Mechanical support for heart failure 2C04 3C00

Transcription

1 The Intensive Care Society 2013 Mechanical support for heart failure 2C04 3C00 K Salaunkey, J Parameshwar, K Valchanov, A Vuylsteke Critically ill patients at extremes of physiology may benefit from mechanical support for heart failure and intensive care practitioners should be knowledgeable about these options. In this article we will discuss the mechanical support for critically ill patients in heart failure. Referral to a specialist centre should be considered early for maximal patient benefit. Keywords: heart failure; intra aortic balloon pump; extracorporeal membrane oxygenation; mechanical circulatory support; left ventricular assist device Introduction The definition of heart failure 1 has evolved over the years. The European Society of Cardiology and the American College of Cardiology/American Heart Association define advanced heart failure as a clinical syndrome manifested by the presence of the following symptoms despite optimal therapy: dyspnoea of NYHA class III or IV severity, episodes of fluid retention, severely impaired functional capacity (six-minute walk <300 meters, peak oxygen consumption <12 to 14 ml/kg/m 2 ), objective evidence of severe cardiac dysfunction (left ventricular ejection fraction <30%), pseudo-normal or restrictive left ventricular filling pattern on Doppler studies (pulmonary wedge capillary pressure > 16 mm Hg or right atrial pressure >12 mm Hg), hospitalisations related to heart failure (more than one in the past six months) elevated blood levels of natriuretic peptides. Epidemiology Heart failure affects over 900,000 people in the UK with 60,000 new cases diagnosed per year. 2 It has an overall population prevalence of up to 3%, rising to 10% in the very elderly. Patients admitted with chronic advanced heart failure are relatively younger, have male preponderance, are dyslipidemic and have coronary artery disease, in comparison to patients admitted with acute decompensated heart failure. 3 Following a first hospital admission for heart failure, patients have a five-year mortality of 75%, which is worse than that for most forms of cancer. 4 Approximately 5% of congestive heart failure patients develop advanced heart failure (ACHF). 3 The typical ACHF patient is admitted to the intensive care unit (ICU) in the context of acute decompensated heart failure and is most commonly older than 70 years of age, has a history of heart failure, coronary artery disease and hypertension. There are equal numbers of men and women. Life expectancy after a diagnosis of heart failure has been improving 5 but the in-hospital mortality is as high as 4-7 %. 6 For the survivors, the risk of subsequent hospital readmission is high. Clinicians must now also consider the increasing number of young adults with grown-up congenital heart disease (GUCH) developing advanced heart failure needing intensive care. 7 Pathophysiology Several pathophysiological models have been proposed to explain the heart failure syndrome 8 but no single theory has done justice to the subject. The cardio-renal model proposed that sodium and water retention was caused by abnormal renal blood flow. The cardio-circulatory model proposed that low cardiac output and peripheral vasoconstriction were the primary problems. The neuro-humoral model attempted to explain the syndrome as a prolonged and pathological activation of several homeostatic and compensatory mechanisms in response to end-organ damage. Recently, immunological and genetic factors have been shown to affect susceptibility and severity. Ventricular remodelling and endothelial dysfunction are also features of this syndrome. 9 Pharmacological treatment The various pathophysiological models have led to the development of therapeutic strategies including diuretics, angiotensin-converting enzyme inhibitors, β-blockers and aldosterone antagonists. They act by preventing the progression of heart failure, improving symptoms, reducing the risk of hospitalisation and improving survival. 10,11 These treatment strategies are suitable for chronic heart failure patients but may not be applicable to the acutely decompensated patient needing intensive care. Admission to ICU Patients with acute or acute on chronic heart failure may require admission to ICU when cardiac output and tissue viability are compromised. In these situations, treatment is initially directed to increasing the cardiac output and correcting precipitating factors such as infection. The clinical management may comprise an array of modalities to improve blood flow and alleviate the symptoms of heart failure. The use of ultrafiltration, the administration of vasodilators, inotropes or a combination, are all very effective in reducing venous congestion and improving cardiac output. None of these therapies are curative 220 Volume 14, Number 3, July 2013 JICS

2 Balloon inflation in diastole Unassisted pressure trace IABP augmented pressure trace Diastolic augmentation Balloon Balloon deflation in systole Decrease in afterload with assisted systole Dicrotic notch Figure 1 Intra aortic balloon pump (IABP). IABP is inserted into the descending aorta and its balloon is inflated with helium during diastole, then rapidly deflated during systole. The first diagram shows inflation of the balloon in diastole, causing diastolic pressure augmentation resulting in improved coronary perfusion. The second picture shows deflation in systole, causing decreased afterload. The triggers for inflation and deflation of the balloon are preferably derived from the ECG but can also be derived from the arterial pressure trace. and are only suitable for a short period of time. In patients who deteriorate despite conventional therapy, mechanical support should be considered in selected cases. This allows the maintenance of tissue perfusion while awaiting a definitive solution. Cardiac transplantation Replacing the damaged heart by a new one, ie cardiac transplantation, is a possibility for some patients. The mismatch between the demand and availability of organs, the physiological conditions at presentation, and the waiting time makes this option unrealistic for many patients. Mechanical support is an immediate solution that can be used as a bridge to transplantation (with a few patients recovering while waiting). In some circumstances, mechanical support may be the only treatment offered (destination therapy). Other methods of promoting myocardial recovery (gene therapy, stem cell therapy) may also be used in the future on a platform of mechanical support. 12 Mechanical cardiovascular support History The development of cardiopulmonary bypass in the 1950s demonstrated that the circulation could be supported mechanically for short periods. In 1964, the National Institute of Health funded the artificial heart programme to promote interest in this nascent field. Michael DeBakey reported the first clinical use of a short-term device to support a patient post-cardiotomy until native heart function recovered 13 and this was closely followed by a similar report by Kantrovitz. 14 Classification of mechanical circulatory support (MCS) devices Mechanical circulatory support can be classified based on: the duration of support that can be provided (short or long term); the flow characteristics of the pump (pulsatile or continuous flow); the ventricle supported (right/left/ biventricular support); the pump driving mechanism (pneumatic/ electrical). Intra-aortic balloon counterpulsation The intra-aortic balloon pump (IABP) (Figure 1) was developed in the early 1960s. 15 It improves the ratio between oxygen demand and supply in the myocardium by causing systolic unloading and diastolic coronary blood flow augmentation. As a consequence, there is an increase in cardiac output, coronary perfusion, renal and splanchnic blood flow with a concomitant decrease in left ventricular (LV) wall stress, systemic vascular resistance, and pulmonary capillary wedge pressure. The IABP is commonly used in the management of cardiogenic shock, principally when recovering from cardiac surgery or acute myocardial infarction, while early use in heart failure has been reported as advantageous 16 and associated with better outcomes. 17,18 Recent evidence has challenged this with a large randomised controlled trial of IABP in acute cardiogenic shock failing to demonstrate any benefit. 19 Extracorporeal membrane oxygen (ECMO) Veno-arterial ECMO (VA ECMO) has been successfully used in the paediatric heart failure population. Its use in adult patients has been increasing in recent years. It offers temporary support until a decision is made between the options of longer-term mechanical support, cardiac transplantation, or withdrawal of therapy. ECMO is an adaptation of cardiopulmonary bypass technology and can be inserted centrally (using intrathoracic cannulation sites) or peripherally (usually using a percutaneous approach to cannulate the femoral vessels). It functions as an artificial heart and lung by providing nonpulsatile blood flow through an external circuit and an interface for oxygen and carbon dioxide exchange. 20 Peripheral VA ECMO is less invasive and can be instituted at the bedside. However, it may not adequately decompress the left ventricle. Limb ischaemia distal to the cannulated femoral artery is a potential complication, especially when support is continued for prolonged periods. Central VA ECMO offers excellent flows and better left- JICS Volume 14, Number 3, July

3 Cannula penetrating the interatrial septum aspirating oxygenated blood from the left atrium Right atrium Right ventricle Figure 2 Schematic representation of the Centrimag pump head. The figure shows a magnetic disc levitated in a magnetic field which due to its rotations imparts kinetic energy to the blood flow coming into the chamber. The flow of blood outside the chamber is after load dependent. ventricular decompression. It necessitates chest opening and is associated with higher bleeding and infection risks. It is always carried out by a cardiac surgeon in an operating theatre. Short-term ventricular assist devices (VADs) The CentriMag CentriMag (Figure 2) is a continuous-flow device used successfully for short-term cardiovascular support. The internal impeller is electromagnetically levitated and centred, eliminating the need for shafts, seals, and bearings in the pump thus causing less haemolysis, thrombus and particle formation. 21 It is a simple uni- or bi-ventricular support device. The blood is drained from the patient through a centrally or percutaneously placed venous cannula in the venae cavae, and oxygenated blood returned to the patient through a centrally or percutaneously placed arterial cannula in the ascending aorta or femoral artery respectively. 22 Percutaneous continuous flow systems To avoid the need for sternotomy exclusively percutaneous continuous flow systems have been developed. The most commonly used ones are the Tandem Heart pump and the Impella. The Tandem Heart pump (Figure 3) provides the circulating power to pull oxygenated blood from the left atrium and to return it to the systemic arterial circulation. It requires percutaneous placement of a cannula in the left atrium accessed via the femoral vein and a trans-septal puncture. A femoral arterial cannula is placed for systemic return. It can achieve up to 4 L/m of continuous flow with the aid of an externally placed pump. The trans-septal puncture can be difficult and requires fluoroscopy or transoesophageal echocardiography. 23 Complications of trans-septal puncture include cardiac perforation and tamponade. The Impella (Figure 4) is a percutaneously placed partial circulatory assist device. It is a non-pulsatile micro-axial continuous flow blood pump that spans the aortic valve. It has Femoral artery Pump Left ventricle Femoral Vein Figure 3 Tandem Heart in situ, showing trans-septal puncture of drainage line aspirating blood from the left atrium and being returned into the femoral artery. Right atrium Pulmonary valve Right ventricle Aorta Pulmonary artery Aortic valve Impella Figure 4 The Impella in situ, showing aortic valve spanning micro axial pump. been advocated for temporary support during high-risk percutaneous interventions. It aspirates blood from the left ventricle and displaces it into the ascending aorta, rapidly unloading the left ventricle and increasing forward flow. The Impella received FDA approval in 2008 for up to six hours of partial circulatory support. In Europe, the Impella 2.5 is approved for use up to five days. Due to technical limitations it may not provide sufficient flow for some ACHF patients. 24 Long-term ventricular assist devices (VADs) VADs provide mechanical circulatory support by removing blood from the left ventricle via an inflow cannula, driving the flow through a pump, and returning the blood into the ascending aorta through an outflow cannula. This 222 Volume 14, Number 3, July 2013 JICS

4 Outflow returned into the ascending aorta Outflow returned into the ascending aorta Left ventricular inflow cannula To aorta From ventricle Aorta Heartmate II pump Left ventricular inflow cannular Battery pack Pump Battery pack Heartmate XVE pump Power unit controller Drive line Power unit controller Figure 5 Heartmate XVE. From pump to aorta From ventricle to pump 6a Aorta From pump to pulmonary artery Drive line (power line) Pulmonary artery Right ventricle From pump to aorta From ventricle to pump decompresses the left ventricle and provides enough flow for most circumstances. A drive line exits from the anterior abdominal wall and is connected to the controller and power source. Although initial research into LVAD technology was directed towards chronic support, the success of heart transplantation in the early 1980s and the subsequent shortage of donor hearts led to these devices being introduced to bridge critically ill patients to transplantation. The REMATCH trial 25 compared optimal medical therapy with the HeartMate XVE (a pulsatile device) (Figure 5) and demonstrated a significant improvement in survival and quality of life at one and two years. On the basis of this study, this was the first device approved for destination therapy by the FDA. 26 Pulsatile flow VADs were constructed to mimic normal human physiology and to maintain the normal neuro-hormonal profile of patients in heart failure, which could theoretically be altered by continuous flow. Pulsatile flow has also been shown to improve mechanical unloading and remodelling of the failing myocardium in comparison to the continuous flow devices, 27 6b LVAD RVAD LVAD Figure 6 Thoratec IVAD being used as LVAD(6a)and BiVAD(6b). Figure 7 The Heartmate II pump. but this has not translated into clinical benefits. 28 Many pulsatile VADs have been used over the last 30 years, including the HeartMate, 29 Abiomed, and Thoratec 30 systems. A typical example of a paracorporeal pulsatile MCS device is the Thoratec Paracorporeal ventricular assist device (PVAD) (Figure 6). It is an electro-pneumatically driven pump implanted in a preperitoneal position and connected to an external pneumatic driver. It can be used as LVAD or BiVAD, and offers transplant candidates the option to recover and be discharged home while waiting for a suitable donor offer. 31 Pulsatile flow VADs tend to be larger, are associated with more drive-line infections, thromboembolic episodes and are less reliable in comparison to continuous flow devices when used for long-term support. 32,33 The large size of these devices preclude their use in smaller patients and children. The large size causes abdominal discomfort, gastric compression and consequent malnutrition. The devices are noisy and have large drive lines which have an impact on quality of life. 29 Continuous flow devices The development of continuous flow VADs was a response to the mechanical problems observed with pulsatile devices and an attempt to make them smaller. Continuous flow VADs have a simplified design that has only a single moving part, leading to better long-term reliability. They are quiet, their drive lines are smaller, thromboembolism is less frequent and quality of life is significantly better than with pulsatile devices. A commonly used continuous flow pump is the HeartMate II (Figure 7). It has an internal axial-flow blood pump with a percutaneous lead, which connects the pump to an external system driver and power source. The pump contains an internal rotor with helical blades that curve around a central shaft. When the rotor spins on its axis, kinetic energy is imparted to the blood, which is drawn continuously from the left ventricular apex and pumped into the ascending aorta. 34 HeartMate II has FDA approval for bridge to transplant and destination therapy. 12 There is a substantial reduction in the rate of thromboembolism, infection, and device failure. The risk of bleeding persists due to the higher degree of anticoagulation needed. It is also hypothesised that continuous flow devices JICS Volume 14, Number 3, July

5 cause von Willebrand factor (vwf) deficiency by a mechanism akin to the acquired vwf deficiency in severe aortic stenosis, wherein the large multimeric protein of vwf is deformed and lysed during its passage through the VAD. The narrow pulse pressure occurring with these devices causes an increased intraluminal pressure in the capillaries and consequently dilated mucosal veins, leading to increased development of gastrointestinal angiodysplasia posing a further risk of gastrointestinal bleeding. 35 Initially, there was concern that other end organs might suffer due to reduction in pulsatility, but this has not been documented. Total artificial heart The SynCardia total artificial heart (TAH) 36 is approved in Europe and the US as an alternative to biventricular devices in the bridge to transplant setting. It is suitable only for a limited population because of its size. Rapid improvements in technology have improved the safety and reliability of the continuous flow VADs. They are gaining widespread clinical acceptance. In the future, smaller devices, improvements in battery technology and the introduction of totally implantable pumps are likely to increase the pool of patients who can benefit from this form of treatment. Management of patients with advanced heart failure in ICU Critically ill patients may require resuscitation, ultrafiltration, inotropic support and ultimately, mechanical circulatory support. Diligent standard care of patients, including the management of nutrition, infection, anticoagulation, and social support is mandatory. Intensivists co-ordinate the expertise of different teams to offer maximal benefit for the patient. 37 Stabilisation of ACHF patients in the ICU provides time to explore treatment options such as mechanical circulatory support and transplantation, and facilitates decision-making. Cardiac transplantation is an option for a selected subset of patients with heart failure. Common reasons for exclusions are neurological dysfunction, pulmonary hypertension, renal failure, and diabetes with end-organ damage. Some patients with reversible contraindications (eg renal dysfunction secondary to heart failure, pulmonary hypertension associated with high left-sided filling pressure) may be rendered transplantable after a period of mechanical circulatory support. Mechanical circulatory support as a bridge to recovery Patients with potentially reversible conditions such as fulminant myocarditis may benefit from the use of MCS to support the circulation while awaiting myocardial recovery. There are also reports of patients with long-standing dilated cardiomyopathy who recover sufficient function for the device to be explanted without transplantation. 22 Conclusion Donor organ shortage and the improved safety profile of mechanical support devices has driven the expansion of the use of these devices for patients with advanced heart failure. With further miniaturisation, technological advancement of the devices and improved clinical expertise of the medical teams, the substantial risks and complications of placing and managing these devices is constantly decreasing. It is likely that devices will be used earlier in the course of the patient s disease in the future. Conflict of interest None declared. Acknowledgement The authors would like to thank Mr S Nallode for drawing the figures in this article. References 1. Metra M, Ponikowski P, Dickstein K et al. Advanced chronic heart failure: A position statement from the Study Group on Advanced Heart Failure of the Heart Failure Association of the European Society of Cardiology. Eur J Heart Fail 2007;9: Petersen S RM, Wolstenholme J. Coronary Heart Disease Statistics: Heart failure supplement. British Heart Foundation Costanzo MR, Mills RM, Wynne J. 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6 18.Goldberg RJ, Samad NA, Yarzebski J et al. Temporal trends in cardiogenic shock complicating acute myocardial infarction. N Engl J Med 1999;340: Thiele H, Zeymer U, Neumann FJ et al. Intraaortic balloon support for myocardial infarction with cardiogenic shock. N Engl J Med 2012;367: Hung M, Vuylsteke A, Valchanov K. Extracorporeal membrane oxygenation: coming to an ICU near you. JICS 2012;13: Thomas HL, Dronavalli VB, Parameshwar J et al. Incidence and outcome of Levitronix CentriMag support as rescue therapy for early cardiac allograft failure: a United Kingdom national study. Eur J Cardiothorac Surg 2011;40: John R, Long JW, Massey HT et al. Outcomes of a multicenter trial of the Levitronix CentriMag ventricular assist system for short-term circulatory support. J Thorac Cardiovasc Surg 2011;141: Kar B, Adkins LE, Civitello AB et al. Clinical experience with the TandemHeart percutaneous ventricular assist device. Tex Heart Inst J 2006;33: Bennett MT, Virani SA, Bowering J et al. The use of the Impella RD as a bridge to recovery for right ventricular dysfunction after cardiac transplantation. Innovations (Phila) 2010;5: Rose EA, Moskowitz AJ, Packer M et al. The REMATCH trial: rationale, design, and end points. Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure. Ann Thorac Surg 1999;67: Rose EA, Gelijns AC, Moskowitz AJ et al. Long-term use of a left ventricular assist device for end-stage heart failure. N Engl J Med 2001;345: Kato TS, Chokshi A, Singh P et al. Effects of continuous-flow versus pulsatile-flow left ventricular assist devices on myocardial unloading and remodeling. Circ Heart Fail 2011;4: Slaughter MS, Rogers JG, Milano CA et al. Advanced heart failure treated with continuous-flow left ventricular assist device. N Engl J Med 2009;361: Frazier OH, Rose EA, Oz MC et al. Multicenter clinical evaluation of the HeartMate vented electric left ventricular assist system in patients awaiting heart transplantation. J Thorac Cardiovasc Surg 2001;122: Berman M, Parameshwar J, Jenkins DP et al. Thoratec implantable ventricular assist device: the Papworth experience. J Thorac Cardiovasc Surg 2010;139: Slaughter MS, Sobieski MA, Martin M et al. Home discharge experience with the Thoratec TLC-II portable driver. ASAIO J 2007;53: El-Banayosy A, Arusoglu L, Kizner L et al. Novacor left ventricular assist system versus Heartmate vented electric left ventricular assist system as a long-term mechanical circulatory support device in bridging patients: a prospective study. J Thorac Cardiovasc Surg 2000;119: El-Banayosy A, Deng M, Loisance DY et al. The European experience of Novacor left ventricular assist (LVAS) therapy as a bridge to transplant: a retrospective multi-centre study. Eur J Cardiothorac Surg 1999;15: Miller LW, Pagani FD, Russell SD et al. Use of a continuous-flow device in patients awaiting heart transplantation. N Engl J Med 2007;357: Crow S, John R, Boyle A, Shumway S et al. Gastrointestinal bleeding rates in recipients of nonpulsatile and pulsatile left ventricular assist devices. J Thorac Cardiovasc Surg 2009;137: Jaroszewski DE, Anderson EM, Pierce CN, Arabia FA. The SynCardia freedom driver: a portable driver for discharge home with the total artificial heart. J Heart Lung Transplant 2011;30: Valchanov K Parameshwar J. Inpatient management of advanced heart failure. Cont Educ Anaesth Crti Care Pain 2008;8: Kiran Salaunkey Clinical Fellow, Department of Anaesthesia Jayan Parameshwar Consultant Cardiologist, Deputy Director, Transplant Services Kamen Valchanov Consultant Anaesthetist and Intensivist, Department of Anaesthesia Alain Vuylsteke Consultant Anaesthetist and Intensivist, Department of Anaesthesia a.vuylsteke@nhs.net Papworth Hospital, Cambridge JICS Volume 14, Number 3, July