Washington, November 25 : Blood pressure readings taken in a doctor's clinic may not be helpful in predicting future heart risks, according to a new study.
Appearing in the Archives of Internal Medicine, one of the JAMA/Archives journals, the study suggests that continuously measuring blood pressure may instead help predict heart disease and related deaths among individuals with treatment-resistant hypertension.
Background information in the research article suggests that about 10-30 per cent of patients with high blood pressure have a condition known as resistant hypertension, in which blood pressure remains high despite treatment with at least three antihypertensive drugs, always including a medication that increases urine output.
The authors write that measuring blood pressure at regular intervals throughout the day is increasingly important in managing patients with this condition because of the possibility of a white-coat effect, when an individual only has high blood pressure at the physician's office.
Dr. Gil F. Salles studied 556 patients with resistant hypertension who attended an outpatient clinic between 1999 and 2004.
During the study, the participants underwent a clinical examination and had their blood pressure monitored continuously during a 24-hour period, which was conducted in every 15 minutes throughout the day and every 30 minutes at night. They were followed up at least three to four times a year until December 2007.
The researchers observed after a median follow-up period of 4.8 years that 109 (19.6 percent) of participants had a cardiovascular event or died of cardiovascular disease.
Those cases included 44 strokes, 21 heart attacks, 10 new cases of heart failure, and five sudden deaths. Seventy patients (12.6 percent) died, including 46 (8.3 percent) of cardiovascular causes.
The research team said that blood pressure measured in the office did not predict any of those events, whereas higher average ambulatory blood pressures were associated with the occurrence of fatal and non-fatal heart events.
They revealed that that link remained after controlling for office blood pressure and other risk factors for heart disease.
The researchers also observed that nighttime blood pressure was superior to daytime blood pressure in predicting heart events.
"This study has important clinical implications. First, it reinforces the importance of ambulatory blood pressure monitoring performance in resistant hypertensive patients. Furthermore, ambulatory blood pressure monitoring should be performed during the whole 24 hours, with separate analyses of the daytime and nighttime periods, because it seems that nighttime blood pressures are better cardiovascular risk factors than are daytime blood pressures," the authors write.
"Second, it raises the question of whether therapeutic interventions directed specifically at controlling nighttime hypertension will be able to improve cardiovascular prognosis compared with the traditional approach of controlling daytime blood pressure levels. This important clinical question should be addressed in future prospective interventional studies," they conclude.