Although intravascular ultrasound (IVUS) can detect plaque rupture, the fibrous cap remnant has not previously been studied in detail. The aim of the present study is to assess the fibrous cap remnants by IVUS in ruptured plaques.

In 53 patients, a ruptured plaque with a fibrous cap remnant was studied by IVUS.

In 36 (68%) patients, the rupture of the fibrous cap appeared to have occurred at the shoulder. The absolute length of the fibrous cap remnant was significantly longer in the center rupture site compared with the shoulder rupture site (1.37 ± 0.56 vs 0.84 ± 0.34 mm, P = .001); however, the estimated length of the original fibrous cap did not differ between the 2 rupture site groups (2.28 ± 0.66 vs 2.11 ± 0.69, P = not significant). In none of the patients did the remnants of the fibrous cap cover the entire mouth of the cavity. The estimated absolute length of the missing part of the fibrous cap correlated significantly with the cavity area (r = 0.517, P < .001), the lesion external elastic membrane area (r = 0.330, P = .016), the lumen area (r = 0.289, P = .036), the maximum plaque thickness (r = 0.364, P = .007), and the length of the estimated original fibrous cap (r = 0.709, P < .001).

In general, the postrupture fibrous cap does not cover the entire mouth of the ruptured plaque cavity in its postrupture state. Potential explanations include the following: (1) part of the fibrous cap may be too thin to be visualized with IVUS, (2) part of it may have embolized, or (3) the prerupture fibrous cap may have been stretched and/or there were postrupture changes in lesion geometry.