What is the most likely echocardiographic diagnosis in a patient with low right‑ventricular systolic pressure, severe tricuspid regurgitation, and markedly dilated right and left atria?

Atrial Fibrillation with Severe Functional Tricuspid Regurgitation

The most likely echocardiographic diagnosis is severe functional (secondary) tricuspid regurgitation due to chronic atrial fibrillation with marked biatrial dilatation and tricuspid annular dilatation, occurring in the absence of significant pulmonary hypertension—a distinct clinical syndrome predominantly seen in elderly patients.

Pathophysiology and Mechanism

This presentation represents a well-characterized syndrome where chronic atrial fibrillation drives progressive right atrial remodeling, leading to tricuspid annular dilatation and subsequent severe functional TR 1, 2. The low RV systolic pressure (indicating absence of pulmonary hypertension) combined with severe TR and dilated bilateral atria is pathognomonic for this condition 3, 4.

The mechanism involves:

• Tricuspid annular dilatation (typically >40 mm or >21 mm/m²) causing loss of leaflet coaptation without primary valve pathology 1
• Progressive RV dilatation secondary to chronic volume overload from TR 1
• Marked biatrial enlargement from long-standing atrial fibrillation and atrial remodeling 2
• Absence of elevated pulmonary pressures, distinguishing this from secondary TR due to left heart disease or pulmonary hypertension 4

Clinical Profile

This syndrome characteristically occurs in:

• Elderly patients (typically >75 years old) 5, 3, 4
• Long-standing atrial fibrillation (often >20 years duration) 2
• Episodes of right-sided heart failure responsive to diuretics 5, 2
• Bradycardia and diminished fibrillation waves on ECG, suggesting partial atrial standstill 2

Echocardiographic Diagnostic Criteria

Severe TR Confirmation

The diagnosis requires integration of multiple parameters 1:

Quantitative measures:

• Effective regurgitant orifice area (EROA) ≥40 mm² 1
• Regurgitant volume ≥45 mL 1
• Vena contracta width ≥7 mm 1

Qualitative/semi-quantitative findings:

• Dense, triangular CW Doppler signal with early peaking and low velocity (<2 m/s) indicating pressure equalization between RV and RA 1
• Systolic flow reversal in hepatic veins 1
• Large central or eccentric wall-impinging color jet 1

Chamber Characteristics

• Markedly dilated right atrium (volume typically >86 mL/m²) 3
• Markedly dilated left atrium (reflecting chronic atrial fibrillation) 5, 2
• RV dilatation with preserved or mildly reduced systolic function 1, 3
• Tricuspid annular diameter >40 mm (or >21 mm/m²) 1

Key Distinguishing Features

• Normal or low pulmonary artery systolic pressure (<50 mm Hg), confirmed by low TR jet velocity 4
• Absence of primary valve pathology (no flail leaflets, vegetations, or significant structural abnormalities) 1, 4
• Relatively intact leaflet coaptation allowing adequate pressure estimation 4

Differential Considerations

This presentation must be distinguished from:

1. Secondary TR due to pulmonary hypertension: Would show elevated RV systolic pressure and high-velocity TR jet 1
2. Primary (organic) TR: Would demonstrate structural valve abnormalities (flail leaflets, prolapse, endocarditis) 1
3. TR from left-sided valve disease: Would show evidence of mitral or aortic pathology with elevated pulmonary pressures 1

Clinical Implications

This syndrome carries significant prognostic implications 3, 2:

• High prevalence of right-sided heart failure (approximately 69%) 3
• Progressive nature with worsening RA dilatation and TR severity over time 2
• Demonstrates the "non-benign" nature of chronic atrial fibrillation 3

Management Considerations

Transthoracic echocardiography with Doppler is the key diagnostic modality for complete assessment 1. The evaluation must include:

• Valve morphology and mechanism of TR 1
• Right heart chamber dimensions and RV function 1
• Pulmonary artery pressure estimation 1
• Inferior vena cava assessment 1
• Evaluation for concomitant left heart disease 1

Right heart catheterization is reasonable when clinical and non-invasive data are discordant or inadequate for assessing pulmonary pressures and hemodynamics 1.

Important Caveats

• TAPSE and systolic myocardial velocities may be less accurate in severe TR due to load dependency, potentially overestimating true RV function 1
• The TR jet velocity itself does not indicate severity—massive TR often presents with low velocity due to RA-RV pressure equalization 1
• 3D echocardiography may provide superior anatomical detail of the tricuspid valve apparatus when available 1