A CAC score of zero rules out significant left main stenosis, AHJ study.

While there is an ongoing debate about medical vs. invasive management of stable coronary artery disease (CAD) patients, especially after publication of ISCHEMIA results, it is notable that patients with significant left main disease were excluded from this trial as guidelines continue to advocate an aggressive invasive approach in such patients.

This calls for a simple and effective screening strategy for identifying left main disease and in this regard, Money et al have recently shown that an easily administered, inexpensive, low radiation coronary artery calcium score (CACS) of zero can identify a large subset of patients with a very low risk of left main coronary stenosis (LMCS). Their findings were recently published in American Heart Journal.

Several recent trials have evaluated invasive versus medical therapy for stable ischemic heart disease. Importantly, patients with significant left main coronary stenosis (LMCS) were excluded from these trials. In the ISCHEMIA trial, these patients were identified by a coronary CT angiogram (CCTA), which adds time, expense, and contrast exposure.

In clinical practice, using CCTA to exclude significant LMCS adds complexity and potential harms, including time delays, expense, and contrast exposure. Alternatively, coronary artery calcium scanning (CACS) is an imaging modality that requires less radiation, no intravenous contrast, and costs much less than CCTA.

The absence of coronary artery calcium (ie, CACS = 0) has been associated with an excellent 5-year prognosis. Using CACS as opposed to CCTA to exclude significant LMCS would be desirable in risk-stratifying patients with stable ischemic heart disease.

The overall aim of this study was to determine if a left main CACS = 0 could reliably exclude patients with significant LMCS, thereby allowing clinicians to safely proceed with intensive medical therapy alone in patients with stable ischemic heart disease.

The authors hypothesized that patients with ≥50% LMCS would have a LM CACS score > 0. As a corollary, they postulated that a LM CACS = 0 would exclude patients with LMCS. To test this, they searched Intermountain Healthcare's electronic medical records database for all adult patients who had undergone non-contrast cardiac CT for quantitative CACS scoring prior to invasive coronary angiography (ICA). Patients 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 ICA findings, respectively.

Among 669 candidate patients with CACS followed by ICA, 36 qualifying patients were identified who had a quantitative CACS score and LMCS ≥ 50%.

Authors found that found that no patients with LMCS ≥ 50% had a LM CACS score of 0. In contrast, 57% of those without LMCS did.

These findings support the proposal that an easily administered, low cost, and low radiation CACS can identify a large subset of stable ischemic heart disease patients (ie, 57%) with a very low risk of LMCS, who potentially would not need CCTA as a screening test prior to triaging them to an initial intensive medical treatment regimen. CCTA then can be reserved for the minority of those with LM CAC > 0 (ie, 43%), in whom the absence of significant LMCS requires quantitative assessment.

If validated, these findings could provide a simplified approach to applying the ISCHEMIA trial algorithm in clinical practice. Excluding LMCS is essential to the safety and applicability of an initial medical treatment approach in patients with stable ischemic heart disease who are shown to have moderate-severe ischemia on stress testing.

This simplified screening approach could allow for the safe and more cost-effective implementation of an intensive medical therapy treatment strategy in ISCHEMIA trial-like patients.

Source: American Heart Journal: https://doi.org/10.1016/j.ahj.2021.05.013