Dilated Cardiomyopathies¶
Chapter 269 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- Dilated cardiomyopathy (DCM) is characterized by decreased left ventricular systolic function with increased left ventricular dimensions.
- Key causes include myocarditis, genetic mutations (e.g., TTN), toxic exposures (e.g., alcohol, anthracyclines), and metabolic disorders (e.g., hemochromatosis).
- Cardiac MRI is essential for diagnosing hemochromatosis and takotsubo cardiomyopathy, with specific findings like iron deposition or apical ballooning.
- Management includes neurohormonal modulation (ACE inhibitors, beta-blockers), diuretics, and implantable defibrillators for arrhythmias.
- Prognosis varies: 50–80% of PPCM patients recover, while alcohol-related DCM has poor outcomes with continued heavy use.
1. DEFINITION & OVERVIEW¶
Dilated cardiomyopathy (DCM) is defined by left ventricular systolic dysfunction with increased left ventricular dimensions, often leading to heart failure. It may present as a restrictive cardiomyopathy with progressive fibrosis. Non-infectious inflammatory myocarditis (e.g., from immune checkpoint inhibitors) and toxic/metabolic causes (e.g., alcohol, chemotherapy) are major contributors. DCM can progress to end-stage heart failure, with variable recovery depending on etiology.
Table 269-1 Major Causes of Dilated Cardiomyopathy¶
| Category | Causes | Examples |
|---|---|---|
| Inflammatory Myocarditis | Viral (e.g., coxsackie, HIV), Bacterial (e.g., diphtheria), Parasitic (e.g., Chagas’ disease) | |
| Noninfective | Granulomatous disease (e.g., sarcoidosis), Checkpoint inhibitors, Transplant rejection | |
| Toxic | Alcohol, Catecholamines (amphetamines, cocaine), Chemotherapy (anthracyclines, trastuzumab) | |
| Metabolic | Hemochromatosis, Thyroid disease, Diabetes mellitus, Obesity | |
| Genetic | Inherited metabolic defects, Familial DCM (e.g., TTN mutations) |
| Category | Causes | Examples |
|---|---|---|
| Miscellaneous | Arrhythmogenic ventricular cardiomyopathy, Peripartum cardiomyopathy, Left ventricular noncompaction |
1.1 Classification¶
DCM is categorized by etiology: infectious (e.g., viral myocarditis), non-infectious (e.g., autoimmune, toxic), metabolic (e.g., hemochromatosis), and genetic (e.g., TTN mutations). Peripartum cardiomyopathy (PPCM) and takotsubo syndrome are distinct subtypes with unique presentations.
2. EPIDEMIOLOGY¶
PPCM affects 1:1000–1:4000 deliveries in the U.S., with higher risk in Black women (4x more common). Alcohol-related DCM is rare but linked to chronic heavy use ( ≥ 60–80 g ethanol/day for ≥ 5 years). Mortality rates for PPCM range from 4–11% in the U.S., with higher rates in Africa. Age, gender, and comorbidities (e.g., hypertension, diabetes) influence outcomes.
2.1 Risk Factors¶
PPCM: older maternal age, multiple pregnancies, malnutrition, tocolytic use. Alcohol: chronic heavy consumption, binge drinking. Genetic: TTN mutations in 15% of PPCM cases. Obesity: associated with HFpEF and metabolic syndrome.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
DCM arises from multifactorial mechanisms: viral myocarditis, immune checkpoint inhibitors (e.g., PD-1/PD-L1 blockade), toxic agents (e.g., anthracyclines), metabolic disorders (e.g., hemochromatosis), and genetic mutations (e.g., TTN). Pathophysiology includes myocyte necrosis, fibrosis, neurohormonal activation, and oxidative stress. Chronic inflammation and apoptosis drive progressive dilation and dysfunction.
3.1 Genetic Factors¶
Truncating TTN mutations are common in DCM and PPCM. Inborn metabolic defects (e.g., Kearns-Sayre syndrome) and familial DCM (e.g., mitochondrial myopathies) contribute to pathogenesis.
4. CLINICAL FEATURES¶
Symptoms: dyspnea, fatigue, edema, arrhythmias. Signs: enlarged heart, elevated BNP/troponin, mitral regurgitation. Complications: thromboembolism, heart failure, sudden cardiac death. Takotsubo syndrome presents with apical ballooning and acute chest pain mimicking MI, resolving within weeks.
4.1 PPCM Presentation¶
Occurs 5–6 months postpartum, with pulmonary congestion, elevated troponin, and LVEF ≤ 0.45. May mimic acute MI but resolves with treatment.
5. DIFFERENTIAL DIAGNOSIS¶
Myocarditis, valvular heart disease, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, and ischemic heart disease. Takotsubo syndrome must be distinguished from MI via coronary angiography and ECG findings.
5.1 Key Differentiators¶
PPCM vs. MI: no coronary artery stenosis; takotsubo vs. MI: preserved epicardial coronary flow. Hemochromatosis vs. DCM: iron overload on MRI, elevated serum iron/transferrin saturation.
6. INVESTIGATIONS & DIAGNOSIS¶
ECG (e.g., arrhythmias, conduction blocks), echocardiography (LVEF, ventricular dilation), cardiac MRI (for hemochromatosis, takotsubo), troponin, BNP, and genetic testing (e.g., TTN mutations). Cardiac MRI is preferred over endomyocardial biopsy for diagnosing hemochromatosis.
6.1 Diagnostic Criteria¶
PPCM: LVEF ≤ 0.45 postpartum without other cardiac disease. Takotsubo: apical ballooning with preserved epicardial coronary flow. Hemochromatosis: iron overload on MRI with elevated serum iron/transferrin saturation.
7. MANAGEMENT & TREATMENT¶
Medical therapy: ACE inhibitors, beta-blockers, diuretics, and mineralocorticoid antagonists. Non-pharmacologic: lifestyle modifications, alcohol cessation, and weight management. Implantable defibrillators for arrhythmias. For PPCM, early diuretics and avoidance of RAAS inhibitors during pregnancy. For hemochromatosis, phlebotomy or chelation.
7.1 Treatment Algorithms¶
- Initiate neurohormonal modulation (ACE inhibitors, beta-blockers). 2. Use diuretics for volume overload. 3. Consider ICD for arrhythmias. 4. For PPCM, avoid RAAS inhibitors during pregnancy. 5. For hemochromatosis, phlebotomy or deferoxamine.
8. PROGNOSIS & COMPLICATIONS¶
PPCM: 50–80% recovery within 6 months; 10% recurrence. Alcohol-related DCM: poor prognosis with continued use. Hemochromatosis: improved with iron removal. Complications: heart failure, arrhythmias, thromboembolism, and sudden death. Mortality rates vary by etiology (e.g., 4–11% for PPCM).
8.1 Recovery Factors¶
PPCM recovery correlates with LVEF >0.30, absence of black race, and early diagnosis. Alcohol cessation improves outcomes, but severe cases may have irreversible fibrosis.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: PPCM risk is 4x higher in Black women; avoid RAAS inhibitors. Pediatrics: DCM in children may resolve with growth. Elderly: increased risk of toxic cardiomyopathy from chemotherapy. Obesity: linked to HFpEF and metabolic syndrome.
9.1 Pregnancy Management¶
Close maternal-fetal monitoring, avoid RAAS inhibitors, and use beta-blockers if needed. Breastfeeding is generally safe with metoprolol, enalapril, and spironolactone.
10. KEY POINTS & CLINICAL PEARLS¶
- DCM is a heterogeneous disease with diverse etiologies, including myocarditis, genetics, and toxins. 2. Cardiac MRI is critical for diagnosing hemochromatosis and takotsubo. 3. PPCM has a high recovery rate but requires early intervention. 4. Alcohol cessation is vital for recovery in alcoholic cardiomyopathy. 5. Genetic testing (e.g., TTN) aids in diagnosing familial DCM.