Defined as BP above target despite 3 antihypertensives at best tolerated doses. However, before diagnosing it, check that that actually is what’s happening:
- Are the drugs being taken as prescribed? Compliance issues, comprehension issues, memory.
- Is BP measurement correct? Poor technique, too small a cuff, etc.
- Is it white coat hypertension? 24-hour ambulatory monitoring (should be below 135/85)
If it is resistant hypertension, look for secondary causes.
- CKD (though chicken and egg…)
- Renal artery stenosis
- Cushing’s syndrome
- Intracranial tumours
Coarctation of the aorta
Also consider drugs (prescribed, OTC, recreational) and salt intake (should be below 6g/day but rarely is).
- Urinalysis for haematuria/proteinuria
- Plasma renin or aldosterone levels
- 24-hr urine for metanephrines or normetanephrines
- Possibly renal ultrasound for renal artery stenosis
Evidence base for treatment is poor. The best treatment, surprisingly, is thought to be spironolactone, as long as the potassium isn’t in the upper range (>4.5) to start with. Spironolactone can help keep better control of the RAAS (helps avoid aldosterone rebound, which is sometimes a problem with long-term blockade) and induces regression of LVH.
- If spironolactone working but not tolerated (usually due to breast tenderness or gynaecomastia) try changing to amiloride or eplenerone, which don’t work as well but have fewer SEs.
- If potassium >4.5 before starting, try increased thiazide instead.
- If not working/not tolerated, could try alpha-blockers, beta-blockers, or centrally acting drugs.
Renal denervation is a new but initially promising alternative for treatment.