WHAT IS NEW?
- This study is based on the large, single-center tetralogy of Fallot (TOF) cohort in China, aimed to clarify annulus-sparing repair has an acceptable surgical effect and is feasible in TOF patients, even those with a severely dysplastic pulmonary valve annulus (PVA).
- This study suggested that full intraoperative relief of supra- and subvalvular tissue can achieve better extension of PVA, promote postoperative PVA growth, and reduce the annular peak gradients (APG).
WHAT ARE THE CLINICAL IMPLICATIONS?
- When intraoperative judgment is based on (1) no right ventricular swelling; (2) hemodynamic stability without use of high doses of vasoactive drugs; (3) no significant tricuspid regurgitation; and (4) sufficient antegrade blood into the lungs determined according to end-tidal carbon dioxide, an APG ≥ 50 mmHg is acceptable level at discharge for TOF patients undergoing annulus-sparing surgery, with a decreasing trend in APG over time.
Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart defect. There is ongoing controversy regarding whether relieving the obstruction of a dysplastic pulmonary valve annulus (PVA) requires transannular patch enlargement (TAPE). The z-score for the PVA is the most commonly used predictor of the need for TAPE. If the PVA z-score is too small, TAPE repair is adopted. However, a critical shortcoming of this method is that the loss of structural integrity of the pulmonary valve will cause progressive pulmonary regurgitation (PR). Some studies have suggested that compensatory responses to right ventricular volume overload are adequate for a long period.[2,3] Progressive right ventricular dilation, biventricular dysfunction, ventricular arrhythmias, and sudden cardiac death have been recognized as late sequelae of chronic PR in patients with repaired TOF.[4,5] Ultimately, these patients will receive pulmonary valve replacement (PVR), but this has not been shown to improve right ventricular function and other adverse outcomes, despite improving PR and reducing right ventricular volumes.
To avoid the long-term disadvantages and reintervention of TAPE, recent surgical efforts have focused on preservation of the structural integrity of pulmonary valves, such as valvoplasty with an autologous pericardium after TAPE, pulmonary arterioplasty and valvular sinus plasty with an autologous pantaloon pericardial patch, pulmonary valve cusp plasty, pulmonary root enlargement, and annulus-sparing (AS) repairs with intraoperative balloon dilation and delamination plasty.[11–14] Furthermore, the PVA is believed to have growth potential.[11,15] In our experience, abnormal supra- and subvalvular apparatuses restrict blood flow into the pulmonary artery and restrict PVA growth. Moreover, recent studies have demonstrated that patients with repaired TOF and similar PR fractions show less dilation and dysfunction of the right ventricular in the presence of some residual PS, and AS is associated with low risk and benefits for right ventricular geometry. Therefore, we hypothesized that relief from total obstruction of the right ventricular outflow tract (RVOT), adequate release of the annulus, and promotion of antegrade blood flow across the PVA could reduce the risk of significant postoperative PR and achieve favorable clinical outcomes and PVA growth with somatic development regardless of a moderate residual annular peak gradient (APG) in early AS repair. We aimed to evaluate the feasibility and surgical effect of consecutive and nonselective AS in TOF populations with a series of surgical strategies.
The study protocol was approved by the ethics review board of the National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College (Beijing, China; No. 2020-1318). Waiver of written informed consent was also approved by the ethics committee.
This was a retrospective cohort study. Patients were enrolled consecutively in our test group and underwent repair by the same surgeon. The control group was matched based on the propensity score.
Patients and echocardiography
All patients with TOF who could tolerate 1-stage repair were included unless: (1) pulmonary blood flow was dependent on major aortopulmonary collaterals; (2) there was a coexisting atrioventricular septal defect; (3) pulmonary valve was absent; (4) any other complex cardiac malformations were present.
All AS patients were divided into 2 groups according to the PVA z-score: AS, PVA z-score ≥−2 group and AS, PVA z-score <−2 group. A dysplastic control group matched 1:1 by the PVA z-score was considered TAPE group (PVA z-score <−2).
A single reviewer measured all available preoperative, postoperative, and hospital discharge transthoracic echocardiography reports independently. Echocardiography reports were obtained using standard views as recommended by published guidelines, and were reviewed for the degree of PR and APG. The PVA z-score was calculated according to an equation used previously. The study dataset was compiled in December 2018, and routine follow-up echocardiography was conducted within or outside the research center at 30 days as well as at 3, 6, 12, 24, and 36 months. We adopted a pulmonary valve-specific technical performance score (TPS) as reported previously to evaluate the adequacy of AS and TAPE according to echocardiography reports. We defined “pulmonary valve TPS” as “class 1” (APG <20 mmHg or no/trivial PR), “class 2” (APG 20–40 mmHg or mild-to-moderate PR), or “class 3” (APG >40 mmHg or moderate or severe PR). We also stratified the TPS for PR in class 3 into “moderate pulmonary regurgitation” and “severe pulmonary regurgitation” to obtain more information. “Severe pulmonary regurgitation” was defined as greater than “moderate pulmonary regurgitation.”
During cardiopulmonary bypass by ascending aortic and bicaval cannulation and under cardioplegic arrest and moderate hypothermia, the infundibulum was incised longitudinally to just below the level of the PVA in all patients. The parietal-muscle bundle was resected, and the ventricular septal defect was closed. Patched enlargement with fresh autologous pericardium was adopted in the main pulmonary artery (MPA) and branch pulmonary artery if necessary. Patients in TAPE group underwent traditional TAPE repair. In the AS groups (AS, PVA z-score ≥−2 group and AS, PVA z-score <−2 group), valvuloplasty usually involved a combination of splitting fused commissures extending to the level of the PVA to achieve a larger effective orifice. In the AS, PVA z-score <−2 group, we used a continued T-shaped approach and an inverted T-shaped approach in the incision of the infundibulum and MPA, extending parallel to the annulus, respectively, to release sub- and supra-valvular tissues, which might restrict PVA growth as much as possible. A longitudinal incision along the middle line of 1 or 2 leaflets to the level of the PVA was undertaken to release constraints on the PVA in patients with a bicuspid pulmonary valve if the effective orifice remained too small after the procedures mentioned above. Pulmonary valve plasty with a large triangular fresh autologous pericardium patch was conducted to prevent PVR and orifice restenosis by stretching the circumference of the PVA to increase the orifice area. A dilator was employed to size the annulus to ensure full release and remained in the inner side of the PVA to avoid annular shrinking and restenosis if pulmonary valve plasty and enlargement of MPA and RVOT were undertaken for continuous sutures and knotting. Often, MPA and RVOT were augmented with a triangular fresh autologous pericardium patch and a rectangular Dacron™ (Maquet Getinge group, Rastatt, Germany) patch lined with autologous pericardium, respectively. In patients who underwent TAPE, a valved bovine jugular vein patch was used to augment the RVOT, annulus, and MPA.
The datasets used and/or analyzed during our study is available from the corresponding author upon reasonable request.
A TPS in a high class has been reported to be associated with a higher risk for reintervention for residual PS. An independent staff member blinded to treatment assignments adjudicated all suspected TPSs. The number and percentage of patients with TPSs for PR and PS were used to evaluate clinical outcomes for all patients who received AS treatment.
Continuous variables were represented as the mean ± standard deviation (SD) or median (Q1, Q3) and were compared using analysis of variance or the Kruskal-Wallis test. Categorical variables were summarized using frequencies and percentages, and were compared using the χ2 test. P < 0.05 was considered significant. We used a time-dependent Kaplan-Meier curve showing freedom from severe PR following AS and TAPE procedures over time. Statistical analyses were performed using SPSS 24 (SPSS, Inc., Chicago, Illinois, USA).
Clinical and procedural characteristics
Among the entire cohort of 375 TOF patients who received primary repairs from January 2014 to June 2017 in the Center for Pediatric Cardiac Surgery of Fuwai Hospital, 60 consecutive and nonselective patients underwent 1-stage repair of TOF with aggressive PVA-preserving strategies performed by a single surgeon were enrolled in AS cohort. In AS cohort, patients were divided into AS, PVA z-score ≥−2 group (33 patients) and AS, PVA z-score <−2 group (27 patients). During the same period, 315 patients (PVA z-score, 0.99 to –7.23) underwent TAPE repair by other surgeons were enrolled as TAPE cohort, of these, 87 patients with PVA z-score ≥−2 underwent TAPE repair were excluded. From the 228 patients in the TAPE group, 27 cases were selected as TAPE, PVA z-score <−2 group according to the propensity score and 1:1 ratio with AS, PVA z-score <−2 group. A flowchart revealing patient inclusion is shown as Figure 1. The preoperative, operative, and postoperative characteristics of 87 patients who underwent TOF repair are presented in Table 1 and Figure 2.
Table 1 -
Preoperative, operative, and postoperative outcomes of 87 patients undergoing TOF repair
||Overall (n = 87)
||TAPE group (n = 27)
P (AS, PVA z-score <−2 vs. TAPE)
|z ≥−2 (n = 33)
||z <−2 (n = 27)
|Age (months), median (Q1, Q3)
||10.7 (7.0, 20.0)
||10.6 (7.1, 14.6)
||13.0 (6.6, 24.0)
||11.0 (8.0, 19.0)
|Weight (kg), mean ± SD
||10.7 ± 7.7
||8.9 ± 3.2
||11.6 ± 9.1
||11.9 ± 9.6
|Female, n (%)
|PVA z score, mean ± SD
||−2.4 ± 1.5
||−0.7 ± 0.9
||−3.2 ± 1.9
||−3.5 ± 0.9
|Preop RVOT peak gradient (mmHg), mean ± SD
||75.7 ± 17.9
||77.7 ± 19.4
||77.7 ± 18.9
||71.4 ± 14.4
|PV morphology, n (%)
|Additional procedures, n (%)
| MPA plasty
| Branch PA plasty
| PV plasty
|APG at final follow-up (mmHg), mean ± SD
||23.1 ± 14.5
||23.4 ± 13.0
||26.4 ± 11.7
||19.6 ± 18.2
|Follow-up duration (months), mean ± SD
||30.3 ± 11.6
||31.8 ± 12.5
||30.3 ± 9.4
||28.4 ± 12.6
APG: Annular peak gradient; AS: Annular sparing; MPA: Main pulmonary artery; PA: Pulmonary artery; Postop: Postoperative; Preop: Preoperative; PV: Pulmonary valve; PVA: Pulmonary valve annulus; RVOT: Right ventricular outflow tract; SD: Standard deviation; TAPE: Transannular patch enlargement; TOF: Tetralogy of Fallot.
The proportion of patients in AS, PVA z-score <−2 group who underwent more additional surgical procedures with pulmonary valve plasty was higher than that in AS, PVA z-score ≥−2 group (48.1% vs. 12.1%; P = 0.003). However, there was no significant difference in cross-clamping time in AS, PVA z-score ≥−2 group versus AS, PVA z-score <−2 group ((93.9 ± 26.4) minutes vs. (77.6 ± 32.9) minutes; P = 0.068) and AS, PVA z-score <−2 group versus TAPE group ((93.9 ± 26.4) minutes vs. (84.1 ± 40.1) minutes; P = 0.289). Compared with AS, PVA z-score ≥−2 group, additional procedures of AS in AS, PVA z-score <−2 group did not increase the duration of postoperative mechanical ventilation, intensive care unit (ICU) stay, or postoperative hospitalization (20 vs. 12 hours, P = 0.072; 2.0 vs. 2.0 days, P = 0.226; 9.0 vs. 8.0 days, P = 0.809, respectively). Moreover, compared with TAPE group, the duration of postoperative mechanical ventilation, ICU stay, and postoperative hospitalization were significantly longer than AS, PVA z-score <−2 group (20 vs. 29 hours, P = 0.039; 2.0 vs. 4.0 days, P = 0.022; 8.0 vs. 11.0 days, P = 0.008, respectively).
Complete follow-up data were available for all included patients in addition to the 1 death (due to respiratory failure). One reintervention occurred in AS, PVA z-score ≥−2 group. Two patients in each group required a return to cardiopulmonary bypass to correct residual obstruction in the RVOT or stenosis in branch pulmonary arteries during the index procedure. The same trend in class 3 was observed if the degree of PS was evaluated by the TPS. A comparatively higher mean APG of (26.4 ± 11.7) mmHg at the final follow-up remained in AS, PVA z-score <−2 group compared with that of AS, PVA z-score ≥−2 group ((23.4 ± 13.0) mmHg, P = 0.364), and of TAPE group ((19.6 ± 18.2) mmHg, P = 0.110) [Table 1]. The TPS for PS in class 2 was 66.7% in AS, PVA z-score <−2 group, 42.4% in AS, PVA z-score ≥−2 group (P = 0.061), and 22.2% in TAPE group (P = 0.001). There was no significant difference in the TPS for PS in class 3 among the 3 groups. The TPS for the degree of PR in class 3 was 26.0% in AS, PVA z-score <−2 group, 9.1% in AS, PVA z-score ≥−2 group (P = 0.097) and 74.1% in TAPE group (P < 0.001). Compared with AS, PVA z-score <−2 group, the prevalence of severe PR was higher in TAPE group when TPS class 3 for PR was subclassified into “moderate pulmonary regurgitation” and “severe pulmonary regurgitation” (26.0% vs. 0, P = 0.010) [Table 2]. The APG in the AS group showed a downward trend [Figure 3A]. Although the APG was significantly lower upon hospital discharge in the TAPE group (P < 0.001), an upward trend appeared with TAPE, and there was no difference in the AS group and TAPE group (P = 0.11) at the final follow-up [Figure 3B]. The event-free Kaplan-Meier curves for each group are displayed in Figure 4. TAPE repair was associated with worse results with regard to freedom from severe PR compared with AS repair (P = 0.007).
Table 2 -
Clinical outcomes of 87 patients who underwent TOF repair
||TAPE group (n = 27)
P (AS, PVA z-score<−2 vs. TAPE)
|z ≥−2 (n = 33)
||z<−2 (n = 27)
|TPS for PS
| Class 1 (APG <20 mmHg)
| Class 2 (APG 20–40 mmHg)
| Class 3 (APG > 40 mmHg)
|TPS for PR
| Class 1 (none/trivial PR)
| Class 2 (mild/mild-moderate PR)
| Class 3 (moderate-or-greater PR)
Data are presented as n (%).
*Patients required a return to cardiopulmonary bypass during the index procedure.
APG: Annular peak gradient; AS: Annular sparing; PR: Pulmonary regurgitation; PS: Pulmonary stenosis; PVA: Pulmonary valve annulus; TAPE: Transannular patch enlargement; TOF: Tetralogy of Fallot; TPS: Technical performance score.
Surgical procedure and strategies
AS repair is in widespread clinical use for individuals with severe pulmonary valve dysplasia. However, many studies have shown a series of AS strategies to be not adopted successfully in all suitable patients, with an AS prevalence of 37.8% to 86%.[8,10,12,13,20,21] All patients enrolled in our test group achieved AS repair, and the minimum PVA z-score with AS repair was −5.6, whereas that in our AS cohort was −5.2. The contributions of different methods for protection of pulmonary valve integrity are controversial. In early research, the methods of pulmonary valve repair that were adopted were associated with a low prevalence of PR. However, 40% of patients suffered from moderate-or-greater PR after >10 years of follow-up. It was believed that TAPE associated with valvuloplasty also resulted in adverse outcomes. Therefore, more importance was attached to PVA protection. To achieve a lower prevalence of TAPE, intraoperative balloon dilation was adopted to stretch the PVA and reduce the postoperative annular gradient. However, such an approach did not change the prevalence of chronic PR, and freedom from at least moderate PR was 77%, 61%, and 43% at 1, 3, and 5 years after repair, respectively.
AS strategies reported previously and our clinical experience have demonstrated that total relief from RVOT obstruction, adequate release of the annulus, and promotion of antegrade blood flow across the PVA can achieve PVA growth regardless of some degree of residual APG in AS repair. Hence, we conducted this retrospective cohort study to further evaluate the surgical effect and clinical outcomes of consecutive and nonselective AS in TOF populations (especially in the severely dysplastic group). Through meticulous attention to technical details and the morphology of the native pulmonary valve, we were able to preserve PVA integrity in 100% of patients undergoing TOF repair. AS strategies in patients with significant annular hypoplasia were demonstrated to be safe and feasible.
More importantly, in our AS cohort, we paid particular attention to addressing bicuspid pulmonary valve, which is often overlooked. Most reports have focused on dealing with adhesive bicuspid-valve commissures to achieve a larger effective orifice, which is sometimes far from sufficient. We believed that the morphology of the bicuspid valve is also more restrictive to the PVA than that of the tricuspid valve. Therefore, we undertook a longitudinal incision along the middle line of 1 or 2 leaflets to the level of the PVA to extend the annulus automatically and used a large fresh autologous pericardium to enlarge the leaflet area, which would not cause shrinking of the effective orifice or restenosis across the PVA, and could prevent severe PR. PR of class 3 appeared in 26.0% of AS patients with a severely dysplastic PVA, which was higher than the prevalence in the well-developed AS group (9.1%), but all PR in patients with class 3 dysplastic AS was moderate. The prevalence of severe PR in patients with dysplastic AS was far lower than that in patients with dysplastic TAPE (26.0%), and did not show a significant difference from that in patients with well-developed AS (6.1%). Only 1 patient in the TAPE group had unicuspid pulmonary valve, so we did not have sufficient data to conduct related analyses.
Pulmonary valve adequacy and clinical outcomes
AS methods to preserve pulmonary valves reported previously have been associated with a prevalence of moderate-or-greater PR as high as 16% to 57% at follow-up,[8,15,20,21] whereas that in our AS cohort was 16.7%, and only 3.3% of patients suffered from severe PR. Although 1 or 2 SDs below the normal population in PVA remaining in the more dysplastic group might cause a residual gradient at the annular level after positive and progressive supra- and subvalvular stenosis release, we believed that this would be endurable. We found that up to 66.7% of AS patients with a severely dysplastic PVA in AS, PVA z-score <−2 group demonstrated a moderate APG (20–40 mmHg). Our experience suggests that an APG <50 mmHg is an acceptable level at which intraoperative judgment should be employed based on: (1) no RV swelling; (2) hemodynamic stability without use of high doses of vasoactive drugs; (3) no significant tricuspid regurgitation; and (4) sufficient antegrade blood into the lungs determined according to end-tidal carbon dioxide. These patients who were weaned from cardiopulmonary bypass demonstrated asymptomatic disease, few reinterventions, and no death after hospital discharge, and the APG in the AS cohort compared with that at hospital discharge showed a downward trend over time, suggesting the growth and excellent ductility of the PVA at the final follow-up.
In addition, increasing clinical evidence has shown that the right ventricular pressure load prevents right ventricular dilation from chronic PR without systolic dysfunction, and that appropriate relief of RVOT obstruction with acceptable residual stenosis is more advantageous than aggressive RVOT enlargement in the long-term outcomes of TOF repair.[16,23] More importantly, we placed emphasis on a certain degree of APG remaining across the annular level. This approach is unlike most reports, in which more emphasis is placed on the APG across the RVOT.[10,12–14,17,21] That approach is misguided and possibly conceals inadequate resection of the infundibulum, hypertrophy of a muscle bundle, or patched enlargement of the pulmonary artery because we believe that the residual gradient remaining below or above the pulmonary valve is unacceptable.
Compared with those in patients undergoing TAPE, AS in patients with a dysplastic PVA resulted in a longer duration of cardiopulmonary bypass due to the requirement for more procedures, a shorter duration of ICU stay, and faster recovery, observations which are in accordance with findings from the study of Hofferberth et al. Furthermore, our AS group had a lower prevalence of severe PR than that in other centers at final follow-up. We believe that our surgical method for complete protection of PVA integrity is beneficial to patients who wish to be free from significant PR. Importantly, TAPE significantly reduced the early postoperative APG in the patients compared with that in the AS group. However, the APG showed an upward trend for dysfunction of the valved bovine jugular vein patch at the final follow-up in TAPE group according to echocardiography.
One AS patient (PVA z-score = −3.3) with a follow-up APG of 52 mmHg who had an intraoperative estimated right ventricular pressure of 50 to 60 mmHg (which was approximately half of the left-ventricular pressure) and residual APG of 47 mmHg at hospital discharge did not demonstrate restricted functional status or cyanosis under final follow-up. Only 1 AS patient (PVA z-score = −1.5) demonstrated an APG > 90 mmHg and needed reintervention 1 year after the surgical procedure. After percutaneous balloon dilation across the PVA, the APG dropped to 50 mmHg with moderate PR. Compared with intraoperative balloon dilation, percutaneous balloon dilation avoids excessive intraoperative PVA extension and is associated with a lower risk of severe PR. Percutaneous balloon dilation is a microinvasive procedure in terms of the requirement for a secondary surgical procedure for PVR due to severe PR. We recommended staged percutaneous balloon dilation to prevent pulmonary valve tearing and pulmonary effusion due to sudden excessive blood flow into the lungs. In addition, a significant correlation between the requirement for reintervention and preoperative severely dysplastic PVA appears to be absent. Furthermore, in our experience, the structural integrity of the PVA might provide a reliable anchoring area that otherwise would cause dilation in the RVOT and hinder anchoring with a valve device due to TAPE.
In most cases, we avoided excessive TAPE treatment to achieve complete relief of the pressure gradient across the annulus, and refute the notion that PS and PR are “two evils” and that the AS concept selects for one of them. The structural integrity of the pulmonary valve (even with a dysplastic annulus) can be protected in a specialist heart center and a satisfactory outcome and PS achieved at an early stage because the APG will decrease over time. In addition, reintervention (which seemed irrelevant to a severely dysplastic PVA) was found to be minimally invasive and elicited a favorable result.
AS repair has an acceptable surgical effect and is feasible in TOF patients, even those with a severely dysplastic PVA. PVA preservation can reduce severe PR and, ultimately, provide long-term benefits. Our experience suggested that full relief of supra- and subvalvular tissue can achieve better extension of PVA and lower the risk of TAPE to promote PVA growth and reduce the APG.
This observational study had several limitations. First, it was not a prospective randomized controlled trial. Second, the study cohort was small. Therefore, more severely hypoplastic patients should be recruited in the future. Third, PR and the APG were assessed based on semiquantitative echocardiography, and data on cardiac catheterization or magnetic resonance imaging were lacking. Fourth, the assessment of PR and APG was limited by the timing of echocardiographic follow-up. Fifth, TAPE procedures in TAPE group were not completed by a single surgeon, and we did not take differences in surgical techniques into consideration. Sixth, follow-up was not long-term.
AS repair was associated with favorable surgical effects in terms of postoperative recovery, survival, or risk of surgical reoperation for recurrent PS and PR prevalence in the early-to-intermediate term. A higher APG was documented upon hospital discharge in patients with a dysplastic PVA (often with a moderate APG) but showed a downward trend over time. AS can become an alternative in most TOF patients.
The study was supported by the Central Public-interest Scientific Institution Basal Research Fund (2019XK320050), Central University Basic Research Fund (APL20100410010302004) and Yunnan Provincial Cardiovascular Disease Clinical Medical Center Project (FZX2019-06-01).
Lizhi Lv and Jinyang Liu participated in the writing of the paper and data analysis. Xianchao Jiang, Yang Liu, Yanjin Tian, and Hong Cao participated in the data collection. Zhimin Liu and Qiang Wang participated in research design.
Conflicts of interest
. Parker SE, Mai CT, Canfield MA, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004–2006. Birth Defects Res Part A Clin Mol Teratol. 2010;88(12):1008–1016. doi:10.1002/bdra.20735.
. Kirklin JK, Kirklin JW, Blackstone EH, et al. Effect of transannular patching on outcome after repair of tetralogy of Fallot. Ann Thorac Surg. 1989;48(6):783–791. doi:10.1016/0003-4975(89)90671-1.
. Murphy JG, Gersh BJ, Mair DD, et al. Long-term outcome in patients undergoing surgical repair of tetralogy of Fallot. N Engl J Med. 1993;329(9):593–599. doi:10.1056/NEJM199308263290901.
. Geva T, Sandweiss BM, Gauvreau K, et al. Factors associated with impaired clinical status in long-term survivors of tetralogy of Fallot repair evaluated by magnetic resonance imaging. J Am Coll Cardiol. 2004;43(6):1068–1074. doi:10.1016/j.jacc.2003.10.045.
. Apitz C, Webb GD, Redington AN. Tetralogy of fallot. Lancet. 2009;374(9699):1462–1471. doi:10.1016/S0140-6736(09)60657-7.
. Bokma JP, Geva T, Sleeper LA, et al. A propensity score-adjusted analysis of clinical outcomes after pulmonary valve replacement in tetralogy of Fallot. Heart. 2018;104(9):738–744. doi:10.1136/heartjnl-2017-312048.
. Sung SC, Kim S, Woo JS, et al. Pulmonic valve annular enlargement with valve repair in tetralogy of Fallot. Ann Thorac Surg. 2003;75(1):303–305. doi:10.1016/s0003-4975(02)03926-7.
. Stewart RD, Backer CL, Young L, et al. Tetralogy of fallot: results of a pulmonary valve-sparing strategy. Ann Thorac Surg. 2005;80(4):1431–1438; discussion 1438-1439. doi:10.1016/j.athoracsur.2005.04.016.
. Hua Z, Li S, Wang L, et al. A new pulmonary valve cusp plasty technique markedly decreases transannular patch rate and improves midterm outcomes of tetralogy of Fallot repair. Eur J Cardiothorac Surg. 2011;40(5):1221–1226. doi:10.1016/j.ejcts.2011.02.035.
. Ito H, Ota N, Murata M, et al. Technical modification enabling pulmonary valve-sparing repair of a severely hypoplastic pulmonary annulus in patients with tetralogy of Fallot. Interact Cardiovasc Thorac Surg. 2013;16(6):802–807. doi:10.1093/icvts/ivt095.
. Bautista-Hernandez V, Cardenas I, Martinez-Bendayan I, et al. Valve-sparing tetralogy of Fallot repair with intraoperative dilation of the pulmonary valve. Pediatr Cardiol. 2013;34(4):918–923. doi:10.1007/s00246-012-0574-3.
. Vida VL, Guariento A, Castaldi B, et al. Evolving strategies for preserving the pulmonary valve during early repair of tetralogy of Fallot: mid-term results. J Thorac Cardiovasc Surg. 2014;147(2):687–694; discussion 694–696. doi:10.1016/j.jtcvs.2013.10.029.
. Vida VL, Angelini A, Guariento A, et al. Preserving the pulmonary valve during early repair of tetralogy of Fallot: anatomic substrates and surgical strategies. J Thorac Cardiovasc Surg. 2015;149(5):1358–1363.e1. doi:10.1016/j.jtcvs.2015.01.030.
. Vida VL, Guariento A, Zucchetta F, et al. Preservation of the pulmonary valve during early repair of tetralogy of Fallot: surgical techniques. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 2016;19(1):75–81. doi:10.1053/j.pcsu.2015.12.008.
. Hofferberth SC, Nathan M, Marx GR, et al. Valve-sparing repair with intraoperative balloon dilation in tetralogy of Fallot: midterm results and therapeutic implications. J Thorac Cardiovasc Surg. 2018;155(3):1163–1173.e4. doi:10.1016/j.jtcvs.2017.08.147.
. Yoo BW, Kim JO, Kim YJ, et al. Impact of pressure load caused by right ventricular outflow tract obstruction on right ventricular volume overload in patients with repaired tetralogy of Fallot. J Thorac Cardiovasc Surg. 2012;143(6):1299–1304. doi:10.1016/j.jtcvs.2011.12.033.
. Hickey E, Pham-Hung E, Halvorsen F, et al. Annulus-sparing tetralogy of fallot repair: low risk and benefits to right ventricular geometry. Ann Thorac Surg. 2018;106(3):822–829. doi:10.1016/j.athoracsur.2017.11.032.
. Pettersen MD, Du W, Skeens ME, et al. Regression equations for calculation of z scores of cardiac structures in a large cohort of healthy infants, children, and adolescents: an echocardiographic study. J Am Soc Echocardiogr. 2008;21(8):922–934. doi:10.1016/j.echo.2008.02.006.
. Nathan M, Marshall AC, Kerstein J, et al. Technical performance score as predictor for post-discharge reintervention in valve-sparing tetralogy of Fallot repair. Semin Thorac Cardiovasc Surg. 2014;26(4):297–303. doi:10.1053/j.semtcvs.2014.12.001.
. Rao V, Kadletz M, Hornberger LK, et al. Preservation of the pulmonary valve complex in tetralogy of fallot: how small is too small. Ann Thorac Surg. 2000;69(1):176–179; discussion 179–180. doi:10.1016/s0003-4975(99)01152-2.
. Hoashi T, Kagisaki K, Meng Y, et al. Long-term outcomes after definitive repair for tetralogy of Fallot with preservation of the pulmonary valve annulus. J Thorac Cardiovasc Surg. 2014;148(3):802–808; discussion 808–809. doi:10.1016/j.jtcvs.2014.06.008.
. Kim H, Sung SC, Choi KH, et al. Long-term results of pulmonary valve annular enlargement with valve repair in tetralogy of Fallot. Eur J Cardiothorac Surg. 2018;53(6):1223–1229. doi:10.1093/ejcts/ezx497.
. Puranik R, Tsang V, Lurz P, et al. Long-term importance of right ventricular outflow tract patch function in patients with pulmonary regurgitation. J Thorac Cardiovasc Surg. 2012;143(5):1103–1107. doi:10.1016/j.jtcvs.2011.09.039.