Continuous-Flow Left Ventricular Assist Device Thrombosis: A Danger Foreseen is a Danger Avoided

Temporarily Reversing Warfarin With Low-Dose 4-Factor Prothrombin Complex Concentrate in Left Ventricular Assist Device Patients Undergoing an Invasive Procedure

BACKGROUND

American Association for Thoracic Surgery and The International Society for Heart and Lung Transplantation (AATS/ISHLT) guidelines recommend warfarin in patients with continuous-flow left ventricular assist devices (LVADs) to reduce the risk of device thrombosis and systemic embolization. Left ventricular assist device patients often undergo elective and emergent procedures that require interrupted anticoagulation. Data and experience vary on the optimal strategy to rapidly reverse warfarin in LVAD patients when an emergent procedure is planned.

OBJECTIVE

The purpose of this study was to describe the use of 4-factor prothrombin complex concentrate (PCC4) for warfarin reversal in patients with LVADs undergoing elective and emergent procedures.

METHODS

This retrospective, single-center, cohort review describes the use of PCC4 in patients with LVADs who require warfarin reversal for elective or emergent procedures. The primary outcome was a composite incidence of pump thrombosis, venous thromboembolism, and ischemic stroke within 30 days of PCC4 administration.

RESULTS

In total, 14 patients received 17 administrations of PCC4. One patient received 3 administrations, and 1 other patient received 2 administrations during separate encounters. The median dose was 500 units or 6.6 units/kg (range = 4.2-14.1 units/kg). Of the PCC4 administrations, 82% (14/17) were for low bleed risk procedures and 76% (13/17) were for elective procedures. There were no cases of pump thrombosis, venous thromboembolism, or stroke within 30 days of the procedure.

CONCLUSIONS AND RELEVANCE

Low-dose PCC4 appears to be a safe and effective temporary reversal strategy for patients with LVADs undergoing low-bleed risk elective procedures.

Titanium is a potent inducer of contact activation: implications for intravascular devices

BACKGROUND

Titanium (Ti) and its alloys are widely used in manufacturing medical devices because of their strength and resistance to corrosion. Although Ti compounds are considered compatible with blood, they appear to support plasma contact activation and may be thrombogenic.

OBJECTIVES

The objective of this study was to compare Ti and titanium nitride (TiN) with known activators of contact activation (kaolin and silica) in plasma-clotting assays and to assess binding and activation of factor XII, (FXII), factor XI (FXI), prekallikrein, and high-molecular-weight kininogen (HK) with Ti/TiN.

METHODS

Ti-based nanospheres and foils were compared with kaolin, silica, and aluminum in plasma-clotting assays. Binding and activation of FXII, prekallikrein, HK, and FXI to surfaces was assessed with western blots and chromogenic assays.

RESULTS

Using equivalent surface amounts, Ti and TiN were comparable with kaolin and superior to silica, for inducing coagulation and FXII autoactivation. Similar to many inducers of contact activation, Ti and TiN are negatively charged; however, their effects on FXII are not neutralized by the polycation polybrene. Antibodies to FXII, prekallikrein, or FXI or coating Ti with poly-L-arginine blocked Ti-induced coagulation. An antibody to FXII reduced FXII and PK binding to Ti, kallikrein generation, and HK cleavage.

CONCLUSION

Titanium compounds induce contact activation with a potency comparable with that of kaolin. Binding of FXII with Ti shares some features with FXII binding to soluble polyanions but may have unique features. Inhibitors targeting FXII or FXI may be useful in mitigating Ti-induced contact activation in patients with titanium-based implants that are exposed to blood.

Artificial Muscles and Soft Robotic Devices for Treatment of End-Stage Heart Failure

Medical soft robotics constitutes a rapidly developing field in the treatment of cardiovascular diseases, with a promising future for millions of patients suffering from heart failure worldwide. Herein, the present state and future direction of artificial muscle-based soft robotic biomedical devices in supporting the inotropic function of the heart are reviewed, focusing on the emerging electrothermally artificial heart muscles (AHMs). Artificial muscle powered soft robotic devices can mimic the action of complex biological systems such as heart compression and twisting. These artificial muscles possess the ability to undergo complex deformations, aiding cardiac function while maintaining a limited weight and use of space. Two very promising candidates for artificial muscles are electrothermally actuated AHMs and biohybrid actuators using living cells or tissue embedded with artificial structures. Electrothermally actuated AHMs have demonstrated superior force generation while creating the prospect for fully soft robotic actuated ventricular assist devices. This review will critically analyze the limitations of currently available devices and discuss opportunities and directions for future research. Last, the properties of the cardiac muscle are reviewed and compared with those of different materials suitable for mechanical cardiac compression.

Comparing left ventricular assist device inflow cannula angle between median sternotomy and thoracotomy using 3D reconstructions

BACKGROUND

Left ventricular assist device (LVAD) implantation via thoracotomy has many potential advantages compared to conventional sternotomy, including improved inflow cannula (IFC) positioning. We compared the difference in IFC angles, postoperative, and long-term outcomes for patients with LVADs implanted via thoracotomy and sternotomy.

METHODS

A single-center, retrospective analysis of 14 patients who underwent thoracotomy implantation was performed and matched with 28 patients who underwent sternotomy LVAD implantations for a total of 42 patients. Inclusion required a minimum LVAD support duration of 30 days and excluded concomitant procedures. A postoperative CT-chest was used to measure the angle the between the IFC and mitral valve in two-dimensions and results were compared with three-dimensional reconstruction using the same CT chest. Outcome data were extracted from medical records.

RESULTS

There was no significant difference in gender, INTERMACS score, BMI, or age between the two groups. Median cardiopulmonary bypass time was longer in the thoracotomy group compared to the sternotomy group, 107 min (86-122) versus 76 min (56-93), p < 0.01. 3D reconstructions revealed less deviation of the IFC away from the mitral valve in devices implanted via thoracotomy compared to sternotomy, median (IQR) angle 16.3° (13.9°-21.0°) versus 23.2° (17.9°-26.4°), p < 0.01. Rates of pump thrombosis, stroke, and gastrointestinal bleeding were not significantly different.

CONCLUSIONS

Devices implanted via thoracotomy demonstrated less deviation away from mitral valve. However, there was no difference in morbidity between the two approaches. 3D reconstruction of the heart is an innovative technique to measure angulation and is clinically advantageous when compared to 2D imaging.

Accelerated LVAD pump thrombosis in COVID-19 patient: Case report and mini review

BACKGROUND

Coronavirus (COVID-19) infection exposes patients with heart failure specially who are on mechanical support to a higher risk of morbidity and mortality.

AIMS

To investigate the impact of COVID-19 infection on left ventricular assist device (LVAD) thrombosis in heart failure patients.

MATERIALS & METHODS

We searched the medical electronic records, Medline, PubMed and Cochrane databases for; (LVAD) AND (thrombosis)) AND (covid-19)) AND (heart failure). We divided cases reported into, LVAD thrombosis with COVID-19 infection and compare them with LVAD thrombosis without COVID-19 infection. Demographic data, LVAD device, presentation, treatment and outcomes were reviewed in all the LVAD thrombosis patients.

RESULTS

In addition to our case, 8 other cases of LVAD thrombosis associated with COVID and 9 cases of LVAD thrombosis without covid infection were found. Patients with Covid infection had worse presentation and outcomes (3 deaths VS. 1 death in non-covid group).

DISCUSSION

In LVAD patients, pump malfunction due to thrombus development in the inflow cannula, device body, or outflow graft can result in hemodynamic instability, hemolysis and other life-threatening complications. COVID infection significantly increases the risk of mortality in LVAD patient by accelerating the pump thrombosis due to elevated levels of endothelial protein C receptor and thrombomodulin along with procoagulants such as factor VIII, P-selectin, and von Willebrand factor.

CONCLUSION

Significant morbidity and mortality are attributed to LVAD thrombosis, which are exasperated by prothrombotic conditions created in COVID-19 infections.

Rescue extracorporeal life support as a bridge to durable left ventricular assist device

BACKGROUND

The ideal timing of a durable assist device implantation in patients with end-stage heart failure presenting with INTERMACS profile I is still controversial. The data on extracorporeal life support (ECLS) bridge to durable left ventricular assist device (LVAD) in these patients is limited.

MATERIALS AND METHODS

We retrospectively analyzed the outcomes of 35 patients in acute cardiogenic shock (CS) who, between December 2013 and September 2020, were bridged with ECLS to durable LVAD. The mean age was 52.3 ± 12.0 years. The primary endpoints of this study were in-hospital, 30-day, 6-month, and 1-year mortality. The secondary endpoint was the development of any postoperative adverse events and other characteristics during the follow-up period. We also assessed the impact of the rescue ECLS on the recovery of the end-organ function.

RESULTS

In-hospital, 30-day, 6-month, and 1-year survival was 65.6%, 75.9%, 69.2%, and 62.7% respectively. The median time on ECLS was 7 days (IQR 5.0-13.0). We observed a high incidence of a severe right heart failure (22.9%), acute kidney injury on dialysis (68.6%), and respiratory failure (77.1%). Bridge with ECLS provided a significant recovery of liver and kidney function prior to durable LVAD implantation.

CONCLUSION

The concept of bridging patients presenting in end-stage heart failure and cardiogenic shock with ECLS prior to durable LVAD implantation is a feasible method to ensure acceptable survival rates and significant recovery of the end-organ function.

Complications in children with ventricular assist devices: systematic review and meta-analyses

Heart failure is a significant cause of mortality in children with cardiovascular diseases. Treatment of heart failure depends on patients' symptoms, age, and severity of their condition, with heart transplantation required when other treatments are unsuccessful. However, due to lack of fitting donor organs, many patients are left untreated, or their transplant is delayed. In these patients, ventricular assist devices (VADs) are used to bridge to heart transplant. However, VAD support presents various complications in patients. The aim of this study was to compile, review, and analyse the studies reporting risk factors and aetiologies of complications of VAD support in children. Random effect risk ratios (RR) with 95% confidence intervals were calculated to analyse relative risk of thrombosis (RR = 3.53 [1.04, 12.06] I² = 0% P = 0.04), neurological problems (RR = 0.95 [0.29, 3.15] I² = 53% P = 0.93), infection (RR = 0.31 [0.05, 2.03] I² = 86% P = 0.22), bleeding (RR = 2.57 [0.76, 8.66] I² = 0% P = 0.13), and mortality (RR = 2.20 [1.36, 3.55] I² = 0% P = 0.001) under pulsatile-flow and continuous-flow VAD support, relative risk of mortality (RR = 0.45 [0.15, 1.37] I² = 36% P = 0.16) under left VAD and biVAD support, relative risk of thrombosis (RR = 1.72 [0.46, 6.44] I² = 0% P = 0.42), infection (RR = 1.77 [0.10, 32.24] I² = 46% P = 0.70) and mortality (RR = 0.92 [0.14, 6.28] I² = 45% P = 0.93) in children with body surface area < 1.2 m² and > 1.2 m² under VAD support, relative risk of mortality in children supported with VAD and diagnosed with cardiomyopathy and congenital heart diseases (RR = 1.31 [0.10, 16.61] I² = 73% P = 0.84), and cardiomyopathy and myocarditis (RR = 0.91 [0.13, 6.24] I² = 58% P = 0.92). Meta-analyses results show that further research is necessary to reduce complications under VAD support.

Small Left Ventricular Size Is an Independent Risk Factor for Ventricular Assist Device Thrombosis

The prevalence of ventricular assist device (VAD) therapy has continued to increase due to a stagnant donor supply and growing advanced heart failure (HF) population. We hypothesize that left ventricular (LV) size strongly influences biocompatibility and risk of thrombosis. Unsteady computational fluid dynamics (CFD) was used in conjunction with patient-derived computational modeling and virtual surgery with a standard, apically implanted inflow cannula. A dual-focus approach of evaluating thrombogenicity was employed: platelet-based metrics to characterize the platelet environment and flow-based metrics to investigate hemodynamics. Left ventricular end-diastolic dimensions (LVEDds) ranging from 4.5 to 6.5 cm were studied and ranked according to relative thrombogenic potential. Over 150,000 platelets were individually tracked in each LV model over 15 cardiac cycles. As LV size decreased, platelets experienced markedly increased shear stress histories (SHs), whereas platelet residence time (RT) in the LV increased with size. The complex interplay between increased SH and longer RT has profound implications on thrombogenicity, with a significantly higher proportion of platelets in small LVs having long RT times and being subjected to high SH, contributing to thrombus formation. Our data suggest that small LV size, rather than decreased VAD speed, is the primary pathologic mechanism responsible for the increased incidence of thrombosis observed in VAD patients with small LVs.

Computational characterization of flow and blood damage potential of the new maglev CH-VAD pump versus the HVAD and HeartMate II pumps

Left ventricular assist devices are routinely used to treat patients with advanced heart failure as a bridge to transplant or a destination therapy. However, non-physiological shear stress generated by left ventricular assist devices damages blood cells. The continued development of novel left ventricular assist devices is essential to improve the left ventricular assist device therapy for heart failure patients. The CH-VAD is a new maglev centrifugal left ventricular assist device. In this study, the CH-VAD pump was numerically analyzed and compared with the HVAD and HeartMate II pumps under two clinically relevant conditions (flow: 4.5 L/min, pressure head: normal ~80 and hypertension ~120 mmHg). The velocity and shear stress fields, washout, and hemolysis index of the three pumps were assessed with computational fluid dynamics analysis. Under the same condition, the CH-VAD hemolysis index was two times lower than the HVAD and HeartMate II pumps; the CH-VAD had the least percentage volume with shear stress larger than 100 Pa (i.e. normal condition: 0.4% vs HVAD 1.0%, and HeartMate II 2.9%). Under the normal condition, more than 98% was washed out of the three pumps within 0.4 s. The washout times were slightly shorter under the hypertension condition for the three pumps. No regions inside the CH-VAD or HVAD had extremely long residential time, while areas near the straightener of the HeartMate II pump had long residential time (>4 s) indicating elevated risks of thrombosis. The computational fluid dynamics results suggested that the CH-VAD pump has a better hemolytic biocompatibility than the HVAD and HeartMate II pumps under the normal and hypertension conditions.

Stem Cells in Cardiovascular Medicine: Historical Overview and Future Prospects

Cardiovascular diseases remain the leading cause of death in the developed world, accounting for more than 30% of all deaths. In a large proportion of these patients, acute myocardial infarction is usually the first manifestation, which might further progress to heart failure. In addition, the human heart displays a low regenerative capacity, leading to a loss of cardiomyocytes and persistent tissue scaring, which entails a morbid pathologic sequela. Novel therapeutic approaches are urgently needed. Stem cells, such as induced pluripotent stem cells or embryonic stem cells, exhibit great potential for cell-replacement therapy and an excellent tool for disease modeling, as well as pharmaceutical screening of novel drugs and their cardiac side effects. This review article covers not only the origin of stem cells but tries to summarize their translational potential, as well as potential risks and clinical translation.

Impact of preoperative extracorporeal life support on left ventricular assist device outcomes: A comparative study

Background:

To investigate whether preoperative short-term extracorporeal life support therapy in patients undergoing continuous-flow left ventricular assist device implantation has an impact on the outcome regarding survival and adverse events.

Methods:

Between January 2011 and May 2018, 100 consecutive patients received HeartMate II, HeartWare, or HeartMate III for end-stage heart failure. Mean age was 64.2 ± 10.3 years. Three patient groups were identified: without preoperative extracorporeal life support (non-extracorporeal life support group, n = 80), with preoperative extracorporeal life support due to postcardiotomy shock after conventional cardiac surgery (postcardiotomy shock group, n = 9), and with preoperative extracorporeal life support without previous surgery (non-postcardiotomy shock group, n = 11). The primary endpoint was overall survival after device implantation. Secondary endpoints were adverse events during the follow-up period.

Results:

Survival was significantly different between the groups (p < 0.05): 30-day, 6-month, and 1-year survival rates were 85%, 68%, and 61% for non-extracorporeal life support group; 44%, 22%, and 22% for postcardiotomy shock group; and 45%, 27%, and 24% for non-postcardiotomy shock group, respectively. Furthermore, in both extracorporeal life support groups (postcardiotomy shock and non-postcardiotomy shock), there were a higher incidence (p < 0.05) of postoperative right heart failure (30% vs 66.7% vs 54.5%), acute renal failure requiring dialysis (20% vs 77.8% vs 54.5%), and respiratory failure (31.3% vs 88.9% vs 81.8%).

Conclusion:

Continuous-flow left ventricular assist device implantation with prior extracorporeal life support appears to have a worse outcome regarding survival, right heart failure, renal and respiratory dysfunction (p < 0.05). Future studies have to be done to evaluate the outcome after extracorporeal life support bridge pre-left ventricular assist device, especially as ultima ratio in postcardiotomy shock patients.

Effects of Cone-Shaped Bend Inlet Cannulas of an Axial Blood Pump on Thrombus Formation: An Experiment and Simulation Study

Background

Cannula shape and connection style influence the risk of thrombus formation in the blood pump by varying the blood flow characteristics inside the pump. Inlet cannulas should be designed based on the need for anatomical fit and reducing the risk of thrombus generation in the blood pump. The effects on thrombus formation of the cone-shaped bend inlet cannulas of axial blood pumps should be studied.

Material/Methods

The cannulas were designed as cone-shaped, with 1 bent section connecting 2 straight sections. Both the silicone tube and novel cone-shaped cannula were simulated for comparison. The flow fields of a blood pump with inlet cannula were simulated by computational fluid dynamics (CFD) at flows of 2.0, 2.5, and 3.0 liters per minute (lpm), with pump rotational speeds of 7500, 8000, and 8500 rpm, respectively. Then, 6 two-dimensional (2D) particle image velocimetry (PIV) tests were conducted and the velocity distributions were analyzed.

Results

A low-velocity region was located inside the pump entrance when a soft silicone tube was used. At 8500 rpm and 3.0 lpm working condition, the minimum velocity inside the pump with cone-shaped cannulas was 2.5×10⁻¹ m/s. The cone-shaped cannulas eliminated the low-velocity region inside the pump. Both CFD and PIV results showed that the low-velocity region did not spread to the entrance of the blood pump within the flow range from 2.0 lpm to 7.0 lpm.

Conclusions

The designed cone-shaped bent cannulas can eliminate the low-velocity region inside the blood pump and reduce the risk of thrombus formation in the blood pump.

Total Artificial Heart Implantation After Undifferentiated High-Grade Sarcoma Excision

Background

Total artificial heart (TAH) implantation in patients with aggressive tumor infiltration of the heart can be challenging.

Case Report

We report on a patient with a rare primary undifferentiated high-grade spindle cell sarcoma of the mitral valve and in the left atrium, first diagnosed in 2014. The referring center did a first resection in 2014. In the course of 17 months, computer tomography (CT) scan again showed massive invasion of the mitral valve and left atrium. Partial resection and mitral valve replacement was not an option. We did a subtotal heart excision with total artificial heart implantation. In this report we discuss complications, risk factors, and perioperative management of this patient.

Conclusions

Patients with aggressive tumors of the heart can be considered for TAH implantation.

Effect of Different Rotational Directions of BJUT-II VAD on Aortic Swirling Flow Characteristics: A Primary Computational Fluid Dynamics Study

Background

The BJUT-II VAD is a novel left ventricular assist device (LVAD), which is thought to have significant effects on the characteristics of aortic swirling flow. However, the precise mechanism of the rotational direction of BJTU-II VAD in the aortic swirling flow is unclear.

Material/Methods

A patient-specific aortic geometric model was reconstructed based on the CT data. Three pump’s output flow profiles with varied rotational direction, termed “counterclockwise”, “flat profile”, and “clockwise”, were used as the boundary conditions. The helicity density, area-weighted average of helicity density (Ha), localized normalized helicity (LNH), wall shear stress (WSS), and WSS spatial gradient (WSSG) were calculated to evaluate the swirling flow characteristics in the aorta.

Results

The results demonstrated that the swirling flow characteristics in the aorta and 3 branches are directly affected by the output blood flow of BJUT-II VAD. In the aortic arch, the helicity density, supported by the clockwise case, achieved the highest value. In the 3 branches, the flat profile case achieved the highest helicity density, whereas the maximum WSS and WSSG generated by clockwise case were lower than in other cases.

Conclusions

The outflow of the BJUT-II VAD has significant effects on the aortic hemodynamics and swirling flow characteristics. The helical blood profiles can enhance the strength of aortic swirling flow, and reduce the areas of low WSS and WSSG regions. The clockwise case may have a benefit for preventing development of atherosclerosis in the aorta.

Pulsatile Support Mode of BJUT-II Ventricular Assist Device (VAD) has Better Hemodynamic Effects on the Aorta than Constant Speed Mode: A Primary Numerical Study

Background

BJUT-II VAD is a novel left ventricular assist device (LVADs), directly implanted into the ascending aorta. The pulsatile support mode is proposed to achieve better unloading performance than constant speed mode. However, the hemodynamic effects of this support mode on the aorta are still unclear. The aim of this study was to clarify the hemodynamic effects BJUT-II VAD under pulsatile support mode on the aorta.

Material/Methods

Computational fluid dynamics (CFD) studies, based on a patient-specific aortic geometric model, were conducted. Wall shear stress (WSS), averaged WSS (avWSS), oscillatory shear index (OSI), and averaged helicity density (Ha) were calculated to compare the differences in hemodynamic effects between pulsatile support mode and constant speed mode.

Results

The results show that avWSS under pulsatile support mode is significantly higher than that under constant speed mode (0.955Pa vs. 0.675Pa). Similarly, the OSI value under pulsatile mode is higher than that under constant speed mode (0.104 vs. 0.057). In addition, Ha under pulsatile mode for all selected cross-sections is larger than that under constant mode.

Conclusions

BJUT-II VAD, under pulsatile control mode, may prevent atherosclerosis lesions and aortic remodeling. The precise effects of pulsatile support mode on atherosclerosis and aortic remodeling need to be further studied in animal experiments.

Use of PTFE patch for pericardial closure after minimal invasive LVAD implantation

The left ventricular assist device (LVAD) is now a routine therapy for advanced heart failure. The thoracotomy approach for LVAD implantation, in which the left ventricle is approached through a pericardial rent, is becoming popular. We demonstrate closure of the pericardial rent with a polytetrafluoroethylene (PTFE) patch and its advantages.