Heartmate II axial-flow left ventricular assist system: management, clinical review and personal...

C

Original article

Heartmate II axial-flow left ventricular assist system:management, clinical review and personal experienceAntonino Loforte, Andrea Montalto, Federico Ranocchi, Giovanni Casali,Giampaolo Luzi, Paola Lilla Della Monica, Fabio Sbaraglia, Vincenzo Polizzi,Giada Distefano and Francesco Musumeci

Objectives The excellent results with left ventricular assist

devices (LVADs) have revolutionized the treatment options

for end-stage heart failure. The use of pulsatile devices is

associated with significant comorbidity and limited

durability. The axial-flow HeartMate II LVAD represents the

new generation of devices. The clinical use of this pump

resulted in superior outcomes. We review the HeartMate II

technology, management, clinical usage and our

experience.

Methods Between 3/2002 and 12/2008, 18 transplantable

adult patients were supported on long-term HeartMate II

LVAD at our institution (13 men, age 52 W 8.4 years, range:

31–64 years). Primary indications were: ischemic

cardiomyopathy (CMP) (n U 13), idiopathic CMP

(n U 5). All patients were in New York Heart Association

(NYHA) Class IV heart failure. None of patients had prior

open-heart surgery. Implantation via cannulation of the left

ventricular apex and the ascending aorta was always

elective.

Results Mean support time was 217 W 212.3 days (range:

1–665 days). Early (30-day) mortality was 27.7% (five

patients) with multiple organ failure and sepsis as main

causes of death. Bleeding requiring reoperation occurred in

six (33.3%) cases. Cerebral hemorrhage occurred in one

patient. There were two driveline infections and no device

opyright © Italian Federation of Cardiology. Unau

1558-2027 � 2009 Italian Federation of Cardiology

failure. Twelve (66.6%) patients were successfully

discharged home. Overall nine patients (50%) were

transplanted and two patients are actually waiting for a

suitable organ (n U 2 patients discharged home and n U 1

patient in hospital). At latest, follow-up survival rate after

heart transplantation is 66.6% (six patients).

Conclusion Long-term HeartMate II LVAD provides good

mid-term, long-term results. This new technology requires

delicate management. Functional status and quality of life

greatly improve in patients who survive the perioperative

period. J Cardiovasc Med 10:765–771 Q 2009 Italian

Federation of Cardiology.

Journal of Cardiovascular Medicine 2009, 10:765–771

Keywords: heart failure, left ventricular assist device, mechanical support

Department of Cardiac Surgery and Heart Transplantation, San Camillo Hospital,Rome, Italy

Correspondence to Dr Antonino Loforte, Cardiac Surgeon, Department ofCardiac Surgery and Heart Transplantation, S. Camillo Hospital, P.za C. Forlaninin.1, 00151 Rome, ItalyTel: +39 06 5870 4401; fax: +39 06 5870 4706;e-mail: [email protected]

Received 23 January 2009 Revised 6 April 2009Accepted 23 April 2009

IntroductionThe HeartMate II left ventricular assist system (LVAS)

(Thoratec, Inc.; Pleasanton, California, USA) is a rotary

blood pump with axial flow design that represents a

second generation of implantable assist devices designed

to be a small, more reliable device suitable for long-term

outpatient circulatory support. The major advantage of

the HeartMate II LVAS is the axial flow design that

reduces significantly its size and weight compared with

the current generation of implantable, pulsatile pumps

(e.g. HeartMate XVE, Thoratec, Inc., Pleasanton,

California, USA; Novacor LVAD, World Heart, Inc.,

Ottawa, Canada; Thoratec IVAD, Thoratec, Inc.), princi-

pally through elimination of a blood sac or reservoir

necessary for pulsatile systems.

The initial development of the HeartMate II LVAS

began in the early 1990s as a collaborative project

between the engineering and clinical teams of Nimbus,

Inc. (Rancho Cordova, California, USA) and the Univer-

sity of Pittsburgh [1–4]. Early development of the pump

was supported by the National Institutes of Health-Small

Business Innovative research grants and later in 1997 by

an award from the National Institutes of Health program

for innovative ventricular assist development [4]. In 1998

Nimbus, Inc. was acquired by ThermoCardiosystems,

Inc. (Woburn, Massachusetts, USA). Initial animal test-

ing suggested that the HeartMate II LVAS had good

hemodynamic performance with excellent potential for

5-year durability [5,6]. In 2001 ThermoCardiosystems,

Inc. was acquired by Thoratec Corporation (Pleasanton,

thorized reproduction of this article is prohibited.

DOI:10.2459/JCM.0b013e32832d495e

mailto:[email protected]

http://dx.doi.org/10.2459/JCM.0b013e32832d495e

Cop

766 Journal of Cardiovascular Medicine 2009, Vol 10 No 10

California, USA), which currently leads development and

clinical testing of the HeartMate II LVAS.

In this report we review the HeartMate II technology,

management, clinical usage and our initial experience

with the device.

Device descriptionThe left ventricular assist system consists of an internal

blood pump with a percutaneus lead that connects the

pump to an external system driver (computer controller)

and power source (batteries or power base unit/battery

charger) [1–4]. The blood pump component of the

HeartMate II LVAS is a 12-mm-diameter straight tube

made of titanium alloy [1–4,7]. The 12-mm straight tube

incorporates the hydraulic components of the pump that

include the inlet stator (the fixed component that forms

the pivot or housing for the rotor), a pump rotor (the

rotational component that includes the impeller blades)

that incorporates a pump magnet, and an outlet stator.

Blood entering the tube passes through the inlet stator

supported by three guide vanes that straighten the flow of

blood as it passes across the inlet stator. The blood next

flows around the pump’s internal rotor. As the blood flows

around the pump rotor, the spinning action of the pump

rotor with its three curving blades introduces a radial or

tangential velocity to the blood flow and imparts kinetic

energy to the blood, which then flows past the outlet

stator vanes. The twisted shape of the outlet stator vanes

converts the radial velocity of the blood flow to an axial

direction [5]. As the blood flow is being turned through

the outlet stators, its kinetic energy is converted to static

pressure, producing a blood flow field that increases

pressure across the pump. The other components of

the pump assembly include the inlet cannula that carries

blood from the left ventricular apex to the pump inlet,

and outlet cannula that returns blood from the pump

outlet to the ascending aorta.

The power to drive the pump rotor is developed by an

integrated electric motor located in the hub of the rotor.

The motor magnet is located within the pump rotor and

orientated at the center line of the axis of the pump

windings and centered longitudinally with respect to the

coil’s length. Electric current is sequentially commutated

to the coils and this creates a spinning magnetic field.

This action creates tourque and angular velocity to the

motor magnet located within the pump rotor. The pump

rotor spins on two bearings located at the inlet and outlet

stators that consist of a ball-and-socket hydrodynamic

composite design. These bearings support radial and

axial loads from the pump rotor. The stationary element

of each bearing is located in the hub of the respective

inlet and outlet stators. The boundaries between the

static and moving surfaces of the ceramic bearings are

washed by the flow of blood. A major advantage of this

pump design is that the rotor that spins within the

yright © Italian Federation of Cardiology. Unauth

magnetic field on the inlet and outlet bearings represents

the only moving component of the pump.

The outlet cannula of the pump, screw-connected to the

pump by a rigid elbow, is made of woven Dacron and

requires preclotting. The inlet cannula has several

important design features that include a flexible joint

between the intraventricular portion of the cannula and

its union to a titanium 908 elbow joining the pump, and an

intraventricular rigid cannula that has been extended in

length and is intended to open the mid left ventricular

cavity. The longer intraventricular cannula is believed to

improve reliability of continuous flow throughout cardiac

systole and diastole and at varied levels of left ventricular

filling. The flexible portion of the inlet cannula is made of

woven Dacron and is compressed into accordion-like

ridges. The flexible portion of the inlet cannula was

added to reduce the risk for malalignment of the intra-

ventricular portion of the inlet cannula caused by the

pump. The pump rotor, blood tube within the pump

housing, and inlet and outlet stators are smooth titanium

surfaces. The inlet and outlet elbows and the intraven-

tricular cannula are textured with titanium microsphere

coatings similar to the HeartMate XVE design [8,9].

The system driver sends power and operating signals to

the pump and receives information from the pump. The

driver is wearable and is powered by a power base unit or

by two 12-volt rechargeable batteries that can provide

approximately 2–4 h of power under normal operating

conditions. The system monitor communicates to a sys-

tem driver and pump through the power base unit and is

made up of a series of display screens for checking and

altering pump functions.

An assessment of pump flow for the HeartMate II LVAS

is provided through use of a flow estimator that is based

on the relationship between pump motor rpm speed and

time-varying electrical power consumption of the pump

motor [10,11]. For any given pump rpm speed, pump flow

is related linearly to power over a limited power range,

and there is an anticipated range of flow and power

consumption for the pump. The relationship between

pump motor speed and power consumption does not

accurately predict estimates of pump flow less than

3 l/min. An additional relationship to understand for

pump operation is the term pulsatility index. Pulsatility

index is a measure of flow pulse through the pump and is

described by the relationship: pulsatility index¼ (maxi-

mum flow – minimum flow)/mean flow. When preload

increases in the native left ventricle, the Starling curve is

impacted and the pulsatility increases. When preload

decreases, the pulsatility of the left ventricle decreases.

Pump flow for the HeartMate II LVAS is not measured

directly through use of a sensor or flow meter. This

indirect assessment of pump flow can have significant

limitations in providing useful clinical information if the

orized reproduction of this article is prohibited.

C

HeartMate II LVAD mechanical support Loforte et al. 767

pump is operating in a power range that is not typical for

the pump motor speed. In clinical situations in which

assessment of hemodynamic performance of the pump is

needed, invasive monitoring with a Swan–Ganz catheter

or use of echocardiography is thus important to trouble-

shoot potential patient or pump problems.

The approximate weight of the pump is 350 g and the

approximate size of the pump is 7.0 cm in length and

4.0 cm in diameter at its largest diameter. The pump has

an operating rpm range of 6000–15 000 and is capable of

generating up to 10 l/min of flow at an approximate

pressure of 100 mmHg. In addition, the axial flow design

and absence of a blood sac eliminates the need for

venting, currently for the first generation of implantable

pumps, thus reducing the size of the percutaneous drive

lead and eliminating the need for internal one-way

valves. These design features facilitate future conversion

to a completely implantable system because of the

absence of a requirement for a compliance chamber.

Design modificationsFuture design enhancements include development

and refinement of a computer algorithm for auto mode

operation of the system to optimize left ventricle (LV)

unloading [10,11] and potential conversion to a totally

implantable system with transcutaneous energy trans-

mission system (TETS) technology [12].

Device implantation and operativeconsiderationsThe pump is designed to be surgically implanted below

the left costal margin and under the left rectus abdominus

muscle in a preperitoneal position. The inflow cannula

exits the left ventricular apex and crosses the diaphragm

at the costophrenic angle and enters a subrectus pocket

under the left rib margin to attach to the pump. The

pump is intended to lie parallel to the diaphragm. The

outflow cannula is tunnelled back under the sternum to

the ascending aorta. The percuteous driveline consists of

a small-diameter electrical cable that is tunneled through

the abdominal wall and exits the right upper quadrant at

the midclavicular line approximately 3–4 cm below the

costal margin. The percutaneous driveline then is con-

nected to an external system driver and power source.

The system also can be configured to be a completely

implantable system using TETS technology and an

implantable system driver [12].

AnticoagulationThe anticoagulation regimen used for the pilot clinical

investigation includes initiation of heparin therapy within

12–24 h of pump implantation when chest tube drainage

decreased to approximately less than 50 ml/h. The

recommendations are to achieve a partial thromboplastin

time (PTT) of 45 s (1.2–1.4 times control) during the

initial 24 h of therapy and gradually increase over 48–72 h


to a target goal PTT of approximately 55 to 65 s (1.5–1.8

times control. Antiplatlet therapy with aspirin 81 to

100 mg daily and dipyridamole 75 mg three times daily

is initiated at 48–72 h following pump implantation.

Conversion of heparin to warfarin therapy is initiated

at the discretion of the physician (approximately at day

five) to achieve a target international normalized ratio

(INR) of 2.0 to 3.0. Heparin is discontinued after obtain-

ing a stable therapeutic INR.

Special management issuesPump thrombusAn abnormal power increase unrelated to actual changes

in pump flow (e.g. thrombus on the pump rotor) produces

an inaccurate estimate of pump flow. With thrombus on

the rotor (resulting in significant rotor drag), power con-

sumption would increase, causing an inaccurately high

estimate of pump flow and decrease in pulsatility index

caused by the reduction in cyclic power consumption

(continuously high power consumption caused by the

thrombus). The patient’s aortic pulse pressure may

remain unchanged in this situation. With inlet obstruc-

tion (e.g. inlet cannula malalignment to thrombus on

the orifice of the inlet cannula) or outflow obstruction

(e.g. kinking of the aortic outflow graft or anastomotic

narrowing), power consumption, pump flow and pulsati-

lity index all decrease and are associated with an increase

in the patient’s aortic pulse pressure. Diagnosis of this

scenario can be aided with echocardiography demonstrat-

ing a dilated LV and changes in LV unloading perhaps

not responsive to increasing pump rpm speeds.

Ventricular suctionThe HeartMate II LVAS additionally incorporates a suc-

tion detection algorithm to reduce the risks for unwonted

suction events. The system monitors sudden changes in

pump flow pulsatility indirectly through analysis of the

time-dependent current trace and its derivatives (pulsa-

tility index). If a sudden change in pump flow pulsatility

is detected, the pump speed automatically reduces to

9000 rpm to avoid suction. Immediately following an

event, the operating speed displayed on the monitor is

lower than the set speed and then slowly returns to the set

pump speed. During a suction event, pump flow, power

consumption, and pulsatility index decrease. The patient

may or may not have a change in the aortic pulse pressure.

MethodsBetween March 2002 and December 2008, we enrolled

18 patients with severe heart failure. There were 15 men

and three women with a mean age of 52� 8.4 years

(range, 31–64 years), and a mean body surface area

(BSA) of 1.76� 0.18 m2 (range, 1.54–1.96 m2). The

indication for use was bridge to transplantation (BTT)

in all patients. The diagnosis was ischemic cardiomyo-

pathy in 13 patients and idiopathic cardiomyopathy in

five. A viable area less than 20% of the total heart area was


Cop


detected by positron emission tomography (PET) with

fluorodeoxyglucose (FDG) in ischemic cardiomyopa-

thies, all with functional moderate mitral regurgitation

and no graftable target vessels, and consequently con-

sidered not suitable for conventional surgical procedures

according to Hausmann et al. [13]. Additionally, the

correction of functional mitral valve regurgitation with

annuloplasty alone results in partial reversal of left ven-

tricular remodeling and the long-term benefit of this

procedure has yet to be demonstrated by randomized

trials comparing optimal medical management with

mitral valve surgery, and a recent retrospective study

showed no demonstrable decrease in long-term mortality

in patients affected by severe mitral regurgitation and

considerable left ventricular dysfunction and undergoing

mitral valve repair [14].

At the time of preoperative evaluation, all 18 patients

were classified in New York Heart Association (NYHA)

functional class IV and were receiving optimal medical

management in the hospital. Nine patients were being

supported by an intraaortic balloon pump (Datascope), and

one patient had been supported by Jostra RotaFlow

(Maquet Cardiopulmonary AG, Hirrlingen, Germany)

extracorporeal membrane oxygenation (ECMO) system

before receiving the LVAD. The HeartMate II was placed

in one patient after a HeartMate XVE device failed.

Implantation via cannulation of the left ventricular apex

and the ascending aorta was performed traditionally.

Patients received routine, postimplantation medical sup-

port after their operation. The anticoagulation protocol

proposed by Thoratec Inc. was adopted [5]. Once

patients are stabilized and become ambulatory, proper

nutrition, rehabilitation and education become a focus of

care. After discharge from the hospital, patients return to

our heart failure clinic for routine follow-up monthly and

at a decreasing frequency, depending on their needs.

Serial echocardiographic studies are performed at regular

intervals for inpatients and outpatients to evaluate the

adequacy of ventricular unloading.

Statistical analysisAll values are expressed as means� standard deviation.

All analyses were performed using SPSS for Windows

Release 11.5 (SPSS Inc., Chicago, Illinois, USA).

ResultsThe average duration of support was 217� 212.3 days

(range, 1–665 days). All patients survived the operation.

Of the 18 implanted patients, 13 (72.2%) survived the

operation without significant complications in the early

postoperative period and 12 (66.6%) were discharged from

the hospital in NYHA functional class I. Overall, survived

HeartMate II recipients were discharged a mean of 38 days

(range, 25–110 days) after implantation. Nine (50%)

patients underwent heart transplantation (Htx). At latest,


follow-up survival rate after Htx is 66.6% (six patients).

Two patients died of early primary graft failure unsuccess-

fully treated with peripheral ECMO support and one

patient died suddenly of unknown causes 8 months after

Htx. There were three episodes in three different patients

of rejection greater than International Society of Heart and

Lung Transplantation (ISHLT) grade 3A, during the

posttransplant first year, treated successfully with medi-

cations. LVAD support is ongoing in three discharged

home patients who are waiting for a suitable organ. One

of these patients was recently readmitted to hospital due to

fever and suspicion of infection. None of the patients died

while receiving device support. Five patients died during

the early postoperative period (30-day mortality) because

of a combination of right-sided heart failure and multiple

system heart failure, leading tosepsis. Re-thoracothomy for

bleeding occurred in six (33.3%) patients. Thrombus

generation in thenoncoronary sinus occurred in one patient

with extremely poor myocardial contractility associated

with a constant lack of aortic valve opening in the early

postoperative period, treated successfully intravenously

with a higher dosage infusion of heparin for a few days.

Heparin-induced thrombocytopenia occurred in one

patient who underwent temporary bivalirudin infusion.

None of the removed devices at the time of transplantation

showed incidence of thrombus. In the early postoperative

period, one patient developed ventricular arrhythmias and

ventricular fibrillation, possibly generated by contact of the

intraventricular cannula with the endocardium due to too

low a volume of the left ventricle chamber, which needed

electric cardioversion for resuscitation. Cerebral hemor-

rhage occurred in one patient. Two patients underwent

right ventricular assist device (RVAD) (Levitronix Cen-

triMag, Levitronix LLC, Waltham, Massachusetts, USA)

placement intraoperatively due to preoperative laboratory,

hemodynamicandechocardiographic assessment ofa mod-

erate right ventricle dysfuntion considered not ideal for

LVAD placement according to the Berlin algorithm [15].

Both patients were weaned successfully from RVAD,

which was removed through a right lateral minithoracoth-

omy without reopening the sternum (13 and 17 days of

CentriMag support, respectively). Superficial driveline

infection occurred in two (11.1%) patients, all treated

successfully with aggressive daily local wound care. The

Heartmate XVE to HeartMate II pump-exchange patient

has been discharged, transplanted and is doing well.

Hemodynamic function improved from preoperative

levels in all patients during support with HeartMate II.

By48 h afterdevice implantation, the averagecardiac index

had increased significantly; from 1.8� 0.26 to 3.5� 0.9 l/

(min�m2), and pulmonary wedge pressure had decreased

significantly, from 23.7� 10 to 17.4� 5.2 mmHg. Inotropic

support was reduced after implantation, and all patients

were weaned within the first week. Serial echocardio-

graphic studies showed improvement in left ventricular

dimensions.


C


In the 12 patients who were discharged, hemoglobin,

hematocrit, and end-organ function had reached normal

levels by the time of discharge and remain normal in all

current outpatients.

The technical performance of the HeartMate II has been

excellent, and patients have been satisfied with this small

and quiet pump.

Before discharge, all patients were trained in the care and

use of their equipment and batteries. The patients

participated in a physical rehabilitation program that

was composed of graduated ambulation within the hos-

pital and treadmill exercise under observation. There

were no life-threatening arrythmias during rehabilitation.

No device malfunction or system problem has been seen

in the outpatient setting.

DiscussionThe first human implantation of the HeartMate II LVAS

was performed in 2000 in Israel. This experience was

followed by nine additional implants at two European

sites [16]. In the initial experience, the HeartMate II

LVAS was designed with sintered or textured surfaces on

the inlet and outlet stators that resulted in significant

incidence of pump thrombus formation. Following rede-

sign and application of smooth surfaces to the inlet and

outlet stators, a clinical pilot trial of the redesigned

HeartMate II LVAS was initiated in humans in Novem-

ber 2003 and completed in November 2004 [17,18]. The

most recent data analysis of the pilot trial was performed

on 27 May, 2005. A total of 34 patients were enrolled at 11

clinical sites; 24 (71%) patients were enrolled from

clinical sites in the United States and 10 (29%) patients

were enrolled from European centers. Notably, of the 34

patients enrolled in the study, 15 (44%) patients were

women, representing a larger pencentage of women than

typically treated with the current generation of implan-

table pulsatile pumps [19]. The median body surface area

was 1.8 m2 (1.63 m2 for females and 1.99 m2 for males).

The causes and severity of heart failure mirrors other

recent trials. As expected, hemodyamic measurements at

24 h following HeartMate II LVAS implantation were

improved significantly, with no significant change in

systolic blood pressure or central venous pressure. An

initial significant increase in serum total bilirubin was

noted at 7 days, which normalized by day 30 following

pump implantation. There was a significant improvement

in functional activity reflected by a greater proportion of

patients able to complete a 6-min walk at day 30 com-

pared with baseline, greater distance achieved during the

6-min walk, and improvement in NYHA functional class.

Ten (29%) patients died while on LVAD support. A total

of 22 (65%) were discharged home during LVAD support.

The median duration of pump support was 160 days, with

a range of 6–562 days. No pump failures were reported in

the early experience. The importance of adequate right


ventricular function is underscored by the four (12%)

patients who required a RVAD for right-sided circulatory

failure, of which one patient weaned and survived and

three patients expired. Six (18%) patients experienced

eight neurological events, including two transient

ischemic events, one stroke, a perioperative encephalo-

pathy, and two perioperative seizures. Hemolysis,

defined as two consecutive plasma free-hemoglobin

values greater than 40 md/dl, occurred in only two

(6%) patients. In one of these patients, right-sided cir-

culatory failure with significant left ventricular collapse

was present for an extended period. There were a total of

10 deaths; the most frequent cause was multisystem

organ failure (five patients).

All pumps were operated in a fixed rpm speed during the

clinic pilot trial. The pumps were maintained at a mean

pump speed of 9.172 rpm at 24 h following implant,

9.255 rpm at day 7, and 9.366 at day 30. The minimum

and maximum pump speeds during the trial were 7.790

and 10.200 rpm, respectively.

The results of the initial pilot trial of the HeartMate II

LVAS demonstrated the efficacy of rotary pumps with

axial flow design for hemodynamic improvement and

organ recovery in humans. In addition the HeartMate

II LVAS provided excellent support in the outpatient

setting with significant improvement in functional

activity, easy use, and comfort related to the smaller size

of the driveline. The early experience with the Heart-

Mate II LVAS has also exposed a need for developing a

better understanding of the parameters to assess optimal

LV unloading, to maximize patient functional abilities

and LV recovery and prevent suction events or right-

sided circulatory failure. The HeartMate II LVAS cur-

rently is undergoing further clinical investigation in two

pivotal phase trials that include a multicenter, nonrando-

mized evaluation of the HeartMate II LVAS in patients

awaiting heart transplantation and a multicenter, random-

ized evaluation of the HeartMate II LVAS compared

with the HeartMate XVE in patients meeting criteria for

destination therapy. Recently, according to the data

presented at ISHLT 28th annual meeting 2008, Boston,

Massachusetts, USA, as ‘one year follow-up’ of above

multicenter evaluation of HeartMate II LVAS [20], 327

heart failure patients had undergone implantation of the

axial flow pump as BTT and 194 had reached 1 year since

implant. The median support was 131 days (longest: 844

days). Forty-two patients have been supported for more

than 1 year and five patients more than 2 years. At

12 months, 149 (77%) of the 194 patients survived, with

53% undergoing transplantation, 2% cardiac recovery

with device removal, and 22% ongoing device support.

Adverse events included percutaneous lead (12%) and

pocket (2%) infections, device thrombosis (2%), perio-

perative (3%) and postoperative (6%) stroke, and need for

RVAD (5%). The median time to Htx in the first year was


Cop


102 days. HeartMate II improved significantly 6-min

walk distance and NYHA functional class. Of the 42

patients supported for more than 1 year, nine have under-

gone transplantation, two recovered, five died, and 26

remain ongoing with a median duration of 513 days.

In a retrospective analysis of the first 101 consecutive

cases in Europe [21] the perioperative mortality post-

implant was 20% in BTT patients and 7% in the destina-

tion therapy arm. After 1 year a comparable survival was

observed in both groups (69% destination therapy, 63%

BTT). Main cause of death was multiple organ failure.

Our initial experience with the redesigned HeartMate II

has been favorable and has shown this model to be well

tolerated, durable and effective. The technical function

of the device has been excellent. We did not see any

pump failure or operational problems with this technol-

ogy to date.

In our series, 12 patients were discharged from the

hospital, and problems with the HeartMate II system

have been minimal. Arrythmia has been noted, particu-

larly if the patient becomes volume depleted or if the

pump’s unloading of the ventricle is excessive. Lowering

the rpm and ensuring adequate volume status, especially

during postoperative period, can solve this issue.

The small size and reduced weight of this technology

have enabled us to implant the device in women and

young smaller patients who suffer from end-stage heart

failure. The HeartMate II allows an easy intrapericardial

fitting of the device. We eventually open the left pleura

to gain more space, as done in three patients.

Again, a positive goal we reached in our experience with

the HeartMate II has been the possibility to discharge

home several patients, thus recovering a good social life

(this was not the case with the paracorporeal devices).

Discharging patients home is an important therapeutic

option both for the individual and to optimize health-care

resources, considering the long time on the waiting list

for Htx.

The progress of rotary blood pump technology has been

so fast that during the past 5 years all so-called second-

generation rotary blood pumps with blood immersed

bearings, such as the earlier discussed HeartMate II

(Thoratec), the MicroMed (Houston, Texas, USA)

DeBakey VAD, and the Jarvik 2000 FlowMaker (Jarvik

Heart), the development of which had been started in

1995, have already been implanted in several selected

end-stage cardiac patients for bridge to transplantation

and for destination therapy. Although considered unphy-

siological as cardiac support, the continuous flow or

reduced pulsatility continues to work in humans for a

duration of as long as 5.5 years [22]. Beyond second-


generation devices, third-generation mechanical noncon-

tact devices utilizing magnetic suspension mechanisms,

such as the Terumo DuraHeart and the Berlin Heart

INCOR system, and hydrodynamic bearing mechanisms,

such as Arrow International’s (Reading, Pennsylvania,

USA) CorAide and Ventracor’s (Chatswood, New South

Wales, Australia) Ventr-Assist VADs, are actually making

their way into clinical applications [22].

All the continuous-flow technology has shown defini-

tively that ambulatory, effective circulatory support can

be achieved in the long-term in patients with advanced

heart failure who require cardiac support. However, by

changing the internal physiology, this therapy introduces

physiologic phenomena and accompanying clinical pro-

blems, such as arteriovenous malformations leading to

gastrointestinal bleeding, septal shift with resultant right-

sided heart-failure, thrombosis of the aortic valve non-

coronary sinus, aortic valve fusion, and aortic valve insuf-

ficiency. These problems are medically manageable, but

physicians must be aware of them when applying this

life-saving technology.

Miyamoto et al. [23] showed that increases in the amount

of left ventricular unloading led to incremental decreases

in the derivative of right ventricular pressure (right ven-

tricular dP/dt), effectively reducing right ventricular

function. Unlike pulsatile ventricular assist devices, com-

plete left ventricular unloading is avoided with Heart-

Mate II LVAS and other second- and third-generation

axial flow pumps. Our sense and that of other investi-

gators [24] is that there is less right ventricular failure with

the axial flow pumps owing to maintenance of left ven-

tricular end-diastolic volume, maintained septal position,

and preservation of right ventricular mechanics. There-

after, according to the recently developed Berlin echo-

cardiographic algorithm for biventricular support [15], in

our opinion, a temporary right ventricular support at the

same time of LVAD placement should be considered in

the case of a moderate preoperative right ventricular

dysfunction assessment and mainly a preoperative left

ventricle end-diastolic diameter less than 68 mm which is

unable to eventually avoid a leftward septum shift, as we

recently performed in only two patients. Five patients, at

the beginning of our experience, complicated by multiple

organ failure, had similar preoperative echocardiographic

ventricle geometry and dimensions as the earlier ones but

were not supported immediately by a temporary RVAD

placement and the outcome was bad.

We pay particular attention to the proper level of anti-

coagulation, recently focusing on thromboelastogram and

platelet aggregation test monitoring to reach the correct

equilibrium among the three systems involved: the plate-

lets, the procoagulant system, and the fibrinolytic system.

The effect on the blood and the coagulation system varies

from pump to pump, depending on its materials, pumping


C


methodology, texture of the surface and design. The

patients vary dramatically in their comorbidities, genetic

composition, drug intake and level of compliance. All

of these complexities make it impossible to develop

a universal anticoagulation/antiaggregation regimen for

patients who have mechanical circulatory assist devices.

Rotary blood pumps show a greater tendency for shear

stress, which is actually optimized by tuning the gaps and

the angles of the impeller blades, thus minimizing turbu-

lence and vortex formation, and using particle image

velocimetry and flow visualization, and monitoring the

results with in vitro testing of blood parameters, such as

hemolysis testing. Consequently, an important array of

methodologies should actually be available for monitoring

the anticoagulation and antiaggregation status of patients

to provide the correct management.

Another delicate issue is the measurement and control of

blood pressure, even by means of Doppler testing per-

ipherally, in patients without a detectable pulse. To date,

experience with these pumps in a limited patient popu-

lation has suggested an increased incidence of hemor-

rhagic stroke [25]. This may be related to the difficulty of

properly monitoring blood pressure due to absent or

dampened pulses imparted by this technology. If hyper-

tension is present but not easily measurable, inadequate

pharmacologic control of blood pressure may result, in

turn subjecting these patients to an increased risk of

hypertensive hemorrhagic stroke. An additional concern

is that the altered stress on the aortic valve may result in

valve leaflet fusion and aortic insufficiency and stenosis.

This has been particularly reported in patients with

pulsatile assist pumps, but also seen in patients with

continuous-flow pumps.

Our initial experience with the 18 patients described here

has been favorable. We are encouraged by our results

with the use of the redesigned HeartMate II in the

treatment of patients with advanced heart failure. We

believe that this small, axial-flow blood pump is durable

and well tolerated and will offer an extended, improved

quality of life for critically ill heart failure patients of

varying size and clinical status.

AcknowledgementsThe authors are grateful to Mr Carlo Contento and all the

Cardio-Perfusion Team for the enormous contribution in

the technical and clinical management of VAD patients.

References1 Butler KC, Thomas D, Antaki J, Borovetz H, Griffith B, Kameneva M, et al.

Development of the Nimbus/Pittsburgh axial flow left ventricular assistsystem. Artif Organs 1997; 21:602–610.

2 Thomas DC, Butler KC, Taylor LP, Le Blanc P, Rintoul TC, Petersen TV,et al. Progress on development of the Nimbus-University of Pittsburgh axialflow left ventricular system. ASAIO J 1998; 44:M521–M524.

3 Butler KC, Dow JJ, Litwak P, Kormos RL, Borovetz HS. Development of theNimbus/University of Pittsburgh innovative ventricular assist system. AnnThorac Surg 1999; 68:790–794.


4 Griffith BP, Kormos RL, Borovetz HS, Litwak K, Antaki JF, Poirier VL, ButlerKC. HeartMate II left ventricular assist system: from concept to first clinicaluse. Ann Thorac Surg 2001; 71:116–120.

5 Song X, Trockmorton AL, Untaroiu A, Patel S, Allaire PE, Wood HG, OlsenDB. Axial flow blood pumps. ASAIO J 2003; 49:355–364.

6 Litwak P, Poirier V, Butler K. In vivo development tests of an axial flow pumpbased LVAS. Artif Organs 1999; 23:678.

7 Burgreen GW, Antaki JF, Wu J, le Blanc P, Butler KC. A computational andexperimental comparison of two outlet stators for the Nimbus LVAD.ASAIO J 1999; 45:328–333.

8 Slater JP, Rose EA, Levin HR, Frazier OH, Roberts JK, Weinberg AD, OzMC. Low thromboembolic risk without anticoagulation using advanced-design left ventricular assist devices. Ann Thorac Surg 1996; 62:1321–1328.

9 Rose EA, Levin HR, Oz MC, Frazier OH, Macmanus Q, Burton NA, LefrakEA. Artificial circulatory support with textured interior surfaces. Acounterintuitive approach to minimizing thromboembolism. Circulation1994; 90 (Part 2):II87–II91.

10 Konishi H, Antaki JF, Boston JR, et al. Controller for an axial flow pumpLVAD [abstract]. Am Soc Artif Intern Organs 1994; 23:35.

11 Konishi H, Antaki JF, Amin DV, Boston JR, Kerrigan JP, Mandarino WA, et al.Controller for an axial flow blood pump. Artif Organs 1996; 20:618–620.

12 Burke DJ, Burke E, Parsaie F, Poirier V, Butler K, Thomas D, et al. TheHeartMate II. Design and development of a fully sealed axial flow leftventricular assist system. Artif Organs 2001; 25:380–385.

13 Hausmann H, Topp H, Siniawski H, Holz S, Hetzer R. Decision making inend stage coronary artery disease; revascularization or hearttransplantation? Ann Thorac Surg 1997; 64:1296–1302.

14 Kron IL, Green GR, Cope JT. Surgical relocation of the posterior papillaremuscle in chronic ischemic mitral regurgitation. Ann Thorac Surg 2002;74:600–601.

15 Potapov EV, Stepanenko A, Dandel M, Kukucka M, Lehmkuhl HB, Weng Y,et al. Tricuspid incompetence and geometry of the right ventricle aspredictors of right ventricular funtion after implantation of a left ventricularassist device. J Heart Lung Transplant 2008; 27:1275–1281.

16 Maher T, Butler K, Poirier V, Gernes DB. HeartMate left ventricular assistdevices: a multigeneration of implanted blood pumps. Artif Organs 2001;25:422–426.

17 HeartMate II Pilot Trial Investigators.18 Frazier OH, Delgado RM III, Kar B, Patel V, Gregoric ID, Myers TJ. First

clinical use of redesigned HeartMate II left ventricular system in the UnitedStates. Tex Heart Inst J 2004; 31:157–159.

19 Pagani FD, Strueber M, Naka Y, et al. Initial multicenter clinical results withthe HeartMate II axial flow left ventricular assist device [abstract]. J HeartLung Transplant 2005; 24 (Suppl I):74.

20 Conte JV, Miller LW, Pagani FD, Russell SD, et al. One year follow-up with acontinuous flow LVAD as a bridge to heart transplantation [abstract].J Heart Lung Transplant 2008; 27 (2S):S244.

21 Strueber M, Sander K, Lahpor J, Ahn H, Litzler PY, Drakos SG, et al.HeartMate II left ventricular assist device; early European experience. Eur JCardio-thorac Surg 2008; 34:289–294.

22 Hoshi H, Shinshi T, Takatani S. Third-generation blood pumps withmechanical noncontact magnetic bearings. Artif Organs 2006; 30:324–338.

23 Miyamoto AT, Tanaka S, Matloff JM. Right ventricular function during leftheart bypass. J Thorac Cardiovasc Surg 1983; 85:49–53.

24 Patel ND, Weiss ES, Schaffer J, Ullrich SL, Rivard DC, Shah AS, et al. Rightheart dysfunction after left ventricular assist device implantation: acomparison of the pulsatile HeartMate I and the axial-flow HeartMate IIdevices. Ann Thorac Surg 2008; 86:832–840.

25 Frazier OH, Gemmato C, Myers TJ, Gregoric ID, Radovancevic B, LoyalkaP, Kar B. Initial clinical experience with the HeartMate II axial-flow leftventricular assist device. Tex Heart Inst J 2007; 34:275–281.


Heartmate II axial-flow left ventricular assist system: management, clinical review and personal...

Documents

Transcript of Heartmate II axial-flow left ventricular assist system: management, clinical review and personal...