Genetic susceptibility, elevated blood pressure and risk of atrial fibrillation

Background

Whether elevated blood pressure (BP) is a modifiable risk factor for atrial fibrillation (AF) is not established.

Purpose

We tested (1) whether the association between BP and risk of AF is causal, (2) whether it varies according to individual's genetic susceptibility for AF, and (3) the extent to which specific BP-lowering drugs are expected to reduce this risk.

Methods

First, causality of association was assessed through two-sample Mendelian Randomization (MR), using data from two independent genome-wide association studies that included a total of one million European population. Second, UK Biobank individual participant data of 329,237 participants at baseline was used to study the effect of BP on AF according to genetic susceptibility of developing AF. Third, a possible treatment effect with BP-lowering drug classes on AF risk was predicted through genetic variants in druggable genes that code proteins related to the function of each drug class. Estimated drug effects were compared with effects on incident coronary heart disease, for which direct trial evidence exists.

Results

The two-sample MR analysis indicated that on average each 10-mm Hg increment in systolic BP increased the risk of AF (odds ratio [OR]: 1.23 [1.11 to 1.36]). This association was replicated in the UK biobank using individual participant data. However, in a further genetic risk-stratified analysis, there was evidence for a linear gradient in the relative effects of systolic BP on AF; while there was no conclusive evidence of an effect in those with low genetic risk, a strong effect was observed among those with high genetic susceptibility for AF (Figure). The indirect comparison of predicted treatment effects using genetic proxies for three main drug classes (angiotensin-converting enzyme inhibitors, beta-blockers and calcium channel blockers) suggested similar average effects for prevention of atrial fibrillation and coronary heart disease.

Conclusions

The association between elevated BP and higher risk of AF is likely to be causal, suggesting that BP-lowering treatment may be effective in AF prevention. However, average effects masked clinically important variations, with a more pronounced effect in individuals with high genetic susceptibility.

Figure 1

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): British Heart Foundation

Addressing low consumption of fruit and vegetables in England: a cost-effectiveness analysis

Background

Most adults do not meet the recommended intake of five portions per day of fruit and vegetables (F&V) in England, but economic analyses of structural policies to change diet are sparse. This study aimed to estimate (1) the health and economic burden attributable to the low intake of fruit and vegetables (F&V) by English adults, and (2) the cost-effectiveness of three policies promoting consumption of F&V in England - a universal 10% subsidy, a targeted 30% subsidy for low-income households, and a nationwide social marketing campaign (SMC).

Methods

Using published data from official statistics and meta-epidemiological studies, we estimated the deaths, years-of-life lost (YLL), and the healthcare costs attributable to consumption of F&V below the recommended five portions per day by English adults. Then, we estimated the cost-effectiveness from governmental and societal perspectives of three policies.

Results

Low consumption of F&V accounted for 16,321 [10,091-23,516] deaths and 238,767 [170,350-311,651] YLL due to cardiovascular diseases, type 2 diabetes and cancer in England in 2017, alongside £705,951 [398,761-1,061,559] million in healthcare costs. From a societal perspective, the incremental cost-effectiveness ratios were £22,891 [22,300-25,079], £16,860 [15,589-19,763], and £25,683 [25,237-28,671] per life-year saved for the universal subsidy, targeted subsidy and SMC, respectively. At a threshold of £20,000 per life-year saved, the likelihood that the universal subsidy, the targeted subsidy and the SMC were cost-effective was 84%, 19% and 5%, respectively. The targeted subsidy was the only policy that would also reduce inequalities.

Conclusions

Both a SMC and subsidies can significantly increase consumption of F&V and reduce the attributable burden of disease and healthcare costs, but their cost-effectiveness varies substantially. A targeted subsidy to low-income households is most likely cost-effective and can additionally reduce inequalities.

Key messages

Low intake of fruit and vegetables accounts for a substantial number of deaths and years of life lost and represents a heavy burden for the healthcare system in England. From a societal perspective, a targeted subsidy to low-income households was most likely cost-effective and it would reduce inequalities.

P1548Long-term past, current and usual systolic blood pressure and incident cardiovascular disease: risk prediction using large-scale, routinely recorded clinical data

Background

The impact of long-term exposure to elevated systolic blood pressure (SBP) on future cardiovascular disease (CVD) in “real-world” settings, and its relevance to risk prediction, are less investigated.

Purpose

To examine the risk of incident CVD in relation to long-term past, current, and usual SBP, and compare their predictive performance, using evidence from large-scale electronic health records (EHR).

Methods

Using data extracted from UK primary care linked EHR, we applied a landmark cohort study design, by including patients aged 40 (N≈64,000), 50 (N≈80,000) and 60 (N≈67,000) years (y) at study entry who had recorded SBP and with no prior CVD or previous antihypertensive or lipid-lowering prescriptions at baseline. We estimated past SBP (mean, time-weighted mean, and variability recorded up to 10 years prior to baseline) and usual SBP (correcting current values for past time-dependent SBP variability). We used Cox regression to estimate hazard ratio (HR), and applied Bayesian analysis within a machine learning framework in developing and validating models. To evaluate predictive performance of the models, we used discrimination (area under the curve [AUC]) and calibration metrics. The outcome was incident CVD (first hospitalisation for or death from coronary heart disease or stroke/transient ischaemic attack). Analyses were conducted separately for each age cohort.

Results

After a mean follow-up of 8 years, the numbers of patients who developed incident CVD were over 1000 (40y), 3000 (50y) and 5000 (60y). Higher past, current and usual SBP values were separately and independently associated with increased incident CVD risk. Per 20-mmHg rise in SBP, the HR (95% credible interval [CI]) for current SBP for ages 40, 50 and 60 years were 1.18 (1.08 to 1.26), 1.22 (1.18 to 1.30) and 1.22 (1.19 to 1.24); the corresponding HR were stronger in magnitude for past SBP (mean and time-weighted mean) and usual SBP (HR ranged from: 40y=1.31 to 1.41, 50y=1.39 to 1.45 and 60y=1.32 to 1.48). For each age cohort, the AUC (95% CI) for the model that included current SBP, sex, smoking, deprivation, diabetes and lipid profile in the validation sample were: 40y=0.739 (0.730 to 0.746), 50y=0.750 (0.716 to 0.810), and 60y=0.647 (0.642 to 0.658). Adding past SBP mean, time-weighted mean or variability to this model were associated with modest increases in the AUC and all models showed good calibration. Small improvements in the AUC were similarly observed when evaluating models separately for men and women within each age cohort.

Conclusion

Using multiple SBP recordings from patients' EHR showed stronger associations with incident CVD than a single SBP measurement, but their addition to multivariate risk prediction models had negligible effects on model performance.

Acknowledgement/Funding

Oxford Martin School and National Institute for Health Research Oxford Biomedical Research Centre

P5732Effects of blood pressure lowering drugs in heart failure: a systematic review and meta-analysis of randomised controlled trials

Background

Observational studies have reported a J-shaped relationship between blood pressure (BP) and all-cause and cardiovascular mortality in patients with heart failure (HF). Although decreasing BP significantly reduces the risk of fatal and non-fatal cardiovascular outcomes in the general population across a range of baseline BP categories, the extent to which those findings are applicable to HF patients and whether the relationship holds true when baseline BP is very low remain unclear. Therefore, it is yet to be established whether the observed J-shaped relationship between BP and clinical outcomes in patients with HF is causal and/or modified by antihypertensive treatment.

Purpose

We aimed to combine evidence from all HF trials that have investigated the effects of drugs with BP-lowering properties to assess (1) the extent to which such drugs reduce BP in HF, (2) the association between the net change in BP between treatment arms and cause-specific outcomes, and (3) whether treatment effects (including benefits and potential harms) vary according to baseline BP.

Methods

We conducted a systematic review and meta-analysis including randomised clinical trials of drugs with BP-lowering properties conducted in patients with chronic HF with at least 300 patient-years follow-up.

Results

We included a total of 37 trials (91,950 patients) and showed that treatment with drugs with BP-lowering properties significantly reduced SBP by 2.0 mmHg in all trials and by 2.4 mmHg in placebo-controlled trials (Figure 1). There was no evidence that BP reduction in placebo-controlled trials varied across strata of baseline BP, but there was suggestive evidence for differential effects by drug class, with renin-angiotensin-aldosterone system inhibitors reducing SBP by 3.2 mmHg (95% CI [−4.0, −2.4]), whilst BB appeared to have a neutral effect on BP. There was no evidence that the relative risk reduction afforded by treatment with BP-lowering drugs on all-cause mortality, cardiovascular mortality and HF hospitalisation was significantly different across categories of baseline BP. There was also no strong evidence for heterogeneity of treatment effect on adverse events leading to treatment discontinuation by baseline BP. Meta-regression did not show significant associations between the magnitude of BP reduction achieved in each trial and risk of those clinical outcomes.

Figure 1

Conclusions

Treatment with drugs with BP-lowering properties resulted in a small but significant decrease in SBP in patients with HF irrespective of baseline BP. There was no evidence that the effects of those drugs differed across the range of baseline SBP, thus supporting the efficacy and safety of those drugs in patients with low baseline BP. Data from published reports was insufficient to adequately investigate whether BP-dependent mechanisms contribute to the effect of BP-lowering drugs on clinical outcomes in patients with HF.

Acknowledgement/Funding

None

Variation between hospitals in outcomes following cardiac surgery in the UK

INTRODUCTION

We examine the influence of variations in provision of cardiac surgery in the UK at hospital level on patient outcomes and also to assess whether there is an inequality of access and delivery of healthcare. Cardiothoracic surgery has pioneered the reporting of surgeon-specific outcomes, which other specialties have followed. We set out to identify factors other than the individual surgeon, which can affect outcomes and enable other surgical specialties to adopt a similar model.

MATERIALS AND METHODS

A retrospective analysis of prospectively collected data of patient and hospital level factors between 2013 and 2016 from 16 cardiac surgical units in the UK were analysed through the Society for Cardiothoracic Surgery of Great Britain and Ireland and the Royal College of Surgeons Research Collaborative. Patient demographic data, risks factors, postoperative complications and in-hospital mortality, as well as hospital-level factors such as number of beds and operating theatres, were collected. Correlation between outcome measures was assessed using Pearson's correlation coefficient. Associations between hospital-level factors and outcomes were assessed using univariable and multivariable regression models.

RESULTS

Of 50,871 patients (60.5% of UK caseload), 25% were older than 75 years and 29% were female. There was considerable variation between units in patient comorbidities, bed distribution and staffing. All hospitals had dedicated cardiothoracic intensive care beds and consultants. Median survival was 97.9% (range 96.3-98.6%). Postoperative complications included re-sternotomy for bleeding (median 4.8%; range 3.5-6.9%) and mediastinitis (0.4%; 0.1-1.0%), transient ischaemic attack/cerebrovascular accident (1.7%; range 0.3-3.0%), haemofiltration (3.7%; range 0.8-6.8%), intra-aortic balloon pump use (3.3%; range 0.4-7.4%), tracheostomy (1.6%; range 1.3-2.6%) and laparotomy (0.3%; range 0.2-0.6%). There was variation in outcomes between hospitals. Univariable analysis showed a small number of positive associations between hospital-level factors and outcomes but none remained significant in multivariable models.

CONCLUSIONS

Variations among hospital level factors exists in both delivery of, and outcomes, following cardiac surgery in the UK. However, there was no clear association between these factors and patient outcomes. This negative finding could be explained by differences in outcome definition, differences in risk factors between centres that are not captured by standard risk stratification scores or individual surgeon/team performance.

Population-based cohort study of variation in the use of emergency cholecystectomy for benign gallbladder diseases

Background

The aims of this prospective population-based cohort study were to identify the patient and hospital characteristics associated with emergency cholecystectomy, and the influences of these in determining variations between hospitals.

Methods

Data were collected for consecutive patients undergoing cholecystectomy in acute UK and Irish hospitals between 1 March and 1 May 2014. Potential explanatory variables influencing the performance of emergency cholecystectomy were analysed by means of multilevel, multivariable logistic regression modelling using a two-level hierarchical structure with patients (level 1) nested within hospitals (level 2).

Results

Data were collected on 4744 cholecystectomies from 165 hospitals. Increasing age, lower ASA fitness grade, biliary colic, the need for further imaging (magnetic retrograde cholangiopancreatography), endoscopic interventions (endoscopic retrograde cholangiopancreatography) and admission to a non-biliary centre significantly reduced the likelihood of an emergency cholecystectomy being performed. The multilevel model was used to calculate the probability of receiving an emergency cholecystectomy for a woman aged 40 years or over with an ASA grade of I or II and a BMI of at least 25·0 kg/m2, who presented with acute cholecystitis with an ultrasound scan showing a thick-walled gallbladder and a normal common bile duct. The mean predicted probability of receiving an emergency cholecystectomy was 0·52 (95 per cent c.i. 0·45 to 0·57). The predicted probabilities ranged from 0·02 to 0·95 across the 165 hospitals, demonstrating significant variation between hospitals.

Conclusion

Patients with similar characteristics presenting to different hospitals with acute gallbladder pathology do not receive comparable care.