What is the most likely diagnosis for a patient with a dilated right ventricle and right atrium, normal tricuspid annular plane systolic excursion (TAPSE), and atrial fibrillation?

Diagnosis: Atrial Secondary Tricuspid Regurgitation (A-STR)

The most likely diagnosis is atrial secondary tricuspid regurgitation (A-STR), a distinct phenotype characterized by right atrial and tricuspid annular dilation in the setting of atrial fibrillation, with preserved right ventricular systolic function as evidenced by normal TAPSE.

Pathophysiology and Clinical Context

This presentation represents a specific phenotype of functional tricuspid regurgitation where the primary mechanism is right atrial enlargement driving tricuspid annular dilation, rather than ventricular dysfunction 1. The preserved TAPSE (normal RV systolic function) is the key distinguishing feature that differentiates this from the more common ventricular phenotype of secondary TR 2.

Key Diagnostic Features Present:

• Dilated right atrium and right ventricle - consistent with chronic volume overload from TR
• Normal TAPSE - indicates preserved RV longitudinal systolic function (normal >16 mm) 3
• Atrial fibrillation - the primary driver of atrial remodeling in this phenotype

Mechanistic Understanding

In A-STR, the pathophysiology follows this sequence 1, 4:

1. Long-standing atrial fibrillation causes progressive right atrial remodeling and enlargement
2. Tricuspid annular dilation occurs secondary to RA enlargement (annulus becomes planar and circular, dilating in anterior-posterior direction) 5
3. Insufficient adaptive leaflet growth - tricuspid leaflets fail to grow adequately to cover the enlarged annular area
4. Minimal leaflet tethering - unlike ventricular TR, there is typically trivial tethering because RV function remains preserved
5. Progressive TR develops from leaflet malcoaptation due to annular dilation alone

Clinical Significance and Prognosis

A-STR accounts for 10-15% of clinically relevant tricuspid regurgitation and has better outcomes compared to the ventricular phenotype 1. This is critical for prognostication and treatment planning.

Important Caveats:

TAPSE may be falsely reassuring in severe TR - Guidelines explicitly warn that TAPSE and systolic myocardial velocities are load-dependent and may not reflect true RV myocardial function in severe TR 2. The volume overload from severe TR can maintain normal TAPSE values despite underlying RV dysfunction. Consider additional parameters:

• RV fractional area change (normal >32%)
• 2D longitudinal strain (less load-dependent)
• RV end-systolic area (<16 cm² is normal) 2

Differential Considerations to Exclude

Before confirming A-STR, systematically exclude:

1. Primary tricuspid valve pathology 5:

   • Rheumatic disease, endocarditis, prolapse, Ebstein's anomaly
   • Carcinoid, radiation damage, trauma
   • Device leads causing leaflet damage or perforation 6

2. Pulmonary hypertension - Check estimated PA systolic pressure on echo 5, 3

3. Left-sided heart disease - Evaluate for mitral valve disease, LV dysfunction 5

4. Arrhythmogenic cardiomyopathy - Look for regional RV wall motion abnormalities, fatty infiltration, family history 7

Diagnostic Workup Algorithm

Echocardiographic assessment should include 5, 3, 5:

1. Severity of TR - Vena contracta width, PISA radius, regurgitant volume
2. RA volume - Maximal 2D RA volume (normal ≤33 mL/m²) 2
3. Tricuspid annular diameter - Diastolic diameter >40 mm or >21 mm/m² indicates significant dilation 3
4. RV dimensions:
   • Mid-RV dimension (normal ≤33 mm)
   • RV end-diastolic area (normal ≤28 cm²)
   • RV end-systolic area (normal ≤16 cm²) 2
5. Multiple RV function parameters:
   • TAPSE (normal >16 mm)
   • RV fractional area change (normal >32%)
   • Tissue Doppler S' velocity (normal >10 cm/s) 3
6. IVC diameter and respiratory variation - Assess RA pressure 2
7. Pulmonary artery systolic pressure - Exclude pulmonary hypertension 5
8. Left-sided valve function and LV function - Rule out secondary causes 5

If echocardiography is suboptimal, consider CMR or 3D echocardiography for accurate RV volumetric assessment 5.

Management Implications

Recent data suggest patients with A-STR may benefit from more aggressive rhythm control and timely valve interventions 1. The case report literature demonstrates that successful rhythm control can lead to reverse RA remodeling and resolution of TR 8.

Treatment Strategy:

1. Aggressive rhythm control - Cardioversion and maintenance of sinus rhythm (pharmacologic or ablation) may reverse atrial remodeling 8, 4

2. Monitor for progression - RA size progressively increases with worsening TR in long-standing AF 4

3. Consider intervention timing - Unlike ventricular TR, A-STR has better prognosis, but intervention should occur before irreversible RV dysfunction develops 1

4. Tricuspid valve intervention - When indicated, repair is preferred over replacement 9

Critical Clinical Pitfall

Do not assume normal TAPSE equals normal RV function in the presence of severe TR. The volume overload state artificially maintains longitudinal excursion. Always integrate multiple functional parameters and consider strain imaging for more accurate assessment 2.