1351623 - Final CMR Diagnosis and Associations with Future Major Adverse Cardiovascular Events in Patients Referred for Acute Myocarditis: Findings from the CIROC Registry

Acute myocarditis (AM) is suspected across a range of clinical presentations, inclusive of unexplained chest pain syndromes or new-onset heart failure. Need to guide care in this population supports the established diagnostic role of cardiac magnetic resonance (CMR) to differentiate etiology of disease. However, the prevalence of establishing a final CMR-based diagnosis and the respective prognostic implications of such diagnoses in this population are poorly explored. Using a large cohort of referral-coded patients from the Cardiovascular Imaging Registry of Calgary (CIROC) we examined the distribution and prognostic relevance of final CMR-based diagnoses among patients referred for clinically suspected AM.

Methods:

A total 1096 patients referred for suspected acute myocarditis were identified from the CIROC Registry. Referral indications were adjudicated by review of clinical history to identify patients with high clinical suspicion of AM by objective criteria. Baseline health questionnaires, laboratory, pharmacy, and administrative health data were provided by Registry-supported resources. CMR was performed using standardized protocols at 3T with image analysis and interpretation conducted by standardized operational procedures. Final CMR-based diagnoses were adjudicated by two individuals by consensus opinion, coded as: AM, Acute Myocardial Infarction (AMI), Dilated Cardiomyopathy (DCM), or No Identifiable Cause (NIC). All Registry patients were followed for clinical outcomes from date of CMR. The composite MACE outcome of all-cause mortality, survived cardiac arrest, ventricular tachycardia or fibrillation, hospital admission for heart failure, cardiac transplant, or LVAD implantation was chosen. Multivariable modelling was performed to assess for independent associations of each final CMR-based diagnosis with the occurrence of MACE.

Results:

Of 1096 patients with suspected acute myocarditis 416 (38%) met updated Lake Louise Criteria for AM, 174 (16%) had AMI, 215 (20%) had DCM (with no evidence of AM), and 291 (27%) had NIC. Of AMI patients, 26 had findings of prior (healed) myocarditis. Respective baseline demographics, health profiles and cardiac MRI phenotypes are provided in Table 1. Over a median follow-up of 1159 days, patients who received an AM diagnosis showed similar cumulative event rates to NIC (8% vs 7%; HR 1.05 p=0.86). In contrast, event rates for DCM (26%) and AMI (16%) were 4.3 and 2.3-fold higher, respectively, for MACE versus NIC. The Kaplan-Meier curve is shown in Figure 1. The association for DCM was maintained following adjustment for baseline clinical characteristics (Table 2).

Conclusion:

In patients referred to CMR for suspected AM, a final clinical diagnosis was established in 73%. Of these, AM was dominant and, with contemporary medical management, was not associated with higher MACE versus those with no identifiable diagnosis. However, patients provided a CMR diagnosis of DCM or AMI show significantly higher MACE.