Stable and unstable angina, stress testing and management

Overview

Angina pectoris is chest discomfort caused by myocardial ischaemia: the heart muscle needs more oxygen than the coronary arteries can deliver. The usual cause is atherosclerotic narrowing of the coronary arteries.

Angina matters because it is a warning sign of coronary artery disease, which can progress to unstable angina, myocardial infarction, heart failure and sudden death. Good treatment controls symptoms and improves outlook.

Why ischaemia happens

Reduced supply:

• Atheroma (by far the commonest), thrombus, coronary spasm, embolus, arteritis.
• Low oxygen delivery: anaemia, carbon monoxide, hypotension.

Increased demand:

• Aortic stenosis, hypertrophic cardiomyopathy, severe hypertension (thick muscle).
• Tachycardia, thyrotoxicosis.

A coronary narrowing becomes flow-limiting at about 50% of the diameter (about 70% of the cross-sectional area). At this point the small vessels beyond are already maximally dilated, so any rise in demand causes ischaemia. Ischaemic metabolites such as adenosine stimulate nerve endings and produce the pain.

Risk factors for coronary artery disease

Types of angina

Typical, atypical and non-anginal pain

Three features define typical angina:

1. Constricting discomfort in the front of the chest, neck, jaw, shoulders or arms.
2. Brought on by physical exertion or emotional stress.
3. Relieved by rest or GTN within about 5 minutes.

Canadian Cardiovascular Society (CCS) grading

Clinical assessment

• History is the key to diagnosis.
• Examination is often normal. Look for:
  • Aortic stenosis (slow-rising pulse, ejection systolic murmur to the carotids). It is an important cause of angina with normal coronaries.
  • Anaemia, thyroid disease.
  • Hyperlipidaemia signs: corneal arcus, xanthelasma, tendon xanthomas.
  • Hypertension, BMI, waist size.

Investigations

First-line tests

• Bloods: FBC (anaemia), fasting glucose and HbA1c, fasting lipids, renal function, thyroid function, troponin if unstable.
• Resting 12-lead ECG: often normal; may show old Q waves, LVH, LBBB or ST–T changes.
• Echocardiography: regional wall motion, ejection fraction, valve disease (AS), other causes.
• Chest X-ray if atypical, or if lung disease or heart failure is suspected.

Anatomical versus functional tests

• Anatomical: CT coronary angiography (CTCA) and invasive coronary angiography show the narrowing itself. Current UK guidance favours CTCA for most new patients with suspected angina.
• Functional (stress) tests: show whether a narrowing causes ischaemia. These are the TOS tests below.

Stress testing

Exercise stress test (exercise ECG)

Principle: exercise raises myocardial oxygen demand; a narrowed artery cannot raise flow enough, so ischaemia appears on the ECG.

Method: the patient walks on a treadmill with speed and slope increased every few minutes (Bruce protocol) while a 12-lead ECG, BP and symptoms are monitored.

Positive (ischaemic) result:

• ST depression of more than 1 mm that is horizontal (planar) or down-sloping, in leads facing the ischaemic area.
• Up-sloping ST depression is non-specific.
• ST elevation during exercise (rare) means transmural ischaemia from spasm or a critical stenosis.
• Changes are seen most often in V5 (anterior/lateral) and aVF (inferior).

Markers of high risk (severe disease):

• Fall in blood pressure during exercise.
• Ischaemia at a low workload; exercise time under 6 minutes carries a poorer outlook.
• Frequent ventricular ectopics or ventricular arrhythmia.
• Slow return of heart rate to baseline.

Limits: low sensitivity, so it is used less than before. It cannot be interpreted if the resting ECG is abnormal (LBBB, paced rhythm, digoxin effect, LVH with strain), and it needs a patient who can walk.

Do not perform in unstable angina or recent infarction, severe symptomatic aortic stenosis, uncontrolled arrhythmia or heart failure, or acute illness such as myocarditis or aortic dissection.

Chemical (pharmacological) stress test: dobutamine stress echo

Who: patients who cannot exercise (arthritis, stroke, lung disease, frailty) or need imaging.

Principle: dobutamine (a β1 agonist) is infused in rising doses to raise heart rate and contractility, mimicking exercise. Echo watches the walls of the left ventricle.

Findings:

• A wall segment that contracts normally at rest but becomes weak or stops thickening under stress = ischaemia in the artery supplying it.
• A segment that is weak at rest but improves at low-dose dobutamine = viable (hibernating or stunned) myocardium that may recover after revascularisation.
• A segment weak at rest and still weak at all doses = scar.

Risks: ventricular arrhythmias (uncommon).

Other drug stressors: adenosine or dipyridamole dilate normal coronary arteries and are used mainly with perfusion scans or MRI. They cause flushing and can trigger bronchospasm.

Nuclear test: thallium (myocardial perfusion) scan

Principle: thallium-201 behaves like potassium and is taken up by living heart cells in proportion to blood flow. Technetium-99m-labelled tracers (sestamibi, tetrofosmin) work similarly. Images are made with a gamma camera, usually as SPECT.

Method:

1. Inject tracer at peak stress (exercise or drug). Image at once: poorly perfused areas look dark (cold spots).
2. Image again after redistribution (thallium spreads evenly into all living cells over about 2–24 hours) or after a separate rest injection.

Interpretation:

Comparison of stress tests

Management of stable angina

General measures

• Explain the condition and reassure: the outlook of stable angina is good when treated.
• Stop smoking, healthy diet, regular exercise, weight control, limit alcohol.
• Control BP, diabetes and lipids.

Drugs to relieve symptoms

For attacks: sublingual glyceryl trinitrate (GTN) tablet or spray, before or during exertion. Repeat after 5 minutes if needed; if pain lasts after repeated doses, seek emergency help (possible ACS). Side effects: headache, flushing, hypotension.

To prevent attacks (step-wise):

1. First line: a beta-blocker (e.g. bisoprolol) or a rate-limiting calcium channel blocker (verapamil, diltiazem).
2. If not controlled: beta-blocker plus a dihydropyridine CCB (amlodipine, nifedipine).
3. If either is not tolerated, or symptoms continue on two drugs: add or switch to a long-acting nitrate (isosorbide mononitrate), ivabradine, nicorandil or ranolazine.
4. If still symptomatic on two drugs: consider revascularisation.

Drugs to prevent events

• Aspirin 75 mg daily (clopidogrel 75 mg if aspirin is not tolerated).
• High-intensity statin (e.g. atorvastatin 80 mg), aiming for LDL below 1.8 mmol/L.
• ACE inhibitor if there is also hypertension, diabetes, heart failure or kidney disease.

Variant (Prinzmetal) angina

• Calcium channel blockers and nitrates are the mainstay.
• Avoid non-selective beta-blockers (unopposed alpha-mediated spasm).
• Stop smoking; avoid triggers such as cocaine and triptans.

Revascularisation

Indicated when symptoms persist despite good medical treatment, or to improve survival in high-risk anatomy.

Percutaneous coronary intervention (PCI):

• A balloon and stent are passed to the narrowing, usually via the radial artery (fewer bleeding complications).
• Drug-eluting stents reduce re-narrowing (restenosis) compared with bare-metal stents.
• Dual antiplatelet therapy (aspirin plus clopidogrel) after elective stenting, usually for 6–12 months.
• Fractional flow reserve (FFR) measured with a pressure wire tells whether a narrowing is significant; a value above 0.80 can be treated with drugs.
• Complications: bleeding, access-site haematoma, dissection, stent thrombosis, MI, stroke.

Coronary artery bypass grafting (CABG):

• Grafts (internal mammary artery or saphenous vein) bypass blocked segments.
• Internal mammary artery grafts last longer than vein grafts.

PCI or CABG?

The decision is made by a heart team of cardiologists and surgeons.

Unstable angina

Unstable angina is managed as an acute coronary syndrome: admission, aspirin plus a second antiplatelet drug, anticoagulant, nitrates, beta-blocker, risk scoring and coronary angiography. See the acute coronary syndrome chapter.

Quick revision

• Angina = demand outstrips coronary supply; usually atheroma.
• Stable: exertional, settles with rest/GTN. Unstable: new, crescendo or rest pain, troponin normal.
• Prinzmetal: rest pain, transient ST elevation, spasm; use CCB, avoid beta-blockers.
• Exercise ECG positive: ≥1 mm planar/down-sloping ST depression; BP fall = severe disease.
• Dobutamine stress echo: new wall-motion abnormality; for those who cannot exercise.
• Thallium: reversible defect = ischaemia; fixed defect = scar.
• GTN for attacks; beta-blocker or CCB first line; then add the other class or a second-line agent.
• Aspirin 75 mg and high-intensity statin for all.
• CABG for left main or three-vessel disease with diabetes; PCI for simpler disease.

Written by The House Job from standard references (Kumar and Clark's Clinical Medicine).

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