Tricuspid Atresia

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).

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.

Flow Pathway : Systemic venous return $\to$ RA $\to$ ASD/PFO $\to$ LA (mixes with pulmonary venous return) $\to$ LV $\to$ Aorta (Systemic).
Pulmonary Flow Source : LV $\to$ VSD $\to$ Hypoplastic RV $\to$ 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.

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)).

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).

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).

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

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.

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.

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.

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.