The 31P-NMR stress test: an approach for detecting myocardial ischemia.

31P-NMR spectroscopy has the potential to assess myocardial damage directly and noninvasively by ascertaining the relative abundances of phosphorus-containing compounds relevant to metabolism under stress conditions. Decrease in the PCr/ATP ratio during exercise is an indicator of the level of stress to which the myocardium is subject. This ratio will remain constant under mild to moderate exercise conditions in a healthy subject, but may show a precipitous decrease even under mild exercise when regions of the myocardium are ischemic. The studies examined here indicate that cardiac patients with some forms of ischemia showed a PCr/ATP ratio decrease even under light exercise, while no decrease was observed in patients whose heart disease was known to be nonischemic. Hypertension and nonstenotic chest pain in women can, in some cases, produce a decrease in PCr/ATP ratio. Only the hypertensive patients showed a significant difference in the prestress PCr/ATP ratio when compared with controls. These studies suggest that 31P-NMR spectroscopy before and during mild exercise in the bore of the magnet can be a useful indicator of the presence or absence of an ischemic component to myocardial disorder.