MVP is considered to be the current standard of care for the treatment of children with mitral valve abnormalities. Unfortunately, there are certain pediatric patients who will need an MVR instead of an unsuccessful MVP; difficulties for both decision-making and treatment options may arise[5]. The most common indications for MVR in children include rheumatic disease, endocarditis, mitral stenosis in Shone’s syndrome or failed auriculoventricular (AV) canal repair. In our studies, over 50% of the patients were diagnosed with mitral valve disease with infective endocarditis and failed auriculoventricular septal repair. Bioprostheses were not the appropriate choices for MVR in children and infants due to the lack of durability and unavailability of small-sized prostheses. The pulmonary autograft replacement of the MV and Contegra conduit were employed to treat pediatric patients with small annular to avoid long-term anticoagulation. However, because of accelerated degeneration and calcification, these techniques require long-term follow-up[6, 7]. The Ross II procedure changed one-valve problem to two-valve problems, similar to the Ross procedure, possibly resulting in early regurgitation due to the lack of valve commissural support and higher trans-valvar pressure differences. Considering their better durability, availability, and hemodynamic performance, mechanical valves are the preferred mitral valve substitute in children.
Historically, MVR in infants has been associated with significant morbidity and mortality and long-term survival is lower than that of infant MV repair[8]. Consequently, surgical techniques and strategies have evolved to optimize outcomes. The reported operative mortality for MVR in infants is 5–30% and the 10- and 30-year survival for these patients has been recently reported up to 75%[5] (Table 5). Heart block requiring pacemaker implantation, endocarditis, thrombosis, stroke, an increased ratio of prosthetic size/weight and supra-annular position were all found to be statistically significant predictors of early mortality[9]. In our institute, the early mortality is 33.33% with 100% survival after discharge. Among the three patient deaths, one died from a fungal infection and two died from low cardiac output syndrome. Although there were a relatively small number of deaths in our study, we found that smaller annulus, heart failure before the procedure and fungal infections were risk factors for short-term mortality. Previous studies demonstrated that age less than 2 years old at MVR was a risk factor for operative mortality[10]. Rafii et al. found that there was no significant difference in survival between patients aged less than 2 years and patients aged 2 to 18 years, and age less than 2 years remained a risk factor for reoperation but not for mortality[11]. Bileaflet mechanical prostheses from ATS Medtronic (Minneapolis, Minnesota) were implanted in nine patients in our study. Because the smallest size of the available mechanical mitral valve in our institute is 25 mm, six patients were implanted with mechanical aortic valve prostheses. Due to the low profile, excellent hemodynamics and good durability, a bileaflet mechanical valve is the prosthesis of choice in the mitral position in children[12]. Size mismatch between the mechanical prosthesis and mitral valve annulus is considered to be a risk factor for operative mortality[13]. Caldarone et al. showed that the prosthesis size–to–patient body weight ratio was < 2 and 1-year survival rate was 91%; however, the survival rate was only 61% when the value was > 4 and only 37% when the ratio was < 5[1]. In our study, the ratio ranged from 2.1 to 5 and the ratios of the deceased patients were all over 3. This suggests that an appropriate mechanical prosthesis is essential for successful MVR in children. Prosthesis size should be carefully chosen based on the body weight, age, and mitral valve annular size of an individual patient.
Table 5
Literature review of long-term survival and freedom from redo MVR after MVR
Studies | Cases | Age | Follow up | Survival rate | Free from Redo MVR |
Mater, Kathryn. 2019. Australia9 | 22 | Mean age 6.8 ± 4.1 months | 6.2 ± 4.4 years | 100% | 86.1% at 1 years, 80.7% at 5 years and 21.2% at 10 years |
Raffaele Giordano. 2015. Italy2 | 7 | Mean age 13.3 ± 11.2 months | 67.1 ± 34.8 months | 100% | 71.4% |
Christopher A. Caldarone .2015. USA1 | 139 | Mean age 1.9 ± 1.4 years | Median 6.2 years | 74% | |
Jiyong Moon. 2015.J apan20 | 18 | Mean age 4.0 ± 1.8 months | 4.5 ± 3.8 years | 89.1% | 57.8% at 10 years |
John W. Brown. 2012. USA18 | 97 | Median age 8 years | 12.8 ± 10.1 years | 71% | 94% at 1 year, 82% at 5 years, 71% at 10 years, and 63% at 20 and at 35 years |
Hyung-Tae Sim. 2012. Korea21 | 19 | Mean age 7.6 ± 5.5 years | 76 ± 56 months | 100% | 94.7 ± 5% at 10 years |
Daniela Y. Rafifii. 2011. USA11 | 18 | Median age 1.2 years | Median 5.4 years | 82% | 69% at 5 years and 40% at 10 years |
Kirk R. Kanter. 2011. USA22 | 15 | Mean age 337 ± 412 days | 4.3 ± 2.8 years, | 84% | 69% at 5 years and 21% at 10 years |
BahaaldinAlsoufi. 2010. Canada22 | 79 | Median age 24 months | 4.1 ± 3.7 years | 62% | |
ElifSeda Selamet Tierney. 2008. USA8 | 118 | Median age 16.3 months | Over 30 years | 56% | 72% at 5 years and 45% at 10 years |
J. S. Sachweh. 2007. Germany23 | 17 | Mean age 4.3 ± 4.3 years | 9.1 ± 6.6 years | 94.1% | 93.4% at 1 year 89.0% at 5 and 10 years |
Wolfram Beierlein. 2007. UK24 | 54 | Median age 3.0 years | Median 9.2 years | 33% | 45.3% at 5 years and 17.3% at 10 years |
Hunaid A. Vohra. 2007. UK12 | 24 | Mean age 1.4 ± 1.3 years | Median 7.5 years | 75.7% | |
Naoki Wada. 2005. Japan25 | 18 | Mean age 1.02 ± 0.72 years | 3.3 ± 3.5 years | 68.9% | 87.1% at 5 years and 69.6% at 10-years |
Multiple surgery techniques were employed in the MVR. The appropriate available mechanical valve was implanted in the annulus if the size matched. Because of the link between the mechanical valve size and freedom from redo MVR, a large mechanical prosthesis was implanted to the smaller annulus, possibly causing atrioventricular block and left ventricle outflow tract obstruction related to valve impingement on surrounding cardiac structures[14]. In the neonate or infant with a small native annulus, implantation of commercially available prosthetic valves in the annular position can be problematic. Placing the prosthesis in a supra-annular position is an alternative when a more traditional annular implantation is not possible. The prosthetic valve was implanted with interrupted pledget polyester sutures with the pledgets on the atrial side of the prosthesis[15]. Previous publications suggested that the early results with supra-annular MVR in children were discouraging and identified it as a risk factor for early mortality because of the reduction of LA volume and compliance and aneurysm formation in the segment of LA between the prosthesis and the annulus[2]. One of our patients had valves implanted with a tilt, similar to that described by Moon and colleagues[15], which involved suturing part of the valve onto the native annulus and the remainder to the left atrial wall or atrial septum. The prosthesis was thereby implanted supra-annularly with a tilt either anteriorly or posteriorly to prevent impingement on the LVOT, pulmonary vein orifices, and conduction tissue. Two weeks later, the patient underwent redo MVR for the periprosthetic leakage and died for acute low cardiac output syndrome. We suggest that implanting the prothesis supra-annularly with a tilt may have caused the periprosthetic leakage and the immediate redo MVR. Three patients had Dacron Hemashield (Meadox Medicals, Inc, Oakland, NJ) with interrupted sutures sewn to the native valve annulus, after which the prosthetic valve was sewn with running sutures into the conduit. We employed the Dacron conduit that would be softer and provide better hemodynamics than the Gore-Tex conduit. The prosthetic valves were implanted to the conduit follow suturing the pipe to the annulus, which may provide convenience for the surgeon to implant a larger valve in a smaller space, also reducing the occurrence of periprosthetic leakage[16]. The technique of intermittent suture would preserve the growth potential and may provide the possibility for the replacement of a larger mitral valve in the future. The mitral valve on the annulus will inevitably lead to the reduction of the left atrium content, possibly leading to pulmonary vein obstruction or even pulmonary hypertension. In our case, we did not find the existence of pulmonary hypertension. We believe that the larger left atrium has sufficient space for buffering and grasping the height of the Dacron conduit that can effectively avoid this complication.
Redo valve replacement is inevitable following infant MVR because of somatic growth. The duration has been reported to be 8.6 ± 6.6 years in children < 5 years of age at initial MVR and 7.3 years following infant MVR[17]. The most common reported indication for early redo valve replacement is excessive pannus formation, particularly in infants and young children. valve type, size, and positioning were thought to optimize the longevity of the implanted prosthesis and maximize time until redo MVR[18]. As presented in our follow-up results, the transvalvular gradients of the implanted mechanical aortic valve and mitral valve demonstrated no significant differences. Studies indicated that choosing a mechanical valve larger than 19 mm could considerably delay the redo MVR[5], due to valve size ≥ 19 mm. There were no redo MVRs for somatic growth in our cohort.
There are several limitations to this study. First, it was a single-centre study, and therefore may be subject to selection bias. For this reason, we instituted strict inclusion and exclusion criteria. Multi-centre studies are needed to validate our findings. Bedsides that, study is limited by its retrospective design and the relatively small patient population.