Surgically corrected univentricular hearts. Anatomical, haemodynamic and functional status at a long-term follow-up
Abstract: The Fontan operation and its modifications are applied to a large spectrum of congenital heart defectswith univentricular physiology. The Fontan circulation is characterised by a reduced, non-pulsatilepulmonary blood flow and the elevated central venous pressure is the main driving force for thepulmonary blood flow. This has important consequences for the cardiorespiratory response toexercise.The development of pulmonary arteriovenous malformations is a major cause of progressivecyanosis after surgery.Aims: To investigate the prevalence of pulmonary arteriovenous malformations in patients withdifferent forms of cavopulmonary anastomosis, to evaluate the role of hepatic venous blood in theirdevelopment and to compare the sensitivity of contrast echocardiography with that of pulmonaryangiography in detecting the shunts. To study to what extent a long-standing situation of reducedpulmonary blood flow has had effects on the lung function and exercise capacity and to study thecardiac output regulation and pulmonary gas exchange at rest and during exercise.Material and Methods: We studied 20 of the surviving Fontan patients operated between 1980-1991in Göteborg. The median age at investigation was 17.5 years and the median follow-up time was11.5 years. All patients underwent cardiac catheterisation, pulmonary angiography and bubble contrastechocardiography. They also performed lung function tests. Fifteen patient were subjected to cardiacoutput determination, measurements of intraarterial blood pressure and pulmonary gas exchange.Results: Nine (45%) of the 20 patients, had positive contrast echocardiography. In only two cases wasthere angiographic evidence of pulmonary arteriovenous malformations (10%). All patients had thepulmonary arteriovenous malformations in the lung with no or minimal hepatic venous blood flow.The lung volumes, maximal expiratory flows and diffusion capacity were significantly lower thanexpected. The median maximal oxygen uptake was 25 ml/kg/min. Cardiac output was lower thanexpected at all exercise levels. The patients compensated for the reduced cardiac output with anincreased arteriovenous oxygen difference. Patients with known moderate or severe right-to-left shuntshad lower PaO2 and SaO2 values and higher PA-aO2 values both at rest and during maximal exercise,compared to those with mild or no shunts.Summary: Bubble contrast echocardiography is much more sensitive in detecting pulmonaryarteriovenous malformations than pulmonary angiography. Lack of hepatic venous blood flow to thepulmonary circulation is probably the most important factor for the development of the shunts. Thepatients had small lung volumes, markedly reduced exercise capacity and low maximal heart rate. Thecause of the reduced exercise is multifactorial. Abnormal exercise performance is characterised byincreased O2-extraction and a depressed stroke volume. Preload to the systemic ventricle in a Fontancirculation is determined by the pulmonary blood flow. A reduced pulmonary blood flow leeds toreduced filling of the systemic ventricle. A reduced preload is therefore of great importance to explainthe reduced stroke volume. An impaired chronotropic function was also present and influenced theexercise capacity but was not the main factor.
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