Exploring Standard and Alternative Sites for Left Ventricular Assist Device Inflow Cannula and Outflow Graft Placement

Abstract

Left ventricular assist device (LVAD) therapy is an essential tool in the armamentarium for managing refractory heart failure. The traditional LVAD placement involves insertion of the inflow cannula (IC) at the left ventricle’s true apex and attachment of the outflow graft (OG) to the ascending aorta (AA), which ensures alignment with physiological blood flow and minimizes complications. However, patient-specific anatomical variations and prior medical interventions necessitate considering alternative IC and OG placement techniques. This chapter reviews the standard and alternative IC and OG placement sites and emphasizes the importance of adapting LVAD component placement to individual patient needs, highlighting the potential of alternative techniques in improving outcomes. Despite the predominance of standard sites due to their proven efficacy, the heterogeneity of patient conditions underscores the need for flexible, patient-tailored approaches.

1. Introduction

Implantable left ventricular assist devices (LVADs) have become an integral part of the therapeutic arsenal for managing end-stage heart failure [1, 2]. Whether serving as a bridge to transplantation or as a long-term solution, the success of these devices is critically dependent on the appropriate placement of their components, primarily the inflow cannula and the outflow graft. This chapter reviews the standard and alternative placement sites for these vital components of contemporary continuous-flow LVADs.

2. Standard and alternative inflow cannula placement

The LVAD relies on three principal blood-contacting components to function: the inflow cannula (IC) – which draws blood from the left side of the heart; the pump – which propels the blood; and the outflow graft (OG) – which returns the blood to the systemic circulation [3, 4]. The placement and position of the IC, however, are crucial considerations for ensuring proper LVAD function, optimal cardiac support, and patient outcomes [3, 5, 6, 7, 8, 9]. The left ventricle’s (LV) true apex has historically been considered the best placement position of the LVAD’s IC and is, therefore, standard [1, 5, 10] (Table 1). Several factors rationalize this: IC’s placement through the true apex ensures reproducible surgical placement technique. While there may be anatomical variations among patients, the true apex remains a consistently identifiable anatomical landmark [1, 5, 10]. Given its pointed structure and relative anatomical isolation, the LV apex allows for straightforward insertion and secure cannula anchoring. The area is also less prone to hypertrophy, providing a consistent myocardial texture for cannula insertion. From a hemodynamic standpoint, using the true apex as an IC placement entry point ensures the IC’s physiological orientation, aligning it with the direction of the physiological blood flow towards the apex [6, 7]. This facilitates more direct flow from the mitral valve to the IC, enhances the device’s efficiency, and minimizes blood stasis [6, 8]. The IC must point towards the mitral valve [7] so that its long axis matches the long axis (natural flow axis) of the LV, ensuring that the inflow cannula’s orientation is in synchrony with the LV’s natural flow trajectory [10, 11]. It also facilitates the direction of the IC that best accommodates the anticipated reductions in LV chamber size occurring over time [8]. Angulation of the IC off-axis towards the interventricular septum or left ventricular free wall may cause intermittent partial occlusion of the IC and suction events, which may lead to poor flow into the LVAD with consequent poor ventricular unloading and possible hemolysis or thromboembolic complications [3, 6, 7, 8, 9]. The standard IC placement technique - ensuring that the IC’s orientation aligns with the direction of physiological blood flow towards the apex, facilitating direct flow from the mitral valve to the IC -should therefore reduce the risk of inflow obstruction, suction events, and thrombosis that can lead to ventricular arrhythmias or device alarms and stroke [7, 9]. Numerical (in silico) and clinical data support the adverse effects of off-axis angulation of the IC [7, 9, 11, 12, 13]. The attachment of the IC to the myocardium is facilitated by a sewing ring that is attached to the epicardial surface near the LV’s true apex, usually at its anterior wall, about 2 cm lateral to the left anterior descending coronary artery [1, 5, 10]. A circular knife creates a myocardial core directed towards the mitral valve and parallel to the interventricular septum [14]. Different IC surgical fixation techniques exist [15]. In this regard, in in-vitro studies, the sew-then-core technique using epicardial stitching, in which partial-thickness suture bites do not penetrate the endocardium, appears to be associated with the lowest risk of suction events or thrombosis formation [15]. Although lacking robustness, available clinical data has indeed shown a trend towards a higher risk of stroke when the cut-then-sew“ technique is utilized compared to the “cut-then-sew” approach [16]. Future studies should also confirm whether surgical access techniques (lateral thoracotomy versus conventional full sternotomy) play a role in optimal IC positioning [12].

Summary of the insertion technique	Advantages	Disadvantages	Contraindications/Unsuitability	Reasons for unsuitability
Technique of left ventricular assist device (LVAD) implantation that involves direct insertion of the inflow cannula (IC) into the true apex of the left ventricle (LV) via; Surgical access: full median sternotomy or lateral thoracotomy or lateral thoracotomy combined with upper hemisternotomy	Well-established with proven outcomes; Facilitates standardized LVAD placement; Facilitates optimal blood flow from the left ventricle into the LVAD; Reduces the risk of inflow obstruction/suction by adjacent structures.	Potential for ventricular arrhythmias due to manipulation or irritation at the apical site.; Risk of inflow cannula malposition due to cardiac remodeling over time.; Loss of viable myocardium due at the site of IC placement	Extensive recent myocardial infarction involving the left ventricular apex; Extensive myocardial calcifications or thinning at the apex; Previous apical surgeries or interventions that have altered the LV anatomy	Extensive myocardial scarring or thinning can result in inadequate or unstable cannula fixation, increasing the risk of complications such as bleeding or device malfunction.; Previous surgical interventions can present anatomical challenges or increase risks.

Table 1.

Left ventricular assist device implantation with inflow cannula placement at the true apex.

The choice of the apical site for IC has been supported by decades of clinical experience. However, it is crucial to consider the individual patient’s anatomy, comorbidities, and potential for complications when opting for the standard site [1, 10]. In this regard, several clinical scenarios, such as previous cardiac surgery, severe apical calcifications, aneurismal dilation or thinning of the apical wall, apical hypertrophy, or unique anatomical variations may make apical IC placement unpractical, risky, or undesirable [1, 5, 10, 17] (Table 2). These special situations might require exploring unconventional IC placement sites with a certain degree of surgical flexibility and innovation [10], tailored to serve patient’s needs best [1, 5, 10]. A recent extensive myocardial necrosis involving the apex may also preclude safe anchoring of the IC’s sewing ring. In this case, the IC’s sewing ring may be attached to a Dacron patch used to reconstruct the excised necrotic apex [18]. That can also be applied in the cases of concomitant left ventricular reconstruction for (severely calcified) ventricular aneurism or a previous Dor procedure [10, 19, 20, 21, 22]. Cannulation of the left ventricular diaphragmatic wall may be a viable alternative to this [1, 10]. Attachment of the IC to the diaphragmatic wall may also be useful in cases of a markedly enlarged LV with altered geometry, the presence of post-myocardial infarction apical aneurysm, and patients with constricted thoracic anatomy [1, 5, 10]. Next, with a significant representation of about 2% among LVAD recipients, patients with restrictive or hypertrophic cardiomyopathy are more prone to right ventricular failure, suction events, and death during LVAD support [23, 24]. The adverse outcomes observed in this specific fraction of LVAD patients are likely due to their distinctive anatomy – having small left ventricular cavities [23, 24] and making them ineligible or challenging for standard apical cannulation [23, 25, 26]. In these cases, a myectomy may be necessary so that enough space is created for the IC [25]. Alternatively, atrial cannulation can be performed, especially considering considerable left atrial enlargement in this patient population [23]. A novel transseptal technique has been described, in which the IC is connected to the left atrium through a Gore-Tex® tube placed into the right atrium and sewn to the surgically created interatrial septum defect [23, 27]. In this case, the sewing ring is attached to the right atrium and the interposition graft [23, 28].

Summary of the insertion technique	Advantages	Disadvantages	Contraindications/Unsuitability	Reasons for unsuitability
Technique of left ventricular assist device (LVAD) implantation that involves placing the inflow cannula at a site other than the standard apical location (e.g., left atrium, left ventricular basal wall, in a patch used for LV reconstruction (Dor procedure)).; Surgical access: full median sternotomy.	Addresses patient-specific anatomical challenges and facilitates optimal IC positioning and LVAD function (significant LV hypertrophy/small LV cavity, apical aneurism with/without thrombus formation)	Increased operative complexity/technical challenges	Cases suitable for IC placement into the true apex; IC placement in the lateral LV free wall	IC placement in the lateral LV free wall could increase the risk of suboptimal IC position, suction events and suboptimal LVAD function

Table 2.

Left ventricular assist device implantation with alternative inflow cannula placement.

Ultimately, a novel technique intending to overcome the risks associated with the development of intracavitary clot formation and its sequelae has been proposed, in which the IC is attached to a cone-shaped prosthesis connecting the left ventricular apex with the mitral valve [29].

Conclusively, while the true apex of the LV remains the standard and most widely used site for IC placement, the vast array of individual patient anatomies, previous medical interventions, and unique conditions dictate the necessity for adaptable and innovative approaches, guided by the overriding principles of ensuring the best possible outcomes for the patient.

3. Standard and alternative outflow graft placement

The outflow graft is attached to the ascending aorta (AA) in an end-to-side fashion, facilitating blood flow from the LVAD to the systemic circulation, and is considered the standard practice in most LVAD implantations [1, 5, 10]. The recommended and preferred anastomosis site at the AA is at its right concavity, about 2 cm above the sinotubular junction [1, 10] (Table 3). In patients with an untouched pericardium (no previous pericardiotomy) for instance, the recommended course of the OG should be intrapericardial, along the inferior right ventricular surface and between the right atrium and pericardium so that the right ventricular outflow tract remains uncrossed [1]. Optionally, tunneling the outflow graft through the transverse sinus with OG anastomosis at the posterolateral aspect of the AA may also be considered [1]. Ultimately, while still preferably connecting it to the AA, routing the OG within the left pleural cavity may also be considered to reduce operative complexity in redo procedures [1].

Summary of the insertion technique	Advantages	Disadvantages	Contraindications/Unsuitability	Reasons for unsuitability
Technique of left ventricular assist device (LVAD) implantation involving anastomosing the outflow graft (OG) to the ascending aorta (AA).; Surgical access: full median sternotomy or less invasive (a lateral thoracotomy combined with an upper hemisternotomy or bilateral thoracotomy) with routing of the OG between the right atrium and the pericardium or the transverse sinus.	Well-established with proven outcomes; Facilitates standardized LVAD placement; Direct flow into the aorta; Reduced risk of OG kinking or obstruction	Requires mediastinal (re-) entry/surgical exposure of the AA; Risk of complications in patients with severe atherosclerosis of the AA; a “hostile chest” (previous cardiac surgery/mediastinal radiation leading to mediastinal scarring/adhesions/severe chest wall deformities	Severe atherosclerosis of the AA; “Hostile chest” (previous cardiac surgery/mediastinal radiation leading to mediastinal scarring/adhesions/severe chest wall deformities	Increased risk of embolism/stroke/aortic dissection in cases of severe atherosclerosis of the AA; Limited surgical access and increased surgical complexity due to mediastinal adhesions/patent coronary artery bypass grafts/severe chest wall deformities.; Risk of inadvertent damage to mediastinal structures due to severe mediastinal adhesions; Risk of inadvertent damage to patent coronary artery bypass grafts

Table 3.

Left ventricular assist device implantation with outflow graft placement to the ascending aorta.

The ascending aorta is a central conduit in the systemic circulation, making it a logical point to introduce blood pumped by the LVAD to be distributed throughout the body. Attaching the OG to the AA is favored because of the AA’s large diameter, good anatomical accessibility, the relative ease with which the anastomosis is completed, postulated in decades of clinical experience. Besides the precise positioning of the IC, however, optimal LVAD performance is equally contingent upon the rigorous positioning of the outflow graft. Traditionally, the AA is the gold standard for OG anastomosis, capitalizing on its central position in the systemic circulation and its presumably resilient anatomy to withstand long-term pressure and flow conditions impaired by the LVAD. That said, the proximal aorta does undergoes dilation under LVAD support [30]. This, on the other side, has been correlated to the development of de novo aortic valve regurgitation, which is more likely to occur in patients with preexisting (before LVAD implant) aortic dilation [30, 31]. These alterations are presumably the results of the LVAD support-induced unphysiological hemodynamics [30, 31]. In this regard, the results of computational fluid dynamics studies confidently advocate for positioning the OG so that it directs the jet of blood towards the lumen of the aortic arch, aiming to prevent turbulent flow, subsequently reducing wall stress and backward pressure in the aortic root [32]. Both in-silico studies and existing clinical data have confirmed that any deviation of the LVAD outflow jet from the normal flow direction in the AA can lead to flow stasis, aortic root thrombosis, and thromboembolic complications [33, 34, 35, 36]. Indeed, a 45° angulation of the outflow graft-to-ascending aorta anastomosis to reduce the risk of de novo aortic valve regurgitation during LVAD support is currently recommended by experts in the field [1]. Nevertheless, the optimal orientation of the OG anastomosis, as well as its distance from the aortic root, are yet to be established in future research [32].

Further, just as the LV’s anatomy and function govern the complexities of the inflow cannula’s positioning, it is crucial to consider the individual patient’s anatomy, comorbid conditions, and potential for complications – and all that in the context of the surgeon’s expertise when opting for placement of the OG anastomosis to the standard site. An improperly placed OG might impede natural blood flow, potentially leading to complications such as graft occlusion, turbulent blood flow, or even damage to the aorta itself. Besides that, OG anastomosis to the AA may be nonamenable in patients with hostile chest anatomy or porcelain aorta [1, 10]. Anatomical variations (i.e., severe aortic calcifications, severe chest wall deformities, presence of patent grafts from prior coronary artery bypass surgery, previous AA procedures) or presence of extensive mediastinal adhesions (e.g., post radiation therapy or prior previous cardiac surgery) may deem the surgical access or placement of the OG anastomosis at the AA challenging, high-risk or even prohibitively hazardous, even in experienced hands. To specifically address this, surgical LVAD implantation techniques involving alternative OG landing sites have been developed [1, 10, 37] (Figure 1, Table 4). Several surgical techniques involving OG placement to the innominate artery, axillary/subclavian artery, descending aorta, or supra-celiac abdominal aorta have been described [4, 32]. While these unconventional sites may offer certain benefits resulting from the less invasive operative technique, like the potentially reduced operative exposure, the use of blood products, the incidence of right heart failure, or avoiding sternotomy in redo surgeries, they come with challenges, including ensuring proper graft orientation and strategies to prevent kinking of the OG and increased operative complexity [10, 38, 39]. In this line of thought, the seemingly indispensable reinforcement of the OG using a (ringed) vascular graft protector has been associated with the development of the unique late complication - OG stenosis, in some patients [40, 41]. Moreover, minimally invasive approaches for LVAD implantation with OG anastomosis to the AA have been standardized, and their benefits are well described [38, 42, 43, 44]. Yet, LVAD placement with OG to the left axillary/subclavian artery or descending aorta offers one more advantage, that is, “the preservation of a virgin chest” in patients who are deemed transplant candidates [39, 45]. However, the clinically significant hemodynamic sequelae and long-term outcomes associated with these alternative OG locations are unknown [39, 46], and they are therefore to be regarded as valid but not equal alternatives to the standard OG location [1, 39].

Figure 1.

Standard and alternative outflow graft anastomosis sites. Schematic depiction of left ventricular assist device placed onto the left ventricular apex with outflow graft anastomosis to the ascending aorta (A), subclavian/axillary artery (B) and descending aorta (C).

Summary of the insertion technique	Advantages	Disadvantages	Contraindications/Unsuitability	Reasons for unsuitability
Technique of left ventricular assist device (LVAD) implantation involving OG placement to the innominate artery, axillary/subclavian artery, descending aorta, or supra-celiac abdominal aorta.; Surgical access: less-invasive sternotomy-sparing approaches (lateral thoracotomy (thoracotomies), or thoracotomy combined with an upper abdominal incision, depending on the chosen anastomosis site).	Useful in cases of a “hostile chest” or severe atherosclerosis/calcifications to the ascending aorta; Preservation of a virgin mediastinum	Challenges in graft routing to prevent OG kinking or twisting; Limited target vessel diameter for OG anastomosis; Risk of arm hyperperfusion/swelling; Limited data on long-term outcomes and clinical consequences of a retrograde flow systemic perfusion and altered “washout” of the aortic root and ascending aorta	Significant atherosclerosis at the anastomosis site; Coarctation of the aorta/severe atherosclerotic obstruction proximal to the anastomosis; Small-caliber vessel for the distal OG anastomosis	Significant atherosclerosis at the anastomosis site may increase the risk of vascular dissection/embolization.; Coarctation can impact flow dynamics, affecting LVAD function and patient hemodynamics.; A too small vessel diameter might not allow for optimal (LVAD) blood flow or may complicate the anastomosis procedure.

Table 4.

Left ventricular assist device implantation with alternative outflow anastomosis sites.

In the end, the choice of OG placement should be determined by a combination of the patient’s unique anatomy, clinical history, and the surgeon’s expertise, always with an eye on ensuring the longevity and efficiency of the LVAD system.

4. Conclusion

While LVAD technology and surgical techniques continue to evolve, the standard sites for inflow and outflow component placement remain prevalent due to their ease of access, reduced surgical complexity, and favorable long-term outcomes. Nevertheless, ongoing research and clinical experience continue to inform best practices, suggesting that what is considered “standard” today may be subject to change in the light of new evidence.

5. Discussion

Implantable LVADs have revolutionized the treatment of end-stage heart failure [2, 47]. The placement of the IC into the true LV apex and the OG at the ascending aorta have become standards in LVAD implantation techniques with implications in ways that go beyond simple surgical convenience - the optimal positioning of these components has a significant impact on patient outcomes and the efficiency of the LVAD system [1, 2, 47, 48]. However, modifications to the standard surgical techniques of IC and OG placement exploiting their different landing sites and attachment methods can be made to address particular patient demands [10]. Such alternative techniques might also gain popularity as our knowledge of the dynamics and physiology of heart failure advances, and new technical advancements take hold. Moreover, avoiding access to the ascending aorta in the cases of alternative OG placement techniques offers the convenience of a quasi-virgin mediastinum, which should ease future reoperation and improve outcomes in heart transplant recipients [39, 45, 49]. Big, granular data on long-term outcomes with alternative IC and OG placement techniques is not available yet, and standard implantation sites remain predominant in clinical practice due to their proven efficacy, as evidenced by decades of clinical experience [1]. Nevertheless, the vast heterogeneity of patient conditions and clinical scenarios necessitates the consideration of alternative and unconventional approaches to device placement, which provide invaluable solutions in situations when patient-specific variables prevent routine implantation [1, 10, 37]. These approaches are not merely alternatives, but often tailored strategies devised in the face of challenges that the standard practices cannot address.

Further detailed research assessing the standard and alternative LVAD implantation techniques should provide insights that facilitate further refinements in these approaches that translate into improvements in patient outcomes. As the field continues to advance, it is paramount to prioritize patient-specific considerations while pursuing optimization, durability, and safety.

Acknowledgments

We are thankful to Alica Dimitrova for the design of Figure 1.

Conflict of interest

The authors declare no conflict of interest.