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Ann Thorac Surg 2003;76:562-566
© 2003 The Society of Thoracic Surgeons
a Department of Cardiovascular Surgery and Pediatric Cardiology, Kyushu Kosei-Nenkin Hospital, Kitakyushu, Japan
Accepted for publication February 27, 2003.
* Address reprint requests to Dr Tanoue, Department of Cardiovascular Surgery, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
e-mail: tanoue{at}heart.med.kyushu-u.ac.jp
| Abstract |
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METHODS: We measured percent normal systemic ventricular end-diastolic volume (%N-EDV), contractility (end-systolic elastance [Ees]), afterload (effective arterial elastance [Ea]), and ventricular efficiency (ventriculoarterial coupling [Ea/Ees]) based on cardiac catheterization data before and after both BDG and staged TCPC in 30 patients. Ees and Ea were approximated as follows: Ees = mean arterial pressure/minimal ventricular volume, and Ea = maximal ventricular pressure/(maximal ventricular volume - minimal ventricular volume), and Ea/Ees was then calculated. Ventricular volume was divided by body surface area.
RESULTS: The %N-EDV decreased both after BDG and after staged TCPC, thus resulting in an improvement of Ees. Although Ea increased both after BDG and after staged TCPC, Ea decreased during the interval between BDG and staged TCPC. These changes resulted in an improvement in Ea/Ees during the interval period and after staged TCPC, although Ea/Ees worsened after BDG.
CONCLUSIONS: Correction of afterload mismatch during the interval period between BDG and staged TCPC is considered to be one of the most important factors for obtaining excellent clinical results when selecting a staged strategy to treat high-risk Fontan candidates.
| Introduction |
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There have been many reports discussing the importance of the pulmonary artery size and systemic ventricular function in Fontan candidates [68]. A few studies have been undertaken to investigate in detail the hemodynamic conditions in Fontan circulation focusing on the ventricular efficiency. Nogaki and colleagues [9] reported that contractility of Fontan circulation was lower than that of the normal circulation, whereas afterload of the Fontan circulation was higher than that of the normal circulation based on an evaluation with a theoretical model. We previously reported that the volume load reduction of BDG preceding TCPC allowed for any afterload mismatch to be corrected, thereby improving ventricular efficiency after staged TCPC in clinical patients [10]. In this previous study, we combined this approximation of the end-systolic elastance (Ees), the effective arterial elastance (Ea), and the ventriculoarterial coupling (Ea/Ees) with the cardiac catheterization data before and after TCPC, and then compared the ventricular mechanics of the patients treated by staged TCPC with that of the patients treated by primary TCPC. In the present study, we focused on Fontan candidates who underwent BDG and staged TCPC. The purpose of this study was to analyze the time course of the ventricular efficiency in Fontan candidates who underwent both BDG and staged TCPC with the same method as that described in our previous study.
| Material and methods |
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The mean age of the patients was 2.6 ± 2.6 years (0.5 to 10 years old) for BDG and 4.5 ± 3.2 years (1.8 to 14 years old) for staged TCPC. The mean weight was 10.5 ± 5.4 kg (4.6 to 27.2 kg) for BDG and 15.2 ± 9.1 kg (7.4 to 49.5 kg) for staged TCPC. The anatomic diagnoses of children are summarized in Table 1. The morphologic characteristics of the dominant ventricle were observed in the left ventricle in 9 patients, and in the right ventricle in 21 patients. The operative procedures before BDG were as follows: a modified Blalock-Taussig shunt was performed in 18 patients; pulmonary artery banding was performed in 5 patients; a repair of a total anomalous pulmonary venous connection was performed in 1 patient; a Blalock-Hanlon atrial septectomy was performed in 1 patient; and a Norwood procedure with the use of a right ventricular-pulmonary artery conduit instead of a systemic-pulmonary shunt was performed in 1 patient [11, 12]. At the time of staged TCPC, the pulmonary blood flow was supplied by Glenn anastomosis alone in 27 patients and by Glenn anastomosis plus another source (modified Blalock-Taussig shunt) in 3 patients.
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BDG
A bidirectional cavopulmonary shunt was made by direct end-to-side anastomosis between the superior vena cava and the pulmonary artery. When the bilateral superior venae cavae were present, bidirectional cavopulmonary anastomoses were done separately. Regarding concomitant procedures, the augmentation of the pulmonary artery was performed in 22 patients; atrioventricular valvuloplasty was performed in 9 patients; a release of the systemic ventricular outflow obstruction was performed in 2 patients; and a repair of the total anomalous pulmonary venous connection was performed in 2 patients.
Staged TCPC
For inferior cavopulmonary anastomosis, the lateral tunnel technique [15] was performed in 2 patients, whereas the extracardiac conduit approach using a 16-mm to 20-mm polytetrafluoroethylene graft [16] was performed in 28 patients. Fenestration was created in 1 patient (the fenestration was closed on postoperative cardiac catheterization). Regarding concomitant procedures, the augmentation of the pulmonary artery was performed in 5 patients; atrioventricular valvuloplasty was performed in 5 patients; and a release of the systemic ventricular outflow obstruction was performed in 1 patient.
Data analysis
All patients underwent cardiac catheterization both before and about 4 to 6 weeks after the operation (both BDG and staged TCPC). The volumes of the left dominant type ventricle were calculated by the area-length method [17], and the volumes of the right dominant type ventricle were calculated according to Simpsons rule [18]. The percent of normal systemic ventricular end-diastolic volume (%N-EDV) was calculated based on the method described in a report by Nakazawa and coworkers [19]. The calculations of Ees (contractility), Ea (afterload), and Ea/Ees (ventricular efficiency) were performed based on the pressure and volume data of cardiac catheterization by the approximation method as previously described [10, 20]. The approximation of Ees and Ea were performed as follows: Ees = mean arterial pressure/minimal ventricular volume, and Ea = maximal ventricular pressure/(maximal ventricular volume - minimal ventricular volume). The ventricular volume was divided by the body surface area considering the increment in body mass of patient with age. The point of this approximation is that the end-systolic ventricular volume is not the same as the minimal ventricular volume, and the end-diastolic ventricular volume is also not the same as the maximal ventricular volume. Normally, the end-systolic ventricular volume is larger than the minimal ventricular volume and the end-diastolic ventricular volume is smaller than the maximal ventricular volume. Similarly, the end-systolic ventricular pressure is smaller than the maximal ventricular pressure.
Statistical analysis
The results are presented as mean ± SD. Repeated measures analysis of variance was used for the variables at four points (before BDG, after BDG, before staged TCPC, and after staged TCPC). Student-Newman-Keuls test was used as post hoc test.
| Results |
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| Comment |
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Volume load reduction and afterload mismatch
The introduction of BDG preceding TCPC has been demonstrated to improve the clinical results of Fontan operation in high-risk candidates [1, 2]. Many studies have reported the excellent clinical results of the staged strategy in high-risk Fontan candidates [35]. The preservation of the ventricular function by relieving the volume load on the single ventricle is speculated to be one of the explanations for such excellent results when using the staged strategy [2, 5]. We previously reported that the volume load reduction of BDG preceding TCPC allowed for any afterload mismatch to be corrected, thereby improving ventricular efficiency after staged TCPC [10]. In this previous study, we also validated the approximation of Ees and Ea using a canine right-heart bypass model with a conductance catheter in the left ventricular cavity [22, 23]. We combined this approximation of the Ees, Ea, and Ea/Ees with the cardiac catheterization data before and after TCPC, and then compared the ventricular efficiency of the patients treated by staged TCPC with that of the patients treated by primary TCPC [10].
In the present study we analyzed the time course of the ventricular efficiency in Fontan candidates who underwent BDG and staged TCPC, and elucidated that Ea increased after both BDG as well as TCPC, although an afterload mismatch and deterioration in Ea/Ees also occurred. However, Ea decreased and Ea/Ees improved during the interval period between BDG and staged TCPC. Senzaki and colleagues [24] reported that the systemic vascular compliance increases with the body surface area during childhood. The increase in the systemic vascular compliance during the interval period between BDG and staged TCPC is considered to contribute to the decrease in the afterload of the systemic ventricle. We have no definite information regarding the mechanism that causes the systemic vascular compliance to increase during the interval period between BDG and staged TCPC. We consider the adaptation of vascular system, especially the pulmonary vessels, to be associated with the increase in systemic vascular compliance. However, this hypothesis remains only a speculation. At our hospital any concomitant procedures, such as atrioventricular valvuloplasty and the release of a systemic ventricular outflow obstruction, are completed during the BDG operation as far as possible. This strategy is also considered to help improve the ventricular efficiency during the interval period between BDG and staged TCPC. The present study confirms that not only the volume load reduction of the systemic ventricle on BDG, but also the correction of the afterload mismatch during the interval period between BDG and staged TCPC, is one of the most important factors for obtaining good clinical results.
Afterload increasing effect of cavopulmonary connection
We demonstrated Ea to increase after both BDG and TCPC in the present and previous studies [10]. Akagi and colleagues [8] reported the systemic vascular resistance to increase after the Fontan operation. Nogaki and coworkers [9] evaluated the Fontan circulation with a theoretical model, and demonstrated Ea of the Fontan circulation to be higher than that of the normal circulation, while Ees of the Fontan circulation was lower than that of the normal circulation. These reports and our studies strongly suggest the cavopulmonary connection increases afterload of the single ventricle and, thus, can cause an afterload mismatch. The afterload increasing effect of primary TCPC (when both the superior vena cava and inferior vena cava are connected to the pulmonary artery) would be larger than that of BDG (when only the superior vena cava was connected to the pulmonary artery). Sano and colleagues [25] reported that an afterload mismatch in patients with a right ventricular type of univentricular heart tend to manifest an impairment of the pump function. An excessive acute volume load reduction gives rise to a fatal afterload mismatch in high-risk Fontan candidates. Masuda and associates [3] suggested that the staged strategy might avoid the deleterious effect of a sudden decrease in the diastolic ventricular volume. The increase in Ea and the deterioration in Ea/Ees after operation would have been more severe if the patients in this series had undergone primary TCPC instead of BDG, and some patients would have been unable to stand the more severe afterload mismatch.
Limitations and future studies
The approximation of Ees and Ea in this study inherently has limitations and does not amount to the measurement by a conductance catheter. However, the present approximation enables us to evaluate ventricular contractility, afterload, and ventriculoarterial coupling from the conventional cardiac catheterization data [10, 20]. It is difficult to accurately measure the end-systolic ventricular volume and the end-diastolic ventricular volume from the cardiac catheterization data because pressure-volume loops were not available. The influence of the morphologic dominant ventricle, the variable presence of congestive heart failure, the degree of atrioventricular valve regurgitation, and additional pulmonary flow should be weighed. However, this analysis could not be performed in this study due to small number of patients. Finally, the long-term changes of Ees, Ea, and Ea/Ees after TCPC would be the next interesting problem. Further studies of the long-term period after TCPC are thus called for.
In conclusion, the correction of the afterload mismatch during the interval period between BDG and staged TCPC is thus considered to be one of the most important factors for obtaining excellent clinical results using a staged strategy for the treatment of high-risk Fontan candidates.
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