The EVAHEART 2 (Sun Medical Technology Research Corporation, Nagano, Japan) centrifugal left ventricular assist device (LVAD) adopted a new inflow cannula to mitigate the risk for wedge thrombus formation and subsequent stroke events (Figure 1). This new “double cuff tipless” (DCT) inflow cannula eliminates protrusion of the cannula tip where thrombi form, which promotes tolerance of cannula malposition.1 To achieve the intended performance of the DCT inflow cannula, it is crucial to establish a training methodology before the device is deployed clinically and to then adhere to the recommended surgical procedures.2 Large animal explanted hearts or acute studies in vivo (i.e., swine, bovine) have commonly been used as surgical training models. These models have anatomical limitations, however, for mimicking the geometry of the ventricular apex in human patients with dilated cardiomyopathy, who have a thin myocardium and dilated left ventricle (LV). We previously introduced a polymer-based dilated cardiomyopathy apex model. Here, we describe the use of this model for inflow cannula implantation training in which we simulated appropriate and inappropriate implantation techniques.
Materials and Methods
According to the manufacturer’s instructions for use, the EVAHEART coring knife, suture guide, and braided double-needle mattress sutures with pledget (2-0 Ti-Cron CV-300, Covidien/Medtronic, Minneapolis, MN) were prepared. A polymer-based model of the LV apex (EVI Japan, Fukushima, Japan) was used. The apex model was made of a polyvinyl alcohol (PVA) hydrogel containing over 90% water and had a simulated coefficient of elasticity (0.05–0.13 MPa) that was adjusted on the basis of explanted swine heart tissue and actual cutting feel. The inner side of the apex model was coated with a white-colored polymer of high tear strength to mimic the endocardial layer. A computer-aided design (CAD) data set was purchased to recreate a dilated LV chamber simulating a large LV volume (approximately 460 ml) with a thinner apical wall thickness (7–8 mm) than in a healthy human (the STL CAD file was fully deidentified; thus, no patient-specific medical data were included). The LV apex model was installed into the human torso model with the LV apex in an upward position. The overall inflow implantation technique is described elsewhere.1 After coring of the LV apex, the EVAHEART 2 DCT inflow cannula was implanted by using both the recommended technique and an inappropriate technique, respectively.
Appropriate (Recommended) Technique
With the appropriate technique, the pledgeted mattress sutures should penetrate the entire myocardial wall from the epicardium to the endocardium (Figure 2A). In particular, it is very important to securely anchor the endocardium by pulling it toward the mesh suture cuff of the DCT inflow cannula. The needle entry point should be about 10 mm away from the cored edge, and the needle exit point should be 3–5 mm away from the cored edge of the endocardium (Figure 2B). A suture bite that is too big may result in a “dog-eared” finish or may increase the risk for endocardial tearing. After placement of all mattress sutures in the myocardium with use of the pledget (Figure 2C), the needle should be threaded through the double suture cuff (the proximal mesh cuff and the distal polytetrafluoroethylene [PTFE] felt cuff). The most critical technique is the needle entry point in the mesh suture cuff. The optimal entry point is a few millimeters away (about 3 mm) from the metal inflow ostium (Figure 2D).
In the inappropriate technique, the needle exits from the cored cross-sectional myocardium (Figure 3, A–C). This technique does not engage the endocardium or mesh suture cuff; therefore, the cut surface of the myocardium may be exposed to the bloodstream. As opposed to the recommended procedure, the needle is threaded from the junction between the end of the mesh and the smooth metal ostium (Figure 3D). Because the edge of the endocardium is too near the mesh suture cuff, there may be a risk of tissue (endocardium) overhanging the smooth metal orifice and possible pannus formation.
Figure 4 shows an intraventricular view of the LV apex after implantation of the DCT inflow cannula. With the use of the appropriate suturing technique, the cut endocardium is secured to the mesh suture cuff and exposure of the cut myocardial surface to the bloodstream is avoided. The endocardium is aligned with a circumferential line on the mesh cuff. As a result, the mesh-endocardium interface is kept away from the metal inflow orifice (Figure 4A). The narrow segment of the mesh exposed to the bloodstream will be endothelialized after implantation because of its antithrombogenic properties. The metal surface of the inflow is coated with a long-lasting, antithrombogenic polymer (2-methacryloyloxyethyl phosphorylcholine (MPC) coating), which will inhibit cell deposition (i.e., platelets) and thrombus formation.
In contrast, the inappropriate technique did not contribute to the “tipless” inflow concept. The inappropriate technique, which was represented by a worst-case suturing scenario, resulted in misalignment of the inflow ostium, which exposed the cut myocardial cross-section to the bloodstream. This misalignment can predispose to platelet deposition, thrombus formation, and pannus formation with long-term support (Figure 4B).
Surgical technique is one of the influential factors associated with post-LVAD adverse events and survival.2–4 In particular, the technique used to implant the EVAHEART DCT inflow cannula is somewhat unique owing to the proprietary double cuff and tipless design, compared with the conventional tubular-type inflow that protrudes into the LV. Surgical training using an animal heart model has limitations for studying dilated cardiomyopathy in humans owing to different anatomical characteristics. The nontissue, polymer-based heart model may thus be a useful tool for training.5 The polymer (PVA hydrogel) apex model used in this study mimics the anatomy of the myocardium and endocardium and their mechanical properties and was validated with a healthy swine heart. This apex model is routinely used for preoperative training to confirm whether the DCT inflow position is optimal in the LV. In the clinical setting, patient myocardial thickness is variable. We reported a unique adaptability of the DCT inflow cuff with various ventricular wall thicknesses (i.e., thin wall, normal, and hypertrophic myocardium).1 Technical proficiency can be achieved by using multiple apex models with different wall thickness before clinical implementation of new inflow cannula.
It is important to achieve technical proficiency for demonstrating the performance of the EVAHEART 2 DCT inflow cannula. Rigorous skills training and adherence to recommended procedures are crucial for ensuring good clinical outcomes.
The authors thank Jennifer Holmes for the medical editing services she provided for this manuscript.
1. Motomura T, Tuzun E, Yamazaki K, et al. Preclinical evaluation of the EVAHEART 2 centrifugal left ventricular assist device
in bovines. ASAIO J .68: 845-854, 2019
2. Adamson RM, Mangi AA, Kormos RL, Farrar DJ, Dembitsky WP. Principles of HeartMate II implantation to avoid pump malposition and migration. J Card Surg 2015.30: 296–299.
3. Maltais S, Kilic A, Nathan S, et al. PREVENtion of HeartMate II pump thrombosis through clinical management: The PREVENT multi-center study. J Heart Lung Transplant 2017.36: 1–12.
4. Taghavi S, Ward C, Jayarajan SN, Gaughan J, Wilson LM, Mangi AA. Surgical technique influences HeartMate II left ventricular assist device
thrombosis. Ann Thorac Surg 2013.96: 1259–1265.
5. Hanke JS, Krabatsch T, Rojas SV, et al. In vitro
evaluation of inflow cannula
fixation techniques in left ventricular assist device
surgery. Artif Organs 2017.41: 272–275.