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Pediatric Cardiac Surgery, University of Michigan, 5144 Cardiovascular Center, SPC 5864, Ann Arbor, MI 48109-5864
(Email: jhirsch{at}umich.edu).
The long-term fate of the right ventricle (RV) for patients with hypoplastic left heart syndrome (HLHS) remains unknown. Physicians have focused on preserving RV function through improvements in operative management, early volume unloading procedures, and afterload reduction. However, there is little understanding of the baseline characteristics of the single RV before any postnatal intervention. The article by Szwast and colleagues [1] analyzes the inherent capabilities of the fetal RV in HLHS compared with age-matched normal fetal hearts before the physiologic load of postnatal life. They found that the RV in a fetus with HLHS has a 20% decrease in cardiac output despite preserved systolic function. The authors demonstrated increased RV ejection force and increased myocardial performance indices that suggest impaired diastolic dysfunction in utero, before the postnatal stressors are present.
The finding of inherent diastolic dysfunction and decreased cardiac output in utero for HLHS patients could have significant implications for patient management and prognostication of the long-term viability of the systemic RV. Earlier studies support their finding of increased RV ejection forces; however, their study details the systolic and diastolic components of RV performance [2]. The etiology of the diastolic dysfunction may be the result of a hypertrophic response to increased preload. Alternatively, fetal animal studies have suggested an early hyperplastic response [3]. Further understanding of the mechanism of the diastolic dysfunction may be helpful. Fetal diagnosis of HLHS has dramatically improved timely postnatal care for these patients; perhaps fetal intervention to mitigate negative alterations or to encourage positive compensatory changes may affect late RV function.
This study examined only a single time point during fetal development. With the interesting findings of this study, a longitudinal comparison of individual fetal and postnatal echocardiograms would be useful. The authors found that the RV ejection force increases significantly during gestation. A better understanding of the time course of these changes within gestation and a correlation of the degree of changes with postnatal function and RV performance before stage 1 palliation may be valuable in helping clinicians counsel parents and possibly tailor early management.
It would be interesting to see if the fetal findings for single ventricle patients with a dominant RV are also present in patients with a single dominant LV. These data may help to define if the alterations in performance are inherent to the ventricle or if they are related to single ventricle physiology. Many physicians believe that patients with a single systemic LV will do better in the long-term compared with those with a single systemic RV. Although we have not observed this survival benefit in our patients, it would be interesting to understand if single RV and LV patients start with the same baseline ventricular performance or if the same characteristics develop overtime [4].
The thought-provoking findings of this study raise important questions regarding how the inherent alterations in RV performance should be incorporated into the management of single ventricle patients. These limitations in RV performance could be related to the observed incidence of lower birth weight, microcephaly, and central nervous system abnormalities observed after staged reconstruction. The ability to antenatally assess RV function may allow providers to intervene in utero or to alter postnatal management to mitigate some of these effects. It is possible that better understanding of prenatal RV function may allow physicians to make treatment decisions about transplantation vs Norwood or RV-to-pulmonary conduit vs modified Blalock-Taussig shunt to optimize outcomes. The ability to intervene early, even antenatally, and to tailor care not only to the diagnosis but also to individual characteristics of a specific patient will allow physicians to maximize long-term outcomes.
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