Abstract Body (Do not enter title and authors here): Background:
Pulmonary arteriovenous malformations (PAVMs) are a universal complication in single ventricle heart disease, but the tools to assess them are limited. In this study, we examined how a novel angiographic method of PAVM measurement, pulmonary capillary transit time (PCTT) - the time taken for contrast to traverse the pulmonary capillary bed - compared with the conventional diagnostic standard of bubble echocardiography. We also compared PCTT across single ventricle palliative stages (pre-Glenn, pre-Fontan, and post-Fontan), as well as to another conventional PAVM diagnostic tool, pulmonary vein oxygen saturations.

Methods:
We performed a retrospective study of patients who underwent single ventricle palliation at Children’s Wisconsin from 2012 to 2024. We identified patients who had bubble echocardiography performed concurrently with pre-Fontan catheterization and then measured PCTT (number of cardiac cycles) for each lung independently and compared this to ipsilateral bubble echo severity (trivial/mild, moderate, or severe). We also identified patients with catheterizations at each circulatory stage (pre-Glenn, pre-Fontan, and post-Fontan) and measured PCTT at each stage.

Results:
Among 28 patients with concurrent cardiac catheterization and bubble echocardiography at the pre-Fontan stage, PCTT was lowest in lungs with severe bubble echo shunting (Trivial/mild: 2.85 ± 0.50; moderate: 2.40 ± 0.38; severe: 1.60 ± 0.57; p<0.001 for severe compared to both trivial/mild and moderate). PCTT also correlated with concurrent descending aorta saturation (R²=0.16, p=0.04) and peripheral oxygen saturation prior to Fontan (R²=0.17, p=0.03). Among 19 patients who had cardiac catheterizations performed at each palliative stage, PCTT was shortest in those with Glenn circulation (pre-Glenn: 3.23 ± 1.01; pre-Fontan: 2.12 ± 0.57; post-Fontan: 2.90 ± 0.76; p<0.01 for pre-Fontan compared to both pre-Glenn and post-Fontan).

Conclusions:
We show that shorter PCTT is associated with severe PAVM shunting on concurrent bubble echocardiography. Our findings reproduce and add to previous findings that PCTT is a promising and novel diagnostic tool for assessing severity of single ventricle PAVMs. PCTT may help facilitate multi-institutional studies into single ventricle PAVMs and obviate the need for bubble echocardiography in these patients.