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MINI-FOCUS ISSUE: THE FONTAN PROCEDURE

Fontan Fenestration Closure Has No Acute Effect on Exercise Capacity but Improves Ventilatory Response to Exercise

Jeffery Meadows, MD^_*,_*, Peter Lang, MD^_*,, Gerald Marx, MD^_*, and Jonathan Rhodes, MD^_*,

^_* Department of Cardiology, Children's Hospital–Boston, Boston, Massachusetts
Department of Pediatrics, Harvard Medical School, Boston, Massachusetts.

Manuscript received October 1, 2007; revised manuscript received December 12, 2007, accepted December 18, 2007.

^_* Reprint requests and correspondence: Dr. Jeffery J. Meadows, University of California at San Francisco, Department of Pediatric Cardiology, Box 0632, 505 Parnassus Avenue, San Francisco, California 94143. (Email: Jeffery.meadows{at}ucsf.edu).

Objectives: The aim of this study was to prospectively examine the effects of elective Fontan fenestration closure upon exercise capacity and ventilatory abnormalities.

Background: For patients undergoing Fontan procedures as palliation of single ventricle physiology, the addition of a fenestration to the procedure mitigates perioperative morbidity. Although some fenestrations may close spontaneously, many remain patent and subject patients to arterial hypoxemia and risk for paradoxical emboli. For these reasons fenestration closure is routinely performed post-operatively in the cardiac catheterization laboratory. Although closure of Fontan fenestrations typically results in an immediate improvement in systemic arterial oxygen saturation, it is also associated with an acute decrease in cardiac index and systemic O₂ delivery. The sum result of these physiologic changes upon exercise capacity has not been examined.

Methods: Twenty consecutive patients, age 5 to 46 (median 10) years, underwent pre- and post-fenestration closure exercise testing with expiratory gas analysis.

Results: Before fenestration closure, peak oxygen consumption (VO₂) was depressed and there was systemic desaturation at rest that worsened with exercise. The ventilatory response to exercise was also abnormal, characterized by elevation of the minute ventilation (VE)/CO₂ elimination slope (VE/VCO₂), a low end-tidal CO₂, and high end-tidal O₂ at the ventilatory anaerobic threshold. Although arterial saturation improved significantly after fenestration closure, there was no change in peak VO₂ (70.9 ± 18.6% to 74.0 ± 18.6%, p = NS), heart rate, or O₂ pulse at peak exercise. In contrast, ventilatory abnormalities (VE/VCO₂) improved considerably (44.4 ± 10.9 to 33.3 ± 5.5, p 0.001).

Conclusions: Fontan fenestration closure does not significantly improve peak VO₂. However, ventilatory abnormalities improve considerably.

Key Words: congenital heart disease • exercise testing • fenestrated Fontan

Abbreviations and Acronyms   pCO2 = partial pressure of carbon dioxide   pETCO2 = partial pressure of end-tidal carbon dioxide   pETO2 = partial pressure of end-tidal oxygen   pO2 = partial pressure of oxygen   QpQs = ratio of pulmonary to systemic blood flow   RER = respiratory exchange ratio   VAT = ventilatory anaerobic threshold   VE = minute ventilation   VE/VCO2 = minute ventilation/carbon dioxide elimination   VO2 = oxygen consumption

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