These authors, funded by government, foundations, and industry, linked data from the Spanish Ambulatory Blood Pressure Registry to the national vital statistics databases. The registry included 59,124 adults who met guideline-recommended indications for ambulatory blood pressure monitoring, which included suspected white-coat hypertension, refractory or resistant hypertension, assessment of drug treatment efficacy, high-risk hypertension, labile or borderline hypertension, and the study of circadian blood pressure patterns. Clinic blood pressures were based on the average of 2 readings recorded after 5 minutes of rest. The 24-hour ambulatory monitors measured blood pressure every 20 minutes during the day and every 30 minutes at night, and the researchers calculated the average for all valid readings.
The registry participants were, on average, 58.7 years of age, with a mean clinic blood pressure of 148/86.5 and a mean ambulatory blood pressure of 128.8/76.2. Slightly more than half (53%) were male. Over a median 9.7 years of follow-up, 7174 (12.1%) of the participants died; 2361 (4.0%) of those deaths were attributed to cardiovascular causes. Clinic and ambulatory pressures were only modestly correlated (0.43 and 0.52 for systolic pressure and diastolic pressure, respectively). After adjusting for many factors associated with mortality (age, sex, smoking status, body mass index, diabetes status, dyslipidemia, previous cardiovascular disease, and number of antihypertensive drugs), the authors report that clinic systolic pressure was modestly associated with all-cause mortality (hazard ratio [HR] 1.08) and cardiovascular mortality (HR 1.11), while the associations with all-cause mortality and cardiovascular mortality were greater for ambulatory systolic pressure (HRs 1.30 and 1.41, respectively), daytime systolic pressure (HRs 1.25 and 1.35), and nocturnal systolic pressure (HRs 1.36 and 1.46).