A method of transcutaneously adjustable pulmonary artery banding for staged left ventricular retraining

Pathogenesis and Surgical Treatment of Congenitally Corrected Transposition of the Great Arteries (ccTGA): Part III

Congenitally corrected transposition of the great arteries (ccTGA) is an infrequent and complex congenital malformation, which accounts for approximately 0.5% of all congenital heart defects. This defect is characterized by both atrioventricular and ventriculoarterial discordance, with the right atrium connected to the morphological left ventricle (LV), ejecting blood into the pulmonary artery, while the left atrium is connected to the morphological right ventricle (RV), ejecting blood into the aorta. Due to this double discordance, the blood flow is physiologically normal. Most patients have coexisting cardiac abnormalities that require further treatment. Untreated natural course is often associated with progressive failure of the systemic right ventricle (RV), tricuspid valve (TV) regurgitation, arrhythmia, and sudden cardiac death, which occurs in approximately 50% of patients below the age of 40. Some patients do not require surgical intervention, but most undergo physiological repair leaving the right ventricle in the systemic position, anatomical surgery which restores the left ventricle as the systemic ventricle, or univentricular palliation. Various types of anatomic repair have been proposed for the correction of double discordance. They combine an atrial switch (Senning or Mustard procedure) with either an arterial switch operation (ASO) as a double-switch operation or, in the cases of relevant left ventricular outflow tract obstruction (LVOTO) and ventricular septal defect (VSD), intra-ventricular rerouting by a Rastelli procedure. More recently implemented procedures, variations of aortic root translocations such as the Nikaidoh or the half-turned truncal switch/en bloc rotation, improve left ventricular outflow tract (LVOT) geometry and supposedly prevent the recurrence of LVOTO. Anatomic repair for congenitally corrected ccTGA has been shown to enable patients to survive into adulthood.

Use of Flow Restrictors in Congenital Heart Disease

The surgical pulmonary artery band was first introduced in 1952 and, to this day, can produce challenges in regard to the ideal amount of restriction and the need for reoperations. A transcatheter option may be the ideal solution as it allows for a less-invasive approach for a better hemodynamic assessment and easier re-intervention. To date, multiple approaches have been developed with device modifications to create restrictions to flow, each with advantages and limitations. Continued experience is still necessary to determine the ideal device to use to create an adequate and modifiable level of restriction.

Transcatheter Pulmonary Artery Banding in High-Risk Neonates: In-Vitro Study Provoked by Initial Clinical Experience

PURPOSE

Very high-risk, ductal-dependent or complex two-ventricle patients with associated comorbidities often require pulmonary blood flow restriction as bridge to a more definitive procedure, but current surgical options may not be well-tolerated. An evolving alternative utilizes a fenestrated Micro Vascular Plug (MVP) as a transcatheter, internal pulmonary artery band. In this study, we report a case series and an in-vitro evaluation of the MVP to elicit understanding of the challenges faced with device implantation.

METHODS

Following single-center, retrospective review of eight patients who underwent device placement, an in-vitro flow study was conducted on MVP devices to assess impact of device and fenestration sizing on pulmonary blood flow. A mathematical model was developed to relate migration risk to vessel size. Results of the engineering analysis were compared to the clinical series for validation.

RESULTS

At median follow-up of 8 months (range 1-15), survival was 63% (5/8), and 6 (75%) patients underwent subsequent target surgical intervention with relatively low mortality (1/6). Occluder-related challenges included migration (63%) and peri-device flow, which were evaluated in-vitro. The device demonstrated durability over normal and supraphysiologic conditions with minimal change in fenestration size. Smaller vessel size significantly increased pressure gradient due to reduced peri-device flow and smaller effective fenestration size.

CONCLUSION

Device oversizing, with appropriate adjustment to fenestration size, may reduce migration risk and provide a clinically appropriate balance between resulting pressure gradient and Qp:Qs. Our results can guide the interventionalist in appropriately selecting the device and fenestrations based on patient-specific anatomy and desired post-implantation flow characteristics.

Dilatable Pulmonary Artery Banding Palliation in Congenital Heart Disease

BACKGROUND

Surgical pulmonary artery banding (PAB) has been limited in practice because of later requirement for surgical removal or adjustment. The aim of this study is to describe our experience creating a dilatable PAB via transcatheter balloon dilation (TCBD) in congenital heart disease (CHD) patients.

METHODS

Retrospective chart review of adjustable PAB-outline anatomical variants palliated and patient outcomes.

RESULTS

Sixteen patients underwent dilatable PAB-median age 52 days (range 4-215) and weight 3.12 kg (1.65-5.8). Seven (44%) of the patients were premature, 11 (69%) had ventricular septal defect(s) with pulmonary over-circulation, four (25%) atrioventricular septal defects, and four (25%) single ventricle physiology. Subsequent to the index procedure: five patients have undergone intracardiac complete repair, six patients remain well palliated with no additional intervention, and four single ventricles await their next palliation. One patient died from necrotizing enterocolitis (unrelated to PAB) and one patient required a pericardiocentesis postoperatively. Five patients underwent TCBD of the PAB without complication-Two had one TCBD, two had two TCBD, and another had three TCBD. The median change in saturation was 14% (complete range 6-22) and PAB diameter 1.7 mm (complete range 1.1-5.2). Median time from PAB to most recent outpatient follow-up was 868 days (interquartile range 190-1,079).

CONCLUSIONS

Our institution has standardized a PAB technique that allows for transcatheter incremental increases in pulmonary blood flow over time. This methodology has proven safe and effective enough to supplant other institutional techniques of limiting pulmonary blood flow in most patients-allowing for interval growth or even serving as the definitive palliation.

Expandable Valves, Annuloplasty Rings, Shunts, and Bands for Growing Children

In congenital heart surgery, the surgeon must constantly consider how a palliative or corrective procedure could be impacted by the child's somatic growth. Within pediatric valve surgery, existing valve repair techniques lack growth-accommodating prostheses. Valve replacement options are fixed in size and unable to grow with the child, thus subjecting children to repeated valve reoperations. When creating a systemic-to-pulmonary artery shunt, replacing a branch pulmonary artery or conduit, creating an extracardiac Fontan pathway, or banding the pulmonary artery, the implant size must factor in both the child's current size and his or her anticipated growth. A variety of growth-accommodating technologies have been developed to fill this unmet need. Some devices have reached the clinical arena, while several are in preclinical development. The purpose of this review is to characterize the clinical need for growing device technology, and then review established and developing technologies for growth accommodation in congenital heart surgery.

Congenitally corrected transposition of the great arteries

Congenitally corrected transposition of the great arteries (CCTGA) is a rare congenital heart lesion with varied morphological presentation and can often by asymptomatic. A failing systemic right ventricle (RV) or increasing tricuspid regurgitation are generally indications for surgical intervention. The surgical approach depends upon the age of the patient and morphology of the lesion. Anatomical correction is associated with satisfactory long-term results.

Utility of the Medtronic microvascular plug™ as a transcatheter implantable and explantable pulmonary artery flow restrictor in a swine model

BACKGROUND

A surgical pulmonary artery band (PAB) is used to control excessive pulmonary blood flow for certain congenital heart diseases. Previous attempts have been made to develop a transcatheter, implantable pulmonary flow restrictor (PFR) without great success. We modified a microvascular plug (MVP) to be used as a PFR. The objectives of this study were to demonstrate feasibility of transcatheter implantation and retrieval of the modified MVP as a PFR, and compare PA growth while using the PFR versus PAB.

METHODS AND RESULTS

The PFR was implanted in eight newborn piglets in bilateral branch pulmonary arteries (PAs). Immediately post-PFR implantation, the right ventricular systolic pressure increased from a median of 20-51 mmHg. Transcatheter retrieval of PFR was 100% successful at 3, 6, and 9 weeks and 50% at 12-weeks post-implant. A left PAB was placed via thoracotomy in four other newborn piglets. Debanding was performed 6-weeks later via balloon angioplasty. On follow-up, the proximal left PA diameters in the PFR and the PAB groups were similar (median 8 vs. 7.1 mm; p = 0.11); albeit the surgical band sites required repeat balloon angioplasty secondary to recurrent stenosis. By histopathology, there was grade II vessel injury in two pigs immediately post-retrieval of PFR that healed by 12 weeks.

CONCLUSIONS

Transcatheter implantation and retrieval of the MVP as a PFR is feasible. PA growth is comparable to surgical PAB, which is likely to require reinterventions. The use of the MVP as a PFR in humans has to be trialed before recommending its routine use.

Surgical technique of double switch procedure: Senning with arterial switch operation for congenitally corrected transposition of the great arteries with ventricular septal defect

We present a case of 12-month-old boy with congenitally corrected transposition of great arteries with L-looped ventricles and L-transposition of great arteries and ventricular septal defect. When admitted to the hospital, the patient had the appearance of congestive heart failure due to moderate to severe tricuspid valve regurgitation and right ventricle dysfunction. The pulmonary artery (PA) banding was required first because of low systolic pressure in the morphological left ventricle less than 70% confirmed by catheterization. Three months later, the patient appeared to be a good candidate for anatomical repair and a double switch procedure-Senning with arterial switch-was performed. The early postoperative period was relatively smooth and uneventful. Tricuspid valve insufficiency was resolved immediately after surgery. Mild systolic dysfunction of the left ventricle with mild mitral insufficiency was confirmed by the 2D strain method of echocardiography on the second day of the postoperative period and it improved over the next 21 days. Thirty days later after the procedure, the patient underwent catheterization of his superior vena cava tunnel because of the slightly increased blood flow velocity diagnosed by echocardiography. In 3 months after the surgery, the boy was asymptomatic and was doing well. The patient's functional status was I according to the NYHA classification.

Left ventricular retraining: theory and practice

Congenitally corrected transposition of the great arteries or l-transposition of the great arteries is characterized by discordance of both the atrioventricular and ventriculoarterial connections. Physiologic repair of associated conditions, whereby the morphologic right ventricle remains the systemic ventricle, has resulted in unsatisfactory long-term outcomes due to the development of right ventricular failure and tricuspid valve regurgitation. While intuitively attractive, anatomic repair also has inherent challenges and risks, particularly for those patients who present late and require left ventricular retraining. Although early and intermediate-term outcomes for anatomic repair have been encouraging, longer-term follow-up has demonstrated concern for late left ventricular dysfunction in this subgroup of patients. Continued monitoring of this challenging patient population will clarify late outcomes and inform clinical management in the future.

Arterial switch for transposed great vessels with intact ventricular septum beyond one month of age

BACKGROUND

Late referral of patients with transposition of the great arteries (TGA) and intact ventricular septum (IVS) is common in China. This study investigates the impact of later age on the arterial switch operation (ASO) performed for TGA-IVS beyond 1 month of age.

METHODS

From 2000 to 2011, a total 109 patients with TGA-IVS were referred over 1 month of age. In group A, 78 patients with satisfactory left ventricular (LV) geometry underwent a one-stage ASO. In group B, 31 patients with LV regression underwent a two-stage ASO with prior LV retraining.

RESULTS

The median age at ASO was older in group B (6 months, versus group A 1.9 months; p = 0.01). Group A had more frequent patent ductus arteriosus (70.5%, versus group B 38.7%; p = 0.02). The in-hospital mortality was similar in both groups (group A 2.6%, group B 9.7%; p = 0.14). Late mortality was higher in group B (16%, versus group A 2.7%; p = 0.03), as well as aortic regurgitation rate (group A 9.8% versus group B 33.3%; p = 0.01). The median duration of retraining in group B was 18 days. There were no deaths at retraining, although 2 patients required revision of the pulmonary artery banding. The only significant risk factor for late mortality in group B was age at retraining, as continuous variable (p = 0.04). Age beyond 3 months at LV retraining was associated with late impaired LV ejection fraction (p = 0.01).

CONCLUSIONS

The overall outcomes of ASO for TGA-IVS performed beyond 1 month of age are satisfactory. Two-stage ASO has higher late mortality and more neoaortic regurgitation. Later age at retraining is associated with higher late mortality. Age beyond 3 months at retraining is associated with impaired LV function.

Vascular histopathologic reaction to pulmonary artery banding in an in vivo growing porcine model

Pulmonary artery banding (PAB) is used as a surgical palliation to reduce excessive pulmonary blood flow caused by congenital heart defects. Due to the lack of microscopic studies dealing with the tissue remodeling caused by contemporary PAB materials, this study aimed to assess histologic changes associated with PAB surgery by analyzing local tissue reaction to the presence of Gore-Tex strips fixed around the pulmonary artery. Gore-Tex strips were used for PAB in a growing porcine model. After 5 weeks, histologic samples with PAB (n = 5) were compared with healthy pulmonary arterial segments distal to the PAB or from a sham-treated animal (n = 1). Stereology was used to quantify the density of the vasa vasorum and the area fraction of elastin, smooth muscle actin, macrophages, and nervi vasorum within the pulmonary arterial wall. The null hypothesis stated that samples did not differ histopathologically from adjacent vascular segments or sham-treated samples. The PAB samples had a greater area fraction of macrophages, a lower amount of nervi vasorum, and a tendency toward decreased smooth muscle content compared with samples that had no PAB strips. There was no destruction of elastic membranes, no medionecrosis, no pronounced inflammatory infiltration or foreign body reaction, and no vasa vasorum deficiency after the PAB. All the histopathologic changes were limited to the banded vascular segment and did not affect distal parts of the pulmonary artery. The study results show the tissue reaction of palliative PAB and suggest that Gore-Tex strips used contemporarily for PAB do not cause severe local histologic damage to the banded segment of the pulmonary arterial wall after 5 weeks in a porcine PAB model.