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a Department of Pediatric Cardiology, Sejong General Hospital, Bucheon, Korea
b Department of Cardiac Surgery, Sejong General Hospital, Bucheon, Korea
c Department of Pediatrics, Seoul National University College of Medicine, Seoul National University Children's Hospital, Seoul, Korea
Accepted for publication October 14, 2008.
* Address correspondence to Dr Bae, Department of Pediatrics, Seoul National University College of Medicine, Seoul National University Children's Hospital, 28 Yeongeon-dong, Jongno-Gu, Seoul, 110-744, Korea (Email: eunjbaek{at}snu.ac.kr).
| Pediatric cardiac surgery:
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| Abstract |
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Methods: We studied 33 patients who already had clinical and subclinical PAVFs after BCPS. All patients have taken Fontan completion with HV inclusion. The state of PAVFs was reevaluated by pulmonary angiogram, contrast echocardiography, and lung scintigraphy 7.7 ± 2.4 years after HV inclusion.
Results: After Fontan completion, the mean oxygen saturation increased from 80.2 ± 7.4% to 91.5 ± 9.8% in the entire cohort. Moreover, the amount of right-to-left shunting through the PAVFs, measured by lung scintigraphy, was decreased from a mean of 23.8 ± 15.1 to 13.0 ± 8.2%. The degree of severity, for most patients, was decreased as demonstrated by contrast echocardiography. However, 5 patients (16.7%) showed persistent PAVFs, even after the HV inclusion. They all had left isomerism with azygous continuation of the IVC and the conduit was positioned on the contralateral side to the SVC with azygous drainage.
Conclusions: Most PAVFs regressed after Fontan completion. Left isomerism with azygous continuation of the IVC had risk for persistent PAVFs when the HV conduit was positioned at the contralateral side to the SVC receiving the azygous drainage. Therefore, appropriate design avoiding unilateral streaming of HV flow should be considered for HV inclusion surgery.
The bidirectional cavopulmonary shunt (BCPS) has been increasingly implemented as a preparatory procedure for a Fontan operation. The BCPS provides an excellent first or second stage palliation in patients with a functional single ventricle and has resulted in more favorable post-Fontan outcome with lower surgical mortality rates compared with that of the nonstaged approach [1–3]. The development of pulmonary arteriovenous fistulas (PAVFs) was first noticed during the follow-up of patients who had undergone a Glenn shunt [4, 5]. Although physiologically similar to the classic Glenn operation, current methods of the BCPS have been shown to cause bilateral rather than ipsilateral PAVFs under certain conditions, but at a lower incidence. The lower incidence of the BCPS may be partly related, being that the BCPS is usually performed as one part of a staged approach, which was followed relatively quickly by final completion of the Fontan operation. The hepatic vein (HV) inclusion to pulmonary circulation has been reported to improve cyanosis in patients with PAVFs. We reported previously that most patients with the BCPS showed subclinical evidence of right to left intrapulmonary shunting [6]. However, the consequences of this pulmonary vascular abnormality after a BCPS have not determined clearly.
The purpose of this study was to determine the effect of redirecting the HV effluent to the pulmonary circulation in the patients who already had PAVFs.
| Patients and Methods |
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Eighteen patients underwent a BCPS at a median age of 8.5 months (range, 3 to 28). Fifteen patients underwent the Kawashima operation (BCPS in patients with IVC interruption) at a median age of 20 months (range, 7 to 124) and 14 patients had left isomerism (polysplenia syndrome). Twelve patients who had bilateral SVC underwent a bilateral BCPS. Eight patients had pulsatile pulmonary blood flow. The median systemic arterial oxygen saturation (SaO 2) at the time of PAVFs diagnosis was 80.2% (range, 60% to 90%). Eleven patients (33.3%) had clinical PAVFs and 21 (66.7%) had subclinical PAVFs before the Fontan operation. Among the 11 patients with the clinical PAVFs, 7 patients (63.6%) had an interrupted IVC and 9 patients (81.8%) had the heterotaxy syndrome. The Sejong General Hospital Institutional Review Board reviewed and approved this study and individual consent was waived.
Diagnosis of the PAVFs
Contrast echocardiography, lung scincitigraphy, and pulmonary angiography were performed for the diagnosis of PAVFs before and after HV inclusion. To exclude venovenous collaterals and to evaluate the status of PAVFs on each side of the lung separately, we did SVC venography and contrast echocardiography at each branch pulmonary artery.
According to our previous study [6], clinical PAVFs were considered by the following: (1) a systemic arterial desaturation of 80% or less on room air, without any evidence of parenchymal lung disease; and (2) one or more positive findings on one or more of the three diagnostic modalities (an extrapulmonary shunt fraction greater than 11% on technetium-99-labeled macroaggregated albumin (99mTcMAA) lung scintigraphy, a positive contrast echocardiogram, or positive pulmonary angiographic results). In addition, we defined the subclinical PAVFs as systemic arterial saturation more than 80% and one or more signs of intrapulmonary shunting on one or more of the three modalities used for the diagnosis of PAVFs as described previously.
After HV inclusion, we considered the PAVFs completely resolved when the Sa was greater than 90% on room air and when there was no evidence of intrapulmonary shunting by the diagnostic modalities used for diagnosing the PAVFs.
Statistical Analysis
The SPSS statistical program for Windows version 14 (SPSS, Chicago, IL) was used to perform the data analysis. Data are expressed as mean, median, and range and a p value less than 0.05 was considered statistically significant. Risk factors were evaluated by multivariate analysis for the development of PAVFs and included the following: the age at the BCPS (more or less than 12 months), the interval from the BCPS to HV inclusion (more and less than 2 years), the presence of pulsatile blood flow during the BCPS stage, heterotaxy, left isomerism, IVC interruption, follow-up duration, weight at surgery, gender, previous cardiac operations, concomitant cardiac operation, and presence of a bilateral or contralateral SVC. The analysis was performed with the Cox proportional hazards regression model.
| Results |
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All 33 patients with intrapulmonary right-to-left shunting underwent a Fontan completion using an extracardiac conduit between February 1997 and June 2004. The HV inclusion procedures were done at a median age of 41 months (range, 22 to 143). A time interval between a BCPS and a HV inclusion procedure was 23 months (range, 11to 133). An expanded polytetrafluoroethylene tube conduit (Gore-tax stretch vascular graft; W. L. Gore & Assoc, Flagstaff, AZ) was used. The median diameter of the conduit was 18 mm (range, 16 to 22 mm), the indexed mean diameter of the conduit was 30.9 ± 7.2 mm/m2, and the indexed mean area of the conduit was 449.5 ± 104.0 mm2/m2 for the BCPS patients. The median diameter of the conduit was 17 mm (range, 14 to 22 mm), the indexed mean diameter of the conduit was 22.2 ± 4.1 mm/m2, and the indexed mean area of the conduit was 306.4 ± 78.9 mm2/m2 for the Kawashima patients. We chose a smaller-sized graft for previous Kawashima procedures (p = 0.000 for the diameter and p = 0.000 for the area of the conduit). Most of the patients who had clinical PAVFs (8 of 11) did not require fenestration. Concomitant surgical procedures are shown in Table 1.
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After the HV inclusion procedure, the mean SaO 2 increased from 80.2 ± 7.4% (range, 60% to 90%) to 91.5 ± 9.8% (range, 54% to 98%) in all patients (p = 0.000) and from 73.9 ± 9.4% (range, 60% to 87%) to 91.1 ± 13.2%(range, 54% to 98%) in the clinical PAVFs group (p = 0.031) (Fig 1). The hypoxemia had gradually improved until median 4 months (range, 1 to 13 months) after discharge. Moreover, the amount of right-to-left shunting through the PAVFs, detected by lung scintigraphy, was decreased from a mean of 23.8 ± 15.1% (range, 7% to 63%) to 13.0 ± 8.2% (range, 4% to 33%) in all patients (p = 0.001) (Fig 2). The severity score on contrast echocardiography in the whole cohort was improved as shown in Figure 3.
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The univariate analysis demonstrated the interrupted IVC (p = 0.000), heterotaxy syndrome (p = 0.004), left isomerism (p = 0.000), and presence of bilateral or contralateral SVC to HV (p = 0.005) as predictors of persistent PAVFs even after HV inclusion. The multivariate analysis demonstrated interrupted IVC (p = 0.000) as a predictor of persistent PAVFs even after HV inclusion.
| Comment |
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It was not until 1994, when Srivastava and colleagues [9] conclusively demonstrated that PAVFs were due to the absence of a "hepatic factor" or a "mesenteric factor" 10], and that an unidentified element in the hepatic venous drainage inhibited the recruitment and dilatation of preexisting pulmonary arteriovenous connections. Duncan and Desai [11] further elaborated the mechanisms for the etiology of PAVFs and demonstrated that they were likely due to greatly increased numbers of abnormal and dilated channels, and suggested an angiogenic process as well as recruitment of preexisting channels that dilated when there was an absence of hepatic venous return to the pulmonary circulation. Alternatively, these authors hypothesized that the liver may be responsible for the degradation of a vasodilating substance that is not removed after a BCPS.
Clinically important PAVFs may develop in up to 52.4% of patients after the Kawashima operation; it can cause clinically severe arterial oxygen desaturation and heart failure [12]. In addition, we noted clinically important PAVFs in up to 50% of patients after the Kawashima operation in a previous study [6] and recommended early detection of PAVFs using contrast echocardiography or lung scintigraphy in patients with left isomerism and an interrupted IVC who had a Kawashima procedure. We also demonstrated [6] that subclinical PAVFs were significantly prevalent in patients with a BCPS. We ultimately performed Fontan completion within 1 to 2 years of the Kawashima operation in all patients with left isomerism and azygous continuation of the IVC.
Surgical redirection of the hepatic venous blood flow to the pulmonary arterial circulation causes PAVFs to regress [13, 14]. The Fontan procedure reliably leads to regression of the PAVFs that occur after a BCPS [9]. Shah and colleagues [14] and Duncan and Desai [11] corroborated these findings and showed that PAVFs would regress within 7 months after Fontan completion. By contrast, several reports demonstrated the development of PAVFs after the Fontan procedure [10, 15]. In these cases, it was closely associated with the uneven perfusion of the hepatic venous drainage and the excluded HV blood flow from the pulmonary circulation similar to TCPS.
In our study, the hypoxia improved within 2 months to 2 years after cavopulmonary incorporation of the hepatic vein and not only clinical PAVFs but also subclinical PAVFs resolved in the majority of patients after the HV inclusion. The time course of improved SaO 2 after the HV inclusion was inconsistent with the explanation that hypoxia improved simply because the hepatic right-to-left shunting was eliminated; the early postoperative SaO 2 was very low in most patients, improving by the time of hospital discharge to some extent, and only gradually increasing to above 90% over the next month to year. Elimination of the hepatic right-to-left shunting alone should have improved the hypoxemia immediately after the redirection of the HV flow, whereas resolution of the PAVFs might be expected to occur gradually. Fenestration of the HV pathway may prevent sufficient HV flow from reaching the pulmonary circulation, and should be limited to patients with specific indications. Fortunately, in our study most of the patients with PAVFs did not require fenestration because the PAVF itself may have lowered the pulmonary resistance, and may function as a fenestration after the Fontan completion during the early postoperative period.
However, 5 patients had severe hypoxemia due to the PAVFs even after the HV inclusion procedure in our study. They all had left isomerism with azygous continuation of the IVC and had the HV conduit on the contralateral side to the SVC receiving azygous drainage. This anatomic configuration caused streaming of the flow in the HV-PA pathway such that the HV blood flowed exclusively or primarily to one lung, in which the PAVFs had resolved, while the PAVFs persisted in the contralateral lung. Even the presence of bilateral SVCs could not prevent streaming of the hepatic venous blood to one lung in 3 patients with bilateral SVCs in our study. Even if bilateral SVCs are present, the SVC receiving the azygous return carries at least 50% of the upper body venous return and essentially all of the lower body and nonsplanchnic abdominal venous return. If this SVC was contralateral or had only small offset to the HV conduit, there was no mechanical impetus for the HV effluent to flow to the lung on that side [16].
As investigators have shown using in vitro and computational simulations, offset between the IVC-PA and SVC-PA connections can produce complete or near-complete streaming of the HV effluent to the ipsilateral lung [17]. It is therefore essential to design the hepatic venous channel in relation to the anastomosis between the SVC and pulmonary artery. However, sometimes it is not easy to achieve balanced perfusion of the hepatic venous blood to the lungs bilaterally in patients with left isomerism with an interrupted IVC. The reason is that the position of the conduit may be inevitably in the contralateral side of azygous continuation, if the main mass of ventricle is in the same side of the azygous continuation. In this anatomy, a more medially connected initial BCPS would facilitate more balanced perfusion after Fontan completion.
The presence of the conduit position on the side contralateral to the SVC with azygous drainage, or the side with a solitary SVC without interrupted IVC, was not associated with resolution of hypoxemia after the HV inclusion. The options for redirection of the hepatic venous drainage include rerouting of the hepatic veins to the azygous vein as an attractive option [18]. In addition, when the resolution of the PAVF does not occur, even after the HV inclusion, the large PAVFs may be embolized at catheterization or surgical resection may be required.
In conclusion, most patients who had PAVFs improved after inclusion of the hepatic venous flow to the pulmonary circulation. However, some patients may have hypoxemia due to persistent PAVFs if they had streaming of the hepatic venous flow into the unilateral pulmonary artery even after the HV inclusion. These cases had left isomerism with azygous continuation of the IVC, and had the conduit position at the contralateral side to the SVC receiving the azygous drainage. Furthermore it is essential to design a BCPS and hepatic venous channel to achieve the best offset from the initial stage of palliation. Although there are limited experiences on the direct anastomosis of the hepatic veins to the azygous vein, the primary Kawashima operation may be combined with a direct anastomosis of the hepatic veins to the azygous vein as a complete Fontan operation, especially for the high risk patients for persistent PAVFs after conventional Fontan procedure.
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