Elevated Blood Pressure in the Emergency Department: A Risk Factor for Incident Cardiovascular Disease

High blood pressure (BP) is commonly observed in the emergency department (ED).¹ Finding and treating patients with hypertension is a priority in cardiovascular prevention. Studies have shown that for every 10 to 20 mm Hg reduction in systolic blood pressure (SBP), there is a substantial risk reduction for CVD,^2–4 and that patients with higher BP levels benefit from more-intensive drug intervention.⁵ However, a majority of the patients with high BP do not achieve BP control (BP<140/90 mm Hg), and many are unaware of their condition.⁶

In the ED, BP is measured on almost every patient to assess the patient’s condition and acuity^7,8 regardless of the presenting chief complaint. Previous research has reported that up to one-third of the patients in the ED have BP levels above the threshold for hypertension, and severely elevated levels have been observed in 20% of the cases.⁷ Elevated BP in the ED can be explained by factors such as pain, anxiety, or other stressors, which raises the question of its predictive value and whether hypertension screening based on routine recordings in the ED are useful.^1,9

It is unknown whether a high BP in the ED is associated with incident atherosclerotic cardiovascular disease (ASCVD), and the benefit of acting on a high BP in this setting is unclear. Therefore, we aimed to examine if the first measured BP in the ED is associated with incident ASCVD, myocardial infarction (MI), or stroke during a long-time follow-up. We also aimed to assess the potential benefits of screening for patients with hypertension in the ED by estimating the number needed to screen and treat to prevent ASCVD.

The authors declare that all supporting data are available in the article and its online-only Data Supplement.

A total of 300 193 patients were included after the inclusion criteria (Figure 1). The mean age was 50.0±20.2 years, female patients comprised 53.9% (n=161 707) of the study population, and the mean SBP was 139.9 mm Hg (Table 1). Subjects were followed for a mean time of 3.5 years, which resulted in 1.1 million person-years. The most common chief complaint was abdominal pain, chest pain, breathing difficulties, headache, and fever (Table S6). SBP data were missing for 59 (0.02%) subjects, and 1992 (0.67%) subjects had data missing for DBP. No subjects were missing data for both SBP and DBP. Outcome data were obtained for all included participants.

Incident ASCVD occurred in 3.0% (n=8999) of the cohort during a median follow-up for 42 months (range, 0–84 month). Men were more likely to develop ASCVD (60.7%) compared with females (39.3%). Both SBP and DBP was associated with incident ASCVD with a progressively increased hazard ratio across BP categories above the reference (Table 2). The 6-year cumulative incidence of ASCVD for the reference SBP group (120–129 mm Hg) was 2% compared with 12% in SBP category ≥180 mm Hg (Figure 2), while patients with DBP ≥110 mm Hg had a 10% 6-year cumulative incidence (Figure S1). When adjusted for age, sex, inclusion year, and site, the HR (95% CI) for incident ASCVD per 20-mm Hg increase of SBP was 1.13 (1.11–1.14), and per 10-mm Hg DBP increase, the HR was 1.03 (1.03–1.04; Table S7).

For the secondary end point MI, a total of 4847 (1.6%) events occurred in the cohort, the majority 63.2% (n=3117) among men. There was a statistically significant association between SBP and incident MI with a gradually increased HR by higher SBP above the reference category (Figure 3). Similar associations were observed for DBP (Figure S2). The 6-year cumulative incidence was 1% for the reference category compared with 6.5% in the highest SBP group (Figure S3).

A total of 6661 (2.2%) all-cause stroke events occurred, and of those were 51.0% male (n=3470). Patients with DBP ≥110 had more than a 2-fold association (HR, 2.16 [95% CI, 1.93–2.41]) with a stroke event (Figure S2). The 6-year cumulative incidence was 1% for the reference category compared with 9% in the highest SBP group (Figure S4).

For the end points ischemic stroke and intracerebral hemorrhage, a total of 5355 respectively 1119 events occurred. The highest HR for ischemic stroke was in the ≥110 mm Hg DBP category (HR, 1.91 [95% CI, 1.68–2.17]). The strongest association with intracerebral hemorrhage was in the top DBP category (HR, 3.56 [95% CI, 2.80–4.52]) (Figure S2).

The main finding in this study was the strong association between a first BP recorded in the ED and incident ASCVD during a long-time follow-up. Strong associations were observed, irrespective of the acuity, whether patients were admitted to inpatient care or had a history of hypertension or CVD. In patients without a history of hypertension, the association with incident ASCVD was stronger than for those with hypertension. By using effect sizes for antihypertensive treatment from meta-analysis,⁴ we estimated that to prevent one future ASCVD event during a median of 42 months of follow-up, antihypertensive treatment needed to be initiated in 71 patients with an ED-measured SBP ≥140 mm Hg.

The association with incident ASCVD was gradually stronger for both DBP and SBP levels that corresponded to Hypertension grade 1, 2, and 3¹⁰ (Table S1). Furthermore, a statistically significant association with incident ASCVD was observed for patients with DBP level in the high normal category. Our findings show that hypertension grades may be of interest for the ED setting, and ED-measured BP is of value not only to evaluate the acuity of the patient’s health but also to identify patients at high risk for cardiovascular events in the long term and therefore provides a tool to prevent them.

Previous population-based research has shown that an increase in SBP results in a substantially increased risk for cardiovascular events, irrespective of baseline BP.^2,3 While findings in the present study showed a strong association between BP and incident ASCVD, the magnitude of the effect was smaller in comparison to the population-based studies. We observed a HR of 1.13 per 20-mm Hg increase of SBP whereas Rapsomaniki et al reported a HR of 1.26. The current study did not account for the regression dilution bias due to single BP measurements, and thereby our findings probably underestimate the true association between BP in the ED and incident ASCVD.¹³ The influence of different stressors, both related to acute disease and the ED environment, may cause an increase of BP in the ED, and elevated BP levels are commonly observed.¹ Previously, the prognostic relevance of elevated BP in the ED, and if it can be a basis for decisions to initiate or intensify antihypertensive treatment in this setting has been unknown. However, it should be noted that BP measured during other stress, such as exercise, previously have provided independent prognostic information regarding incident ASCVD.^14,15 To estimate if stressors or pain influenced the association between BP and incident ASCVD, we performed subgroup analyses for ED triage categories. A strong association with the outcome was observed irrespective of the acuity of the patients. Although it can be speculated that different mechanisms influence BP in the ED and its association with ASCVD, which may explain some of the differences in this study compared with the population-based studies. Here we, for the first time, provide evidence that a first BP obtained in the ED among an unselected population with ED visitors is associated with incident ASCVD.

The estimated NNS was based on the assumption that all detected patients with an SBP ≥140 mm Hg were prescribed adequate antihypertensive therapy and succeeded a 10-mm Hg SBP reduction. Prior research has presented a NNS for hypertension with BP-lowering actions,¹⁶ to the best of our knowledge, none have reported the potential benefit of using BPs obtained in the ED with an estimated potential benefit of reduced events. Findings in this study indicate that the ED setting has great potential to find undiagnosed and undertreated hypertension, which will reduce morbidity and mortality in CVD if effective antihypertensive therapy is initiated.

The main strength of this study was the large cohort size and the long follow-up period, which yielded a strong statistical power. The Swedish National Patient Register is well-known for its high-quality and accurate data, with a high reported positive predictive value, for most of the diagnoses. The reported sensitivity was high for MI (above 90%) but lower for hypertension.¹⁷ Therefore, the Prescribed Drugs Register was used to obtain all pick-ups of antihypertensive drugs to improve sensitivity.¹⁸

One potential weakness in this study was the uncertainty of how BP was measured, and due to discrepancies in methods for obtaining BP, deviations for BP may vary from case to case. Any changes in antihypertensive treatment that were initiated based on elevated ED-measured BP were not considered. Such treatment may have attenuated the association with incident ASCVD and therefore underestimated the true association. Another limitation is that the estimates for NNS and number needed to treat were based on relative risk reduction reported by previous research performed in different settings.⁴

The clinical value of the findings in this study is that ED-measured BP has a great potential to find undiagnosed hypertension and to prevent future ASCVD events if antihypertensive therapy is initiated. Patients directly discharged from the ED should be assessed more carefully as no further inpatient BP recordings take place. One ASCVD event could be prevented for every 107 discharged patients with a high BP if effective antihypertensive therapy is initiated. It is conceivable that the external validity of this study applies to other EDs, particularly considering the broad inclusion criteria.

In conclusion, findings in this study show that elevated BP, when measured in the ED, is strongly associated with incident ASCVD, MI, and stroke. High BP recordings in EDs should not be disregarded as isolated events, but an opportunity to detect and improve the treatment of hypertension. Patients with elevated BP in the ED should be followed up and treated if necessary. ED measurements of BP provide an important and underused tool with great potential to reduce morbidity and mortality associated with hypertension.

In summary, a first recorded BP in the ED was associated with incident ASCVD during a long-time follow-up. The risk increased gradually across both DBP and SBP levels that corresponded to Hypertension grades 1, 2, and 3. Strong associations were observed irrespective of the acuity of the condition in the ED, whether patients were admitted to inpatient care of had a history of hypertension or CVD. To prevent one ASCVD event during a median follow-up of 42 months, the NNS was estimated to 151 patients in the ED, whereas the number needed to treat to 71. The ED setting provides an opportunity to detect and improve the treatment of hypertension and are an underused tool with great potential to reduce morbidity and mortality associated with hypertension. Elevated BP recordings in the ED should not be disregarded as isolated events, but an opportunity to follow up and treat if necessary.

P. Svensson conducted the study, acquired all data and the ethical permit contributed by P. Oras, H. Häbel, and P.H. Skoglund. P. Oras wrote the manuscript supervised by P. Svensson and supported by P.H. Skoglund and H. Häbel. H. Häbel performed the statistical analysis and interpreted the data with support by P. Oras, P. Svensson, and P.H. Skoglund. All authors critically revised the manuscript for intellectual content and approved the final version of the report. The corresponding author had access to all data and is responsible for the decision to submit this study.

This study has been approved by the Regional Ethical Review Board in Stockholm, without the requirement of informed consent. Ethical review number 2016/888-31.