Review Article
Electrical and mechanical support in advanced
heart failure
Rationale and feasibility of a combined management strategy
F. Duru
1, R. Candinas
1, M. Lachat
2, M. Rahn
2, G. Noll
1, T. F. Lu
¨ scher
1and
M. Turina
21Cardiology and2Cardiovascular Surgery, Cardiovascular Center, University Hospital, Zurich, Switzerland
Introduction
Treatment for congestive heart failure has improved markedly in recent years, particularly with the introduc-tion of newer pharmacological regimens. However, in patients with severely depressed left ventricular dysfunc-tion caused by different aetiologies, prognosis still remains poor despite best medical management[1,2]. Heart transplantation is an accepted therapeutic option for the management of patients with end-stage heart failure, but a growing number of these patients who are on the waiting list for heart transplantation die due to a shortage of suitable donor grafts[3,4].
The worsening supply–demand imbalance over the years has stimulated a search for alternative means of ‘bridge to transplantation’. Given the fact that about one-third of all deaths occur suddenly, use of implant-able cardioverter defibrillators (ICDs) were considered in the management of these patients[5]. However, there is considerable concern that death from terminal pump failure may nullify the survival benefit conferred by an ICD. On the other hand, arrhythmic death may occur in patients with mechanical pumps, which may justify the strategy of using combined electrical and mechanical support as a bridge to transplantation. In this review, we discuss the rationale and feasibility of this combined clinical management strategy.
Electrical support for bridge to
transplantation
The implantation of an ICD for the management of patients with end-stage heart failure and life-threatening ventricular arrhythmias who are waiting for cardiac transplantation has been a controversial issue (Table 1). ICD therapy can be justified given the fact that as many as 25%–40% of patients die suddenly while waiting for a donor heart[6,7] and recipients of these devices have a high incidence of appropriate shocks that occur very early after implantation[8]. Several investigators could demonstrate that ICD implantation prevented sudden death in patients with end-stage heart failure until a donor heart became available[9–14]. In a case control study, Grimm et al. compared 30 patients who survived sudden cardiac death and subsequent ICD implantation with a matched group of 30 patients who had no ICD implanted for various non-medical reasons[15]. During the median waiting time to transplantation of 5·7 months, seven of 30 non-ICD patients (five sudden cardiac deaths) died, whereas there was only one non-sudden death among 30 ICD recipients.
Although ICD implantation prevents sudden death in high-risk patients with very poor ventricular function, the effect on long-term survival may be limited by the high rate in non-sudden cardiac mortality as the waiting list and waiting time to transplantation lengthens. Sweeney et al. analysed the effect of ICD therapy as compared to antiarrhythmic drugs and no antiarrhyth-mic treatment on total mortality and mode of cardiac death in 291 patients evaluated for heart transplanta-tion[16]. Sudden death rates were lowest in the ICD group at 12 months in this study. However, total mor-tality was not different among the three treatment groups. This and other observations have suggested that ICD therapy converts the mode of death from sudden to
Key Words: Heart failure, implantable cardioverter
defibrillator, mechanical support, assist device, blood pumps, transplantation.
Revision submitted 30 July 2001, accepted 1 August 2001, and published online 14 January 2002.
Correspondence: Fırat Duru, MD, Division of Cardiology,
Cardio-vascular Center, University Hospital, Ra¨mistr. 100 CH-8091, Zurich, Switzerland.
a non-sudden cardiac death if transplantation cannot be performed soon[17–19].
More recent data indicate that patients who are most likely to benefit from receiving an ICD were also those at highest overall risk of death. Patients in the highest risk group were older, had poor left ventricular systolic function, and had poor functional status (NYHA class III or IV)[20]. Likewise, patients with very poor left ventricular function appear to benefit from ICD therapy, although this benefit seems to be restricted to the early follow-up period[5,21]. Improvements in ICD technology (enhanced tachycardia discrimination capabilities, antitachycardia pacing and dual-chamber antibradycardia functions, etc.) may account for improved ICD efficacy reported in more recent studies.
Mechanical support as a bridge to
transplantation
The concept of mechanical circulatory support as a bridge to transplantation in patients with end-stage heart failure has gained widespread interest in recent years. While this form of temporary therapy may be lifesaving in some patients until a donor heart becomes available, there is also evidence that these devices may be useful in providing myocardial functional recovery in some forms of heart disease[22–25].
Some mechanical circulatory support devices are used in the ‘acute’ setting[26]. Intra-aortic balloon pumps, centrifugal pumps, roller pumps, and veno-arterial
extracorporeal membrane oxygenation can be classified in this category. Since long-term support using these devices often results in host deterioration, candidates for cardiac transplantation are best managed with ‘long-term’ devices. These pumps allow increased patient mobility; nevertheless, they are more expensive and more complicated to install[26]. Clinically available ventricular assist devices provide either extracorporeal or intracorporeal circulatory support (Table 2). Ventricular assist devices for long-term support may also be classified according to whether they provide pulsatile or continuous flow. Pulsatile pumps can pro-duce physiological pulsatile flow, driven by pneumatic or electric power. They include the HeartMate (Thermo Cardiosystems, Inc, Woburn, MA, U.S.A.), Novacor (Baxter Healthcare Corporation, Oakland, CA, U.S.A.), and Thoratec pump (Thoratec Laboratories, Berkeley, CA, U.S.A.). Centrifugal pumps and axial flow pumps are classified as non-pulsatile or continuous flow pumps. Recently available continuous flow pumps for long-term support include the DeBakey pump (MicroMed Technology, Inc., Houston, TX, U.S.A.), the Jarvik 2000 Heart (Jarvik Heart Inc, New York, NY, U.S.A.), and the HeartMate-II ventricular assist device (Figs 1–4). The first clinical experiences with these devices have demonstrated that they provide promising measures of mechanical support in advanced heart failure[27–36].
Implantable ventricular assist devices offer certain advantages over extracorporeal devices[37,38]. A major advantage is the ability for the patient to be discharged and followed-up in an outpatient setting. However, small patient size has been a limitation for the implan-tation of the earlier generation intracorporeal devices. In contrast, extracorporeal devices can be placed in much smaller patients and without the need for cardio-pulmonary bypass. One particular advantage of extra-corporeal devices is the capability to provide left, right, or biventricular support. The recent introduction of miniaturized implantable ventricular assist devices with continuous flow pumps, such as the MicroMed DeBakey ventricular assist device, gives a treatment hope to those with smaller body sizes. Since pumping of blood does not rely on the expulsion of a certain stroke volume from a chamber, these devices are not as bulky as pulsatile pumps. These compact devices have low power
Table 1 Some of the studies reporting ICD use as a bridge to transplantation
Author Patients n Age (years) LVEF (%) Follow-up (months) ICD discharge Patient outcome Transplant Death Bolling[9] 14 508 137 8·5 12 (86%) 5 2 Jeevanandam[10] 16 5111 153 54 15 (94%) 12 0 Lorga-Filho[11] 19 5411 2210 65 12 (71%) 17 1 Saxon[13] 15 529 205 1112 9 (60%) 7 0 Grimm[15] 30 549 155 10·4 26 (87%) 19 1
Sweeney[16] 59 4911 189 36 n.a. n.a. 5 LVEF=left ventricular ejection fraction; n.a.=not available.
Table 2 Some of the currently available extracorporeal and intracorporeal assist devices
Extracorporeal
Thoratec VAD system Pulsatile Pneumatic Abiomed BVS-5000 VAD Pulsatile Pneumatic Intracorporeal
Novacor Pulsatile Electric
HeartMate
HeartMate IP Pulsatile Pneumatic HeartMate VE Pulsatile Electric Heartmate-II Non-pulsatile Axial flow pump MicroMed DeBakey VAS Non-pulsatile Axial flow pump Jarvik 2000 Heart Non-pulsatile Axial flow pump
requirements and could possibly be more durable and less expensive, and can be used as a bridge to myocardial recovery, as well as to transplantation or long-term support[29]. The effect of non-pulsatile flow on organ function and on the hormonal circadian is still
debated[39–43]. However, it has recently been demon-strated that, despite non-pulsatile flow produced with the turbine of the DeBakey ventricular assist device, flow pulsatility in the peripheral vessel increases continu-ally after ventricular assist device implantation possibly due to contractions of the unloaded left ventricle and the partially recovered right ventricle[31].
Rationale of the combined electrical and
mechanical support strategy
Among ICD recipients, candidates for transplantation have a shorter time to the first appropriate discharge as compared to other ICD patients[8], and up to 94% of the patients with end-stage heart failure receive appropriate shocks during the waiting period[5]. Because of haemo-dynamic instability and given the high incidence of non-sudden cardiac death in ICD recipients if time to transplantation is prolonged, implantation of a ventricu-lar assist device may also be required in these patients. Although one may suggest that an implanted ventricular assist device may protect a patient from immediate arrhythmogenic cardiac death, the true nature of the arrhythmic problem may go unrecognized and may
Outflow graft Inlet cannula
Figure 1 The MicroMed DeBakey VAD is a miniatur-ized, auxiliary heart pump (93 g in weight) designed to provide increased blood flow to patients who suffer from end-stage heart failure. The components of the system consist of the titanium axial-flow pump, a titanium inlet cannula connecting the apex of the left ventricle to the pump, an outflow graft connecting the pump to the ascend-ing aorta, an ultrasonic flow probe placed around the outflow conduit, an external controller unit, percutane-ous cables connecting the flow probe and the pump to the controller, and an external clinical data acquisition system. Blood flow Flow tube Inducer/impeller Diffuser Stator housing Motor stator Flow straightener
Figure 2 The MicroMed DeBakey axial flow pump is driven by a direct current (DC) motor stator that is contained in the stator housing and moves only the inducer/impeller component. The pump (spinning at 7500 to 12 500 rpm) is capable of generating flows in excess of 10 l . min1. Operating parameters of the pump, such as pump speed, flow rate, power usage and remaining battery life can be monitored by the controller, which is a rela-tively small external device connected to the pump and the flow probe by percutaneous cables, and provides mobilization of the patient.
Figure 3 The schematic drawing of the Jarvik 2000 Heart. This device is an axial flow impeller pump weighing 90 g which is implanted into the apex of the failing left ventricle. A vascular graft conveys blood to the descending thoracic aorta, as seen in the schema. The impeller spins at 8000 to 12 000 rpm, delivering a systemic blood flow of 3–8 l . min1, depending on the systemic vascular resist-ance. The power cable is connected percutaneously to an external portable controller and battery.
eventually lead to lethal consequences[44]. Therefore, a combined electrical and mechanical support strategy may be justifiable in the management of a selected group of patients with end-stage heart failure.
There are reports describing simultaneous use of an ICD and a ventricular assist device in patients with advanced heart failureTable 3. Skinner et al. reported
the use of a HeartMate left ventricular assist device for the first time, in a 51-year-old man with cardiogenic shock, which was implanted 5 years after implantation of an ICD system with epicardial patch electrodes[45]. This patient successfully received a transplant after 54 days of circulatory support. Recently, Deng et al. reported the Mu¨nster experience with the ventricular assist device–ICD combination, which is the only patient series published so far[44]. Ten patients had undergone ventricular assist device implantation either after or before implantation of an ICD. Among these patients, three were successfully transplanted, five died (multi-organ failure: three, cerebrovascular accident: one, cachexia: one), and two were still on ventricular assist device support. More recently, Ankersmit reported the combined use of an ICD and a biventricular assist device (Thoratec) as a successful bridge to transplantation in a patient with sarcoidosis and medically intractable heart failure[46]. All these reports concluded that combination therapy of ventricular assist device and ICD is techni-cally feasible and may be required in certain situations. In our experience, as well, a continuous flow ventricular assist device may be used successfully in an ICD recipi-ent. Figure 5 shows the chest X-ray of a patient with advanced heart failure and life-threatening ventricular tachyarrhythmias who underwent subsequent implanta-tion of a transvenous ICD system (CPI Ventak Mini III and an active fixation endocardial electrode, Guidant Corporation, St Paul, MN, U.S.A.) and a MicroMed DeBakey axial-flow ventricular assist device at our insti-tution. This observation may have important clinical implications since many advantages may be associated with these compact pumps with axial flow design.
Potential interactions between implanted
ICD and ventricular assist device systems
Possible theoretical interactions between various pulsa-tile and non-pulsapulsa-tile ventricular assist devices and ICD
TETS Power Oscillator Controller Battery TETS Coils
Figure 4 The schematic drawing depicts the trans-cutaneous HeartMate-II. This system utilizes an axial-flow pump and is totally implanted without percutaneous access. Additional implanted components include a con-troller, an energy transfer coil, and an optional emergency battery pack. External components include a matching energy transfer coil, a belt-worn system controller, and two rechargeable batteries. The pump impeller continu-ously rotates to generate the pressure to move blood from the left ventricle to the aorta. TETS=transcutaneous energy transmission system.
Table 3 Published reports of combined electrical and mechanical support in advanced heart failure
Author Patient Age Sex Etiology Initial implant ICD type VAD type
Skinner[45] 1 51 M CAD ICD epicardial Heartmate
Deng[44] 2 54 M DCM ICD epicardial Novacor
3 54 M DCM ICD transvenous+array Novacor
4 50 M DCM ICD transvenous Novacor
5 33 M DCM VAD transvenous Novacor
6 53 M CAD ICD epicardial Novacor
7 51 M CAD VAD transvenous Heartmate
8 50 M ARVD ICD transvenous Thoratec BiVAD
9 38 F PPCM ICD transvenous Novacor
10 57 M DCM ICD transvenous Novacor
11 58 M DCM ICD transvenous Novacor
Ankersmit[46] 12 30 M Sarcoidosis ICD transvenous Thoratec BiVAD
Duru 13 47 M DCM ICD transvenous MicroMed DeBakey
CAD=coronary artery disease; DCM=dilated cardiomyopathy; ARVD=arrhythmogenic right ventricular dysplasia; PPCM=peripartum cardiomyopathy; BiVAD=biventricular assist device.
systems include: (1) the effect of pump-induced motion artifacts on the arrhythmia sensing function of ICDs (which is programmed to be very sensitive to detect fine ventricular fibrillation), (2) the effect of the magnetic components of the pump on the ICD reed-switch (which may inactivate the antitachycardia functions of the device), and (3) possible alterations in defibrillation threshold. Our preliminary experience with the com-bined use of a pectorally implanted transvenous ICD system and the MicroMed DeBakey ventricular assist device suggests that neither device interferes with the function of the other. The ventricular assist device did not cause electrical artifacts in the sensing circuits of the ICD; there were no inappropriate ICD discharges, and the bradycardia pacing function performed properly. Likewise, the function of the ventricular assist device was not affected. The pump of the ventricular assist device is fully enclosed in a titanium flow tube that has been hermetically sealed and is protected against exter-nal defibrillation up to energy levels of 4000 Volts. Previous studies have shown that external application of
electrical energy does not adversely affect the volume sensing or pumping performance of paracorporeal ad intracorporeal ventricular assist devices. Our obser-vations were in accordance with the three previously published reports on technical feasibility of combined electrical and mechanical support therapy albeit using a different mechanical pump.
Conclusion and future perspectives
In the last two decades, we have observed a remarkable evolution in the field of electrical therapy of ventricular tachyarrhythmias. In parallel to the advances in tech-nology, the well-established clinical efficacy of ICDs have dramatically changed their use from a measure of last resort to first-line therapy in patients with life-threatening arrhythmias. A similar technical evolu-tion has also occurred in mechanical support devices for circulatory assistance. There are currently some pulsatile and non-pulsatile cardiac assist devices, which are mostly intended for use as a bridge to heart transplan-tation in patients with end-stage heart failure. However, since the supply of donor hearts is limited and the number of patients with advanced heart failure can be expected to increase in the years to come, the investiga-tors are targeting development of devices for long-term or permanent support. This requires manufacture of devices with a small design that will allow patient comfort and mobility without compromising safety.Clinical evidence from preliminary reports suggests that electrical and mechanical support devices provide added benefits in the management of patients with advanced heart failure. The combination of an axial– flow ventricular assist device and a pectorally implanted transvenous ICD system has been shown to be a feasible strategy for this purpose. However, the impact of com-bination therapy on survival has to be investigated in future studies. Development of a single device combin-ing a mechanical pump with the capability of delivercombin-ing pacing and high voltage shock therapies represents the next logical step in the management of patients with advanced heart failure. Technological advances may enable construction of a totally implantable com-bined electrical and mechanical support system in the foreseeable future.
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