Clinic vs. Ambulatory Blood Pressure Measurements and Mortality
Is there a difference between the associations of blood pressure (BP) measured in the clinic (clinic BP) and 24-hour ambulatory blood pressure (ABP) with all-cause and cardiovascular (CV) mortality in patients in primary care?
The authors analyzed data from a registry-based, multicenter, national cohort that included 63,910 adults recruited from 2004-2014 in Spain. Clinic BP and 24-hour ABP were examined in the following categories: sustained hypertension (elevated clinic and elevated 24-hour ABP) “white-coat” hypertension (elevated clinic and normal 24-hour ABP), masked hypertension (normal clinic and elevated 24-hour ABP), and normotension (normal clinic and normal 24-hour ABP). Analyses were conducted with Cox regression models, adjusted for clinic and 24-hour ABP and for confounders.
58% were male, and mean age was 57 years in those alive and 67 years in those who died during a median follow-up of 4.7 years. Mean clinic BP was 149/87 mm Hg, mean daytime 24-hour ABP was 132/80 mm Hg, and mean 24-hour ABP was 129/77 mm Hg. The hypertension phenotypes were: normotension 6.6%, white-coat hypertension 27.7%, masked hypertension 8.4%, and sustained hypertension 46.8%. A total of 3,808 patients died from any cause, and 1,295 of these patients died from CV causes. In a model that included both 24-hour and clinic measurements, 24-hour systolic BP was more strongly associated with all-cause mortality (hazard ratio [HR], 1.58 per 1-standard deviation [SD] increase in pressure; 95% confidence interval [CI], 1.56-1.60, after adjustment for clinic BP) than the clinic systolic BP (HR, 1.02; 95% CI, 1.00-1.04, after adjustment for 24-hour systolic ABP). Corresponding HRs per 1-SD increase in pressure were 1.55 (95% CI, 1.53-1.57, after adjustment for clinic and daytime BPs) for nighttime ambulatory systolic BP and 1.54 (95% CI, 1.52-1.56, after adjustment for clinic and nighttime BPs) for daytime ambulatory systolic pressure. These relationships were consistent across subgroups of age, sex, and status with respect to obesity, diabetes, CV disease, and antihypertensive treatment. Masked hypertension was more strongly associated with all-cause mortality (HR, 2.83; 95% CI, 2.12-3.79) than sustained hypertension (HR, 1.80; 95% CI, 1.41-2.31) or white-coat hypertension (HR, 1.79; 95% CI, 1.38-2.32). Results for CV mortality were similar to those for all-cause mortality.
Ambulatory BP measurements were a stronger predictor of all-cause and CV mortality than clinic BP measurements. White-coat hypertension was not benign, and masked hypertension was associated with a greater risk of death than sustained hypertension.
Many experts recommend that all patients with hypertension or suspected to have hypertension by office BP have baseline 24-hour ABP monitoring. The recommendation is based on relatively small population-based studies. This study, conducted using data from the Spanish Ambulatory BP Registry in a large cohort of patients in primary care practice, validates that recommendation, and will play a major role in future guidelines. It is unique in regards to the size of the cohort, the duration of follow-up, the standardized clinic BP measurements, and the primary care setting. Note the >15 mm Hg higher clinic BP compared to the daytime ambulatory systolic BP. Most important is the unique finding that masked hypertension is associated with greater mortality than sustained hypertension, as is masked uncontrolled treated hypertension.
Keywords: Ambulatory Care Facilities, Blood Pressure, Blood Pressure Monitoring, Ambulatory, Diabetes Mellitus, Hypertension, Masked Hypertension, Metabolic Syndrome X, Obesity, Primary Health Care, Primary Prevention, Systole, White Coat Hypertension
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