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Dilated Cardiomyopathy and Myocarditis

Dilated Cardiomyopathy

Definition and Epidemiology

Dilated cardiomyopathy is defined by left ventricular dilation, with an LV end-diastolic dimension exceeding two standard deviations above normal for age and body surface area, accompanied by reduced systolic function with an ejection fraction below 50%, in the absence of coronary artery disease or abnormal loading conditions sufficient to explain the degree of dysfunction. The prevalence is estimated at approximately 1 in 250 to 500 individuals, making it the most common indication for heart transplantation worldwide. There is a notable male predominance at roughly a 3:1 ratio, with peak incidence occurring between the ages of 20 and 60 years.

Etiologies

Genetic (30-50% of "Idiopathic" DCM)

Genetic causes account for 30 to 50% of cases previously classified as idiopathic dilated cardiomyopathy, underscoring the importance of systematic genetic evaluation in all patients presenting with this phenotype. Titin truncating variants represent the most common genetic cause, responsible for approximately 25% of familial DCM cases. These typically present with a milder phenotype and better prognosis, and patients frequently respond well to guideline-directed medical therapy with frequent ejection fraction recovery. Lamin A/C mutations account for 5 to 10% of familial DCM and carry a notably aggressive phenotype characterized by early conduction disease including left bundle branch block and atrioventricular block, atrial fibrillation, and a high risk of sudden cardiac death. The ICD implantation threshold is lower in this population, with consideration at an ejection fraction below 45% or in the presence of nonsustained ventricular tachycardia, and ICD is often indicated regardless of ejection fraction.

Desmoplakin and other desmosomal gene mutations create an overlap with arrhythmogenic cardiomyopathy, presenting as left ventricle-dominant arrhythmogenic cardiomyopathy with subepicardial and mid-wall fibrosis in which ventricular arrhythmias are prominent and exercise may accelerate disease progression. Filamin C mutations produce DCM with overlapping restrictive physiology, mid-wall fibrosis, and high arrhythmia risk. RBM20 mutations cause severe early-onset DCM with high arrhythmia risk and poor prognosis. Additional less common but clinically significant mutations include BAG3, PLN, MYH7, TNNT2, and SCN5A. Genetic testing is recommended for all DCM patients, along with first-degree relative screening with echocardiography and electrocardiography.

Toxic

Alcohol-related cardiomyopathy develops with chronic heavy use, typically defined as more than 7 to 8 drinks per day for five or more years. The condition is reversible with abstinence in early stages, with approximately 50% ejection fraction improvement expected at six months with cessation. Cocaine and methamphetamine cause cardiomyopathy through direct cardiotoxicity, catecholamine surges, and coronary vasospasm. Anthracyclines such as doxorubicin and daunorubicin produce dose-dependent, irreversible type I cardiotoxicity, with cumulative doxorubicin doses exceeding 400 mg/m^2 carrying significant risk. Preventive strategies include dexrazoxane administration, liposomal formulations, and dose limitation. Trastuzumab produces type II toxicity that is usually reversible upon discontinuation, mediated through ErbB2 pathway inhibition, and requires monitoring of left ventricular ejection fraction every three months during therapy. Immune checkpoint inhibitors can cause myocarditis rather than classic DCM, with a potentially fulminant course that warrants troponin monitoring.

Metabolic/Endocrine

Thyroid disorders contribute to cardiomyopathy through different mechanisms: hypothyroidism produces reversible dysfunction with thyroid hormone replacement, while thyrotoxicosis initially causes high-output physiology that may progress to DCM. Pheochromocytoma produces catecholamine-mediated cardiomyopathy that is reversible after tumor resection. Acromegaly causes biventricular hypertrophy that may progress to dilated cardiomyopathy. Beriberi from thiamine deficiency produces high-output heart failure, known as wet beriberi, which is common in chronic alcoholism, after bariatric surgery, and with hyperemesis gravidarum. This condition demonstrates a dramatic response to intravenous thiamine replacement.

Tachycardia-Mediated Cardiomyopathy

Sustained tachycardia, typically with heart rates exceeding 100 to 110 beats per minute for prolonged periods, can cause reversible dilated cardiomyopathy. Common culprits include uncontrolled atrial fibrillation, atrial flutter, incessant atrial tachycardia, and frequent premature ventricular complexes with a burden exceeding 15 to 20%. Treatment centers on rate or rhythm control of the tachyarrhythmia or PVC ablation. Ejection fraction recovery typically occurs within three to six months, though full recovery may take up to 12 months. Distinguishing tachycardia-mediated cardiomyopathy from DCM complicated by secondary atrial fibrillation remains a diagnostic challenge, and a trial of rhythm control or ablation often helps clarify the relationship.

Peripartum Cardiomyopathy

Peripartum cardiomyopathy presents during the last month of pregnancy through five months postpartum, defined by an ejection fraction below 45% without prior cardiac disease. Risk factors include age over 30, multiparity, preeclampsia, African descent, and twin pregnancy. Approximately 50% of patients recover within six months, while roughly 20% progress to chronic heart failure or require transplant. Bromocriptine, based on the 16-kDa prolactin hypothesis, has limited evidence but may accelerate recovery when given at 2.5 mg twice daily for two weeks followed by 2.5 mg daily for six weeks, with concomitant anticoagulation required. Breastfeeding is contraindicated if bromocriptine is used. A wearable defibrillator such as the LifeVest should be considered if ejection fraction falls to 35% or below during the recovery period. Subsequent pregnancy carries approximately a 20% relapse risk, necessitating shared decision-making, with higher risk when ejection fraction has not fully recovered to 50 to 55%.

Diagnostic Workup

The echocardiographic evaluation typically reveals left ventricular dilation, reduced ejection fraction with global hypokinesis, possible right ventricular involvement, and functional mitral regurgitation as a common finding. Cardiac MRI serves a critical role in assessing fibrosis pattern, with mid-wall septal late gadolinium enhancement present in approximately 30% of DCM cases and associated with increased arrhythmia risk and worse prognosis. Importantly, cardiac MRI helps exclude an ischemic pattern of subendocardial or transmural late gadolinium enhancement. Coronary evaluation through coronary angiography or coronary CT angiography is required in all new DCM diagnoses to exclude an ischemic etiology. A comprehensive cardiomyopathy gene panel should be obtained. Laboratory evaluation should include TSH, iron studies including ferritin and transferrin saturation to screen for hemochromatosis, thiamine levels if risk factors are present, HIV, hepatitis panel, and ANA with ESR if connective tissue disease is suspected. Endomyocardial biopsy should be considered in fulminant presentations, suspected giant cell myocarditis, eosinophilic myocarditis, cardiac sarcoidosis, or when a specific histological diagnosis would change management.

<image> A diagnostic workup algorithm for new-onset dilated cardiomyopathy. Central box: "New Diagnosis DCM (LV dilation + EF < 50%)." Branch 1 (top): "Exclude Ischemic Etiology" → Coronary angiography or CCTA → if significant CAD: "Ischemic cardiomyopathy - assess viability, consider revascularization." Branch 2 (left): "Cardiac MRI" with three sub-patterns shown as small images: (a) mid-wall linear enhancement = idiopathic/genetic DCM, (b) subendocardial enhancement = ischemic, (c) subepicardial/patchy enhancement = myocarditis. Branch 3 (right): "Laboratory evaluation" listing TSH, iron studies, HIV, hepatitis, BNP/NT-proBNP, troponin, autoimmune markers. Branch 4 (bottom left): "Genetic Testing" → if positive → cascade family screening. Branch 5 (bottom right): "Consider EMB" if: fulminant course, unexplained ventricular arrhythmias, suspected GCM/eosinophilic myocarditis, cardiac sarcoidosis, treatment-refractory HF. Color code: blue for imaging, green for laboratory, orange for genetic, red for invasive. </image>

Myocarditis

Etiology

Viral infections represent the most common cause of myocarditis in developed countries, with Coxsackievirus B historically the most frequently implicated agent. Other important viral etiologies include parvovirus B19, human herpesvirus 6, adenovirus, SARS-CoV-2, influenza, HIV, and hepatitis C. Immune-mediated causes encompass giant cell myocarditis, eosinophilic myocarditis, systemic autoimmune diseases such as systemic lupus erythematosus, sarcoidosis, and scleroderma, as well as immune checkpoint inhibitor-associated myocarditis. Toxic and drug-related causes include cocaine, catecholamines, lithium, and clozapine.

Clinical Presentations

Acute myocarditis typically presents with chest pain that may be pericarditic or ischemic in character, accompanied by dyspnea, fever, and a history of viral prodrome one to two weeks prior. Troponin is elevated and the presentation may closely mimic acute coronary syndrome. Fulminant myocarditis is characterized by rapid hemodynamic deterioration within two to four weeks of symptom onset, progressing to cardiogenic shock. Paradoxically, this form carries a better prognosis than acute myocarditis if the patient survives the initial crisis, with approximately 75% survival when aggressive support is provided. Chronic active myocarditis has an insidious onset with a relapsing course and progressive left ventricular dysfunction. Giant cell myocarditis follows a fulminant course with biventricular failure and new-onset ventricular tachycardia, carrying a mean survival of only 5.5 months without transplant. It is associated with autoimmune diseases including inflammatory bowel disease, thymoma, and thyroiditis. Eosinophilic myocarditis may result from drug hypersensitivity, which is the most common cause, hypereosinophilic syndrome, or parasitic infection, and features endomyocardial involvement known as Loeffler endocarditis along with peripheral eosinophilia.

Diagnosis

Cardiac MRI (Non-Invasive Gold Standard)

The Modified Lake Louise Criteria of 2018 provide the framework for non-invasive diagnosis. The T2-based criterion detects myocardial edema through increased T2 signal or elevated T2 mapping values, offering sensitivity for acute inflammation. The T1-based criterion identifies elevated native T1, elevated extracellular volume fraction, or late gadolinium enhancement in a non-ischemic pattern, typically subepicardial or mid-wall, often involving the inferolateral wall. Supportive findings include pericardial effusion and regional wall motion abnormalities. When both T1 and T2 criteria are positive, diagnostic accuracy is high, with sensitivity approximately 85% and specificity approximately 90%. The late gadolinium enhancement pattern is particularly instructive: subepicardial enhancement, especially in the inferolateral wall, is classic for viral myocarditis, while patchy mid-wall enhancement may also occur. The extent of late gadolinium enhancement predicts arrhythmia risk and functional recovery.

Endomyocardial Biopsy

The Dallas criteria define active myocarditis as inflammatory infiltrate with myocyte necrosis, and borderline myocarditis as inflammatory infiltrate without necrosis. However, sensitivity is low at approximately 50% due to the patchy nature of disease and sampling error, and at least four to six right ventricular septal biopsies are recommended. Immunohistochemistry offers improved sensitivity over the Dallas criteria, with diagnostic thresholds of 14 or more infiltrating leukocytes per square millimeter, including CD3-positive T cells at 7 or more per square millimeter, with increased HLA-DR expression. Viral genome detection by PCR can identify the causative virus and guide potential antiviral therapy. Indications for endomyocardial biopsy include fulminant myocarditis, suspected giant cell or eosinophilic myocarditis, failure to improve with standard therapy, and new-onset heart failure with ventricular arrhythmias.

Management

Supportive Care

Standard heart failure with reduced ejection fraction therapy forms the foundation of treatment, including ACE inhibitors or ARBs (avoiding ARNI in the acute phase due to hypotension risk), beta-blockers started at low dose and cautiously in the acute phase, mineralocorticoid receptor antagonists, and SGLT2 inhibitors. Hemodynamic support in cardiogenic shock involves inotropes such as dobutamine and milrinone, vasopressors such as norepinephrine, and mechanical circulatory support including Impella and ECMO. For fulminant myocarditis, early deployment of VA-ECMO as a bridge to recovery is critical, with LV venting if needed and biventricular Impella if right ventricular failure develops. Exercise should be avoided during active myocarditis, with a minimum restriction of three to six months from competitive sports after resolution, per the 2015 eligibility recommendations. Return to sport requires normalization of ejection fraction, absence of late gadolinium enhancement progression, no arrhythmias on Holter monitoring, normal biomarkers, and a normal exercise test.

Immunosuppressive Therapy

Giant cell myocarditis requires treatment with cyclosporine combined with corticosteroids, with or without azathioprine. This regimen delays the need for transplant but the overall transplant or death rate remains high, and post-transplant recurrence of giant cell myocarditis occurs in approximately 20 to 25% of cases. Eosinophilic myocarditis responds to high-dose corticosteroids at 1 mg/kg of prednisone, withdrawal of the offending drug, and rapid improvement is expected. Immune checkpoint inhibitor myocarditis demands permanent discontinuation of the ICI agent and high-dose methylprednisolone at 1 gram daily for three days. If refractory, mycophenolate, tacrolimus, or anti-thymocyte globulin may be added. Abatacept, a CTLA-4 agonist, is emerging as a targeted therapy. Mortality in fulminant cases ranges from 25 to 50%. Cardiac sarcoidosis is treated with prednisone at 30 to 40 mg daily, tapered over months, with steroid-sparing agents including methotrexate, azathioprine, and mycophenolate for maintenance. FDG-PET is used to monitor treatment response. For viral myocarditis, immunosuppression is not recommended if viral genome is detected on endomyocardial biopsy, as it may worsen viral replication. Antiviral therapy with intravenous immunoglobulin or interferon-beta has limited evidence, and management is largely supportive.

<image> A comparison panel showing cardiac MRI findings in myocarditis versus myocardial infarction. Two columns side by side. Left column labeled "Myocarditis" with three rows: (1) T2 mapping showing elevated T2 values in the inferolateral wall highlighted in red/yellow on a color map (indicating edema), (2) Native T1 mapping showing elevated T1 in the same region, (3) LGE image showing subepicardial enhancement in the inferolateral wall (arrows pointing to the bright signal in the subepicardial layer, sparing the subendocardium). Right column labeled "Myocardial Infarction (LAD territory)" with three corresponding rows: (1) T2 mapping showing edema in the anteroseptal region, (2) Native T1 mapping with corresponding elevated T1, (3) LGE showing subendocardial-to-transmural enhancement in the anteroseptal wall following the LAD territory. Each image should be a short-axis view of the LV with clear labeling. Include a color bar for T1/T2 maps with normal and abnormal value ranges. Caption emphasizing that the pattern of LGE (subepicardial vs. subendocardial) is the key differentiating feature. </image>

Arrhythmogenic Cardiomyopathy (ACM)

Beyond Classic ARVC

The concept of arrhythmogenic cardiomyopathy has evolved significantly beyond the classic description of arrhythmogenic right ventricular cardiomyopathy. Classic ARVC presents as the right ventricle-dominant form with fibrofatty replacement, caused by desmosomal gene mutations, with plakophilin-2 being the most common followed by desmoglein-2, desmocollin-2, desmoplakin, and junctional plakoglobin. Left-dominant arrhythmogenic cardiomyopathy involves predominant left ventricular involvement with subepicardial and mid-wall fibrosis, caused by mutations in desmoplakin, filamin C, and phospholamban, and may present as dilated cardiomyopathy with prominent ventricular arrhythmias. Biventricular arrhythmogenic cardiomyopathy involves both ventricles and carries the worst prognosis.

Diagnosis (2010 Task Force Criteria, Padua Criteria 2020)

Diagnosis is based on major and minor criteria spanning structural findings including right ventricular dilation and wall motion abnormality with or without left ventricular involvement, tissue characterization through fibrofatty replacement on cardiac MRI or biopsy, ECG abnormalities such as T-wave inversions in leads V1 through V3 and beyond along with epsilon waves and prolonged terminal activation duration, arrhythmia criteria including left bundle branch block morphology ventricular tachycardia and more than 500 PVCs per 24 hours, and family history or genetic findings. A definite diagnosis of ARVC requires two major criteria, or one major plus two minor, or four minor criteria from different categories.

Management

Exercise restriction is essential, as competitive sports and high-intensity exercise are contraindicated because they accelerate disease progression and arrhythmia risk. Desmosomal disease is inherently exercise-sensitive. Antiarrhythmic therapy with sotalol, amiodarone, or flecainide combined with an AV nodal blocker is used for ventricular tachycardia suppression. ICD implantation is recommended for secondary prevention following VT or VF arrest and for primary prevention when high-risk features are present, including syncope, significant right or left ventricular dysfunction, or extensive arrhythmia burden. Catheter ablation using epicardial and endocardial approaches addresses recurrent ventricular tachycardia and reduces VT episodes but does not prevent sudden cardiac death, making it a palliative rather than curative intervention. Standard guideline-directed medical therapy should be initiated if ejection fraction is reduced, and transplant evaluation is appropriate for refractory heart failure or arrhythmia storm.

Key Clinical Pearls

• Always rule out coronary artery disease in new-onset DCM -- even in young patients; coronary angiography or CCTA is mandatory; ~40% of presumed "non-ischemic" DCM will have significant CAD
• LMNA cardiomyopathy carries the highest SCD risk among genetic DCMs -- ICD should be considered at EF < 45% (lower threshold than standard primary prevention) or with NSVT, even without severe LV dysfunction
• Fulminant myocarditis, paradoxically, has better long-term prognosis than acute myocarditis if the patient survives the initial crisis -- aggressive MCS (ECMO) as bridge to recovery can be life-saving
• Immune checkpoint inhibitor myocarditis has 25-50% mortality; troponin monitoring during ICI therapy is recommended; any troponin rise with new symptoms warrants urgent evaluation and ICI discontinuation
• PVC-mediated cardiomyopathy is highly reversible -- PVC ablation when burden > 15-20% can restore normal EF within months; always Holter-monitor DCM patients to quantify PVC burden
• Exercise restriction in desmosomal cardiomyopathy is critical -- even asymptomatic gene carriers should avoid competitive athletics and high-intensity exercise

References

• Bozkurt B, et al. Current Diagnostic and Treatment Strategies for Specific Dilated Cardiomyopathies: AHA Scientific Statement. Circulation. 2016;134:e579-e646.
• Caforio ALP, et al. Current State of Knowledge on Aetiology, Diagnosis, Management, and Therapy of Myocarditis: ESC Working Group Statement. Eur Heart J. 2013;34:2636-2648.
• Ferreira VM, et al. Cardiovascular Magnetic Resonance in Nonischemic Myocardial Inflammation: Expert Recommendations (Lake Louise Criteria 2018). JACC. 2018;72:3158-3176.
• Arbelo E, et al. 2023 ESC Guidelines for the Management of Cardiomyopathies. Eur Heart J. 2023;44:3503-3626.
• Ammirati E, et al. Management of Acute Myocarditis and Chronic Inflammatory Cardiomyopathy: An Expert Consensus Document. Circ Heart Fail. 2020;13:e007405.

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