Author: Destiny F. Chau MD - Arkansas Children’s Hospital /University of Arkansas for Medical Sciences, Little Rock, AR.
A 6-month-old infant is undergoing a full repair for Tetralogy of Fallot. The patient separates from cardiopulmonary bypass (CPB) on milrinone 0.05 mcg/kg/min, dexmedetomidine 0.5 mcg/kg/h and morphine 0.025 mg/kg/h. The surgeon measures a right ventricular (RV)-to-aortic pressure ratio of 0.5, and right ventricular outflow tract (RVOT) gradient of 30 mmHg. Ten minutes later the vital signs are: BP 50/38, HR 167 bpm in sinus rhythm, SpO2 100%, with adequate anesthetic depth. The transesophageal echocardiogram (TEE) is now showing hyperdynamic right ventricular systolic function with subvalvar obstruction. In addition to volume administration, what is the recommended next step in management?
Tetralogy of Fallot is the most common type of cyanotic congenital heart disease, representing approximately 10% of all congenital heart defects with an estimated incidence of 1 in 2,500– 3,000 live births. It was first comprehensively described by Etienne Fallot in 1888 as a group of four characteristic features: ventricular septal defect (VSD), overriding aorta, right ventricular outflow tract obstruction (RVOTO) and right ventricular hypertrophy. In 1924, Maude Abbott coined this cardiac abnormality as “tetralogy of Fallot”.
Tetralogy of Fallot was the cardiac anomaly for which the first Blalock-Taussig-Thomas shunt (BTTs) was performed to augment pulmonary blood flow in 1945. This successful operation launched the modern era of congenital cardiac repair. Although the timing, techniques and approaches of surgical repair, and overall medical management of TOF have evolved in the decades since the BTTs, the surgical goals remain the same: closure of the VSD and establishment of pulmonary blood flow.
A 2022 expert consensus from the American Association for Thoracic Surgery by Miller et al published recommendations for the management of pediatric patients with tetralogy of Fallot. For assessing adequacy of surgical repair, the panel recommends direct pressure measurements to objectively evaluate for residual obstruction and guide any need for reintervention, and recommends to aim for RV-to-aortic pressure ratio of 0.5 or less with an RVOT gradient less than 30 to 40 mm Hg. These parameters must be considered in the context of the patient’s condition and specific anatomic limitations to surgical resection. After relief of RVOTO , dynamic outflow obstruction associated with a hypertrophied RV is not uncommon, especially in the setting of relative hypovolemia and a hypercontractile right ventricle. Anticipatory management for set hemodynamic goals is indicated, which includes optimization of RV preload with adequate volume administration, minimization of hypercontractility, and maintaining adequate diastolic filling time via heart rate control. Hyperdynamic obstruction improves over time as the hypertrophied RV remodels once the primary obstruction has been reduced.
In the setting of adequate surgical results which in this case is supported by the initial RVOT gradient and RV-to-aorta pressure ratio, the hemodynamic decline in this patient is most likely due to hyperdynamic obstruction from the pre-existing hypertrophied RV. Management for this condition would be to maintain filling pressures with volume administration, minimization of inotropic agents such as calcium and epinephrine, and slowing of the heart rate to allow for increased diastolic filling time. An esmolol drip is helpful for controlling the tachycardia. If these medical interventions fail to restore hemodynamic stability, other etiologies should be sought. The surgeon should be notified and the cardiac status reevaluated via TEE and repeat pressure measurements as necessary. A return to CPB may be needed if evidence suggests that surgical reintervention is necessary.
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