Exercise Tolerance in Extracardiac Total Cavopulmonary Connection
Antonio F Corno, MD, FRCS(Glas), FACC, FETCS
Antonio F Corno MD, FRCS(Glas), FACC, FETCS Tel: +44 151 2824 514-5 Fax: +44-151-2525-643 Email: Antonio.Corno{at}alderhey.nhs.uk, Consultant Paediatric Cardiac Surgeon, University of Liverpool, Alder Hey Children NHS Foundation Trust, Eaton Road, Liverpool, UK.
The authors have presented their clinical experience of evaluating exercise tolerance after extracardiac total cavopulmonary connection in 41 patients. The preoperative hemodynamic data (end-diastolic ventricular pressure, mean pulmonary artery pressure, pulmonary vascular resistance, oxygen saturation) reported with the characteristics of the patient population confirm that the authors included some who were less than ideal candidates for a Fontan-type circulation, because of either elevated end-diastolic ventricular pressure or elevated pulmonary artery pressure and resistance. From the available clinical data, it seems also that a previous bidirectional Glenn anastomosis (end-to-side superior vena cava-to-right pulmonary artery) had been performed in only 4/41 (10%) patients; if the interpretation of this figure is correct, in 90% of patients, the total cavopulmonary connection was performed as a one-stage surgical procedure, policy quite different from that in the vast majority of clinical practices where the bidirectional Glenn precedes completion of the total cavopulmonary connection to volume unload the functionally single ventricle. This observation should be taken in account when considering the evaluation of exercise tolerance in patients with a mean age of 4 ± 3.6 years (range, 3–28 years) with a functionally single ventricle exposed to chronic volume overload. Unfortunately, a comparison with the results after long-term palliation with the bidirectional Glenn has not been undertaken; this information would be particularly useful considering the recent literature advocating the bidirectional Glenn with another source of antegrade pulmonary blood flow as a very good alternative to a total cavopulmonary connection in selected groups of patients.
Most of the discussion focused on the delicate balance between increased venous return to the left atrium during exercise in patients with a fenestrated total cavopulmonary connection, thanks to the increased right-to-left shunt in correspondence with the fenestration, and the subsequently decreased systemic oxygen saturation with worsening cyanosis and activity intolerance. In this regard however, the most original and intriguing message coming from this paper is the correlation between the increase in heart rate with physical exercise and enhancement of sinus node excitability due to an increase in temperature of the blood perfusing the sinus node, due to muscle heat production on exercise. The authors do not provide any evidence to support their speculation. No evidence has been given regarding heat produced in the systemic venous blood from physical activity, nor on the effects of this heat on sinus node function for temperature considered to be around the normal value of 37°C. Furthermore, the authors have not considered the effect on physical activity of the temperature of the pulmonary venous return, possibly modified by respiration; the external air temperature could play a role. Finally, if their hypothesis is correct, better performance should have been observed in the group of patients without fenestration than in those with fenestration; in fact, in the first group, warmer blood reaches the sinus node later than in the group with fenestration, and thus better performance should be obtained in the presence of a fenestration.
The suggestion of considering an extracardiac total cavopulmonary connection with autologous pedicled pericardium to preserve SA node function is definitely another option favoring long-term preservation of myocardial function. Finally, the authors did not provide information on their indications for fenestration at the time the study was performed. It would be interesting for readers to know about any changes in their policy after completion of the current study.
Asian Cardiovasc Thorac Ann 2009;
17:45
© 2009 by SAGE Publications
DOI: 10.1177/0218492309102259
