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Mechanical Circulatory Support Devices: What You Need to Know (Part 2 of 2)
The Rise of Mechanical Circulatory Support Devices
What Critical Care Physicians Need to Know
Part 2 of 2 (read part 1)
II. 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 IIa1. [gallery size="medium" columns="2" link="none" ids="15071,15068"] 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 reported6. [gallery columns="2" link="none" size="medium" ids="15072,15069"] 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.
Left ventricular assist device (LVAD) CentriMag® and Rotaflow® The CentriMag® and Rotaflow® devices are all small centrifugal pumps with a magnetically levitated impeller widely used in the US, 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.
Conclusions 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 and intensivists have a key role, identifying patients that might benefit from this type of support and activating appropriate teams early. Table 1. Classification of devices, mechanisms, hemodynamic effects and common indications. Type of MCS Device Mechanism Effects Indications Percutaneous 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. Intracorporeal 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. Extracorporeal 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
Felipe Teran-Merino M.D.
Divisions of Emergency Ultrasound and Emergency Critical Care
Department of Emergency Medicine
Icahn School of Medicine at Mount Sinai
A version of this post was originally published in the newsletter of the American College of Emergency Physicians. References (see part 1)