In vivo critical fibrous cap thickness for rupture-prone coronary plaques assessed by optical coherence tomography

The widely accepted threshold of <65 μm for coronary plaque fibrous cap thickness was derived from postmortem studies of ruptured plaques and may not be appropriate for in vivo rupture-prone plaques. We investigated the relationship between fibrous cap thickness and plaque rupture using optical coherence tomography (OCT).

We studied 266 lesions (103 from patients with acute coronary syndrome and 163 from patients with stable angina) before percutaneous coronary intervention using OCT. Ruptured and non-ruptured lipid-rich plaques were identified and the thinnest and most representative fibrous cap thickness were determined. Cap thickness was reliably measured in 71 ruptured and 111 non-ruptured plaques. From the ruptured plaques, the median thinnest cap thickness was 54 μm (50-60). The median most representative cap thickness was 116 μm (103-136). For non-ruptured plaques, the median thinnest cap thickness was 80 μm (67-104) and 182 μm (156-216) for most representative cap thickness. In 95% of ruptured plaques, the thinnest cap thickness and most representative cap thickness were <80 and <188 μm, respectively. The best cut-offs for predicting rupture were <67 μm (OR: 16.1, CI: 7.5-34.4, P < 0.001) for the thinnest cap thickness and <151 μm (OR: 35.6, CI: 15.0-84.3, P < 0.001) for most representative cap thickness. These two measures were modestly correlated (r(2) = 0.39) and both independently associated with rupture.

In vivo critical cap thicknesses were <80 μm for the thinnest and <188 μm for most representative fibrous cap thickness. Prospective imaging studies are required to establish the significance of these values.