To the Editor.—I read with considerable interest the article "Salvage of the Ischemic Lower Extremity in Patients With Poor Runoff" (Arch Surg 109:784, 1974), as well as the editorial comment by Mannick (Arch Surg 109:786, 1974). A critical point in both presentations was the status of the "runoff." The qualitative evaluation of the runoff was based on angiographic observations, yet the details of how the angiograms were performed were omitted.
Angiographic data may be either positive or negative. Positive observations are judgments based on the appearance of an opacified artery, ie, the presence, number, site, and length of obstructions, as well as their degree and whether atheromas are ulcerated and so forth. Negative observations are based on the failure to fill certain vessels or segments of vessels. From such negative observations one may infer that vessels are obstructed. The confidence with which one can make such an inference is