The relief of chest pain with nitroglycerin has been reported by cardiovascular textbooks as an important diagnostic clue in supporting a myocardial ischemia etiology. Shry and associates used a retrospective record review to evaluate the diagnostic value of responses to nitroglycerin administration in the emergency department.

Patients presenting to the emergency department with ongoing chest pain who were treated with sublingual nitroglycerin and aspirin for 10 minutes and whose response and follow-up data were available were included in the study. Chest pain of cardiac etiology was documented when any of the following criteria were noted: (1) dynamic or new electrocardiographic changes, (2) myocardial necrosis confirmed by elevated cardiac-specific enzyme elevations, (3) abnormal stress test, (4) significantly abnormal cardiac catheterization, and (5) diagnosis of cardiac etiology by a staff cardiologist without meeting any of the prior criteria. Patient chest pain before and after nitroglycerin administration was documented using a numeric pain scale of 1 to 10, with zero representing no pain and 10 denoting maximal pain. Response to nitroglycerin was defined as a decrease in pain by at least two numbers on the scale, and complete pain resolution was defined as the absence of chest pain. Pain response occurring more than 10 minutes after nitroglycerin administration was excluded because previous studies have demonstrated nitroglycerin's rapid clinical effect.

Of the 223 patients (mean age: 60 years) included in the study, 67 percent were identified as having noncardiac chest pain and 33 percent had a cardiac etiology for myocardial ischemia. Ninety percent of the patients responded to nitroglycerin with an 88 percent response rate among those who were identified as having a cardiac etiology and a 92 percent response rate among those identified as not having a cardiac etiology. If complete chest pain resolution was used as the end point, response to nitroglycerin was again high and not significantly different between the two groups.

The authors conclude that patients presenting to the emergency department with chest pain often have partial or complete relief of pain shortly after sublingual nitroglycerin administration, regardless of the etiology of chest pain. Pain relief may be the effect of nitroglycerin on smooth muscle relaxation resulting in improvement in pain of esophageal origin, and a significant placebo effect also may be occurring in this setting. A patient's response to nitroglycerin should not be used to support or exclude the diagnosis of myocardial ischemia.