Background

Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart disease (CHD).¹ Early management of this condition is typically dictated by the degree of pulmonary stenosis (PS) and resulting oxygen saturations. There is variation in clinical practice in both preoperative and postoperative follow-up and timing for intervention for patients with TOF.²

Historically, this was the first cyanotic heart condition treated by surgical intervention. In 1944, the Blacklock-Taussig-Thomas anastomosis of the subclavian artery to the pulmonary arteries (PAs) supplied much needed additional pulmonary blood flow.² In the following two decades, effective cardiopulmonary bypass, prostaglandin therapy, rise of echocardiography, and advanced surgical techniques allowed for intracardiac repairs that have forever changed the long-term outcomes for patients with this condition.² More recently, advances in interventional cardiology techniques have allowed for nonsurgical options for both palliation before complete repair and pulmonary valve (PV) replacement later in life.^2,3

Goals and Details of the Algorithm

This clinical practice algorithm was developed with the primary goal of creating a decision support tool to help cardiologists and other health care providers in the management of TOF both before and after repair. These recommendations do not replace clinical judgment but rather attempt to improve the value of care by reducing practice variation and optimizing resource utilization. For algorithm development, TOF was divided into unrepaired and repaired states. Important considerations include age of the patient, degree of PS, presence of patent ductus arteriosus (PDA), evidence of hypercyanotic spells, and degree of residual lesions following repair. Patients with major aortopulmonary collaterals, absent PV, or significant comorbidities (including significant CHD, such as atrioventricular septal defects) were excluded because their management is different and more complex. Of note, patients with DiGeorge (22q11.2 deletion) syndrome remain included, both because they constitute a significant proportion of patients with TOF (8-35%) and because their cardiac management and outcomes do not significantly differ from others.⁴

Broad unrepaired physiologic categories include inadequate pulmonary blood flow, well-balanced circulation, or pulmonary overcirculation. Oxygen saturations should be monitored closely to determine physiologic condition and guide timing of intervention. If PS is minimal, presence of symptoms of pulmonary overcirculation is an indication for medical therapy followed by surgical intervention similar to isolated large ventricular septal defects (VSDs). Well-balanced circulation suggests there is adequate PS to allow for both an adequate amount of pulmonary blood flow and protection from overcirculation. These patients will typically undergo surgical repair at 3-6 months of age.² Patients with significant PS prohibiting adequate flow to the lungs require earlier intervention: systemic-to-PA shunt/PDA stent palliation versus complete repair. If a neonatal intervention is necessary, the specific decision on intervention (surgical shunt, PDA stent, right ventricular [RV] outflow tract stent, or neonatal repair) should be based on individual patient characteristics and institutional preferences. Additional imaging, such as cross-sectional imaging, may be needed to assist planning of intervention. Notably, neonatal repair has been shown to be associated with increased morbidity and mortality compared with repair later in infancy, although some centers have been able to achieve excellent outcomes.⁵ In addition, palliative procedures carry their own risks, such as the potential for shunt/stent narrowing or occlusion as well as the need for re-intervention.

Similarly, anatomical characteristics and institutional practices dictate the type of complete repair, including transannular patch or valve-sparing approaches, or placement of an RV-to-PA conduit. It is important to note that the natural history of PS is to increase over time, and dynamic obstruction and changes in pulmonary vascular resistance can result in hypercyanotic spells, acutely limiting pulmonary blood flow and necessitating urgent evaluation.¹ Beta-blocker therapy is often used in patients with evidence of dynamic obstruction, slowing the heart rate to allow for improved cardiac output, although there is no evidence to support this management.

Follow-up and management of patients with repaired TOF is primarily dictated by degree of residual lesions, including residual PS, resultant pulmonary regurgitation (PR), or residual VSD. Patients with repaired TOF require lifelong periodic surveillance testing even if residual lesions are minimal and without symptoms, as intervention is often recommended before development of symptoms.^6-8 Comprehensive care of patients with repaired TOF is necessary and requires multiple diagnostic tools. Echocardiography is an accessible and noninvasive method to routinely evaluate for structural changes over time, and cardiopulmonary exercise testing can assist with understanding functional capacity as well. Patients are also at risk of arrhythmia and sudden cardiac death, so electrocardiograms and ambulatory monitors offer periodic electrophysiologic evaluation. Cardiac magnetic resonance imaging should also be obtained at regular intervals to better quantify important measures, such as ventricular systolic function, RV size, and degree of valvular regurgitation.⁹ Addressing residual PS or PR can be accomplished surgically or by catheter-based PV replacement. The specific choice for re-intervention remains patient and institution specific. Most patients will require more than one re-intervention in their lifetimes, which is often a blend of the two options.

Methods: Algorithm Development

The CHD Clinical Practice Algorithm for Unrepaired and Repaired TOF was developed by the Quality Working Group of the American College of Cardiology (ACC) Adult Congenital and Pediatric Cardiology (ACPC) member section. This group includes experienced pediatric and adult congenital cardiologists with multidisciplinary expertise and diverse training and practice backgrounds. This algorithm was designed in a similar fashion to previously published practice algorithms from the same group on other forms of CHD. Existing guidelines were used when available and applicable.^6,7,9,10 The included TOF algorithm was discussed and peer reviewed for consensus.

Future Directions

The goal of the ACC ACPC Quality Working Group is to provide clinical practice tools for cardiology providers, ultimately to reduce practice variability in CHD. In addition, the use of these algorithms for the education of noncardiologists may prevent inappropriate referrals and unnecessary resource utilization.

References

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2. Clarke NS, Thibault D, Alejo D, et al. Contemporary patterns of care in tetralogy of Fallot: analysis of the Society of Thoracic Surgeons data. Ann Thorac Surg 2023;116:768-75.
3. Georgiev S, Ewert P, Eicken A, et al. Munich Comparative Study: prospective long-term outcome of the transcatheter Melody valve versus surgical pulmonary bioprosthesis with up to 12 years of follow-up. Circ Cardiovasc Interv 2020;13:[ePub ahead of print].
4. Goldmuntz E. 22q11.2 deletion syndrome and congenital heart disease. Am J Med Genet C Semin Med Genet 2020;184:64-72.
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10. Stout KK, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ACC guideline for the management of adults with congenital heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol 2019;73:e81-e192.