The influence of left ventricular assist device inflow cannula position on thrombosis risk

Abstract

The use of left ventricular assist devices (LVADs) as a treatment method for heart failure patients has been steadily increasing; however, pathological studies showed presence of thrombi around the HeartWare ventricular assist device inflow cannula (IC) in more than 95% of patients after device explantation. Flow fields around the IC might trigger thrombus formation and require further investigation. In this study flow dynamics parameters were evaluated for different patient geometries using computational fluid dynamics (CFD) simulations. Left ventricular (LV) models of two LVAD patients were obtained from CT scans. The LV volumes of Patient 1 (P1) and Patient 2 (P2) were 264 and 114 cm 3 with an IC angle of 20° and 9° from the mitral‐IC tip axis at the coronal plane. The IC insertion site at the apex was central for P1, whereas it was lateral for P2. Transient CFD simulations were performed over 9 cardiac cycles. The wedge area was defined from the cannula tip to the wall of the LV apex. Mean velocity magnitude and blood stagnation region (volume with mean velocity <5 mm/s) as well as the wall shear stress (WSS) at the IC surface were calculated. Cardiac support resulted in a flow mainly crossing the ventricle from the mitral valve to the LVAD cannula for P2, while the main inflow jet deviated toward the septal wall in P1. Lower WSS at the IC surface and consequently larger stagnation volumes were observed for P2 (P1: 0.17, P2: 0.77 cm 3 ). Flow fields around an LVAD cannula can be influenced by many parameters such as LV size, IC angle, and implantation site. Careful consideration of influencing parameters is essential to get reliable evaluations of the apical flow field and its connection to apical thrombus formation. Higher blood washout and lower stagnation were observed for a central implantation of the IC at the apex.

Optimal cannula positioning of HeartMate 3 left ventricular assist device

“…For the HeartMate II LVAD, a narrow angle between the inflow cannula and pump body is associated with pump thrombosis 8 . For the HeartWare LVAD (Medtronic, Minneapolis, MN), a narrow cannula coronal angle is associated with improved left ventricular (LV) unloading and adverse outcomes 9,10 …”

“…8 For the HeartWare LVAD (Medtronic, Minneapolis, MN), a narrow cannula coronal angle is associated with improved left ventricular (LV) unloading and adverse outcomes. 9,10 Although there are no reports among the HeartMate 3 LVAD cohort, the knowledge of appropriate device positioning might make it easier to achieve optimal hemodynamics which is associated with reduced rates of HF readmission and HRAEs. [11][12][13] In this study, we investigated the association between HeartMate 3 device position, cardiac unloading, and clinical outcomes.…”

A new pathophysiology in heart failure patients

“…Accordingly, if the recovery from LVAD is the best perspective in LVAD patients, monitoring intraventricular regional hemodynamics during LVAD flow reduction is mandatory to assess the restoration of a normal pattern, although this approach is never applied. In fact, it is known that adaptation to flows in the presence or absence of the cannula determines favorable conditions to the thrombi’s formation, even after the explant has taken place 18 . Furthermore, many other factors such as cannula material and surface characteristics, as well as the patients' coagulation status may be of some clinical significance, explaining the differences observed in the flow field 19 …”

“…In fact, it is known that adaptation to flows in the presence or absence of the cannula determines favorable conditions to the thrombi's formation, even after the explant has taken place. 18 Furthermore, many other factors such as cannula material and surface characteristics, as well as the patients' coagulation status may be of some clinical significance, explaining the differences observed in the flow field. 19 We believe that, once the stabilization and well-being of patients have been achieved, major efforts should be made to progressively and slowly reduce LVAD pump flow, allowing the restoration of left ventricular performance.…”

Multi‐constituent simulation of thrombus formation at LVAD inlet cannula connection: Importance of Virchow’s triad

“…[2][3][4][5] Thrombosis around the VAD inlet cannula (IC) has been recently highlighted as a possible source of ischemic stroke events in patients receiving a left ventricular assist device (LVAD). 6,7 In fact, the potential role of the ventricular cannula in thrombosis-related complications has motivated numerical, in vitro, and clinical studies for over two decades. [7][8][9][10][11][12][13][14] The majority of studies have concentrated on the intraventricular flow dynamics, specifically in the region of the ventricular apex, but have neglected the many biochemical factors involved in the coagulation cascade.…”