Relationship between syringomyelia and myxomatous mitral valve disease in Cavalier King Charles spaniels

BACKGROUND

Syringomyelia (SM) and myxomatous mitral valve disease (MMVD) are highly prevalent in Cavalier King Charles spaniels (CKCS). Cardiac status in CKCS with and without SM is currently unknown.

OBJECTIVES

To investigate the association between SM and MMVD severity in CKCS and CKCS with SM with and without clinical signs of SM.

ANIMALS

Fifty-five CKCS: 40 with SM (22 symptomatic and 18 asymptomatic) and 15 without SM.

METHODS

A combined retrospective and prospective study. MRI and echocardiography were used to diagnose SM and MMVD, respectively. The association between SM and MMVD severity (left ventricle internal diameter in diastole normalized to bodyweight [LVIDDN] and left atrium to aortic ratio [LA/Ao]) were tested using multivariable linear regression analysis adjusting for sex and age.

RESULTS

Overall, no significant difference in LVIDDN and LA/Ao was found between CKCS with or without SM. However, CKCS with symptomatic SM had significantly smaller LVIDDN (1.45 [1.30-1.50]) (median [IQR]) and LA/Ao (1.20 [1.10-1.28]) compared to CKCS with asymptomatic SM (1.60 [1.50-1.90] and 1.40 [1.20-1.75]) as well as CKCS without SM (0.24 [0.03-0.45] and 0.30 [0.05-0.56]) (all P values <.03).

CONCLUSIONS AND CLINICAL IMPORTANCE

An association between MMVD and SM was not confirmed in this cohort of CKCS, indicating that MMVD and SM do not co-segregate. However, CKCS with symptomatic SM had smaller left ventricle and atrial size compared to CKCS with asymptomatic SM and CKCS without SM.

Inverse probability of treatment weighting with generalized linear outcome models for doubly robust estimation

There are now many options for doubly robust estimation; however, there is a concerning trend in the applied literature to believe that the combination of a propensity score and an adjusted outcome model automatically results in a doubly robust estimator and/or to misuse more complex established doubly robust estimators. A simple alternative, canonical link generalized linear models (GLM) fit via inverse probability of treatment (propensity score) weighted maximum likelihood estimation followed by standardization (theg $$ g $$ -formula) for the average causal effect, is a doubly robust estimation method. Our aim is for the reader not just to be able to use this method, which we refer to as IPTW GLM, for doubly robust estimation, but to fully understand why it has the doubly robust property. For this reason, we define clearly, and in multiple ways, all concepts needed to understand the method and why it is doubly robust. In addition, we want to make very clear that the mere combination of propensity score weighting and an adjusted outcome model does not generally result in a doubly robust estimator. Finally, we hope to dispel the misconception that one can adjust for residual confounding remaining after propensity score weighting by adjusting in the outcome model for what remains 'unbalanced' even when using doubly robust estimators. We provide R code for our simulations and real open-source data examples that can be followed step-by-step to use and hopefully understand the IPTW GLM method. We also compare to a much better-known but still simple doubly robust estimator.

Estimation of separable direct and indirect effects in a continuous-time illness-death model

In this article we study the effect of a baseline exposure on a terminal time-to-event outcome either directly or mediated by the illness state of a continuous-time illness-death process with baseline covariates. We propose a definition of the corresponding direct and indirect effects using the concept of separable (interventionist) effects (Robins and Richardson in Causality and psychopathology: finding the determinants of disorders and their cures, Oxford University Press, 2011; Robins et al. in arXiv:2008.06019 , 2021; Stensrud et al. in J Am Stat Assoc 117:175-183, 2022). Our proposal generalizes Martinussen and Stensrud (Biometrics 79:127-139, 2023) who consider similar causal estimands for disentangling the causal treatment effects on the event of interest and competing events in the standard continuous-time competing risk model. Unlike natural direct and indirect effects (Robins and Greenland in Epidemiology 3:143-155, 1992; Pearl in Proceedings of the seventeenth conference on uncertainty in artificial intelligence, Morgan Kaufmann, 2001) which are usually defined through manipulations of the mediator independently of the exposure (so-called cross-world interventions), separable direct and indirect effects are defined through interventions on different components of the exposure that exert their effects through distinct causal mechanisms. This approach allows us to define meaningful mediation targets even though the mediating event is truncated by the terminal event. We present the conditions for identifiability, which include some arguably restrictive structural assumptions on the treatment mechanism, and discuss when such assumptions are valid. The identifying functionals are used to construct plug-in estimators for the separable direct and indirect effects. We also present multiply robust and asymptotically efficient estimators based on the efficient influence functions. We verify the theoretical properties of the estimators in a simulation study, and we demonstrate the use of the estimators using data from a Danish registry study.

Functional and morphological renal changes in a Göttingen Minipig model of obesity-related and diabetic nephropathy

Obesity-related glomerulopathy and diabetic nephropathy (DN) are serious complications to metabolic syndrome and diabetes. The purpose was to study effects of a fat, fructose and cholesterol-rich (FFC) diet with and without salt in order to induce hypertension on kidney function and morphology in Göttingen Minipigs with and without diabetes. Male Göttingen Minipigs were divided into 4 groups: SD (standard diet, n = 8), FFC (FFC diet, n = 16), FFC-DIA (FFC diet + diabetes, n = 14), FFC-DIA + S (FFC diet with extra salt + diabetes, n = 14). Blood and urine biomarkers, glomerular filtration rate (GFR), blood pressure (BP) and resistive index (RI) were evaluated after 6-7 months (T1) and 12-13 months (T2). Histology, electron microscopy and gene expression (excluding FFC-DIA + S) were evaluated at T2. All groups fed FFC-diet displayed obesity, increased GFR and RI, glomerulomegaly, mesangial expansion (ME) and glomerular basement membrane (GBM) thickening. Diabetes on top of FFC diet led to increased plasma glucose and urea and proteinuria and tended to exacerbate the glomerulomegaly, ME and GBM thickening. Four genes (CDKN1A, NPHS2, ACE, SLC2A1) were significantly deregulated in FFC and/or FFC-DIA compared to SD. No effects on BP were observed. Göttingen Minipigs fed FFC diet displayed some of the renal early changes seen in human obesity. Presence of diabetes on top of FFC diet exacerbated the findings and lead to changes resembling the early phases of human DN.

Estimation of separable direct and indirect effects in continuous time

Many research questions involve time-to-event outcomes that can be prevented from occurring due to competing events. In these settings, we must be careful about the causal interpretation of classical statistical estimands. In particular, estimands on the hazard scale, such as ratios of cause-specific or subdistribution hazards, are fundamentally hard to interpret causally. Estimands on the risk scale, such as contrasts of cumulative incidence functions, do have a clear causal interpretation, but they only capture the total effect of the treatment on the event of interest; that is, effects both through and outside of the competing event. To disentangle causal treatment effects on the event of interest and competing events, the separable direct and indirect effects were recently introduced. Here we provide new results on the estimation of direct and indirect separable effects in continuous time. In particular, we derive the nonparametric influence function in continuous time and use it to construct an estimator that has certain robustness properties. We also propose a simple estimator based on semiparametric models for the two cause-specific hazard functions. We describe the asymptotic properties of these estimators and present results from simulation studies, suggesting that the estimators behave satisfactorily in finite samples. Finally, we reanalyze the prostate cancer trial from Stensrud et al. (2020).

Discussion of "A formal causal interpretation of the case-crossover design"

Discussion on "A formal causal interpretation of the case-crossover design" by Zach Shahn, Miguel A. Hernan, and James M. Robins.

Development of upper gastrointestinal cancer in patients with symptomatic gallstones, cholecystectomy, and sphincterotomy: A nationwide cohort study

BACKGROUND AND OBJECTIVE

Exposures of gallstones and treatments thereof in relation to development of cancer have not been explored before in long-term follow-up studies. Our objective was to determine whether symptomatic gallstones, cholecystectomy, or sphincterotomy were associated with development of upper gastrointestinal cancers.

METHODS

This is a nationwide cohort study of persons born in Denmark 1930-1984 included from age 30 years with long-term follow-up (1977-2014). Exposures were hospital admissions with gallstones, cholecystectomy, and sphincterotomy. Time-varying covariates were included in analyses to allow the impact of exposures to change with time. Follow-up periods were 2-5 and > 5 years. Hazard ratios (HR) with 95% confidence intervals (CI) were reported.

RESULTS

A total of 4,465,962 persons were followed. We found positive associations between sphincterotomy and biliary (>5 years HR 4.34, CI [2.17-8.70]), gallbladder (2-5 years HR 20.7, CI [8.55-50.1]), and pancreatic cancer (2-5 years HR 3.68, CI [2.09-6.49]). Cholecystectomy was positively associated with duodenal (2-5 years HR 2.94, CI [1.31-6.58]) and small bowel cancer (2-5 years HR 2.75, CI [1.56-4.87]). Inverse associations were seen for cholecystectomy and biliary (>5 years HR 0.60, CI [0.41-0.87]), pancreatic (>5 years HR 0.45 CI [0.35-0.57]), esophageal (>5 years HR 0.57, CI [0.43-0.74]), and gastric cancer (>5 years HR 0.68, CI [0.55-0.86]) and for gallstones and pancreatic cancer (>5 years HR 0.66, CI [0.47-0.93]). Gallstones were positively associated with gallbladder (>5 years HR 3.51, CI [2.02-6.10]) and small bowel cancer (2-5 years HR 3.21, CI [1.60-6.45]).

CONCLUSIONS

A positive association between sphincterotomy and biliary cancer was identified. Cholecystectomy seems to be inversely associated with biliary, pancreatic, esophageal, and gastric cancer. Associations should be explored in similar large cohorts.

Maternal intake of folate during pregnancy and risk of cerebral palsy in the MOBAND-CP cohort

BACKGROUND

Folate prevents neural tube defects and may play a role in some neurodevelopmental disorders.

OBJECTIVES

We investigated whether higher intakes of periconceptional or midpregnancy folate, as recommended, were associated with a reduced risk of offspring cerebral palsy (CP).

METHODS

We included participants from the Nordic collaboration cohort consisting of mother-child dyads in the Danish National Birth Cohort and the Norwegian Mother, Father, and Child Cohort Study [combined as MOthers and BAbies in Norway and Denmark (MOBAND-CP)]. A total of 190,989 live-born children surviving the first year of life were included. Missing covariate data were multiply imputed. Our exposures were defined as any or no folic acid supplementation in gestational weeks (GWs) -4 to 8 (periconceptional), 9 to 12, and -4 to 12, and supplemental, dietary, and total folate during midpregnancy (GWs 22-25). CP overall and the unilateral and bilateral spastic subtypes, as well as CP with low or moderate/high gross motor function impairments, were our outcomes of interest.

RESULTS

Periconceptional folic acid supplementation was not associated with CP [adjusted odds ratio (aOR), 1.02; 95% CI: 0.82-1.28]. However, supplementation in GWs 9 to 12 was associated with a reduced risk of CP (aOR, 0.74; 95% CI: 0.57-0.96), and inverse associations were indicated for both the unilateral (aOR, 0.68; 95% CI: 0.46-1.02) and bilateral (aOR, 0.70; 95% CI: 0.49-1.02) spastic subtypes, although the associations were not statistically significant. Supplemental or dietary folate in midpregnancy alone were not associated with CP. Strong inverse associations were observed with low gross motor function impairment (aOR, 0.49; 95% CI: 0.29-0.83), while for unilateral CP the aOR was 0.63 (95% CI: 0.34-1.22) for intakes of ≥500 compared to ≤199 dietary folate equivalents/day during midpregnancy.

CONCLUSIONS

Our findings suggest that folate intakes in GWs 9 to 12 and midpregnancy were associated with lower risks of CP, while no association was observed for periconceptional supplementation.

Analysis of time-to-event for observational studies: Guidance to the use of intensity models

This paper provides guidance for researchers with some mathematical background on the conduct of time-to-event analysis in observational studies based on intensity (hazard) models. Discussions of basic concepts like time axis, event definition and censoring are given. Hazard models are introduced, with special emphasis on the Cox proportional hazards regression model. We provide check lists that may be useful both when fitting the model and assessing its goodness of fit and when interpreting the results. Special attention is paid to how to avoid problems with immortal time bias by introducing time-dependent covariates. We discuss prediction based on hazard models and difficulties when attempting to draw proper causal conclusions from such models. Finally, we present a series of examples where the methods and check lists are exemplified. Computational details and implementation using the freely available R software are documented in Supplementary Material. The paper was prepared as part of the STRATOS initiative.

Subtleties in the interpretation of hazard contrasts

The hazard ratio is one of the most commonly reported measures of treatment effect in randomised trials, yet the source of much misinterpretation. This point was made clear by Hernán (Epidemiology (Cambridge, Mass) 21(1):13-15, 2010) in a commentary, which emphasised that the hazard ratio contrasts populations of treated and untreated individuals who survived a given period of time, populations that will typically fail to be comparable-even in a randomised trial-as a result of different pressures or intensities acting on different populations. The commentary has been very influential, but also a source of surprise and confusion. In this note, we aim to provide more insight into the subtle interpretation of hazard ratios and differences, by investigating in particular what can be learned about a treatment effect from the hazard ratio becoming 1 (or the hazard difference 0) after a certain period of time. We further define a hazard ratio that has a causal interpretation and study its relationship to the Cox hazard ratio, and we also define a causal hazard difference. These quantities are of theoretical interest only, however, since they rely on assumptions that cannot be empirically evaluated. Throughout, we will focus on the analysis of randomised experiments.

S100B and NSE in Cluster Headache - Evidence for Glial Cell Activation?

OBJECTIVE

Neuronal-specific enolase (NSE) and protein S100B have gained considerable interest as the markers of CNS injury, glial cell activation, and/or blood-brain barrier (BBB) disruption. No studies have investigated NSE and S100B in cluster headache (CH), but these biomarkers could contribute to the understanding of CH.

METHODS

Patients with episodic CH in bout (eCHa), in remission (eCHr), and chronic CH (cCH) were included in this randomized, double-blind, placebo-controlled, 2-way cross-over provocation study carried out at the Danish Headache Center. The primary endpoints included (1) differences of NSE and S100B in between groups (eCHa, eCHr, and cCH) at baseline; (2) differences over time in plasma concentrations of NSE and S100B between patient developing an attack and those who did not; (3) differences in plasma concentrations over time of NSE and S100B between active day and placebo day. Baseline findings were compared to the historical data on migraine patients and healthy controls and presented with means ± SD.

RESULTS

Nine eCHa, 9 eCHr, and 13 cCH patients completed the study and blood samples from 11 CGRP-induced CH attacks were obtained. There were no differences in NSE levels between CH groups at baseline, but CH patients in active disease phase had higher levels compared with 32 migraine patients (9.1 ± 2.2 µg/L vs 6.0 ± 2.2 µg/L, P < .0001) and 6 healthy controls (9.1 ± 2.2 µg/L vs 7.3 ± 2.0 µg/L, P = .007). CGRP-infusion caused no NSE changes and, but a slight, non-significant, increase in NSE was seen in patients who reported a CGRP-induced CH attack (2.39 µg/L, 95% Cl [-0.26, 3.85], P = .061). At baseline S100B levels in eCHa patients were higher compared to cCH patients (0.06 ± 0.02 µg/L vs 0.04 ± 0.02 µg/L, P = .018). Infusion of CGRP and CGRP-induced attacks did not change S100B levels. Apart from induced CH-attacks no other adverse events were noted.

CONCLUSIONS

At baseline eCHa patients had higher S100B plasma levels than cCH patients and there was a slight, however not significant, NSE increase in response to CGRP-induced CH attack. Our findings suggest a possible role of an ictal activation of glial cells in CH pathophysiology, but further studies are warranted.

Intermittent mitral regurgitation in Cavalier King Charles spaniels: Short-term progression and influence of stress tests

In young Cavalier King Charles spaniels (CKCS), intermittent mitral regurgitation (iMR; defined as moderate to severe mitral regurgitation [MR] in a small proportion of heartbeats), has been associated with an increased risk of cardiac death due to myxomatous mitral valve disease (MMVD). It is associated with increased R-R interval variability. Little is known about response to physiological factors and whether iMR is a precursor for developing significant MR. The aim of this study was to determine the effect of stress testing on the presence of iMR and heart rate, and short-term (1-2 year) progression of MR in CKCS with and without iMR. In total, 52 CKCS were included. Substudy 1 enrolled six dogs with iMR and 11 dogs without iMR. Substudy 2 enrolled 14 dogs with iMR and 28 dogs without iMR. Substudy 1 prospectively assessed the influence of stress testing on the presence of iMR and heart rate. Substudy 2 retrospectively evaluated short-term progression of iMR. During stress testing, iMR disappeared in 50% of CKCS and no iMR was recorded at mean heart rates >150 beats/min. Heart rate response did not differ between CKCS with or without iMR. CKCS with iMR did not have a higher odds (odds ratio = 5.2; 95% confidence interval, 0.7-38.2) of MR progression compared to controls (P = 0.1). In conclusion, physical stress influenced the occurrence of iMR in CKCS, but heart rate response was not different from CKCS without iMR. Intermittent mitral regurgitation did not significantly predict short-term MR progression. In stressed CKCS with early disease, iMR may be overlooked.

Rivaroxaban Versus Apixaban for Stroke Prevention in Atrial Fibrillation

Background:

The comparative effectiveness of non-vitamin K antagonist oral anticoagulants (NOACs) is uncertain, as they have not been compared directly in randomized trials. Previous observational comparisons of NOACs are likely to be biased by unmeasured confounders. We sought to compare the efficacy and safety of rivaroxaban and apixaban for stroke prevention in patients with atrial fibrillation (AF), using practice variation in preference for NOAC as an instrumental variable.

Methods and Results:

Patients started on apixaban or rivaroxaban after newly diagnosed AF were identified using Danish nationwide registries. Patients were categorized according to facility preferences for type of NOAC, independent of actual treatment, measured as fraction of the prior 20 patients with AF initiated on rivaroxaban in the same facility. Facility preference for NOAC was used as an instrumental variable. The occurrence of stroke/thromboembolism, major bleeding, myocardial infarction, and all-cause mortality over 2 years of follow-up were investigated using adjusted Cox regressions. We analyzed 6264 patients with AF initiated on rivaroxaban or apixaban. NOAC preference was strongly related to actual choice of treatment but not associated with any other measured baseline characteristics. Patients treated in facilities that had preference for rivaroxaban had more major bleeding: compared with patients treated in facilities that used rivaroxaban in 0% to 20% of cases, the adjusted hazard ratio for bleeding was 1.06 when treated in a facility with 25% to 40% use; 1.41 with 45% to 60% use; 1.51 with 65% to 80% use; and 1.81 with 0% to 100% use ( P trend =0.01). Higher facility preference for rivaroxaban was not significantly associated with increased risk of stroke/thromboembolism ( P trend =0.06), myocardial infarction ( P trend =0.65), or all-cause mortality ( P trend =0.89). When we used the instrumental variable to model the causal relationship between choice of NOAC and major bleeding, relative risk with rivaroxaban was 1.89 (95% CI, 1.06–2.72) compared with apixaban.

Conclusions:

Using instrumental variable estimation in a cohort of patients with AF, rivaroxaban was associated with higher risk of major bleeding compared with apixaban. No significant associations to other outcomes were found in main analyses.

A causal proportional hazards estimator under homogeneous or heterogeneous selection in an IV setting

In this paper we present a framework to do estimation in a structural Cox model when there may be unobserved confounding. The model is phrased in terms of a selection bias function and a baseline model that describes how covariates affect the survival time in a scenario without exposure. In this way model congeniality is ensured. The method uses an instrumental variable. Interestingly, the formulated model turns out to have similarities to the so-called Cox-Aalen survival model for the observed data. We exploit this to enhance estimation of the unknown parameters. This also allows us to derive large sample properties of the proposed estimator.

P4779High facility preference for rivaroxaban in atrial fibrillation increases risk of major bleeding compared to facility preference for apixaban

Background

No randomized trial has compared efficacy and safety of non-vitamin K antagonist oral anticoagulants (NOACs) in atrial fibrillation (AF). Previous real-world comparisons could be biased by patient characteristics of importance for treatment selection, but instrumental variables could potentially account for measured and unmeasured confounders.

Purpose

To compare efficacy and safety of rivaroxaban and apixaban using facility preference for type of NOAC as instrumental variable.

Methods

AF patients started on apixaban or rivaroxaban were identified using nationwide registries. We categorized patients according to facility preference for type of NOAC, measured as percentage of the prior 20 AF patients started on rivaroxaban in the same facility. Occurrence of stroke/thromboembolism (TE), major bleeding, myocardial infarction and all-cause mortality during two years of follow-up were investigated using adjusted Cox regressions. To further examine general frailty according to facility preferences we also investigated occurrence of cancer, urogenital tract infection, dehydration and fracture.

Results

We analyzed 6264 AF patients initiated on rivaroxaban or apixaban. Compared with patients treated in facilities that used rivaroxaban in 0–20% of cases, the adjusted hazard ratio for bleeding was 1.05 when treated in a facility with 25–40% use; 1.40 with 45–60% use; 1.50 with 65–80% use; and 1.81 for 85–100% use (Ptrend=0.002). Higher facility level use of rivaroxaban was not associated with increased risk of stroke/TE (Ptrend=0.06), myocardial infarction (Ptrend=0.87) or all-cause mortality (Ptrend=0.91), and there was no association between facility preference for rivaroxaban and risk of cancer (Ptrend=0.83), urogenital tract infection (Ptrend=0.49), dehydration (Ptrend=0.91) or fracture (Ptrend=0.47).

Characteristics by facility preference Percent of previous AF patients from facility started on rivaroxaban P for trend 0–20% 25–40% 45–60% 65–80% 85–100% No. of patients 1406 1421 1551 930 956 Received rivaroxaban, (%) 279, (19.8) 499, (35.1) 711, (45.8) 632, (68.0) 774, (81.0) <0.001 Standard dose, (%) 1216, (86.5) 1232, (86.7%) 1366, (88.1%) 793, (85.3%) 824, (86.2%) 0.62 Median age, (interquartile range) 70, (63.3–74) 69, (63–74) 70, (64–74) 70, (64–75) 70, (63–75) 0.11 Below median income, (%) 740, (52.6) 699, (49.2) 764, (49.3) 458, (49.3) 471, (49.3) 0.31 Prior stroke, (%) 99, (7.0) 115, (8.1) 134, (8.6) 69, (7.4) 74, (7.7) 0.56 Prior bleeding, (%) 136, (9.7) 141, (9.9) 163, (10.5) 91, (9.8) 97, (10.1) 0.51 Antiplatelet therapy, (%) 445, (31.7) 465, (32.7) 491, (31.7) 303, (32.6) 317, (33.2) 0.49

Rate of events according to instrument

Conclusion

High facility preference for rivaroxaban increases risk of major bleeding compared to facility preference for apixaban.

Acknowledgement/Funding

This study was funded by an unrestricted grant from the Capital Region of Denmark, Foundation for Health Research.

Instrumental variables estimation under a structural Cox model

Instrumental variable (IV) analysis is an increasingly popular tool for inferring the effect of an exposure on an outcome, as witnessed by the growing number of IV applications in epidemiology, for instance. The majority of IV analyses of time-to-event endpoints are, however, dominated by heuristic approaches. More rigorous proposals have either sidestepped the Cox model, or considered it within a restrictive context with dichotomous exposure and instrument, amongst other limitations. The aim of this article is to reconsider IV estimation under a structural Cox model, allowing for arbitrary exposure and instruments. We propose a novel class of estimators and derive their asymptotic properties. The methodology is illustrated using two real data applications, and using simulated data.

Survivor bias in Mendelian randomization analysis

Mendelian randomization studies employ genotypes as experimental handles to infer the effect of genetically modified exposures (e.g. vitamin D exposure) on disease outcomes (e.g. mortality). The statistical analysis of these studies makes use of the standard instrumental variables framework. Many of these studies focus on elderly populations, thereby ignoring the problem of left truncation, which arises due to the selection of study participants being conditional upon surviving up to the time of study onset. Such selection, in general, invalidates the assumptions on which the instrumental variables analysis rests. We show that Mendelian randomization studies of adult or elderly populations will therefore, in general, return biased estimates of the exposure effect when the considered genotype affects mortality; in contrast, standard tests of the causal null hypothesis that the exposure does not affect the mortality rate remain unbiased, even when they ignore this problem of left truncation. To eliminate "survivor bias" or "truncation bias" from the effect of exposure on mortality, we next propose various simple strategies under a semi-parametric additive hazard model. We examine the performance of the proposed methods in simulation studies and use them to infer the effect of vitamin D on all-cause mortality based on the Monica10 study with the genetic variant filaggrin as instrumental variable.

Recurrent event survival analysis predicts future risk of hospitalization in patients with paroxysmal and persistent atrial fibrillation

Background

In patients with paroxysmal atrial fibrillation (PAF) or persistent atrial fibrillation (PeAF) symptom burden and fear of hospital readmission are major causes of reduced quality of life. We attempted to develop a prediction model for future atrial fibrillation hospitalization (AFH) risk in PAF and PeAF patients including all previously experienced AFHs in the analysis, as opposed to time to first event.

Methods

Recurrent event survival analysis was used to model the impact of past AFHs on the risk of future AFHs. A recurrent event was defined as a hospitalization due to a new episode of AF. Death or progression to permanent AF were included as competing risks.

Results

We enrolled 174 patients with PAF or PeAF, mean follow up duration was 1279 days, and 325 AFHs were observed. Median patient age was 63.0 (IQR 52.2–68.0), 29% had PAF, and 71% were male. Highly significant predictors of future AFH risk were PeAF (HR 3.20, CI 2.01–5.11) and number of past AFHs observed (HR for 1 event: 2.97, CI 2.04–4.32, HR for ≥2 events: 7.54, CI 5.47–10.40).

Conclusion

In PAF and PeAF patients, AF type and observed AFH frequency are highly significant predictors of future AFH risk. The developed model enables risk prediction in individual patients based on AFH history and baseline characteristics, utilizing all events experienced by the patient. This is the first time recurrent event survival analysis has been used in AF patients.

Goodness of fit tests for estimating equations based on pseudo-observations

We study regression models for mean value parameters in survival analysis based on pseudo-observations. Such parameters include the survival probability and the cumulative incidence in a single point as well as the restricted mean life time and the cause-specific number of years lost. Goodness of fit techniques for such models based on cumulative sums of pseudo-residuals are derived including asymptotic results and Monte Carlo simulations. Practical examples from liver cirrhosis and bone marrow transplantation are also provided.

Calcitonin-gene related peptide and disease activity in cluster headache

OBJECTIVE

To investigate the role of calcitonin gene-related peptide, pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) and vasoactive intestinal polypeptide in cluster headache, we measured these vasoactive peptides interictally and during experimentally induced cluster headache attacks.

METHODS

We included patients with episodic cluster headache in an active phase (n = 9), episodic cluster headache patients in remission (n = 9) and patients with chronic cluster headache (n = 13). Cluster headache attacks were induced by infusion of calcitonin gene-related peptide (1.5 µg/min) in a randomized, double-blind, placebo controlled, two-way cross-over study. At baseline, we collected interictal blood samples from all patients and during 11 calcitonin gene-related peptide-induced cluster headache attacks.

RESULTS

At baseline, episodic cluster headache patients in remission had higher plasma levels of calcitonin gene-related peptide, 100.6 ± 36.3 pmol/l, compared to chronic cluster headache patients, 65.9 ± 30.5 pmol/l, ( p = 0.011). Episodic cluster headache patients in active phase had higher PACAP38 levels, 4.0 ± 0.8 pmol/l, compared to chronic cluster headache patients, 3.3 ± 0.7 pmol/l, ( p = 0.033). Baseline levels of vasoactive intestinal polypeptide did not differ between cluster headache groups. We found no attack-related increase in calcitonin gene-related peptide, PACAP38 or vasoactive intestinal polypeptide levels during calcitonin gene-related peptide-induced cluster headache attacks.

CONCLUSIONS

This study suggests that cluster headache disease activity is associated with alterations of calcitonin gene-related peptide expression. Future studies should investigate the potential of using calcitonin gene-related peptide measurements in monitoring of disease state and predicting response to preventive treatments, including response to anti-calcitonin gene-related peptide monoclonal antibodies.

Use of paracetamol, ibuprofen or aspirin in pregnancy and risk of cerebral palsy in the child

Background

It has been debated whether mild analgesics, mainly paracetamol, adversely affect aspects of neurodevelopment. We examined whether mother's use of paracetamol, aspirin or ibuprofen in pregnancy is associated with increased risk of cerebral palsy (CP) in the child.

Method

We included 185 617 mother-child pairs from the Danish National Birth Cohort and the Norwegian Mother and Child Cohort Study. We created harmonized definitions of analgesic use in pregnancy, as well as indications for analgesic use and other potential confounders. Children with CP were identified in nationwide registers. We estimated the average causal effect of analgesics on risk of CP using marginal structural models with stabilized inverse probability weights.

Results

Paracetamol use was reported in 49% of all pregnancies, aspirin in 3% and ibuprofen in 4%. Prenatal exposure to paracetamol ever in pregnancy was associated with increased risk of overall CP [adjusted odds ratio (aOR) 1.3, 95% confidence interval (CI): 1.0-1.7] and unilateral spastic CP (aOR 1.5, 95% CI: 1.0-2.2). The association appeared to be driven by an increased risk of unilateral spastic CP in children exposed in second trimester (aOR 1.6, 95% CI: 1.0-2.5). Children ever prenatally exposed to aspirin in pregnancy had an elevated risk of bilateral spastic CP (aOR 2.4, 95% CI: 1.1-5.3) compared with unexposed.

Conclusion

We observed an increased risk of spastic CP in children prenatally exposed to paracetamol and aspirin. Although we controlled for several important indications for analgesic use, we cannot exclude the possibility of confounding by underlying diseases.

On doubly robust estimation of the hazard difference

The estimation of conditional treatment effects in an observational study with a survival outcome typically involves fitting a hazards regression model adjusted for a high-dimensional covariate. Standard estimation of the treatment effect is then not entirely satisfactory, as the misspecification of the effect of this covariate may induce a large bias. Such misspecification is a particular concern when inferring the hazard difference, because it is difficult to postulate additive hazards models that guarantee non-negative hazards over the entire observed covariate range. We therefore consider a novel class of semiparametric additive hazards models which leave the effects of covariates unspecified. The efficient score under this model is derived. We then propose two different estimation approaches for the hazard difference (and hence also the relative chance of survival), both of which yield estimators that are doubly robust. The approaches are illustrated using simulation studies and data on right heart catheterization and mortality from the SUPPORT study.

Instrumental variables estimation with competing risk data

Time-to-event analyses are often plagued by both—possibly unmeasured—confounding and competing risks. To deal with the former, the use of instrumental variables (IVs) for effect estimation is rapidly gaining ground. We show how to make use of such variables in competing risk analyses. In particular, we show how to infer the effect of an arbitrary exposure on cause-specific hazard functions under a semi-parametric model that imposes relatively weak restrictions on the observed data distribution. The proposed approach is flexible accommodating exposures and IVs of arbitrary type, and enabling covariate adjustment. It makes use of closed-form estimators that can be recursively calculated, and is shown to perform well in simulation studies. We also demonstrate its use in an application on the effect of mammography screening on the risk of dying from breast cancer.

Effects of apolipoprotein M in uremic atherosclerosis

BACKGROUND AND AIMS

Chronic kidney disease is characterized by uremia and causes premature death, partly due to accelerated atherosclerosis. Apolipoprotein (apo) M is a plasma carrier protein for the lipid sphingosine-1-phosphate (S1P). The Apom-S1P complex associates with HDL, and may contribute to its anti-atherosclerotic effects. The role of Apom/S1P in atherosclerosis is presently controversial and has not been explored in a uremic setting. We aimed to explore whether plasma concentrations of Apom/S1P are altered by uremia and whether Apom overexpression or deficiency affects classical and uremic atherosclerosis.

METHODS

Mild to moderate uremia was induced by subtotal nephrectomy (NX) in 86-92 Apoe-deficient mice that were either Apom-wild type, Apom-deficient, or overexpressed Apom (∼10 fold). The effects of uremia on plasma Apom/S1P and atherosclerosis were evaluated and compared to non-nephrectomized controls.

RESULTS

Uremia increased plasma Apom by ∼25%, but not S1P. Plasma S1P was elevated by ∼300% in mice overexpressing Apom, and decreased by ∼25% in Apom-deficient mice. Apom overexpression augmented aortic root atherosclerosis and plasma cholesterol. In contrast, aortic arch atherosclerosis was unaffected by the Apom genotype. There was no effect of Apom-deficiency or Apom overexpression on uremic atherosclerosis.

CONCLUSIONS

This study highlights the complexity of Apom/S1P in atherosclerosis and challenges the notion that the Apom/S1P complex is anti-atherogenic, at least in Apoe-deficient mice.

Estimation of average causal effect using the restricted mean residual lifetime as effect measure

Although mean residual lifetime is often of interest in biomedical studies, restricted mean residual lifetime must be considered in order to accommodate censoring. Differences in the restricted mean residual lifetime can be used as an appropriate quantity for comparing different treatment groups with respect to their survival times. In observational studies where the factor of interest is not randomized, covariate adjustment is needed to take into account imbalances in confounding factors. In this article, we develop an estimator for the average causal treatment difference using the restricted mean residual lifetime as target parameter. We account for confounding factors using the Aalen additive hazards model. Large sample property of the proposed estimator is established and simulation studies are conducted in order to assess small sample performance of the resulting estimator. The method is also applied to an observational data set of patients after an acute myocardial infarction event.

Mitral Regurgitation Severity and Left Ventricular Systolic Dimension Predict Survival in Young Cavalier King Charles Spaniels

Background

Development and progression of myxomatous mitral valve disease (MMVD) in dogs are difficult to predict. Identification at a young age of dogs at high risk of adverse outcome in the future is desirable.

Hypothesis/Objectives

To study the predictive value of selected clinical and echocardiographic characteristics associated with MMVD obtained at a young age for prediction of long‐term cardiac and all‐cause mortality in Cavalier King Charles Spaniels (CKCS).

Animals

1125 privately owned CKCS.

Methods

A retrospective study including CKCS examined at the age of 1–3 years. Long‐term outcome was assessed by telephone interview with owners. The value of variables for predicting mortality was investigated by Cox proportional hazard and Kaplan‐Meier analyses.

Results

Presence of moderate to severe mitral regurgitation (MR) (hazard ratio (HR) = 3.03, 95% confidence interval (95% CI) = 1.48–6.23, P = 0.0025) even intermittent moderate to severe MR (HR = 2.23, 95% CI = 1.48–6.23, P = 0.039) on color flow Doppler echocardiography was significantly associated with increased hazard of cardiac death. An interaction between MR and sex was significant for all‐cause mortality (P = 0.035), showing that males with moderate to severe MR had a higher all‐cause mortality compared to males with no MR (HR = 2.38, 95% CI = 1.27–4.49, P = 0.0071), whereas no difference was found between female MR groups. The risk of cardiac (HR = 1.37, 95% CI = 1.14–1.63, P < 0.001) and all‐cause (HR = 1.13, 95% CI = 1.02–1.24, P = 0.016) mortality increased with increasing left ventricular end‐systolic internal dimension normalized for body weight (LVIDS_N).

Conclusions and clinical importance

Moderate to severe MR, even if intermittent, and increased LVIDS_N in dogs <3 years of age were associated with cardiac death later in life in CKCS.

Instrumental variables estimation of exposure effects on a time-to-event endpoint using structural cumulative survival models

The use of instrumental variables for estimating the effect of an exposure on an outcome is popular in econometrics, and increasingly so in epidemiology. This increasing popularity may be attributed to the natural occurrence of instrumental variables in observational studies that incorporate elements of randomization, either by design or by nature (e.g., random inheritance of genes). Instrumental variables estimation of exposure effects is well established for continuous outcomes and to some extent for binary outcomes. It is, however, largely lacking for time-to-event outcomes because of complications due to censoring and survivorship bias. In this article, we make a novel proposal under a class of structural cumulative survival models which parameterize time-varying effects of a point exposure directly on the scale of the survival function; these models are essentially equivalent with a semi-parametric variant of the instrumental variables additive hazards model. We propose a class of recursive instrumental variable estimators for these exposure effects, and derive their large sample properties along with inferential tools. We examine the performance of the proposed method in simulation studies and illustrate it in a Mendelian randomization study to evaluate the effect of diabetes on mortality using data from the Health and Retirement Study. We further use the proposed method to investigate potential benefit from breast cancer screening on subsequent breast cancer mortality based on the HIP-study.

Corn-Soy-Blend Fortified with Phosphorus to Prevent Refeeding Hypophosphatemia in Undernourished Piglets

BACKGROUND

Phosphorus (P) levels in refeeding diets are very important as undernourished children are at risk of hypophosphatemia during refeeding. For this reason, conventional corn-soy-blends (CSB) have been reformulated by the World Food Programme to obtain a mono-calcium-phosphate fortified product (CSB+) and a product further fortified with skim milk powder (CBS++).

METHODS

Using a piglet model of undernourished children, we hypothesized that feeding of CSB+, CSB++ or CSB+ with added whey permeate (CSB+/wp) would help to prevent refeeding hypophosphatemia. Pigs were weaned at 4 weeks of age and undernutrition was induced with a nutritionally inadequate pure maize diet for 7 weeks, after which they were refed for 3 weeks with either CSB+ (n = 10), CSB++ (n = 10) or CSB+/wp (n = 10). For reference, a fourth group continued on the maize diet (REF, n = 10).

RESULTS

Following induction of undernutrition, body weight and length were 29±5% and 67±4% (means±SD) of values in age-matched pigs fed a nutritionally adequate diet, and the mean serum P level was 1.77±0.34 mmol/l. During the first week of refeeding, P levels in the CSB+ pigs decreased to 55% of values before refeeding (P < 0.05) while values in the CSB++ and CSB+/wp pigs were able to maintain their plasma phosphate at a similar level as before refeeding.

CONCLUSION

We conclude that fortification of CSB with only monocalcium-phosphate does not prevent hypophosphatemia. Dairy products like skim milk powder or whey permeate may represent relevant sources of phosphorus during refeeding. The content and form of phosphorus in such diets need to be carefully evaluated, and the undernourished piglet may be used to test the efficacy of such diets.

Cox regression with missing covariate data using a modified partial likelihood method

Missing covariate values is a common problem in survival analysis. In this paper we propose a novel method for the Cox regression model that is close to maximum likelihood but avoids the use of the EM-algorithm. It exploits that the observed hazard function is multiplicative in the baseline hazard function with the idea being to profile out this function before carrying out the estimation of the parameter of interest. In this step one uses a Breslow type estimator to estimate the cumulative baseline hazard function. We focus on the situation where the observed covariates are categorical which allows us to calculate estimators without having to assume anything about the distribution of the covariates. We show that the proposed estimator is consistent and asymptotically normal, and derive a consistent estimator of the variance-covariance matrix that does not involve any choice of a perturbation parameter. Moderate sample size performance of the estimators is investigated via simulation and by application to a real data example.

Breeding Restrictions Decrease the Prevalence of Myxomatous Mitral Valve Disease in Cavalier King Charles Spaniels over an 8- to 10-Year Period

BACKGROUND

Cavalier King Charles Spaniels (CKCS) are predisposed to myxomatous mitral valve disease (MMVD). Studies have indicated a strong genetic background.

OBJECTIVE

The aim of this study was to evaluate the effect of a breeding scheme involving auscultation and echocardiography.

ANIMALS

In the Danish Kennel Club mandatory breeding scheme, 997 purebred CKCS were examined during the period 2002-2011. Each dog was evaluated 1-4 times with a total of 1,380 examinations.

METHODS

Auscultation and echocardiography were performed to evaluate mitral regurgitation murmur severity and degree of mitral valve prolapse (MVP). The odds of having mitral regurgitation murmur or MVP > grade 1 in 2010-2011 compared to 2002-2003 were estimated using logistic regression analysis including age and sex as covariates. Odds were estimated for dogs that were products of the breeding scheme (defined as dogs with both parents approved by the breeding scheme before breeding) and non-products of the breeding scheme (defined as dogs with at least 1 parent with unknown cardiac status).

RESULTS

In 2010-2011, the odds of having mitral regurgitation murmur were 0.27 if dogs were a product of the breeding scheme compared with dogs in 2002-2003, reflecting a 73% decreased risk (P < .0001). If non-products of the breeding scheme examined in 2010-2011 were compared with dogs in 2002-2003, no difference in odds was found (P = .49).

CONCLUSION AND CLINICAL IMPORTANCE

A mandatory breeding scheme based on auscultation and echocardiography findings significantly decreased the prevalence of MMVD over the 8- to 10-year period. Such a breeding scheme therefore is recommended for CKCS.

Göttingen minipig model of diet-induced atherosclerosis: influence of mild streptozotocin-induced diabetes on lesion severity and markers of inflammation evaluated in obese, obese and diabetic, and lean control animals

Background

From a pharmacological perspective, readily-available, well-characterized animal models of cardiovascular disease, including relevant in vivo markers of atherosclerosis are important for evaluation of novel drug candidates. Furthermore, considering the impact of diabetes mellitus on atherosclerosis in human patients, inclusion of this disease aspect in the characterization of a such model, is highly relevant. The objective of this study was to evaluate the effect of mild streptozotocin-induced diabetes on ex- and in vivo end-points in a diet-induced atherosclerotic minipig model.

Methods

Castrated male Göttingen minipigs were fed standard chow (CD), atherogenic diet alone (HFD) or with superimposed mild streptozotocin-induced diabetes (HFD-D). Circulating markers of inflammation (C-reactive protein (CRP), oxidized low-density lipoprotein (oxLDL), plasminogen activator inhibitor-1, lipid and glucose metabolism were evaluated together with coronary and aortic atherosclerosis after 22 or 43 diet-weeks. Group differences were evaluated by analysis of variance for parametric data and Kruskal–Wallis test for non-parametric data. For qualitative assessments, Fisher’s exact test was applied. For all analyses, p < 0.05 was considered statistically significant.

Results

Overall, HFD and HFD-D displayed increased CRP, oxLDL and lipid parameters compared to CD at both time points. HFD-D displayed impaired glucose metabolism as compared to HFD and CD. Advanced atherosclerotic lesions were observed in both coronary arteries and aorta of HFD and HFD-D, with more advanced plaque findings in the aorta but without differences in lesion severity or distribution between HFD and HFD-D. Statistically, triglyceride was positively (p = 0.0039), and high-density lipoprotein negatively (p = 0.0461) associated with aortic plaque area.

Conclusions

In this model, advanced coronary and aortic atherosclerosis was observed, with increased levels of inflammatory markers, clinically relevant to atherosclerosis. No effect of mild streptozotocin-induced diabetes was observed on plaque area, lesion severity or inflammatory markers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0670-2) contains supplementary material, which is available to authorized users.

Serotonin markers show altered transcription levels in an experimental pig model of mitral regurgitation

Serotonin (5-hydroxytryptamine, 5-HT) signalling is implicated in the pathogenesis of myxomatous mitral valve disease (MMVD) through 5-HT1B receptor (R), 5-HT2AR and 5-HT2BR-induced myxomatous pathology. Based on increased tryptophan hydroxylase-1 (TPH-1) and decreased serotonin re-uptake transporter (SERT) in MMVD-affected valves, increased valvular 5-HT synthesis and decreased clearance have been suggested. It remains unknown how haemodynamic changes associated with mitral regurgitation (MR) affect 5-HT markers in the mitral valve, myocardium and circulation. Twenty-eight pigs underwent surgically induced MR or sham-operation, resulting in three MR groups: control (CON, n = 12), mild MR (mMR, n = 10) and severe MR (sMR, n = 6). The gene expression levels of 5-HT1BR, 5-HT2AR, 5-HT2BR, SERT and TPH-1 were analysed using quantitative PCR (qPCR) in the mitral valve (MV), anterior papillary muscle (AP) and left ventricle (LV). MV 5-HT2BR was also analysed with immunohistochemistry (IHC) in relation to histological lesions and valvular myofibroblasts. All 5-HTR mRNAs were up-regulated in MV compared to AP and LV (P <0.01). In contrast, SERT and TPH-1 were up-regulated in AP and LV compared to MV (P <0.05). In MV, mRNA levels were increased for 5-HT2BR (P = 0.02) and decreased for SERT (P = 0.03) in sMR vs. CON. There were no group differences in 5-HT2BR staining (IHC) but co-localisation was found with α-SMA-positive cells in 91% of all valves and with 33% of histological lesions. In LV, 5-HT1BR mRNA levels were increased in sMR vs. CON (P = 0.01). In conclusion, these data suggest that MR may affect mRNA expression of valvular 5-HT2BR and SERT, and left ventricular 5-HT1BR in some pigs.

Time elapsed after transplantation influences the relationship between the number of regulatory T cells in lung allograft biopsies and subsequent acute rejection episodes

BACKGROUND

Regulatory T lymphocytes (Tregs) play an important role in acute rejection after lung transplantation. However, the importance of the time elapsed after transplantation on the Treg response requires further investigation. We aim to evaluate the change over time in the frequency of Tregs in lung allograft biopsies and to assess how Tregs relate to simultaneous and subsequent acute cellular rejection.

MATERIALS AND METHODS

A total of 258 biopsy samples obtained 0.5, 1, 3, 12 and 24 months after transplantation from 58 consecutive lung transplant patients were included. The biopsies were scored for acute rejection according to the ISHLT criteria (A0-A4) and immunohistochemically stained with antibodies against FoxP3.

RESULTS

There was a tendency for a decrease in the number of Tregs/mm2 with time. However, the previous levels of Tregs/mm2 did not have any significant effect on future levels of Tregs/mm2. For biopsies taken 0.5 and 1 month after transplantation, a significant correlation between Tregs/mm2 and the degree of acute rejection was found, and logistic regression analysis using updated values for Tregs/mm2 showed a significant relationship between Tregs/mm2 at 2 weeks and an A-score≥2 after 1 and 3 months. At later time points, this correlation disappeared.

DISCUSSION AND CONCLUSION

Our data indicate that the time elapsed after transplantation is an important parameter influencing the Treg response after lung transplantation. This observation is in accordance with studies indicating a narrow therapeutic window for induction of tolerance by specifically targeting T-cells. The results also indirectly indicate that Tregs early after transplantation could have an impact on the long-term outcome.

On adjustment for auxiliary covariates in additive hazard models for the analysis of randomized experiments

We consider additive hazard models (Aalen, 1989) for the effect of a randomized treatment on a survival outcome, adjusting for auxiliary baseline covariates. We demonstrate that the Aalen least squares estimator of the treatment effect parameter is asymptotically unbiased, even when the hazard's dependence on time or on the auxiliary covariates is misspecified, and even away from the null hypothesis of no treatment effect. We moreover show that adjustment for auxiliary baseline covariates does not change the asymptotic variance of the Aalen least squares estimator of the effect of a randomized treatment. We conclude that, in view of its robustness against model misspecification, Aalen least squares estimation is attractive for evaluating treatment effects on a survival outcome in randomized experiments, and that the primary reasons to consider baseline covariate adjustment in such settings may be the interest in subgroup effects, or the need to adjust for informative censoring or for baseline imbalances. Our results also shed light on the robustness of Aalen least squares estimators against model misspecification in observational studies.

Determinants of developmental coordination disorder in 7-year-old children: a study of children in the Danish National Birth Cohort

AIM

The aim of this study was to investigate early life determinants of developmental coordination disorder (DCD) in 7-year-old children.

METHOD

The study was based on data from 33,354 women and their children who participated in the 7-year follow-up study of the Danish National Birth Cohort. Information on several potential determinants (maternal age at conception, maternal occupational status, smoking and alcohol consumption during pregnancy, child's sex, intrauterine growth restriction, degree of preterm birth, and age at walking) was obtained from population registries, from interviews during pregnancy and when the child was 18 months old. The outcome in this study was DCD at 7 years of age, measured by the validated Developmental Coordination Disorder Questionnaire. The associations between the potential determinants and DCD were estimated using logistic regression.

RESULTS

The study population consisted of 17,065 males and 16,289 females (141 [0.4%] born very preterm [23(+0)-31(+6) wk]; 1281 [3.8%] born moderately preterm [32(+0)-36(+6) wk]; 29,044 [87.1%] were born term [37(+0)-41(+6) wk], and 2888 [8.7%] were born post-term [≥ 42(+0) wk]). Independently of each other, the following determinants were predictors of DCD: being a female (odds ratio [OR] 0.36 [95% confidence interval {CI} 0.31-0.41]); being born very preterm (OR 6.28 [95% CI 3.99-9.89]) or moderately preterm (OR 2.10 [95% CI 1.65-2.67]); being small for gestational age (OR 1.74 [95% CI 1.46-2.08]); being 15 months of age or more at walking attainment (OR 3.05 [95% CI 2.57-3.60]); and maternal occupational status (higher grade professionals (OR 1.28 [95% CI 1.02-1.61); economically inactive (OR 1.43 [95% CI 1.07-1.91]). Young maternal age and smoking were risk factors among term-born children.

INTERPRETATION

The risk of DCD increases with decreasing gestational age. Intrauterine growth restriction is also a strong risk factor, as well as delayed walking.

Optimism and survival: does an optimistic outlook predict better survival at advanced ages? A twelve-year follow-up of Danish nonagenarians

BACKGROUND AND AIMS

Studies examining predictors of survival among the oldest-old have primarily focused on objective measures, such as physical function and health status. Only a few studies have examined the effect of personality traits on survival, such as optimism. The aim of this study was to examine whether an optimistic outlook predicts survival among the oldest-old.

METHODS

The Danish 1905 Cohort Survey is a nationwide, longitudinal survey comprising all individuals born in Denmark in 1905. At baseline in 1998, a total of 2,262 persons aged 92 or 93 agreed to participate in the intake survey. The baseline in-person interview consisted of a comprehensive questionnaire including physical functioning and health, and a question about whether the respondent had an optimistic, neutral or pessimistic outlook on his or her own future.

RESULTS

During the follow-up period of 12 years (1998-2010) there were 2,239 deaths (99 %) in the 1905 Cohort Survey. Univariable analyses revealed that optimistic women and men were at lower risk of death compared to their neutral counterparts [HR 0.82, 95 % CI (0.73-0.93) and 0.81, 95 % CI (0.66-0.99), respectively]. When confounding factors such as baseline physical and cognitive functioning and disease were taken into account the association between optimism and survival weakened in both sexes, but the general pattern persisted. Optimistic women were still at lower risk of death compared to neutral women [HR 0.85, 95 % CI (0.74-0.97)]. The risk of death was also decreased for optimistic men compared to their neutral counterparts, but the effect was non-significant [HR 0.91, 95 % CI (0.73-1.13)].

CONCLUSION

An optimistic outlook appears to be a significant predictor of survival among the oldest-old women. It may also be a significant predictor for men but the sample size is small.