Evaluation of the extent and duration of the "ABPM effect" in hypertensive patients

OBJECTIVES The goal of this study was to test and quantify the extent and duration over time of a possible pressor effect due to ambulatory monitoring. BACKGROUND The use of ambulatory blood pressure monitoring has provided a method of blood pressure (BP) assessment that compensates for some of the limitations of office values. While a "white-coat" pressor effect on conventional measurements has been defined and frequently used for the improved evaluation of hypertensive patients, there has not been dear indication that the ambulatory technique could also influence BP. METHODS We studied 538 mild-to-moderate hypertensive patients (233 men), 54.2 +/- 14.2 (mean +/- SD) years of age. Blood pressure and heart rate were measured at 20-min intervals during the day and at 30-min intervals at night for 48 consecutive hours, and physical activity was simultaneously evaluated at 1-min intervals with a wrist actigraph. One-third of the patients were evaluated twice or more times. RESULTS In both treated and untreated hypertensive patients evaluated for the first time, results indicate a statistically significant (p < 0.001) reduction during the second day of monitoring as compared with the first in the diurnal mean of systolic and diastolic BP, but not in heart rate or physical activity. This pressor effect remains statistically significant for the first 6 h to 8 h of monitoring independently of gender, days of the week of monitoring or number of antihypertensive drugs used by the treated patients. The nocturnal mean of BP was, however, similar between both days of sampling. This "ambulatory monitoring effect" was not observed when the patients were evaluated after the same sampling scheme for the second or successive times three months apart. CONCLUSIONS Ambulatory monitoring for 48 consecutive hours reveals a statistically significant pressor response that could reflect a novelty effect in the use of the monitoring device for the first time. This effect has marked implications in both research and clinical daily practice for a proper diagnosis of hypertension and evaluation of treatment efficacy by the use of ambulatory monitoring. (C) 2002 by the American College of Cardiology Foundation.