A Pathologist’s view of quantitative coronary arteriography

Summary

The arteriographic lumen outline has major drawbacks in assessing wall disease. Atherosclerotic vessels dilate in a remodelling response to preserve lumen dimensions; only when the capacity of this response is overcome does stenosis occur. In diffuse atherosclerosis the media remodels to allow an overall increase in the external diameter of the vessel often with an increase in lumen diameter above normal at that site. Localised plaques are associated with atrophy of the subjacent media and rupture of the internal elastic lamina allowing the plaque to bulge outward into the adventitia. Vessels which appear angiographically normal or slightly irregular may therefore contain large plaques. Arteries which have been distended during fixation show that normal segments have a round lumen; at sites of eccentric stenosis the residual segment of normal vessel wall has a round profile while the more rigid plaque is straighter giving a D shape to the lumen.

The implications of these facts for methods of quantification which compare the lumen diameter at a point of stenosis with an adjacent normal reference segment are:

• 1. The lumen shape at eccentric stenosis is not round and will alter both in shape, and size, with variation of tone within the normal residual wall segment.

• 2. The reference segment, taken as normal, may either be narrowed or dilated.

The progression of coronary atherosclerosis is dependent, in part, on episodes of thrombosis the majority of which are clinically silent. Unless major intraluminal thrombosis has occurred, angiography may be relatively insensitive at detecting these unstable plaques The repair response in these plaques involves smooth muscle proliferation to smooth the lumen outline. Angiographic changes due to these repair responses may considerably alter both the test and reference segment in the time interval between two angiograms and may be erroneously regarded as regression of the basic atherosclerotic process.