Angina module 6: secondary prevention and treatment

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Introduction

There are several sets of national and international guidelines for the treatment of chronic stable angina. The following section will focus mainly on the most recent UK guidelines (2011) from the National Institute for Health and Clinical Excellence (NICE).1 There are earlier guidelines (2006) from the European Society of Cardiology (ESC),2 which were updated in 2013,3 and from the Scottish Intercollegiate Guideline Network (SIGN) also published in 2006.4 Guidelines are also under revision from the American Heart Association/American College of Cardiology (AHA/ACC) but these will not be reviewed in this module.

Objectives for treatment

The goals of drug therapy for patients with stable angina pectoris are to:

  • enhance quality of life through reduction of symptoms
  • improve prognosis through reduction of risk of future myocardial infarction or death
  • be well tolerated, and cause minimal side effects.

As emphasised by NICE,1 treatment and care should take into account angina patients’ individual needs and preferences. Good communication is essential, supported by evidence-based information, to allow patients to reach informed decisions about their care. If the patient agrees, families and carers should have the opportunity to be involved in decisions about treatment and care.

Figure 1. Aspirin bottle, 1899

Cardiovascular disease (CVD) predominantly affects people older than 50 and age is the main determinant of risk. Apart from age and sex, three modifiable risk factors – smoking, raised blood pressure, and cholesterol – make a major contribution to CVD risk, particularly in combination. These account for 80% of all cases of premature coronary heart disease (CHD) (see Angina module 2: prevention). Aggressive risk factor modification is therefore vitally important for all angina patients. These are dealt with in detail in module 2 but are summarised later.

Secondary prevention treatment

A number of pharmacologic treatments are described as, ‘disease modifying’ in that they can improve outcomes in patients with stable CHD, and reduce risk of future cardiovascular events. The following section reviews some of these ‘secondary prevention’ agents.

Antiplatelet agents

All angina patients, unless there are contraindications, are recommended to take low-dose daily aspirin (figure 1). It is important to consider, however, any co-morbidities and bleeding risk. A meta-analysis5 of 16 secondary prevention trials in 17,000 individuals at high cardiovascular risk shows that aspirin therapy is associated with about a one fifth reduction in coronary events and in ischaemic stroke, the downside being a  non-significant increase in haemorrhagic stroke.  The absolute benefit seen in major coronary events in secondary prevention trials was an impressive 1% per year.

These findings are in contrast to primary prevention trials conducted in patients without prior CVD, where aspirin is of uncertain net value in preventing vascular events, as its effects are offset by an increase in major bleeds. This has been confirmed in a more recent meta-analysis6 of primary prevention trials showing that over six years, aspirin reduced total CVD events by about 10% but benefits were offset by major bleeding events. The message is therefore that:

  • routine use of aspirin for primary prevention is not warranted and that;
  • treatment decisions need to be decided on a case-by-case basis.

The optimal dose range in angina appears to be 75-150 mg/day and the lowest effective dose should be used in order to reduce gastrointestinal side effects. Evidence suggests that patients should remain on aspirin long-term; discontinuation may result in an increased risk of cardiovascular events.7 Non-adherence in patients is the most common reason for discontinuation of aspirin.  Stopping aspirin increases the short-term risk of non-fatal myocardial infarction (MI) or death from CHD by about 50% in primary care patients with a history of ischaemic events, according to one recent study.

The thienopyridine agent, clopidogrel 75 mg/day might be considered as an alternative treatment in patients with aspirin intolerance at high risk of cardiovascular events.