Task Force II: Blood pressure measurement and cardiovacular outcome

Abstract

OBJECTIVE: To reach a consensus on the prognostic significance of new techniques of automated blood pressure measurement. METHODS: A Task Force on the prognostic significance of ambulatory blood pressure monitoring wrote this review in preparation for the Eighth International Consensus Conference (28-31 October 2001, Sendai, Japan). This synopsis was amended to account for opinions aired at the conference and to reflect the common ground reached in the discussions. POINTS OF CONSENSUS: (1) Prospective studies in treated and untreated hypertensive patients and in the general population have demonstrated that, even after adjusting for established risk factors, the incidence of cardiovascular events is correlated with blood pressure on conventional as well as ambulatory measurement. Ambulatory monitoring, however, significantly refines the prediction already provided by conventional blood pressure measurement. (2) White-coat hypertension is usually defined as an elevated clinic blood pressure in the presence of a normal daytime ambulatory blood pressure. Event-based studies in hypertensive patients have convincingly demonstrated that the risk of cardiovascular disease is less in patients with white-coat hypertension than in those with higher ambulatory blood pressure levels even after controlling for concomitant risk factors. Based on prognostic evidence, white-coat hypertension can now be defined as a conventional blood pressure that is persistently equal to or greater than 140/90 mmHg with an average daytime ambulatory blood pressure of below 135/85 mmHg. The issue of whether or not white-coat hypertension predisposes to sustained hypertension needs further research. (3) There is a growing body of evidence showing that a decreased nocturnal fall in blood pressure (<10% of the daytime level) is associated with a worse prognosis, irrespective of whether night-time dipping is studied as a continuous or a class variable. (4) Intermittent techniques of ambulatory blood pressure monitoring are limited in terms of quantifying short-term blood pressure variability. Proven cardiovascular risk factors such as old age, a higher than usual blood pressure and diabetes mellitus are often associated with greater short-term blood pressure variability. After adjusting for these risk factors, some - but not all - studies have nevertheless reported an independent and positive relationship between cardiovascular outcome and measures of variability of daytime and night-time blood pressure, for example standard deviation. (5) Reference values for ambulatory blood pressure measurement in children are currently based on statistical parameters of blood pressure distribution. In children and adolescents, functional rather than distribution-based definitions of ambulatory hypertension have yet to be developed. (6) Several studies of gestational hypertension have shown that, compared with office measurement, ambulatory blood pressure monitoring is a better predictor of maternal and fetal complications. Pregnancy is a special indication for ambulatory monitoring so that the white-coat effect can be measured and pregnant women are not given antihypertensive drugs unnecessarily. (7) Ambulatory pulse pressure and the QKD interval are measurements obtained by ambulatory monitoring that to some extent reflect the functional characteristics of the large arteries. The QKD interval is correlated with left ventricular mass, and ambulatory pulse pressure is a strong predictor of cardiovascular outcome. (8) Under standardized conditions, the self-measurement of blood pressure is equally as effective as ambulatory blood pressure monitoring in identifying the white-coat effect, but further studies are required to elucidate fully the prognostic accuracy of self-measured blood pressure in comparison with conventional and ambulatory blood pressure measurement. CONCLUSIONS: Ambulatory blood pressure measurement refines the prognostic information provided by conventional blood pressure readings obtained in the clinic or the doctor's office. Longitudinal studies of patients with white-coat hypertension should clarify the transient, persistent or progressive nature of this condition, particularly in paediatric patients, in whom white-coat hypertension may be a harbinger of sustained hypertension and target-organ damage in adulthood. Finally, the applicability, cost-effectiveness and long-term prognostic accuracy of the self-measurement of blood pressure should be evaluated in relation to conventional blood pressure measurement and ambulatory monitoring.