The most comprehensive data available on early survival of neonates born with critical aortic valve stenosis are those reported from the Congenital Heart Surgeons Society study: an initial “biventricular repair”, essentially balloon or open aortic valvotomy, was done in 116 patients, and an initial Norwood operation in 179.2
Mathematical models for survival were calculated for each pathway and then used to predict the optimal pathway for each patient, based on functional and morphological features. Not surprisingly, the neonates entered on the biventricular repair pathway had greater aortic valve, aortic root, and mitral valve indexed diameters than the Norwood cohort. Surprising, perhaps, was a predicted five year survival benefit favouring the Norwood pathway in 50% of those who had biventricular repair. Conversely, biventricular repair was predicted as more favourable in 20% of those neonates who underwent the Norwood procedure. The main risk factors for death after aortic valvotomy were young age, a small aortic valve, a short left ventricle, and a high grade of “endocardial fibroelastosis”. The last of these was graded subjectively by echocardiography, but this grading correlated only weakly with necropsy grading of endocardial fibroelastosis in the hearts that were available for comparison. This suggests that it should not be assumed that bright endocardial echoes necessarily reflect the same process, even if this appearance provides useful prognostic information.
Late follow up data after neonatal interventions for critical aortic stenosis are lacking. Our previous experience was that hospital survivors of aortic valvotomy had reasonable medium term survival (93% at 10 years, 84% at 15 years) with a good functional result, though often with the need for further left ventricular outflow tract surgery.1
We had not recognised late pulmonary hypertension in survivors of neonatal intervention for critical aortic stenosis at the time of that report. Similar medium term (more than five years) follow up data were reported for neonates operated in the same era.4,5
Left ventricular outflow tract obstruction in fetal life is known to cause endocardial fibroelastosis,6,7
with increased production of collagen and elastic fibres. There may also be other myocardial changes such as fibrosis, necrosis, or calcification, perhaps explaining some of the discrepancy between bright left ventricular endocardial echoes and the histological diagnosis of endocardial fibroelastosis. Almost certainly, an increasing number of neonates with these myocardial changes in the context of critical aortic valve stenosis have been surviving neonatal interventions over the past decade.
The likely explanation for the severe pulmonary hypertension persisting up to 12 years after neonatal aortic valve surgery in the patients in this report is restriction to left ventricular filling. Bright left ventricular endocardial echoes were seen prenatally in the two patients who underwent prenatal echocardiography. Endocardial fibroelastosis was confirmed by left ventricular myocardial biopsy in a third patient. Pulmonary hypertension is a well known consequence of restrictive cardiomyopathy8
and isolated endocardial fibroelastosis.9
Interestingly, isolated endocardial fibroelastosis is now rarely seen, possibly because of a link between this condition and the mumps virus, which is now uncommon since the introduction of the MMR vaccine.10
The recent data referred to above have provided information about the interventional strategy (aortic valvotomy versus Norwood procedure) that is most likely to result in survival up to five years after neonatal intervention for critical aortic valve stenosis.2,3
However, it was acknowledged that these data could not yet examine long term complications.3
Late problems occur with a functionally single ventricle surgical strategy, even in patients with a good medium term outcome. In those who undergo biventricular repair, the likely need for further intervention because of recurrent left ventricular outflow obstruction or aortic regurgitation is well known. Restriction to left ventricular filling secondary to altered heart muscle physiology may be an additional important determinant of the long term outcome. Further information about this previously unreported late complication of “biventricular repair” may help to inform the decision about whether to use neonatal aortic valvotomy or the Norwood operation, and may also lead to consideration of additional or alternative surgical approaches such as left ventricular endocardial resection and autograft replacement of the aortic root, or transplantation, in selected patients.