new noninvasive test for the cause of chest pain

Jun 25 (HeartCenterOnline) - A new noninvasive test may help physicians diagnose the cause of chest pain in women, according to a new study published in the June 22 issue of Circulation: The Journal of the American Heart Association.
Diagnosing coronary artery disease in women is often difficult because women have smaller, more slender coronary arteries. In almost half the cases, the cause of chest pain in women cannot be determined, even by angiography.

The new test, called phosphorus-31 nuclear magnetic resonance spectroscopy, requires women to simply squeeze a handgrip while lying inside an MRI unit. The unit scans measures the levels of two phosphates found in heart tissue. The two phosphates occur naturally and supply the energy source for the heart. A large drop in the ratio of these phosphates is considered to be a sign that heart tissue is not getting enough oxygen-rich blood.

Coronary artery disease is the biggest killer of both men and women. Although women are about as likely to have a heart attack as men are, they are more likely to die after their first heart attack. Symptoms of a heart attack are often different in women, and about 35 percent of heart attacks in women go unnoticed or unreported to physicians.

The study suggests that the test may be useful to evaluate women with chest pain, particularly if standard tests do not uncover a cause for the recurring pain. However, nuclear magnetic resonance spectroscopy is currently available only at a few institutions and academic medical centers.

http://content.nejm.org/cgi/content/abstract/342/12/829
ABSTRACT

Background After hospitalization for chest pain, women are more likely than men to have normal coronary angiograms. In such women, myocardial ischemia in the absence of clinically significant coronary-artery obstruction has long been suspected. Most methods for the detection of the metabolic effects of myocardial ischemia are highly invasive. Phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy is a noninvasive technique that can directly measure high-energy phosphates in the myocardium and identify metabolic evidence of ischemia.

Methods We enrolled 35 women who were hospitalized for chest pain but who had no angiographically significant coronary-artery obstructions and 12 age- and weight-matched control women with no evidence of heart disease. Myocardial high-energy phosphates were measured with 31P-NMR spectroscopy at 1.5 tesla before, during, and after isometric handgrip exercise at a level that was 30 percent of the maximal voluntary grip strength. We measured the change in the ratio of phosphocreatine to ATP during exercise.

Results Seven (20 percent) of the 35 women with chest pain and no angiographically significant stenosis had decreases in the phosphocreatine:ATP ratio during handgrip that were more than 2 SD below the mean value in the control subjects without chest pain. There were no significant differences between the two groups with respect to hemodynamic variables at rest and during handgrip, risk factors for ischemic heart disease, findings on magnetic resonance imaging and radionuclide perfusion studies of the heart, or changes in brachial flow during the infusion of acetylcholine.

Conclusions Our results provide direct evidence of an abnormal metabolic response to handgrip exercise in at least some women with chest pain consistent with the occurrence of myocardial ischemia but no angiographically significant coronary stenoses.