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Ann Thorac Surg 2004;78:1971
© 2004 The Society of Thoracic Surgeons
Department of Surgery, Columbia Presbyterian Medical Center, 3959 Broadway, CHN #274, New York, NY 10032, USA
Ventricular function and cardiac work are crucial determinants in the outcome of patients with palliated single ventricle anatomy. Optimizing ventricular mass/volume ratio and controlling the ventricular afterload are critical to promote ventricular efficiency. Selecting the appropriate aortopulmonary shunt size, an interval bidirectional Glenn (BDG), and removal of branch pulmonary artery stenosis are all thought to positively contribute to improved ventricular performance, yet, their effects remain largely unproven.
The concept of a right ventricular to pulmonary artery (RV-PA) connection as a source of pulmonary blood flow was reintroduced to the Norwood procedure in an attempt to capitalize on the improved diastolic hemodynamics for coronary perfusion. Uncertainties include a ventriculotomy in a systemic RV, the degree and significance of "pulmonary insufficiency," the size of the RV-PA conduit as it relates to total pulmonary blood flow, and changes in the timing of the second stage palliation dictated by earlier systemic arterial desaturation. Most studies now demonstrate equivalent or improved early survival but long-term effects on ventricular function are unknown.
The authors utilize cardiac catheterization data (pressures) and Simpson's rule (RV volume) to derive right ventricular functional data. This method, unlike conductance catheter or sonomicrometric derived data, provides only two points of reference during the cardiac cycle, end systole and end diastole. No filling or empyting curves are generated and a number of assumptions are made in the derivations. This "approximation method" has not yet been validated in humans.
With these caveats, the authors have reported some interesting findings. The comparison of shunted patients (N-S/P) with those receiving an RV-PA conduit (N-RV/PA) revealed no difference in indices of ventricular performance following the Norwood procedure. Ees (contractility) in the N-RV/PA group was reduced when compared to N-S/P after the BDG and TCPC, yet this was offset by a reduction in Ea (afterload) in the N-RV/PA group leading to no significant difference in ventricular efficiency (Ea/Ees) between groups. Thus, the effect of a ventriculotomy remains a concern, and the importance of afterload reduction is underscored.
A variety of issues limit the scientific value of the study; its retrospective, nonrandomized design, the effect of tricuspid and pulmonary insufficiency as well as additional sources of pulmonary blood flow on RV volume calculations and its derivatives (Ea, Ees). The next step should be a validation of this data in humans and/or a comparison to conductance-derived indices. Despite these shortcomings, the authors should be applauded as having made a first attempt to quantitatively compare ventricular performance in these patients.
Related Article
Ann. Thorac. Surg. 2004 78: 1965-1971.
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