Discrete Event Simulation for Decision Modeling in Health Care: Lessons from Abdominal Aortic Aneurysm Screening

Markov models are often used to evaluate the cost-effectiveness of new healthcare interventions but they are sometimes not flexible enough to allow accurate modeling or investigation of alternative scenarios and policies. A Markov model previously demonstrated that a one-off invitation to screening for abdominal aortic aneurysm (AAA) for men aged 65 y in the UK and subsequent follow-up of identified AAAs was likely to be highly cost-effective at thresholds commonly adopted in the UK (£20,000 to £30,000 per quality adjusted life-year). However, new evidence has emerged and the decision problem has evolved to include exploration of the circumstances under which AAA screening may be cost-effective, which the Markov model is not easily able to address. A new model to handle this more complex decision problem was needed, and the case of AAA screening thus provides an illustration of the relative merits of Markov models and discrete event simulation (DES) models. An individual-level DES model was built using the R programming language to reflect possible events and pathways of individuals invited to screening v. those not invited. The model was validated against key events and cost-effectiveness, as observed in a large, randomized trial. Different screening protocol scenarios were investigated to demonstrate the flexibility of the DES. The case of AAA screening highlights the benefits of DES, particularly in the context of screening studies

Meta-analysis of individual-patient data from EVAR-1, DREAM, OVER and ACE trials comparing outcomes of endovascular or open repair for abdominal aortic aneurysm over 5 years

Background: The erosion of the early mortality advantage of elective endovascular aneurysm repair (EVAR) compared with open repair of abdominal aortic aneurysm remains without a satisfactory explanation.Methods: An individual-patient data meta-analysis of four multicentre randomized trials of EVAR versus open repair was conducted to a prespecified analysis plan, reporting on mortality, aneurysm-related mortality and reintervention.Results: The analysis included 2783 patients, with 14 245 person-years of follow-up (median 5.5years). Early (0-6 months after randomization) mortality was lower in the EVAR groups (46 of 1393 versus 73 of 1390 deaths; pooled hazard ratio 0.61, 95 per cent c. i. 0.42 to 089; P = 0010), primarily because 30-day operative mortality was lower in the EVAR groups (16 deaths versus 40 for open repair; pooled odds ratio 040, 95 per cent c. i. 022 to 074). Later (within 3 years) the survival curves converged, remaining converged to 8 years. Beyond 3 years, aneurysm-related mortality was significantly higher in the EVAR groups (19 deaths versus 3 for open repair; pooled hazard ratio 516, 149 to 1789; P = 0010). Patients with moderate renal dysfunction or previous coronary artery disease had no early survival advantage under EVAR. Those with peripheral artery disease had lower mortality under open repair (39 deaths versus 62 for EVAR; P = 0022) in the period from 6 months to 4 years after randomization.Conclusion: The early survival advantage in the EVAR group, and its subsequent erosion, were confirmed. Over 5 years, patients of marginal fitness had no early survival advantage from EVAR compared with open repair. Aneurysm-related mortality and patients with low ankle : brachial pressure index contributed to the erosion of the early survival advantage for the EVAR group. Trial registration numbers: EVAR-1, ISRCTN55703451; DREAM(Dutch Randomized Endovascular Aneurysm Management), NCT00421330; ACE (Anevrysme de l'aorte abdominale, Chirurgie versus Endoprothsse), NCT00224718; OVER (Open Versus Endovascular Repair Trial for Abdominal Aortic Aneurysms), NCT00094575.</p

Observations from the IMPROVE trial concerning the clinical care of patients with ruptured abdominal aortic aneurysm.

BACKGROUND: Single-centre series of the management of patients with ruptured abdominal aortic aneurysm (AAA) are usually too small to identify clinical factors that could improve patient outcomes. METHODS: IMPROVE is a pragmatic, multicentre randomized clinical trial in which eligible patients with a clinical diagnosis of ruptured aneurysm were allocated to a strategy of endovascular aneurysm repair (EVAR) or to open repair. The influences of time and manner of hospital presentation, fluid volume status, type of anaesthesia, type of endovascular repair and time to aneurysm repair on 30-day mortality were investigated according to a prespecified plan, for the subgroup of patients with a proven diagnosis of ruptured or symptomatic AAA. Adjustment was made for potential confounding factors. RESULTS: Some 558 of 613 randomized patients had a symptomatic or ruptured aneurysm: diagnostic accuracy was 91·0 per cent. Patients randomized outside routine working hours had higher operative mortality (adjusted odds ratio (OR) 1·47, 95 per cent confidence interval 1·00 to 2·17). Mortality rates after primary and secondary presentation were similar. Lowest systolic blood pressure was strongly and independently associated with 30-day mortality (51 per cent among those with pressure below 70 mmHg). Patients who received EVAR under local anaesthesia alone had greatly reduced 30-day mortality compared with those who had general anaesthesia (adjusted OR 0·27, 0·10 to 0·70). CONCLUSION: These findings suggest that the outcome of ruptured AAA might be improved by wider use of local anaesthesia for EVAR and that a minimum blood pressure of 70 mmHg is too low a threshold for permissive hypotension

Regional brain metabolism in a murine systemic lupus erythematosus model

Systemic lupus erythematosus (SLE) is characterized by multiorgan inflammation, neuropsychiatric disorders (NPSLE), and antinuclear antibodies. We previously identified a subset of anti-DNA antibodies (DNRAb) cross-reactive with the N-methyl-D-aspartate receptor, present in 30% to 40% of patients, able to enhance excitatory post-synaptic potentials and trigger neuronal apoptosis. DNRAb + mice exhibit memory impairment or altered fear response, depending on whether the antibody penetrates the hippocampus or amygdala. Here, we used 18F-fluorodeoxyglucose (FDG) microPET to plot changes in brain metabolism after regional blood-brain barrier (BBB) breach. In DNRAb + mice, metabolism declined at the site of BBB breach in the first 2 weeks and increased over the next 2 weeks. In contrast, DNRAb mice exhibited metabolic increases in these regions over the 4 weeks after the insult. Memory impairment was present in DNRAb + animals with hippocampal BBB breach and altered fear conditioning in DNRAb + mice with amygdala BBB breach. In DNRAb + mice, we observed an inverse relationship between neuron number and regional metabolism, while a positive correlation was observed in DNRAb mice. These findings suggest that local metabolic alterations in this model take place through different mechanisms with distinct time courses, with important implications for the interpretation of imaging data in SLE subjects

Of precarity and conspiracy: introducing a socio-functional model of conspiracy beliefs

Conspiracy Beliefs (CB) are a key vector of violent extremism, radicalism and unconventional political events. So far, social-psychological research has extensively documented how cognitive, emotional and intergroup factors can promote CB. Evidence also suggests that adherence to CB moves along social class lines: low-income and low-education are among the most robust predictors of CB. Yet, the potential role of precarity—the subjective experience of permanent insecurity stemming from objective material strain—in shaping CB remains largely unexplored. In this paper, we propose for the first time a socio-functional model of CB. We test the hypothesis that precarity could foster increased CB because it undermines trust in government and the broader political ‘elites’. Data from the World Value Survey (n = 21,650; Study 1, electoral CB) and from representative samples from polls conducted in France (n = 1760, Study 2a, conspiracy mentality) and Italy (n = 2196, Study 2b, COVID-19 CB), corroborate a mediation model whereby precarity is directly and indirectly associated with lower trust in authorities and higher CB. In addition, these links are robust to adjustment on income, self-reported SES and education. Considering precarity allows for a truly social-psychological understanding of CB as the by-product of structural issues (e.g. growing inequalities). Results from our socio-functional model suggest that implementing solutions at the socio-economic level could prove efficient in fighting CB

Comparative clinical effectiveness and cost effectiveness of endovascular strategy vs open repair for ruptured abdominal aortic aneurysm: three year results of the IMPROVE randomised trial

Objective To assess the three year clinical outcomes and cost effectiveness of a strategy of endovascular repair (if aortic morphology is suitable, open repair if not) versus open repair for patients with suspected ruptured abdominal aortic aneurysm. Design Randomised controlled trial. Participants 613 eligible patients (480 men) with a clinical diagnosis of ruptured aneurysm, of whom 502 underwent emergency repair for rupture. Interventions 316 patients were randomised to an endovascular strategy (275 with confirmed rupture) and 297 to open repair (261 with confirmed rupture). Main outcome measures Mortality, with reinterventions after aneurysm repair, quality of life, and hospital costs to three years as secondary measures. Results The maximum follow-up for mortality was 7.1 years, with two patients in each group lost to follow-up by three years. After similar mortality by 90 days, in the mid-term (three months to three years) there were fewer deaths in the endovascular than the open repair group (hazard ratio 0.57, 95% confidence interval 0.36 to 0.90), but by seven years mortality was about 60% in each group (hazard ratio 0.92, 0.75 to 1.13). Results for the 502 patients with repaired ruptures were more pronounced: three year mortality was lower in the endovascular strategy group (42% v 54%; odds ratio 0.62, 0.43 to 0.88), but after seven years there was no clear difference between the groups (hazard ratio 0.86, 0.68 to 1.08). Reintervention rates up to three years were not significantly different between the randomised groups (hazard ratio 1.02, 0.79 to 1.32); the initial rapid rate of reinterventions was followed by a much slower mid-term reintervention rate in both groups. The early higher average quality of life in the endovascular strategy versus open repair group, coupled with the lower mortality at three years, led to a gain in average quality adjusted life years (QALYs) at three years of 0.17 (95% confidence interval 0.00 to 0.33). The endovascular strategy group spent fewer days in hospital and had lower average costs of −£2605 (€2813; $3439) (95% confidence interval −£5966 to £702). The probability that the endovascular strategy is cost effective was >90% at all levels of willingness to pay for a QALY gain. Conclusions At three years, compared with open repair, an endovascular strategy for suspected ruptured abdominal aortic aneurysm was associated with a survival advantage, a gain in QALYs, similar levels of reintervention, and reduced costs, and this strategy was cost effective. These findings support the increasing use of an endovascular strategy, with wider availability of emergency endovascular repair. Trial registration Current Controlled Trials ISRCTN48334791; ClinicalTrials NCT00746122This project was funded by the UK National Institute for Health Research (NIHR) Health Technology Assessment (HTA) programme (project No 07/37/64). The views and opinions expressed herein are those of the authors and do not necessarily reflect those of the HTA programme, NIHR, National Health Service, or the Department of Health. Neither the funder nor the sponsor had any role in study design, data collection, analysis and interpretation of the findings