Intravascular Ultrasound Validation of Contemporary Angiographic Scores Evaluating the Severity of Calcification in Peripheral Arteries

Abstract

Purpose: To validate 3 angiographic scoring systems for peripheral artery calcification using intravascular ultrasound (IVUS) as the gold standard. Methods: The study employed preprocedure angiography and IVUS data from 47 patients (median age 72 years; 34 men) in the 55-patient JetStream G3 Calcium Study ( ClinicalTrials.gov identifier NCT01273623) to validate the 3 angiographic scoring systems [Peripheral Academic Research Consortium (PARC), Peripheral Arterial Calcium Scoring System (PACSS), and the DEFINITIVE Ca++ trial]. Preprocedure angiograms were analyzed using conventional quantitative vessel analysis software in 2 orthogonal views. Calcium length was evaluated by markers placed beside the artery during the procedure; calcium deposit(s) were assessed as being on one or both sides of the vessel wall. The 3 calcium scoring systems used these 2 basic angiographic elements to evaluate calcium severity. Based on these criteria, calcium severity varied from none to focal, mild, moderate, or severe in PARC; grade 0 to 4 in PACSS; and none, moderate, or severe in the DEFINITIVE Ca++ system. Calcium location on IVUS was classified as superficial, deep, or mixed. Lesion length was the segment between the most normal looking proximal and distal reference sites. Superficial, deep, and calcium length were based on motorized IVUS pullback. Results: IVUS detected calcium in 44/47 (93.6%) lesions, and angiography detected calcium in 26/47 (55.3%) lesions (p<0.001). The sensitivity, specificity, positive predictive value, and negative predictive value of angiography relative to IVUS were 59%, 100%, 100%, and 14%, respectively. With increasing severity of angiographic calcium, there was a stepwise increase in the prevalence of IVUS superficial calcium and the maximum arc and length of superficial calcium. Using PARC criteria, with increasing severity of calcification, IVUS maximum calcium arc increased from 120° for none to 305° for severe (p<0.001); the length of calcium increased from 7 to 68 mm (p<0.001). Though a similar trend was seen in IVUS superficial calcium, it was not observed in IVUS deep calcium. Similar observations were seen when using the PACSS and DEFINITIVE Ca++ scoring systems. Conclusion: IVUS confirmed that the PARC, PACSS, and DEFINITIVE Ca++ calcium scoring systems can be used to classify the degree of calcium in peripheral artery disease, especially superficial calcium.