Microvascular Angina

Microvascular angina is angina caused by dysfunction of coronary microcirculation in the absence of obstructive epicardial disease. It is part of the INOCA spectrum (ischaemia with nonobstructive coronary arteries).

More common in women (about 2:1), and in the perimenopausal period.

Mechanisms: endothelial dysfunction, impaired smooth muscle relaxation, microvascular remodelling and increased resistance, with low oestrogen, inflammation and insulin resistance contributing.

Associated with diabetes, hypertension, obesity, left ventricular hypertrophy and chronic inflammatory disease.

Prognosis is not benign. Adverse event rates are 2 to 3% yearly with higher rates of heart failure with preserved ejection fraction and hospitalisation.

• Exertional chest pain similar to obstructive angina, but often prolonged, slower to resolve and variably nitrate responsive.
• Symptoms with mental stress and at rest.
• Dyspnoea, fatigue and reduced exercise capacity.
• Normal examination.

• Exclude obstructive disease with coronary CT angiography or invasive angiography.
• Stress testing may be positive. Perfusion PET or cardiac MRI shows reduced myocardial perfusion reserve (below 2.0 on PET).
• Invasive physiology: coronary flow reserve below 2.0 and index of microcirculatory resistance 25 or more with adenosine 140 micrograms/kg/min. Acetylcholine testing separates endothelial dysfunction from epicardial or microvascular spasm.
• Echocardiography for diastolic dysfunction and hypertrophy.

• Aggressive risk factor control: statin (atorvastatin 40 mg), ACE inhibitor (ramipril 5 to 10 mg, improves flow reserve), blood pressure and glucose control, weight loss and aerobic exercise.
• Antianginal therapy guided by endotype:
  • Reduced flow reserve: beta blocker (bisoprolol, nebivolol 5 mg) or diltiazem.
  • Vasospastic microvascular: calcium channel blockers and nitrates.
  • Ranolazine 500 to 1000 mg twice daily, nicorandil, trimetazidine, ivabradine as add ons.
• Refractory pain: imipramine 50 mg at night, aminophylline 100 to 200 mg twice daily, or enhanced external counterpulsation.
• Low dose aspirin when there is evidence of atherosclerosis.
• Cognitive behavioural therapy and cardiac rehabilitation.
• Avoid repeated invasive procedures and nonspecific reassurance alone.