Tetralogy of Fallot/Pulmonary Atresia/Major Aortopulmonary Collateral Arteries

Tetralogy of Fallot/Pulmonary Atresia/Major Aortopulmonary Collateral Arteries

Anesthetic relevance
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Signs and symptoms
Diagnosis
Treatment
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Major aortopulmonary collateral arteries (MAPCAs) are present in 20-25% of patients with Tetralogy of Fallot plus pulmonary atresia. Overall condition of TOF/PA/MAPCAs incidence of 0.7 per 10,000 live births. Associated DiGeorge syndrome (22q11 deletion) in >35% of patients. Oxygenation dependent on ratio of pulmonary to systemic blood flow (Qp/Qs). Often undergo a single complete repair vs. a staged repair.

Anesthetic implications

Preoperative optimization

Basic laboratory data including CBC with differential, basic metabolic panel, and coagulation studies. ECG, chest X-ray. Recent (within 6 months) transthoracic echocardiography. Cardiac catheterization with angiography with characterization of MAPCAs. Review prior cardiac catheterization anesthetic record for hemodynamic instability or desaturations, which may be an indication of MAPCA spasms (can occur again during surgical dissection).

Intraoperative management

Most patients can safely undergo inhalational induction with sevoflurane (except those with congestive heart failure or extreme cyanosis). Adjust FiO2 to maintain oxygen saturation 75-85% (balanced Qp/Qs). DiGeorge patients may prove more difficult to intubate.

Patients may have tortuous peripheral veins. Due to large potential blood loss, recommend 2 large peripheral IVs for patients having initial surgery; for patients with prior sternotomies or thoracotomies, recommend single lumen introducer and rapid blood product infuser. Additionally, placement of RIJ CVC for CVP monitoring. Try to save femoral veins for future cardiac catheterization procedure, however, can use if need more access. Arterial access in a radial artery for blood pressure monitoring and obtaining blood gas samples. May consider a femoral artery catheter if concerned about accurate blood pressure waveform; alternatively, can request surgeon connect pressure tubing to arterial bypass cannula to transduce aorta (temporary until recovery of radial waveform).

To avoid drops in systemic blood pressure, avoid inhaled anesthetic agents after induction. Maintenance with TIVA: various combinations of infusions of fentanyl, midazolam, ketamine, or dexmedetomidine with a longer acting nondepolarizing neuromuscular blocker infusion. Tend to avoid propofol due to risk of interfering with cardiopulmonary bypass oxygenator, or concern of metabolic acidosis.

Dissection around MAPCAs with large contributions to pulmonary blood flow may lead to desaturations and metabolic acidosis. Usually done off CPB if tolerated.

Postoperative management

Transfer to CVICU intubated for continued monitoring and resuscitation/repletion of blood products.

Related surgical procedures

Cardiac catheterization lab procedures after surgical repairs: branch PA stenosis ballooning, Melody or Harmony valves

Pathophysiology

Oxygenation dependent on ratio of pulmonary to systemic blood flow (Qp/Qs). MAPCA morphology can be a large determinant of this balance of blood flows. Large unobstructed MAPCAs can lead to adequate oxygenation but over-circulation due to unrestricted pulmonary blood flow, which may cause heart failure. Stenotic or tortuous MAPCAs lead to restricted pulmonary blood flow with limited oxygenation, but seldom to cause heart failure.

Diagnosis

Neonatal evaluation:

Estimate overall pulmonary blood flow, based on systemic oxygen saturation: high pulmonary blood flow >90%, low pulmonary blood flow < 75%, balanced pulmonary blood flow 75-90%. In most cases, newborns are within 75-90% systemic oxygen saturation and there no clinical need for neonatal intervention*.

*Two variants of pulmonary blood supply merit neonatal intervention: 1) unilateral ductus arteriosus (or anomalous PA from ascending aorta) with MAPCAs to other lung. 2) centrally confluent native PAs that arborize to all lung segments, with all dual supply MAPCAs

If systemic oxygen saturation <75% or > 90% (regardless of anatomy of pulmonary blood supply), then neonatal surgery is performed

Pre-surgical work-up:

Intracardiac anatomy determined by echocardiography.

Computed tomography or angiography used to determine the anatomy of the pulmonary blood supply including presence of central pulmonary arteries and MAPCA supply (single vs dual).

Treatment

Surgery

If stable, elective repair at around 4-7 months old.

Single-staged complete repair: complete unifocalization and intracardiac repair (VSD closure and conduit from right ventricle to unifocalized pulmonary arteries)

Palliation: AP window or unifocalization to a shunt (systemic to PA)

Note that unifocalization refers to incorporation of MAPCAs and PAs into a single central pulmonary artery system, additionally with augmentation/reconstruction of stenotic or hypoplastic branches.

A flow study can be conducted intra-operatively to assess for candidacy for intracardiac repair. Patients with a flow study with low PA pressures (<= 25 mmHg) at physiologic flows will have a intracardiac repair performed. Patients with a flow study with high PA pressures (> 25 mmHg) at slightly supraphysiologic levels of flow will have a systemic-to-PA shunt placed.

Epidemiology

Overall condition of TOF/PA/MAPCAs incidence of 0.7 per 10,000 live births. Associated DiGeorge syndrome (22q11 deletion) in >35% of patients.