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FA 2016

Editor’s Note:

A colleague of mine, Michael, asked me during a conversation if there was any information out there regarding the increased frequency or use of ECLS systems throughout the emergency departments in hospitals across the US.  Interestingly enough, I find myself later in the day, monitoring one of these devices in vivo.

Below is a good article, that I think a is very clear hint at the direction we are heading with the increasingly better and more mobile ventricular or lung assist devices on the market.  Having been a paramedic in my earlier days, I totally appreciate how far technology has come in terms of our ability to interdict and save lives closer (in real time) to when a patient collapses and needs assistance.

God Bless- 🙂

Frank

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The Rise of Mechanical Circulatory Support Devices; What and why Emergency Physicians should know about them

 

Cardiohelp

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Felipe Teran-Merino, MDFelipe Teran-Merino, MD
Divisions of Emergency Ultrasound and Emergency Critical Care
Department of Emergency Medicine
Icahn School of Medicine at Mount Sinai

A 35 year old woman with no significant past medical history presents with 3 days of acutely worsening dyspnea. She just recovered from an upper respiratory infection, which left her with some residual cough. In the ED, she looks anxious and uncomfortable. She is tachypneic to 30/min, has sinus tachycardia to 130s, pulse oximetry shows saturation of 92% on a non-rebreather (NRB) mask placed by triage nurse, with crackles in both lung bases. Her blood pressure is 84/50 mmHg and her extremities are cold. Point of care (POC) lactate is 4,5. She has no risk factors for PE and her EKG shows no signs of ischemia. After initial evaluation you attempt non-invasive ventilation (NIV) to improve oxygenation, while you wait for labs and cardiology. Saturation improves, but pressure drops to systolic of 70 mmHg. You anticipate the need for intubation, but want to improve her acidemia and hypotension before proceeding. Infusion of norepinephrine and dobutamine is started but the patient continues to deteriorate. What else can you consider at this point?

While clinicians working in acute care settings may infrequently face challenging cases like the one described above, when they present, they often demand multiple interventions that if promptly established can change the outcome of patients. In order to do this, it is critical to understand the pathophysiology of cardiogenic shock, the rationale and goals of therapy and different therapeutic options.

The rising field of mechanical circulatory support (MCS) offers a spectrum of therapies and devices with the potential to rescue patients with life-threatening cardiogenic shock.1 Traditionally within the domain of cardiothoracic surgeons and interventional cardiologists, the expansion of indications for some of these support strategies outside the operating room and cardiac catheterization lab creates the need for multidisciplinary teams to care for these patients.

Emergency physicians and other acute care physicians must be familiar with developments in this field, as they often are the first providers to encounter the patient and therefore play a key role in directing their care during the crucial initial hours.

Understanding the vicious cycle of pump failure

Cardiogenic shock is often defined as sustained hypotension (SBP < 90 mmHg or 30 mmHg bellow known baseline), low cardiac output (CO) defined by cardiac index (CI) < 2.2 l/min/m2, high central filling pressures defined by pulmonary capillary wedge pressure (PCWP) > 12 mmHg and signs of diminished tissue perfusion.

From a physiological standpoint, what specifically distinguishes cardiogenic shock is the mechanical impairment of the pump function (contractility), which leads to insufficient CO. When patients develop pump failure, they enter a vicious cycle of intra-cardiac and systemic changes, which lead to a further decrease in the stroke volume (SV). Increased left ventricular (LV) end-diastolic pressures lead to increased LV wall tension, which leads to coronary ischemia affecting contractility. The systemic hypotension resulting from the fall in SV leads to tissue hypoperfusion with subsequent acidemia, which further impairs contractility,

The role and hemodynamic effects of MCS

The treatment of cardiogenic shock is directed to break this cycle and is two-fold: fix the triggering factor and support pump function. If the underlying problem is evident, such as an acute myocardial infarction, an acute valvular failure or a medication overdose (eg, calcium channel blocker overdose), specific therapies should be instituted. However, in many cases like the one described here, the heart will need time (hours, days or weeks) to recover. In these cases, the mainstay therapy is “buying time” for the patient.

Inotropic agents are the first line therapy in cardiogenic shock and they attempt to break the cycle by directly augmenting contractility (beta-adrenergic effect or phosphodiesterase-3 inhibition) as well as improving systemic hypoperfusion by increasing vascular resistance (alpha effect).

While these agents (eg, epinephrine, dobutamine, milrinone, etc.) all have the potential to improve the hemodynamics and stabilize some patients, when there is severe failure, pharmacologic therapy alone is generally going to come at very high price from the perspective of both the myocardium and the peripheral and splanchnic circulations. Beta-adrenergic stimulation may improve contractility of areas that are perfused, but it will greatly increase myocardial oxygen demand, feeding into and fueling the vicious cycle.

Alfa-adrenergic vasoconstriction may improve coronary and systemic perfusion pressures, but will increase both systemic and pulmonary vascular resistance,2 making it harder for failing ventricles to maintain ejection fraction. It will also leave the peripheral and splanchnic beds vasoconstricted and tissues underperfused.

This is where MCS comes into play. Mechanical circulatory support involves a wide range of devices that share the common function of supporting or even replacing the pump function of the failing ventricle. They decrease LV wall tension, improving coronary flow and contractility. Unlike inotropic agents, MCS devices restore the balance between myocardial oxygen supply and demand, and generate effective systemic perfusion.

Depending on the location of the pump, MCS devices are classified as intracorporeal (an implanted device), percutaneous or extracorporeal. They are also classified as short term (or rescue), and long-term therapies, according to the time they are intended to provide support for.

Examples of intracorporeal devices include left, right or biventricular Assist Devices (VADs) and the Total Artificial Heart. Percutaneous devices include the intra-aortic balloon pump (IABP), the Impella®, and the TandemHeart®. Extracorporeal devices include the Centrimag®, Rotaflow® and the CardioHelp®. Classification of devices, mechanisms, hemodynamic effects and common indications are summarized in Table 1.

Why is it important that emergency physicians are familiar with the field of MCS?

Given the rapidly growing number of patients with advanced heart failure who are being managed with long-term MCS devices (specifically LVADs), emergency physicians and other acute care providers are encountering these patients with increasing frequency.3 Patients with implanted devices may present to the ED with acute complaints and MCS–related complications that clinicians must understand to appropriately manage.4 For instance ventricular arrhythmias, driveline infections, GI bleed or suction events in the LVAD patient.5

Furthermore, the large experience gained in the field of MCS in long-term support strategies over the past decade, along with significant improvements in the technologies (making more durable and safer devices, with easier implantation), has led to the expansion to short-term applications. This experience has also prompted the development of new devices specifically designed to provide emergency support (e.g. Impella® or CardioHelp® ECMO). These applications are still largely supported only by observational data but if patients have been successfully supported with these life-saving therapies when emergencies have occurred in the operating room6 or the cardiac catheterization lab,7 it seems reasonable to offer the same opportunity to selected patients in the ED or ICU. Patients in the ED who could potentially benefit from MCS, will never get access to them unless the emergency provider considers this possibility and contacts the appropriate teams early enough to avoid perpetuating the vicious cycle of pump failure to a point of irreversible organ damage. As stated in the 2015 SCA/ACC/HFSA/STS consensus recommendations on the use of percutaneous MCS devices: “Early initiation of MCS support can mitigate the consequences of systemic hypoperfusion, worsening acidemia, and declining cardiac function.”8

Indications for Mechanic Circulatory Support

Classic long-term indications for MCS include bridge to transplant and destination therapy.9 In bridge to transplant a patient with advanced non-reversible heart failure with an indication for cardiac transplant can be bridged with MCS until the organ is available and / or the patient is fit for transplant. In destination therapy MCS devices are implanted as a life-long strategy for patients who are not candidates for transplantation. Emerging short-term indications include bridge to recovery and immediate survival.

Bridge to recovery: this is the case of the patient described above. A patient with acute severe heart failure, with a known recoverable underlying etiology can be transiently supported with a mechanical device until native function is recovered.

Bridge to immediate survival: this is a new and promising indication that includes the deployment of either percutaneous or extracorporeal devices during a life-threatening event. In this group we have any confirmed or suspected treatable precipitating etiology. For instance, a patient with an acute MI who repeatedly goes into VF and needs to be bridged to have PCI, or a patient with massive PE who is bridged to go for thrombectomy.10

Main MCS devices used for emergency and short-term support

Intra-Aortic Balloon Pump

The oldest and simplest mechanical device is the intra-aortic balloon pump (IABP). Introduced in 1968, the IABP is still used as a ventricular assist device in many centers across the US. It consists of a catheter with a balloon on its end, which is inserted percutaneously into the femoral artery and advanced retrograde up to the aorta just distal to the left subclavian artery. The IABP is inflated during diastole, improving coronary perfusion by increasing DBP. During systole the balloon is actively deflated unloading the LV by decreasing the afterload. The IABP can improve CO by 25-30%. The main limitation of the IAPB is that it relies on the native LV function. While used widely over the past two decades, on the basis of registry data and retrospective meta-analyses and randomized trials that failed to demonstrate a mortality benefit, the AHA in its 2013 Guidelines for the management of STEMI, downgraded the recommendation from Class I to Class IIa.11

Impella®
The Impella is a family of minimally invasive, catheter-based cardiac assist devices designed to increase cardiac output and partially unload the LV, thus reducing the myocardial workload and oxygen consumption. Impella pumps are percutaneously inserted through standard catheterization of the femoral artery into the ascending aorta, across the aortic and mitral valves and into the LV. The pump pulls blood from the LV through an inlet area near the tip and expels blood from the catheter into the ascending aorta. There are currently two types of pumps available in different catheters, providing 2.5 and 5.0 L/min of blood flow rate. An important practical difference is that the Impella®5.0 requires surgical cut down insertion. These devices are being increasingly used during high risk PCI (< 6 hours) and to support patients in cardiogenic shock following myocardial infarction (< 4 days) who are refractory to pharmacological therapy. Cases of successful emergency support during cardiac arrest have also been reported.6

LVADs
The fundamental component of LVADs is an internal pump and two cannulae that draw blood from the left ventricle and deliver it to the aorta, connected to a controller and power source typically outside of the patient. LVADs can be classified as first, second and third generation devices.

First generation devices are no longer in use (HeartMate VE, HeartMate XVE and Novacor); they provided pulsatile flow, were bulky, required complex cardiothoracic surgery and had limited durability. The vast majority of devices currently in use are second-generation devices; smaller pumps that generate continuous flow (therefore the lack of pulse in many patients). Advantages of this continuous flow technology include a significant decrease in hemolysis, smaller drivelines, lower incidence of infection and less invasive surgery needed for implantation. The two second-generation devices currently in use in the U.S. are the HeartMate II and the Jarvik 2000. Looking to further reduce complications and increase durability, third generation devices are now being utilized, incorporating frictionless impellers that use either magnetic forces or hydrodynamic levitation to avoid mechanical contact of the bearings within the blood chamber. The HeartMate III, the newest device, has the ability to match the patient’s heartbeat to the pumping of the device, and is currently being evaluated in the MOMENTUM 3 Trial.

CentriMag® and Rotaflow®
The CentriMag® and Rotaflow® devices are all small centrifugal pumps with a magnetically levitated impeller widely used in the US and in Europe to provide short-term support. As with other short-term devices, the pumps remain paracorporeal connected to cannulae in the heart and great vessels. Despite their small size, they can provide flow rates of up to 9.9 liters per minute and can pump through a membrane oxygenator if ECMO is desired. These pumps are frequently used in intensive care and cardiothoracic ICUs to provide circulatory support after unsuccessful weaning from bypass as well as to provide ECMO in conjunction with an in-line oxygenator membrane.

CARDIOHELP®
The CARDIOHELP® is a compact, lightweight heart-lung assist system designed to provide circulatory and / or pulmonary support in emergency situations with an all-in-one machine. It contains a pump (similar to the CentriMag or Rotaflow described above), a membrane oxygenator and a display to control all parameters. Due to its compact design this machine is being used in centers providing Extracorporeal Life Support (ECLS) and emergency ECMO.

Case resolution

Echocardiography showed severe myocardial dysfunction with EF 10%, biopsy later confirmed fulminant myocarditis. The patient presented with cardiogenic shock and quickly deteriorated despite inotropic support. After early consultation of cardiac surgery and cardiology, the patient was transiently supported with an Impella device, which helped improve hemodynamics and allowed intubation. Hours later underwent implantation of a LVAD. Cardiac catheterization showed no coronary obstruction. Patient recovered with no organ damage and had LVAD explanted months later with minimal residual myocardial dysfunction.

Patients in cardiogenic shock remain to have high mortality despite pharmacologic therapy and early revascularization in AMI. Mechanical circulatory support devices represent today an available therapy for these patients at many tertiary centers. While there is limited clinical data, and several knowledge gaps exist regarding indications, patient selection and cost effectiveness, these devices represent a reasonable alternative for a group of patients refractory to first line medical therapy. Emergency physicians have a key role, identifying patients that might benefit from this type of support and activating appropriate teams early.

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Table 1. Classification of devices, mechanisms, hemodynamic effects and common indications.

Device Mechanism Effects Indications
IABP Catheter with balloon inserted percutaneously into the femoral artery and advanced retrograde up to the aorta just distal to the left subclavian artery. Increases DBP, decreases afterload and modestly increases CO. Modest LV unloading. Cardiogenic shock due to due to AMI and as rescue device during complicated PCI.
Impella® Catheter-based pump. Pump at the end of catheter is inserted retrograde via femoral artery into LA and LV. Increases CO, unloads LV. Flow max of 2.5 or 5.0 LMP. Bridge to immediate survival:
Emergency support during cardiac cath, cardiogenic shock post AMI and transient support (hours) in cardiogenic shock as bridge to VAD or transplant.
TandemHeart® Continuous flow centrifugal pump that remains in leg, with cannulas are inserted via femoral vein into the LA. Increases CO and unloads LV. Flow max of 5.0 LPM. Bridge to immediate survival:
Emergency support during cardiac cath, cardiogenic shock post AMI and transient support (hours) in cardiogenic shock as bridge to VAD or transplant.
LVAD, RVAD, BiVAD Pumps implanted with two cannulas that draw blood from the left ventricle and deliver it to the aorta. Increase LV, RV or biventricular CO and unloads LV. Flow max of 10 LPM (HeartMate III) Bridge to recovery (e.g. myocarditis), bridge to transplant and destination therapy.
Total Artificial Heart Pneumatic pulsatile pump that replaces ventricles and all 4 valves. Replace biventricular function. Flow max of 9,5 LPM. Bridge to transplant in patients with end-stage heart failure.
CentriMag® Extracorporeal centrifugal VAD. Increase LV, RV or biventricular output. Flow max of 9,9 LMP. Transient support as bridge to recovery in patients unable to wean from cardiopulmonary bypass.
Rotaflow® Extracorporeal centrifugal VAD. Increase LV, RV or biventricular output. Flow max of 9,9 LMP. Transient support as bridge to recovery in patients unable to wean from cardiopulmonary bypass.
Cardiohelp® system All-in-one heart and lung machine. Contains pump, oxygenator and controller. Allow VV and VA ECMO. Flow max of 7 LMP. Bridge to immediate survival. Emergency ECMO, ECLS (initiated intra-arrest). Common clinical scenarios include:
Refractory VF
Arrest due to AMI, massive PE or drug overdose
Arrest in accidental hypothermia

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References:

  1. Eckman PM, Hryniewicz K. Prime Time for Temporary Mechanical Circulatory Support. J Cardiovasc Transl Res. 2015 Jul;8(5):281-2.
  2. Barnard MJ, Linter SP. Acute circulatory support. BMJ. 1993 Jul 3;307(6895):35-41.
  3. Kirklin JK, Naftel DC, Pagani FD, et al. Seventh INTERMACS annual report: 15,000 patients and counting. J Heart Lung Transplant. 2015 Dec;34(12):1495-504.
  4. Sen A, Larson JS, Kashani KB, et al. Mechanical circulatory assist devices: a primer for critical care and emergency physicians. Crit Care. 2016 Jun 25;20(1):153.
  5. Burke MA, Givertz MM. Assessment and management of heart failure after left ventricular assist device implantation. Circulation. 2014 Mar 11;129(10):1161-6.
  6. Desai N, Chaudhry K, Aji J. Impella left ventricular assist device in cardiac arrest after spinal anaesthesia for caesarean section. BMJ Case Rep. 2015 Oct 28;2015.
  7. Heidlebaugh M, Kurz MC, Turkelson CL, et al. Full neurologic recovery and return of spontaneous circulation following prolonged cardiac arrest facilitated by percutaneous left ventricular assist device. Ther Hypothermia Temp Manag. 2014 Dec;4(4):168-72.
  8. Rihal CS, Naidu SS, Givertz MM, et al; 2015 SCAI/ACC/HFSA/STS Clinical Expert Consensus Statement on the Use of Percutaneous Mechanical Circulatory Support Devices in Cardiovascular Care. J Am Coll Cardiol. 2015 May 19;65(19):e7-e26.
  9. Shreenivas SS, Rame JE, Jessup M. Mechanical Circulatory Support as a Bridge to Transplant or for Destination Therapy. Current Heart Failure Reports.2010;7(4):159-166. doi:10.1007/s11897-010-0026-4.
  10. Spangenberg T, Meincke F, Brooks S, et al. Shock and Go? extracorporeal cardio-pulmonary resuscitation in the golden-hour of ROSC. Catheter Cardiovasc Interv. 2016 Jun 17.
  11. O’Gara PT, Kushner FG, Ascheim DD, et al; 2013 ACCF/AHA guideline for the management of ST-elevation myocardial infarction: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines: developed in collaboration with the American College of Emergency Physicians and Society for Cardiovascular Angiography and Interventions. Catheter Cardiovasc Interv.. 2013 Jul 1;82(1):E1-27.

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