Blood pressure: measure, manage, monitor

• BP lowering is an important component in the primary prevention of cardiovascular disease. Use absolute cardiovascular risk rather than isolated risk factors to inform treatment decisions in adults aged ≥ 45 years (≥ 35 years for Aboriginal and Torres Strait Islander adults).
  
• Out-of-clinic BP values are a useful adjunct to in-clinic readings.
  
• Start pharmacotherapy with a single active ingredient rather than a fixed-dose combination containing two or more BP lowering medicines.
  
• Consider coexisting conditions when choosing BP lowering therapy. Ensure active ingredients of all medicines are identified to reduce risk of adverse events from drug–drug interactions or inadvertent duplication.
  
• Review and encourage patient adherence to lifestyle modifications and prescribed medicines at every opportunity.

Blood pressure is a well-established and important modifiable risk factor for cardiovascular disease (CVD).

In Australia, elevated BP has been the most frequently managed problem in general practice for the past decade.¹ In the recent 2011–12 Australian Health Survey, one in five adults had BP ≥ 140/90 mmHg^2,3 – the commonly accepted cut-off where BP shifts from being described as 'normal' to 'high', and traditionally identifies a person with hypertension.⁴

While it may be practical to have a BP value that is universally understood to represent a disease threshold, observational studies show that BP and cardiovascular risk have a log–linear relationship.^5-7

In the Prospective Studies Collaboration meta-analysis involving a million adults aged 40–69 years with no previous CVD, the risk of CVD death doubled with each increase of 20 mmHg in systolic BP or around 10 mmHg in diastolic BP – from pressures as low as 115/75 mmHg.⁷ Moreover, CVD is multifactorial and studies show that the cumulative effect of these risk factors may be synergistic.^8-10

Such observations have challenged the clinical relevance of using BP thresholds in isolation to determine if treatment is needed to reduce CVD risk.^8,9,11

'Hypertension should be managed within a comprehensive management plan to reduce BP, reduce overall cardiovascular risk and minimise end-organ damage'¹² – National Heart Foundation

CVD is the leading cause of morbidity and mortality in Australia, affecting an estimated 22% of the adult population (3.7 million people)¹³ and accounting for 31% of all deaths.¹⁴ CVD is also a major contributor to our national burden of disease (18% overall), second only to cancer.¹⁵ Many of the factors underlying and driving this CVD burden are largely modifiable and include high BP, high cholesterol, lack of exercise, high body mass index and smoking (Figure 1).

To account for the large number of possible risk factors and the potential interplay between them, local and international guidelines for primary CVD prevention have been moving away from managing isolated risk factors, instead basing management on absolute CVD risk.^11,16-19

Such an approach is advocated²⁰ because it:

• reduces the chance of undertreating patients with multiple – but only slightly abnormal – risk factors, who are actually at high overall risk of CVD^8,11,21
  
• minimises over-treatment of patients with only a single raised risk factor but who are at low overall risk of CVD^8,11,21
  
• maximises the effectiveness and cost-effectiveness of treatment by targeting individuals most likely to benefit from intervention.^11,21
  

Several tools, including web-based risk calculators and charts are available for Australian health professionals to assess an individual's absolute CVD risk and provide a more complete picture of cardiovascular health.

These tools are based on the Framingham risk equation that combines major risk factors such as age, sex, smoking, BP and cholesterol levels to calculate the likelihood (as a percentage) of a person experiencing a cardiovascular event (ie, stroke, transient ischaemic attack, myocardial infarction, angina) within the next 5 years.²⁰ This likelihood (absolute risk) is categorised as being low (< 10%), moderate (10%–15%) or high (> 15%).²⁰

When and who to assess – it's not one size fits all

All adults from 18 years of age should have their BP measured at least every 2 years.²⁸

Consider absolute risk calculations for adults aged 45–74 years (or 35­–74 years for Aboriginal and Torres Strait Islander adults) who are not known to have CVD.²⁰

Some individuals will not need a formal absolute CVD risk calculation (regardless of their age) because they are already at high risk of a cardiovascular event.²⁰ This group includes those with:

• history of cardiovascular events or known CVD
  
• diabetes and age > 60 years
  
• diabetes with microalbuminuria (> 20 micrograms/min or urinary albumin:creatinine ratio > 2.5 mg/mmol for males, > 3.5 mg/mmol for females)
  
• moderate or severe chronic kidney disease
  
• previous diagnosis of familial hypercholesterolaemia
  
• systolic BP ≥ 180 mmHg or diastolic BP ≥ 110 mmHg
  
• serum total cholesterol > 7.5 mmol/L
  
• Aboriginal and Torres Strait Islander adults aged over 74 years.^11,16,20
  

In people younger than 45 years, or 35 years for Aboriginal and Torres Strait Islander people, who present with high BP but do not fit any criteria listed above, investigate for undiagnosed causes of secondary hypertension such as sleep apnoea.²⁰

Room to improve

Current research suggests the uptake and implementation of absolute risk guidelines are not consistent among Australian GPs.^22-26

Use of CVD risk calculators was reported by only 60% of GPs participating in the AusHEART study,²³ while a recent analysis from the BEACH program noted that 47% of patients with high BP had not undergone absolute risk assessment in the past.²⁷

Discordance between GP estimates of risk and actual calculated risk has also been recorded, leading to treatment decisions that are often inconsistent with guidelines.^23,24,26 For example, in AusHEART 45% of patients (with or without CVD) not prescribed BP-lowering medicines were indicated for treatment when Australian guidelines were applied.

Similarly, 40% of patients receiving medicines were assessed as low absolute risk according to the same guidelines and may have been effectively managed with lifestyle modification.²³ In some cases this discordance may be because a GP has determined risk based on individual risk factors in preference to absolute risk.²⁴

Encouraging changes in lifestyle or adherence to medicines can be problematic in at-risk patients who are asymptomatic. Using a visual aid such as the Australian cardiovascular risk charts or an interactive tool such as the online calculator may help some people better understand the cumulative effect of their risk factors and how these may be attenuated.

Open the online cardiovascular risk calculator

Recent Australian research has reported that GPs use a number of strategies to communicate absolute risk, depending on their perception of patient risk, motivation and anxiety. For example, a 'positive' strategy that provided reassurance and motivation was employed for people perceived to be at lower CVD risk, while for patients at higher risk GPs described using the absolute risk tools as a 'scare tactic' strategy to motivate action.^22,31

Inform treatment using absolute risk and thorough clinical assessment

Figure 2: Cardiovascular risk assessment and management algorithm²⁰

Adapted with permission from NVDPA

When assessing absolute risk, it is also important to check for associated clinical conditions (eg, diabetes, cerebrovascular disease, CHD) and/or end-organ damage (eg, left ventricular hypertrophy, microalbuminuria, chronic kidney disease, vascular disease).¹² This information is essential to assist with the development of a comprehensive management plan that may include recommendations for lifestyle and behavioural changes as well as pharmacological interventions to reduce CVD risk.^12,20

Current guidelines provide general recommendations around treatment options according to absolute risk levels and other clinical characteristics that may be present (Figure 2).

'Blood pressure must be measured accurately to ensure patients in need of treatment are correctly identified.'³²

In-clinic BP measurements are the frontline of BP assessment and monitoring in primary care. When taken with a calibrated sphygmomanometer these values can be very accurate if measured using best practice.¹²

However, in-clinic measurements can be confounded by limitations such as the reliability of the devices or techniques used to obtain a reading, the potential for a 'white coat' or 'masked' effect, or the small number of readings able to be taken in a single visit.³³

In addition, given that BP naturally fluctuates throughout the day and can be affected by different activities and substances,¹² in-clinic measurement can at best provide only a snapshot.

To achieve a good assessment of BP take multiple measurements on separate occasions.¹² At the initial BP assessment, take measurements from both arms. If there is a variation of > 5 mmHg between arms, use the arm with the higher reading for all subsequent measurements.¹²

For manual devices the recommendation is that at least two measurements are taken one or more weeks apart (unless BP elevation is severe, in which case a clinician may take the follow-up measurement earlier).¹² If an automated device is used, take at least three measurements, and average the second and third measurements.^36,37

Multiple factors can affect the accuracy of an in-clinic BP reading and cause a discrepancy between actual and measured BP (Table 1).³⁸

Table 1. Factors that can increase in-clinic SBP measurements³⁸

When to consider out-of-clinic measures

Assessment of BP outside the clinic, using either 24-hour ambulatory BP monitoring (ABPM) or home BP monitoring (HBPM), can complement in-clinic BP measurements and better characterise BP profiles in some patients.^{12,20,33,37,39-41} Evidence also suggests that out-of-clinic BP measurements may be more useful for predicting future CV risk than those recorded in-clinic.^33,39

Use out-of-clinic BP monitoring to confirm the presence of persistently elevated BP before calculating absolute CVD risk; convert the reading to an in-clinic equivalent before use.^39,40 At present, only ambulatory BP readings have published in-clinic equivalents (Table 2).³⁹

However, it is widely recognised in the literature that home BP values:

• are similar to daytime ambulatory BP values^42-45 – with both sharing the same threshold of 135/85 mmHg for 'high' BP^12,41
  
• are generally lower than in-clinic values¹⁸ although the difference between the two decreases as BP approaches 'normal values'.^43,44
  

Table 2. Ambulatory BP and in-clinic BP systolic BP equivalents^a (can be used to calculate absolute cardiovascular risk)^12,39

^aAmbulatory BP predicted from daytime seated in-clinic BP (n = 5327)⁴⁶ grouped by age and sex.

ABPM and HBPM can also be used to confirm the presence of white-coat (elevated in-clinic but normal out-of-clinic BP) and masked hypertension (normal in-clinic but elevated out-of-clinic BP),^12,33,39 while ABPM is also indicated when nocturnal hypertension, or nocturnal non-dipping (no night-time lowering of BP) are suspected.^12,39

Once identified, these patients benefit from continued monitoring,^33,39 as both white-coat and masked hypertension have been associated with the development of high BP and the development of impaired glucose tolerance or diabetes,⁴⁷ while nocturnal non-dipping has been associated with increased risk of stroke, end-organ damage and cardiovascular events, including death.^48,49

Recommend lifestyle modification regardless of risk level

Positive changes to lifestyle may help to avoid, delay or reduce the need for BP-lowering medicines.^12,20,50

Studies have demonstrated that, regardless of a patient's absolute risk, lifestyle modifications are an important and effective component of any CVD risk-reducing strategy.⁵⁰ Substantial improvements to BP and cardiovascular risk can be achieved with lifestyle modifications such as changes to eating patterns, moderating alcohol intake, weight loss, stopping smoking and regular physical activity.^50,51

Further information for encouraging and maintaining lifestyle changes can be found in the RACGP SNAP guide. 

When lifestyle interventions alone cannot reduce absolute risk sufficiently, guidelines recommend starting treatment with one of the following main classes of BP-lowering medicines:^12,20,37

• angiotensin-converting enzyme inhibitor (ACE inhibitor)
  
• angiotensin-II receptor blockers (ARB)
  
• calcium-channel blockers (CCB)
  
• low-dose thiazide diuretics.
  

As several large systematic reviews and meta-analyses have demonstrated that at standard doses all these classes lower BP to a similar extent,^52-56 base choice of initial and subsequent treatments, if needed, on:^12,20,37

• patient age
  
• presence of clinical comorbidities or end-organ damage
  
• presence of other coexisting conditions that either favour or limit the use of particular classes
  
• potential interactions with other medicines
  
• implications for adherence
  
• cost.
  

Beta blockers are no longer a recommended first-line medicine for primary prevention of CVD, as evidence suggests they are less effective for preventing stroke.^52,55,56

Use a stepwise approach to lower BP

In adults with uncomplicated high BP who are unable to achieve BP control with monotherapy, first consider possible barriers to adherence. However, it is generally accepted that most patients will require a combination of two or more BP-lowering agents to achieve adequate BP lowering.^12,57

If a satisfactory reduction in BP is not achieved after an appropriate trial of monotherapy, consider a stepwise approach in which medicines from different classes are gradually introduced.¹² There are also some specific combinations that have proven more effective than others based on a range of patient factors (Table 3).¹²

Table 3. Recommendations for combining BP-lowering medicines^12,37

Fixed-dose combinations – evidence still unclear

Current guidelines acknowledge that fixed-dose combination (FDC) medicines can offer convenience to patients and may simplify therapy.^12,19,20,37 However, data supporting their use in treatment-naïve patients are limited⁵⁸ and there is lack of consensus on when they can be introduced in a treatment strategy.^{12,19 ,20,37,59}

In Australia, PBS-listed FDC medicines are listed as restricted benefits and are not subsidised if used to start BP-lowering treatment. The National Heart Foundation recommends an FDC only after dual or triple combination therapy (as separate products) has been established.¹² Other local guidelines discuss FDCs as an option when initial management with monotherapy has been ineffective.³⁷

Introducing an FDC after BP has been stabilised on the individual components may also reduce potential risk of adverse events among people in whom a large drop in BP might be poorly tolerated (ie, elderly patients).⁵⁹

A key to success in preventing and managing cardiovascular disease is adherence to, and persistence with, prescribed medicines and lifestyle recommendations.⁶¹

Non-adherence to BP lowering medicines and lifestyle changes can have a direct impact on patient outcomes (ie, increased rates of cardiovascular events or death).^61-63

However, given the largely asymptomatic nature of high BP, patients may not understand or accept the health risks associated with their diagnosis and be less motivated to take medicines or follow lifestyle recommendations.^61,62

This can make encouraging adherence for a long-term condition such as high BP challenging.⁶⁴

Multiple reasons underlying patient non-adherence have been identified. These can be intentional (eg, an active patient decision, based on balancing perceived benefits of treatment against the perceived risks) or unintentional (eg, patient doesn't know how/is unable to take their medicine(s), forgetfulness). Adherence can also be influenced by:^{5,62,65 ,66}

• factors such as ethnicity, education, beliefs, motivation and attitude
• the patient–prescriber relationship
  
• health literacy
  
• therapy-related factors (eg, treatment complexity, treatment duration, medication side effects)
  
• economic factors (eg, cost and income, social support).
  

Assess and optimise adherence at every opportunity

View each meeting with a patient as an opportunity to encourage and assess adherence to lifestyle modification and medication.

There is currently no gold standard for measuring medicine adherence in patients, although there are strategies available to use in everyday practice such as: ⁶¹

• pill counts
  
• pharmacy refill records
  
• prescription records in electronic medical notes
  
• patient self-reporting (eg, diary).
  

Asking specific and structured questions may identify patients who require help to improve adherence. For example, an Australian study using a validated four-item patient questionnaire – the Morisky instrument – reported that patients who answered yes to the question 'Did you ever forget to take your medication?' were significantly more likely to experience a first cardiovascular event or a fatal other cardiovascular event compared with patients who answered no.⁶³

Deliver information in a tailored and timely way

Several interventions have been shown to modestly improve adherence to medicines in people with high BP.^68,69 However, no single strategy has consistently demonstrated effectiveness and no strategy has utility for all patient groups.^61,62,66,69

People differ in the type and amount of information they need and want.⁶⁶ Use clinical judgment and an understanding of the patient's social, cultural and medical background to guide when and how much information is required and which interventions may be most appropriate to support adherence for an individual patient.

Successful strategies that have been reported to improve adherence include:^41,68,69

• simplification of treatment and of medication packaging (eg, WebsterPaks)
  
• home BP monitoring by patients
  
• patient-centred motivational counselling
  
• daily reminder charts
  
• social and family support
  
• telephone calls from nurses (and pharmacists?)
  
• telephone-linked computer counselling.
  

The MedicineWise smartphone app allows patients to set alarms for medicine doses and set calendar reminders for refilling prescriptions.

For further information on assessing and addressing adherence to medicines

• National Heart Foundation of Australia. Improving adherence in cardiovascular care: A toolkit for health professionals 2011
  
• Therapeutic Guidelines. Cardiovascular disease: adherence to drug therapy
  

Prof Nicholas Zwar, School of Public Health and Community Medicine, University of New South Wales, Sydney