A new approach in diagnosing and managing stable angina, introduced.

Background

Chest pain requires immediate action if it signals an acute condition or, if it does stable angina, determination of the extent and severity of coronary artery disease. Accounting for 1% of primary care visits and 25-40% of emergency admissions, chest pain prevalence in the general population is estimated to be 20-40% (1,2). 

1 - Symptom characteristics of angina

While unstable angina and identified myocardial injuries require emergency coronary angiography to restore myocardial blood flow, the diagnosis of stable angina relies on triage which is described is the 2013 guidelines on stable coronary artery disease (SCAD) (3). The criteria is 1) typicality of symptoms 2) pretest probability assessment (using a validated scoring system) and 3) either functional and anatomical assessment of myocardial ischaemia or that of coronary arteries. 

Indeed, SCAD replaces the former "stable angina pectoris" from the 2006 guidelines. Suspected or known stable coronary artery disease includes a broader spectrum of symptomatic as well as asymptomatic patients with a history of suspected or known stable coronary artery disease. The classical definition of typical angina is retained as 1) sub-sternal chest discomfort of characteristic quality and duration 2) provoked by exertion or emotional stress and 3) that can be relieved in minutes by rest or nitrates. Atypical (probable) angina has two of these features while non-anginal chest pain needs only one.
The Canadian cardiovascular society's symptom assessment scale may be used to quantify symptoms as regards to activity: functional severity is assessed at 1-4, 1 being the least limiting and at 4 symptoms are so severe that they cause an inability to carry out any physical activity.

2 - Pre-test probability assessment

The use of scores, with the entering of simple clinical findings further assists the physician in the triage of chest pain patient, in view of an optimal use of resources. The pre-test probability (PTP) is a clinician's pre-test estimates and takes into account the performance of a given diagnostic test in a given patient.
The Dukes treadmill score (4), is included in 2010 National Institute of Clinical Excellence recommendations (5) and was so in the previous guidelines. However, data used to develop this system is based on the Diamond-Forrester publication from studies carried out in the US in the 1970s.
Furthermore, it does not take older patients into account and classifies them above the age of 70 as high risk while also overestimating the probability of CAD in middle age women especially(6). More recent CAD prevalence estimates taken from 6 countries including in Europe serve as basis for the Genders et al (Table 1) recommended prediction model for the presence of CAD. A patent’s age, gender, typicality of angina, risk factors - diabetes, dyslipidaemia, smoking, hypertension - are taken to measure epicardial coronary artery disease defined as >50% luminal stenosis and also factors in the CT coronary calcium score (when available).

• A clinical estimate of disease at less than 15% likelihood is a low PTP and no further testing is required. 

Other causes of chest pain of non-cardiac causes or functional coronary artery disease are to be entertained such as microvascular angina or coronary spasm.

• A clinical estimate of disease of over 85% calls for immediate ICA.

Indeed, performing no test in a patient with fewer than a 15% likelihood of disease will yield a more accurate diagnosis - no CAD - than performing one since 15% of test results are incorrect (specificity and sensitivity of tests is of 85%). Inversely, for patients who have a more than 85% likelihood of disease, testing is more likely to yield false negatives, therefore patient is assumed to have CAD and sent to ICA.

Table 1. Online pretest prediction model for coronary artery disease >50% epicardial coronary artery stenosis by Genders et  al. 2011 Eur Heart Journal (6).

3 - Functional and anatomical assessment of myocardial ischaemia and coronary arteries

Patients with a higher than 85% PTP of CAD should immediately be sent for ICA. Those under 15% should be examined for other causes. Patients with a probability score between 15% and 85% should give rise to functional and anatomical assessment of myocardial ischaemia and coronary arteries. These patients are at intermediate PTP and tests will determine a risk of annual mortality according to the extent of myocardium at risk and/or extent of coronary artery disease. More specifically, patients with:

• Left ventricular EF< 50% with typical symptoms should undergo invasive coronary angiography (ICA).
• No symptoms (LVEF<50%) would undergo functional testing. 
• Normal LVEF are recommended to undergo stress imaging testing  i.e. stress echocardiography, CMR perfusion, Nuclear perfusion imaging. 

• Patients with a PTP between 15%-50% should be considered for multi-slice CT coronary angiography (CTCA).

The cut-off of PTP of 50% was chosen since those with higher score are more likely to have significant coronary calcification that limits accurate assessment of coronary artery stenosis by CTCA. Of note however, there is overlap and interaction between functional and anatomical assessment of coronary artery disease as a true multimodality approach (Fig. 2).

• Patients with PTP >85% have high probability of mortality and should be commenced on anti-anginal medication and tight risk factor management.

Once diagnosis of SCAD has been confirmed on the basis of the outcome of the functional stress tests and anatomical imaging patients are risk stratified into low – intermediate – high risk groups (Table 1).

• Patients with intermediate and high risk and those with low risk features but symptomatic in spite of OMT would be considered for ICA.

5 - Revascularisation

Patients with proven SCAD and limiting symptoms in spite of OMT should undergo ICA with view to revascularisation (functional flow reserve measurement should be considered if equivocal lesion on ICA). Depending on the anatomical, clinical, technical and local factors, patients can be considered for percutaneous coronary angioplasty (PCI) coronary artery bypass graft surgery (CABG), or hybrid intervention.
Patients unsuited for revascularisation with refractory symptoms could be considered for spinal cord stimulation, external counter-pulsation, chronic pain syndrome management, stem cell therapy.
Decisions regarding the type of revascularisation elected for symptomatic patients with high risk SCAD should be made by a Heart Team involving representation by an interventional cardiologist, a cardiothoracic surgeon, a non-invasive cardiologist and preferably patient and their representatives.

Conclusions

The diagnosis of SCAD is based on a triage of symptoms, PTP assessment and multimodality cardiac imaging involving functional stress tests for ischaemia detection and multi-slice CTCA for anatomical assessment. These image modalities are interchangeable and need to be tailored to individual patients' need according to PTP assessment.
Treatment of SCAD encompasses lifestyle and risk factor modification as well as OMT for angina control. The guidelines advise against performing diagnostic testing to detect ischemia in patients with a PTP < 15% (CAD is assumed not to be present) or > 85% (presence of CAD is assumed). If intermediate and high risk patients remain symptomatic in spite of OMT, revascularisation should be considered after a comprehensive heart team discussion. Patients with high risk features who are not suitable for revascularisation should undergo alternative pain control management.

Fig. 1 : ESC guidelines on the management of stable coronary artery disease.

Fig. 2: Non-invasive testing in suspected SCAD with intermediate PTP.


Next week's issue will focus on non-invasive testing for diagnosis.