Among patients with resistant hypertension (RH) – defined as the failure to control blood pressure (BP) despite optimal treatment with at least 3 antihypertensive drugs in full dosages – controversy exists regarding the additive prognostic value of ambulatory blood pressure monitoring (ABPM) over clinic blood pressure readings (CBPR).  The prevalence of RH ranges from 10% to 30% of hypertensive subjects however these patients remain generally understudied.

In order to explore whether ABPM provided a better estimate of cardiovascular risk above and beyond that achieved with CBPR and other traditional risk factors, Salles and co-workers prospectively studied 556 patients with RH.  At baseline all patients underwent ABPM and CBPR and clinical outcome was recorded over a median follow up period of 4.8 years.   The authors found that unlike CBPR, which failed to demonstrate any prognostic importance, ABPM provided significant prognostic information for all 3 end points studied; (i) fatal and non-fatal cardiovascular events (reached in 109 patients), (ii) all cause mortality (70 patients), (iii) cardiovascular death (46 patients).

Ambulatory systolic and diastolic BP were equivalent predictors of risk; hazard ratios associated with 1 standard deviation (SD) for daytime and nighttime systolic BP respectively were 1.26 (95% CI 1.04-1.53) and 1.38 (1.13-1.68), and for diastolic BP, 1.31 (1.05-1.63) and 1.36 (1.10-1.69). However, elevation of BP at night was observed to be a stronger risk marker than daytime BP with a 1 SD increase in night-time systolic BP (22mmHg) and in diastolic BP (14mmHg) corresponding respectively with a 38% and a 36% higher risk of future cardiovascular events.  Furthermore, ABPM diagnosis of true RH was an independent predictor of cardiovascular events, with a fully adjusted hazards ratio of 2.11, which was not altered by the presence or absence of left ventricular hypertrophy demonstrated on echocardiography

Although BP measurements repeated during the follow up period were not analysed as part of this study, and therefore response to therapy cannot be commented on, the present work reinforces the prognostic importance of ABPM over CBPR, and highlights the potential usefulness of nighttime measurements in the risk stratification of patients with RH.

• Salles GF, Cardoso CRL, Muxfeldt ES.  Prognostic Influence of Office and Ambulatory Blood Pressures in Resistant Hypertension.  Arch Intern Med 2008;168(21):2340-2346