What causes dilation of the left atrium (LA), right atrium (RA), and right ventricle (RV) on an echocardiogram?

Causes of LA, RA, and RV Dilation on Echocardiography

The most common causes of combined left atrial (LA), right atrial (RA), and right ventricular (RV) dilation include severe tricuspid regurgitation (TR), pulmonary hypertension, left-sided valvular disease (particularly mitral regurgitation or stenosis), and biventricular heart failure. 1

Primary Mechanisms by Chamber

Left Atrial Dilation

• Chronic elevation of LV filling pressures is the primary driver of LA enlargement, reflecting cumulative effects over time from conditions such as hypertension, aortic stenosis, LV diastolic dysfunction, or mitral valve disease 1
• Mitral regurgitation causes volume overload leading to progressive LA dilation 1
• Atrial fibrillation itself causes LA dilation independent of ventricular dysfunction, particularly in chronic cases 1
• LA volume index >34 mL/m² indicates significant enlargement and predicts mortality, heart failure, stroke risk, and AF 1

Right Atrial Dilation

• Functional (secondary) tricuspid regurgitation accounts for approximately 80% of significant TR and is the most common cause of RA enlargement, resulting from RV dysfunction and tricuspid annular dilatation (>35 mm absolute or >21 mm/m²) 2
• Elevated right atrial pressure from any cause, including RV failure, severe TR, or pulmonary hypertension 1
• Left-sided heart disease causing backward transmission of elevated pressures through the pulmonary circulation 2
• RA larger than LA on apical four-chamber view is an independent predictor of all-cause mortality in heart failure patients 3

Right Ventricular Dilation

• RV volume overload from TR, pulmonary regurgitation, or atrial septal defects 1, 4
• RV pressure overload from pulmonary hypertension (systolic PA pressure >55 mmHg commonly causes RV dilation with anatomically normal valves) 2, 4
• Progressive RV remodeling leads to tricuspid annular dilatation, papillary muscle displacement, and leaflet tethering, creating a vicious cycle of worsening TR and further RV dilation 1, 2
• In chronic severe TR, the RV is classically dilated, though in acute severe TR the RV size may still be normal 1

Specific Disease States Causing Multi-Chamber Dilation

Severe Tricuspid Regurgitation

• Signs of severe TR include RA and RV dilatation, dilated and pulsatile inferior vena cava and hepatic vein, dilated coronary sinus, and systolic bowing of the interatrial septum toward the LA 1
• An end-systolic RV eccentricity index >2 (longest right lateral distance divided by distance connecting ventricular septum to RV free wall) favors severe TR with 79% sensitivity 1
• Systolic hepatic vein flow reversal is specific for severe TR 1

Pulmonary Hypertension

• Isolated pulmonary hypertension was observed in 43.2% of patients with refractory ARDS, while RV dilation with pulmonary hypertension occurred in 23% 5
• Progressive disease leads to RV dilatation becoming more prominent than hypertrophy, representing maladaptive remodeling 4

Left-Sided Valvular Disease

• Mitral stenosis or mitral regurgitation causes elevated pulmonary pressures, leading to functional TR and right heart chamber enlargement 2
• The backward transmission creates a cascade: LA dilation → pulmonary hypertension → RV dysfunction → RA dilation 1

Biventricular Heart Failure

• Ventricular interdependence effects: Severe RV dilation causes interventricular septal shift toward the LV, reducing LV cavity size and restricting LV filling, which can worsen LA pressure elevation 1, 2
• This creates biventricular diastolic dysfunction with multi-chamber dilation 2

Less Common Causes

Congenital Heart Disease

• Atrial septal defects cause RV volume overload with RA and RV dilation 1, 4
• Ebstein's anomaly can cause massive RA enlargement (volumes >1400 mL reported) 6

Iatrogenic Causes

• Intra-annular RV pacemaker or ICD leads cause functional TR through mechanical interference 2
• Post-cardiac transplant biopsy-related trauma 2

Atrial Functional MR

• Pure mitral annular dilation from chronic atrial fibrillation or restrictive cardiomyopathy causes LA dilation and secondary MR without primary LV dysfunction 1

Critical Diagnostic Pitfalls

• **Do not assume TR with PA pressure <40 mmHg indicates primary valve pathology**—functional TR can occur at lower pressures if significant annular dilatation is present (>35 mm or >21 mm/m²) 2
• Massive TR often presents with low jet velocity (<2 m/s) due to near-equalization of RV and RA pressures, not reflecting severity 1
• RA and RV size are usually normal in mild TR; their presence suggests at least moderate severity unless other causes exist 1
• Mid-RV dimension >33 mm, RV end-diastolic area >28 cm², and RA volume >33 mL/m² indicate significant right heart enlargement 1

Prognostic Implications

• RV dilation (RV end-diastolic area/LV end-diastolic area ratio) is an independent predictor of in-ICU mortality in critically ill patients 5
• LA volume index provides diagnostic and prognostic information about chronicity of disease and predicts death, heart failure, AF, and ischemic stroke 1
• RA larger than LA independently predicts all-cause mortality in elderly heart failure patients regardless of LVEF 3