International Journal of Cardiovascular ResearchISSN: 2324-8602

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Research Article,  Int J Cardiovasc Res Vol: 8 Issue: 3

Surgical Management of Tetralogy of Fallot with Inadequate Size Pulmonary Artery Branches

Ahmed MF Ghoneim*, Ahmed Farouk and Ahmed I Ismail

Pediatric Cardiothoracic Surgery Unit, Cardiothoracic Surgery Department, Assiut University, Assiut, Egypt

*Corresponding Author: Ahmed MF Ghoneim, MD
Professor and Chairman, Cardiothoracic Surgery Department, Faculty of Medicine, Assiut University, Assiut 71526, Egypt
Tel: +20 100 121 5565
Fax: +20 88 233 3327
E-mail: [email protected]

Received: May 02, 2019 Accepted: June 11, 2019 Published: June 22, 2019

Citation: Ghoneim AMF, Farouk A, Ismail AI (2019) Surgical Management of Tetralogy of Fallot with Inadequate Size Pulmonary Artery Branches. Int J Cardiovasc Res 8:3. doi: 10.4172/2324-8602.1000379

Abstract

Background: Tetralogy of Fallot (TOF) with inadequate size pulmonary artery (PA) branches continues to be a problem in many developing countries due to late presentation. Surgical management is still debatable in clinical practice. Our aim is to review our experience with different surgical modalities for management of this subset of patients.

Methods: Between 2012 and 2018, out of 314 operations for TOF at our unit, there were 26 cases judged either pre-operatively or intraoperatively to have PA branches inadequate for total correction (McGoon’s ratio ≤ 1.5 or pulmonary branch size <-2 Z-value of expected size). Modified Blalock-Taussig shunt (MBTS) was done in 11 cases (shunt strategy). Open-heart surgery, involving going on cardiopulmonary bypass and cardiac arrest, was done in 15 cases (right ventricular outflow tract, RVOT, reconstruction strategy). The main PA was opened and the PA branches were sized from inside using Hegar sizers and Z-scores obtained. In 6 cases, the measured PA branches were smaller than the -2 Z-value, so, RVOT reconstruction without ventricular septal defect (VSD) closure (antegrade palliation) was done. The PA patch was adjusted to get a main PA annular diameter of not more than Z-value of -4, and to get an oxygen saturation on 25% FiO2 not exceeding 90%. In the remaining 9 cases, the sizes of the PA branches were found to accommodate a Hegar sizer within -2 Z-values. So, in those 9 patients, we proceeded to total repair with VSD closure.

Results: There were no statistically significant differences between the 2 strategies (shunt vs. RVOT reconstruction) as regarding the preoperative parameters (age, weight, preoperative oxygen saturation on room air and the preoperative McGoon’s ratio of branch pulmonary arteries size). As regarding the postoperative data, there was statistically significant difference in the total mortality being less in RVOT reconstruction (1/15, 6.6%) compared to MBTS (4/11, 36.4%). The ratio between the diameters of branch pulmonary arteries was significantly lower in antegrade palliation than with MBTS, denoting more equal and even growth of pulmonary artery branches after antegrade palliation.

Conclusion: In TOF patients judged preoperatively to have small PA branches not suitable for total correction, intra-operative direct assessment of the sizes of pulmonary artery branches by Hegar sizers is more accurate and reliable than preoperative imaging studies, and offered to save many patients from a two-stage repair allowing them a primary total repair with perfect results. In cases that needed a two-stage repair because of small PA branches, antegrade palliation yielded better early outcome than MBTS and furthermore provides uniform branch pulmonary arteries growth, which facilitates the 2nd stage total correction.

Keywords: Tetralogy of Fallot; Pulmonary arteries; Antegrade palliation; Systemic-to-pulmonary shunts

Introduction

Tetralogy of Fallot is one of the first surgically managed congenital cardiac lesions; whether by palliative systemic to pulmonary artery shunts by Blalock [1], or by total correction using pump-oxygenator by Kirklin et al. [2]. Since those ingenious early efforts, a staged repair starting with a systemic-to pulmonary shunt (modified Blalock-Tausig shunt) was advocated for those cases not suitable for direct single stage total correction; such as young infants with severe symptoms, and cases with small pulmonary artery (PA) branches. Nonetheless, management strategies moved more and more towards early single stage repair even in young infants, leaving small PA branches as the main indication for systemic-to pulmonary shunt. However, in neonates or young infants it should be noted that small size PAs, measured by echocardiography, might simply reflect low flow, with the potential capacity to dilate with increased flow [3].

We decided to review our experience with different surgical modalities used in management of tetralogy of Fallot (TOF) with small pulmonary artery branches, considered inadequate for total correction.

Patients and Methods

This is a retrospective comparative study of surgical strategies used in our center for management of TOF with small pulmonary artery branches, considered inadequate for total correction. The Research and Ethics Committee within our Faculty have reviewed the study proposal, and waiver of consent was approved, as it is a retrospective study.

According to our database, from 2012 to 2018, 314 cases of TOF underwent surgical intervention. We included in this study all cases TOF that had small branch pulmonary arteries judged to be inadequate in size for primary total repair (based upon the preoperative McGoon’s ratio ≤ 1.5 by echocardiography or cardiac catheterization pulmonary angiography). Cases with Tetralogy of Fallot and pulmonary atresia, or those associated with other anomalies were excluded from this study. Twenty-six cases were identified (8.2% of total Fallot’s operations) fulfilling the above criteria.

Collected preoperative data included the age, weight, preoperative oxygen saturation on room air, and preoperative McGoon’s ratio for PA branches size.

Management strategies

2 Management strategies were used in our unit for dealing with such cases:

1. Systemic-to-pulmonary shunt: This was done through a modified Blalock-Taussig shunt (MBTS) in 11 cases. (7 through a median sternotomy and 4 through left thoracotomy) followed later by total correction when PA branches sizes became adequate for total correction.

2. Since 2015, a different strategy was adopted in 15 cases (right ventricular outflow tract reconstruction); involving going on cardiopulmonary bypass and cardiac arrest. The main PA was opened longitudinally and the branch pulmonary arteries were sized from inside, using Hegar dilators. The measured sizes of the PA branches were compared with the expected sizes calculated according to body surface area of the child and Z-scores were obtained [4].

In 6 cases, the measured PA branches were smaller than the -2 Z-score of the calculated expected size, so, right ventricular outflow tract reconstruction without VSD closure (antegrade palliation) was done in those 6 cases. The right ventricular outflow tract reconstruction (whether through a trans-annular patch or pulmonary artery patch) is adjusted to get an annular diameter not larger than Z-score of -4 of the expected size according to body surface area, and to get an oxygen saturation on 25% FiO2 not more than 90%; to avoid pulmonary overflow and postoperative heart failure as the VSD was not closed. The patch can be extended into one or both PA branches to augment them if needed.

In the remaining 9 cases, the sizes of the PA branches were found to accommodate a Hegar sizer within -2 Z-score of the expected size according to the child’s body surface area. So, in those 9 patients we proceeded to primary total repair including VSD patch closure & right ventricular outflow tract reconstruction using a pericardial patch extending as far as needed into the distal LPA or RPA. It is of importance to mention here that the branch pulmonary arteries that appear to be smaller than the expected size during echocardiography, CT angiography, catheter angiography or even during the naked eye examination at operation may be underestimated regarding its actual size due to the under filling of the PA branches. Therefore, measuring of the PA branches from inside using Hegar sizers allows proper estimation of the artery, not to mention the property of distensibility of the arterial wall. In such cases, total repair should be accompanied by other measures to minimize pulmonary regurgitation. A transannular patch should be avoided as possible, and consider an annulus size of Z-value as small as -2 to be adequate. If inevitable, the trans-annular patch should be restricted allowing limited annular enlargement to get a Z-value of only -2, and extended just few millimeters below the annulus limiting the resulting ventriculotomy. If the infundibulum is diffusely hypo plastic and long right ventriculotomy is needed, a monocusp pulmonary valve should be constructed during the trans-annular patching. After weaning from cardiopulmonary bypass, RV/LV pressure ratio was measured in all cases undergoing total correction.

Collected postoperative data included postoperative mortality, the length of postoperative ventilator support, inotropic support, hospital stay, and oxygen saturation on room air at time of discharge.

Pre-discharge and follow-up echocardiographies were done in all cases that had staged repair. Pulmonary artery branches were measured and compared; preoperative McGoon’s ratio vs. immediate postoperative vs. pre-total correction measurements. Also, comparisons of the left vs. right pulmonary artery branch sizes after the palliative repair immediately prior to total correction.

Statistical analysis

Analysis was done using the statistical package SPSS PC (version 20) (SPSS INC., 444 N. Michigan Avenue, Chicago, IL 60611, USA). Continuous variables were presented as means ± standard deviations and categorical variables were presented as percentages. Comparison between means was achieved using independent samples T-test. The level of statistical significance was set at a p-value of 0.05 or less.

Results

There was no statistically significant difference between the 2 strategies (systemic-to-pulmonary shunt vs. right ventricular outflow tract reconstruction) as the regarding the preoperative parameters (age, weight, preoperative oxygen saturation on room air and the preoperative McGoon’s ratio of branch PA size) (Table 1).

Group Statistics
Variables Group N Mean Std. Deviation p-value
Age (in years) A 11 2.464 1.3170 0.086 NS
B 15 1.667 0.9582
Weight (in kg) A 11 10.27 2.005 0.497 NS
B 15 9.73 1.944
Preoperative oxygen saturation (%) A 11 79.09 4.437 0.369 NS
B 15 77.40 4.793
Preoperative McGoon’s ratio A 11 1.418 0.1471 0.63 NS
B 15 1.333 0.1496
Postoperative oxygen saturation (%) A 11 89.27 1.954 0.35 NS
B 15 92.67 4.716
Total mortality A 4 (3 early & 1 late): 4/11 0.000 SS
B 1 (early): 1/15
Postoperative ventilation duration (in hours) A 11 22.75 5.203 0.034 SS
B 15 17.53 5.303
Postoperative inotropic support duration (in hours) A 11 68.75 12.37 0.042 SS
B 15 86.8 21.657
Postoperative hospital stay (in days) A 8 6.75 1.035 0.506 NS
B 14 7.13 1.407
McGoon’s ratio one month postoperative A 8 1.500 0.1095 0.294 NS
B 14 1.320 0.5454
McGoon’s ratio before 2nd stage (total correction) A 8 1.813 0.1126 0.113 NS
B 6 1.943 0.1813
RPA /LPA prior 2nd stage (total correction) A 8 1.250 0.1195 0.003 SS
B 6 1.043 0.0976

Table 1: Comparison between the 2 strategies; (A) systemic to pulmonary shunt vs. (B) right ventricular outflow tract reconstruction, as regarding preoperative data and postoperative outcome

As regarding the postoperative data, there was statistically significant difference in the total mortality (Table 1) being less in strategy (B); 1/15 (6.6%) vs. 4/11 (36.4%) for strategy (A).

Weak statistically significant difference was found as regarding the postoperative ventilation duration [lower duration in strategy (B) patients than in strategy (A)] and the duration of postoperative inotropic support [lower in strategy (A) patients than in strategy (B)] (Table 1).

Weak statistically significant difference was found as regarding the postoperative ventilation duration [lower duration in strategy (B) patients than in strategy (A)] and the duration of postoperative inotropic support [lower in strategy (A) patients than in strategy (B)] (Table 1).

In strategy (A) patients (systemic-to-pulmonary shunt group)

There were 3 early mortalities (27%); 14-38 hours (27 ± 4.2) postoperatively due to high output heart failure in spite of good contractility, and using 4 mm Gore-Tex grafts between right subclavian and right pulmonary arteries. The 8 remaining patients survived to total correction 9-21 months after the 1st stage. One case died during total correction because of bleeding during takedown of the systemic-to-pulmonary shunt, previously done thorough left thoracotomy. Two cases had distortion and uneven growth of pulmonary artery branches that required branch pulmonary artery angioplasty using patches at time of total repair.

In strategy (B) patients (RVOT reconstruction group)

The antegrade palliation subgroup (B1) showed no early mortality. However, one patient required re-exploration for pulmonary overflow that caused unsatisfactory arterial oxygen tension in the blood gases and plethoric lung fields in chest X-ray with subsequent failure of weaning from mechanical ventilation. During re-exploration, tightening sutures were taken in the pericardial patch at the level of the pulmonary annulus. The patient was extubated smoothly after 20 hours. There was no late mortality during the 2nd stage of repair. At the time of the redo surgery for total correction of the “antegrade palliation” patients, bilateral even growth of pulmonary branches was noticed; therefore, no further pulmonary branch angioplasty was needed. In two cases no further pulmonary artery (RVOT) patch enlargement was required. While in the remaining 4 cases, additional patch enlargement (using Gore-Tex patches) was required to reach a pulmonary artery size with Z-value of 0.

As regarding the primary total repair subgroup (B2) (9 patients), there was one case of early mortality due to low cardiac output. This patient had post-repair RV/LV ratio of 0.9 with expected failure of weaning from cardiopulmonary bypass. So decision was made to do fenestration of the VSD patch. The patient was weaned successfully from cardiopulmonary bypass, on high doses of inotropic support (Adrenaline + Milrinone). However, few hours postoperatively, the patient developed low cardiac output with persistent acidosis and died on the 2nd postoperative day. In the remaining patients, RV/LV ratio after weaning from bypass was 0.5 – 0.75 (0.6 ± 0.13).

The preoperative McGoon’s ratio was significantly less in group B1 patients (Antegrade palliation) in comparison to group B2 patients (Primary total correction), (p-value=0.01, Table 2).

Variables Antegrade Palliation (Group B1) Primary total correction (Group B2) p-value
Number of patients 6 9 -
Age in years (mean ± SD) 2.086 ± 1.2562 1.300 ± 0.3928 0.116 NS
Weight in kg (mean ± SD) 10.14 ± 2.268 9.38 ± 1.949 0.466 NS
Preoperative oxygen saturation (mean ± SD) 79.00 ± 15.164 76.00 ± 14.276 0.24 NS
Preoperative McGoon’s ratio (mean ± SD) 1.214 ± 0.1069 1.438 ± 0.0916 0.01 SS

Table 2: Comparison of the preoperative data of patients undergoing Antegrade Palliation vs. those undergoing Primary Total Correction.

Discussion

Tetralogy of Fallot is a congenital heart disease characterized by central pulmonary stenosis involving variable levels of right ventricular outflow tract, pulmonary valve and main pulmonary artery. Rarely branch pulmonary arteries are involved in stenosis and if so it is usually proximally.

Surgical treatment of tetralogy of Fallot with inadequate sized pulmonary artery branches is still debatable in the clinical practice. The subgroup of patients with diminutive pulmonary arteries cannot tolerate total correction. In such patients, the ability of the pulmonary vascular bed to accept full cardiac output, without increase the right ventricular pressure more than two thirds of the systemic pressure, is the determinant factor whether the VSD can be closed safely or not.

Investigators, reporting on the selection criteria for total correction, have emphasized the importance of the pulmonary arteries size. Unlike ventricular septal defect with pulmonary atresia, in TOF usually there are no major aorto-pulmonary collateral arteries, therefore, all lung segments are supplied by central (native) pulmonary arteries. However, the long-standing reduction of the central pulmonary blood flow by the severe RVOT-PA stenosis causes the growth of the pulmonary vascular bed to be hampered. Therefore, the pulmonary vascular bed cannot accommodate the sudden increase in the RV output, resulting in RV/LV pressure ratio after VSD closure to be >0.7 with subsequent RV failure and failure of weaning from CPB or inotropic support or even sudden death later. Thus, it is important to have some tools that can help to predict the adequacy of pulmonary vascular bed [5-7].

In situations where the pulmonary vascular bed is predicted to be inadequate for RV outflow after VSD closure; surgical strategies to promote the growth of such diminutive pulmonary arteries are needed. In our study we adopted two strategies to help promote the growth of the small central pulmonary arteries branches deemed unsuitable for primary total correction; systemic-to-pulmonary shunt in 11 cases and antegrade palliation in 6 cases. There have been conflicting reports regarding the growth of pulmonary arteries after palliation with the systemic-pulmonary shunts. Some investigators have shown good satisfactory growth of the pulmonary annulus and pulmonary arteries after Blalock-Taussig shunts [3,8-10]. However, others have expressed concern about the high incidence of kinking and stenosis when the Blalock-Taussig shunts are performed on infants with diminutive pulmonary arteries. Such potential shuntrelated complications have been reported in as high as 36% of neonates and small children, increasing the risk of morbidity and mortality in subsequent corrective surgery. However, even perfect shunts might result in unbalanced development of central pulmonary arteries, with preferential growth of the ipsilateral or contralateral pulmonary artery branches [3,11-14]. Lamberti et al. reported a more symmetrical and greater increase in the diameter of the pulmonary artery after more centrally placed shunts in comparison to the peripherally placed Blalock-Taussig shunts [15].

In our study, eight patients survived after Blalock-Taussig shunts to have their 2nd stage repair (total correction). Two out of the eight cases, had distortion and uneven growth of pulmonary artery branches that required pulmonary arteries angioplasty using patches at time of total repair. Also, when measuring the ratio between the diameters of LPA and RPA at time of 2nd stage (total repair) we found that it was greater than that after antegrade palliation (p-value=0.003); denoting more equal and even growth of pulmonary artery branches after antegrade palliation compared to systemic-to-pulmonary shunts.

As regarding the mortality after systemic-to-pulmonary shunts in our study, we had three early mortalities (27%) due to heart failure in spite of good contractility, and one late mortality due to bleeding during shunt takedown. In an article about the mortality risk estimated for 148 types of operative procedures, using data from 77,294 operations of EACTS and STS Congenital Heart Surgery Databases between 2002 and 2007, the estimated mortality risk of modified Blalock-Taussig shunt was 8.9%, and that of shunt take down was 4.5% [16]. The cause of mortality in our study was shunt overflow with subsequent cardiac output stealing to pulmonary circulation and congestive heart failure. We think that the increased mortality from shunt over flow in our patients is due to the capacious pulmonary vascular bed indicated by the immediate increase of the McGoon’s ratio from preoperative ratio of 1.418 ± 0.1471to a postoperative ratio of 1.7 ± 0.109 in the ICU. This means that those pulmonary arteries diagnosed preoperatively to be inadequate could have allowed total repair with VSD closure to avoid difficult postoperative management of lungs not accustomed to this sudden increase in pulmonary flow. Alkhulaifi et al. in their study on the early outcome of 79 systemicto- pulmonary shunts reported 3 early deaths, all attributed to shunt overflow [13].

On the other hand, many authors have reported excellent surgical results of right ventricular outflow tract reconstruction for symptomatic patients with tetralogy using cardiopulmonary bypass [7,10,17-19]. The practical advantage of the palliative right ventricular outflow tract reconstruction (antegrade palliation) is that it offers substantially greater, more rapid, more uniform, and more predictable pulmonary arteries growth than systemic-topulmonary shunts. Piehler et al. reported a 2.20 fold increase in mean pulmonary artery size 26 months after outflow tract reconstruction in 12 patients [7]. Okita et al. reported 25 cases of TOF underwent palliative reconstruction of the right ventricular outflow tract without closure of the ventricular septal defect, 8 of them had 13 prior Blalock-Taussig shunts that failed to enlarge the small hypoplastic pulmonary arteries. They reported an increase in the size of the pulmonary artery McGoon’s from 0.72 to 2.06 (p less than 0.01) [19]. In our study, we had 6 patients with TOF with McGoon’s ratio of 1.214 ± 0.1069 underwent palliative right ventricular outflow tract reconstruction without VSD closure. There was no early mortality, however one patient required re-exploration for pulmonary overflow that was managed by retightening sutures of the pulmonary annulus at the trans-annular patch. Also, there was no late mortality during the 2nd stage of repair (total correction). At the time of the redo surgery for total correction, the McGoon’s ratio increased to 1.943 ± 0.1813 (p-value=0.05), and there was bilateral even growth of pulmonary branches (RPA/LPA diameter ratio prior 2nd stage total correction=1.04 ± 0.09) so no further pulmonary branch angioplasty was required at time of total repair.

Of importance to mention here that the branch pulmonary arteries that appear to be smaller than the expected size during echocardiography, CT angiography, catheter angiography or even intraoperatively before doing the shunt or antegrade palliation, may be underestimated of its actual size due to the under filling of the PA branches, so measuring of the PA branches from inside using Hegar sizers allows proper estimation of the artery, not to mention the distensibility property of the arterial wall.

In our study 9 of the 15 patients of TOF with preoperatively assumed small pulmonary arteries (McGoon’s ratio 1.438 ± 0.0916) had total correction after finding that those assumed small pulmonary arteries were able to accommodate Hegar sizers of more than -2 of their calculated Z-value. The post repair RV/LV pressure ratio of these cases were 0.5-0.75 (0.6 ± 0.13) with one postoperative mortality. Groh et al. in their study about total repair of 58 infants with TOF, 15 of them with McGoon’s ratio 1.2 to 1.5 found that Right ventricular/left ventricular pressure was 0.55 ± 0.03 in infants with McGoon’s ratios of 1.2-1.5 compared to 0.46 ± 0.03 in patients with ratios of 1.6-2.0, and 0.47 ± 0.03 in patients with ratios greater than 2.0 (p=0.01) with no hospital deaths in all of them [20]. So, we believe that McGoon’s ratio between 1.2 and 1.4 is the cut line between one stage and two-stage repair of TOF. In fact, relating the sizes of pulmonary artery branches to the patient’s body size or surface area (Z-scores) is more accurate than relating them to the descending aorta (McGoon’s ratio). Nakata et al. stated that the incidence of low cardiac output was higher in patients with a smaller PA-index, especially when the PAindex was less than 150 mm2/m2 BSA [5]. Pulmonary artery branches Z-value of -2 is comparable to pulmonary artery index of 150 mm2/ m2 BSA [4]. Therefore, in practice, many surgeons nowadays, depend on measuring the pulmonary artery Z-value that is easily obtained through preoperative echocardiography. Still however, a more accurate method would be measuring them intraoperatively using the Hegar sizers.

Many investigators have shown that TOF can be repaired in the first few months of life with excellent results [21-24]. Groh et al. [20] argue that one stage total repair could be done with excellent results irrespective to the size of the pulmonary arteries (all of their patients had McGoon ratio ≥ 1.2). Reddy et al. [24] found that that postrepair peak systolic right ventricular-to-peak systolic left ventricular pressure ratio did not correlate with the branch pulmonary artery size (p-value=0.96). The age of patients in our study was 2.04 ± 1.1701 due to delayed presentation to the surgeons in our locality which resulted in many of them had small sized pulmonary artery branches due to inadequate forward flow which hampered their growth with time. So, we think that early screening and referral, as well as increasing experience in managing small weights will allow routine intervention in the first few months of life and thus omit this problem in the future.

Limitations

The small number of patients in this study does not allow us to make hard recommendations towards routine intra-operative direct assessment of the sizes of pulmonary arteries, or towards routine antegrade palliation strategy. This study just sheds the light on the false low measurement of those pulmonary arteries that we might get due to under filling, and the possible advantages of direct intraoperative assessment using Hegars. A larger study population or even a multicenter wide scope study may provide us with clear guidelines for managing those patients presenting late, with inadequate size pulmonary arteries.

Conclusion

In patients with TOF, judged preoperatively to have small pulmonary artery branches not suitable for total correction, intraoperative direct assessment of the sizes of pulmonary artery branches by Hegar dilators is more accurate and reliable than preoperative imaging studies. Adopting this strategy allowed us to save many patients from a staged repair, giving them a primary total repair with perfect results.

In patients who need a staged repair because of true small pulmonary artery branches, antegrade palliation (using PA patch adjusted to get an annular diameter of not more than Z-value of -4 and to get an oxygen sat on 25% FiO2 not exceeding 90%) yielded better early outcomes than modified Blalock-Taussig shunt and provided uniform bilateral pulmonary arteries growth, thus facilitating the 2nd stage total correction.

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