Abstract 13551: Identifying Left Main Coronary Artery Disease Using Coronary Artery Calcium Scans

Abstract

Introduction: The ISCHEMIA trial tested an invasive vs. an initial medical strategy in patients (pts) with stable coronary disease and evidence of ischemia. No significant difference between strategies in cardiovascular events was found at 3.2 years. However, pts were screened before randomization by coronary CT angiography (CCTA) to exclude ≥50% left main coronary stenosis (LMCS). CCTA adds complexity to routine medical practice, including time delays, expense, and safety concerns. We tested whether a coronary artery calcium scan (CACS), a simpler, less expensive test, could replace CCTA to exclude significant LMCS. Methods: We hypothesized that pts with ≥50% LMCS would have a LM CACS score>0. As a corollary, we postulated that a LM CACS=0 would exclude pts with LMCS. To test this, we searched Intermountain Healthcare’s electronic medical records database for all adult pts who had undergone non-contrast cardiac CT for quantitative CACS scoring prior to selective coronary angiography (SCA) and were found to have a LMCS ≥50%. Pts aged <50 and those with a heart transplant were excluded. Cases with incomplete (qualitative) angiographic reports for LMCS and those with incomplete or discrepant LM CACS results were reviewed and reassessed blinded to CACS or SCA findings, respectively. Results: Among 674 candidate pts with CACS followed by SCA, 24 qualifying pts were identified who had a quantitative CACS score and LMCS ≥50%. Their age averaged 71 ± 11 years, and 83% were men. Angiographic LMCS averaged 77% (range 50%-99%). A heavy burden of both total CAC and LM CAC was typically present. Total CACS score averaged 2,545 Agatston Units (AU), range 571-6,636. LM CACS score averaged 214 AU, range 47-610. Importantly, no LMCS pt had a LM CACS score of 0 vs. 57% (368/650) of non-LMCS controls (p<0.00001). Conclusions: Our results support the hypothesis that an easily administered, inexpensive, low radiation CACS can identify a large subset of pts with a very low risk of LMCS without the need for routine CCTA. Using CACS to exclude LMCS may efficiently allow for safe implementation of an initial medical therapy strategy in clinical practice for ISCHEMIA trial-like pts with at least moderate ischemia on stress testing. These promising results deserve validation in larger data sets.