Ventricular Volume Overload as an Overlooked Complication of IPAS: A Call for Comprehensive CMR Evaluation.

Description of Clinical Presentation: We present a case of asplenia syndrome patient with single ventricle, pulmonary atresia, and massive atrioventricular valve regurgitation, who underwent Glenn procedure and atrioventricular valve replacement (AVVR) in early infancy. At four months of age, Intrapulmonary Artery Septation (IPAS) procedure was performed due to insufficient right pulmonary growth. Given the patient's unexpectedly stable post-IPAS course and preserved cardiac function, we were monitoring for the optimal timing for Fontan completion by combining cardiac catheterization and CMR, as suggested by Ishidou et al. The patient underwent a shunt revision from a 3mm BT shunt (BTS) to a 3.5mm central shunt at two years of age. At five years of age, the patient underwent an reAVVR with simultaneous relief of right pulmonary vein stenosis (PVS). However, a repeat PVS relief was needed seven months after the previous surgery due to the re-stenosis, during which the central shunt was also upsized to 4 mm. Three months postoperatively, however, a follow-up cardiac catheterization revealed a rise in both end diastolic pressure (EDP) and mean pulmonary pressure (mPAP), as well as progressive ventricular dilation also confirmed by CMR.

Diagnostic Techniques and Their Most Important Findings: We calculated the right and left pulmonary vascular resistance by combining pressure data from cardiac catheterization with pulmonary flow data from CMR. Based on these values, the predicted total post-Fontan PVR (ptPVR) and the pulmonary blood flow distribution were serially assessed at each shunt upsizing. The ptPVR was remained 1.9WU/m² regardless of whether the shunt size was 3.0mm or 3.5mm. However, the ptPVR deteriorated to 2.5WU/m² after the shunt upsizing from 3.5 mm to 4.0mm. PA Index has improved from 120 to 180mm²/m² and the right-to-left pulmonary flow ration was improved to 4:6. However, at the same time, end diastolic volume index was enlarged from116 to152ml/m². The cardiac catheterization also revealed a rise in EDP from 3mmHg to 7mmHg. We hypothesize that the shunt-induced pulmonary overcirculation resulted in chronic volume overload, subsequently elevating the EDP and causing a secondary increase in mPAP and PVR. The patient's data were within the acceptable range for a Fontan procedure. We concluded that any further waiting would only lead to clinical deterioration. Therefore, a Fontan procedure is currently being planned.

Learning Points from this Case: The management of IPAS patients, particularly after PVO relief, requires a delicate balance. While waiting for pulmonary artery growth is a goal, clinicians must be vigilant for the risks of shunt-related volume overload. An overly conservative 'wait-and-see' approach　can paradoxically become a significant risk to the patient. Therefore, in the CMR assessment, attention should not be limited to calculating flow distribution and resistance; a thorough and serial analysis of ventricular volumes and function is essential to detect early signs of decompensation.