Tetralogy of Fallot (TOF) Hemodynamics

Date
July 20, 2025
URL
https://x.com/WithAScalpel/status/1946902694372737238
Categories
TOF

Tetralogy of Fallot (TOF) – Hemodynamics

Preoperative Hemodynamics

Tetralogy of Fallot is defined by the classic tetrad: right ventricular outflow tract obstruction (RVOTO), ventricular septal defect (VSD), overriding aorta, and right ventricular hypertrophy.

  • Right-to-left shunt: Due to RVOTO and VSD, blood is shunted from the right to the left ventricle, producing systemic desaturation and cyanosis.
  • Reduced pulmonary blood flow: The obstruction decreases pulmonary perfusion, leading to reduced left ventricular preload. Chronic underfilling often results in a small LV.
  • Overriding aorta: The aorta straddles the septal defect, receiving mixed blood from both ventricles, further contributing to systemic desaturation.
  • RV pressure load: The elevated right ventricular pressure caused by RVOTO leads to RV hypertrophy. Pulmonary arteries are frequently hypoplastic, and in some cases, pulmonary blood supply depends on major aortopulmonary collateral arteries (MAPCAs).

Postoperative Hemodynamics

Surgical repair of TOF typically involves closure of the VSD and relief of RVOTO, often with a transannular patch across the pulmonary valve annulus.

  • Improved LV preload: Restoration of pulmonary blood flow increases pulmonary venous return, improving LV filling and growth.
  • Pulmonary regurgitation (PR): A nearly universal consequence of transannular patch repair, PR imposes chronic RV volume overload. This is one of the most important long-term issues after TOF repair.
  • RV dysfunction and arrhythmias: Extensive RV incision or patch enlargement can compromise RV contractility and predispose to ventricular arrhythmias. Chronic RV dilation and dysfunction are major determinants of late morbidity and mortality.

Clinical Summary

  • Before repair: TOF physiology is dominated by a right-to-left shunt across the VSD, reduced pulmonary blood flow, systemic desaturation, and RV hypertrophy. The LV is often underfilled and hypoplastic.
  • After repair: Hemodynamics improve with restoration of pulmonary flow and LV preload, but long-term outcomes depend on management of pulmonary regurgitation, RV dilation, and arrhythmia risk.