High Blood Pressure Can Mask Dangerous Chest Pain

MONTREAL, July 11 -- Patients with high blood pressure may be at risk for silent ischemia because they have a decreased perception of the pain that would otherwise signal heart disease, researchers here said.

In a prospective study of 907 men and women suspected of having myocardial ischemia, those with high blood pressure tended to have significantly lower pain scores during exercise (P=0.003) than those with normal pressure, according to Bianca D'Antono, Ph.D., of the Montreal Heart Institute, and colleagues.

The relationship was present whether or not imaging showed an actual deficit in perfusion, the researchers reported in the July issue of Psychophysiology.

Previous studies - using experimental models of pain - have suggested that people with high blood pressure feel less discomfort, but this is one of the first to look at pain in a more natural setting, the researchers said.

From 2000 through 2003, men and women referred to the Montreal Heart Institute for diagnosis of possible myocardial ischemia were asked to take part in the study, which measured their pain both at rest and during exercise stress testing.

Patients' cardiac perfusion was measured using single positron emission tomography (SPECT) at baseline, at rest, and after a stress test. The participants also filled out the short form of the McGill Pain Questionnaire on the rest day and after exercise.

The exercise test itself was conducted on a treadmill using the Bruce protocol and was stopped when a patient reported considerable pain, was out of breath, showed anomalies on an electrocardiogram, or reached 90% of the maximal heart rate expected for the patient's age.

The cohort was divided in two on the basis of median post-exercise systolic blood pressure, with the cut-off for high blood pressure being 170 millimeters of mercury.

In a general linear model of total score on the pain questionnaire, ischemia, post-exercise systolic blood pressure, and exercise duration were significant predictors of pain.

Specifically:

• Patients who had ischemia, as determined by SPECT, felt significantly more pain during exercise, at P=0.025.
• Patients who exercised longer had significantly less pain, at P<0.001.
• Patients with high post-exercise systolic blood pressure had significantly less pain, at P=0.003, regardless of whether they had a perfusion deficit or EEG anomalies.

The patients also evaluated their pain as being more or less widespread. Analysis of those evaluations showed that exercise duration was significantly associated (at P<0.001) with the perception of widespread pain, but blood pressure was not, the researchers said.

They noted that the inverse relationship between blood pressure and pain remained significant after adjustment for a range of possible confounding variables.

The researchers also evaluated exertional chest pain during daily living, using the Canadian Cardiovascular Society grading scale. Again, higher blood pressure was significantly associated at P=0.001 with lower angina, they found.

The latter findings are important, the researchers concluded, because "the clinical problems associated with silent ischemia, such as failure to take medication or seek medical care, are related to the experience of angina in the daily life rather than in the hospital."