Definition & Pathology
- Definition : Congenital absence/agenesis of tricuspid valve.
- Anatomic Hallmarks : Complete obstruction of Right Atrium (RA) to Right Ventricle (RV) blood flow.
- Obligate Shunt : Right-to-Left shunt at atrial level (ASD/PFO) essential for survival.
- Ventricular Status : Hypoplastic RV / Enlarged Left Ventricle (LV).
Morphologic Subtypes
| Subtype | Anatomic Detail |
|---|---|
| Muscular | Most common / Muscular wall lines RA floor overriding ventricular septum. |
| Membranous | Membranous AV septum lines RA floor. |
| Ebstein-like | Imperforate partially delaminated valve / Atrialized RV. |
| Valvar | Fused leaflets and chordae without inflow. |
Hemodynamics
- Flow Pathway : Systemic venous return $\rightarrow$ RA $\rightarrow$ ASD/PFO $\rightarrow$ LA (mixes with pulmonary venous return) $\rightarrow$ LV $\rightarrow$ Aorta (Systemic).
- Pulmonary Flow Source : LV $\rightarrow$ VSD $\rightarrow$ Hypoplastic RV $\rightarrow$ Pulmonary Artery (PA) OR via Patent Ductus Arteriosus (PDA).
- Physiologic Determinants : Degree of pulmonary blood flow (PBF) dictated by VSD size, great artery relationship, and Right Ventricular Outflow Tract (RVOT) obstruction.
Classification
| Type | Great Artery Relation | Incidence | PBF Status | Clinical Consequence |
|---|---|---|---|---|
| Type I | Normally related (Aorta from LV, PA from RV) | 70-80% | Decreased (usually) | Cyanosis / Duct-dependent. |
| Type II | d-Transposition (Aorta from RV, PA from LV) | 12-25% | Increased (usually), | Congestive Heart Failure (CHF) / Pulmonary overcirculation. |
| Type III | l-Transposition or Complex (Truncus/AVSD) | Rare | Variable | Dependent on associated lesions. |
(Note: Subclassified into A (Pulmonary Atresia), B (Pulmonary Stenosis), C (No Pulmonary Stenosis)).
Clinical Presentation
Signs & Symptoms
- Cyanosis : Present at birth (Type I / restricted PBF).
- Heart Failure : Tachypnea / Poor feeding / Diaphoresis at 4-8 weeks (Type II / unrestricted PBF).
- Apical Impulse : LV type impulse (Unique among cyanotic CHD).
- JVP : Prominent 'a' wave (RA contraction against atretic valve).
- Auscultation : Single S2 / Holosystolic murmur at left sternal border (VSD) / Continuous murmur (PDA).
Diagnostics
Bedside & Imaging
- ECG : Left Axis Deviation (LAD) (-45°) / Left Ventricular Hypertrophy (LVH) / Right Atrial Enlargement (tall spiked P waves in lead II). Diagnostic hallmark differentiating TA from Tetralogy of Fallot (TOF).
- CXR : Pulmonary undercirculation (Type I) OR Pulmonary overcirculation (Type II) / Cardiomegaly (LV/RA enlargement).
- Echocardiography (Diagnostic) : Fibromuscular membrane substituting TV / Hypoplastic RV / VSD size / ASD size / Great vessel orientation.
- Cardiac Catheterization : Right-to-Left atrial shunt / Angiographic filling defect between RA and LV / Useful for evaluating pulmonary vascular resistance (PVR).
Differential Diagnosis (Cyanotic CHD)
| Feature | Tricuspid Atresia | Tetralogy of Fallot (TOF) |
|---|---|---|
| ECG Axis | Left Axis Deviation (LAD) | Right Axis Deviation (RAD) |
| Ventricular Hypertrophy | Left Ventricular Hypertrophy (LVH) | Right Ventricular Hypertrophy (RVH) |
| Apical Impulse | LV type | RV type heave |
Management
Medical Management
- PGE1 (Alprostadil) / Infusion / Maintain ductal patency : Prevents severe hypoxia in duct-dependent PBF / 0.05-0.1 μg/kg/min.
- Rashkind Balloon Atrial Septostomy / Procedure / Decompress RA : Relieves restrictive ASD / Improves right-to-left mixing.
- Diuretics & Afterload Reduction / Medication / Manage CHF : Used in Type II (Transposition) with pulmonary overcirculation.
Surgical Palliation (Staged Univentricular Pathway)
Goal: Separate systemic and pulmonary circulations, offload LV, bypass right heart.
| Stage | Timing | Procedure | Indication / Detail |
|---|---|---|---|
| Stage 1 | Neonatal | Modified Blalock-Taussig (BT) Shunt | Type I with restricted PBF (creates stable PBF). |
| Pulmonary Artery (PA) Banding | Type II with unrestricted PBF (controls pulmonary overcirculation). | ||
| Damus-Kaye-Stansel (DKS) / Norwood | Type II with restrictive VSD/systemic outflow obstruction. | ||
| Stage 2 | 3-6 Months | Bidirectional Glenn (BCPA) | Superior Vena Cava to PA anastomosis / Unloads volume from LV. |
| Stage 3 | 2-3 Years | Modified Fontan (TCPC) | Inferior Vena Cava to PA connection / Eliminates right-to-left shunt / Places circulations in series. |
Complications, Nuances & Prognosis
Hemodynamic Nuances
- Spontaneous VSD Closure / Complication / Alters hemodynamics : Occurs in ~40% of patients.
- In Type I (Normal Great Arteries): Worsening cyanosis due to restricted PBF.
- In Type II (d-TGA): Systemic hypoperfusion / Subaortic stenosis / Cardiogenic shock.
Long-Term Prognosis
- Unoperated Survival : <10% survival at 1 year (diminished PBF group) / 50% survival at 1 year (increased PBF group).
- Post-Fontan Sequelae : Atrial arrhythmias / Protein-losing enteropathy / Hepatic dysfunction / Progressive LV dysfunction.
- Transplant-Free Survival (Post-Fontan) : ~90% at 10 years. Prognosis heavily dependent on preservation of LV function and competence of mitral valve prior to Fontan completion.