VAD Implantation in Single Ventricle Patients

This article is part of CTSNet’s Guest Editor Series, Insights Into Pediatric Mechanical Circulatory Support. Congenital and pediatric surgeon Dr. Sandeep Sainathan invited accomplished pediatric surgeons from around the world to contribute clinical videos on the surgical aspects of pediatric mechanical circulatory support as a bridge to cardiac transplantation or recovery of cardiac function.    

Over the previous 12 years, the authors have implanted ventricular assist devices (VADs) in more than 30 single ventricle patients. This included patients with Norwood, modified Blalock-Taussig-Thomas shunt (mBTTS), Glenn, or Fontan circulations. In a slightly more difficult population, those with a Norwood/Sano, the authors have placed the VAD outflow in a Y configuration to include the Sano conduit or converted to mBTTS, with the latter being their preferred approach. This video shows the evolution of their technique to how it is currently performed in this patient with Norwood/mBTTS anatomy. 
 
As these procedures can be difficult redo operations and the patients require anticoagulation, efforts are made to limit heparin administration and prevent bleeding. With that in mind, many of these procedures can often be performed off-pump. When not tolerated, the patients may need extracorporeal membrane oxygenation (ECMO) support, which the authors prefer to limit anticoagulation. If further decompression is necessary or intracardiac work is needed, the procedure can be performed on cardiopulmonary bypass.  

For the VAD cannulas, a Berlin atrial cannula was preferred, sewn to the common atrium via the atrial appendage and angled toward the atrial septal defect. A hybrid cannula made from an appropriately sized Berlin apical cannula was used for the outflow cannula, ,  positioned at the base of the sternotomy, with a Gore-Tex tube graft extension allowing for a gentle curve to the aorta. The authors have found this approach to be easier than working with the standard Berlin aortic cannula with its stiffer collar. They also prefer this approach to using a tube graft extension from an aortic cannula due to the risk of kinking and causing hemolysis. 

 A redo sternotomy was performed in the standard fashion. During many of the authors’ palliative procedures, a Gore-Tex pericardial membrane is placed, which they have  found to make the sternotomy safer and faster. The redo dissection was performed with a focus on the areas that would be cannulated for the VAD. Additional dissection must be considered if it is likely extracorporeal support will be necessary. 
 
Dissection of the right atrial appendage was done thoroughly down into the atrioventricular groove to allow sufficient room for clamp placement, trabecular resection, and cannula placement. The aorta was thoroughly mobilized, which allowed for the placement of a partial occlusion clamp as well as an arterial cannula if necessary. If this dissection is difficult and it is determined that the patient is likely to require extracorporeal support, the innominate artery can be dissected, and a chimney can be sewn for arterial cannulation. 

A partial occlusion clamp was tested to ensure that there was sufficient aorta exposed. Hemodynamics and ST segments were monitored to determine patient stability with the clamp in place. A decision was made regarding whether it could be expected the patient would tolerate the partial occlusion clamp for the anticipated time it would take to sew the outflow cannula. In this case, the neoaorta was small, and placement of the partial occlusion clamp was not tolerated well. The decision was made to perform the procedure on ECMO support. 
 
Based on the size of the aorta, a Gore-Tex tube graft size was selected. Considering the size of the apical Berlin cannula, the Gore-Tex tube graft needed to be dilated to allow it to slide over the apical cannula. In this case, an 8 mm Gore-Tex tube graft was used with a 6 mm apical Berlin cannula. To get it over the beveled cannula, it needed to be dilated to accommodate an 11 Hegar dilator. This often requires some force. While a larger graft could be used, it poses some challenges regarding the size of the eventual aortotomy, especially if the plan is to perform the procedure off-pump.  

The Gore-Tex graft was placed over the bevel and abutted the sewing ring of the apical cannula. Four mattress Prolene sutures were brought through the Gore-Tex tube graft to secure it to the sewing ring. Three additional silk sutures were placed.  
 
The trajectory of the VAD cannulas was planned to determine the exit site, ensuring that  it occurred within the velour of the cannula and that it was lateral to the midline. An incision was carried down to the posterior rectus fascia. The fascia was followed up to the chest, and a ½ inch Penrose drain was passed. Hegar dilators were then passed within the Penrose drain to dilate the tract, repeating this until it was approximately the size of the VAD cannula.  

It is important when making the exit sites to consider both patient body wall edema (which will be reduced later with diuresis) and patient growth, anticipating the future location to ensure a portion of the velour segment remains outside of the body. Since 
 
ECMO support was necessary in this case, cannulation was then performed. If the aorta is to be cannulated, it must be high. As the atrial appendage will be used for the VAD cannula, a different site must be used for the ECMO venous cannula. In this case, the innominate vein was utilized.  
 
The ideal length of the tube graft of the outflow cannula can be estimated. If the tube graft is left a bit long, the cannula can be pulled further down;  if it is too short, it can sit higher while allowing for a bit of stretch. Although there is some margin, if the graft is too short, it can pull excessively or cause the sewing ring to sit on the ventricle when the sternum is closed potentially resulting in compression. The outflow graft was cut at a slight bevel to allow for easier alignment. More recently, the authors have used a cuff of pericardium to reduce bleeding from the needle holes in the Gore-Tex graft. 
 
The partial occlusion clamp was placed, and the arteriotomy was performed. However, as these aortas are often reconstructed and may contain homograft material, identifying the layers can be more challenging. The importance of having adequate mobilization and support to allow for sufficient purchase of the partial occlusion clamp cannot be overstated. 
 
The aortotomy was performed to approximate the size of the Gore-Tex tube graft. The anastomosis was performed in the standard fashion. Once completed, the partial occlusion clamp was released, allowing the cannula to fill with blood in a retrograde fashion before being clamped. The anastomosis was inspected for any bleeding. Once this was deemed satisfactory, the partial occlusion clamp was replaced, vacuum was applied to the cannula, and CoSeal was sprayed to seal the needle holes, allowing the CoSeal to be drawn into the needle exit sites. If the patient is coagulopathic, the authors have found this step to help substantially. Additionally, for this anastomosis, the authors prefer a Hemoseal needle to minimize the size of the needle holes within the Gore-Tex graft.  

The outflow cannula was sealed with the provided plastic bullet and left untunneled to allow positioning out of the way.  
 
Attention was then turned to the VAD inflow cannula. With sufficient mobilization of the right atrial appendage, a large purse-string suture was placed, providing additional safety for subsequent steps. A side-biting clamp was applied, and the atrium was opened, with any trabeculations resected. The cannula was inserted into the right atrium while an assistant released the clamp and pulled up on the purse string, which was subsequently snared.  
 
The sewing ring was then sewn to the atrium while the assistant pushed the tip of the cannula in and elevated the back end. The purse string was ultimately tied around the cannula.  

The cannula was filled in a retrograde fashion with the patient positioned head-down and temporarily coming off ECMO support to allow filling and avoid air entrainment. Since the venous cannula would be under negative pressure, there is less concern about bleeding form this site.  
 
With both cannulas filled and capped, they were brought through their respective tracts using the Penrose drain, making sure that the orientation was appropriate without undue twisting. 
 
The cannulas were hooked to whichever pump the team had decided upon. Importantly, the flows needed by these patients can be a bit unpredictable. It may be helpful to initially connect to an easily titratable continuous flow device such as a PediMag. With this device, the ideal flows can be determined and subsequently transitioned to a Berlin device. This is the authors’ preferred approach, as it allows for easy titrations in the acute postoperative period and minimizes the risk of stroke in the longer-term while awaiting an appropriate donor. 
 
Once on the device, flows were titrated up while ECMO or bypass support was brought down. Protamine was administered, and the patient was decannulated (if the procedure was performed with extracorporeal support). Time was then spent optimizing hemostasis. Due to the risk of mediastinitis, the authors prefer to close the sternum if hemostasis and hemodynamics allow, which is the case the majority of the time. If closing the sternum at the initial operation, the authors elect to leave a Gore-Tex membrane. However, if the sternum cannot be closed, the authors avoid Gore-Tex placement at the time of the delayed sternal closure, as the VAD cannulas themselves provide sufficient elevation of the sternum for safe reentry at the time of transplant. 

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