Transient Performance Analysis of Centrifugal Left Ventricular Assist Devices Coupled With Windkessel Model: Large Eddy Simulations Study on Continuous and Pulsatile Flow Operation

Computational fluid dynamics (CFD) simulations are widely used to develop and analyze blood-contacting medical devices such as left ventricular assist devices (LVADs). This work presents an analysis of the transient behavior of two centrifugal LVADs with different designs: HeartWare VAD and HeartMate3. A scale-resolving methodology is followed through Large Eddy Simulations, which allows for the visualization of turbulent structures. The three-dimensional (3D) LVAD models are coupled to a zero-dimensional (0D) 2-element Windkessel model, which accounts for the vascular resistance and compliance of the arterial system downstream of the device. Furthermore, both continuous- and pulsatile-flow operation modes are analyzed. For the pulsatile conditions, the artificial pulse of HeartMate3 is imposed, leading to a larger variation of performance variables in HeartWare VAD than in HeartMate3. Moreover, CFD results of pulsatile-flow simulations are compared to those obtained by accessing the quasi-steady maps of the pumps. The quasi-steady approach is a predictive tool used to provide a preliminary approximation of the pulsatile evolution of flow rate, pressure head, and power, by only imposing a speed pulse and vascular parameters. This preliminary quasi-steady solution can be useful for deciding the characteristics of the pulsatile speed law before running a transient CFD simulation, as the former entails a significant reduction in computational cost in comparison to the latter.

Outcomes of outflow graft stenting in HeartMate 3 left ventricular assist devices: A systematic review and individual patient data meta-analysis

PURPOSE

LVAD outflow graft stenosis continues to remain prevalent with a high complication rate. We sought to pool the existing evidence on indications, utilization patterns, and outcomes of transcatheter interventions for outflow graft stenosis in the HeartMate 3 LVAD.

METHODS

An electronic search was performed to identify all studies in the English literature reporting on HeartMate 3 LVAD outflow graft stenting. Patient-level data were extracted for analysis.

RESULTS

Thirteen published reports and one unpublished case comprising a total of 28 patients were included. Median patient age was 68.5 years [Interquartile range: 58, 71] and 25.9% (7/27) were female. Dyspnea [60.7% (17/28)] was the most common presenting symptom. Low flow alarms were present in 60% (15/25) of patients. Findings included external compression [35.7% (10/28)], graft twist [21.4% (6/28)], graft twist and external compression [14.3% (4.28)], intraluminal thrombus [10.7% (3/28)], graft twist and intraluminal thrombus [3.6% (1/28)], and pseudoaneurysm of outflow graft [3.6% (1/28)]. Median time from LVAD implantation to stenting was 2.1 years [1.4, 3]. Immediate flow normalization after stenting was observed in 85.7% (24/28). The 30-day mortality was 12% (3/25). Overall mortality was 12% (3/25) at a median follow-up of 3.9 months [1, 17].

CONCLUSION

Outflow graft stenting in the HeartMate 3 LVAD appears to be a reasonable treatment option for outflow graft stenosis, with low overall rates of complications and mortality. Further refinement of indications and approaches may improve outcomes.

Pulsatility and flow patterns across macro- and microcirculatory arteries of continuous-flow left ventricular assist device patients

BACKGROUND

Reduced arterial pulsatility in continuous-flow left ventricular assist devices (CF-LVAD) patients has been implicated in clinical complications. Consequently, recent improvements in clinical outcomes have been attributed to the "artificial pulse" technology inherent to the HeartMate3 (HM3) LVAD. However, the effect of the "artificial pulse" on arterial flow, transmission of pulsatility into the microcirculation and its association with LVAD pump parameters is not known.

METHODS

The local flow oscillation (pulsatility index, PI) of common carotid arteries (CCAs), middle cerebral arteries (MCAs) and central retinal arteries (CRAs-representing the microcirculation) were quantified by 2D-aligned, angle-corrected Doppler ultrasound in 148 participants: healthy controls, n = 32; heart failure (HF), n = 43; HeartMate II (HMII), n = 32; HM3, n = 41.

RESULTS

In HM3 patients, 2D-Doppler PI in beats with "artificial pulse" and beats with "continuous-flow" was similar to that of HMII patients across the macro- and microcirculation. Additionally, peak systolic velocity did not differ between HM3 and HMII patients. Transmission of PI into the microcirculation was higher in both HM3 (during the beats with "artificial pulse") and in HMII patients compared with HF patients. LVAD pump speed was inversely associated with microvascular PI in HMII and HM3 (HMII, r2 = 0.51, p < 0.0001; HM3 "continuous-flow," r2 = 0.32, p = 0.0009; HM3 "artificial pulse," r2 = 0.23, p = 0.007), while LVAD pump PI was only associated with microcirculatory PI in HMII patients.

CONCLUSIONS

The "artificial pulse" of the HM3 is detectable in the macro- and microcirculation but without creating a significant alteration in PI compared with HMII patients. Increased transmission of pulsatility and the association between pump speed and PI in the microcirculation indicate that the future clinical care of HM3 patients may involve individualized pump settings according to the microcirculatory PI in specific end-organs.

Hemocompatibility and hemodynamic comparison of two centrifugal LVADs: HVAD and HeartMate3

Mechanical circulatory support using ventricular assist devices is a common technique for treating patients suffering from advanced heart failure. The latest generation of devices is characterized by centrifugal turbopumps which employ magnetic levitation bearings to ensure a gap clearance between moving and static parts. Despite the increasing use of these devices as a destination therapy, several long-term complications still exist regarding their hemocompatibility. The blood damage associated with different pump designs has been investigated profoundly in the literature, while the hemodynamic performance has been hardly considered. This work presents a novel comparison between the two main devices of the latest generation-HVAD and HM3-from both perspectives, hemodynamic performance and blood damage. Computational fluid dynamics simulations are performed to model the considered LVADs, and computational results are compared to experimental measurements of pressure head to validate the model. Enhanced performance and hemocompatibility are detected for HM3 owing to its design incorporating more conventional blades and larger gap clearances.

Cerebrovascular Events in Patients with Centrifugal-Flow Left Ventricular Assist Devices: A Propensity Score Matched Analysis from the Intermacs Registry

Background: Ischemic and hemorrhagic cerebrovascular accidents (ICVA and HCVA, respectively) remain common among patients with centrifugal-flow left ventricular assist devices (CF-LVADs), despite improvements in survival and device longevity. Therefore, the incidence of neurological adverse events (NAEs) associated with two contemporary CF-LVADs, the Abbott HeartMate3^® (HM3) and the Medtronic HeartWare^™ HVAD^® (HVAD), were compared. Methods: Using the Society of Thoracic Surgeons Interagency Registry for Mechanically Assisted Circulatory Support (Intermacs), we collected data on adult patients who received a CF-LVAD as a primary isolated implant between 1/1/2017 and 9/30/2019. Major NAEs were defined as transient ischemic attack (TIA), ICVA, and HCVA. The association of HVAD with risk of NAE in the first year post implant was evaluated using propensity score matching to balance for pre-implant risk factors. After matching, freedom from first major NAE in the HM3 and HVAD cohorts was compared with Kaplan-Meier curves. A secondary analysis using multivariable multiphase hazard models was used to identify predictors of NAE, which uses a data driven parametric fit of the early declining and constant phase hazards and the associations of risk factor with either phase. Results: Of 6,205 included patients, 3,076 (49.6%) received the HM3 and 3,129 (50.4%) received the HVAD. Median follow-up was 9 and 12 months (HM3 and HVAD). HVAD patients had more major NAEs (16.4% vs. 6.4%, p<0.001), as well as each subtype (TIA: 3.3% vs. 1.0%, p<0.001; ICVA: 7.7% vs. 3.4%, p<0.001; and HCVA: 7.2% vs. 2.0%, p<0.001), than did HM3 patients. A propensity-matched cohort balanced for pre-implant risk factors showed that HVAD was associated with higher probabilities of major NAEs (% freedom from NAE: 82% vs. 92%, p<0.001). Device type was not significantly associated with NAEs in the early hazard phase, but HVAD was associated with higher incidence of major NAEs during the constant hazard phase (hazard ratio: 5.71, confidence interval: 3.90-8.36). Conclusions: HM3 is associated with lower hazard of major NAEs than is HVAD beyond the early post-implantation period and during the constant hazard phase. Defining the explanation for this observation will inform device selection for individual patients.

Study results suggest less invasive HeartMate 3 implantation is a safe and effective approach for obese patients

BACKGROUND

Historically, obesity was considered a relative contraindication to left ventricular assist device (LVAD) implantation with less invasive surgery (LIS). The present study aimed to compare the outcomes of obese patients who underwent LVAD implantation through LIS with those who received full sternotomy (FS) implantation.

METHODS

We retrospectively reviewed all patients implanted with HeartMate 3 LVAD in our institution between September 2015 and June 2020. Obese patients (BMI ≥ 30 kg/m²) were included and dichotomized based on surgical approach into the FS or LIS cohort.

RESULTS

Of 231 implanted patients, 107 (46%) were obese and included in the study. FS was performed in 26 (24%) patients and LIS approach in 81 (76%) patients. Preoperative patient characteristics were similar between the cohorts. Postoperatively, patients in LIS cohort had less bleeding (p = 0.029), fewer transfusions (p = 0.042), shorter duration of inotropic support (p = 0.049), and decreased incidence of severe RV failure (11.1% vs 30.8%, p = 0.028). Survival to discharge for the obese population was 87.5% overall and did not differ based on an approach (91.4% LIS vs 76.9% FS, p = 0.079). More LIS patients were discharged home (60.0% vs 82.4%, p = 0.041) rather than to rehabilitation center.

CONCLUSION

Our results showed that the LIS approach in obese patients is associated with fewer postoperative complications and a trend towards better short-term survival. These results suggest that less invasive LVAD implantation is a safe and effective approach for obese patients. Future prospective randomized trials are required to substantiate these results.

Cerebral vasoreactivity in HeartMate 3 patients

BACKGROUND

While rates of stroke have declined with the HeartMate3 (HM3) continuous- flow (CF) left ventricular assist device (LVAD), the impact of non-pulsatile flow and artificial pulse physiology on cerebrovascular function is not known. We hypothesized that improved hemodynamics and artificial pulse physiology of HM3 patients would augment cerebrovascular metabolic reactivity (CVR) compared with HeartMate II (HMII) CF-LVAD and heart failure (HF) patients.

METHODS

Mean, peak systolic and diastolic flow velocities (MFV, PSV, MinFV, respectively) and cerebral pulsatility index were determined in the middle cerebral artery (MCA) before and after a 30 sec breath-hold challenge in 90 participants: 24 healthy controls; 30 HF, 15 HMII, and 21 HM3 patients.

RESULTS

In HM3 patients, breath-holding increased MFV (Δ8 ± 10 cm/sec, p < .0001 vs baseline) to levels similar to HF patients (Δ9 ± 8 cm/sec, p > .05), higher than HMII patients (Δ2 ± 8 cm/sec, p < .01) but lower than healthy controls (Δ13 ± 7 cm/sec, p < .05). CF-LVAD altered the proportion of systolic and diastolic flow responses as reflected by a differential cerebral pulsatility index (p = .03). Baseline MFV was not related to CVR (r² = 0.0008, p = .81). However, CF-LVAD pump speed was strongly inversely associated with CVR in HM II (r² = 0.51, p = .003) but not HM3 patients (r² = 0.01, p = .65).

CONCLUSIONS

Compared with HMII, HM3 patients have a significantly improved CVR. However, CVR remains lower in HM3 and HF patients than in healthy controls, therefore suggesting that changes in cerebral hemodynamics are not reversed by CF-LVAD therapy. Further research on the mechanisms and the long-term impact of altered cerebral hemodynamics in this unique patient population are warranted.

Validation of non-invasive ramp testing for HeartMate 3

Aims

Ramp testing in the postoperative period can be used to optimize left ventricular assist device (LVAD) speed for optimal left ventricular (LV) unloading. We tested the hypothesis that a non‐invasive echocardiographic ramp test post‐HeartMate 3 implantation improves LV unloading immediately after and 1–3 months after as compared with before the test. We also tested a secondary hypothesis that speed adjustments during echocardiography‐guided ramp testing do not worsen right ventricular (RV) function immediately after and 1–3 months after.

Methods and results

We retrospectively reviewed data from patients who underwent an echocardiographic ramp test. A total of 14 out of 19 patients were clinically stable and were enrolled. Adequate LV unloading was defined as no more than mild mitral regurgitation, and intermittent aortic valve (AV) opening or closed AV, and reduction of left ventricular end‐diastolic diameter (LVEDD); and for the follow‐up measurement, decreased NT‐proBNP. Median (interquartile range) time from implantation to ramp test was 27 (16; 56) days, and median time from ramp test to follow‐up echocardiography was 55 (47; 102) days. Median LVAD speed achieved during ramp testing was 5550 (5375; 6025) revolutions per minute (rpm), and median final LVAD speed was 5200 (5000; 5425) rpm. Ramp testing resulted in final LVAD speed increase in 11 (79%) patients and a median net change of 200 (200; 300) rpm. Speed adjustments after ramp testing resulted in improved LVAD unloading that was achieved in additional 3 (21%) patients who were not originally optimized. RV function did not worsen significantly during ramp testing or at final LVAD speed.

Conclusions

The echocardiographic ramp test allowed LVAD speed adjustment and optimization and improved LV unloading during ramp testing and at final speed with no evidence of worsening of RV function.

Early outcomes with durable left ventricular assist device replacement using the HeartMate 3

BACKGROUND

The HeartMate 3 (HM3) left ventricular assist device (LVAD) (Abbott, Inc, Chicago, Ill) is a fully magnetically levitated centrifugal implantable pump used to treat patients with chronic heart failure. The MOMENTUM (Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy With HeartMate 3) trial demonstrated that patients treated with the HM3 experienced reduced need for reoperation for LVAD replacement compared with a control group receiving an axial flow design, Heartmate II (Abbott, Inc). However, there are few reports of using HM3 as the replacement pump in patients who already are supported by a durable LVAD and experience a device-related complication necessitating replacement.

METHODS

An institutional LVAD database was used to identify 19 consecutive patients who underwent pump replacement to HM3 (group 1) versus 85 consecutive control patients who underwent pump replacement to either Heartmate II or HeartWare Ventricular Assist Device (Medtronic Inc, Minneapolis, Minn) (group 2), at a single institution from January 2010 to August 2018. Patient baseline characteristic and outcomes were obtained from a prospectively maintained database. The primary endpoint was a composite of freedom from death or need for another replacement surgery.

RESULTS

There was no difference between the groups in heart failure etiology, indication for replacement, as well as the average days on the previous pump or the type of previous pump. The HM3 group did have a significantly greater body mass index (37 vs 31.6 P = .01), a greater number of previous LVAD implants (36.8% vs 5.9%, had 2 previous LVADs, P < .001), and a greater number of previous sternotomies (31.6% vs 7.1%, had 3 previous sternotomies, P = .001). No difference was found between the groups in terms of postoperative adverse event rates. With regards to the primary endpoint, the patients with HM3 replacements (group 1) versus group 2 experienced significantly greater freedom from either death or need for another replacement during the follow-up period (P = .039). During follow-up, there were no thrombosis events for the patients who received replacement with HM3.

CONCLUSIONS

LVAD replacement with HM3 can be performed safely and may be considered as the pump of choice in patients requiring LVAD replacement.