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Ann Thorac Surg 1996;61:849-850
© 1996 The Society of Thoracic Surgeons
Department of Cardiovascular Surgery Boston Children's Hospital 300 Longwood Ave Boston, MA 02115
This article by Miyaji and co-workers in which a pulsatile bidirectional cavopulmonary shunt (BCPS) operation is advocated raises important conceptual questions regarding the management of patients with functional single ventricle. These issues include (1) the effects of chronic volume loading on the function of a single ventricle and atrioventricular valve, (2) the effect of pulsatile versus nonpulsatile blood flow on central pulmonary artery growth and on pulmonary arteriolar resistance, (3) and the aggregate effects of the first two issues on the suitability of a given patient for a Fontan-type operation.
Intuitively, I have always thought that chronic volume loading of a single ventricle, as occurs when pulmonary blood flow is provided by the single ventricle (either pulmonary stenosis [native or pulmonary artery band] or a systemic-to-pulmonary artery shunt) will be detrimental to the function of that single ventricle. One of the benefits of the ``nonpulsatile'' BCPS is that it allows these systemic-to-pulmonary artery connections (which provide the ventricular volume load) to be eliminated. Therefore, when such connections are allowed to persist as advocated by Miyaji and co-workers, the benefit provided by the BCPS to reduce the volume load is lost. The data in the article showing that postoperative ventricular end-diastolic volume did not change are consistent with this hypothesis. The unanswered question is whether or not the, continued volume load prevents patients from being candidates for Fontan operations, and this question cannot be answered from the data in this article as the number of patients is too small. However, 1 patient in the series did have worsening atrioventricular valvar regurgitation and died late after the pulsatile BCPS.
The second issue is the effect of the pulsatile BCPS operation on the growth of the central pulmonary arteries and on pulmonary arteriolar resistance. Prior reports from various institutions have reached opposite conclusions regarding the impact of pulmonary artery dimensions per se on the outcome of Fontan operations. My colleagues and I have noted an effect of unrepaired pulmonary artery distortions on outcome of Fontan operations, but successful relief of pulmonary artery distortion in conjunction with a Fontan operation is very much compatible with a good outcome. Whether the preservation of pulsatile flow and its effects on central pulmonary artery size will have an important impact on Fontan outcome remains unclear to me because we have a large number of patients who had ``nonpulsatile'' BCPS operations followed by a fenestrated Fontan procedure with a failure rate (death or takedown) of approximately 5%. Of equal concern is the effect of pre-Fontan palliative operations on pulmonary arteriolar resistance. If patients tolerate the ``pulsatile'' BCPS procedure without a severe superior vena cava syndrome, then it is likely that the pulmonary arterial (and superior vena caval) pressures will not be high enough to cause elevated pulmonary arteriolar resistance. However, in making comparisons of pulmonary arteriolar resistance between ``pulsatile'' and ``nonpulsatile'' BCPS patients, it must be recalled that resistance measured under pulsatile flow conditions is likely to be lower than under nonpulsatile conditions. In our own determinations of suitable criteria for Fontan operations, I will accept a higher calculated pulmonary arteriolar resistance in a ``nonpulsatile'' BCPS patient than in one with a systemic-to-pulmonary artery shunt or pulmonary stenosis. It is worthy of emphasis that when continuous variables (such as pressure or dimension) are considered as ``risk factors,'' the risk generally rises incrementally as the value of the variable increases (or decreases). Where the ``cutoff'' point is for a given variable is somewhat arbitrary and depends at least in part on how much risk the patient and surgeon are willing to take and what the alternative forms of therapy are. Given the difficulty in measuring pulmonary blood flow by any means (Fick or indicator dilution), particularly when various sources of pulmonary blood flow have differing oxygen contents, it seems to me that it would be unwise to deny a patient a Fontan procedure if the calculated pulmonary arteriolar resistance is marginally beyond some limit (eg, 2.3 Wood units) if all other patient variables seemed favorable. In our experience, the use of a fenestration as part of the Fontan procedure has allowed us to successfully carry out Fontan procedures in patients who do not meet one or more criteria for the operation.
Finally, the overall benefit of a strategy using ``pulsatile'' versus ``nonpulsatile'' BCPS as an intermediate step to a Fontan operation cannot be determined from this article by Miyaji and co-workers, or from data reported from several other centers. The essentially opposite conclusions reached by various groups regarding the value of a ``pulsatile'' BCPS suggests that much more experience and analysis of that experience will be necessary before meaningful conclusions can be drawn. The optimal management plan for the patient with single ventricle beginning at the time of birth remains one of the major challenges for congenital heart surgeons and pediatric cardiologists. A multiinstitutional study starting at the time of birth with long-term follow-up is clearly necessary to answer these and many other questions on the management of the single ventricle patient. It is my opinion that it is highly unlikely that a single management strategy will be optimal for this heterogeneous group of patients.
Related Article
Ann. Thorac. Surg. 1996 61: 845-850.
This article has been cited by other articles:
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  R. D. Mainwaring and J. J. Lamberti Usefulness of pulsatile bidirectional cavopulmonary shunt in high-risk Fontan patients Ann. Thorac. Surg., December 1, 2003; 76(6): 2167 - 2167. [Full Text] [PDF]
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