Nighttime Hypertension—Not Daytime or Clinic—Predicts MI and Stroke in Meta-Analysis

May 19, 2014

NEW YORK CITY, NY — A large analysis of more than 13 000 patients reveals that blood pressure measured in the clinic had no association with the risk of cardiovascular outcomes, including stroke[1]. In contrast, nighttime blood pressure was associated with a risk of adverse clinical outcomes.

For every 10-mm-Hg increase in nighttime systolic blood pressure, the risk of cardiovascular outcomes was increased 25%, report investigators.

Speaking with heartwire at the American Society of Hypertension 2014 Annual Scientific Meeting , lead investigator Dr George Roush (St Vincent's Medical Center, Bridgeport, CT) said that despite being able to measure daytime and nighttime blood pressure with 24-hour ambulatory blood-pressure monitoring (ABPM) for more than 30 years, as well routinely taking clinic measurements, it is still not known what reading is best for predicting clinical outcomes.

"There has been some suggestion that nighttime blood pressure is the most predictive of cardiovascular events and maybe the best target for antihypertensive therapy," he said.

Nighttime Hypertension at the Risk of MI and Stroke

The analysis included nine cohorts from Europe, Brazil, and Japan that had received 24-hour ABPM. With these data, the researchers were able to identify patient-specific information on nighttime and daytime blood-pressure levels among the 13 843 patients included in the meta-analysis. Patients were followed for a minimum of one year, and clinic blood-pressure measurements were also available for all patients.

"It's actually one of the largest assemblages of patients receiving ambulatory blood-pressure monitoring with cardiovascular events as the outcome," said Roush. "So we were able to address the issue of sample size." Previous studies looking at the effects of nighttime vs daytime vs clinic blood pressures on clinical outcomes has been limited by small patient numbers. "Also, to really make the decision about which measure is best, you need to put all three measures in the same statistical model."

Individually, each 10-mm-Hg increase in blood pressure assessed during nighttime, daytime, and clinic was associated with a 25%, 20%, and 11% increased risk of MI and stroke, respectively. However, after adjustment for multiple confounding variables, including age, gender, diabetes, smoking status, and drug treatment, among others, only the nighttime measurement of blood pressure was predictive of MI and stroke.

"When you put all three measurements in the same model, nighttime persists at the same level of prediction, but day and clinic are totally useless," said Roush. "Every practical clinical decision we make is based on clinic blood pressure, yet it's the least predictive of all three."

In a related study, Dr Pauli Niiranen (National Institute for Health and Welfare, Turku, Finland) presented data from 464 patients who underwent ABPM between 1992 and 1996 and were followed for 16 years. The primary end point of the analysis was a composite of cardiovascular events, including cardiovascular mortality, nonfatal MI, nonfatal stroke, hospitalization for heart failure, and coronary revascularization[2].

Like the study by Roush and colleagues, the Finnish researchers reported that each 1-mm-Hg increase in systolic blood pressure assessed in the clinic, at home, and with ABPM was associated with a significantly increased risk of cardiovascular events. However, when the investigators included all three measurements into the model simultaneously, only increases in blood pressure assessed with ABPM were predictive of clinical events. With ABPM, each 1-mm-Hg increase in systolic blood pressure was associated with a 3.3% increased risk of cardiovascular events.

Future Research

To heartwire , Roush said that European and Japanese physicians frequently take advantage of 24-hour ABPM more than in the US. At present, there are ongoing clinical trials testing whether treating nighttime blood pressure reduces cardiovascular events when compared with treating daytime or clinic blood pressure, but as yet the answer to that question is unknown.

Also, Roush said it is not yet known why nighttime blood pressure is more predictive of clinical outcomes compared with the other two measurements.

"One of the possibilities is that nighttime hypertension is a marker for something else," said Roush. "For example, usually the blood pressure drops because the sympathetic tone declines at night. But we know that too much sympathetic tone increases stroke and heart-attack risks. So maybe elevated nighttime blood pressure is just a marker for elevated sympathetic tone? Another possibility is that when the vessels dilate at night and patients maintain high blood pressure in the face of dilated nighttime arterioles, it could be they are exposing their brain and heart to an increased blood-pressure load. These are just some of things that might be going on."


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.