Clinical background
Angina pectoris is a subjective symptom whose severity ranges from mild discomfort on strenuous exertion to pain at rest. Without a standardised grading, clinical documentation and treatment decisions become inconsistent between assessors and over time. The Canadian Cardiovascular Society (CCS) angina class serves that purpose: to code the functional impact of stable exertional angina on a four-level ordinal scale. The instrument is not a risk calculator and gives no absolute risk, but a common language for symptom severity that guides decisions on uptitrating medication, referral for coronary angiography and assessment of the treatment response over time.
Determining the Canadian Cardiovascular Society (CCS) angina class
The CCS angina class is an ordinal classification without a mathematical formula. The patient is assigned to one of four classes (I to IV) according to the degree of physical exertion that provokes angina:
| Class | Definition |
|---|---|
| I | Angina only on strenuous or prolonged exertion |
| II | Slight limitation of ordinary activity |
| III | Marked limitation of ordinary activity |
| IV | Inability to carry out any activity without angina, or angina at rest |
The classification was developed in 1972 by an ad hoc committee of the Canadian Cardiovascular Society, led by Louis Campeau at the Montreal Heart Institute, with a remit to standardise the terminology for reporting coronary artery disease and coronary bypass surgery [1]. It was formally published in 1976 as a short letter in Circulation [1]. The system is a four-level scale inspired by the New York Heart Association (NYHA) functional classification and the American Medical Association's classification of organic heart disease [2]. The derivation cohort consisted of patients evaluated for and treated with coronary bypass surgery at the Montreal Heart Institute; the aim was to allow the severity of exertional angina, and changes over time, to be assessed reliably by independent observers [2].
Interpretation in practice
The CCS angina class is intended for stable exertional angina and is coded from the patient's symptoms at a given time. The class is not static and should be reassessed when the symptom pattern changes or after a change of treatment.
| Class | Clinical action |
|---|---|
| I | Optimised pharmacotherapy; lifestyle advice. No urgent referral for invasive investigation on the basis of symptoms alone. |
| II | Intensify pharmacotherapy (increase the beta blocker, add a nitrate or ivabradine). Refer for coronary angiography if symptoms are not controlled or if there is objective ischaemia. |
| III | Reserve for invasive coronary angiography. Rapid optimisation of pharmacotherapy; in a suitable candidate, consider revascularisation. |
| IV | Refer for urgent invasive assessment. Angina at rest is a warning sign that may point to unstable coronary artery disease and requires immediate management under the acute coronary syndrome protocol. |
A shift from, for example, class II to class III at follow-up means worsening symptom control and should prompt reconsideration of pharmacotherapy and of the indication for invasive investigation.
Validation and performance
Reproducibility. In a Danish study, two independent observers classified 56 patients referred for coronary angiography because of stable angina. The observers agreed on the CCS class in 86 per cent of cases; the remaining disagreements involved only one class. Agreement of 100 per cent was recorded for the presence or absence of angina, and 93 per cent for the type of chest pain [3]. The observed reproducibility was thus considerably higher than for the NYHA class, which achieved only 75 per cent agreement in the same cohort [3].
Prognostic validity. In the prospective ACRE study, 2,849 consecutive patients with angina undergoing coronary angiography in London were followed for 2.5 years. A higher CCS class was linearly associated with a greater number of diseased vessels and with impaired left ventricular function (P<0.001) [4]. After adjustment for age, sex, smoking, hypertension, diabetes, the number of diseased vessels, left ventricular function, medication and revascularisation status, an association remained with the rate of revascularisation and with death or non-fatal myocardial infarction (CCS IV compared with I: hazard ratio 2.44; 95 per cent CI 1.46 to 4.09) [4].
In a retrospective cohort from American veterans' hospitals (299,577 patients, of whom 14,216 had a documented CCS class extracted by natural language processing), all-cause mortality over 3.4 years of follow-up was 4.58, 4.60, 6.22 and 6.83 deaths per 100 person-years for classes I to IV respectively [5]. After multivariable adjustment, the hazard ratio for all-cause mortality was 1.05 (95 per cent CI 0.95 to 1.15) for class II, 1.33 (95 per cent CI 1.20 to 1.47) for class III and 1.48 (95 per cent CI 1.25 to 1.76) for class IV, compared with class I [5]. The rate of percutaneous coronary intervention was almost doubled for class IV compared with class I (HR 1.92) and that of coronary bypass surgery more than doubled (HR 2.51) [5].
Predictive value against objective findings. The clinical angina classification nonetheless had a low predictive value for underlying coronary artery disease and perfusion abnormalities. The positive and negative predictive values for typical/atypical angina were 55/82 per cent against perfusion abnormalities and 53/82 per cent against coronary artery disease in the Danish study [3]. Clinical assessment could therefore not predict abnormal perfusion or coronary artery disease with reasonable confidence, particularly for confirming disease (a low positive predictive value).
Limitations
The CCS angina class applies only to stable exertional angina. In unstable angina or NSTEMI, the classification should not be used to guide management; there the acute coronary syndrome protocol applies irrespective of symptom level.
The most criticised aspect of the system concerns the criterion "anginal syndrome may be present at rest" in class IV, which Campeau himself described 30 years later as inappropriate and confusing, since exertional angina and rest angina are different pathophysiological states [2]. The system is fundamentally a symptom and severity classification, not a prognostic instrument, and Campeau noted that its prognostic information is insufficient [2].
The classification is subjective and is influenced by the patient's activity level, insight into their condition and reporting, as well as by the observer's experience. A patient who avoids exertion for fear of symptoms may be coded as milder than they are, since the class is defined by what actually provokes angina, not by what might provoke it at a higher level of activity. This is a systematic source of error that can lead to underestimation of the condition in sedentary patients.
The CCS angina class correlates poorly with objective ischaemia and coronary anatomy according to the Danish study [3]. This means that a high class justifies invasive investigation but does not guarantee the presence of significant coronary artery disease, and that a low class does not exclude significant coronary artery disease in patients with a low activity level or atypical symptoms.
References
- Campeau L. Grading of angina pectoris. Circulation 1976;54(3):522–3. PMID: 947585
- Campeau L. The Canadian Cardiovascular Society grading of angina pectoris revisited 30 years later. Can J Cardiol 2002;18(4):371–9. PMID: 11992130
- Christensen HW et al. Observer reproducibility and validity of systems for clinical classification of angina pectoris: comparison with radionuclide imaging and coronary angiography. Clin Physiol Funct Imaging 2006;26(1):26–31. PMID: 16398667
- Hemingway H et al. Prospective validity of measuring angina severity with Canadian Cardiovascular Society class: The ACRE study. Can J Cardiol 2004;20(3):305–9. PMID: 15054509
- Owlia M et al. Angina severity, mortality, and healthcare utilization among veterans with stable angina. J Am Heart Assoc 2019;8(15):e012811. PMID: 31362569
