THE CONTEXT
Myocardial oxygen balance depends on cardiac work, coronary blood flow and oxygenation. Angina with normal coronary angiography may still have objective evidence of myocardial ischaemia.
Determinants of myocardial oxygen demand
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Factors influencing cardiac work and oxygen demand include heart rate, blood pressure and myocardial contractility.
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Left ventricular hypertrophy and valve disease also influence myocardial oxygen demand.
Determinants of myocardial oxygen supply
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Coronary blood flow is influenced by the duration of diastole, coronary perfusion pressure and coronary vasomotor tone.
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Coronary perfusion pressure is aortic diastolic pressure minus coronary sinus or right atrial diastolic pressure.
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Coronary blood flow occurs mainly in diastole.
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Haemoglobin and oxygen saturation are factors influencing oxygenation.
Syndrome X and microvascular angina
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Typical angina on effort, normal coronary arteries on angiography and objective myocardial ischaemia on stress testing constitute syndrome X, also called ischaemia with no obstructive coronary arteries (INOCA).
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Women account for 80%–90% of these patients, and the mechanisms of their symptoms are unclear.
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A subset has impaired myocardial vasodilatory reserve, giving rise to terms such as microvascular angina or angina with no obstructive coronary arteries (ANOCA).
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In the absence of coronary atherosclerosis, these disorders carry a good prognosis and respond variably to anti-anginal therapy.
Other associated conditions
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Angina can occur with aortic stenosis, hypertrophic obstructive cardiomyopathy and aortitis.
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Some types of systemic vasculitis are rare associations of angina.