Stress Cardiac Magnetic Resonance in Patients With Prior Percutaneous Coronary Intervention: A Gatekeeper Before Repeating Invasive Angiography

Nearly 1 million percutaneous coronary revascularization (PCI) procedures are annually performed for coronary artery disease (CAD) in the United States. Patients with prior PCI experience elevated long-term cardiovascular risk including a cardiovascular mortality rate that approaches 4% at 5 years.¹ High rates of major adverse cardiovascular events (MACEs) have systematically been shown to drive excessive testing and unnecessary downstream coronary angiographies in those patients. In the 250 350-patient National Cardiovascular Data Registry Medicare claims review, almost 60% of the cohort were subject to a pattern of routine surveillance stress testing or even repeat invasive angiography, far exceeding patient rates of new or worsening ischemic symptoms.² A 2014 meta-analysis in 12 874 patients post-PCI demonstrated that an abnormal stress echocardiography or stress SPECT were associated with a 2-fold higher risk for nonfatal myocardial infarction or cardiovascular death.³ However, 68% of patients were asymptomatic and only 1 out of 30 of those tested underwent repeat revascularization within 90 days, raising questions regarding the appropriateness of stress testing. Such observations suggest that a significant portion of post-PCI care continues to adhere poorly to current guidelines and Appropriate Use Criteria, with frequent use of routine surveillance testing on asymptomatic patients.⁴

In this issue of Circulation: Cardiovascular Imaging, Pezel et al⁵ provide insights into stress perfusion cardiac magnetic resonance (CMR) as a robust risk stratification tool in patients with a history of PCI. The authors included 1624 consecutive patients with prior PCI referred for stress CMR and followed for MACE—defined by cardiovascular death or nonfatal myocardial infarction—over a median of 6.7 years. The main observations were that (1) CMR-assessed inducible ischemia and late gadolinium enhancement were independent predictors of MACE and cardiovascular mortality and (2) the addition of inducible ischemia provided incremental predictive value for the prediction of MACE and cardiovascular mortality, after adjustment for established cardiovascular risk factors. Specifically, among the 54% of patients with new symptoms of angina or dyspnea, presence of ischemia portended to a 6-fold increased risk of MACE. The authors concluded that stress perfusion CMR has excellent long-term prognostic value for the occurrence of MACE in symptomatic patients following PCI.

As a modality, stress CMR has unique attributes to diagnosing the cause of chest pain and risk stratifying patients with prior PCI. It is extensively validated in its characterization of the spectrum and extent of myocardial changes because of CAD and the corresponding inferred patient risk. Furthermore, it has advantages over anatomic assessment in patients with prior CAD or elevated baseline cardiovascular risk. While easy to perform, assessment of the coronary arteries by coronary computed tomography angiography becomes significantly more complex in post-PCI patients due to artifacts related to a higher proportion of coronary calcifications, presence of coronary stents, and a higher prevalence of intermediate coronary stenoses. In the observational STRATEGY trial (Stress Cardiac Magnetic Resonance Versus Coronary Computed Tomography Angiography for the Management of Symptomatic Revascularized Patients) evaluating 600 symptomatic patients with prior revascularization undergoing coronary computed tomography angiography versus stress CMR, stress CMR led to lower use of both invasive and noninvasive downstream cardiac testing, lower cumulative medical costs, as well as lower rates of MACE at 2 years of follow-up.⁶

In patients with CAD, stress CMR has shown high concordance with invasive fractional flow reserve in characterizing physiological significance of coronary stenoses.⁷ In patients with typical angina and intermediate-to-high pretest likelihood of CAD, the recent randomized MR-INFORM trial (Stress Cardiac Magnetic Resonance Perfusion Imaging to Guide Management of Patients With Stable Coronary Artery Disease) comparing stress CMR to invasive angiography and fractional flow reserve to guide patient management, demonstrated a lower rate of revascularization with stress CMR and similar rates of MACE.⁸ In addition, there is extensive evidence that stress CMR effectively diagnoses and prognosticates patients with low-to-intermediate cardiovascular risk and chest pain syndromes.^9–11 The study by Pezel et al clearly adds to the current body of evidence supporting that stress CMR has consistent and strong prognostic value for risk stratification of patients presenting with a broad risk-spectrum of chest pain syndromes.^8–11

Several findings are noteworthy in this noninvasive assessment of patients with a prior PCI. Fifty-four percent of the cohort had symptoms of angina or dyspnea. In the remaining 46%, stress CMR was ordered as asymptomatic control following PCI (35%) or inconclusive stress testing or CTA (estimated 11%, symptomatology unclear). While presence of ischemia by CMR demonstrated a 6-fold increased risk of MACE among symptomatic patients, it did not demonstrate any significant association with cardiac events among the asymptomatic subgroup. According to current Appropriate Use Criteria, noninvasive stress tests in asymptomatic patients with known CAD are rarely appropriate during a period of 2 years after PCI.⁴ While asymptomatic patients in Pezel et al may not all fit in that category given that CMR was performed at a median 3.2 years after PCI, the clinical indication for this subgroup to undergo noninvasive stress testing is uncertain in the era of conservative management using optimized medical therapy. The pattern of routine referral for noninvasive surveillance in patients with prior PCI or history of CAD, unfortunately remains common across all imaging modalities and keeps contributing to unnecessary invasive investigations and health care costs.

In the current era of stable CAD management where first-line optimized medical therapy should be paramount, invasive angiography should be considered in case of specific strong evidence in favor of cardiovascular risk-reduction or symptomatic improvement from invasive revascularization.^12,13 Stress CMR has demonstrated in randomized trials an ability to safely guide optimized medical therapy and effectively reduce referrals to invasive angiography.^8,11 However, like any other imaging technology, stress CMR is as good a tool as the indications to using it in the first place. Beyond the efforts in Appropriate Use Criteria and CAD guidelines, more work in educating referral clinicians is still warranted to align patients’ symptoms and their investigative approaches.