne, and Philips. Dr Praz has received travel expense reimbursement from Edwards Lifesciences, Abbott Vascular, and Polares Medical. Dr Hausleiter has received speaker honoraria and research support from Abbott Vascular and Edwards Lifesciences; and is a consultant to Abbott Vascular and Edwards Lifesciences. Dr Fam is a consultant to Edwards Lifesciences, Abbott, and Cardiovalve. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background The prevalence of calcific aortic stenosis and amyloid transthyretin cardiomyopathy (ATTR-CM) increase with age, and they often coexist. The objective was to determine the prevalence of ATTR-CM in patients with severe aortic stenosis and evaluate differences in presentations and outcomes of patients with concomitant ATTR-CM undergoing transcatheter aortic valve implantation. Methods and Results Prospective screening for ATTR-CM with Technetium 99 -3,3-diphosphono-1,2-propanodicarboxylic acid bone scintigraphy was performed in 315 patients referred with severe aortic stenosis between August 2019 and August 2021. Myocardial Technetium 99 -3,3-diphosphono-1,2-propanodicarboxylic acid tracer uptake was detected in 34 patients (10.8%), leading to a diagnosis of ATTR-CM in 30 patients (Perugini ≥2: 9.5%). Age (85.7±4.9 versus 82.8±4.5; P =0.001), male sex (82.4% versus 57.7%; P =0.005), and prior carpal tunnel surgery (17.6% versus 4.3%; P =0.007) were associated with coexisting ATTR-CM, as were ECG (discordant QRS voltage to left ventricular wall thickness [42% versus 12%; P <0.001]), echocardiographic (left ventricular ejection fraction 48.8±12.8 versus 58.4±10.8; P <0.001; left ventricular mass index, 144.4±45.8 versus 117.2±34.4g/m 2 ; P <0.001), and hemodynamic parameters (mean aortic valve gradient, 23.4±12.6 versus 35.5±16.6; P <0.001; mean pulmonary artery pressure, 29.5±9.7 versus 25.8±9.5; P =0.037). Periprocedural (cardiovascular death: hazard ratio [HR], 0.71 [95% CI, 0.04-12.53]; stroke: HR, 0.46 [95% CI, 0.03-7.77]; pacemaker implantation: HR, 1.54 [95% CI, 0.69-3.43]) and 1-year clinical outcomes (cardiovascular death: HR, 1.04 [95% CI, 0.37-2.96]; stroke: HR, 0.34 [95% CI, 0.02-5.63]; pacemaker implantation: HR, 1.50 [95% CI, 0.67-3.34]) were similar between groups. Conclusions Coexisting ATTR-CM was observed in every 10th elderly patient with severe aortic stenosis referred for therapy. While patients with coexisting pathologies differ in clinical presentation and echocardiographic and hemodynamic parameters, peri-interventional risk and early clinical outcomes were comparable up to 1 year after transcatheter aortic valve implantation. REGISTRATION URL: https://www.clinicaltrials.gov. Unique identifier: NCT04061213.

Background: One-third of patients undergoing transcatheter aortic valve implantation (TAVI) have an indication for long-term oral anticoagulation (OAC)., Aims: We aimed to investigate whether continued non-vitamin K antagonist oral anticoagulant (NOAC) therapy compared with continued vitamin K antagonist (VKA) therapy during TAVI is equally safe and effective.  Methods: Consecutive patients on OAC with either NOAC or VKA undergoing transfemoral TAVI at five European centres were enrolled. The primary outcome measure was a composite of major/life-threatening bleeding, stroke, and all-cause mortality at 30 days., Results: In total, 584 patients underwent TAVI under continued OAC with 294 (50.3%) patients receiving VKA and 290 (49.7%) patients receiving NOAC. At 30 days, the composite primary outcome had occurred in 51 (17.3%) versus 36 (12.4%) patients with continued VKA and with continued NOAC, respectively (odds ratio [OR] 0.68, 95% confidence interval [CI]: 0.43-1.07; p=0.092). Rates of major/life-threatening bleeding (OR 0.87, 95% CI: 0.52-1.47; p=0.606) and stroke (OR 1.02, 95% CI: 0.29-3.59; p=0.974) were not different between groups. In a multivariate Cox regression analysis, continued NOAC, compared with continued VKA, was associated with a lower risk for all-cause 1-year mortality (hazard ratio [HR] 0.61, 95% CI: 0.37-0.98; p=0.043). The analysis of the propensity score-matched cohort revealed similar results., Conclusions: Continued NOAC compared with continued VKA during TAVI led to comparable outcomes with regard to the composite outcome measure indicating that continued OAC with both drugs is feasible. These hypothesis-generating results need to be confirmed by a dedicated randomised controlled trial.

Purpose of Review: The burden of tricuspid regurgitation (TR) is high in the aging population, almost 4% in the age group over 75 have moderate or more TR. This carries a poor prognosis and an increased incidence of mortality, prolonged hospitalization, and rehospitalization in symptomatic patients with severe TR is observed. Percutaneous tricuspid valve intervention has emerged as a viable therapeutic option, with an increasingly large toolbox of both tricuspid repair and replacement devices. The optimal strategy, timing and patient selection for transcatheter intervention are yet to be determined. This review focuses on the current strengths and limitations of transcatheter tricuspid repair vs. replacement, drawing on lessons learned from surgery., Recent Findings: Early outcome studies have been published in the last 2 years for many of the new percutaneous tricuspid valve devices. We have summarized these results and compared them to surgical tricuspid valve repair and replacement. We found that surgical data shows a tendency to better outcome with tricuspid valve repair compared to replacement. For transcatheter interventions studies comparing repair and replacement are lacking but both interventions show good procedural success rates and are efficient in reducing the grade of tricuspid regurgitation., Summary: Transcatheter tricuspid valve interventions offer a safe and effective alternative to tricuspid surgery or medical therapy. The decision between valve replacement and repair should be based on patient anatomy, operator experience and device availability until head-to-head comparison of different devices are available., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Myocardial strain is an established parameter for the assessment of cardiac function and routinely derived from speckle tracking echocardiography (STE). Novel post-processing tools allow deformation imaging also by 4D cardiac computed tomography angiography (CCT). This retrospective study aims to analyze the reproducibility of CCT strain and compare it to that of STE., Methods: Left (LV) and right ventricular (RV), and left atrial (LA) ejection fraction (EF), dimensions, global longitudinal (GLS), circumferential (GCS) and radial strain (GRS) were determined by STE and CCT feature tracking in consecutive patients with severe aortic stenosis evaluated for transcatheter aortic valve implantation., Results: 106 patients (mean age 79.9 ​± ​7.8, 44.3% females) underwent CCT at a median of 3 days (IQR 0-28 days) after STE. In CCT, strain measures showed good to excellent reproducibility (intra- and inter-reader intraclass correlation coefficient ≥0.75) consistently in the LV, RV and LA. In STE, only LV GLS and LA GLS yielded good reproducibility, whereas LV GCS and LV GRS showed moderate, and RV GLS and free wall longitudinal strain (FWLS) poor reproducibility. Agreement between CCT and STE was strong for LV GLS only, while other strain features displayed moderate (LV GCS, LA GLS) or weak (LV GRS, RV GLS and FWLS) inter-modality correlation., Conclusion: LV, RV and LA CCT strain assessments were highly reproducible. While a strong agreement to STE was found for LV GLS, inter-modality correlation was moderate or weak for LV GCS, LV GRS, and RV and LA longitudinal strain, possibly related to poor reproducibility of STE measurements., Competing Interests: Declaration of competing interest No specific funding was obtained for this work. The study was approved by the local ethics committee and was conducted in accordance with the Declaration of Helsinki. All patients provided written informed consent. The paper is not under consideration elsewhere, nor has the paper's contents been previously published. All authors have significantly contributed to the study and have the following disclosures: Dr. Okuno receives speaker fees from Abbott. Dr. Huber has received research grants from the Swiss National Science Foundation, the Helmut-Hartweg Foundation and the Foundation to Fight against Cancer, all for work outside the submitted study. Dr. Stortecky is the recipient of research grants to the institution from Edwards Lifesciences, Medtronic, Abbott Vascular and Boston Scientific, is a consultant for BTG and Teleflex and has received speaker fees from Boston Scientific. Dr. Windecker has received research grants to his institution from Abbott, Amgen, Boston, Biotronik, and St. Jude Medical, he has received no speaker fee. Dr. Pilgrim has received research grants to his institution from Edwards Lifesciences, Symetis, and Biotronik; has received speaker fees from Boston Scientific; and has received reimbursement for travel expenses from St. Jude Medical. Dr. Gräni received research funding from Swiss National Science Foundation and Innosuisse outside of the submitted work. Further Dr. Gräni received travel fees from Amgen and Bayer. All other authors report no conflicts., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Purpose: As the Radiation Exposure Information and Reporting System (REIRS) celebrates 50 years of existence, this is an appropriate time to reflect on the innovative and novel system and how it has shaped the study of occupational radiation exposure. It is also fitting to appreciate the vision and initiative of the individuals who recognized the future value of the collection and analysis of this information to better inform regulations, policies, and epidemiologic studies, and thus contribute to the protection of workers and the public from the adverse health effects of radiation exposure., Conclusions: REIRS has evolved and expanded over its 50-year history and has played a central role in providing the radiation exposure monitoring records for the Million Person Study for individuals monitored as NRC licensees and at DOE facilities. REIRS has played two major functions in epidemiologic studies. First, it has provided dosimetry information on individual workers in occupational studies to ensure nearly complete ascertainment of career doses. Second, REIRS was used as the primary data source for large cohorts within the Million Person Study: nuclear power plant workers ( n ∼140,000) and industrial radiographers ( n ∼130,000). The legacy that REIRS continues to uphold is a model for creating and maintaining a successful tool throughout decades of political, technological, and demographic change.

The prevalence of severe tricuspid regurgitation in older patients is high, and the clinical relevance is perceived more and more in recent years. Many of these patients are not suitable for surgery because of their age and comorbidities. Therefore, a variety of percutaneous interventions have been developed to address this unmet need. Procedural success strongly depends on adequate imaging during the intervention. Although transesophageal echocardiography is the standard of care, imaging may be limited due to anatomic factors and adverse acoustic shadowing. In this review, we discuss the current and future role of intracardiac echocardiography in tricuspid valve interventions., Competing Interests: Disclosure N.P. Fam is a consultant for Edwards Lifesciences and Abbott. Daniel Hagemeyer is supported by Gottfried Und Julia Bangerter-Rhyner-Stiftung, Bern. The remaining authors have no disclosures., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Purpose: Scientific Committee 6-9 was established by the National Council on Radiation Protection and Measurements (NCRP), charged to provide guidance in the derivation of organ doses and their uncertainty, and produced a report, NCRP Report No. 178, Deriving Organ Doses and their Uncertainty for Epidemiologic Studies with a focus on the Million Person Study of Low-Dose Radiation Health Effects (MPS). This review summarizes the conclusions and recommendations of NCRP Report No. 178, with a concentration on and overview of the dosimetry and uncertainty approaches for the cohorts in the MPS, along with guidelines regarding the essential approaches used to estimate organ doses and their uncertainties (from external and internal sources) within the framework of an epidemiologic study., Conclusions: The success of the MPS is tied to the validity of the dose reconstruction approaches to provide realistic estimates of organ-specific radiation absorbed doses that are as accurate and precise as possible and to properly evaluate their accompanying uncertainties. The dosimetry aspects for the MPS are challenging in that they address diverse exposure scenarios for diverse occupational groups being studied over a period of up to 70 y. Specific dosimetric reconstruction issues differ among the varied exposed populations that are considered: atomic veterans, U.S. Department of Energy workers exposed to both penetrating radiation and intakes of radionuclides, nuclear power plant workers, medical radiation workers, and industrial radiographers. While a major source of radiation exposure to the study population comes from external gamma- or x-ray sources, for some of the study groups, there is also a meaningful component of radionuclide intakes that requires internal radiation dosimetry assessments.

Athletes of pediatric age are growing in number. They are subject to a number of risks, among them sudden cardiac death (SCD). This study aimed to characterize the pediatric athlete population in Switzerland, to evaluate electrocardiographic findings based on the International Criteria for electrocardiography (ECG) Interpretation in Athletes, and to analyze the association between demographic data, sport type, and ECG changes. Retrospective, observational study of pediatric athletes (less than 18 years old) including medical history, physical examination, and a 12-lead resting ECG. The primary focus was on identification of normal, borderline, and abnormal ECG findings. The secondary observation was the relation between ECG and demographic, anthropometric, sport-related, and clinical data. The 891 athletes (mean 14.8 years, 35% girls) practiced 45 different sports on three different levels, representing all types of static and dynamic composition of the Classification of Sports by Mitchell. There were 75.4% of normal ECG findings, among them most commonly early repolarization, sinus bradycardia, and left ventricular hypertrophy; 4.3% had a borderline finding; 2.1% were abnormal and required further investigations, without SCD-related diagnosis. While the normal ECG findings were related to sex, age, and endurance sports, no such observation was found for borderline or abnormal criteria. Our results in an entirely pediatric population of athletes demonstrate that sex, age, and type of sports correlate with normal ECG findings. Abnormal ECG findings in pediatric athletes are rare. The International Criteria for ECG Interpretation in Athletes are appropriate for this age group., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Objectives: This study investigated whether transcatheter aortic valve replacement (TAVR) with peri-procedural continuation of oral anticoagulation is equally safe and efficacious as TAVR with peri-procedural interruption of anticoagulation., Background: A significant proportion of patients undergoing TAVR have an indication for long-term oral anticoagulation. The optimal peri-procedural management of such patients is unknown., Methods: Consecutive patients on oral anticoagulation who underwent transfemoral TAVR at 5 European centers were enrolled. Oral anticoagulation was either stopped 2 to 4 days before TAVR or continued throughout the procedure. Primary safety outcome was major bleeding. Secondary efficacy endpoints included vascular complications, stroke, and mortality., Results: Of 4,459 patients, 584 patients were treated with continuation of anticoagulation and 733 with interruption of anticoagulation. At 30 days, major or life-threatening bleedings occurred in 66 (11.3%) versus 105 (14.3%; odds ratio [OR]: 0.86; 95% confidence interval [CI]: 0.61 to 1.21; p = 0.39) and major vascular complications in 64 (11.0%) versus 90 (12.3%; OR: 0.89; CI: 0.62 to 1.27; p = 0.52) of patients with continuation and with interruption of anticoagulation, respectively. Transfusion of packed red blood cells was less often required in patients with continuation of anticoagulation (80 [13.7%] vs. 130 [17.7%]; OR: 0.59; 95% CI: 0.42 to 0.81; p = 0.001). Kaplan-Meier estimates of survival at 12 months were 85.3% in patients with continuation of anticoagulation and 84.0% in patients with interruption of anticoagulation (hazard ratio: 0.90; 95% CI: 0.73 to 1.12; p = 0.36)., Conclusions: Continuation of oral anticoagulation throughout TAVR did not increase bleeding or vascular complication rates. Moreover, packed red blood cell transfusions were less often required in patients with continuation of oral anticoagulation., Competing Interests: Author Disclosures Dr. Mangner has received speaker honoraria from Edwards Lifesciences, Medtronic, Novartis, Sanofi Genzyme, and AstraZeneca; and has received consultant honoraria from Biotronik, outside the submitted work. Dr. Kobza has received institutional grants from Abbott Vascular, Boston Scientific, Biosense Webster, Biotronik, Medtronic, and Sis-Medical. Dr. Linke has received institutional grants from Novartis; and has received personal fees from Medtronic, Abbott Vascular, Edwards Lifesciences, Boston Scientific, AstraZeneca, Novartis, and Pfizer. Dr. Stortecky has received institutional research grants from Edwards Lifesciences, Medtronic, and Boston Scientific; and has been a consultant for Boston Scientific, BTG, and Teleflex. Dr. Nietlispach has been a consultant for Edwards Lifesciences and Abbott Vascular. Dr. Pilgrim has received institutional research grants from Edwards Lifesciences, Biotronik, and Boston Scientific; and has received personal fees from Biotronik and Boston Scientific. Dr. Toggweiler has been a proctor for Boston Scientific, Medtronic, Biosensors/New Valve Technology, and Abbott Vascular; has been a consultant for Carag, Medira, Boston Scientific, Medtronic, Biosensors/New Valve Technology, and Abbott Vascular; has received institutional research grants from Boston Scientific and Fumedica; and holds equity in Hi-D Imaging. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2021 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: The aim of this study was to investigate the impact of valvular and nonvalvular atrial fibrillation (AF) in patients undergoing transcatheter aortic valve replacement (TAVR)., Background: AF has been associated with adverse clinical outcomes after TAVR. However, the differential impact of valvular as opposed to nonvalvular AF has not been investigated., Methods: In a retrospective analysis of a prospective registry, valvular AF was defined as AF in the setting of concomitant mitral stenosis or the presence of a mitral valve prosthesis. The presence of mitral stenosis was determined by pre-procedural echocardiography. The primary endpoint was a composite of cardiovascular death or disabling stroke at 1 year after TAVR., Results: Among 1,472 patients undergoing TAVR between August 2007 and June 2018, AF was recorded in 465 patients (31.6%) and categorized as nonvalvular in 376 (25.5%) and valvular in 89 (6.0%). AF scores including HAS-BLED, CHADS 2 , and CHA 2 DS 2 -VASc were comparable between patients with nonvalvular and valvular AF. The primary endpoint occurred in 9.3% of patients with no AF, in 14.5% of patients with nonvalvular AF (hazard ratio: 1.57; 95% confidence interval: 1.12 to 2.20; p = 0.009), and in 24.2% of patients with valvular AF (hazard ratio: 2.75; 95% confidence interval: 1.71 to 4.41; p < 0.001). Valvular AF conferred an increased risk for cardiovascular death or disabling stroke compared with nonvalvular AF (hazard ratio: 1.77; 95% confidence interval: 1.07 to 2.94; p = 0.027)., Conclusions: The presence of valvular AF in patients undergoing TAVR increased the risk for cardiovascular death or disabling stroke compared with both no AF and nonvalvular AF. (SWISS TAVI Registry; NCT01368250)., (Copyright © 2020 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: This study aimed to systematically assess the importance of left ventricular outflow tract (LVOT) calcification on procedural outcomes and device performances with contemporary transcatheter heart valve (THV) systems., Background: LVOT calcification has been associated with adverse clinical outcomes after transcatheter aortic valve replacement (TAVR). However, the available evidence is limited to observational data with modest numbers and incomplete assessment of the effect of the different THV systems., Methods: In a retrospective analysis of a prospective single-center registry, LVOT calcification was assessed in a semiquantitative fashion. Moderate or severe LVOT calcification was documented in the presence of 2 nodules of calcification, or 1 extending >5 mm in any direction, or covering >10 % of the perimeter of the LVOT., Results: Among 1,635 patients undergoing TAVR between 2007 and 2018, moderate or severe LVOT calcification was found in 407 (24.9%). Patients with moderate or severe LVOT calcification had significantly higher incidences of annular rupture (2.3% vs. 0.2%; p < 0.001), bailout valve-in-valve implantation (2.9% vs. 0.8%; p = 0.004), and residual aortic regurgitation (11.1% vs. 6.3%; p = 0.002). Balloon-expandable valves conferred a higher risk of annular rupture in the presence of moderate or severe LVOT calcification (4.0% vs. 0.4%; p = 0.002) as compared with the other valve designs. There was no significant interaction of valve design or generation and LVOT calcification with regard to the occurrence of bailout valve-in-valve implantation and residual aortic regurgitation., Conclusions: Moderate or severe LVOT calcification confers increased risks of annular rupture, residual aortic regurgitation, and implantation of a second valve. The risk of residual aortic regurgitation is consistent across valve designs and generations. (SWISS TAVI Registry; NCT01368250)., (Copyright © 2020 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

The minimal invasive anterolateral Yale 2-incision approach for total hip arthroplasty aims minimizing damage to the muscles for faster recovery of function. Therefore the hypothesis was investigated, that during the rehabilitation process the Yale approach shows a faster return to natural gait than a conventional lateral approach. Nineteen patients had the Yale, 16 the conventional Bauer approach. Instrumented gait analysis was performed 3 days, 3 and 12 month post operatively. Velocity, cadence, step length, weight bearing, thorax lean, Trendelenburg limp, hip abduction moments, and hip muscle activation times were evaluated. Three days post-surgery a significantly greater loading of the treated limb and increased hip abduction moment were observed in the Yale group. In addition, the Yale group showed its greatest improvement in walking speed and step length between at 3 days and 3 months, whereas the conventional group showed an additional significant gain between 3 and 12 month to reach a similar walking speed as the Yale group. For all hip muscles investigated, only muscle tensor fasciae latae in the conventional group showed a significant increase in activation time between 3 days and 3 months. This study showed significantly faster return to natural gait in the Yale compared to the conventional approach, which could be biomechanically related to less impairment of abductor muscles in the Yale approach., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The primary aim of the epidemiologic study of one million U.S. radiation workers and veterans [the Million Worker Study (MWS)] is to provide scientifically valid information on the level of radiation risk when exposures are received gradually over time and not within seconds, as was the case for Japanese atomic bomb survivors. The primary outcome of the epidemiologic study is cancer mortality, but other causes of death such as cardiovascular disease and cerebrovascular disease will be evaluated. The success of the study is tied to the validity of the dose reconstruction approaches to provide realistic estimates of organ-specific radiation absorbed doses that are as accurate and precise as possible and to properly evaluate their accompanying uncertainties. The dosimetry aspects for the MWS are challenging in that they address diverse exposure scenarios for diverse occupational groups being studied over a period of up to 70 y. The dosimetric issues differ among the varied exposed populations that are considered: atomic veterans, U.S. Department of Energy workers exposed to both penetrating radiation and intakes of radionuclides, nuclear power plant workers, medical radiation workers, and industrial radiographers. While a major source of radiation exposure to the study population comes from external gamma- or x-ray sources, for some of the study groups, there is a meaningful component of radionuclide intakes that requires internal radiation dosimetry assessments. Scientific Committee 6-9 has been established by the National Council on Radiation Protection and Measurements (NCRP) to produce a report on the comprehensive organ dose assessment (including uncertainty analysis) for the MWS. The NCRP dosimetry report will cover the specifics of practical dose reconstruction for the ongoing epidemiologic studies with uncertainty analysis discussions and will be a specific application of the guidance provided in NCRP Report Nos. 158, 163, 164, and 171. The main role of the Committee is to provide guidelines to the various groups of dosimetrists involved in the MWS to ensure that certain dosimetry criteria are considered: calculation of annual absorbed doses in the organs of interest, separation of low and high linear-energy transfer components, evaluation of uncertainties, and quality assurance and quality control. It is recognized that the MWS and its approaches to dosimetry are a work in progress and that there will be flexibility and changes in direction as new information is obtained with regard to both dosimetry and the epidemiologic features of the study components. This paper focuses on the description of the various components of the MWS, the available dosimetry results, and the challenges that have been encountered. It is expected that the Committee will complete its report in 2016.