EDITORIAL COMMENT
Ventilatory Efficiency and Aerobic Capacity Predict Event-Free Survival in Adults With Atrial Repair for Complete Transposition of the Great Arteries*
David Driscoll, MD*
Mayo Clinic College of Medicine, Rochester, Minnesota
* Reprint requests and correspondence: Dr. David Driscoll, Mayo Clinic, 200 1st Street SW, Rochester, Minnesota 55905-0001 (Email: driscoll.david{at}mayo.edu).
Key Words: transposition of great vessels • exercise • prognosis
The evolution of the surgical treatment of complete d-transposition of the great arteries (d-TGA) is an important and fascinating story of man's ingenuity in dealing with a lethal congenital anomaly. Although survival of patients beyond infancy with transposition with associated atrial and/or ventricular septal defects was possible without operation, the majority of patients with transposition died in infancy. Those rare infants who survived did so with significant exercise limitation, and with the morbidity and mortality associated with erythrocythemia and Eisenmenger syndrome.
The earliest operation described for d-transposition was the creation of an atrial septal defect by Blalock and Hanlon (1950) (1). This ingenious operation preceded the introduction of the heart–lung machine, and was done on the beating heart. This operation had a relatively high mortality because these infants were very ill and usually quite acidotic. However, it resulted in survival beyond infancy. In 1956, Baffes (2) described a partial repair of d-TGA. The "Baffes" procedure involved connecting the inferior vena cava to the left atrium and connecting the right pulmonary veins to the right atrium. Senning (1959) (3) described a complete rerouting of the system and pulmonary venous return that resulted in complete separation of the pulmonary and systemic venous returns. In 1964, in a single case report, Mustard (4) described an operation that also resulted in complete separation of the pulmonary and system venous circulations. However, both operations result in the right ventricle remaining as the systemic ventricle. Although the "Mustard" operation had the same end result as the "Senning" operation, the former was more popular in the U.S. From 1959 to 1975, the Senning and Mustard operations were the mainstay of "corrective" operations for patients with d-TGA without a ventricular septal defect (VSD), and many of these patients now are adults.
In 1975, Jatene et al. (5) resurrected the concept and described a number of successful arterial switch procedures. Since the early 1980s, the arterial switch operation has been the operation of choice for patients with d-TGA, with or without VSD, but without significant pulmonary valve stenosis. The Senning and Mustard operations still are performed today but only for very few patients who are not candidates for an arterial switch or Rastelli procedure. When the Jatene operation was introduced, the operative mortality for the Senning and Mustard operations actually was lower than for the Jatene procedure. However, it was anticipated that the operative mortality for the Jatene procedure would decline significantly as surgeons gained experience with the operation and that the long-term results for the Jatene operation would be superior to those of the Senning and Mustard operation. Time has proven that both of these assumptions are true.
The quest for an operation to replace the Senning or Mustard procedure was spurred on because of the long-term complications inherent to these 2 operations. The complications included superior and/or inferior vena cava obstruction, pulmonary vein obstruction, arrhythmias, and right ventricular (systemic ventricular) failure. Generally, caval and pulmonary venous obstruction can be resolved with conventional operations or interventional cardiac catheterization procedures. However, systemic ventricular failure and some serious arrhythmias may be amenable only to cardiac transplantation or conversion of the Mustard/Senning to an arterial switch procedure. Cardiac transplantation is costly and is associated with significant mid- and long-term morbidity and mortality. Conversion to an arterial switch usually requires banding of the pulmonary artery to prepare the left ventricle. Both the pulmonary banding procedure and the arterial switch operation in these adult patients are associated with significant mortality and the long-term outcome is poorly understood. Thus, it is important to identify predictors of death and significant morbidity in these patients so that they are not subjected, prematurely, to the rigors and risks of cardiac transplantation or other high-risk procedures.
In this issue of the Journal, Giardini et al. (6) report that decreased oxygen uptake and  E/CO
2 response during exercise was associated with an increased risk of death or cardiac-related emergency hospital admission. There have been several excellent studies consistent with the Giardini et al. (6) report that have demonstrated a strong relationship between E/CO
2 slope and outcome in patients with a heart failure and a variety of congenital heart defects (7,8). Although reduced O
2 max has been recognized for many years as having a strong relationship with poor health and the severity of cardiac disease, E/CO
2 may, in fact, have an even stronger relationship. Patients with a right-to-left shunt have markedly elevated E/CO
2, reduced end-tidal PCO
2, but near-normal systemic arterial PCO
2. Simplistically, more CO2 needs to be eliminated with each breath to compensate for the retention of CO2 in the blood that shunts right to left and does not have access to the alveoli, and hence cannot be eliminated. If this did not occur, the patient would become quite hypercapnic. It follows that increased E/CO
2 would occur with V/Q mismatch. V/Q mismatch occurs with reduced cardiac output and reduced pulmonary perfusion, both of which result from cardiac dysfunction. Increased E/CO
2 slope during exercise has been described with pulmonary hypertension (9). Also, increased pulmonary venous pressure and increased lung water may result in J-receptor stimulation that produces increased ventilation.
Although the results of the current study may help clinicians make better decisions regarding the timing of interventions for these patients, nothing this complicated can be decided based upon the results of 1 test. Indeed, in the current study, the sensitivity and specificity of O
2 were 76% and 72%, and for E/O
2, they were 81% and 83%, respectively. Together with historical and clinical findings, and measures of ventricular function, measurement of the cardiorespiratory response to exercise can provide important information regarding outcome in this group of patients. The results of this study will be very valuable to clinicians who need to properly select patients for necessary but risky procedures.
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Footnotes
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* Editorials published in the Journal of the American College of Cardiology reflect the views of the authors and do not necessarily represent the views of JACC or the American College of Cardiology. 
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References
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1. Blalock A, Hanlon C. The surgical treatment of complete transposition of the aorta and the pulmonary artery Surg Gynec Obstet 1950;90:1-15.[Medline]2. Baffes TJ. A new method for surgical correction of transposition of the aorta and pulmonary artery Surg Gynecol Obstet 1956;102:227-233.[Web of Science][Medline] 3. Senning A. Surgical correction of transposition of the great arteries Surgery 1959;45:966-980.[Web of Science][Medline] 4. Mustard WT. Successful two-stage correction of transposition of the great vessels Surgery 1964;55:469-472.[Web of Science][Medline] 5. Jatene A, Fontes V, Paulista P, et al. Successful anatomic correction of transposition of the great vessels: a preliminary report ARQ Bras Cardiol 1975;28:461-464.[Medline] 6. Giardini A, Hager A, Lammers AE, et al. Ventilatory efficiency and aerobic capacity predict event-free survival in adults with atrial repair for complete transposition of the great arteries J Am Coll Cardiol 2009;53:1548-1555.[Abstract/Free Full Text] 7. Giardini A, Specchia S, Berton E, et al. Strong and independent prognostic value of peak circulatory power in adults with congenital heart disease Am Heart J 2007;154:441-447.[CrossRef][Web of Science][Medline] 8. Arena R, Myers J, Aslam S, Varughese E, Peberdy M. Peak VO2 and VE/VCO2 slope in patients with heart failure: a prognostic comparison Am Heart J 2004;147:354-360.[CrossRef][Web of Science][Medline] 9. Reybrouck T, Mertens L, Schulze-Neick I, et al. Ventilatory inefficiency for carbon dioxide during exercise in patients with pulmonary hypertension Clin Physiol 2008;18:337-344.
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