Continuous Blood Pressure Monitoring, A Predictor of Future Heart Events

In the largest study of its kind to date, researchers have shown that continually monitoring blood pressure (BP) — called ambulatory BP monitoring (ABPM) — is a predictor of future cardiovascular events in patients with resistant hypertension, but office BP is not .

Resistant hypertension is defined as the failure to control office BP despite optimal treatment with at least 3 antihypertensive drugs in full dosages, always including a diuretic. Its prevalence ranges from 10% to almost 30% of patients with general hypertension. ABPM has become increasingly important in the management of patients with hypertension, especially in patients with resistant hypertension to differentiate from white-coat resistant hypertension. Currently, the prognostic value of office and ABPM in patients with resistant hypertension is uncertain.

 

The aim of this study was to evaluate the prognostic importance of ABPM for the future occurrence of fatal and nonfatal cardiovascular events.

Salles et al explain that about 10% to 30% of individuals with high BP have resistant hypertension. In these patients, BP remains high despite treatment with at least three antihypertensive drugs, including a diuretic. ABPM — which measures blood pressure at regular intervals throughout the day — is increasingly important in managing patients with this condition because of the possibility of a white-coat effect, when an individual only has high BP at the physician’s office.

In their prospective study, they followed 556 patients with resistant hypertension who attended an outpatient clinic between 1999 and 2004. Participants underwent a clinical examination and had their blood pressure monitored continuously during a 24-hour period (every 15 minutes throughout the day and every 30 minutes at night). They were followed-up at least three or four times a year until December 2007.

The primary end point was a composite of fatal and nonfatal cardiovascular events and all-cause and cardiovascular mortalities. Multiple Cox regression was used to assess associations between BP and subsequent end points.

After a median follow-up period of 4.8 years, 109 participants (19.6%) had had a cardiovascular event or had died of cardiovascular disease. This included 44 strokes, 21 myocardial infarctions, 10 new cases of heart failure, and five sudden deaths. Seventy patients (12.6%) died, 46 (8.3%) of cardiovascular causes.

After multivariate adjustment, office BP did not predict any of these events, whereas higher mean ambulatory BPs (both systolic and diastolic) were independent predictors of the composite end point.

Ambulatory systolic and diastolic BPs were equivalent predictors and both were better than pulse pressure; nighttime BP was superior to daytime BP.

But ABPM did not predict cardiovascular deaths alone or coronary heart disease (CHD) events, although it did predict some outcomes, such as stroke.

“The relatively few cardiovascular deaths and CHD events probably contributed to the failure to demonstrate the prognostic value of ambulatory BPs for these end points, owing to insufficient statistical power,” the researchers observe.

“This study has important clinical implications,” the authors write. “First, it reinforces the importance of ABPM performance in resistant hypertensive patients . . ., [which] should be performed during the whole 24 hours, with separate analyses of the daytime and nighttime periods, because it seems that nighttime blood pressures are better cardiovascular risk factors than are daytime blood pressures.”

Salles notes: “In this particular subgroup of hypertensives, those with resistant hypertension, the antihypertensive treatment should be based on ambulatory BP levels, with particular attention to nighttime BP, instead of on office BPs.”

The work raises the question of whether therapeutic interventions directed specifically at controlling nighttime hypertension will be able to improve cardiovascular prognosis compared with the traditional approach of controlling daytime blood pressure levels, he adds. “This important clinical question should be addressed in future prospective interventional studies.”
The researchers also point out that a simple ABPM diagnosis of true or “white coat” resistant hypertension at baseline “provides useful independent prognostic information for cardiovascular morbidity and for all-cause mortality.”

Practice Pearls

• Resistant hypertension is defined as the failure to control office BP despite optimal treatment with at least 3 antihypertensive drugs in full dosages, always including a diuretic.
• Higher ABPM predicts cardiovascular morbidity and mortality in patients with resistant hypertension, whereas office BP has no prognostic value.

Salles GF, Cordoso CRL, Muxfeldt ES. Prognostic influences of office and ambulatory blood pressures in resistant hypertension. Arch Intern Med. 2008;168:2340-2346. (University Hospital Clementino Fraga Filho, Rio de Janeiro, Brazil)