EFFECTS OF CYCLIC FLEXION OF CORONARY-ARTERIES ON PROGRESSION OF ATHEROSCLEROSIS

The purpose of this investigation was to test the hypothesis that cycl ic flexion of the coronary arteries contributes to the progression of atherosclerotic plaques. Coronary arteriograms were evaluated in 33 un selected patients who underwent 2 studies over a period of 25 +/- 16 m onths (mean +/- SD). Among the 33 patients, 103 plaques were identifie d. Plaques that showed progression were compared with plaques that sho wed no progression. The angle of flexion that occurred during systole at the site of the plaque was measured on the first arteriogram. In co mparing progression versus no progression, the interval between arteri ograms was 29 +/- 18 versus 23 +/- 14 months (p = NS) and percent sten osis at the first arteriogram was 42 +/- 28 versus 45 +/- 19% (p = NS) . Percent stenosis at the time of the second arteriogram among plaques that progressed was 78 +/- 21%, and by definition, it remained 45 a 1 9% among those that did not progress. Among arteries with plaques that showed a progression of stenosis, the angle of flexion during systole was 19 +/- 13 degrees versus 9 +/- 15 degrees among arteries with pla ques that did not progress (p <0.01). Linear regression showed that th e correlation of the angle of flexion with percent change of stenosis was relatively low (r = 0.32) but statistically significant (p <0.005) . Mathematic modeling of flexible and stiff plaques showed stresses ap proximately 1.5 to 1.9 times greater with 20 degrees than with 10 degr ees flexion. Stresses due to flexion were usually greatest proximal an d distal to the plaque along the subendothelial layer of the inner wal l of the curved vessel. Data show that the angle of cyclic flexion, an d consequently the stresses due to cyclic flexion of the artery were g reatest in the region of plaques that progressed over the period of ob servation. Such stresses may have contributed to tissue damage or fati gue resulting in a more rapid progression of the atheromatous plaques.