Recognition of a cardiac differential diagnosis for bronchiolitis: coronary steal phenomenon in a baby with anomalous right pulmonary artery arising from the aorta

A COVID-19-positive baby with acute respiratory failure and a working diagnosis of bronchiolitis deteriorated rapidly despite usual resuscitative measures. Respiratory acidosis and oxygenation improved with invasive ventilation; however, the patient became progressively hypotensive and showed a poor response to vasopressors. Bedside ultrasound showed right heart dilatation, troponin was raised, and the ECG had ischaemic changes. Echocardiography diagnosed anomalous aortic origin of the right pulmonary artery (RPA), with continuous left-to-right shunt and holodiastolic flow reversal in the abdominal aorta. This raised suspicion of a coronary steal phenomenon, explaining deterioration in response to typical resuscitation. An oxygen saturation (SpO2) target of 80-88% and permissive hypercapnia helped restore balanced circulations and improve coronary perfusion. He ultimately underwent a complete surgical repair with good recovery. We discuss opportunities for earlier recognition of cardiac differential diagnoses in a neonate with respiratory failure, including the use of bedside ultrasound, which is of interest to paediatric generalists, intensivists and emergency practitioners.