INTRODUCTION — Ambulatory blood pressure monitoring (ABPM) is being increasingly recommended for routine clinical practice. It may be particularly useful in evaluating the patient with variable blood pressure readings in the office, or the patient with wide discrepancies between the blood pressure readings at home and the clinician’s office (i.e., “white coat” hypertension).
MEASUREMENT OF ABPM — ABPM is determined using a device worn by the patient that takes blood pressure (BP) measurements over a 24 to 48 hour period, usually every 15 to 20 minutes during the daytime and every 30 to 60 minutes during sleep. These blood pressures are recorded on the device, and the average day (diurnal) or night (nocturnal) blood pressures are determined from the data by a computer.
INTERPRETATION OF ABPM —
● 24-hour average BP − Normotension is defined as a BP less than 130/80 mmHg, and hypertension is defined as a BP greater than or equal to 135/85 mmHg.
● Daytime (awake) BP − Normotension is defined as a BP less than 135/85 mmHg, and hypertension is defined as a BP greater than or equal to 140/90 mmHg.
● Night-time (asleep) BP − Normotension is defined as a BP less than 120/70 mmHg, and hypertension is defined as a BP greater than or equal to 125/75 mmHg.
Masked hypertension — As many as 10 to 40 percent of patients who are normotensive by conventional clinic measurement are hypertensive by ABPM. This phenomenon is called masked hypertension or isolated ambulatory hypertension. It has only been identified by screening clinical studies, since patients who are normotensive by office readings do not typically undergo ambulatory monitoring. Masked hypertension has been associated with an increased long-term risk of sustained hypertension and cardiovascular morbidity. Because of the risk associated with masked hypertension, ambulatory blood pressure monitoring should be considered in patients referred for possible hypertension (for a variety of reasons, such as left ventricular hypertrophy) despite repeatedly normal BP when measured in the clinic.
Nocturnal blood pressure and nondippers
The average nocturnal BP is approximately 15 percent lower than daytime values in both normals and hypertensive patients . Failure of the BP to fall by at least 10 percent during sleep is called nondipping. Independent of the degree of hypertension, nondipping is a risk factor for the development of left ventricular hypertrophy (LVH), heart failure and other cardiovascular complications.
INDICATIONS FOR ABPM — In accordance with published practice guidelines and expert panel recommendations, ambulatory monitoring should be considered in the following circumstances:
● Suspected white coat hypertension
● Suspected episodic hypertension (eg, pheochromocytoma)
● Hypertension resistant to increasing medications
● Hypotensive symptoms while taking antihypertensive medications
● Autonomic dysfunction
There are a number of other potential indications advocated by some, which include:
● To establish nondipper status or nocturnal hypertension
● Large variations in self-measured blood pressure values
● To evaluate whether antihypertensive therapy is moderating the early morning blood pressure surge
● Elevated office blood pressure in pregnant women, with preeclampsia suspected