Case against routine use of glyceryl trinitrate before coronary angiography.

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Abstract
Changes in coronary artery tone are often neglected in the angiographic assessment of patients with chest pain. To determine the contributions of dynamic coronary artery diameter changes to the degree of coronary narrowing, 47 consecutive chest pain patients were studied without premedication by analyzing selective coronary angiograms before and after glyceryl trinitrate. Proximal coronary diameters were measured in superimposed frames with callipers. Lumen diameter increased after glyceryl trinitrate 15 .+-. 2% in the left main, 18 .+-. 2% in the left anterior descending, 16 .+-. 2% in the circumflex and 17 .+-. 2% in the right coronary arteries (all P < 0.01). Coronary artery narrowings (119) of < 90% were measured (narrowings > 90% were excluded because of measurement inaccuracy) . Of 81 narrowings < 50%, 24 became .gtoreq. 50% because of dilatation of the adjacent region. The diameter of the narrowed segment also changed significantly after glyceryl trinitrate, increasing in 28 and decreasing in 3. Of the 28 obstructions which dilated after glyceryl trinitrate, 4 were clinical and angiographic examples of coronary arterial spasm. In 4 other coronary arteries with only outline irregularities before glyceryl trinitrate a localized narrowing (25-50%) was seen after glyceryl trinitrate as the proximal artery dilated. The routine use of glyceryl trinitrate before coronary angiography alters the measured degree of coronary artery narrowing and obscures the angiographic interpretation.