Mechanical and structural characteristics of vulnerable plaques: analysis by coronary angioscopy and intravascular ultrasound.

OBJECTIVES Mechanical and structural characteristics of vulnerable plaques were evaluated using coronary angioscopy and intravascular ultrasound. BACKGROUND Mechanical stress and composition of plaques play an important role in plaque disruption. METHODS Thirty-eight lesions in 38 patients were examined pre-interventionally. The plaques were classified as either yellow or white using coronary angioscopy. Intravascular ultrasound imaging was performed simultaneously with electrocardiographic and intracoronary pressure recordings to calculate distensibility index and stiffness beta. Moreover, the type of remodeling was classified. RESULTS We identified 27 patients with yellow plaques and 11 patients with white plaques. Patients with yellow plaques presented acute coronary syndromes more frequently than stable angina (85% vs. 36%, p < 0.01). The distensibility index in yellow plaques was significantly greater than it was in white plaques (2.7 +/- 0.8 mm Hg(-1) vs. 0.7 +/- 0.8 mm Hg(-1), p < 0.0001), while stiffness beta for white plaques was significantly greater than it was for yellow plaques (34.9 +/- 16.3 vs. 8.7 +/- 2.7, p < 0.0001). Compensatory enlargement occurred more frequently with yellow plaques than with white plaques (56% vs. 9%, p < 0.01), while paradoxical shrinkage occurred more frequently with white plaques than it did with yellow plaques (64% vs. 4%, p < 0.001). CONCLUSIONS Yellow plaques with an increased distensibility and a compensatory enlargement may be mechanically and structurally weak. As a result, mechanical "fatigue," caused by repetitive stretching, may lead to plaque disruption. Plaques with a high distensibility and a compensatory enlargement may be vulnerable.