Know the Backup Mechanism of Action and Requirements for Electrical Cardioversion and Anticoagulation for Ventricular Assist Devices



Know the Backup Mechanism of Action and Requirements for Electrical Cardioversion and Anticoagulation for Ventricular Assist Devices


Elizabeth A. Martinez MD, MHS



More than 2 million Americans have congestive heart failure and of these, approximately 60,000 meet criteria for some type of cardiac support or transplant. Despite expansion of criteria in the donor pool, there remains a limited number of donors. This number has essentially plateaued over the last decade between 2,000 and 3,000 annually. Because heart transplantation is not a viable option for many patients, there has been significant effort and research in the development of alternative medical and mechanical therapies. Mechanical ventricular assist devices (VADs) are currently used as a temporizing measure in the setting of acute heart failure, a bridge to transplantation, or as destination therapy. These devices are reported to improve the quality of life in these patients who are otherwise crippled by their heart failure despite maximal medical therapy.

VADs can be categorized in many ways: short term or long term; pulsatile or nonpulsatile; internal or external (i.e., intra- or extra-corporeal). Short-term devices include cardiopulmonary bypass, extracorporeal membrane oxygenation (ECMO), and the Abiomed BVS. Long-term devices include the Novacor, the HeartMate I and II, Thoratec, and the newer Abiomed AB5000 Ventricle. The nonpulsatile devices are cardiopulmonary bypass and ECMO in addition to the HeartMate II. The permanent devices have an internal chamber. No device has a totally implantable energy source.

All VADs except the HeartMate II, which generates nonpulsatile flow using a rotarylike motor, generate pulsatile flow because of their design with unidirectional flow valves. They operate in a fill-to-empty cycle, similar to the action of the native ventricle (i.e., diastole and systole). The determinants of the stroke volume are the pre-ejection chamber volume (preload) and the outflow resistance, either pulmonary or systemic, depending which side is mechanically supported. Emptying is initiated when the control unit senses that the chamber is nearly full. The rate of the ejection is volume, or preload, dependent. It is important to note that the rate of output is independent of the native cardiac rhythm. The goal is to maintain unloading

of the ventricle, especially in those patients who have had this placed with planned removal after recovery of the myocardium. This typically is limited to the postcardiac surgery patient in which a temporary device is placed.








TABLE 73-1 CLINICAL CHARACTERISTICS OF COMMONLY USED VENTRICULAR ASSIST DEVICES
























































































DEVICE ABIOMED (AB5000) THORATEC NOVACOR HEARTMATE I HEARTMATE II
Arterial tracing Pulsatile Pulsatile Pulsatile Pulsatile Nonpulsatile
Valves Angioflex polyurethane Mechanical Bioprosthetic Porcine n/a
Implantation Paracorporeal Para- or intra-corporeal Intracorporeal Intracorporeal Intracorporeal
Control unit Not portable, large device Portable, not wearable Portable, worn as “belt” Portable, worn as “belt” (electrical model) Portable, worn as “belt”
Anticoagulation Coumadin Coumadin Coumadin Aspirin Coumadin
Maximum stroke volume 100 mL 65 mL 70 mL 85 mL n/a
Backup mechanism Backup pump (also has pneumatic hand pump) Pneumatic handheld pump Backup controller needed; no manual mechanism Pneumatic handheld pump Backup controller needed; no manual mechanism
Maximum flow rate 4–6 L/min 7 L/min 10 L/min 10 L/min 10 L/min
Electrical cardioversion No issuea No issue No issue Need to turn electrical device off (electrical model)b External paddle cardioversion: no issue; internal paddle cardioversion: must remove controllerb
Cautery No issue No issue No issue May produce erratic pump output No issue
Precautions Acetone can crack the housing device Acetone can crack the housing device   Controller and filter port must remain free of liquids Controller must remain free of liquids
aMay perform external or internal cardioversion with the device functioning.
bSpecific instructions should accompany the device. It includes multiple steps that need to be performed in a specific sequence.

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Jul 1, 2016 | Posted by in ANESTHESIA | Comments Off on Know the Backup Mechanism of Action and Requirements for Electrical Cardioversion and Anticoagulation for Ventricular Assist Devices

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