Twenty-four-hour ambulatory blood pressure monitoring in the evaluation of antihypertensive drugs: methodological aspects.
Ambulatory blood pressure monitoring (ABPM) provides reproducible measurements over 24 h, avoiding the alerting reaction. However, the reproducibility of mean hourly ambulatory values is poorer by far than the whole day average. In phases II and III clinical triams ABPM seems to evaluate the time-course of the antihypertensive effect and helps to determine the trough: peak ratio. The potential advantage of the method could be an increase in statistical power of the trial, with regard to the number of patients to include, according to the study design. ABPM led to the identification of 'white-coat' hypertension with elevated clinic blood pressure measurements and persistently normal ABPM over time. No epidemiological evidence to include patients in trials according to ABPM criteria has been provided to date, but a subsequent stratification on the initial ABPM data has to be performed. Although an insignificant effect on the 24 h mean blood pressure values in short-term trials, the use of placebo seems to be necessary to supply reference blood pressure values for dosing and trough: peak ratio determination. Whether ABPM is able to decrease the number of patients to include remains debated. It has been noted that an increasing number of readings could lead to a decrease in SD and that a decrease in the number of patients required can be expected both in parallel and in cross-over design trials. However, it has been reported that the advantage of the higher reproducibility of ABPM could be lost in parallel design trials and that analysis of the antihypertensive effect of the drug throughout the 24 h could then require more patients. In order to conduct multicentre trials using ABPM, a consensus among investigators is needed for the presentation and analysis of the results. We have to overcome these difficulties in order to avoid a 'centre effect' and to allow for the expected increase in power of the trial. In such a trial the comparability of parallel groups could be jeopardized by a misadherence to the ABPM protocol. How can ABPM modify the doctor-patient relationship?. A pedagogical approach seems necessary, namely to inform the patients concerning technical and medical prerequisites of the method, in order to conform to the 'guidelines'. ABPM might constitute a new determinant of compliance with treatment; but its influence, beneficial or not, remains to be assessed. Compliance evaluation could be combined with ABPM, in order to provide a better evaluation of the antihypertensive effect of the drugs.
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Service de Médecine Interne et d'Hypertension Artérielle, Toulouse, France.