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Techniques for Venoarterial Extracorporeal Membrane Oxygenation Support and Conversion to Temporary Left Ventricular Assist Device

  • Ashok Babu
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    Address reprint requests to Ashok Babu, MD, Division of Cardiothoracic Surgery, University of Colorado, 12631 E 17th Ave, Mailstop C310, Aurora, CO 80045.
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    Division of Cardiothoracic Surgery, University of Colorado, Aurora, CO
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Open AccessPublished:December 05, 2014DOI:https://doi.org/10.1053/j.optechstcvs.2014.11.003
      Veno-arterial ECMO is a powerful tool for resuscitating patients in refractory cardiogenic shock. However, outcomes are poor unless it is implemented correctly and converted to more long term devices in a stepwise and timely fashion. In this article we detail the steps required to guarantee the highest survival rate for these critically ill patients.

      Keywords

      Introduction

      Venoarterial extracorporeal membrane oxygenation (ECMO) has emerged as the device of choice to provide rapid and definitive support in patients with refractory cardiogenic shock or postcardiotomy patients with biventricular dysfunction or cardiopulmonary failure. Correct cannulation technique, aggressive left ventricular venting, and early conversion to temporary left ventricular assist device are the critical principles to achieving a high survival for these complex patients. The following techniques apply to patients with acute, acute-on-chronic, or postcardiotomy heart failure as a bridge to recovery or to durable left ventricular assist device (LVAD) (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7).
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      Figure 1Peripheral venous cannulation via femoral vein or right internal jugular vein. When instituting ECMO urgently, femoral cannulation is the most rapid and reliable place to gain venous return. The left or right common femoral vein is accessed via ultrasound guidance and a 5-F micropuncture system. The microneedle is advantageous in the case of unintended arterial puncture. Amplatz 180-cm Super Stiff guidewire is placed into the right atrium under fluoroscopic guidance or transesophageal echo guidance or both. Guidewires that are less stiff can kink during dilation and lead to loss of access. The tract is then serially dilated to the desired size and the venous cannula is placed with its tip near the SVC-RA junction. If femoral access fails or one is converting to ambulatory configuration, the right internal jugular vein is the preferred choice. The process is the same except the wire must be advanced to the abdominal IVC bifurcation to ensure that the tip of the cannula remains in the IVC. Otherwise it could be inadvertently placed into a hepatic vein. Additionally, when cannulating from the neck, the cannula is placed so that its last sidehole is at least in the SVC and the tip terminates in the IVC. A 25-F venous cannula is ideal for most adults. (A) Femoral vein. ECMO = extracorporeal membrane oxygenation; IVC = inferior vena cava; SVC-RA = superior vena cava-right artery.
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      Figure 1(Continued) (B) R internal jugular vein. ECMO = extracorporeal membrane oxygenation. R = right.
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      Figure 2(A) Femoral artery cannulation with percutaneous superficial femoral artery limb perfusion cannula. In a similar fashion to the venous cannulation, percutaneous femoral arterial cannulation is the mainstay of arterial access during urgent conditions. Technique is critical to avoid bleeding complications and limb ischemia. The antegrade limbsaver cannula can be very difficult to place once the main arterial cannula is already in place. Thus, we recommend gaining wire access in an antegrade fashion first. One can place this limbsaver cannula directly into the SFA or more preferably into the CFA and traversing into the SFA. Access is gained percutaneously using a 5-F micropuncture set and ultrasound guidance, and the wire is observed to traverse the SFA on fluoroscopy. A 5-F sheath is placed over the wire as the antegrade limb perfusion cannula. Care should be taken to avoid placing this cannula into the profunda femoris artery by utilizing fluoroscopy if available. Under ultrasound guidance, the common femoral artery is identified and cannulated using a 5-F micropuncture kit. Care is taken to avoid the standard Seldinger backwall technique and ideally have only a “frontwall” puncture. The Amplatz Super Stiff wire is advanced via the 5-F access to the abdominal aorta under fluoroscopic guidance. Serial dilation is conducted over the wire and the chosen cannula is placed. An 18- to 20-F sized arterial cannula is ideal for most adults, but one must customize this to the visualized size of the vessel by ultrasound. The Luer lock port on the arterial cannula is connected to the 5-F limbsaver sheath to perfuse the extremity, even if the main cannula occludes the femoral artery. Sidearm cannulation of the femoral artery can be performed as described in in cases where small arterial size or atherosclerosis precludes direct cannulation. In this configuration, bidirectional flow is established, and no limb perfusion cannula is required. CFA = common femoral artery; SFA = superficial femoral artery.
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      Figure 2(Continued) (B) Retrograde limb perfusion cannula via posterior tibial artery. When patients are cannulated during CPR, it is not possible to place the antegrade limbsaver cannula. Alternatively, sometimes it is technically difficult to do so even in the non-CPR setting. An excellent technique popularized by the group at the University of Michigan involves retrograde perfusion of the limb from the ankle via the posterior tibial artery. A transverse incision is made posterior to the medial malleolus. Transverse dissection through the subcutaneous tissue is performed until one finds the posterior tibial artery. It is quite superficial in this location. If large enough, one may be able to access it with a micropuncture kit. If it is very small, direct incision with direct cannulation may be required. Again, a 5-F sheath is the preferred cannula. Blood from this cannula will flow retrograde to the trifurcation of the popliteal artery to perfuse the entire limb. CPR = cardiopulmonary resuscitation.
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      Figure 3Axillary artery cannulation with sidearm graft. The axillary artery can be used when converting to an ambulatory configuration or when the femoral artery is unusable. Direct cannulation is possible, but patients may experience arm ischemia owing to occlusion of the vessel. Sidearm grafting resolves this issue, but it does leave a pressurized suture line that can lead to bleeding complications. Additionally, there is an incidence of hyperperfusion syndrome of the extremity, but a technique to address this is stated later. Incision is made in the infraclavicular fossa on the left or right side. Right side is preferred if there is any hypoxia issue as this will guarantee the best oxygen delivery to arch vessels. This also leaves the left side available for implantable defibrillator placement if the need arises. The pectoralis major is divided along the line of the incision. The pectoralis minor is reflected inferiorly to gain access to the axillary fat pad. It is here that the vein, artery, and nerves lie. The artery is usually posterior to the vein, and one can access it by reflecting the vein superiorly, although occasionally the vein is reflected inferiorly. The artery is freed up and elevated by a vessel loop. After heparinization, it is clamped distally and proximally. A longitudinal incision is made and can be extended using an aortic punch. We use a 10-mm sealed Dacron graft as the sidearm. This graft is beveled and sewn in an end-to-side fashion using 6-0 prolene on a small needle (CV-1 USS, BV-1 Ethicon). Meticulous hemostasis is critical to the success of this cannulation technique. We first remove the distal clamp to allow collateral circulation to pressurize the anastomosis. The graft is clamped with a padded vascular clamp to prevent damage to the gelatin coating. All bleeding, even needle-hole–associated bleeding, is repaired with small sutures. Small felt or pericardial pledgets can be used if required. The proximal clamp is then removed to fully pressurize the graft. Again, all bleeding must be resolved at this point. A 32-F malleable venous cannula is used to cannulate this graft to allow connection to the 3/8 in tubing. We cut the tip off the venous cannula to allow a large end hole to reduce shear stress. This cannula is tunneled into the wound in a subpectoral tunnel using a 36-F chest tube to avoid damaging it or allowing debris to enter its lumen. This is then inserted into the Dacron graft to within 2 cm of the anastomosis and tied in placed with several heavy ties. The cannula is then pulled back until the Dacron graft lies well without any kinking. The Dacron graft will lie partially in the tunnel but should not come close to the external tunneling site. Only the cannula should be exiting the skin to prevent Dacron graft infection. The cannula is then affixed to the skin with multiple sutures. If one is concerned about potential hyperperfusion syndrome of the extremity, placement of a flow restrictor on the distal axillary artery is an option. Our experience suggests that patients with relatively small axillary arteries are at higher risk for this complication so they can be used selectively. If one decides to do so, a vessel loop can be double wrapped (Potts) around the distal axillary artery and then secured with medium clips until the desired level of occlusion is achieved. One must significantly impair the lumen (80% stenosis) to create adequate flow restriction. One alternative can be to use dual radial arterial lines and constrict the artery until the mean arterial pressure is equal in both arms, once the circuit has been initiated at full flow. To allow stability of the cannulation site in the early period, an arm sling to immobilize the arm, as one would do with clavicular fracture, can be helpful. LAD = left anterior descending.
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      Figure 4Left ventricular venting via limited anterolateral thoracotomy. VA ECMO provides excellent restoration of flow and oxygen delivery to the body. However, it does not provide cardiac decompression in most cases. Left ventricular distention occurs owing to the increased afterload on the left ventricle as well as incomplete emptying of the right side and ongoing bronchial blood flow. Distention of the left ventricle impairs its ability to recover. Additionally, left atrial hypertension leads to refractory pulmonary edema and ongoing pulmonary hypertension and RV distention. Left ventricular distention will be manifest by refractory pulmonary edema, ongoing wedge pressure elevation, or severe distention by echo. If left ventricular distention is refractory to medical therapy with inotropes and afterload reduction, it must be decompressed to prevent mortality. LVAD or BiVAD placement can be considered but would be a major intervention with considerable morbidity in a critically ill patient. There are several options for LV venting that include surgical and percutaneous approaches. Some have used devices like the TandemHeart transseptal cannula or the Abiomed Impella as a vent. These devices have been reported with some success, but they also have significant drawbacks. Our preference has been for a surgical and ambulatory approach. Transatrial left ventricular venting can be achieved with a cannula from the right superior pulmonary vein or the body of the left atrium in the interatrial groove via right anterior thoracotomy. This cannula can be inserted across the mitral valve under echo guidance and is secured with a Rumel tourniquet. It is connected to the circuit in a similar fashion to what is described previously. Please see for further details on transatrial venting. Alternatively, we have chosen to perform LV venting via the apex through a thoracotomy approach as pictured later. Placement of a large apical cannula definitively treats the LV distention but also allows for conversion to a left ventricular assist device based on this cannula. BiVAD = biventricular assist device; ECMO = extracorporeal membrane oxygenation; LV = left ventricular; RV = right ventricular; VA = venoarterial. (A) Exposure of LV apex. Transthoracic echo is used to localize the true apex of the left ventricle and the correct interspace is marked. If one has to angle the echo probe inferiorly to see the tip of the apex, one probably should choose the lower interspace. There is a large variability in the location of the LV apex based on patient anatomy and degree of cardiac dilation. Incision is made, and the left pleural space is entered. The pericardium is opened along the direction of the ribs over the true LV apex. Pericardial stay sutures are used to gain exposure. A small rib spreader is used. Cannulation in the true apex is important as this hole may be used at subsequent operation for durable LVAD placement. Visualization of the LAD is an important landmark. Also finger palpation is helpful, and finger indentation of the apex can be visualized on TEE. LAD = left anterior descending; LV = left ventricular; TEE = transesophageal echocardiography.
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      Figure 4(Continued) (B) Cannulation of LV apex using direct cannulation via pursestring. The apex can be cannulated directly through 2 concentric “ring of pledget” pursestrings with a 4-0 prolene on a small needle. Before cannulation, the 32- or 34-F venous-type cannula is tunneled in a submuscular location so it exits the skin remotely. The cannula is placed into the ventricle through a cruciate incision. Rumel tourniquets are used to secure the pursestring and tied to the cannula. The suture of the tourniquet is secured by tying to a button so it does not loosen. The Rumel tourniquets are left completely in the intrathoracic space and the incision is closed. The cannula should be secured to the skin as well in multiple locations. LAD = left anterior descending; LV = left ventricular.
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      Figure 4(Continued) (C) Cannulation of LV apex with Thoratec CentriMag LV drainage cannula. If prolonged support is predicted, we use a Thoratec CentriMag LV drainage cannula sewing ring as described in the following figures. This provides a more stable and hemostatic device for prolonged support. The LV apex is exposed and identified as described previously. Interrupted pledgeted sutures are placed in a circular orientation around the apex. The sewing ring is then tied in place to the apex. Hemostasis is ensured at this point. Also myocardial biopsy can be performed at this time of the muscle within the sewing ring. LV = left ventricular.
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      Figure 4(Continued) (D) The provided 34-F malleable cannula is now tunneled in a submuscular fashion. A cruciate incision is then made through the LV apex and the cannula is inserted. Its depth and position can be confirmed by TEE. It is secured to the sewing ring either with the supplied umbilical tapes or with multiple heavy silk ties. It is then secured to the skin as well. LV = left ventricular; TEE; transesophageal echocardiography.
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      Figure 5(A) A 3/8 in Y connector is used to connect the venous cannula and the left ventricular vent to the drainage side of the ECMO circuit. Bright blood from the LV vent will mix with dark blood from the venous line. ECMO = extracorporeal membrane oxygenation; LV = left ventricular.
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      Figure 5(Continued) (B) Bedside conversion to temporary LVAD. LV venting allows rapid decompression of the left atrium and resolution of lung edema. In doing so, pulmonary vascular resistance drops significantly. As a result, the right ventricle begins to recover. After a period of 3-5 days of LV venting, the right ventricle is usually able to support the circulation again. At this point, one can easily assess the ability for LVAD conversion by clamping the venous cannula intermittently to observe RV hemodynamics as well as LVAD flows. Clamping of the venous cannula essentially converts from VA ECMO with LV vent to LVAD. Once the patient is deemed ready, the circuit is stopped, the “Y” connector is removed, and the LV drainage cannula is connected directly to the venous side of the circuit. The venous drainage cannula is removed at the bedside and the hole is closed with a stitch. The patient is now on an LVAD configuration, though the circuit still contains an oxygenator. One can call this “LVAD ECMO.” If there is any concern about the lung, it may be optimal to first convert to LVAD ECMO and then cut the oxygenator out of the circuit once one confirms that the lungs function well with the sweep gas turned off. Once the oxygenator is removed from the circuit, the patient is on a true temporary LVAD from the LV apex cannula to the femoral arterial cannula. If prolonged temporary support is required, the arterial cannula can be moved to the axillary position so the patient can walk. One can then wait weeks for organ recovery before durable LVAD implant or await myocardial recovery. ECMO = extracorporeal membrane oxygenation; LV = left ventricular; RV = right ventricular; VA = venoarterial.
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      Figure 6Central cannulation via R anterior second interspace thoracotomy. Central VA ECMO cannulation in the non–postcardiotomy patient should be avoided if possible owing to bleeding risk. However, when peripheral vascular disease exists or other cannulation sites have failed, this is the last resort. It can be performed via sternotomy, but this may portend increased bleeding risk. An alternative that may be preferable in some settings (when future sternotomy or clamshell incision for lung transplant is planned) is the R anterior second interspace thoracotomy which will provide access to the ascending aorta and right atrial appendage or SVC. If possible, peripheral venous cannulation should still be used. The aorta can be cannulated directly via a pledgeted pursestring suture and secured with a Rumel tourniquet. Alternatively one can sew a 10-mm Dacron graft to the aorta if sufficient exposure is available via thoracotomy. However, this is dependent on patient anatomy. If venous access is needed, one can cannulate the right atrial appendage or the SVC via a pledgeted pursestring as well. A large malleable or right-angle venous cannula can be used in either structure. If the SVC is cannulated, the tip is placed into the right atrium. As mentioned in , if placing a patient on VA ECMO for cardiogenic shock from this approach, one can easily vent the left ventricle using a transatrial left ventricular vent. A pledgeted pursestring can be placed into the right superior pulmonary vein or into the wall of the left atrium in the interatrial groove. A left ventricular vent can be placed across the mitral valve to decompress the left ventricle. ECMO = extracorporeal membrane oxygenation; R= right; SVC = superior vena cava; VA = venoarterial.
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      Figure 7Postcardiotomy cannulation via pre-existing sternotomy. In the postcardiotomy setting, VA ECMO can be used for cardiac failure. Isolated respiratory failure should be treated with VV ECMO, and univentricular failure should be treated with VAD. However, biventricular failure with or without lung issues may be better suited to VA ECMO. If VA ECMO is instituted in the setting of LV failure, one should strongly consider the use of a LV apical vent with a minimum 32-F drainage cannula. Venous drainage can be obtained centrally or preferably via percutaneous femoral or IJ drainage. Aortic access should be obtained via 10-mm Dacron sidearm graft on the ascending aorta. This type of setup also allows bedside ambulatory LVAD conversion once the RV and lungs have recovered as described in . This technique improves outcomes, as it leads to shorter ECMO duration and allows prolonged LV support in a safe ambulatory manner. ECMO = extracorporeal membrane oxygenation; IJ = internal jugular; LV = left ventricular; RV = right ventricular; VA = venoarterial; VAD = ventricular assist device; VV = venovenous.

      Conclusion

      Advances in equipment and increased experience are allowing superior outcomes in patients with refractory cardiogenic shock who are resuscitated with venoarterial ECMO. As a result, use of this technique is increasing worldwide. However, good outcomes can only be achieved with early institution before irreversible organ injury in carefully selected patients. Additionally, proper cannulation techniques and aggressive use of left ventricle venting can have a beneficial effect on outcomes. Early conversion to temporary LVAD is possible in most patients. The temporary LVAD is a safer prolonged support device that can allow patients weeks for physical recovery as well as organ recovery. In this time, one can assess for myocardial recovery in patients who may have reversible disease. Additionally, it will allow the patient to be in excellent condition before durable LVAD implant or even cardiac transplantation. The techniques described in this article are effective in salvaging more than 50% of these patients who are otherwise facing imminent death.