New Diagnostic Criteria and 4-Stage Classification for Myocarditis: Key Insights and Future Directions from ACC 2024

The definition, diagnostic approaches, outlook, and understanding of causes for myocarditis have recently progressed. Currently, there is variation in the classification and diagnostic standards for myocarditis; an emerging role of imaging, biomarkers, and genetics in its diagnosis and risk assessment; and advancements in treatment and management strategies for specific causes and severity of myocarditis. As a result, the American College of Cardiology’s (ACC’s) Science and Quality Committee and the Solution Set Oversight Committee recognized myocarditis as a high-priority subject. Following this, the Writing Committee of the 2024 ACC Expert Consensus Decision Pathway (ECDP) on Strategies and Criteria for the Diagnosis and Management of Myocarditis was assembled.

1. Clinicians need to be aware of the 3 classic presentations of myocarditis - chest pain, heart failure/shock, and/or arrhythmia symptoms. In a young person, the history of a recent viral illness or other risk factors for stage A "at-risk" myocarditis, followed by any of these cardiovascular symptoms, should raise suspicion for this diagnosis.

2. High-sensitivity cardiac troponin is a common diagnostic test, but some patients with myocarditis will not have an elevated troponin. Further research is needed to determine whether a normal troponin level can effectively rule out myocarditis.

3. Cardiac magnetic resonance (CMR) imaging and endomyocardial biopsy (EMB) are considered pivotal diagnostic tests. CMR often allows noninvasive diagnosis of stage B or symptomatic myocarditis, while EMB is the gold standard for characterizing the histological type and specific etiology (including viral).

4. A novel 4-stage classification of myocarditis is proposed: Stage A refers to those at-risk; stage B to asymptomatic individuals with evidence of myocardial inflammation; stage C to those with symptomatic myocarditis; and stage D to advanced myocarditis with hemodynamic or electrical instability.

5. There are many unanswered questions about the trajectories of the 4 stages of myocarditis, including the rates of progression from one stage to the next and the factors that influence disease course and recovery.

6. Patients with severe myocarditis (stage D) should be referred to an advanced heart failure center with a multidisciplinary myocarditis team, as they may require temporary circulatory support, durable ventricular assist devices, or cardiac transplantation.

7. Longitudinal follow-up of myocarditis patients does not end after a few weeks, even with resolution of symptoms. Repeat cardiac imaging and biomarker testing are advised to monitor for recovery and identify any deterioration in ventricular function.

8. Given the increasing recognition of genetic predisposition to myocarditis, genetic counseling and testing is recommended for all consenting patients. Discovery of a pathogenic variant should prompt cascade screening of family members.

9. Safety for return to strenuous physical activity and competitive sports is guided by follow-up CMR, 24-hour arrhythmia monitoring, and exercise testing, typically at 6 months after diagnosis.

10. Further research is needed on a wide range of topics, including the impact of social determinants of health, the development of international registries, improved diagnostic/prognostic phenotyping using novel biomarkers and imaging techniques, the role of immunosuppression, and access and coverage for myocarditis care.

Conclusion and Recommendations

In summary, this document provides new diagnostic criteria and a novel 4-stage classification for myocarditis, emphasizing the pivotal role of advanced imaging and biopsy, the critical need for multidisciplinary team-based care especially for severe cases, and the importance of longitudinal monitoring and genetic evaluation. It highlights numerous knowledge gaps and future research priorities to advance the field of myocarditis.

Key Points

1. Clinicians need to be aware of the 3 classic presentations of myocarditis - chest pain, heart failure/shock, and/or arrhythmia symptoms. A recent viral illness or other risk factors for "at-risk" myocarditis (stage A) followed by these cardiovascular symptoms should raise suspicion for the diagnosis.

2. High-sensitivity cardiac troponin is commonly used, but some patients with myocarditis will not have an elevated troponin. Further research is needed to determine if a normal troponin can reliably rule out myocarditis.

3. Cardiac magnetic resonance (CMR) imaging and endomyocardial biopsy (EMB) are considered key diagnostic tests. CMR can often provide a noninvasive diagnosis of symptomatic myocarditis (stage B), while EMB is the gold standard for determining the histological type and specific etiology (including viral).

4. A novel 4-stage classification of myocarditis is proposed: Stage A refers to those at-risk; stage B to asymptomatic individuals with evidence of myocardial inflammation; stage C to those with symptomatic myocarditis; and stage D to advanced myocarditis with hemodynamic or electrical instability.

5. There are many unanswered questions about the progression between the 4 stages of myocarditis, including the rates of progression and the factors that influence disease course and recovery.

6. Patients with severe myocarditis (stage D) should be referred to an advanced heart failure center with a multidisciplinary team, as they may require temporary circulatory support, ventricular assist devices, or cardiac transplantation.

Reference –

M. Drazner et al. (2024). 2024 ACC Expert Consensus Decision Pathway On Strategies And Criteria For The Diagnosis And Management Of Myocarditis: A Report Of The American College Of Cardiology Solution Set Oversight Committee.. *Journal Of The American College Of Cardiology*. https://doi.org/10.1016/j.jacc.2024.10.080