AMBULATORY blood pressure monitoring (ABPM) is a non-invasive method of obtaining blood pressure readings over a 24-hour period, whilst the patient is in their own environment, representing a true reflection of their blood pressure.

Many studies have now confirmed that blood pressure measured over a 24-hour period is superior to clinic blood pressure in predicting future cardiovascular events and target organ damage.

WHAT DOES ABPM INVOLVE?

Blood pressure is measured over a 24-hour period, using auscultatory or oscillometry devices, and requires the use of a cuff. The monitor takes blood pressure every 20-30 minutes (less frequently overnight eg, one per hour). The patient is able to go about their normal day and have their blood pressure checked throughout the day.

WHAT ARE THE USES OF ABPM?

1. To obtain a 24-hour record: More reliable than one-off measurements. Studies have shown that increased blood pressure readings on ABPM are more strongly correlated to end-organ damage than one-off measurements, for example with increased thickness of the heart muscle.

2. To detect white coat hypertension: For those patients whose blood pressure seem to be high only when they visit the doctor’s office.

3. It has use in hypertension research: For example reviewing 24-hour profile of antihypertensive medication.

4. It may have prognostic use: Higher readings on ABPM are associated with increased mortality.

5. Response to blood pressure treatment.

6. Masked hypertension: Those patients who truly are hypertensive but have normal readings when they attend the doctor’s office.

7. Autonomic dysfunction

8. Hypotensive symptoms whilst on antihypertensive medications, such as light-headedness, near fainting or dizziness.

9. It may be more cost-effective in the long term than office blood pressure measurement.

WHY MAY YOUR DOCTOR REFER YOU FOR ABPM?

• The National Institute for Health and Care Excellence (NICE) in the United Kingdom (UK) recommends that if a clinic blood pressure is 140/90 mm Hg or higher, ABPM should be offered to confirm the diagnosis of hypertension. If a person is unable to tolerate ABPM, home blood pressure monitoring (HBPM) is a suitable alternative to confirm the diagnosis of hypertension.

We don’t currently have Jamaican guidelines for the use of ABPM, but we use international guidelines.

• Poorly controlled hypertension, for example suspected drug resistance.

• Patients who have developed target organ damage despite control of blood pressure.

• Patients who develop hypertension during pregnancy.

• High-risk patients, for example those with diabetes mellitus, those with cerebrovascular disease, and kidney transplant recipients.

• Suspicion of white coat hypertension: High blood pressure readings in clinic, which are normal at home.

• Suspicion of reversed white coat hypertension, that is blood pressure readings are normal in clinic but raised in the patient’s own environment.

•Postural hypotension.

•Elderly patients with systolic hypertension.

UPPER LIMIT OF NORMAL ABPM VALUES

Normal ambulatory blood pressure during the day is <135/<85 mm Hg and <120/<70 mm Hg at night. Levels above 140/90 mm Hg during the day and 125/75 mm Hg at night should be considered as abnormal.

DOWNSIDE TO ABPM

• It is not universally available although this is improving.

• It requires specialist training.

• Some patients find inflation of the cuff unbearable.

• Sleep disturbance.

• Bruising where the cuff is located.

• Background noise may lead to interference (less with oscillometric methods).

• Poor technique and arrhythmias may cause poor readings.

HOW ARE THE RESULTS OF ABPM PROVIDED?

• This varies according to the machines used.

• Usually, they have individual systolic and diastolic pressures. These may also be represented in a graphic form.

• Blood pressure load: The percentage or proportion of readings that are higher than a predetermined level in 24 hours.

• NICE recommends ensuring that at least two measurements per hour are taken during the person’s usual waking hours (for example, between 08:00 and 22:00 hours). Use the average value of at least 14 measurements taken during the person’s usual waking hours to confirm a diagnosis of hypertension.

Dr Claudine Lewis is an adult cardiologist and medical director at Heart Smart Centre in Montego Bay. She is also a cardiologist at the Cornwall Regional Hospital and an associate lecturer with the University of the West Indies. Questions may be sent to questions@heartsmartcentre.com and for additional information call 684-9989 or visit the website www.heartsmartcentre.com