Abstract
This chapter provides an excellent and in-depth discussion on the complexities associated with caring for children with ventricular assist device support. The author provides a thorough analysis of the available support devices in children based on the patients’ indication for support. perioperative management algorithms for patients supported by the continuous flow devices and Berlin devices are suggested. The perioperative approach for these patients is reviewed in detail with respect to VAD/anesthesia interaction.
A three-month-old previously healthy infant presents to the emergency room with increased work of breathing and a two-week history of rhinorrhea and cough. Chest X-ray demonstrates severe cardiomegaly prompting an echocardiogram which reveals severe left ventricular dilation compressing the right ventricle (RV) severe mitral regurgitation, and severely depressed biventricular function. The differential includes viral myocarditis versus dilated cardiomyopathy.
Over the next week, the patient is intubated for respiratory distress and started on inotropic support to optimize cardiac output. In the past 12 hours, the infant has become increasingly tachycardic to the 180s–190s and hypotensive with blood pressures between 45–55/30–40 in spite of escalating inotropy. Labs are significant for increasing creatinine and elevations in liver enzymes. Oxygenation, ventilation, and lung compliance are stable. Due to concerns regarding impending circulatory collapse, the patient is taken to the OR for initiation of mechanical circulatory support via the Berlin Heart EXCOR ventricular assist device (VAD, Berlin Heart GmbH, Berlin, Germany).
Following device placement and stabilization of hemodynamics and bleeding, the patient is extubated, and anticoagulation is started. Two weeks thereafter, the patient becomes acutely hypotensive with decreased device filling. A large black stool is concerning for a gastrointestinal bleed. With continued instability in spite of transfusion, the patient is taken the operating room for exploratory laparotomy.
What Are the Indications for Ventricular Support in Children?
Heart failure in children can be the end result of multiple causes, with common culprits being congenital heart disease, cardiomyopathies, and myocarditis. While many of these patients can be medically or surgically managed, a minority will require mechanical circulatory support in order to maintain end-organ perfusion, either in the form of a VAD or extracorporeal membrane oxygenation (ECMO). Such support can be used as a bridge-to-recovery, bridge-to-transplantation, or bridge-to-decision.
How Is a VAD Different than ECMO?
While both a VAD and ECMO can provide short-term circulatory support, ECMO offers the additional ability to oxygenate and ventilate using the membrane oxygenator. The oxygenator, although beneficial to those in respiratory failure, also promotes an inflammatory response that can adversely affect hemodynamics as well as coagulation. A VAD functions only as ventricular support, does not use an oxygenator, and thus avoids this inflammatory insult.
VADs are better able to decompress the left ventricle (LV) in comparison to ECMO due to their placement in either the left atrium or left ventricle. A secondary goal of mechanical circulatory support is to rest the left heart by minimizing its preload. On ECMO, blood may return to the left ventricle either by inadequate venous drainage or by the presence of aortopulmonary collaterals. This leads to stretching of the left ventricular myocardium with a subsequent increase in oxygen consumption. The increase in left-sided filling may result in left atrial hypertension and worsened pulmonary dysfunction through increased pulmonary venous pressures. To manage the increase in LV pressure, some patients on ECMO require balloon atrial septostomy.
Moreover, while ECMO runs are generally limited (weeks to months) due to its associated complications, short-term VADs achieved through central cannulation can be transitioned more easily to durable VADs to allow for much longer periods of support (months to years).
In Which Situations Would ECMO Be a Better Choice than a VAD?
ECMO is most commonly deployed in the setting of cardiac arrest (extracorporeal cardiopulmonary resuscitation or ECPR) or acute postcardiotomy dysfunction. ECMO would be the preferred choice in patients with pulmonary as well as circulatory failure, or in patients with acute biventricular failure. Clinical scenarios like severe pulmonary edema in the setting of ventricular dysfunction, right ventricular failure due to pulmonary hypertension, or hemodynamic instability due to sepsis would qualify.
What Determines the Timing of Device Placement?
The ideal time to move forward with device placement remains a challenge in pediatrics. Influencing this decision are the patient’s clinical course, body size, and relatedly, the device options available. The goal is to initiate support prior to the development of irreversible end-organ injury, or when medical therapy has failed. Such endpoints are difficult to define as patients can have variable clinical courses with intermittent periods of decline and improvement. Moreover, the devices available to children are not without risk. The Berlin EXCOR is the only VAD currently approved for use in neonates and infants but has a markedly higher rate of pump thrombosis compared to continuous flow VADs. And while larger children and adolescents can accommodate continuous flow VADs like the Heartmate II (Thoratec Corp., Pleasanton, CA) or HeartWare HVAD (HeartWare, Framingham, MA), the experience with these devices in children remains limited. In this setting, the medical team must weigh the risk of device placement versus the risk of worsening end-organ injury with continued medical management alone. A temporary support device or ECMO may be an option in such cases to allow for recovery of end-organ function before placement of a long-term device.
How Do We Select the Type of VAD to Place?
Different algorithms have been generated to assist with device selection. Relevant factors considered include (1) the type of support needed: cardiac-only, cardiopulmonary, left versus right ventricular support, or biventricular support; (2) the anticipated duration of support; and (3) the size of the patient. There are now many devices suitable for use in children (Figure 70.1).
Figure 70.1 Ventricular assist devices. (A) The Jarvik 2000 devices, left to right adult, child and infant Jarvik. (B) The RotaFlow assist device. (C) The PediMag assist device. (D) The TandemHeart assist device. (E) Variety of Berlin Heart EXCOR devices from left to right 60, 50, 30, 25, 10 mL. (F) Thoratec assist device. (G) Heartmate II assist device. (H) Heartware assist device. (I) SynCardia total artificial heart.
What Are the Options for Temporary and Long-Term Support Devices?
Temporary VADs are deployed for settings in which myocardial function may recover within one to two weeks or if end-organ stabilization is desired prior to placement of a long-term VAD or heart transplant. Options for temporary VADs include the PediMag (Thoratec Corporation), RotaFlow (Maquet), TandemHeart (Cardiac Assist, Inc), and Impella (Abiomed), all continuous-flow devices. The PediMag and RotaFlow are extracorporeal centrifugal pumps that can support the range of pediatric sizes, assist both the right and left ventricle, and connect to centrally placed cannulas. The TandemHeart and Impella, in contrast, are percutaneously placed. Due to the size of the sheaths necessary to deploy these devices, their use is limited to large children and adolescents.
Durable or long-term VADs include both pulsatile and continuous-flow devices. They serve as bridges to transplantation, or rarely, as destination therapy. For infants and small-children, the sole device available is the Berlin Heart EXCOR, a pneumatically driven paracorporeal pulsatile pump. In adolescents and larger children, the size mismatch between “adult” devices and the patient is of lesser concern, and so continuous-flow devices such as the Heartmate II and HeartWare are chosen due to their lower risk profile. An alternative option to continuous-flow devices in larger patients is the SynCardia Total Artificial Heart (SynCardia Systems, Inc., Tucson, AZ), a pneumatically-driven device that entirely replaces the valves and ventricles of the native heart.
Which Noncardiac Procedures Are Most Commonly Performed on Patients with VADs?
The range of diagnostic and therapeutic procedures for which these patients can present is broad and include both those related to device complications and the routine management of the critically ill child. Noninvasive procedures most commonly entail imaging studies like CT (MRI is contraindicated due to the device). Invasive procedures include those needed for venous access, imaging of the heart and device via transesophageal echocardiography, or to address otolaryngologic, general surgical, or neurosurgical issues. For those patients with the Berlin Heart EXCOR, device exchange is commonly performed due to the presence of fibrin strands or clot in the pump.
What Preoperative Information Should One Collect Prior to Planning an Anesthetic?
An evaluation of the patient’s underlying cardiac history, native ventricular function, end-organ dysfunction, and device type are essential. To help in this process, the input of the patient’s cardiologist, cardiac surgeon, or VAD coordinator can be elicited. Complications incurred following device placement should also be sought. These can entail bleeding or thromboembolic events that can manifest as neurologic sequelae like strokes or seizures, gastrointestinal bleeds, or pump thrombosis. The balance between clotting and bleeding is tenuous in VAD patients, and a review of the patient’s anticoagulation strategy and current level of anticoagulation may assist in assessing bleeding risk and in deciding which blood products to order.
Other device risks to assess include infection, which may influence the choice of perioperative antibiotics, and the presence of persistent renal or hepatic dysfunction. Even following VAD placement, patients can be anuric and require continuous renal replacement therapy or intermittent dialysis due to the extent of end-organ injury experienced in the pre-device period. Such knowledge may impact anesthetic drug choice or the type and amount of volume to be administered intraoperatively.
What Device Parameters Should One Assess in the Berlin Heart EXCOR, Heartmate II, and Heartware?
Berlin Heart EXCOR
Pump rate
Operates at a predetermined rate but is adjustable
Pump rate × device volume = cardiac output delivered by the device
Per cent time in systole
Set to mimic native physiology in which diastole is longer than systole
Systolic pressure
Set higher than the native systolic blood pressure
Diastolic pressure
Set higher than the native diastolic pressure
Adequacy of pump filling and ejection
Assessed by direct inspection of the pump
– Wrinkling of the chamber in diastole indicates inadequate fill
– Wrinkling of the chamber in systole indicates impaired ejection
Battery life prior to transport
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