2024 ACC Strategies and Criteria for Diagnosis and Management of Myocarditis

 

Top 10 Key Takeaway Points

1.	Clinicians need to be aware of the 3 classic presentations of myocarditis: chest pain, heart failure (HF)/shock, and/or symptoms related to arrhythmia (eg, presyncope or syncope). In a young person, the history of an antecedent viral infection, or other risk factors that define stage A at-risk for myocarditis, followed by any of these cardiovascular symptoms should raise the suspicion of this diagnosis.
2.	High-sensitivity cardiac troponin (hs-cTn) is a common diagnostic test in patients with suspected myocarditis; however, some patients with myocarditis will not have an elevated hs-cTn. Further research is needed to determine whether a normal level below the limits of detection of current fifth-generation assays can serve as an effective rule-out strategy for this diagnosis, and the prognostic utility of serial measurements.
3.	Cardiac magnetic resonance (CMR) imaging and endomyocardial biopsy (EMB) are considered pivotal tests in the diagnosis of myocarditis. The former often allows the noninvasive diagnosis of stage B or symptomatic myocarditis. When CMR is performed, the diagnosis of myocarditis is based on detection of abnormalities in both T1 and T2 imaging; however, in patients with certain presentations—typically those with reduced ventricular function, deranged hemodynamics/symptomatic HF, or electrical instability—an EMB is warranted to diagnose specific conditions that require etiology-directed therapies, including immunosuppressive agents.
4.	A novel 4-stage classification of myocarditis is proposed. Stage A refers to those having or exposed to risk factors; stage B to those asymptomatic but with evidence of myocardial inflammation; stage C to those with symptomatic myocarditis; and stage D to those with advanced myocarditis (hemodynamic or electrical instability requiring intervention).
5.	Research is needed to define the trajectories of the 4 stages of myocarditis, including their risk of progression to chronic HF. Other key unanswered questions include the rate of progression from stage A to higher stages; how commonly stage B myocarditis occurs either during the development or resolution of myocarditis; what explains the variable rates of progression and improvement among patients; and when does stage D become irreversible?
6.	Risk stratification in patients with symptomatic myocarditis guides the decision whether to refer to an advanced HF center with a multidisciplinary myocarditis team. There should be a low threshold to transfer patients with high-risk features, such as severely reduced ventricular function, symptomatic HF, hemodynamic instability, or electrical instability (either ventricular arrhythmias or heart block).
7.	The follow-up of patients with myocarditis does not end after 2 to 3 weeks, even with resolution of symptoms. Two cardiac imaging studies are advised during follow-up. At an early interval after diagnosis (eg, 2-4 weeks), a repeat echocardiogram allows detection of new or progressive deterioration of left ventricular function suggestive of a diagnosis of giant cell myocarditis (GCM). A second follow-up imaging study, either a repeat echocardiogram (low-risk stage C myocarditis) or a CMR (if > low-risk stage C myocarditis or if stage D myocarditis), is advised at 6 months. Advocacy for insurance coverage of these tests is needed.
8.	Given the increasing recognition of genetic predisposition to myocarditis, genetic counseling and testing is advised for all consenting patients. Discovery of a pathogenic variant should be followed by cascade screening of family members, thereby affording undiagnosed relatives the opportunity for clinical surveillance and, when appropriate, guideline-directed management and therapy.
9.	Safety for return to strenuous physical activity is guided by a follow-up CMR, 24-hour monitoring for arrhythmia, and exercise testing, typically at 6 months after diagnosis. In some athletes, these assessments can be made as early as 3 months after the initial episode of myocarditis for consideration of return to competitive sports.
10.	Further research on a wide range of factors is needed. These include how social determinants of health impact the development and progression of myocarditis; a need for international registries with diverse stakeholder involvement; improved phenotyping by novel biomarkers, imaging strategies, and refined pathological interpretation of EMB specimens, including the role of viral polymerase chain reaction (PCR) testing; the benefits of immunosuppression in lymphocytic myocarditis assessed in large prospective randomized clinical trials; whether unloading of the left ventricle for those on extracorporeal membrane oxygenation (ECMO) improves outcomes; and a greater understanding of the psychological burden on patients and caregivers following an episode of myocarditis. https://www.jacc.org/doi/10.1016/j.jacc.2024.10.080