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Stress Cardiac MRI Effective in Known, Suspected Stable CAD
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The use of stress cardiac MRI in patients with known or suspected stable CAD effectively reclassified risk for cardiac death and non-fatal MI beyond clinical covariates, according to study results.
“Cardiac MRI improved risk reclassification in the majority of patients at intermediate-to-high pre-test risk, regardless of status of prior CAD, across American College of Cardiology/American Heart Association practice guideline recommended strata that guide current clinical management decisions,” the researchers wrote.
The study, which was published recently in Circulation, included a cohort of consecutive patients referred for evaluation of myocardial ischemia. Researchers determined net reclassification improvement (NRI) of the primary outcome of MACE, a composite of cardiac death and nonfatal MI; this was incremental to clinical risk models, using guideline-based low (<1%), moderate (1%-3%) and high (>3%) annual risk categories.
Researchers reported that inducible ischemia had a significant association with MACE (HR=14.66; P<.0001), and low event rates of MACE (0.6%) and cardiac death (0.4%). This prognostic utility was observed in patients with prior CAD (HR=8.17; P<.0001).
The addition of inducible ischemia to the multivariable clinical risk model enhanced discrimination of MACE (C-statistic 0.81-0.86, P=.04; adjusted HR=7.37, P<.0001). The addition also reclassified 91.5% of patients at moderate pre-test risk (65.7% moderate-to-low risk; 25.8% to high risk) with corresponding changes in the observed event rates of 0.3% per year for low-risk post-test and 4.9% per year for high-risk post-test.
Additional data indicated a categorical NRI of 0.229 (95% CI 0.063-0.391) and a continuous NRI of 1.11 (95% CI 0.81-1.39).
Disclosure: Shah reports no relevant financial disclosures.
Perspective
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William E. Boden, MD
One of the most challenging diagnostic difficulties clinicians face is quantifying the level of ischemic risk in patients with CAD. The majority of guideline-directed risk stratification tools utilize clinical risk models, where the majority of such patients fall into an intermediate-risk profile. This study by Shah and colleagues showed that stress cardiac MRI provided incremental cardiac risk re-classification in patients with known or suspected CAD, in particular by improving discrimination of MACE in patients with moderate pre-test risk. In their study, Shah and colleagues showed that stress cardiac MRI permitted re-classification in 92% of patients who were deemed intermediate-risk by clinical classification alone, with approximately two-thirds being reclassified as low-risk (with corresponding low MACE rates), while one-quarter were reclassified as high-risk (with corresponding high event rates). Since observational data strongly support the extent and severity of inducible ischemia as an important predictor of worse clinical outcomes, the incremental benefit of stress cardiac MRI to identify severe ischemic risk may help guide clinician decision-making as to which patients may benefit most from revascularization. Whether a cardiac MRI-guided strategy of revascularization for high-risk inducible ischemia can reduce clinical events as compared with optimal medical therapy requires further prospective study.
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