Evolving Therapies and Technologies in Extracorporeal Membrane Oxygenation Left Arterial Venoarterial Extracorporeal Membrane Oxygenation: The Hemodynamic Implications and Current Practice Methodology

Abstract

Since its inception, venoarterial extracorporeal membrane oxygenation (VA-ECMO) has proved to play a pivotal role in providing mechanical circulatory support (MCS) in the setting of refractory cardiac failure. However, the retrograde flow often leads to further deleterious effects with increased afterload, left ventricle (LV) distension, LV wall stress, pulmonary edema, and higher myocardial oxygenation requirements. In lieu of this, an alternative cannulation method has been gaining momentum to provide MCS while simultaneously offloading the LV. Left arterial venoarterial (LAVA)-ECMO utilizes a novel insertion technique of combining left atrial and right atrial drainage and returning this blood supply in oxygenated form to the arterial circulation. This degree of unloading provides simultaneous biventricular unloading and adequate circulatory flow to help rest and allow for possible native heart recovery. This chapter serves as a vehicle for the description of the LAVA-ECMO, but also to discuss the physiology, implementation, cannulation strategies, complications, and implications of the methodology for utilizing this unique technique.

1. Introduction

The mainstream implantation of MCS devices has proven to play a significant role in augmenting hemodynamic support in critically ill patients. The use of MCS has allowed for an opportunity to stabilize and bridge until definitive therapy can be sought. Specifically, the conception of ECMO and its various subsequent iterations has vastly enhanced the abilities of practitioners to provide a more tailored approach. The two main configurations of ECMO that cater to this are veno-venous (VV) ECMO, providing solely pulmonary support and veno-arterial (VA) ECMO, providing both cardiac and pulmonary support. Further configurations can be made to the circuit to accommodate either anticipated outcomes or concurrent complications. In this chapter we will discuss one such configuration, LAVA-ECMO as an adjunct to conventional VA-ECMO.

2. Background

Though significant technological advancements have been made in the realm of cardiac care, the management and treatment of cardiogenic shock (CS) remains challenging, and unfortunately frequently synonymous with mortality. CS remains a common sequela of acute myocardial infarctions, complicating 5–10% of cases with mortality rate of up to 50% [1, 2]. Therapy entails expeditious recognition and initiation of temporizing measures, typically in the form of vasopressors and inotropic agents. Unfortunately, these measures can fall short, either due to the extensive degree of pathology associated with CS or other co-morbidities exacerbating the deleterious systematic effect. As a result, a more aggressive temporizing method is sought until the underlying cause can be remediated. In such scenarios, MCS serves as the next step, stabilizing patients until restoration of native cardiac function can be achieved or definitive therapies can be applied (indwelling cardiac assist device or transplant).

The advent of MCS has been revolutionary, arming practitioners with a means to bridge patients until definitive therapy can be attained. Currently, numerous options are available depending on the availability, experience of the practitioner or institution and physiological demand or limitation of CS etiology. These MCS include intra-arterial balloon pump (IABP), Impella [Abiomed, Danvers, Massachusetts], or ECMO. Each MCS provides their unique sets of advantages and disadvantages, contributing to each specific indication for use. To add to this, various iterations of these MCS have evolved, allowing for a more individualized approach to their implementation. We will focus VA-ECMO and one of its variations, LAVA-ECMO in the subsequent sections.

3. VA-ECMO and LV failure

Of all the available forms of MCS devices, VA-ECMO has the highest ability for greater support by means of higher augmentation of flow rate, unencumbered oxygenation capacity, and uniquely, biventricular support. Therefore, conventional VA-ECMO is commonly recognized as the MCS of choice in patients presenting with biventricular failure with associated hemometabolic CS, serving to preserve organ function and bridge to myocardial recovery or cardiac transplantation.

Conceptually, VA-ECMO functions by draining the body of de-oxygenated blood via venous cannula passing it through an oxygenator and pumping the blood via an external motor back into an arterial cannula that returns blood typically via the iliofemoral system. Important to note that from just a general perspective, VA-ECMO implantation exists in two significantly different modes, central and peripheral. Central VA-ECMO is surgical and requires a cardiothoracic approach, with sternotomy necessary for the implantation of the circuit—typically direct aortic and right arterial cannula insertions. The pros of the approach include higher flows, the use of large bore cannulas, reduced circuit length, avoidance of limb related ischemia, and theoretically improved hemostasis at cannula insertion sites due to surgical insertion. However, the method bears the risks associated with surgery including bleeding, vessel injury and infection. Additionally, central VA-ECMO has been associated with more re-exploration for bleeding and a higher risk of infection [3].

In the case of peripheral VA-ECMO, this method is more readily available due to the ease of insertion via peripheral vasculature without surgical cutdown. The venous drainage is 20–25 Fr with multi-stage holes along the length of the cannula and is inserted via the right or left femoral vein placing the tip of the cannula at the superior vena cava (SVC)-right atrium (RA) junction. The arterial cannula is inserted into the right or left femoral artery with the tip resting in the proximal iliac or distal aorta. Between the two is a motor and oxygenator that is manipulated by a controller. With all these strengths therein lay an inherent set of weaknesses. These issues include distinct perfusion of the upper and lower body—denoted as the watershed phenomenon, LV distention, and increased afterload [4]. Further, peripheral arterial cannulation requires appropriately sized vasculature and even so may result in distal limb ischemia, this resulting in the need for ipsilateral lower limb arterial bypass. Many of these factors cumulatively can lead to ischemic complications, hemorrhage, or progressive LV failure. Specifically, the inability to effectively unload the LV has been associated with poor outcomes and difficulty with MCS weaning. Russo et al. conducted a meta-analysis which demonstrated decreased mortality (p < 0.00001) with LV venting, but inadvertently was associated with greater hemolysis [5, 6]. Furthermore, Al-Fares et al. conducted a meta-analysis which demonstrated that LV unloading showed better success in weaning from MCS (P = 0.001), though survival remained similar [6, 7]. These data points cemented the notion that there remains an obvious beneficial correlation with LV unloading or prevention of LV distension. Therefore, early and at times aggressive measures are critical to circumvent complications associated with the circuit. These include adjustments to the circuit flow, optimizing fluid status, initiation of inotropes, use of additional MCS and finally, the theme of this chapter upgrade to LAVA-ECMO.

4. Indications of LV unloading

As alluded to CS can be difficult to manage, necessitating prompt escalation of care in the form of MCS. Although numerous MCS exist, their functionality can be limited depending on individual scenarios. In the case of VA-ECMO, one inadvertently increases the LV afterload, thereby exacerbating biventricular failure. A sequalae of this is LV distension and wall stress which can further propagate a cascade resulting in LV failure, potentiate severe pulmonary edema, pre-dispose the risk of LV thrombus formation, and impedes ventricular recovery [6].

This is detrimental as increased ventricular load typically will lead to elevated left ventricular end diastolic pressure (LVEDP) which has been associated with propagating myocardial infarctions, reduction in myocardial salvage and an overall increase in risk of mortality [6]. In fact, studies have demonstrated relatively improved outcomes in strategies linked to reduced ventricular load [8]. Therefore, when the constellation of signs for LV distension are noted, such as progressive tachycardia, poor flow, progressive hypoxia, pulmonary congestion, or LA dilation then prompt steps are required to prevent deleterious cardiac effects. Figure 1 demonstrates the indications of LV unloading.

Figure 1.

Illustrates the indications for LV unloading in patients on VA-ECMO.

Historically, conservative measures are pursued to optimize hemodynamic status by means of altering volume status, initiating inotropic agents and vasopressors. Volume status requires tedious monitoring and frequent adjustments. This is guided by pump effort and resistance, pulmonary artery, and central venous pressures, and finally, clinical judgment. Unfortunately, fluid status is a delicate and constantly changing demanding parameter in ECMO management. For instance, if pump chugging is appreciated, volume may be required in the form of blood products or fluids. This is typically accompanied by decreasing flow to avert distension but comes at the risk of further cardiac failure and decreased perfusion. On the contrary, fluid overload can be appreciated with increased pressures on SGC readings, pulmonary edema and resultant ventilatory effort. Such circumstances require aggressive diuresis. Regardless, both these volume states are transient, alternating between an intravascularly hypervolemic and hypovolemic state. Therefore, it is imperative to be cognizant of the overall goal of volume, one that encompasses adequate forward flow thereby supporting and supplying the body, all-the-while inciting appropriate cardiac contractility via Frank-Starling forces. Similar limitations exist with the long-term utilization of inotropes and vasopressors, normally resulting in inotrope-dependence, dysrhythmias, and progressive organ dysfunction.

In the next section we will discuss these methods and others that can provide a temporizing effect but ultimately may fail to alleviate the LV burden. In such circumstances additional MCS to VA-ECMO such as IABP, Impella or other percutaneous LVAD may be required [1]. However, as discussed later, this option may not be optimal and bears risks.

5. Methods of LV decompression

Measures are taken in a systemic and escalating fashion until ultimately hemodynamics are optimized, and a decrease in afterload and LV distension is achieved. This is a constant process which requires strict monitoring with near frequent adjustments. Volume status is routinely assessed by clinical examination, beside echocardiography, non-invasive monitors, and Swan Ganz Catheter (SGC) readings. Diuretics assist in decreasing preload. This allows for a pseudo-inotropic effect, improving cardiac function in the process [9]. Quite often acute kidney injury may develop thereby necessitating a form of renal replacement therapy (RRT). Indications for RRT in ECMO include fluid overload unresponsive to diuretics, refractory metabolic acidosis, sequela of uremia and persistent hyperkalemia [10]. The use of inotropic agents early on can assist in pump weaning and averting progressive deleterious effects on the cardiovascular system. Agents such as dobutamine and milrinone have been historically used as resuscitative therapy for severe CS. In doing so, both agents allow for overall increased cardiac output and decreased left end diastolic ventricular pressure (LVDEP) [11].

Further means of more rapid LV unloading involve percutaneous pigtail drainage of the LV [12]. A benefit of this procedure is it can be readily completed at bedside by means of echocardiogram and hemodynamics measurement. If these measures fail, management is escalated to additional MCS including IABP, Impella and transeptal cannulation to assist in the reduction of LV afterload and subsequent distension [13, 14, 15]. Particularly, the use of Impella in such circumstances has been well documented in current literature. Schrage et al. described the utilization of Impella with VA-ECMO for LV unloaded and demonstrated a mortality reduction with combined use (p < 0.0001), but again there was a higher risk of bleeding and ischemia related to the access site [6].

Finally, a direct method can be implored, one that entails direct left atrium (LA) decompressive therapy to assist in LV recovery by alleviating LV distention. LA decompression can be completed either surgically or percutaneously. This can include LA septostomy and direct LA cannulation. Studies have demonstrated that reduction in LV distension is associated with reduced transcoronary perfusion gradients that are responsible for impairing myocardial perfusion and resulting in injury [16]. This is further seen in a study conducted in pediatric population on VA-ECMO that showed reduced in hospital adverse outcomes with LA decompression (p = 0.007) [16].

To circumvent this, another strategy of implantation and relatively new in practice has been gaining momentum as an attractive alternative. LAVA-ECMO has gained increased notoriety and globally is recognized as a means of emergency biventricular hemodynamic support with concurrent CS. This method was first described in the literature for biventricular CS in 2018 [17]. Unique to LAVA-ECMO enables biventricular atrial drainage, thereby allowing for biventricular unloading, and averting the need for supplementary device. The advantage of LAVA-ECMO is the flexibility it provides in the circuitry method. A single fenestrated cannula can be placed draining both the LA and RA; two separate cannulas can be placed with one in the RA-SVC and the other in the LA with eventually connected via a Y-connector; or a PA cannula positioned and connected to a RA cannula. Table 1 illustrates and compares the numerous methods available to practitioners to provide some degree of decompressive therapy. As visualized, the advantages noted with LAVA-ECMO make it an alluring alternative to other conventional methods.

Table 1.

Illustrates and compares the numerous decompressive therapies available.

6. Hemodynamics of ECMO

The need for MCS in patients with severe refractory CS stems from the overall inability to produce the required cardiac output necessary to provide systemic perfusion. This leads to undesirable effects as a failure to ensure forward flow results in higher preloads, greater intracardiac pressures to generate subpar stroke volumes which collectively propagates further ventricular failure. As mentioned previously, MCS aims to alleviate this, augmenting hemodynamics until cardiac recovery is achieved. Of the numerous MCS devices, ECMO has been demonstrated to have the greatest impact on cardiac function and hemodynamic support. Noted in Figure 2, VA-ECMO results in the increase in the pressure volume area by means of raising systolic pressure, end diastolic pressure, and afterload. This inadvertently results in significant reduction in stroke volume, thereby decreasing ventricular workload. Given the increase in perfusion at the cost LV distension, the utility of combining LA drainage with venous drainage theoretically improves the overall stroke work and thus leading to a greater probability of myocardial recovery.

Figure 2.

(A) Pressure-Volume Loop illustrating the hemodynamic effects of VA-ECMO including improving systolic, end diastolic pressures, and afterload, thereby reducing stroke volume. (B) Specifically highlights the advantages attributed to LA-to-aortic pump with regards to end diastolic and systolic pressure and volume with alterations to total peripheral resistance and end systolic elastance. (C) Further elaborates the impact of flow dependent changes in LA-to-aortic pump by means of a reduction in end diastolic pressure, increased end systolic pressure, showing an overall improvement LV stroke work [18, 19].

7. LAVA-ECMO discussion

The physiologic mechanism key to this involves the insertion and implementation of a unique fenestrated cannula that crosses the intra-atrial septum, allowing for bi-atrial drainage. The cannula drains blood across both systems of the heart, and in doing so assists the LA by reducing the left ventricle end diastolic volume and pressure, along with decreasing preload [1]. This volume is then returned to the circuit via the arterial cannula thereby adding to the ejection fraction of the left heart, improving end tissue perfusion.

As the circuit requires a transeptal cannula, the first step entails accessing the septum anatomy. A transesophageal echocardiogram (TEE) or intracardiac echocardiography (ICE) is utilized to study anatomy and help guide transeptal cannulation. Under sedation the imaging of choice is appropriately positioned. Although it is reasonable to cross anywhere in the fossa ovale, the optimal location for transeptal penetration lies at the mid-portion of the fossa ovale which helps circumvent suction events in the left atrium [20]. If transseptal puncture is not completed, either due to poor imaging visibility or anatomical variations, a PA catheter can be positioned from the right internal jugular vein.

Next, vascular sites need to be inspected to plan the feasibility of cannula support. As such a larger vessel with the prospects of less tortuosity are preferred, thereby averting kinks, disruption or decreased flow, vessel damage and clots. Therefore, peripheral cannulation is performed by means of common femoral artery (CFA) and vein, below the inguinal ligament and above the bifurcation. Although larger cannulas may be suitable and necessary depending on the patient’s need, these are typically associated with increased risk of vascular complications, notably limb ischemia. Other anatomical considerations need attention. Ideally, arterial, and venous cannulation is completed on separate limbs thereby reducing the risk of vascular complications and theoretically will facilitate decannulation when appropriate. Additionally, the venous cannula should be preferably placed in the right femoral vein thereby allowing a straighter path to the right sided circulation. To avoid vessel or surrounding tissue injury, cannulation is best completed via imaging modality such as ultrasound or under fluoroscopy. Often the femoral head can function as a landmark to obtain vascular access along a compressible region of the vessel and preventing pelvic entry. Following delivery of anticoagulation, access is obtained and via seldinger fashion serial dilations are completed until intended cannula is placed. Post-cannulation, placement is verified via fluoroscopy. It is worth mentioning, in rare circumstances femoral access may be unobtainable, either due to severe peripheral vascular disease or vasculature. In these instances, subclavian or axillary artery cannulation can take place. Although these methods pose less risk of limb ischemia, they can minimize the differential oxygenation, prolong patient immobilization, and can result in nerve damage [21]. Finally, distal perfusion needs to be considered, specifically for femoral artery cannulation. Distal perfusion catheters (DPC) are placed into the superficial femoral artery to provide antegrade flow. Both position and verification of flow can be completed by ultrasound guidance and flow dopplers. The need for DPCs is contingent on the retrograde cannula size. The decision to place DPCs is assessed via tissue saturation evaluated by Near-Infrared Spectroscopy. Tissue saturation is recommended above 50–60% with less than 20% difference between both limbs [21]. Regardless, the sidearm of the DPC sheath is connected by means of short tubing and a male-to-male connector to the arterial cannula. Figure 3a demonstrates the complete circuit access points.

Figure 3.

Illustrates two different methods of LAVA-ECMO circuitry. (A) Demonstrates the traditional approach to LAVA-ECMO circuit. This method utilizes a single venous return cannula which allows for a 25 Fr fenestrated cannula to be placed via fluoroscopy and TEE guidance transeptally. The venous inflow is extracted and pumped to a membrane oxygenator before being returned by means of an arterial outflow 19 Fr cannula back to the aorta. A smaller reperfusion cannula is placed in an antegrade fashion to allow for distal extremity perfusion. (B) Is an alternative method of LAVA-ECMO circuit that utilizes two return cannulas (21 Fr Transseptal LA cannula and 25 Fr RA cannula). Both cannulas are connected to a Y-connector prior to supplying return flow to the pump and oxygenator. This mode enables potential reversal back to VA-ECMO and implantation of VAD if clinically indicated.

Blood is constantly exposed to a large area of non-endothelial biosurface, involving the tubing and pump. This predisposes the patient to a pro-thrombotic state. Most commonly unfractionated heparin is used with close monitoring and titration for activated clotting time with goal of 180–220 seconds. Often, other anticoagulation products may be required such as bivalirudin or argatroban if renal or hepatic impairment are prevalent, respectively. Unfortunately, the nature of constant anticoagulation, blood shearing via pump mechanics and large bore cannulation sites make bleeding a common complication with ECMO. The incidence of bleeding varies from 10 to 30%, whereas the incidence of significant thrombosis is 8% [22]. Therefore, a fine balance exists between bleeding and clotting during and after the ECMO cannulation process. The decision to anticoagulant or reverse anticoagulation is contingent on routine coagulation markers monitoring, such as fibrinogen, activated partial thromboplastin time, anti-factor Xa and platelets. Additional complications associated with this will be discussed in subsequent sections.

Other considerations may arise depending on necessity or anticipated complications. It is important to note that the methodology and use of LAVA-ECMO may differ from institution to institution. The use of a single large bore access averts the risks associated with bleeding, stroke, and infection. However, the use of an additional venous access may allow for flexibility in MCS adjustments depending on the patient’s clinical needs. This method of venous access typically involves a left femoral vein to IVC with a 25 Fr cannula and a second 21 Fr transseptal cannula via the right femoral vein. Both venous cannulas are connected via a Y-connector before supplying the oxygenator. The benefit procured by this configuration is that it allows LAVA-ECMO to be weaned to an LVAD. This also allows for the potentially reversal in case VA-ECMO support is again required [2]. For reference, both methods of LAVA-ECMO can be visualized in Figure 4a and b.

8. Percutaneous Techniques

Although procedural steps may differ depending on the comfort or routine of the proceduralist, we will first discuss a generalized method of circuit implantation.

1. The patient is brought to the cardiac catheterization/fluoroscopic laboratory and is prepped and draped in sterile fashion.

2. The pump is prepped and primed with an oxygenator. A Y-connector may be prepared if plans for dual venous drainage, this will go into the oxygenator and further feed blood into the pump.

3. Infiltration of the inguinal region with 2% lidocaine using micropuncture and modified Seldinger technician under fluoroscopic and ultrasound guidance is used to access the right femoral vein.

4. Then once acceptable vessel entry and intraluminal wire placement is established, an 0.035” guidewire is inserted per the micropuncture sheath.

5. Here, two methodologies of LAVA-circuitry can be approached. Regardless, it is recommended to place the femoral arterial and venous cannulation in opposite legs with ideally placing the venous drainage cannula in the right femoral vein. This gives a more direct path to the right atrium. Then an arterial 6 Fr sheath can be placed in the left common femoral artery.

   1. Single LAVA system: entails the use of right CFV for transeptal catheter drainage flow – a single drainage cannula is multi-fenestrated and left CFA for return.

   2. Dual LAVA system: entails the use of right CFV for transeptal LA drainage flow, left CFV for RA drainage, and left CFA for return.

6. On the side of arterial access, typically left CFA, obtain antegrade CFA/SFA using a braided or reinforced sheath.

7. Now focusing on the venous access, a flexible catheter or preshaped sheath is guided to the point of entry along the intra-atrial septum. Puncture is made along the wall, and a 0.035” guidewire is advanced to the left superior pulmonary vein.

8. Starting with the venous cannula, advance the 0.035” guidewire into the right atrium. Create a small skin incision, less than 1 cm, beside the guidewire and dissect the fascia via a small Kelly clamp.

9. Serially dilate the venotomy and tract with dilators. Make sure all the dilators move independently of the guidewire and that the guidewire doesn’t kink.

10. Then advance the venous cannula until the tip is in the mid-right atrium or in the RA/SVC junction – if dual LAVA cannulation is pursed. Remove the guidewire and dilator, de-air, and clamp.

11. Some institutions may opt for a ProTrack pigtail wire – Baylis^TM, thereby not necessitating the need for anchoring. Regardless, an 8.0 mm balloon is guided over the wire to the septum for intraarterial ballon septostomy. If not available, a 14 Fr Dilators can be used as well.

12. Once septostomy is completed, the prepared proprietary 21 Fr fenestrated (Protek Solo [Liva Nova, Pittsburgh, PA]) cannula is fluoroscopically guided over the stiff guidewire.

13. The cannula is advanced into the LA, as far as the proximal left superior pulmonary artery. Important to note.

    1. If a single drainage system is pursued, then the catheter will consist of a single multi-fenestrated cannula allowing for biventricular drainage.

    2. If a double drainage system is pursued, then the LA arterial drainage involves a dedicated LA drainage cannula (ProtekSolo) along with a RA drainage cannula. This RA cannula involves left CFV access with serial dilation until the insertion of a multi-fenestrated cannula to the right atrial-SVC junction. The cannula is then de-aired and clamped. Now, both drainage cannulas are connected using a Y-connector to produce a single drainage limb.

    3. These steps can be visualized in Figure 4a and b.

14. Now, with the drainage system secured arterial cannulation is sought after next. Again, utilizing the modified Seldinger technique and serial dilations, left femoral artery access is obtained.

15. Preclosure of the artery is done prior to insertion of the large-sized cannula to plan for explantation and percutaneous closure.

16. The arterial cannula is inserted in the same way as the venous cannula.

17. With the eventual placement of a 17-21 Fr return cannula to the aorta/proximal iliac artery.

18. Once all large access is completed, the patient should be fully heparinized with an ACT goal of 250–300 seconds.

19. The system is then connected via a wet-to-wet connection with the oxygenator and pump in series circuit. At this stage either:

    1. Single LAVA system: connect single RA-LA cannula to the oxygenator.

    2. Dual LAVA system: ensure single limb drainage from RA and LA cannulas together using a Y-connector to the oxygenator.

20. Arterial cannula should be connected to the antegrade sheath on the ipsilateral side via a male-to-male connectors, again ensuring no air is within the system. At this point, the pump can be turned on. All clamps can be released in sequential fashion from venous to arterial while monitoring for any air in the circuitry and adequate color change in the post-oxygenation arterial limb. The complete circuit can be visualized in Figure 3a and b.

21. ECMO flow can begin, and multiple sutures are placed to secure the cannulas to the skin.

22. Immediate post cannulation bloodwork is collected, including ABG, VBG, CBC, BMP, lactate, and fluoroscopy should be performed to ensure appropriate positioning of the cannula, observe for internal tubing kinks or cracks and the physiologic effects of the circuitry are in line with the patient’s overall clinical presentation.

Figure 4.

Illustrates the procedural steps for transeptal cannulation in LAVA-ECMO. (A) Panel sequence of transeptal cannulation. Steps are (1) Utilizing either intracardiac ultrasound or TEE, the left atrial access site is visualized. (2) Used a steerable catheter or introducer, the needle is guided to obtain access. (3) Once the septum has been penetrated a ProTrack Pigtail wire is guided into the left atrium. If not available, a 0.035″ guidewire is advanced into either the left superior pulmonary vein. (4) Septostomy is completed with an 8.0 mm interaarterial balloon. This step can also be completed by a 14 Fr dilator. Depending on the intended configuration setup; (B) by means of fluoroscopy, a fenestrated cannula (Liva Nova) is positioned over a stiff wire and into the left atrium, typically up to the proximal left superior pulmonary vein. Or (C) partially fenestrated cannula designed for LA drainage is positioned, and a second venous drainage cannula is positioned in the SVC-RA.

Pragmatically a two-team approach is taken during the implantation process. The proceduralist and team works on inspecting and obtaining appropriate access as detailed above. During this time the ECMO team, comprising the intensivist, perfusionist and other critical care team members work to calibrate ventilatory settings, sedation, and vasopressor requirements. Additionally, they will concurrently work on circuit set up. When both teams are ready, the connection will be completed, and the patient transitioned to full ECMO support. This two-team task allocation is seen in Table 2.

Table 2.

Demonstrates a two-team approach for LAVA ECMO cannulation and circuit implantation.

9. Management of circuit

Following implantation of the LAVA-ECMO, the patient requires strict care and monitoring in an intensive care unit. Depending on institutional protocols, a certain subset of parameters is routinely evaluated to prevent any expected or insidious complications. The required sedation and analgesia should be continued. Careful consideration should be pursued when choosing these agents and are contingent on the presenting pathology, underlying disease process and other co-morbidities. Systemic, or at the very least prophylactic antibiotics should be considered during the cannulation process. Finally, invasive hemodynamic should be monitored standard fashion to assist in pump and vasopressor titration during the bypass period. A right radial artery placement is preferrable to monitor right radial oximetry/blood gases to detect dif-ferential body hypoxemia. SGC allows frequent evaluation of left and right sided cardiac function by means of measuring cardiac power output and pulmonary artery pulsatility index (PAPi), respectively. Other estimated values, such as central venous pressure and pulmonary artery pressure can provide an indication of intravascular volume status.

The focus should be to wean off invasive mechanical ventilation sooner and encourage early mobility. However, during ventilatory dependence, lung protective strategies should be pursued to avoid barotrauma. This includes attempting to maintain low tidal volumes and minute/ventilation while relatively high positive end-expiratory pressure. The higher positive pressure also assists by counteracting hydrostatic pressures, thereby preventing, or temporizing pulmonary edema.

As mentioned earlier, anticoagulation is necessary to ensure the system flow is unhindered by the formation of any clots. Typically, the agent of choice is heparin or bivalirudin, depending on the patient’s renal status. It is important to be cognizant that systemic anticoagulation does predispose a greater risk of bleeding. This is especially true given the large bore access and hemolytic process attributed to anticipated blood sheering when run through the circuit pump. Patients on MCS and mechanical ventilation are also predisposed to greater gastrointestinal bleeds, therefore empiric high dose stress ulcer prophylaxis should be considered [23]. Studies have shown no significant difference between the use of proton pump inhibitors and histamine-2-receptor antagonist during endoscopic hemostasis or in-hospital mortality [23].

As alluded to previously, there is a constant struggle between clotting and bleeding once on the circuit. In the case of bleeding or down trending hemoglobin, prompt blood transfusions are required to maintain adequate flow and prevent pump chugging. The threshold for transfusion remains an area of debate but recent literature has demonstrated no increased benefits from a liberal transfusion policy (Hgb 10–12 g/dL), but in fact has shown overall decrease in 30-day mortality within a subgroup of lower illness severity and acute kidney injury with a restrictive transfusion policy (7–9 g/dL). Overall, the mean transfusion threshold was 8 g/dL. On the contrary, the same report mentioned another study that found both policies non-inferior to one another in the case of cardiac surgery [24]. Regardless, institutional standards often dictate transfusion criteria. If hemodynamics is affected, overt hypoxia or ischemia is appreciated and mechanical strain in the form of chugging then transfusion may be indicated.

10. Device explantation and recovery

It’s imperative to provide adequate support to ensure hemodynamic and oxygenation support, while continuously priming and titrating for eventual circuit explantation. This demands frequent re-evaluations of ECMO flow rates, pump support, volume status, sweep gas and ventilator adjustments. The weaning trial first and foremost necessitates overall clinical improvement. The parameters for ECMO weaning can be seen in Figure 5 [25]. In the case of LAVA-ECMO, extra steps are involved depending on the circuit implantation configuration. Particularly, if 2 venous access are present and connected via a Y-connector, a Hoffman clamp can be utilized to control the degree of venous blood drainage. Depending on the volume overload or preload requirements, the Hoffman clamp can be used to de-crease venous return from the LA cannula, preferentially draining the RA or vice versa resulting in univentricular LV support.

Figure 5.

ECMO weaning protocol.

Recovery is a multifaced process, requiring not only cardiovascular-pulmonary recovery but physical and mental healing. This entails an extensive team approach, catering to the entire body with the aim of obtaining maximum functionality. To this, as in the case of other intensive care patients’ early mobility is key to avert prolonged hospitalization and the complications attributed to this. Physical and occupational therapy should be involved early on to ensure this. Post-extubation speech evaluation is necessary to ensure airway protection and further assess the patients’ nutritional needs. Given the duration of bed rest, wound care should be considered to routinely assess for any potential source of infections from lesions or skin breath throughs.

11. Clinical significance of LAVA-ECMO

LAVA-ECMO allows practitioners tremendous flexibility in cardiac augmentation and use in circumstances where contraindications may prohibit certain MCS. This availability of options tailored to the physiologic demands of the patient has enabled it to become a popular means of cardiovascular support. As alluded to earlier, an obvious benefit of LAVA-ECMO is its ability provide biventricular support while simultaneous decompression the RA and LA. This method, which care be completely percutaneous and poses the least risk with effective LV unloading thereby enabling complete cardiac recovery. It does this by decreasing right sid-ed heart pressures, denoted by im-proving PAPi and pulmonary ede-ma all-the-while improving forward flow. This is crucial in conditions such as acute heart failure, post-myocardial infarction (MI) with LV stunting, mitral valve insufficiency, and aortic stenosis or insufficiency. These conditions predispose patients to tenuous states of refractory and progressive volume overload and LV pressures. Early LA/LV venting should be considered as preventive therapy in such individuals.

Furthermore, in situations where access may limited, typically from pathology such as severe peripheral artery disease, hematologic conditions predisposing the patient to an increased bleeding risk, or limited access secondary to planned interventions, the use of a single cannula is an attractive alternative. The latter is notably appreciated in cases of acute myocardial infarction resulting in CS. Here, especially in multivessel disease and possible coronary bypass intervention once hemodynamic stability with MCS is achieved, allocating and conserving access sites is critical. The use of single large bore access also decreases the probability of vascular complications including bleeding, hematoma, hemolysis, stroke, and limb ischemia. On the contrary, other configurations which do entail additional access, at the risk of bleeding, can be utilized for planned or anticipated outcomes. One such configuration involves two cannulations with an SVC-RA drainage and provides the ability for full ECMO support or left ventricular assist device downgrade depending on the clinical requirements and need for additional support. Finally, a third configuration of PA-RA cannula allows for stricter right sided support and hypoxemia, particularly in severe pulmonary hypertension and vascular congestion.

Other indications, or rather lack of contraindications make LAVA-ECMO a superior choice to its MCS counterparts. As described earlier, LAVA-ECMO averts cannula passage through the aortic valve. This is important, as devices such as Impella are contraindicated in aortic valve pathology for this very reason. Therefore, LAVA-ECMO can bridge to definitive therapy for patients with severe aortic stenosis requiring transaortic catheter valve replacement (TAVR) or in patients needed valve-in-valve TAVR following acute flail leaflet resulting in sudden severe aortic insufficiency in aortic bioprosthetic valves. Furthermore, when comparing ECMO and Impella use versus LAVA-ECMO, the latter as shown to provide greater reduction in LV pressure and volume. Another example of LAVA-ECMO superiority to other left ventricular assist devices include in the setting of LV thrombus. Here, LAVA ECMO provides cardiovascular support without the risk of dislodging or propagating thrombi. All these proposed indications of LAVA-ECMO can be seen in Figure 6.

Figure 6.

Illustrated indications for LAVA-ECMO.

12. Complication

One of the biggest potential limitations of LAVA-ECMO is that it requires a transeptal puncture. This step may not be feasible for all practitioners as there lies an element of expertise with said maneuver. Furthermore, despite being guided via TEE or ICE, there lies the possibility of unintended trauma or rupture of the intraarterial septum. Although this is rare, what is not and often expected is the presence of a small residual atrial septal defect post decannulation. If large enough or aided by the patient’s anatomy a left to right shunting may occur resulting in acute and chronic symptomatology. Typically, significant left to right shunting could result in eventual right ventricular failure and tricuspid regurgitation. On the other hand, right to left shunting can exacerbate hypoxia. Finally, the septal defect may predispose the patient to paradoxical systemic emboli. Therefore, depending on the degree and risk factors, the use of a transeptal puncture often necessitates a closure device later.

Regardless of the configuration and number of access sites used, LAVA ECMO carries similar risks associated with other arterial cannulation methods. There remains a risk of vascular complications including strokes, hemorrhage, hematoma, bleeding, and notoriously acute limb ischemia. DPC’s have provided a solution to distal limb perfusion but this requires anticoagulation to maintain patency. Additionally, systemic anticoagulation can induce hematologic reactions and bleeding, commonly via heparin induced thrombocytopenia [22]. Prompt recognition and change or temporary cessation in anticoagulation may be required.

13. Conclusion

The mainstream implantation of MCS devices has proven to play a significant role in augmenting hemodynamic support in critically ill patients. The use of MCS has allowed for an opportunity to stabilize and bridge until definitive therapy can be sought. Specifically, the conception of ECMO and its various iterations has enabled practitioners’ tremendous flexibility in providing care tailored to patient specific needs and presentation. Of these variants, LAVA-ECMO has proven an exciting alternative to conventional ECMO due to its multifaceted benefits, thereby ensuring and augmenting cardiac recovery.

Conflict of interest

The authors declare no conflict of interest.

Acronyms and abbreviations

VA-ECMO	veno-arterial extracorporeal membrane oxygenation
MCS	mechanical circulatory support
LV	left ventricle
LAVA	left atrial venoarterial
VA	veno-arterial
VV	veno-venous
CS	cardiogenic shock
IABG	intra-arterial balloon pump
SVC	superior vena cava
RA	right atrium
SGC	Swan Ganz Catheter
RRT	renal replacement therapy
LVEDP	left ventricular end diastolic pressure
LA	left atrium
TEE	transesophageal echocardiogram
ICE	intracardiac echocardiogram
CFA	Common femoral artery
CFV	Common femoral vein
DPC	distal perfusion catheters
PAPi	pulmonary artery p‑ulsatility index
MI	myocardial infarction
TAVR	transaortic catheter valve replacement