Masked hypertension poses hidden hazard

Patients with "masked" hypertension that is not detected by routine office blood pressure measurements appear to have stroke and death rates similar to that of patients with sustained high blood pressure; whereas patients with so-called "white coat" hypertension appear to have no greater risk than people with normal blood pressure, according to a new study in the Aug. 2, 2005, issue of the Journal of the American College of Cardiology.

"It is important for physicians and other health practitioners to recognize at least the possibility that conventional blood pressure measurements could miss masked hypertension. Otherwise, they may not suspect masked hypertension if a patient develops organ damage or cardiovascular diseases in spite of good control of blood pressure and other risk factors according to measurements taken in the office. If these patients are not identified and do not receive appropriate treatment, they could develop further organ damage or cardiovascular problems," said Takayoshi Ohkubo, M.D., Ph.D., at Tohoku University Hospital in Sendai, Japan.

Almost one out of five participants in this study had masked hypertension; that is, their blood pressure appeared to be normal according to conventional measurements in a clinic, but it was high when measured by a device that was worn by the participant over a 24-hour period.

"White coat" hypertension means that a person’s blood pressure appears high when it is measured during a clinic visit (typically by a physician or nurse in a white coat), but the pressure is lower when measured by the patient outside of the clinic.

This is the first prospective study to reveal the risks associated with masked hypertension and "white coat" hypertension in a representative sample of a general population. The 1,332 participants (872 women and 460 men at least 40 years old) lived in Ohasama, Iwate Prefecture, Japan. In addition to obtaining "casual" blood pressure measurements in typical clinical settings, the study subjects wore ambulatory blood pressure monitors that automatically recorded data over a 24 hour period. Deaths and strokes were tracked for an average of 10 years after the initial blood pressure measurements.

Participants with normal blood pressure (as measured in the clinic and with ambulatory monitoring) or "white coat" hypertension (meaning their clinic measurements were high, but the ambulatory monitor readings were normal) had similar outcomes. However, the risks of stroke or death were significantly higher for both patients with sustained hypertension (elevated both in the clinic and on ambulatory readings) and those with masked hypertension (normal in clinic measurements, but elevated according to ambulatory monitoring).

"Masked hypertension has a poor prognosis, and it may not be identified by conventional blood pressure measurement. The use of ambulatory blood pressure monitoring can identify masked hypertension," Dr. Ohkubo said. "Masked hypertension is a similarly risky condition to sustained hypertension."

Dr. Ohkubo said that ideally every adult should be screened with an ambulatory blood pressure monitor at least once. If universal screening with 24-hour ambulatory monitoring is difficult, he recommended screening individuals who have an elevated risk of cardiovascular disease. Home blood pressure monitors could also be used to help identify patients, he said.

Based on the results of this long-running study, Dr. Ohkubo said individuals with masked hypertension should be treated the same as patients with sustained hypertension. He said individuals with "white coat" hypertension might need blood pressure treatment only if other factors put them at high risk for cardiovascular disease, but he added that they would need to be carefully followed with ambulatory or home blood pressure measurements, since their very long-term prognosis has not been clarified.

The researchers said that randomized, controlled trials and studies of other populations are needed to fully understand the risks and appropriate treatments of masked and "white coat" hypertension.

Franz H. Messerli, M.D., F.A.C.C., at St. Luke’s Roosevelt Hospital Center and Columbia University in New York, who wrote an editorial with Delia Cotiga, M.D., said the results of this study suggest that physicians can be conservative in managing patients with "white coat" hypertension, since it does not appear to greatly elevate the risk of cardiovascular events.

"On the other hand, masked hypertension is a more serious issue. Patients with masked hypertension, as shown in this article, do not have such a good prognosis. They suffer almost as many strokes and heart attacks as patients with untreated hypertension. Therefore, it is extremely important that we do think of masked hypertension and in appropriate situations do a 24-hour ambulatory monitoring in order to find out whether the patient does have masked hypertension," Dr. Messerli said.

Dr. Messerli said masked hypertension should be considered whenever a physician notices abnormalities in heart structure or other organs, such as the kidneys and the brain, that are typically associated with high blood pressure, even if routine blood pressure readings appear normal.

Dr. Robert J. Adolph, M.D., F.A.C.C., at the University of Cincinnati in Ohio, who was not connected with this study, said the results suggest that ambulatory blood pressure measurements may be the only way to identify masked or "white coat" hypertension with certainty.

"It was a very well done study. They followed the participants for a long time, and it was a good cross section of the population," Dr. Adolph said.

He added that he would like to see the results replicated in other populations.

Gianfranco Parati, M.D., at the University of Milano-Bicocca in Milan, Italy, who also was not connected with this study, said the main message is that blood pressure readings taken outside clinical settings have important health implications.

"The problem is now how often should we obtain out of office blood pressure measurements when stratifying the cardiovascular risk of our patients?" Dr. Parati said. "Moreover, the results of this interesting study might need to be confirmed by further investigations, based on a more appropriate approach to compare the value of clinic and ambulatory blood pressures. This is because in this study "casual" blood pressure was based on two measurements taken during one visit only. In addition, casual and ambulatory blood pressures were measured by different techniques (auscultatory or oscillometric). Finally, blood pressure was measured only at the beginning of follow-up. Thus further evidence on this issue is still needed, based on trials comparing ambulatory blood pressure-based management of hypertension with the management based on repeated clinic readings (both obtained by the same technique of measurement), in relation to the risk of cardiovascular events. And, at any rate, this data should not be taken as to disregard office blood pressure readings."

The American College of Cardiology, a 33,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.