Cross sectional coronary artery stenosis

Abstract

Significant obstructive lesions must be demonstrated in the coronary arterial circulation before bypass surgery can be recommended as an effective therapeutic alternative. Nearly total occlusion of an artery is obviously of greater importance than minimal narrowing caused by an eccentrically placed, isolated mural plaque. Not as clear, however, is the significance of a 40% as compared with a 70% narrowing in a coronary artery, especially when the vessel is photographed over the vertebral column or diaphragm on a gray overpenetrated film recorded o n a 9" image screen. Under these conditions any debate concerning the obstructive characteristics of a given lesion would be valueless. But, given a first-quality angiogram obtained with a very small focal spot and high-resolution cesium iodide 6" image intensifier, a discussion of whether the 40% lesion is obstructive would probably be concerned with whether it was the only vessel obstructed or the only remaining vessel patent, whether that obstruction occurred at the bifurcation of the artery or in a relatively smooth part of the vessel, and of the greatest importance, whether or not the obstruction could be demonstrated in more than one projection. In short, the ultimate purpose of coronary arteriography is to accurately estimate crosssectional patency of the coronary arterial tree (1).At least four methods are currently available for use in estimating coronary occlusive disease. 1. Scanning densitometry and computerized curve fitting (2) relies on elaborate and relatively expensive equipment, but it is unsatisfactory for analysis of significant atherosclerotic lesions. 2. Analysis of coronary arterial disease by digital computer processing (3) requires that the angiographer prepare an elaborate schematic diagram of the coronary tree. The method is time-consuming and impractical for routine use. 3. Quantitative coronary arteriography using a three-dimensional computerized approach (4) requires approximately 20 min to evaluate each individual lesion. This technique is chiefly a research tool that is not yet applicable for clinical use. 4. Visual estimation of the degree of coronary obstruction is the simplest arid most popular method currently in use. The multiple limitations of this approach are generally well known. First, intra-and inter-reader variability is quite high. In certain instances estimates of a single vessel lesion have varied by as much as +36% (5,6). Second, since single-projection estimates are commonly used, eccentric narrowing may be interpreted with an error of nearly +300%.The cross-sectional narrowing of an obstructive lesion is the single most important consideration in the evaluation of any coronary hydrodynamic problem (7). This does not detract from the importance of other determinants of flow, such as perfusion pressure, length of lesion, shape of lesion, or blood viscosity, among