Masked Hypertension

Masked hypertension is a normal office blood pressure (under 140/90 mm Hg) with raised out-of-office pressure. Ambulatory daytime mean is 135/85 mm Hg or more, 24-hour mean 130/80 mm Hg or more, or home mean 135/85 mm Hg or more.

In a treated patient it is called masked uncontrolled hypertension. It is found in about 10 to 17% of the general population and in 15 to 30% of treated patients.

It is more frequent with high normal office pressure (130 to 139/85 to 89 mm Hg), younger age, male sex, obesity, diabetes, chronic kidney disease, smoking, alcohol, stress and sleep apnoea.

Cardiovascular risk is close to that of sustained hypertension, and the condition is under recognised because routine clinic checks look normal.

Pathophysiology. Heightened sympathetic reactivity during work, activity, smoking, caffeine, alcohol and sleep apnoea raises daily pressure while the calm clinic reading is normal.

Short acting drugs wearing off at night or in the early morning, non-dipping and a morning surge also contribute. Left ventricular hypertrophy and arterial stiffening follow.

• Asymptomatic, and a normal examination and office pressure.
• Unexplained left ventricular hypertrophy, albuminuria or retinopathy with normal clinic readings.
• Early morning stroke or myocardial infarction, or kidney or heart failure progression despite normal clinic pressures.
• Associated factors: obesity, snoring, high alcohol intake, smoking, stimulant use, shift work.

• Suspect it in high normal office pressure, in normal office pressure with organ damage, and in high risk patients.
• Ambulatory monitoring (preferred) gives daytime, night time and morning pressure, dipping and variability. Night time mean 120/70 mm Hg or more is raised.
• Home monitoring: 7 days, two readings morning and evening, day 1 discarded, mean 135/85 mm Hg or more is raised.
• Organ damage and risk. ECG, echocardiography (left ventricular mass), urine albumin to creatinine ratio, creatinine, eGFR, fundoscopy, glucose, lipids.
• Contributors. Alcohol, stimulants, anti-inflammatory drugs, sleep apnoea screening.

Differential diagnosis.

• White coat hypertension
• Sustained hypertension
• True normotension
• Ambulatory monitoring artefact and poor device validation
• Sleep apnoea and nocturnal hypertension
• Secondary hypertension
• Labile hypertension from stimulants or anxiety
• Short acting drug effect in treated patients

Treat it as sustained hypertension. Out-of-office targets are 24-hour mean under 130/80 mm Hg and home mean under 130/80 mm Hg.

• Lifestyle. Sodium under 2 g daily (salt under 5 g), weight loss, exercise 150 minutes weekly, limited alcohol, smoking cessation and reduced caffeine.
• Drug therapy. Use long acting once daily drugs that cover 24 hours.
  • Ramipril 2.5 mg orally once daily, increased every 2 to 4 weeks to 10 mg once daily (maximum 10 mg daily, and 5 mg daily at creatinine clearance under 30 mL/min). Check potassium and creatinine 1 to 2 weeks after each change. Contraindicated in pregnancy and bilateral renal artery stenosis. Preferred with albuminuria or diabetes.
  • Amlodipine 5 mg orally once daily, increased to 10 mg (maximum 10 mg daily; start 2.5 mg in older adults and liver impairment).
  • Chlortalidone 12.5 mg orally once daily, increased to 25 mg (maximum 50 mg daily), with sodium, potassium and creatinine at 2 weeks and 3 months.
• Treated patients. Switch short acting drugs to long acting ones and add a second or third drug as needed. Evening dosing gives no consistent outcome advantage, so use it only when night time or early morning pressure remains high.
• Remove contributors. Stop anti-inflammatory drugs and stimulants. Treat sleep apnoea with continuous positive airway pressure.
• Cardiovascular risk. Statin by risk (atorvastatin 20 to 40 mg orally once daily, with liver enzymes at baseline and 3 months). Aspirin only for established vascular disease.

Special groups.

• Diabetes and chronic kidney disease: target under 130/80 mm Hg, with an ACE inhibitor or angiotensin receptor blocker when albuminuria is present.
• Pregnancy: stop ramipril and statins, and use labetalol, modified release nifedipine or methyldopa.
• Region: where ambulatory monitoring is limited, use validated home monitoring.

Monitoring. Ambulatory or home monitoring 4 to 8 weeks after each treatment change, then every 3 to 6 months and yearly once stable. Potassium and creatinine 1 to 2 weeks after each change of ramipril and at 2 weeks and 3 months after starting chlortalidone. Left ventricular mass and albuminuria yearly.

Referral and escalation. Refer to a hypertension specialist for resistant, secondary or organ damaging disease. Urgent for hypertensive emergency.