Ambulatory vs. clinic blood pressure better predicts CV, all-cause death
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Key takeaways:
- Ambulatory BP is more informative about all-cause and CV death compared with conventional clinic BP.
- Nighttime ambulatory systolic BP was six times more effective for predicting death vs. clinic systolic BP.
Blood pressure measures obtained through ambulatory monitoring were more informative about risk for all-cause death or cardiovascular death than conventional clinic blood pressure readings, researchers reported.
The analysis of data from nearly 60,000 patients in the primary care setting, published in The Lancet, is the largest single population-based study assessing the relationship between clinic and ambulatory BP with death, Bryan Williams, MD, FMedSci, chair of medicine at University College London, specialist in hypertension at University College London Hospitals and president of the International Society of Hypertension, told Healio. The data, the researchers wrote, “unequivocally demonstrates the dominance of ambulatory BP over clinic BP in the association between BP and all-cause death and cardiovascular death, whether treated for hypertension or not.”
“Ambulatory systolic BP is much more informative than clinic blood BP measurements with regard to the risk for death, either from CVD or all causes of death,” Williams told Healio. “The strength of the relationship between BP and risk for death was strongest for nighttime systolic BP.”
Clinic vs. 24-hour BP
In an observational study, Williams and colleagues analyzed data clinic and ambulatory BP data for 59,124 patients from March 2004 to December 2014, from the Spanish Ambulatory Blood Pressure Registry. The registry included patients from 223 primary care centers from the Spanish National Health System. Researchers followed patients through 2019, or date of death, assessed via the Spanish National Institute of Statistics. Researchers estimated associations between usual clinic or ambulatory BP and mortality, adjusted for confounders and additionally for alternative BP measures. For each measure of BP, researchers stratified patients by quintiles among those who subsequently died.
During a median follow-up of 9.7 years, 12.1% of patients died, including 4% from CV causes.
Researchers observed J-shaped associations for several BP measures. Among the top four baseline-defined fifths, 24-hour systolic BP was more strongly associated with all-cause death, with an HR of 1.41 per 1 standard deviation (SD) increment (95% CI, 1.36-1.47) than clinic systolic BP, which had an HR of 1.18 per 1 SD increment (95% CI, 1.13-1.23).
After adjustment for clinic BP, 24-hour BP remained strongly associated with all-cause death (HR = 1.43; 95% CI, 1.37-1.49); however, the association between clinic BP and all-cause death was attenuated after adjustment for 24-hour BP.
Compared with clinic systolic BP (100%), nighttime systolic BP was most informative about risk for all-cause death (591%) and CV death (604%).
Researchers found elevated all-cause mortality risks for patients with masked hypertension (HR = 1.24; 95% CI, 1.12-1.37) and sustained hypertension (HR = 1.24; 95% CI, 1.15-1.32), but not for white coat hypertension, compared with patients with normal BP. Similarly, researchers observed higher CV mortality risk for those with masked hypertension (HR = 1.37; 95% CI, 1.15-1.63) and sustained hypertension (HR = 1.38; 95% CI, 1.22-1.55) but not white coat hypertension.
Importance of nighttime BP
“Importantly, once 24-hour blood pressure was known, most of the informativeness of clinic systolic blood pressure was lost, whereas associations for ambulatory blood pressure measures were largely unaffected by adjustment for clinic systolic blood pressure,” the researchers wrote. “The relative informativeness of 24-hour ambulatory systolic blood pressure for risk of death was almost five times greater than clinic systolic blood pressure. Furthermore, with respect to ambulatory blood pressure measures, nighttime systolic blood pressure was about six times more informative for death than clinic systolic BP and nearly twice as informative as daytime systolic blood pressure.”
Williams said the findings demonstrate that clinicians must consider ambulatory BP monitoring to confirm a diagnosis of hypertension by excluding white coat hypertension, which was not associated with increased risk for death and does not need drug treatment.
“The importance of night-time BP suggests we need to ensure we have control of BP over the whole 24 hours, especially in higher-risk patients,” Williams told Healio. “If ambulatory BP measurement is not available, home BP is a useful alternative to evaluate BP and exclude white coat hypertension.
“Although ambulatory BP measurement is a stronger predictor of risk, it will be important in the future to determine whether treatment guided by ambulatory BP improves outcomes relative to treatment guided by conventional clinic BP,” Williams told Healio. “We also need to better understand the importance of the striking findings of the link between nighttime BP and risk for death, with regard to whether this association is causal and what the implications might be for treatment.”
For more information:
Bryan Williams, MD, FMedSci, can be reached at bryan.williams@ucl.ac.uk.
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