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Cardiomegaly
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Here is a complete overview of Cardiomegaly, drawn from Harrison's, Robbins Basic Pathology, Goldman-Cecil Medicine, and Frameworks for Internal Medicine.
Cardiomegaly
Definition
Cardiomegaly refers to an enlarged heart, most commonly defined on a posteroanterior (PA) chest radiograph as a cardiothoracic (CT) ratio ≥ 0.5 - the transverse cardiac diameter divided by the maximum internal thoracic diameter. It is not a disease in itself; it is a sign of an underlying condition.
Important caveat: An enlarged cardiac silhouette on CXR does not automatically mean true cardiomegaly. Pericardial effusion, poor inspiratory effort, and AP projections can all falsely enlarge the cardiac shadow. - Frameworks for Internal Medicine
Types of Cardiac Enlargement
1. Concentric Hypertrophy (Pressure Overload)
- Wall thickness increases disproportionately; chamber size decreases
- Results from chronic pressure overload (e.g., hypertension, aortic stenosis)
- Diastolic dysfunction predominates
- May NOT appear cardiomegalic on CXR early on
2. Eccentric Hypertrophy (Volume Overload)
- Ventricular dilation with wall thinning; chamber size increases
- Results from volume overload (e.g., aortic/mitral regurgitation, dilated cardiomyopathy)
- The heart becomes "big and floppy" - systolic dysfunction predominates
- This manifests as cardiomegaly on CXR - Frameworks for Internal Medicine
Causes of Cardiomegaly
Primary (True Myocardial Enlargement)
| Cause | Mechanism |
|---|---|
| Dilated cardiomyopathy (DCM) | All-chamber dilation, systolic dysfunction |
| Hypertensive heart disease | LV hypertrophy -> eventual dilation |
| Ischemic heart disease / MI | LV remodeling and dilation post-infarct |
| Valvular disease | Volume overload (AR, MR) or pressure overload (AS, MS) |
| Alcoholic cardiomyopathy | Toxic myocardial damage |
| Peripartum cardiomyopathy | Unknown etiology; late gestation to months postpartum |
| Hemochromatosis | Iron overload - myocardial injury |
| Doxorubicin toxicity | Anthracycline-induced DCM |
| Viral myocarditis | Coxsackievirus B, parvovirus B-19, HHV-6 |
| Genetic DCM | Titin, dystrophin, desmin, lamin A/C mutations |
From Goldman-Cecil Medicine: "If an enlarged cardiac silhouette is present, it is generally indicative of a previous MI with LV dilation and cardiac remodeling. Other causes of cardiomegaly include long-standing hypertension, concomitant valvular heart disease, pericardial effusion..."
Pseudo-cardiomegaly (Apparent Enlargement Without True Myocardial Hypertrophy)
- Pericardial effusion - fluid accumulation around the heart
- AP chest radiograph (as opposed to PA) magnifies the cardiac silhouette
- Poor inspiratory effort on CXR
Genetics of Dilated Cardiomyopathy (the most common cause)
DCM is hereditary in 20-50% of cases, with autosomal dominant inheritance predominating. Over 50 mutations are known:
Key proteins mutated in DCM (red labels above):
- Titin - most common (~20% of all DCM); spans the sarcomere
- Dystrophin - X-linked DCM; links cytoskeleton to ECM
- Desmin - intermediate filament protein in cardiac myocytes
- Lamin A/C - nuclear structural protein
- β-myosin heavy chain, Troponin T - sarcomere proteins
- Robbins & Kumar Basic Pathology
Cardiomyopathy Functional Patterns (Differential for Cardiomegaly)
| Pattern | EF | Mechanism | Common Causes |
|---|---|---|---|
| Dilated | <40% | Systolic dysfunction | Genetic, alcohol, peripartum, myocarditis, hemochromatosis, doxorubicin |
| Hypertrophic | 50-80% | Diastolic dysfunction | Genetic, Friedreich ataxia |
| Restrictive | 25-50% | Diastolic dysfunction | Amyloidosis, radiation fibrosis |
- Robbins Basic Pathology, Table 9.5
Clinical Features
- Symptoms: Dyspnea on exertion, orthopnea, PND, fatigue, ankle edema (features of heart failure)
- Signs:
- Displaced apex beat (lateral and downward)
- S3 gallop - highly specific for reduced systolic function (HFrEF)
- Raised JVP, peripheral edema, basal crackles
- Murmurs if valvular etiology
- ECG findings:
- Left atrial abnormality (broad, notched P waves; biphasic P in V1)
- LVH criteria
- Right ventricular hypertrophy signs (tall R in V1, right axis deviation) if right-sided cause
- Tachycardia, LBBB pattern in DCM
- CXR: CT ratio >0.5, pulmonary vascular congestion, Kerley B lines if heart failure present
Diagnosis
| Investigation | Finding |
|---|---|
| CXR | CT ratio ≥ 0.5 |
| Echocardiography | Gold standard - chamber dimensions, wall motion, EF, valvular function |
| ECG | LVH, LAE, arrhythmias |
| Cardiac MRI | Structural detail, myocardial fibrosis (late gadolinium enhancement) |
| BNP / NT-proBNP | Elevated in heart failure |
| Troponin | Elevated in myocarditis or ischemic cause |
| Endomyocardial biopsy | For myocarditis or infiltrative causes |
Treatment
Treatment is directed at the underlying cause, not the cardiomegaly itself:
- HFrEF (systolic dysfunction):
- ACE inhibitors/ARBs or ARNI (sacubitril/valsartan)
- Beta-blockers (carvedilol, metoprolol succinate, bisoprolol)
- Mineralocorticoid receptor antagonists (spironolactone, eplerenone)
- SGLT2 inhibitors (dapagliflozin, empagliflozin)
- Diuretics for fluid overload
- ICD / CRT if EF <35% with LBBB
- Hypertension: Antihypertensive therapy
- Valvular disease: Surgical or transcatheter repair/replacement
- Alcohol: Abstinence - DCM may partially reverse
- Peripartum cardiomyopathy: ~50% recover normal function spontaneously
- Pericardial effusion (pseudo-cardiomegaly): Pericardiocentesis if tamponade
- Hemochromatosis: Phlebotomy, chelation
Key Points to Remember
- Cardiomegaly on CXR = CT ratio >0.5 on a PA film
- It is a sign, not a diagnosis - always seek the underlying cause
- Pericardial effusion can mimic cardiomegaly ("water bottle heart")
- DCM is the classic cause - heart up to 2-3x normal weight, all chambers dilated
- Titin mutations are the single most common genetic cause of DCM (~20%)
- S3 gallop + cardiomegaly strongly suggests HFrEF
- Echo is the key investigation to assess structure and function
Sources: Harrison's Principles of Internal Medicine 22E; Robbins & Kumar Basic Pathology; Goldman-Cecil Medicine; Frameworks for Internal Medicine
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