Abstract 19940: Peak Plaque Stress Varies Among Thin Cap Fibroatheromas as Estimated by Finite Element Analysis: Not all TCFAs are High Risk
Introduction: Thin cap fibroatheroma (TCFA) is a vulnerable plaque phenotype containing confluent necrotic core and is associated with sudden cardiac death and MI. In autopsy studies, 50% of TCFA do not rupture. Coronary plaque is increasingly unstable when plaque stress exceeds 300 kPa. We studied the variation in peak plaque stress as a function of fibrous cap (FC) and necrotic core (NC) thickness and NC angle using finite element analysis in a sample of TCFA.
Methods: 1898 IVUS Virtual Histology frames from 303 patients were reviewed; 8 representative TCFA frames were selected. Plain strain finite element models of concentric plaque with NC, defined by FC and NC thickness and NC angle were developed to estimate peak plaque stress. Plaque and media were both modeled as linear elastic and transversely isotropic solids (plaque: Er = 115.6 kPa, Eθ = Ez = 2312 kPa, vrθ = vrz = 0.07, vθz = 0.27 and Grθ = 1175 kPa; media: Er = 10 kPa, Eθ = Ez = 100 kPa, vrθ = vrz = 0.01, vθz = 0.27 and Grθ = 52) defined by the geometry: 2 mm lumen diameter, 4 mm vessel diameter and 250 μm media thickness. NC was modeled as a soft and virtually incompressible linear elastic isotropic solid (E = 1 kPa and v = 0.49) with size systematically varied from 50–400 μm at angles of 10° to 360°. Fibrous cap thickness was varied from 25–200 μm.
Results: 432 TCFA model simulations were performed. Principal factors driving TCFA peak stress beyond a threshold of 300 kPa were FC thickness <50 μm, NC thickness >250 μm, and NC angle >30°. TCFA peak stress was inversely proportional to FC thickness, directly proportional to NC thickness and NC angle and maximized at 30° NC angle. Variation in TCFA peak stress with FC and NC thickness for a 30° NC angle is shown in the figure, with the boxed region representing high risk.
Conclusion: TCFA with FC thickness >50 μm, NC thickness <250 μm and NC angle <30° may be of lower risk, suggesting that not all TCFA lesions are vulnerable.
- © 2010 by American Heart Association, Inc.