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Eur J Cardiothorac Surg 2005;27:956-961
© 2005 Elsevier Science NL
czgorzata ProcelewskaDepartment of Pediatric Cardiac Surgery, Collegium Medicum, Jagiellonian University, 265 Wielicka St., 30-663 Cracow, Poland
Received 21 September 2004; received in revised form 7 February 2005; accepted 4 March 2005.
* Corresponding author. Tel.: +48 12 568 10 23; fax: +48 12 657 39 47. (E-mail: mimalec{at}cyf-kr.edu.pl).
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Abstract |
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 Top Abstract 1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Key Words: Hypoplastic left heart syndrome • Norwood procedure • Hemi-Fontan procedure
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1. Introduction |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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First described by Dr Norwood [3], the use of right ventricle-to-pulmonary artery shunt (RV–PA) as the source of pulmonary blood flow in the first-stage palliation was reintroduced in the late 1990's and popularized by Japanese surgeons: Imoto [4], Kishimoto [5] and Sano [6,7]. The evidence of the favorable physiology associated with RV–PA in the early postoperative period has been recently reported by many centers [7–13]. The advantageous effects of hemodynamic stability, higher postoperative diastolic blood pressure, improved coronary perfusion, balanced pulmonary and systemic circulations result in a significantly lower mortality. However, the late consequences and the usefulness of this modification in preparation for the next stage palliation are still not sufficiently investigated and documented.
The purpose of this study is to assess changes in late hemodynamic status before the hemi-Fontan operation, as well as evaluate the results of the second-stage palliation as affected by the introduction of the right ventricle-to-pulmonary artery shunt instead of a modified Blalock–Taussig shunt (BT) in the Norwood procedure.
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2. Materials and methods |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Initially, in the neonatal period, all the patients underwent the Norwood procedure (atrial septectomy, pulmonary artery to ascending aorta anastomosis with homograft reconstruction of the aortic arch): Group 1 (27 children) with the application of BT (polytetrafluoroethylene—PTFE—tube, IMPRA® ePTFE Vascular Graft, BARD, Tempe, USA; 3.5mm in 6 and 4mm in 21 children) and Group 2 (51 patients), in which the Norwood procedure was completed with constructing a right ventricle-to-pulmonary artery shunt (PTFE, 5mm). Group 1 was made up of 8 girls and 19 boys, at the time of the hemi-Fontan operation aged from 4.8 to 9.7 months (mean 6.89±1.04 months), weighing from 4.5 to 8.7kg (mean 6.22±0.99kg), whereas Group 2 included 12 girls and 39 boys, aged from 5.0 to 10.7 months (mean 6.57±1.12 months), weighing between 4.6 and 8.4kg (mean 6.36±0.86kg).
Each patient underwent a comprehensive preoperative two-dimensional and Doppler echocardiographic examination (ECHO). The diameter of the pulmonary artery branches was measured from the high parasternal short-axis view and the suprasternal short-axis view. The measurements were made just proximal to the takeoff of the first upper-lobe branch. The right and left pulmonary artery index (RPAI, LPAI) was determined by calculating, respectively, the right and left pulmonary artery cross-sectional areas indexed to body surface area (Dubois and Dubois formula). Tricuspid valve regurgitation was graded on a scale from 1 to 3 (mild, moderate, severe) by a measurement of the ratio of regurgitant jet area to the right atrial area. Echocardiography was also used for qualitative assessment of ventricular hypertrophy (mild, moderate, severe).
Cardiac catheterization and angiography using the standard technique was performed in 24 (88.9%) children from Group 1 and in 19 (37.3%) patients from Group 2 in the median interval time before hemi-Fontan operation of 0.3 months (0–0.75 months) and 0.3 months (0–2 months), respectively. The main hemodynamic parameters obtained during the procedure were pulmonary venous wedge pressure, ventricular pressures, aortic pressures, and superior vena cava and aortic saturation, as well as partial arterial oxygen tension (pO2). Calculations for pulmonary-to-systemic blood flow (Qp:Qs) ratio were carried out using the Fick principle. Data from routine blood tests performed before catheterization (hematocrit value, hemoglobin concentration, red blood cell count) were also collected.
All the hemi-Fontan procedures were performed by the same surgeon through a median sternotomy incision. The hypothermic cardiopulmonary bypass was established by cannulation of the ascending neoaorta and the systemic venous atrium. Immediately after the initiation of the bypass, the systemic-to-pulmonary artery shunts were occluded (in Group 1 using metal clips and in Group 2 by the removing the entire polytetrafluoroethylene tube with the occlusion of the distal and proximal ends using a continuous suture). At a rectal temperature of 20°C the circulation was arrested, the ascending aorta was cross-clamped and the crystalloid cardioplegia solution (potassium cardioplegia: 0.9% NaCl with 16mmol/l KCl, 4°C, 15ml/kg) was infused into the aortic root. The hemi-Fontan procedure was based on the technique described by Douville and co-workers [14]. A longitudinal incision was made in the anterior aspect of the confluence of the pulmonary arteries. The Hegar dilators were introduced to the right (RPA) and left pulmonary artery (LPA) to measure intraoperatively the diameter of the vessels. The incision was then extended almost to the level of the origin of the right and left upper lobe branches. The second incision was then made in the most superior portion of the right atrium and was extended to the medial aspect of the superior vena cava (SVC). At the most rightward extent of the pulmonary arteriotomy, the RPA was anastomosed to the posterior wall of the opened SVC. The pulmonary artery homograft patch was used to enlarge the LPA, confluence of the pulmonary arteries and to create a roof over the anastomosis between RPA and SVC. In all the children, the interatrial communication was revised and if necessary enlarged. A round patch cut from a portion of a 10mm polytetrafluoroethylene tube was sewn into the right atrium below the cavoatrial junction separating the atrium from the cavopulmonary anastomosis (to separate the superior and inferior vena caval blood flow). If a left superior vena cava was present (in Group 1 in 2 (7.4%) children and in Group 2 also in 2 (3.9%) patients), it was transected, occluded at its cardiac end and associated in the end-to-side fashion to the left pulmonary artery (the left bidirectional Glenn anastomosis). The azygous vein was left opened in all the children. The cardiopulmonary bypass was reinstituted, the children were rewarmed to 37°C and separated from bypass.
Between the Norwood and hemi-Fontan procedure and after the hemi-Fontan operation, all the children were treated with acetylsalicylic acid (Acidum acetylsalicylicum, Polpharma, PL) (2–5mg/kg per day).
Operative mortality was defined as mortality prior to hospital discharge. The data are represented as mean±standard deviation and range. The statistical analysis was carried out by means of descriptive statistics, 
2 test (with the Yates correction) for non-parametric, and Mann–Whitney's test or Student's t-test for continuous variables. The multivariate analysis of variables found to be significant by the univariate analysis was performed using the multiple regression after eliminations of colinearity of variables (Pearson correlation). Differences were considered statistically significant at the P value of <0.05.
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3. Results |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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In echocardiographic examination before the hemi-Fontan operation, the left pulmonary artery index was significantly larger in patients after RV–PA (P=0.009). The trend towards larger right pulmonary artery index in Group 2 did not reach statistical significance (P=.291) (Table 1). The severe ventricular hypertrophy diagnosed by echocardiography had a significantly lower incidence in Group 2 (2 (3.9%)), in comparison with Group 1 (7 (25.9%)) (P=0.009). There were no significant differences between groups with respect to the incidence of tricuspid regurgitation: mild (Group 1, 11(40.7%); Group 2, 11(21.6%); P=0.127), moderate (Group 1, 5(18.5%); Group 2, 4(7.8%); P=0.302) and severe (Group 1, 1(3.7%); Group 2, 2(3.9); P=0.568). In one child from Group 2, the ECHO imaging revealed the development of a small pseudoaneurysm of the right ventricle infundibulum (about 1cm in diameter) at the site of the anastomosis of the RV–PA. During the hemi-Fontan procedure, the pseudoaneurysm was completely resected; the weaning from bypass and postoperative course in this child was uneventful.
Sinus rhythm was present in all children from both groups and no ventricular arrhythmias were observed.
At the time of the cardiac catheterization before the hemi-Fontan procedure, the two groups showed no significant differences with respect to age (P=0.099). The cardiac catheterization data are presented in Table 2. The univariate analysis revealed that the mean aortic oxygen saturation and pO2, as well as superior vena cava mean oxygen saturation and pO2 were significantly higher in Group 1 (BT) than in Group 2 (RV–PA). The mean Qp:Qs ratio in Group 1 was 1.24±0.43 (0.4–2.1) and significantly differed (P=0.011) from that value in Group 2: 0.8±0.47 (0.3–1.9). The mean right ventricular systolic pressure was higher in Group 1 than in Group 2, but these findings did not reach statistical significance (P=0.087).
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Postoperatively, the two groups did not differ significantly with respect to the mean ventilatory support time (P=0.891) and the mean hospitalization time (P=0.212); however, the mean time of the intensive care unit stay was shorter in Group 2 (P=0.004). The operative mortality was comparable in both groups (Group 1, 3(11.1%); Group 2, 1(1.9%); P=0.229). In Group 1 one child died because of sepsis on the 12th postoperative day. The second child from Group 1 exhibited superior vena cava syndrome and severe hypoxemia, was placed on extracorporeal membrane oxygenation (ECMO) on day 4 postoperatively, subsequently underwent reoperation (the closure of the azygous vein) and died on the 15th postoperative day. The last death in Group 1 occurred in a child who had undergone an emergency hemi-Fontan operation after resuscitation, and was due to poor ventricular function. The only death in Group 2 occurred in a child who after the first stage procedure had required prolonged ventilatory support and after hemi-Fontan exhibited severe superior vena cava syndrome and hypoxemia, was placed on ECMO and died on the 10th postoperative day.
Major postoperative complications in the survivors from Group 1 included: cerebrovascular accident—2(7.4%), sepsis—1(3.7%), phrenic nerve paralysis requiring diaphragm plication—1(3.7%) and need for ECMO due to poor ventricular function—1(3.7%). More severe complications in Group 2 survivors included: pleural effusions (incl. chylothorax)—6(11.8%), diaphragmatic paralysis requiring subsequent operation for plication—2(3.9%), hydropericardium—2(3.9%) and transient cerebrovascular accident—1(1.9%).
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4. Discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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In the univentricular heart, preservation of the ventricle and protection of the pulmonary vascular bed are the crucial goals of preliminary stages of the palliation ending with the Fontan operation.
The numerous favorable effects in the early postoperative period caused by the introduction of the RV–PA instead of BT in the Norwood procedure in children with single ventricle are now widely documented. Higher diastolic pressure [4–6,8,9,11,13,17,18], narrower pulse pressure [8–11,17] and satisfactory systemic oxygen delivery [17] provide stable hemodynamics after first-stage palliation, resulting in significantly higher early survival rates [7,8,12,18]. In comparison with BT, the right ventricle-to-pulmonary artery shunt eliminates diastolic ‘run-off’ from the systemic and coronary circulation into the pulmonary vascular bed (the flow through RV–PA occurs only during the systole; through BT—during diastole and systole). The reversal flow in the aortic arch and descending aorta [19] is no longer observed in children after the Norwood operation with RV–PA [10,12]. Improved coronary perfusion is probably the main reason for early hemodynamic stability [9].
On the other hand, the consequence of the flow though the RV–PA only during the systole (and even the reversal flow to the right ventricle during the diastole, dependent upon the diastolic function of the ventricle) is the significantly lower Qp:Qs ratio [7,9–11,18]. The diastolic flow in the BT adds to the higher pulmonary flow. In the early postoperative period, the systemic oxygen saturation, as well as the systemic oxygen delivery are equivalent in neonates who have undergone the Norwood procedure with BT or RV–PA [8,11,17], although many authors report a higher level of ventilatory support required to achieve equivalent arterial blood gas values [17,18]. In late follow-up, obstruction of the shunt due to intimal hyperplasia, as well as an increased oxygen demand (associated with the child's growing) may cause severe progressive hypoxemia and sudden death [5,7]. We have observed significantly lower arterial and venous oxygen saturation before the second-stage palliation, which is supported by the experience of other authors [7,11]. Our patients after RV–PA had significantly higher hematocrit values, which would be expected to result in a higher incidence of thrombotic events. In our series we did not observe any embolic events before the hemi-Fontan procedure. The postulate of application of larger shunts [4,5] is received with reluctance, because it requires larger ventriculotomy. The suggestion of earlier performance of the second stage, i.e. in 3–4 months of age in case of progressive hypoxemia [18] seems to be a more reasonable and interesting prospect.
Adverse effects of ventriculotomy on the ventricular performance in the univentricular heart was the main concern after the introduction of RV–PA. In spite the of elevated troponin T level in early postoperative period [18], that shows a marked injury of the myocardium caused by the insertion of the shunt, most investigators report good ventricular performance [5,13], and some authors even suggest that the function of the ventricle in patients after RV–PA is better than after BT: the level of inotropic support tend to be lower [17], and the rate of ventricular pressure rise (dp/dt) is higher [18]. The evidence of better ventricular performance is probably caused by more efficient coronary perfusion and lower volume load to the ventricle.
Supporting both the pulmonary and systemic circulation, the single ventricle is exposed to volume overload. The subsequent hypertrophy diminishes the chances of a successful Fontan operation. One of the most important goals in the management of children with single ventricle is avoidance of chronic volume overload. The loss of potential of the single ventricle to return to normal mass and volume, which continues with age [20,21], is a rationale for advocating avoidance of the volume overload caused by palliative procedure, as well as for an early performance of the second stage procedure [16]. In our material, children after RV–PA exhibited significantly lower Qp:Qs ratio and lower incidence of the ventricular hypertrophy before hemi-Fontan. From this point of view, the closure of any additional pre-existing pulmonary blood flow sources during hemi-Fontan is crucial in preserving function of the single ventricle.
The long-term follow-up of patients with other congenital heart defects (for example tetralogy of Fallot) suggests that ventriculotomy may be the substrate for ventricular arrhythmias. The concern for higher incidence of ventricular arrhythmias after RV–PA in children with HLHS has so far been not confirmed by clinical observations made by the present and other authors [7,18].
A theoretical consideration regarding a possible higher incidence of tricuspid valve regurgitation, caused by reversal flow in the shunt during the diastole, has not been confirmed in practice, both in our material, as well as in other reports [7,10].
The appropriate growth of the pulmonary arteries is essential in preparation to the Fontan pathway [15,22,23]. Small pulmonary arteries are associated with an increased risk of an early failure or persistent effusions. Many investigators report a high incidence of asymmetric growth, distortion, stenoses or even acquired discontinuity of the branch pulmonary arteries caused by modified or classic Blalock–Taussig shunt [24]. The distortion may be located in the site of shunt insertion, or be associated with the abnormal distention of the ductal tissue on the opposite side of BT [23,24]. To resolve this problem, some surgeons have proposed to construct the shunts more centrally, closer to the pulmonary artery bifurcation, using the sternotomy approach [25], or to establish central shunts [24]. Central shunts may produce better distribution of blood flow, resulting in more symmetrical development of the pulmonary arteries [25]. In our experience shared by other investigators [9], children after RV–PA show significantly better development of the pulmonary arteries in spite of a lower Qp:Qs ratio. We believe that this phenomenon is caused by two reasons: more centrally located distal end of the shunt with an additional enlarging homograft patch, and more pulsatile flow (the higher pulse pressure in the shunt).
The major limitations of our study include a difference between the two groups in the number of patients who underwent cardiac catheterization and the lack of randomization.
The right ventricle-to-pulmonary artery shunt in the Norwood procedure in children with hypoplastic left heart syndrome provides satisfactory palliation, preserves the ventricular function by reducing the volume load to the single ventricle, and stimulates development of pulmonary arteries, which is crucial. The development of earlier hypoxemia may require performing the second-stage palliation in the younger age.
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Appendix A. Conference discussion |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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Dr Januszewska: In our group we did not observe any stenosis of the central part of the pulmonary arteries. It may be related to the technique of the Norwood procedure. We always used a big, round homograft patch, about 1.5cm in diameter, to enlarge the distal end of the transected pulmonary arteries. And maybe, because of this, we did not observe in our patients the central stenosis of the pulmonary arteries.
Dr S. Daebritz (Munich, Germany): There is currently a lot of discussion about RV–PA shunts. From personal communications with the Boston group I know, that a lot of scaring in the right ventricle around the shunt insertion site has been observed postmortem in two patients. So these patients died. Have you seen regional wall abnormalities in these patients?
And the second question, what do you think is the advantage of this special way of performing the Glenn anastomosis, as you are obviously cross-clamping the aorta for that, or did I misunderstand that?
We are usually very happy not to cross-clamp the aorta in the right ventricle single ventricle anatomy. So why do you perform it this way?
Dr Januszewska: We did not observe in postmortem examination any changes in the place of the insertion of the right ventricle to pulmonary artery shunt. And we did not either notice changes in ECG examination, which might have corresponded to the scarring of the right ventricle. In one patient, there was a small aneurysm located in the proximal end of the shunt and this aneurysm was completely removed during the hemi-Fontan operation without future complications and the postoperative course of this child was uneventful.
As to the second question, we think that hemi-Fontan procedure has many advantages over the bidirectional Glenn with respect to the opportunity for the augmentation of the pulmonary arteries and of the repair of the intracardiac lesions, for example, tricuspid regurgitation. So because of this, we perform the hemi-Fontan procedure instead of the bidirectional Glenn during the second stage procedure.
Dr G. Ziemer (Tuebingen, Germany): I was still reading here ‘acceptable hypoxemia.’ Can you tell us what acceptable hypoxemia is? What may be acceptable for the surgeon to make a patient survive may not be sufficient for the kid to get schooling later on.
Dr Januszewska: Acceptable, of course, from the perspective of the patient, because we did not observe any adverse effects of this hypoxemia meaning neurological complication in early follow up.
Dr Ziemer: What did you look at when you said ‘observe’?
Dr Januszewska: We did not notice, for example, events of cerebrovascular accidents or changes in early neurodevelopment of these children.
Dr Ziemer: I think we have to look much longer at these kids to justify what has been acceptable.
Dr Januszewska: Yes, that's right.
Dr J. Photiadis (Sankt Augustin, Germany): I liked that you looked at Hb, or hematocrit, which is significantly different in between the first and the second group. All other studies that have been published previously never looked at that specifically. And as we all know, after modified ultrafiltration with increased hematocrit, you can easily increase diastolic or mean blood pressure; but no study commented on this.
So don't you think that higher hemoglobin concentration in the second group can also describe the, let's say, less stormy course of the patients with RV to PA conduits, since increasing of hematocrit has been already shown in 1982 by Lister and colleagues to decrease left to right shunt. Do you think that is the reason for the better postoperative course?
Dr Januszewska: In the early postoperative course, after Norwood procedure, we did not observe any differences with respect to the hematocrit value or hemoglobin concentration. The differences are only in the late period, or in other words before the hemi-Fontan procedure. And they result from the lower Qp/Qs ratio and lower oxygen saturation. It's just a reaction of the child to the hypoxemia.
Dr W. Mrowczynski (Poznan, Poland): This year, during the AATS meeting, a system of home monitoring of saturation was presented and the interim survival between two stages was increased. And I would like to ask you about the influence of the potential hypoxia in both groups, although there was no intergroup difference, what was the impact of hypoxemia on survival between two stages?
Dr Januszewska: Between the two stages, in the late postoperative course, one child died because of complications associated with the obstruction of the shunt.
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Footnotes |
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Presented at the joint 18th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 12th Annual Meeting of the European Society of Thoracic Surgeons, Leipzig, Germany, September 12–15, 2004. |
References |
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TopAbstract1. Introduction2. Materials and methods3. Results4. DiscussionAppendix A. Conference...References |
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