Mechanical support of the heart

CARDIAC ANAESTHESIA

Mechanical support of the heart

Learning objectives After reading this article, you should be able to: C summarize the indications for mechanical support C classify ventricular assist devices into three types C list the main specific anaesthetic concerns associated with ventricular assist device implantation

Barbora Parizkova I Gavin Wright Emma J Birks

Abstract

The earliest forms of mechanical cardiac support were cardiopulmonary bypass, introduced in 1953 and used for cardiopulmonary support during cardiac surgery, and intra-aortic balloon counter pulsation (IABP), introduced in 1962 and used for temporary partial haemodynamic support and to improve coronary perfusion. The first left ventricular assist device (LVAD) was implanted by Cooley in 1969. Ventricular assist devices (VADs) enable end-organ perfusion in the setting of heart failure. VADs are used as a ‘bridge to recovery’ to support patients after myocardial infarction and for those with non-ischaemic cardiomyopathy or those who cannot be weaned from cardiopulmonary bypass. VADs are mainly used as a temporary measure to allow patients to survive and improve their overall condition while they wait for heart transplantation (bridge to transplant; BTT). Destination therapy (as an alternative to transplantation) is of growing importance and is expected to be increasingly so in the future.

Mechanical support of the heart can be offered to patients who are refractory to pharmacological treatment, therapy for coronary or valvular disease or resynchronization therapy. Ventricular assist devices enable end-organ perfusion in the setting of heart failure. This can be temporary (as a bridge to recovery or transplantation) or permanent (destination therapy). Devices can be extracorporeal or implanted, and generated flows can be pulsatile or non-pulsatile. Implantation usually requires sternotomy with or without cardiopulmonary bypass, but percutaneous devices exist. Cardiostable anaesthesia with inotropic support is vital. Problems include bleeding versus thrombosis, high pulmonary vascular resistance, right heart failure and late infections. Transoesophageal echocardiography can be used to detect potential right-to-left atrial shunts, aortic regurgitation and cannula malposition, and to monitor filling and right ventricular function after implantation. In the future, total implantability of the devices, including the power source, is likely to occur. Eventually, they are likely to become a widespread alternative to transplantation.

Keywords Bridge to transplantation; destination therapy; heart failure;

Devices

mechanical support; ventricular assist devices

VADs are available as extracorporeal and implantable types. The available devices can be classified into three types: centrifugal pumps, volume-displacement pumps and axial-flow pumps.

Royal College of Anaesthetists CPD Matrix: 3G00

Extracorporeal devices The most commonly used are centrifugal pumps that produce non-pulsatile flows of up to 8 litres/minute. These are used for temporary left, right or biventricular support either as a bridge to decision in moribund patients, for patients with post-cardiotomy heart failure, for temporary right ventricular support, or for posttransplant allograft failure. They can be used with an oxygenator for extracorporeal membrane oxygenation. Heparin is required during use. The Levitronix VAD is an example of a centrifugal pump. Extracorporeal pulsatile pumps include an inflow valve (bioprosthetic or mechanical), which allows unidirectional flow into the device and prevents regurgitation during mechanical systole, and an outflow valve to prevent regurgitation during mechanical relaxation. The Thoratec biventricular assist device (Thoratec Corp., Pleasanton, CA, USA) (Figure 1) is an example of an extracorporeal pulsatile pumps. They require long-term anticoagulation with warfarin with or without aspirin.

Introduction Heart failure is implicated in approximately 20% of all hospital admissions among people older than 65. It has multiple causes, including ischaemic heart disease, cardiomyopathy, valvular heart disease and congenital heart disease. Cardiac transplantation is the first-line treatment for heart failure in patients with New York Heart Association (NYHA) class IV symptoms, but few donor organs are available. Mechanical support of the heart can be offered to patients who are refractory to pharmacological treatment, therapy for coronary or valvular disease or resynchronization therapy. Stem cell and gene therapy both offer promise for the future.

Barbora Parizkova MD is a Consultant Anaesthetist and Intensivist at the Papworth Hospital NHS Foundation Trust, Papworth Everard, Cambridge, UK. Conflicts of interest: none declared.

Total artificial hearts Total artificial hearts are generally volume-displacement devices, generating pulsatile flow through the filling and compression of an internal chamber with air. During implantation of such a device, the patient’s own left and right ventricles are removed and the device is inserted in the same anatomical location as the heart. Examples of total artificial hearts include the CardioWest

I Gavin Wright MB ChB FCA(SA) is a Consultant Anaesthetist and Intensivist at the Royal Brompton and Harefield NHS Trust, London, UK. Conflicts of interest: none declared. Emma J Birks MRCP PhD is a Professor of Medicine and Director of Heart Failure, Transplantation and Mechanical Support at the University of Louisville, USA. Conflicts of interest: none declared.

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Please cite this article in press as: Parizkova B, et al., Mechanical support of the heart, Anaesthesia and intensive care medicine (2015), http:// dx.doi.org/10.1016/j.mpaic.2015.07.003

CARDIAC ANAESTHESIA

passive magnets and a hydrodynamic thrust bearing. The inflow cannula is integrated with the device itself, which is implanted in the pericardial cavity and provides a flow of up to 10 litres/ minute. Most VADs require cardiac surgery for implantation. New percutaneous devices exist. The smallest and least invasive is the Impella pump (Abiomed). It is inserted in the femoral artery and advanced retrogradely into the left ventricle. It aspirates blood from the left ventricle and expels it into the ascending aorta using a microaxial-flow pump located on the distal end of a catheter. Another percutaneous VAD is the TandemHeart (CardiacAssist), which is an extracorporeal centrifugal pump whose inflow catheter is placed percutaneously in the left atrium through a trans-septal approach and whose outflow cannula is placed in the femoral artery. Both devices require systemic anticoagulation to prevent device clotting. The Cardiobridge device (GmbH, Germany) is sited percutaneously in the descending aorta, coronary steal being a theoretical risk. Currently, most of the systems in clinical use are operated in a partial support mode, using a fixed speed mode. Continuous flow is well tolerated. Pulsatility, by virtue of aortic ejection, returns once the heart recovers some function. Before this, a pulsatile arterial trace can exist as ventricular contraction boosts flow through the VAD.

Figure 1 A patient with a Thoratec biventricular assist device (Thoratec Corp., Pleasanton, CA, USA) who underwent intra-abdominal surgery. The device consists of a single-chamber pump with mechanical inflow and outflow valves. Alternating positive and negative air pressure within a flexible sac moves blood through the pump and causes pulsatile flow. A flow rate of 7 litres/minute is possible. The anaesthetist has to consider the effect of surgical positioning (here, lifting of the device with white tapes) on venous return, because an adequate circulating blood volume is an important factor for maintaining device output.

Indications and contraindications for recipients of ventricular assist devices LVADs (as a BTT) are indicated in transplant candidates who are in NYHA class IV or IIIB heart failure despite optimal medical therapy and cannot wait for a donor heart. Patients often require inotropic or IABP support. LVAD implantation can also be indicated in patients with congestive heart failure and elevated pulmonary artery pressures or renal insufficiency likely to reverse after a period of VAD support. Destination therapy candidates are ineligible for heart transplantation. The continuous-flow pumps have better survival rates than pulsatile pumps both when used as a bridge in patients who are waiting for transplantation and as destination therapy. Primary graft dysfunction in heart transplant recipients is an indication for a temporary VAD. Patients with heart failure have low stroke volumes that make them dependent on preload and heart rate to maintain cardiac output. Increasing preload does not improve cardiac performance in these patients because their hearts are often on the flat or even descending limb of the Starling curve, and preload reserve is exhausted. Possible contraindications include severe infection, established renal failure, severe liver impairment, severe pulmonary dysfunction and non-compliance. Severe liver impairment often results in coagulopathy, which increases postoperative bleeding. Patients with heart failure have high levels of circulating catecholamines, leading to down-regulation of b-receptors and a2-receptors. Chronic elevation in left ventricular end-diastolic pressure leads to development of increased pulmonary vascular resistance (PVR). The most important implications of chronic heart failure for anaesthesia are elevated PVR, impaired right ventricular function, coagulopathy and renal insufficiency. Cardiovascular decompensation during induction or maintenance of

device (SynCardia Systems, Tucson, USA) and the AbioCor (Abiomed, Danvers, Massachusetts, USA). Implantable devices These are designed for longer term use and are smaller pumps, allowing patients to have better mobility and quality of life. They generally have lower infection rates, although they still require a power source through a percutaneous driveline, which can be a source of infection. The HeartMate XVE (Thoratec), a very effective pulsatile implantable pump, was available as a bridge to transplantation, and it was also approved for destination therapy. However, its short durability (1e2 years before requiring replacement) along with the high rate of complications restricted the wide adoption of this therapy for patients with end-stage heart failure. There are now two types of continuous-flow pumps: axial and centrifugal. All pumps utilize an impeller to generate flow. The axial pumps include the HeartMate II (Thoratec) (Figure 2) the Jarvik 2000 FlowMaker (Jarvik Heart, New York, NY, USA), and the INCOR (Berlin Heart AG, Berlin, Germany). The spinning of the impeller draws blood from the inflow orifice or cannula through the device to the outflow cannula. The HeartMate II is an axial-flow pump providing flows of 3e10 litres/minute between 8000 and 12,000 rpm. The device measures 4 cm in diameter and 6 cm in length and has a mass of 375 g. The centrifugal pumps include DuraHeart (Terumo Cardiovascular Systems, Ann Arbor, MI, USA), and Heartware (Heartware Inc., Miami, FL, USA). Heartware (Figure 3) is a centrifugal pump with only one moving part, the impeller, and no mechanical bearings. The impeller is suspended within the pump housing through a combination of

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Please cite this article in press as: Parizkova B, et al., Mechanical support of the heart, Anaesthesia and intensive care medicine (2015), http:// dx.doi.org/10.1016/j.mpaic.2015.07.003

CARDIAC ANAESTHESIA

Figure 2 The Heartmate II left ventricular assist device.

Preoperative assessment and induction

anaesthesia can occur with vasodilatation, resulting in hypotension and decreased diastolic coronary perfusion. Decreases in heart rate are dangerous because patients cannot compensate by increasing stroke volume.

Preoperative assessment should evaluate cardiac status, renal function, hepatic function, coagulation status and current drug

Figure 3 The Heartware left ventricular assist device.

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CARDIAC ANAESTHESIA

therapy. The anaesthetist has to be able to manage cardiac decompensation before VAD insertion, and right ventricular failure and severe bleeding after cardiopulmonary bypass. Antibiotic prophylaxis is necessary. Standard cardiac haemodynamic monitoring is used, including a pulmonary artery catheter to assess the PVR for possible administration of pulmonary vasodilator agents when weaning from bypass. Continuous cardiac output catheters or continuous mixed venous oxygen saturation monitoring catheters are available for determining cardiac output. Rapid haemodynamic decompensation can occur if there is a sudden decrease in left ventricular preload or increase in left ventricular afterload, or if PVR or heart rate increase from surgical or intubation stress, hypoxia or hypercapnoea. There is some evidence that volatile anaesthetics might be beneficial in that they confer some measure of protection against ischaemicreperfusion injury. The anaesthetist should maintain inotrope and vasoactive drug infusions. Additionally, norepinephrine, phenylephrine or metaraminol can be used to maintain preload and afterload at suitable levels, while allowing an adequate depth of anaesthesia. Perioperative bleeding can be due to hepatic impairment, extensive surgery, redo surgery or the effects of cardiopulmonary bypass. Perioperative use of antifibrinolytic agents (e.g. tranexamic acid) and low-dose vitamin K can help. Administration of fresh frozen plasma, platelets, blood or cryoprecipitate is guided by the coagulation profile (laboratory tests and thromboelastogram). All fluids should be warmed, and a warming blanket and warming mattress need to be used to avoid hypothermia. Common problems after bypass are right-sided heart failure (20% of patients), vasodilatory shock and cardiac arrhythmias (as a result of a collapsed left ventricle, which occurs if the pump is running too high or the right ventricle is not filling the left). Right ventricular failure secondary to pulmonary hypertension can be treated with inhaled nitric oxide (NO) or epoprostenol, isoprenaline or phosphodiesterase inhibitors, for example milrinone or sildenafil.

Transoesophageal echocardiography evaluation during insertion of a ventricular assist device C

C C C

C

C C

Box 1

embolization and impaired right ventricular function. Air entrainment by the VAD before chest closure can be detected and should be avoided. After bypass, TOE is crucial for monitoring right ventricular function, to guide filling (a neutral ventricular septal position is indicated) and for increasing the pump speed, particularly on closing the chest. Problems associated with these devices remain infection (particularly driveline infection), bleeding (particularly gastrointestinal and cerebral bleeding), right ventricular failure, thromboembolism (particularly pump thrombosis) and dependence on a power source. However, these complications are decreasing and in the future are likely to decrease further, and full implantability of the devices is likely to occur. They are likely to become a widespread alternative to transplantation. A FURTHER READING Birks EJ, Tansley PD, Hardy JN. Left ventricular assist device and drug therapy for the reversal of heart failure. N Engl J Med 2006; 355: 1873e84. El-Magharbel I. Ventricular assist devices and anesthesia. Semin Cardiothorac Vasc Anesth 2005; 9: 241e9. Feldman D, Pamboukian SV, Teuteberg JJ, et al. International Society for Heart and Lung Transplantation. The 2013 International Society for Heart and Lung Transplantation Guidelines for mechanical circulatory support: executive summary. J Heart Lung Transplant 2013; 32: 157e87. Gaunt A. Anaesthesia for cardiothoracic transplantation and ventricular assist devices. Anaesth Intensive Care Med 2006; 7: 317e20. Hirsch DJ, Cooper Jr JR. Cardiac failure and left ventricular assist devices. Anesthesiol Clin North America 2003; 21: 625e38. Mets B. Anesthesia for left ventricular assist device placement. J Cardiothorac Vasc Anesth 2000; 14: 316e26. Tan LH, Cokis C. Anaesthesia for implantation of the Jarvik 2000 Flowmarker LVAD. Anaesth Intensive Care 2006; 34: 746e52.

Transoesophageal echocardiography Transoesophageal echocardiography (TOE) is a very important monitoring and diagnostic tool (Box 1). After intubation, TOE is used to assess cardiac function, particularly of the right ventricle because of a significant incidence of post-implantation right ventricular failure as it is the unsupported ventricle. A right ventricular fractional area change of less than 20% renders patients more likely to have right ventricular failure when LVAD support is started. If a patent foramen ovale or atrial septal defect is found, this needs to be repaired because potentially severe right-to-left shunting could occur after LVAD activation. The absence of aortic regurgitation needs to be established because ventricular unloading increases the regurgitant volume. The presence of mitral stenosis contraindicates placement of a left ventricular apical cannula; therefore, transmitral or left atrial cannulation should be carried out instead. Mitral regurgitation usually decreases with LVAD placement. TOE can be used to monitor de-airing. Inadequate de-airing can lead to coronary

ANAESTHESIA AND INTENSIVE CARE MEDICINE --:-

Ventricular function, size and regional wall motion abnormalities, especially of the unsupported (right) ventricle Presence of intracardiac thrombi Valve anatomy and function, especially aortic valve competence Presence of patent foramen ovale, atrial septal defect or ventricular septal defect or other shunts Examination of cannula position e anatomically correct orientation, free of obstruction Adequate ventricular unloading Ventricular assist device low flows due to hypovolaemia, failure of unsupported ventricle, inflow or outflow cannula obstruction, pericardial tamponade, cannula malposition, pulmonary artery embolism

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Ó 2015 Published by Elsevier Ltd.

Please cite this article in press as: Parizkova B, et al., Mechanical support of the heart, Anaesthesia and intensive care medicine (2015), http:// dx.doi.org/10.1016/j.mpaic.2015.07.003