Authors: Amy Babb, MD - Vanderbilt University Medical Center AND
Kaitlin Flannery, MD - Stanford University
An infant with Tetralogy of Fallot, pulmonary atresia and major aortopulmonary collateral arteries (TOF/PA/MAPCAs) presents for unifocalization. An intraoperative pulmonary artery flow study is requested by the surgeon. Which hemodynamic value obtained during the flow study is MOST likely to predict a successful repair with VSD closure and RV-PA conduit after unifocalization?
EXPLANATION
TOF/PA/MAPCAs describes a heterogeneous type of congenital heart disease with an outlet ventricular septal defect (VSD), pulmonary atresia (PA) and variable sources of pulmonary blood flow via collateral vessels. Standard surgical repair involves unifocalization of MAPCAs to form a reconstructed pulmonary artery tree using both native and homograft tissue. After the pulmonary arteries have been unifocalized, the next step consists of closure of the VSD and addition of an RV-PA conduit. Some patients will undergo unifocalization with complete intracardiac repair in one procedure, while others will require a staged approach.
It remains difficult to predict if a newly reconstructed pulmonary artery bed will be adequate to accommodate a full cardiac output after VSD closure. An insufficient pulmonary bed will result in elevated right ventricular systolic pressure (RVSP) and RV failure. Methods of predicting successful intracardiac repair based on anatomic metrics, such as neopulmonary artery index and pulmonary segment artery ratio, have been tried. In 2009, a study by Honjo et al concluded that a mean pulmonary artery pressure (mPAP) less than 30 mmHg at a cardiac index of 2.5 L/min/m2 could predict a reasonable RV pressure after unifocalization with VSD closure better than anatomic characteristics.1 In 2016, Zhu et al demonstrated that VSD closure with mPAP greater than 25 mmHg on flow study is a predictor of mortality following unifocalization.2
Intraoperative pulmonary artery flow study is performed after PA unifocalization. The surgeon will place an aortic-sized cannula into the newly reconstructed PAs for flow from the cardiopulmonary bypass circuit.3 A small needle is placed into the PAs and attached to pressure tubing with a transducer to monitor PA pressures. The anesthesiologist will ventilate the lungs while the perfusionist ramps up flows into the pulmonary arteries with the goal of achieving a cardiac index of 2.5 – 3.0 L/min/m2. Ventilation with tidal volumes of 2-5 mL/kg with respiratory rate of 30-35 breaths/min will simulate normal cardiopulmonary interactions.4 If mPAPs are higher than 25-30 mmHg at the target cardiac index, the right ventricle will likely struggle with VSD closure. Significant bleeding from the reconstructed PAs should be ruled out for an accurate interpretation. Flow studies have been shown to have reasonable correlation with post-operative RVSP, and be a better predictor than simple anatomic assessments.1 Alternative strategies to VSD closure after failed flow study include central shunt placement or VSD closure with fenestration.
REFERENCES
1. Honjo O, Al-Radi O, MacDonald C, Tran K. et al. The Functional Intraoperative Pulmonary Blood Flow Study is a More Sensitive Predictor than Preoperative Anatomy for Right Ventricular Pressure and Physiologic Tolerance of Ventricular Septal Defect Closure after Complete Unifocalization in Patients with Pulmonary Atresia, Ventricular Septal Defect, and Major Aortopulmonary Collaterals. Circulation. 2009; 120(11) supp 1: s46-s52.
2. Zhu J, Meza J, Kato A, et al. Pulmonary flow study predicts survival in pulmonary atresia with ventricular septal defect and major aortopulmonary collateral arteries. J Thorac Cardiovasc Surg. 2016; 152(6):1494-1503.e1. doi:10.1016/j.jtcvs.2016.07.082
3. Margetson TD, Sleasman J, Kollmann S, McCarthy PJ, et al. Perfusion Methods and Modifications to the Cardiopulmonary Bypass Circuit for Midline Unifocalization Procedures. J Extra Corpor Technol. 2019; 51(3):147-152.
4. Quinonez ZA, Laura D, Abbasi RK, et al. Anesthetic management during surgery for tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries. World J Pediatr Congenit Heart Surg. 2018; 9(2): 236-41.
