a b s t r a c t

Ventricular assist devices (VAD) are being used at increasing rates in patients with severe, end-stage heart failure. Specific indications include VAD placement as a bridge to cardiac function recovery, a bridge to cardiac transplan- tation, or destination therapy (long-term support for patients ineligible for transplant). The assessment and man- agement of the VAD patient is rather complex, requiring a basic knowledge of device structure and function. This article reviews the basic structure and function, discusses the approach to the VAD patient in the ED, and reviews the more common presentations and complications encountered in these technology-complex patients who are critically ill at baseline.

(C) 2018

Introduction

Heart failure continues to be a significant cause of mortality in the United States. According to the American Heart Association, the preva- lence of heart failure has increased from 5.7 million in 2013 to 6.5 mil- lion cases in 2017 [1]. Despite advances in medical treatment, heart failure contributed to 1 out of every 9 deaths in 2009 [2]. Mortality from advanced heart failure is potentially decreased by ventricular as- sist devices (VAD) as compared to medical management alone [3]. VADs, once only used as either a bridge to cardiac transplant or overall improvement in cardiac function, are increasing in prevalence at a rapid rate since their approval for use as destination therapy [4]; estination therapy is defined as the use of a VAD as the primary therapy in a patient with severe heart failure who is not a candidate for trans- plantation or other definitive therapy – in other words, it is offered to patients as a final means of prolonging life in the setting of end-stage heart failure. Thus, the three categories of indication for VAD placement include the following:

• bridge to cardiac transplant;
• bridge to recovery in potentially reversible cardiac pathology; and
• destination therapy, long-term support for patients ineligible for transplant.

According to INTERMACS (Interagency Registry for Mechanically Assisted Circulatory support), there have been 22,866 mechanical

* Corresponding author.

E-mail address: [email protected]. (W. Brady).

circulatory support devices placed between 2006 and 2016, with a cur- rent pace of over 2500 devices implanted per year [5]. With this number of patient’s receiving VADs, it is likely many will present outside of ter- tiary medical centers, in essence VAD centers; therefore, all Emergency practitioners should be competent with management and stabilization of the VAD patient until they can be transferred to a VAD center.

Ventricular assist device components and function

VADs function by receiving blood from the failing ventricle and, with the aid of a mechanic pump, augment cardiac output. In their simplest terms, the VAD consists of the internal pump, an external power source, and a control unit. Placement is indicated in patients with a New York Heart Association Class IIIb – IV heart failure that is worsening despite optimized medical management [4]. Of course, consideration of the ul- timate goal is also made, whether it be a bridge to cardiac transplanta- tion, a period of cardiac function support during recovery, or destination therapy in a patient with no other recourse.

Since the placement of the first pneumatically driven ventricular as- sist devices in 1966, multiple advancements have been made to these devices [6]. First generation VADs had inlet and outlet valves and cre- ated a pulsatile flow; these devices, however, were large and cumber- some – they were not portable in any real sense. These devices gave way to the development of second and third generation VADs that pro- vide a decrease in size while offering an improvement in function. While VADs can be placed in either a right, left or biventricular configu- ration, the most frequently encountered are left ventricular assist de- vices (LVAD).

The pumps employed in VADs can be divided into two primary cat- egories, either pulsatile or continuous-flow. A pulsatile pump mimics

https://doi.org/10.1016/j.ajem.2018.04.047

0735-6757/(C) 2018

the natural pulsatile flow of the heart while the continuous flow device produces a steady perfusion state. Continuous-flow devices account for the vast majority (in excess of 90%) of implanted VADs [5]; this type of device is both more compact smaller and more durable than pulsatile VADs.

The continuous-flow device uses a pump with either centrifugal or axial flow. Both types of continuous-flow device have a central rotor containing permanent magnets. Controlled electric currents running through coils contained in the pump housing cause the rotors to spin. In the centrifugal pump, the rotors accelerate the blood circumferentially, producing flow toward the outer rim of the pump (figure); in the axial flow pump, the rotors are cylindrical with blades that are helical, causing the blood to be accelerated along the axis of the rotors (figure). Physiologically, the continuous-flow pump produces perfusion which is unlike “natural” blood flow; perfusion occurs in a non-physiologic manner and yet provides the more favorable circula- tory support for organ system function – as compared to the pulsatile pump.

Components of the VAD include the following (Fig. 1A): inflow can- nula, pumping chamber, outflow cannula, percutaneous driveline, con- troller, and power source. As noted, the VAD can be placed in either the right or left ventricle. For illustrative purposes, we will assume place- ment in the left ventricle, thus an LVAD. The inflow cannula, placed within the left ventricle, pulls blood from the ventricular cavity into the LVAD pump. The pumping chamber is located at the apex of the left ventricle for the HeartMateIII and HeartWare devices, or in the sudiaphragmatic space for the HeartMateII device, and houses the im- peller, a frictionless rotor which rotates at speeds of approximately 3000 rpm (HeartWare), 5000 rpm (HeartMateIII) and 9000 rpm (HeartMateII); these types of pumps can generate blood flows up to 10 l per minute. The outflow cannula carries blood from the pumping chamber to the Ascending aorta. The percutaneous driveline provides a conduit for the various wires which connect the system controller to the pump; the driveline is tunneled subcutaneously from the pump, exits the skin in the epigastric area, and connects to the controller. The controller performs a number of important functions, including power regulation, LVAD system monitoring, alarm status, battery life, and data download. The controller panel of a has a number of important functions and symbols; an example of the controller panel of a HeartMateIII is shown in Fig. 1B. The batteries are, of course, the power supply; current units carry two rechargeable batteries.

LVADs offer a variety of unique challenges for emergency providers. Herein, we discus some of the most common and life-threatening pre- sentations and offer a basic approach to treatment in the most common continuous flow devices (i.e., HeartMateII, HeartMateIII, HeartWare VAD).

Initial evaluation of the VAD patient

The initial assessment of the patient, including interpretation of vital signs and the physical examination, differs significantly from non-VAD individual, though still needs to be accomplished in a systematic and thoughtful manner. With continuous flow devices, most patients do not have a palpable pulse due to low Pulse pressure, thus making blood pressure determination difficult to obtain by standard technique using sphingomanometry. If the initial evaluation does reveal palpable pulses, it is critically important to determine if the detectable pulse is a new finding as palpable pulses may signal pump thrombosis. Because LVADs, by design, limit the pulsatile ejection of flow out of the left ven- tricle, the mean arterial pressure is the most useful piece of basic hemo- dynamic data in these patients. In an awake and alert LVAD patient, noninvasive blood pressure can best be obtained using a Doppler. This technique is done by obtaining a Doppler signal distal to the manual blood pressure cuff; when the cuff is slowly released, the pressure at which the Doppler signal is again heard is most consistent with the mean arterial pressure. The MAP for an LVAD patient generally should be between 70 and 90 mm Hg. If the patient is unconscious or unstable, the initial Doppler technique can be employed yet, ultimately, invasive monitoring of blood pressure will be needed to obtain a reliable mea- sure of blood pressure. LVAD patients are very sensitive to physiologic alterations in their fluid volume and perfusion states. For instance, low preload states and high afterload states will very significantly impair perfusion.

heart sounds may be completely obscured secondary to the me- chanical hum generated by the device. That said, the presence of a me- chanical hum indicates that the device is powered and, at least, attempting to function, if not working correctly. The device location is not necessarily indicative of the assisted ventricle, whether left, right or biventricular. Drive line sites should be evaluated for any erythema, warmth, and/or discharge concerning for infection; driveline infection is a common complication of VAD placement. Examination of the

Fig. 1A. Ventricular assist device diagram, demonstrating the various components of the system.

Fig. 1B. HeartMateIII controller panel and explanation of various buttons/icons. Cable Disconnect Symbols – indicates cable disconnection; Battery Button – allows user/evaluator to interface with the battery and related power functions; Pump Functioning Symbol – indicates normal pump function when illuminated in GREEN color; User Interface Screen – provides interface between device and user/evaluator; Display Button – activates the User Interface Screen; Battery Power Gauge – indicates approximate charge status of the power source (when a diamond shape is depicted, 15 min or less of power remains; Low Battery Alarm – when RED in color, indicates less than 5 min of remaining battery power; Device Malfunction Alarm – indicates that controller has detected significant device malfunction, requiring immediate attention; Device Function Warning Alarm – indicates that controller has detected a potential device malfunction, involving mechanical, electrical or software issues; and Silence Alarm Button – silences alarms).

driveline exit point at the skin should always be performed with sterile gloves and a mask.

Standard laboratory studies (including lactate dehydrogenase [LDH], plasma free hemoglobin, and haptoglobin), electrocardiogram (ECG), and radiography (Fig. 2) are generally important in the initial evaluation of the patient with cardiorespiratory issues or other systemic com- plaints. The ECG should demonstrate normal sinus rhythm.

The external system controller shows alarms and functional param- eters. This information is important to communicate with the VAD cen- ter and useful in determining etiology of certain presentations common in these patients. VAD parameters include pump speed, pump flow, pulse index, and pump power. The speed is the controlled variable and the pump flow is the dependent variable. Some pocket controllers show various alarms depending on the device. Most have yellow or red battery alarms when the battery needs to be changed and a heart shaped alarm when there are issues with flow or speed; depending on the devices, some will say “low flow” or “high flow.”

Acute presentations and Device-related complications

A range of issues can complicate the VAD patient, including sponta- neous events unrelated to the device (i.e., dysrhythmias and trauma) as well as situations which result solely from the ventricular assist device or related medical therapies. Significant hemorrhage, infection, dys- rhythmia, device malfunction, and thrombosis can occur; these patients not infrequently will initially present to the emergency department for evaluation and management.

Bleeding diatheses

VAD patients are chronically maintained on anticoagulation to pre- vent pump thrombus; consequently, VAD patients can present with hemorrhagic complications. Three to twelve months after placement, bleeding accounts for 4 adverse events for every 100 VAD patient months [5]. Outside of the immediate post-operative period, gastroin- testinal bleeding and hemorrhagic stroke are the common forms of major bleeding in VAD patients. The REMATCH trial [3] notes 15% of pa- tients develop some form of gastrointestinal bleeding in the first year; LVAD patients experience small bowel arteriovenous malformations as well as an acquired von Willibrand disease. Hemorrhagic shock should

be considered in the compromised VAD patient, either spontaneous hemorrhage or after a Traumatic event. The external system may show a “low flow” alarm, resulting from the hypovolemia caused by hemor- rhage. Significant hemorrhage should be treated in similar fashion as in non-LVAD patients, with consideration of appropriate product re- placement and administration of reversal agents. Reversal agent use must be weighed against the potential for thrombotic complication; re- versal of a therapeutic coagulopathy is likely indicated if there is risk of exsanguination or documented intracranial hemorrhage – of course, the physician at the bedside is in the most appropriate position to make this determination. Consultation with the LVAD team is generally appreciated.

Dysrhythmia

Dysrhythmias occur at a rate of 10.45 events per every 100 VAD pa- tient months during the initial three months after placement; subse- quently, the rate decreases to a rate of 1.3 events per 100 patient months [5]. During the initial assessment of the VAD patient, the elec- trocardiogram (ECG) – both single lead monitoring and 12 lead ECG – should be considered. Frequently, patients with severe heart failure have Implantable cardioverter defibrillator (ICDs) in place prior to obtaining a VAD. Surveillance studies demonstrate that ventricular

Fig. 2. Chest radiography of a patient with a ventricular assist device and pacemaker.

arrhythmia occurrence prior to VAD placement is the largest predictor of ventricular arrhythmias after device placement [7,8]; in other words, the greatest risk of malignant ventricular dysrhythmia is a recent history of the same in the VAD patient [7,8]. Again, the controller exter- nal system will show a low flow state in patients who are hypotensive secondary to dysrhythmias. In LVAD patients without ICDs in place, ad- vance life support protocols should be followed with appropriate chem- ical and electric therapy; ventricular tachycardia and ventricular fibrillation should be treated aggressively in symptomatic patients. Ur- gent consultation with VAD personnel and/or center is strongly encouraged.

Sepsis

Infection occurs at a rate of 4.55 events per 100 VAD patient months after the immediate post-operative period [5]. The REMATCH trial [3] reports 42% infection rate within the first year of implantation. These in- fectious events usually occur soon after surgical placement, most often between the initial 2 weeks to 2 months. The entire VAD system is sus- ceptible yet the driveline (Fig. 3) and pump pocket (Fig. 4) are the two most common sites of infection. It is important to use gloves and mask when examining the driveline exit site to keep the area as sterile/ clean as possible.

The external system control may show a “high flow” alarm with nor-

Procedures

Fig. 3. Driveline line infection.

mal power secondary to loss of vascular tone with distributive shock. LVAD patients who present with sepsis require antibiotic therapy and possibly vasopressor support. Initial antibiotic selection should include anti-staphylococcal and anti-pseudomonal coverage. These infections should be considered healthcare associated events. Local infection pat- terns should be kept in mind. Source control measures, such as pocket exploration and/or catheter drainage may be required.

4.4. Suction event

A suction event is seen in low flow states secondary to compromis- ing dysrhythmias, significant hemorrhage, and other hypovolemic states; it can also occur with distributive shock, as seen in the patient with sepsis. “Suction” occurs when there is collapse of the left ventricle, which impedes the inflow to the LVAD pump. A suction event occurs when there is a low preload to the left ventricle. Bedside ultrasound will show diminished LV volume; the parasternal long-axis view is par- ticularly well suited to demonstrate this finding. If the rate were to be slowed, the frequency of suction events should decline as the left ventri- cle will have longer to fill preventing ventricular collapse. Treatment of inadequate preload, and related cause, should be initiated.

4.5. Circuit and pump thrombosis

In the case of an obstructing thrombosis, the external system con- troller will show low flow and high power. A serum lactate dehydroge- nase (LDH) should be checked as a level over 600 correlates with pump thrombosis and is useful information for VAD providers and centers; in addition, plasma free hemoglobin and haptoglobin, when elevated, are suggestive of this diagnosis [9]. These patients are already on anticoagulation and no emergency intervention should be done other than stabilization and involvement of VAD personnel. A patient present- ing with pump stoppage requires special care. Any pump stoppage that is unknown in duration, or known to have lasted more than several mi- nutes, is an emergency. These events may occur during system control- ler exchanges or an internal wire short. It is important not to restart the pump in these circumstances as clot will likely be showered throughout the circulation. In this setting, anticoagulation and consideration for temporary circulatory support should be rapidly considered, as directed by the VAD providers and centers.

Emergency providers should not be hesitant to perform necessary procedures on patients with VADs. These procedures should be done with similar caution as any procedure performed on anticoagulated pa- tients. If necessary, these patients can receive Chest tubes; it is impor- tant, however, to exercise caution regarding the drive line and lateral tube placement is recommended. If Arterial line placement is indicated, then an ultrasound-guided approach should be utilized. One procedure that should not be done on VAD patients is a pericardiocentesis unless clear signs of tamponade are present due to the risk of device complications.

If a VAD patient presents unresponsive and hypotensive, external compressions can be preformed, if indicated. If the patient has a MAP greater than or equal to 50 mm Hg or an end tidal CO₂ greater than 20 in an intubated patient, however, then chest compressions do not need to be performed as the perfusion is likely adequate [10]. While rec- ommendations originally existed that strongly discouraged

Fig. 4. CT image of a patient with VAD-related infection (pump pocket infection).

compression in VAD patients because of fear of dislodgement, a recent review of case studies has shown no dislodgement during the perfor- mance of cardiopulmonary resuscitation [11]. Of course, the VAD pa- tient requiring chest compression is extremely critically ill and highly likely to not survive the event. Defibrillation can still be performed in patients with ventricular dysrhythmias. If possible, place external pads or paddles distant from the pump; of course, the direction of current de- livery must still cross the patient’s heart.

Conclusion

With the increasing prevalence of LVADs, emergency providers will likely manage these patients. Presentations can include inconsequential events unrelated to the VAD as well as life threatening situations resulting from or complicated by the presence of the device. Specialty guidance and consultation are recommended in most of these situations.

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