Venoarterial extracorporeal membrane oxygenation (VA-ECMO) can provide life saving cardiopulmonary support for patients in advanced cardiogenic shock, offering a bridge to recovery, durable mechanical circulatory support, or heart transplantation.1 In recent years, utilization of VA-ECMO has expanded due in large part to improving technologies that have facilitated the delivery of this complex therapy. Such technologies include reliable, easier-to-manage pump systems, high-performance oxygenators, and peripheral cannulation techniques.2 Despite these advancements, there remain significant limitations to VA-ECMO therapy. In particular to the setting of VA-ECMO through peripheral cannulation, three of the major limitations currently encountered include 1) inadequate decompression of the left ventricle (LV), 2) lower limb vascular complications, and 3) the inability to mobilize or ambulate patients.
Insufficient or absent LV ejection is commonly present in VA-ECMO patients and can result in elevated LV pressure and LV distension. This is detrimental for at least several reasons. First, it causes increased myocardial wall tension, which may limit myocardial perfusion and cause increased oxygen consumption, both of which can further exacerbate myocardial injury.3,4 Second, it can result in the onset or worsening of pulmonary edema, which causes lung injury and impedes the process of weaning off VA-ECMO and mechanical ventilation. Finally, stagnation of blood within the LV can give rise to intracardiac thrombus formation and potentially lead to devastating thromboembolic complications, such as stroke.5 Decompression of the LV during VA-ECMO therapy can ameliorate these issues. However, unlike the situation of postcardiotomy VA-ECMO where the open sternum provides ready access for LV decompression, in peripheral VA-ECMO the left heart cannot be easily accessed. This has led a number of groups to suggest alternative means of achieving LV decompression in peripheral VA-ECMO. These approaches have included placement of an axial flow pump across the aortic valve,6,7 percutaneous placement of a decompressive cannula in the pulmonary artery,8 percutaneous atrial septal puncture9,10 with transeptal placement of a decompressive cannula into the left atrium,11,12 and surgical placement of a decompressive cannula through the apex of the LV.13 Although these previously reported methods of left heart decompression hold promise in certain settings, there remains concern over whether transatrial or right-sided heart decompression will achieve adequate flows to decompress the left heart in adult-sized patients. Furthermore, percutaneous methods for left heart decompression do not alleviate the issues of lower limb ischemia or the inability to mobilize VA-ECMO patients.
In total, although much progress has been made to facilitate the delivery of VA-ECMO therapy, there is not yet a well-established method of nonpostcardiotomy VA-ECMO cannulation that provides LV decompression, avoids lower limb vascular complications, and allows for mobilization of the patient. Herein, we report our early experience with a novel cannulation strategy for nonpostcardiotomy VA-ECMO and LV decompression that holds the potential to effectively address each of these limitations.
Operative and VA-ECMO Technique
The general approach for VA-ECMO with minimally invasive left ventricular decompression (MILVD) involves a hybrid peripheral-central cannulation arrangement (Figure 1). For placement of the arterial cannula, the right axillary artery is exposed lateral and inferior to the clavicle at the deltopectoral groove. The fibers of the pectoralis major are split and the aponeurosis of pectoralis minor is divided. The axillary artery is exposed by reflecting the axillary vein inferiorly. Great care is taken while exposing the artery to avoid brachial plexus injury. An 8 or 10 mm Dacron “chimney” graft is then anastomosed to the axillary artery to minimize the risk of ischemic complications to the upper extremity. Specifically, the patient is systemically anticoagulated with 50–100 units/kg of intravenous heparin, the axillary artery is clamped, and the graft is attached to the artery in an end to side fashion using 6-0 polypropylene suture. The graft is then deaired and connected to the ECMO circuit as the arterial outflow using either a 3/8ths inch connector or a large arterial cannula.
For placement of the venous and LV vent cannula, a 6 cm right anterior thoracotomy is created at the level of the fourth intercostal space, centered at the anterior axillary line. The chest is entered and the right lung is packed to prevent it from obstructing the operative field. The pericardium is identified and a pericardial cradle is created with sutures. This provides lateral movement of the mediastinum, bringing the heart closer to the incision and further preventing the right lung from obstructing the view. Waterston’s groove is developed and two pledgeted purse string sutures of 3-0 coated, braided polyester are placed in the left atrium. Similarly, one multipledgeted 3-0 coated, braided polyester suture is placed as a purse string in the body of the right atrium. A 20–26 French (Fr) cannula is inserted through the left atrial purse string guided across the mitral valve into the LV under transesophageal echocardiography guidance. A multistage 36–46 Fr venous cannula is placed through the purse string in the body of the right atrium, across the tricuspid valve, and into the right ventricle. The cannulas are deaired, put together as a “Y,” brought out through the skin wound, and connected to the venous limb of the ECMO circuit. Purse strings are secured and placed within the right pleural cavity to facilitate future decannulation.
To ensure stability of the cannulas externally, the cannulas are attached to the patient’s body with heavy #4 Silk suture and adhesive tubing stabilizers (Figure 1). In the extracorporeal circuit, 3/8″ tubing with synthetic antithrombogenic coating (Maquet Softline coating, Wayne, NJ; or a combination of Softline and Sorin SMARxT coating, Denver, CO) is used. Flow meters (Transonic; Ithica, NY), including a dedicated flow meter for the LV vent, are used to measure flow through the circuit. Generally, the target for VA-ECMO circuit flow is 4–5 L/min, and resultant LV vent flows usually run between 400 and 800 ml/min.
If there is not concern for bleeding, patients are anticoagulated while on VA-ECMO by heparin infusion titrated to an activated partial thromboplastin time of 50–70 seconds. When there is concern for antithrombin-III deficiency, heparin-induced thrombocytopenia, or other contraindication to heparin, a bivalrudin infusion is used as an alternative means of anticoagulation.
Although patients are maintained on VA-ECMO therapy, our general practice is to ventilate patients on the pressure assist/control mode targeted to low tidal volumes (4–6 ml/kg) with a positive end-expiratory pressure of 5–10 cm H2O to reduce barotrauma and promote alveolar recruitment, respectively. In addition, the fraction of inspiratory oxygen (FiO2) is generally kept at 40% or lower to avoid hyperoxic lung injury. Ventilator support settings often must be increased when attempting to wean from VA-ECMO, and the extent to which settings are adjusted in this process is dictated by case-specific factors.
A 57 year old man presented to the emergency department in shock. His past medical history was notable for end-stage idiopathic nonischemic cardiomyopathy (NICM) and pulmonary hypertension for which he was managed on home inotropic therapy. At the time of his admission, he was in the process of being listed for heart transplantation. On initial evaluation in the emergency department, there was concern for sepsis caused by fever, tachycardia, and leukocytosis, and he ultimately would prove to have a methicillin-sensitive staphylococcus aureus central line infection. He was admitted to cardiac intensive care unit (CICU), but despite high-level inotropic and vasopressor therapy and broad antimicrobial coverage, he continued to deteriorate (Table 1). In addition, shortly after his arrival to the CICU, he developed flash pulmonary edema and required intubation and mechanical ventilation with 100% FiO2 to maintain adequate oxygen saturation (Figure 2). He was therefore urgently taken to the operating room for initiation of VA-ECMO. Because of his severe pulmonary edema, the decision was made to use the hybrid peripheral-central cannulation arrangement with placement an LV vent (Table 2). After initiation of VA-ECMO, his hemodynamics stabilized. He was treated appropriately for his central line infection and briefly required continuous venovenous hemodialysis for acute kidney injury. By postoperative day 2 (POD2), he had developed significant swelling in his right upper extremity, presumably caused by the high flow delivered by the arterial limb of the ECMO circuit into the axillary artery through the Dacron graft extension. He therefore was taken to the operating room for coarcation of the efferent end of axillary artery, which resolved this issue. Shortly after this second procedure, he was successfully weaned from the ventilator and extubated while on VA-ECMO. He was then mobilized and ambulated each day after his extubation until ECMO was weaned and discontinued on POD5. He remained in the hospital for approximately 2 weeks until an appropriate heart became available for transplantation. The patient remains alive and is doing well now 20 months from the time of heart transplantation.
A 54 year old man with ischemic cardiomyopathy and pulmonary hypertension presented to the hospital with New York Heart Association class IV heart failure (ejection fraction 5–10%) complicated by cardiorenal syndrome and hepatic congestion. He was managed as an inpatient on the heart failure service during which time he required renal replacement therapy and the process of listing for heart transplantation was initiated. After approximately 3 weeks in the hospital, he developed fever and acutely decompensated. He required placement of an intraaortic balloon pump (IABP) and escalating doses of inotropic and vasopressor support (Table 1). Workup at this time ultimately revealed an enterococcus urinary tract infection with associated bacteremia as his source of sepsis. In addition to antimicrobial therapy, he was placed on VA-ECMO for his refractory shock. The hybrid peripheral-central cannulation arrangement with LV decompression was employed because of the patient’s extremely poor LV ejection to protect his lungs from pulmonary edema and injury (Table 2). On POD5, he was transitioned to an extracorporeal Centrimag biventricular assist device as a bridge to transplantation. His automated implantable cardioverter-defibrillator and associated leads were also removed at this time because of his recent bacteremia. A week later, a tracheostomy was placed after the patient twice failed extubation. Unfortunately, the patient subsequently failed to thrive. He had refractory vasoplegia requiring vasopressors. This was posited to be caused by persistent infection, although he was treated continuously with broad-spectrum antibiotics and he did not have any further positive culture data. In addition, he developed gastrointestinal bleeding which forced cessation of his anticoagulation. He subsequently developed thrombus formation in his centrimag circuit, which had to be surgically replaced. In light of this difficult course and in accordance with his family’s wishes, support was ultimately withdrawn, 18 days after his initial ECMO implantation.
A previously healthy 39 year old man suffered an out-of-hospital witnessed cardiac arrest. After bystander cardiopulmonary resuscitation, he was transported to an outside institution where coronary angiography revealed thrombosis of his proximal left anterior descending (LAD) coronary artery as well as high-grade stenosis of the distal right coronary artery (RCA), which were treated by placement of multiple bare metal stents. Despite these interventions, he remained in shock refractory to IABP placement and high inotropic and vasopressor support (Table 1). In addition, echocardiography at this time demonstrated minimal left ventricular ejection (EF <15%). The patient was therefore placed on peripheral VA-ECMO through the right femoral vessels and transferred to our institution for further management. At presentation to our institution, the decision was made to transition the patient to the hybrid peripheral-central cannulation arrangement with LV decompression because of the presence of minimal LV ejection, severe LV distension, and pulmonary edema. Severe coagulopathic bleeding was present at the time of this operation, which extended the duration of the procedure and necessitated transfusion of multiple blood products (Table 2). On POD1, he had persistent bleeding from the axillary artery cannulation site, which required relocation of arterial limb of his circuit to the aorta through the same right anterolateral thoracotomy that the atrial cannula and LV vent had previously been placed. His cardiac function subsequently improved (EF 25%) to the point where he was transitioned to venovenous ECMO on POD5. Unfortunately, the patient did not demonstrate neurologic recovery and in accordance with his family’s wishes support was withdrawn 7 days after his initial ECMO implantation.
Here, we present our early experience with a novel approach for VA-ECMO cannulation with LV decompression. As mechanical circulatory support technologies continue to advance, there is opportunity to develop new treatment strategies to employ these technologies for optimal patient benefit. Although definitive conclusions on the safety and efficacy of our approach should not be made from this small case series, the proposed cannulation strategy offers the potential to overcome several of the current limitations encountered with the delivery of nonpostcardiotomy VA-ECMO.
Perhaps most importantly, direct cannulation of the LV through the right superior pulmonary vein ensures that decompression will be adequate. When VA-ECMO is employed in cases of severe LV hypokenisis or akinesis, decompression of the LV becomes crucial to reduce ventricular wall stress, limit pulmonary edema, and to prevent thromboembolic complications arising from intracardiac thrombus formation. A number of percutaneous techniques for LV decompression have been proposed. However, these percutaneous approaches have largely been reported in pediatric patients9–12 and it is unclear whether they can reliably achieve sufficient flows for adequate LV decompression in adult-sized patients. In contrast, we have been able to achieve flows of approximately 500 ml/min through the LV vent cannula using our approach, providing for robust LV decompression to promote myocardial recovery and limit the extent of pulmonary edema.
Direct cannulation of the LV through the LV apex is another surgical means for robust left heart decompression in the nonpostcardiotomy setting.13 Although LV apex cannulation may be advantageous in certain circumstances, our approach has the added advantage of allowing central right atrial cannulation and placement of a decompressive LV cannula through a common incision and obviates the need for femoral cannulation, thus avoiding the risks of lower limb vascular complications and offering the potential to mobilize the patient. The emergence of percutaneous cannulation techniques using the femoral artery and vein has allowed rapid deployment of ECMO in the nonpostcardiotomy setting. However, there has also been a significant incidence of lower limb ischemia with peripheral VA-ECMO, sometimes resulting in the need for amputation and leading to death.14 Because the hybrid peripheral-central VA-ECMO cannulation approach utilized in this series avoids the issue of lower limb ischemia altogether, it potentially represents an important advance in cannulation strategy.
Nevertheless, the hybrid peripheral-central cannulation approach we employed was not without its shortcomings in regard to vascular complications. Two of the three patients in this series experienced complications related to the axillary artery cannulation site. It is possible that the axillary artery is not well suited to withstand the high flow from the VA-ECMO circuit for sustained periods of time and therefore may be prone to such complications. The main complications of axillary artery cannulation are bleeding and upper limb hyperperfusion. We now use 6-0 polypropylene suture with a small needle in an effort to minimize needle hole trauma and bleeding. To limit hyperperfusion, we have moved toward routine placement of a circumferential band of polytetrafluoroethylene around the axillary artery distal to the Dacron graft anastomosis to affect a stenosis that decreases right arm pressure (relative to femoral pressure) by at least 10 mm Hg. In addition, we are exploring alternative cannulation strategies, including direct aortic cannulation through the anterior thoracotomy incision. This was the cannulation arrangement employed for the patient 3 after he experienced bleeding from his axillary artery cannulation site.
A final advantage to our cannulation strategy is the potential to mobilize and ambulate patients. It is a well accepted tenet of contemporary surgery and critical care medicine that patients who are immobile postoperatively are at risk for debilitation and have inferior overall outcomes compared with patients who are mobilized early after surgery.15 Patients who are cannulated peripherally through the femoral vessels cannot be mobilized, nor can those who have percutaneous strategies for LV decompression such as transatrial venting or placement of an axial flow pump across the aortic valve. Because our technique for VA-ECMO and LV decompression does not entail cannulation of the femoral vessels, the patient can potentially be mobilized and ambulated. Indeed, one patient in this series was extubated 2 days after initiation of VA-ECMO with MILVD and ambulated for 3 consecutive days after extubation until ECMO was discontinued. It is our view that promoting patient mobilization while on VA-ECMO will limit patient debility and holds potential for improving VA-ECMO outcomes.
Despite the potential benefits offered by our peripheral-central cannulation arrangement, there are several important limitations to this approach that should be considered. First, this cannulation strategy requires operative deployment and cannot be accomplished nearly as rapidly as percutaneous femoral cannulation. As a result, our peripheral-central cannulation approach is poorly suited for situations that require emergent ECMO deployment, such as refractory cardiac arrest. Rather, our cannulation strategy is better utilized for acute decompensated cardiogenic shock that requires VA-ECMO cardiopulmonary support to allow for treatment of inciting factors or as bridge to temporary or permanent ventricular assist device placement or heart transplantation. Alternatively, femorally cannulated VA-ECMO may be transitioned to a hybrid peripheral-central cannulation arrangement with LV vent once the patient has stabilized. This may be appropriate in circumstances where it is felt that robust LV decompression is needed and the patient is otherwise suitable for cannula relocation.
Aside from the increased time needed to deploy ECMO, other potential drawbacks with the peripheral-central cannulation arrangement include the risk for mediastinal contamination and intrathoracic bleeding. Although the hybrid peripheral-cannulation approach preserves a virgin sternum for future ventricular assist device placement or heart transplantation, mediastinal infection and intrathoracic bleeding are potential risks with this approach that can be difficult manage. Important consideration of these potential issues should be given when weighing the risk and benefits of proceeding with hybrid peripheral-central VA-ECMO cannulation.
In conclusion, by limiting LV wall stress, pulmonary edema, and the risk for lower limb ischemia as well as by allowing patient mobilization, the proposed hybrid peripheral-central VA-ECMO cannulation arrangement with LV decompression represents a novel strategy for the delivery of nonpostcardiotomy VA-ECMO that potentially ameliorates some of the current limitations with this therapy. Although additional study will be needed to assess the safety and efficacy of this approach, it presents another option in the armamentarium for the management of advanced heart failure. Continuing to develop innovative approaches for employment of VA-ECMO will become increasingly important as the utilization of this technology for temporary cardiopulmonary support becomes more widespread.
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Extracorporeal membrane oxygenation; ECMO; Ambulation; Cannulation; Left ventricular decompression