Pre-intervention morphologic and functional echocardiographic characteristics of neonates with critical left heart obstruction: a Congenital Heart Surgeons Society (CHSS) inception cohort study. 
The aims of this study were to provide a detailed descriptive analysis of pre-intervention morphologic and functional echocardiographic parameters in a large, unselected, multicentre cohort of neonates diagnosed with critical left heart obstruction and to compare echocardiographic features between the different subtypes of left-sided lesions.  Pre-intervention echocardiograms for 651 patients from 19 Congenital Heart Surgeons' Society (CHSS) institutions were reviewed in a core lab according to a standardized protocol including >150 morphologic and functional variables.  The four most common subtypes of lesions were: aortic atresia (AA)/mitral atresia (MA) (29% of patients), AA/mitral stenosis (MS) (20%), aortic stenosis (AS)/MS (26%), and isolated AS (iAS) (18%).  Only 17% of patients with AS/MS had an apex-forming left ventricle, compared with 0% of those with AA/MA and AA/MS (P < 0.0001).  Aortic arch hypoplasia and coarctation were common across all four groups, while those with AA/MA and AA/MS had the smallest ascending aorta diameters.  Flow in the ascending aorta was retrograde in 43% and 10% of the patients with AS/MS and iAS, respectively.  The right ventricle was apex forming in 100% of patients with AA/MA and AA/MS, 96% with AS/MS and 70% with iAS (P < 0.0001).  Moderate to severe tricuspid regurgitation was present in 13% of all patients.  This large multi-institutional study generates insight into the distribution of the functional and morphologic spectrum in patients with critical left-sided heart disease and identifies differences in these functional and morphologic characteristics between the main anatomic subtypes of critical left heart obstruction.