Emergency care of adults with mechanical circulatory support devices

INTRODUCTION — As the use of mechanical circulatory support (MCS) becomes more widespread, there is growing need for dissemination of guidance on management of patients supported by these devices, particularly in critical clinical settings [1,2]. Patients with MCS are primarily cared for in tertiary care centers with specialized left ventricular assist device (LVAD) and total artificial heart (TAH) programs that have the equipment and medical expertise to deliver this care. In the event of an emergency, patients with MCS should generally be directed to the closest MCS center, but this may not always be possible. It is therefore imperative that emergency care providers, including emergency medicine specialists and cardiologists, are familiar with basic emergency management of MCS patients so that these patients can be appropriately cared for until their care can be transferred to their MCS teams.

This topic synthesizes the key elements of emergency care for patients with MCS (continuous flow LVADs or TAH). Indications for and complications of MCS are discussed separately. (See "Treatment of advanced heart failure with a durable mechanical circulatory support device" and "Management of long-term mechanical circulatory support devices".)

GUIDANCE FOR EMERGENCY MEDICAL SERVICES TEAMS — In the event of an emergency, all efforts should be made to direct patients with MCS to their respective MCS/left ventricular assist device (LVAD) centers.

If an LVAD- or total artificial heart (TAH)-supported patient is directed to a non-device center, it is crucial that emergency medical services personnel make every effort to bring the patient's peripheral equipment needed to maintain LVAD/TAH function (including the batteries, power base unit, and controllers), even if this entails a slight delay in transporting the patient. This equipment will be needed to support the patient until they can be transferred to a center experienced with MCS.

APPROACH TO THE PATIENT WITH A CONTINUOUS FLOW LVAD — This section will focus on the care of patients supported with a continuous-flow (CF) left ventricular assist device (LVADs). Despite subtle differences among CF-LVADs, the approach to the unconscious or hypotensive patient is similar for these devices (eg, HeartMate 3, HeartWare).

Initial clinical assessment — The initial clinical assessment includes history, measurement of blood pressure (BP), physical examination (including assessment of perfusion by skin temperature and capillary refill since there is often no palpable pulse, and assessment of signs of right heart failure such as jugular venous distension and hepatomegaly), and an electrocardiogram (ECG).

Pertinent history (eg, bleeding, fever, severe dyspnea, chest pain, etc) is sought to help guide diagnosis and treatment.

One of the greatest challenges in managing LVAD-supported patients is the difficulty in performing a basic cardiovascular physical exam. With CF devices, there is often no pulse, minimal pulse pressure, and no discernable heart sounds, which makes cardiac assessment difficult and may complicate the initial assessment of a critically ill patient. Heart rate and rhythm should be ascertained by cardiac telemetry or an ECG. The cardiac auscultation is remarkable only for a continuous hum, but presence of this sound confirms that the device is operating. With newer CF pumps such as the HeartMate 3, there will be regular, intermittent interruption of the continuous hum due to the brief programmed slowing of the device that introduces an intermittent pulse, which sometimes, but not frequently, is palpable.

Noninvasive BP measurements are difficult in CF LVAD patients due to diminished pulse pressure, and automated BP monitors may fail to measure BP. Doppler ultrasound is recommended as the most reliable noninvasive method to assess BP in CF LVAD patients. Doppler assessments are achieved in approximately 95 percent of patients and have high accuracy. Doppler BP measurements are obtained using a sphygmomanometer with the Doppler probe placed over the brachial or radial artery. The cuff is inflated until the pulse is no longer audible and then deflated, allowing the reestablishment of blood flow. The BP reading is made when the arterial flow is audible again. This gives a single BP reading, as opposed to systolic and diastolic readings.

Whether Doppler BP more closely approximates systolic or mean arterial BP in LVAD patients is unclear, with some studies demonstrating a better approximation with mean BP and others a better agreement with systolic BP [1,3,4]. Generally, in patients with some pulsatility, the Doppler measurement will more accurately reflect systolic BP, and in the absence of any pulsatility [5], it will better represent the mean BP. Emergency departments and emergency medical services responders should be equipped with Doppler-measuring devices to serve this patient population. Current recommendations are to maintain the mean arterial pressure (MAP) in the range of 70 to 80 mmHg and not to exceed 90 mmHg, as high afterload may compromise optimal function of the LVAD.

Automated BP monitors can be accurate in LVAD patients, but their success rate in measuring BP is low (approximately 50 percent) owing to reduced pulse pressure [3,4,6].

An arterial catheter provides the most accurate (and continuous) BP monitoring and should be placed in hemodynamically unstable patients when feasible. Because the patients do not have a palpable pulse, arterial catheters should be placed with ultrasound guidance. (See "Intra-arterial catheterization for invasive monitoring: Indications, insertion techniques, and interpretation" and 'General measures for hypotensive LVAD patients' below.)

Additional elements of the physical exam that aid in the rapid assessment of the critically ill LVAD patient are evaluation for congestion (ie, presence of jugular venous distension, hepatomegaly, and peripheral edema) or volume depletion, evaluation for hypoxia (by skin color), as well as an assessment of peripheral perfusion by skin temperature and capillary refill. If the patient is awake and has normal gross neurological function, the patient is likely well perfused.

Pulse oximetry may be used in LVAD patients, but a low oximetry reading may reflect the lack of pulsatile flow rather than actual hypoxemia. By contrast, a normal pulse oximetry result in an LVAD patient is likely to be accurate [1].

General measures for hypotensive LVAD patients — In all hypotensive patients with an LVAD, an arterial catheter should be placed, using ultrasound guidance as soon as feasible, in any limb artery to allow continuous monitoring of the BP. With an arterial line, resuscitation can be more tailored, as the clinicians can continuously observe the BP.

If chest compressions are indicated in an unconscious hypotensive patient and the LVAD is functioning, only gentle compressions are required, as all that is needed is to drive blood through the lungs (the LVAD will continue to provide the systemic flow). With an arterial line, the compressions are tailored to that which achieves adequate arterial pressure. Overly vigorous chest compressions should be avoided, particularly in the early postoperative phase, as they can result in cardiac injury and hemorrhage secondary to dislodging of the cardiac attachments of the device or cardiac rupture. (See 'Approach to the unconscious patient' below.)

Approach to hypotension in the conscious patient — Hypotension is present when the MAP is below 60 mmHg. For patients with an LVAD without an arterial catheter in place, the MAP is commonly estimated by the Doppler BP. Emergency personnel should follow their standard approach to history taking and the physical exam, focusing on the volume status and perfusion assessment of the patient. With a conscious hypotensive patient, there is the opportunity to elicit a history, which may help to identify the etiology. A history describing hematemesis or hematochezia will point the clinician to bleeding and volume loss, high fever suggests sepsis, and tea-colored urine suggests pump thrombosis.

An approach for the evaluation of conscious patients with hypotension is provided (algorithm 1). Our approach emphasizes the use of pump flow, power, and alarm readings from the display module, which report data received from the system controller, elements of the physical examination (particularly jugular venous pressure [JVP] and patient temperature), ECG (to identify significant arrhythmias), and bedside echocardiography, to identify the underlying cause of hypotension ranging from hypovolemia (caused by bleeding and other causes of volume loss), biventricular failure (from pump thrombosis, failure, or dysfunction), and sepsis. (See "Management of long-term mechanical circulatory support devices", section on 'Device interrogation'.)

The clinical profiles of common causes of hypotension with low flow are described in the table (table 1). The identified cause will then direct the management, which can range from transfusions, antibiotics, and defibrillation to adjusting the LVAD speed. For device-naïve centers where emergency personnel will have little experience with mechanical support, it is best to approach a device patient in the same manner as any hypotensive patient (table 2), while simultaneously contacting that patient’s LVAD center. Analysis of high- or low-flow alarms or high or low power signals will have little meaning to naïve practitioners, and this information should be used to communicate with the LVAD center but not to act on directly. The table (table 1) emphasizes the use of the physical exam for presence or absence of congestion and quick-look echocardiography as key strategies in diagnosing and managing these patients.

For practitioners familiar with LVAD devices, the approach to the conscious patient with an LVAD with MAP <60 mmHg includes checking LVAD parameters including the flow, pulsatility index, and power. Ideal flow parameters can be estimated either from a patient’s size, from the patient’s history, or from a review of the device history.

Low flow — If the LVAD monitor shows low flow or unrecordable flow, the following approach is recommended to identify and manage the cause (see "Management of long-term mechanical circulatory support devices", section on 'Device interrogation'):

●Is there a low JVP?

•If yes, evaluate causes of hypovolemia (eg, bleeding, diarrhea, vomiting, overdiuresis) and treat (including intravenous bolus fluids).

●If JVP is not low, obtain ECG. Is ventricular fibrillation (VF) or ventricular tachycardia (VT) present?

•If yes, treat with cardioversion and antiarrhythmic therapy.

●If no VF or VT, obtain quick-look echocardiogram. (See 'Echocardiogram' below.)

If the above evaluation, including quick-look echocardiogram, does not reveal a cause of hypotension, other causes of hypotension with low LVAD flow should be considered, such as a combination of causes (eg, right heart failure plus hypovolemia with which echocardiogram may not show right ventricular [RV] dilation). Pneumothorax should be suspected in patients with displaced cardiac chambers on echocardiography.

Echocardiogram — In patients with an LVAD, a focused bedside echocardiogram can identify some causes of hypotension [7]:

●Suction is suggested by the presence of excessive LV decompression with small LV size. If suction is suspected, then LVAD speed is reduced and LV cavity size reassessed. A suction event occurs when LV myocardium partially occludes the LVAD inflow cannula and reduces inflow. Suction events are caused by low LV preload relative to the pump speed. Of note, LV suction can also be a manifestation of severe RV dysfunction or severe hypovolemia, or any other cause of decreased preload to the LV.

●RV dysfunction, which may manifest as RV dilation and/or hypokinesis. RV dysfunction is treated by supportive care including inotropes, optimization of respiratory function, diuresis, or pulmonary vasodilator as appropriate. If pulmonary embolism is suspected, then a computed tomography (CT) angiogram should be performed. (See "Pulmonary hypertension due to left heart disease (group 2 pulmonary hypertension) in adults" and "Epidemiology and pathogenesis of acute pulmonary embolism in adults" and "Clinical presentation, evaluation, and diagnosis of the nonpregnant adult with suspected acute pulmonary embolism".)

●Cardiac tamponade is identified by the usual echocardiographic signs including identifying a pericardial effusion with right atrial, RV, and/or left atrial collapse (see "Cardiac tamponade" and "Pericardial effusion: Approach to diagnosis", section on 'Echocardiography'). If cardiac tamponade is present in a patient with an LVAD, the patient should be referred to an LVAD center, as this will often indicate intrapericardial hemorrhage, which may require surgical treatment. Needle drainage without fluoroscopic imaging is discouraged because of the low yield and also the potential for harm, as the LVAD outflow graft may traverse the typical course for needle pericardiocentesis.

●Signs of inadequate LVAD unloading include increased LV and left atrial chamber size, increased duration of aortic valve opening, increased mitral inflow peak E wave velocity, decreased mitral inflow deceleration time, worsening mitral regurgitation, and elevated pulmonary artery systolic pressure (which may be estimated using the tricuspid regurgitation jet velocity).

●Severe aortic insufficiency appears as retrograde flow through the aortic valve and can result in reduced systemic perfusion or severe pulmonary edema [8].

High flow — If the LVAD monitor shows high flow, does the display show high power or normal power?

●With normal power – Patients with hypotension with high flow and normal power are likely to have distributive (vasodilatory) shock.

•If fever is present, sepsis should be suspected and, if present, treated with appropriate antimicrobial therapy and vasopressor therapy as needed.

•If fever is not present, causes include vasodilator medications, or early sepsis. Vasodilator medications should be discontinued and appropriate antimicrobial therapy and vasopressor therapy is administered as needed.

●With high power – If there is high flow and high power, an echocardiographic ramp test is performed to assess for evidence of LVAD thrombosis (see 'Echocardiographic ramp test' below). An elevated serum lactate dehydrogenase level also suggests pump thrombosis [9].

•If the echocardiographic ramp test is suggestive of LVAD thrombosis, then the patient should receive appropriate treatment, as discussed elsewhere. (See 'Echocardiographic ramp test' below and "Management of long-term mechanical circulatory support devices", section on 'Thrombosis'.)

•If the echocardiographic ramp test is not suggestive of LVAD thrombosis, evaluate for other causes of high power.

Echocardiographic ramp test — An echocardiographic ramp test is performed to determine if there is evidence of LVAD thrombosis [7,10,11]. A ramp test uses echocardiographic parameters (eg, LV end-diastolic diameter, duration of aortic valve opening, and deceleration time of mitral inflow) and pump power readings to assess whether cardiac loading conditions or device performance appropriately change in response to increasing LVAD pump speed. The pump speeds used for a ramp test are unique for each LVAD device (eg, for the HeartMate 3 device, speeds can be tested over a range of 4000 to 7000 rotations per minute).

Approach to the unconscious patient — The approach to cardiopulmonary resuscitation (CPR) in patients with an LVAD is similar to the approach to CPR in other patients (algorithm 2). However, due to the absence of a pulse and variable dependence on the device for circulatory support, experienced providers are required to measure blood pressure and manage possible device failure. In addition, we suggest prompt placement of an end-tidal CO₂ monitor or arterial line to identify and manage circulatory collapse or return of adequate circulation.

If both respirations and perfusion appear adequate and the patient is unconscious, assess for hypoxia, stroke, metabolic causes of coma (eg, hypo- or hyperglycemia), or sedation. Stroke can occur in approximately 10 to 15 percent of device-supported patients [12]. (See "Stupor and coma in adults".)

Our experts agree that starting chest compressions in patients with an LVAD who are unresponsive and have either a low or undetectable blood pressure is preferable to a delay in compressions to assess LVAD function. The latter is the approach of the American Heart Association (AHA) [1]. Our preference is influenced by the complexity of assessing and restarting a dysfunctional LVAD and the potential for a device restart to cause stroke in patients with thrombus formation.

This topic and the 2017 AHA CPR with MCS scientific statement follow an airway, breathing, circulation (ABC) approach to CPR; this method differs from the chest compressions before rescue breaths (CAB) approach in the 2010 AHA adult basic life support guidelines [1,13].

APPROACH TO PATIENTS WITH TAH WHO ARE UNRESPONSIVE, HAVE ALTERED MENTAL STATE, RESPIRATORY DISEASE, OR HYPOTENSION — Use of the total artificial heart (TAH) as a bridge to cardiac transplantation continues, but the volume of TAH implantations is very low (fewer than 100 cases per year in the United States) [12,14]. Most of these patients will remain in their device centers while awaiting transplant. Rarely, patients may be discharged on a portable TAH driver and thus could have medical emergencies in the community.

Implantation of the TAH involves excision of the native heart with anastomoses on the right side to the right atrium and the pulmonary arteries and on the left side to the left atrium and aorta. The pump is rigid and noncompressible and is powered pneumatically by an external driver connected to the TAH by drivelines. Unlike a continuous-flow, left ventricular assist device, the TAH is pulsatile, which allows for standard means of blood pressure measurement.

In regard to cardiopulmonary resuscitation (CPR), there are two major caveats:

●There is no ECG. The heart is removed, and there is no cardiac rhythm. Flatline on the ECG tracing is the norm and should not be treated as asystole.

●The chambers of the device are rigid and noncompressible. Chest compressions are ineffective and should not be attempted.

Hypotension in the early postoperative period is most frequently the result of bleeding. Compression of the pulmonary veins and left atrium can occur from bleeding and requires surgical intervention.

●In the hospital and at home, the most frequent causes of sudden hemodynamic collapse are inadvertent kinking or disconnection of the external pneumatic drivelines. The first response should be to inspect these connections.

●If the device is not pumping, check the power source connections and restart or switch the patient to a back-up console. If the device is not working and function cannot be restored within a few minutes, then anoxic brain injury will invariably occur; for this reason, extracorporeal membrane oxygenation or emergency surgery is not an option for resuscitation, as the outcome will invariably be a severely neurologically injured patient.

If the device is working, check the blood pressure, as increased afterload from severe hypertension can reduce device emptying resulting in pulmonary edema and respiratory distress. This is a rare event, but if observed, treat hypertension with oral nitroglycerin or hydralazine. Hypotension is treated initially with fluids, and the differential diagnosis of bleeding and sepsis is explored by standard diagnostic methods.

In patients with unresponsiveness, neurologic causes of unresponsiveness need to be considered given the frequency of stroke in these patients. (See "Stupor and coma in adults".)

SUMMARY AND RECOMMENDATIONS

●Guidance for emergency medical service teams – In the event of an emergency, all efforts should be made to direct patients with MCS to their respective MCS centers. If a left ventricular assist device (LVAD)- or total artificial heart (TAH)-supported patient is directed to a non-device center, it is crucial that EMS personnel make every effort to bring the patient's peripheral equipment needed to maintain LVAD/TAH function (including the batteries, power base unit, and controllers), even if this entails a slight delay in transporting the patient. This equipment will be needed to support the patient until they can be transferred to a center with LVAD experience. (See 'Guidance for emergency medical services teams' above.)

●General measures for patients with and LVAD and hypotension – Blood pressure (BP) for patients with continuous flow (CF) LVADs is difficult to measure and is best recorded using a Doppler device placed over the brachial or radial artery with a sphygmomanometer, which can be used to approximate mean arterial pressure (MAP). (See 'Initial clinical assessment' above.)

In all persistently hypotensive patients with an LVAD, an arterial catheter should be placed using ultrasound guidance as soon as feasible to allow continuous monitoring of BP. With an arterial line, resuscitation can be more tailored, as the clinicians can continuously observe the BP. (See 'General measures for hypotensive LVAD patients' above.)

●Approach to hypotension – If the MAP is below 60 mmHg and the patient is conscious, elicit a focused history on causes for hypotension such as bleeding or infection, assess fluid status by jugular venous pressure and lung exam, check the ECG, and interrogate the LVAD to detect flow, power, and alarms (algorithm 1). (See 'Approach to hypotension in the conscious patient' above.)

●Advanced cardiac life support and CPR – The approach to cardiopulmonary resuscitation (CPR) in patients with an LVAD is similar to the approach to CPR in other patients (algorithm 2). However, due to the absence of a pulse and the potential for device failure, experience providers are required to measure blood pressure and manage possible device failure. In addition, prompt placement of an end-tidal CO₂ monitor or arterial line enhance the ability to identify and manage circulatory collapse or return of adequate circulation.

●Total artificial heart – In patients with a TAH who are unresponsive, the absence of electrical heart activity (asystole on ECG) is expected. External chest compressions should not be attempted in such patients. In the event of hemodynamic collapse, driveline connections should be checked for kinking, the power source connection verified to be intact, and BP checked. (See 'Approach to patients with TAH who are unresponsive, have altered mental state, respiratory disease, or hypotension' above.)