Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Chapter 5 

Left Ventricular Assist Device– Supported Patient Presenting for Noncardiac Surgery Marc E. Stone, MD

Key Points 1. Regardless of the level of complexity or invasiveness of the planned procedure, the perioperative considerations and the anesthetic approach to left ventricular assist device (LVAD)–supported patients are the same because the removal of sympathetic tone by sedation or induction of general anesthesia should be expected to initially exert the same effect on the physiology of ventricular assist device (VAD)-supported patients regardless of the planned procedure. 2. A team-based approach and preoperative planning regarding intraoperative management and postoperative recovery location are key to the successful perioperative management of VAD-supported patients presenting for noncardiac surgery. 3. An understanding of the physiology of the VAD-supported state is the key to safe intraoperative management. 4. No specific sedatives or anesthetic agents are contraindicated because of the presence of a VAD, but the required anticoagulation often precludes major regional techniques. 5. Most patients with a modern nonpulsatile left VAD (LVAD) do exhibit pulsatility of their circulation; however, they can lose this pulsatility after induction because of the relative hypovolemia and vasodilation that accompany an anesthetic, bringing considerations of appropriate monitoring. 6. Optimization of volume status will help maintain pulsatility of the circulation in a VAD-supported patient. 7. Intraoperative changes to baseline VAD settings are rarely (if ever) needed in a VAD-supported patient who was optimized on these settings when not anesthetized.

ROLE OF VENTRICULAR ASSIST DEVICES IN THE MANAGEMENT OF HEART FAILURE The prevalence of heart failure (HF) worldwide is estimated to be about 26 million people. In the United States alone, there are approximately 5.7 million adults with HF, and this number is projected to increase to approximately 8 million by the year 2030. Mechanical circulatory support (MCS) with a left ventricular assist device (LVAD) is now the standard management for patients with chronic refractory HF. The goals of LVAD support are twofold: (1) to decompress the failing left ventricle, thus dramatically reducing left ventricular (LV) myocardial oxygen demand (which, in certain 100

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Keywords heart failure INTERMACS LVAD left ventricular assist device mechanical circulatory support HeartMate II HeartMate 3

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Table 5.1  Indications, Explanations, Current Frequency, and Current Success Rates for Implantations of Durable LVADs in the United States Indication

Explanation

Bridge to transplantation

The LVAD is used to bridge the patient with chronic, progressive heart failure to transplantation. This includes patients with an acute exacerbation of chronic heart failure. The LVAD is used to restore systemic perfusion to an adequate level and thus improve multisystem organ failure such that the patient might be an acceptable transplant candidate. The LVAD is used as a final, permanent management strategy for end-stage, refractory heart failure in a transplantineligible patient.

Bridge to candidacy

Destination therapy

Current U.S. Frequency (%) 26

Current U.S. Success 86% alive at 1 year 31% transplanted 55% still supported

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

circumstances, may promote recovery of the failing myocardium), and (2) to maintain adequate systemic perfusion to avert cardiogenic shock. The pump itself is attached to the heart and great vessels by cannulae that allow continuous collection of blood returning to the left side of the heart and ejection of that blood into the aorta. According to the latest data from the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), there are currently 2000 to 3000 LVAD implantations annually at approximately 160 centers in the United States alone. Table 5.1 outlines the current indications for long-term LVAD support, as well as the current frequency and current success of each indication in the United States. Until 2009, bridge to transplantation (BTT) was the most common indication for implantation of a durable LVAD, but the approval of the HeartMate II for destination therapy (DT) in 2010 heralded a new era of MCS because before that, a durable device that could provide years of support did not exist. Continuous-flow (CF) devices (e.g., the HeartMate II) have now been used to provide support for 100% of patients implanted for DT since 2010, as well as for more than 95% of all other LVAD indications. The first generation of pulsatile, implantable devices is essentially no longer in use. The most common indication for LVAD implantation is now DT (see Table 5.1), with BTC the second most common indication and BTT (the traditional indication before 2010) now third most common. Overall, all-comer survival with a durable

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84% alive at 1 year 20% transplanted 64% still supported

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>75% alive at 1 year >50% alive at 3 years

LVAD, Left ventricular assist device.

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LVAD now approaches 80% at 1 year, and the 4-year survival rate now approaches 50%. As the survival rate has increased, the number of patients supported by LVADs requiring interventional and diagnostic procedures and noncardiac surgery (NCS) procedures has increased. The volume of NCS in LVAD-supported patients varies from institution to institution and practice to practice, but current trends indicate that the vast majority of NCS procedures performed in this population are now diagnostic and therapeutic endoscopies. Although supported patients still tend to receive their care in the academic VAD centers, there has been some expansion into the private practice settings and even some endoscopy centers.

INTERMACS

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INTERMACS is a North American registry database sponsored by the National Heart, Lung and Blood Institute; the Food and Drug Administration (FDA); and the Centers for Medicare and Medicaid Services (CMS). Centered at the University of Alabama at Birmingham, INTERMACS was established in 2005 for patients receiving long-term MCS therapy with implantable, durable devices to treat advanced HF. Essentially, INTERMACS collects clinical data about VAD patients as it happens. Postimplant follow-up data are collected at 1 week, 1 month, 3 months, and 6 months and every 6 months thereafter. Major outcomes after implant (e.g., death, transplant, explant, rehospitalization, and adverse events) are entered by implanting centers as such events occur and at defined follow-up time points, along with more “complex” endpoints (e.g., the patient’s level of function and quality of life), which are critical to the evaluation of current MCS therapy, for which improvements in both survival and function have been compelling. These indices are becoming increasingly important as survival improves, and new devices will be compared for outcomes beyond simple survival. A similar European-based database called EuroMACS exists in Europe, and there is also a database of pediatric MCS called PEDIMACS. A new international database maintained by the International Society for Heart and Lung Transplantation (ISHLT) called IMACS now exists, and reports of the international experience will soon provide data regarding international outcomes. Regarding LVAD implantation by indication, the most recent INTERMACS data available at the time of this writing report that DT continues to be the most prevalent indication for LVAD implantation, having increased to 45.7% of all implants in 2014 (compared with 14.7% in 2006 and 2007, and 28.6% between 2008 and 2011). In the sixth annual report (released in 2014), BTC was the second most common modern indication for VADs, with BTT in third place, but in the seventh annual report (released in 2015), 30% of patients were already listed for transplantation at the time of implantation, with an additional 23% implanted as a BTC. “Bridge to recovery” with short-term VADs continues to constitute only a very small percentage of the usage of this technology in the most current report (0.2% in 2014). Additional data available from INTERMACS regard survival by both timing of implantation and by type of device. The INTERMACS profile (also called the INTERMACS level) describes the clinical condition of the patient on a scale from 1 to 7, with a numerically lower profile indicating more severe illness. A level 7 patient is simply in the advanced stages of HF (e.g., New York Heart Association class III), and the clinical condition of the patient gets worse as the INTERMACS profile number gets lower. For example, a level 4 patient has symptoms at rest, a level 3 patient is essentially hemodynamically stable but inotrope dependent, a level 2 patient is deteriorating despite inotropes, and a level 1 patient is essentially in cardiogenic shock despite maximal therapy. 102

SPECIFIC DEVICES IN CURRENT USE The two most commonly implanted FDA-approved durable devices in the United States are the HeartMate II (Abbott) and the HeartWare HVAD (Medtronic). The Heartmate 3 is a relatively recently introduced implantable, durable device that has received FDA approval for certain indications, although approval of other indications is still pending at the time of this writing.

HeartMate II The HeartMate II (HM II; Fig. 5.1) is currently the most commonly implanted durable LVAD in the United States and in many countries around the world. The HM II is a miniaturized “second-generation” continuous axial flow pump that was FDA approved as a BTT in 2008 and as DT in 2010. According to the manufacturer, more than 16,000

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

The experience has been that if a durable LVAD is implanted too early (at numerically higher INTERMACS levels), the risks of adverse events outweigh the benefits. Conversely, if the VAD is not implanted until the patient is already likely developing multisystem organ failure (e.g., level 1), the likelihood of ultimate rescue is low, and the survival rate is poor. Survival data suggest that implantation of durable LVADs when the patient is level 3 or 4 would be ideal to balance the risks and benefits. Large multicenter head-to-head trials conducted in the modern era with modern devices (e.g., Momentum 3, Endurance) have reported the profile of risks and benefits associated with each of the modern devices (see Suggested Reading).

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Fig. 5.1  HeartMate II. (Courtesy Abbott/Thoratec, Inc., Pleasanton, CA.)

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patients worldwide have received the HM II, with the longest duration of support more than 8 years. Although the impeller is the only moving part, it is stabilized at both ends by bearings. Current postimplantation protocols call for warfarin anticoagulation to an international normalized ratio (INR) of 2.5 to 3.5 plus aspirin. The currently reported rate of successful BTT with the HM II is approximately 86%. Fig. 5.2 shows and discusses details regarding parameters displayed on the HM II clinical control screen.

HeartWare HVAD The HeartWare HVAD (Fig. 5.3) is a miniaturized CF centrifugal pump with a magnetically driven, hydrodynamically suspended impeller (the impeller floats in the blood without any bearings). This device is implanted within the pericardium without any significant intervening “inflow cannula”; it directly abuts the LV apex. This design provides for potential use in patients with smaller body surface areas and ostensibly results in shorter surgical implantation times. The HVAD was approved as a BTT in 2012. According to the manufacturer, more than 10,000 patients worldwide have received the HVAD, with the longest duration of support more than 7 years. Current postimplantation protocols call for warfarin anticoagulation to an INR of 2.0 to 3.0 plus aspirin. The manufacturer also recommends testing for aspirin resistance and, if detected, the adjunctive use of clopidogrel, dipyridamole, or both. The currently reported rate of successful BTT with the HVAD is 88% to 90%. The HVAD was recently approved as a DT device in the United States as a result of the ENDURANCE trial and the ENDURANCE supplemental trial. Experience with the HVAD as an implantable right ventricular assist device (RVAD) is accruing. Fig. 5.4 shows and discusses details regarding parameters displayed on the HeartWare clinical control screen.

HeartMate 3

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The HeartMate 3 (HM 3, Thoratec, Pleasanton, CA; see Fig. 5.5) is a miniaturized CF centrifugal pump with a magnetically driven, magnetically suspended impeller. It is implanted within the pericardium and thus shares some of the potential advantages of the HVAD. Design features ostensibly improve hemocompatibility and reduce the risk of thrombus formation. Similar to the HM II and the HVAD, the HM 3 can reportedly produce 10 L/min of flow. The HM 3 was demonstrated to be noninferior to the HM II in the MOMENTUM 3 trial regarding survival free from either disabling stroke or reoperation for device malfunction at 6 months after implantation. This third-generation device was FDA approved for “short-term indications” in 2017, and its evaluation for “long-term indications” (e.g., DT) is ongoing.

PERIOPERATIVE MANAGEMENT The perioperative management of an LVAD-supported patient can be divided into preoperative assessment and planning for the case, intraoperative management, and postoperative considerations.

Overview of the Preoperative Assessment Regardless of the venue or level of complexity or invasiveness of the planned procedure, the perioperative considerations and the anesthetic approach to the LVAD-supported 104

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Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Fig. 5.2 Clinical control screen of the HeartMate II (HM II). Pump flow is continuous estimate of the output from the device (derived from the speed of the impeller and the power it takes to achieve that speed). Flows encountered clinically usually range from 4 to 6 L/min, but the device is capable of flowing up to 10 L/min. If the outflow is less than the lower limit set as the alarm condition, three dashes (—) will be displayed in this box instead of a number. This does not necessarily mean there is no outflow. It only means there is less flow than the lower limit set for the alarm. There is a very loud screeching alarm annunciated from the controller if there is no outflow. This is an exceedingly rare thing to encounter. The pump speed is the number of revolutions per minute (rpm) at which the impeller is rotating. In most situations, this is a set and fixed value. Speeds encountered clinically are usually in the range of 9000 to 10,000 rpm, but some centers run the ventricular assist device (VAD) at lower rotational speeds to allow the left ventricle (LV) to do more work. Increases in speed will facilitate ventricular unloading by increasing flow through the pump. If the amount of flow exceeds the available volume in the ventricle, a “suckdown” will occur. Decreasing the speed can potentially increase the volume in the LV, although initial steps to increase LV volume would ideally involve infusing volume or supporting right ventricle (RV) function as needed. The pulsatility index (PI) is a unitless index of how much pulsatility the device senses as a result of ventricular contractions. Initially, the failed ventricle contributes very little (which is why a VAD was needed) but as the excessive wall tension is decreased in the failing ventricle as a result of VAD action, the ventricle begins to recover, and as long as volume in the LV is optimized, the ventricle will again begin to contract, forcing little pulses through the VAD, as well as through the aortic valve. The PI can be used as a trend to assist with optimization of volume status. PI values around 2 to 3 are typical when there is little pulsatility and the VAD is doing most or all of the work. PI values of 4 to 6 are typical when the partially decompressed ventricle recovers. The PI will decrease with hypovolemia and will increase with myocardial recovery. Thus a low (or falling) PI likely indicates the need to increase the volume status or possibly to increase contractility. RV dysfunction can lead to a decreased filling of the LV. Pump power is the energy required to spin the impeller at the set speed and is partially determined by flow. Increases in speed or flow or resistance to flow will require increased power. Power is generally in the range of 5 to 7 W. A sudden increase in the power requirement may suggest significantly increased afterload, but it can also suggest thrombus or other obstruction to rotor rotation. These will be exceedingly rare events. Abrupt increases in power not explainable by an increase in pump speed should always be investigated. A gradual increase in power to high levels over time suggests developing thrombus in the pump.

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Perioperative Medicine Fig. 5.3  HeartWare HVAD. (Courtesy HeartWare Inc., Framingham, MA.)

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Fig. 5.4 

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patient are the same because the removal of sympathetic tone by sedation or induction of general anesthesia should be expected to exert the same initial effect on the physiology of the VAD-supported patient regardless of the planned procedure. Thus a thorough, thoughtful assessment of the VAD-supported patient is mandatory, even for what appear to be the most minor of cases, because (1) even an ambulatory and seemingly uncompromised VAD-supported patient may have some level of underlying renal, hepatic, pulmonary, or central nervous system insufficiency, and (2) the physiology of the VAD-supported state can be adversely affected by inadequate optimization before and during the anesthetic. It should also be appreciated that deterioration in the perioperative period may preclude full recovery or may disqualify a patient from later heart transplantation. 107

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Fig. 5.4, cont’d Clinical control screen of the HVAD. The left side of the HVAD control screen shows a continuous estimate of the output from the device in liters per minute (top left), the speed at which the impeller is rotating in revolutions per minute (rpm) (below the output), a readout of the power consumption in watts (below the pump speed), the mode of operation (in this case, a “fixed” speed) and the status of “the suction alarm.” In the panel to the right are the power and flow waveforms. At the bottom of the screen are indicators of A/C mains power and a battery status meter. According to the manufacturer, the flow estimation (top left) should be used as a trending tool only. The readout of device flow is derived from the speed of the impeller, the power it takes to achieve that speed, and the blood viscosity. The viscosity is calculated from the patient’s hematocrit, so to obtain the most accurate estimate of flows with this device, the patient’s hematocrit must be input into the monitor and the hematocrit updated whenever it changes by 5% or more in either direction. Flows encountered clinically usually range from 4 to 6 L/min, but the device is capable of flowing up to 10 L/min. The amount of flow a centrifugal pump can generate is dependent on a number of factors to do with the diameter and geometry of the impeller, the capacity of the motor, and so on. However, of great importance is the pressure differential across the pump, visualized on the flow rpm at which the impeller is rotating. In most situations, this is a set and fixed value. Speeds encountered clinically are usually in the range of 2400 to 3200 rpm, but the device range is from 1800 to 4000 rpm. Increases in speed will facilitate ventricular unloading by increasing flow through the pump. If the amount of flow exceeds the available volume in the ventricle, a “suckdown” will occur. Infusing volume or decreasing the speed will increase the volume in the left ventricle. Power is the power required to spin the impeller at the set speed and is partially determined by flow. Increases in speed or flow or resistance to flow will require increased power. Power is generally in the range of 5 to 7 W. A sudden increase in the power requirement may suggest significantly increased afterload, but it can also suggest thrombus or other obstruction to rotor rotation. These will be exceedingly rare events. Abrupt increases in power not explainable by an increase in pump speed should always be investigated. A gradual increase in power to high levels over time suggests developing thrombus in the pump. The HVAD provides no numeric readout of the pulsatility, but one can physically see the pulse pressure on the flow waveform. The peaks are the flow during systole and the troughs during diastole, so the difference, in effect, reflects the “pulse pressure” or “pulsatility” of the patient during support. Of course, the difference in velocity is coming from LV contraction, forcing blood through the pump at a higher velocity during systole. This waveform can help greatly with fluid management in real time because just as in a patient without a VAD, one can increase the pulse pressure by administering fluid to optimize volume status. Maintenance of a pulse pressure is also important to prevent retrograde flow through the pump, as well as to prevent suction events. In general, the diastolic flows should be kept greater than 2 L/min, and there should be at least 2 L/min difference between systolic and diastolic flows. Even though suckdown events are rare, one nice feature of the HVAD in this regard is the “suckdown” detection and alarm. The HVAD controller establishes a diastolic flow baseline. If the diastolic flow falls to less than 40% of the established baseline for more than 10 seconds, the suckdown detection alarm will be annunciated. It would be optimal, however, to observe that the diastolic flow is decreasing and proactively prevent suckdown events from occurring in the first place. For example, volume status might be augmented if hypovolemia or vasodilation is believed to be the problem. If right ventricular (RV) dysfunction results in underfilling of the left ventricle, then RV function would be supported with inotropes, decrease the PVR, or both.

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Perioperative Medicine Fig. 5.5  HeartMate 3. (Courtesy Abbott/Thoratec, Inc., Pleasanton, CA.)

If the clinician has questions or concerns, the importance of communicating in advance whenever possible about key issues with a knowledgeable colleague, the physician managing the VAD, the surgeon, and dedicated VAD staff cannot be overemphasized. Fortunately, experience has shown that the anesthetic management of a VAD-supported patient is not so different from that for a nonsupported patient, but an additional level of advanced planning is required. In addition to the usual areas of anesthetic inquiry at the preanesthetic assessment (e.g., airway, dentition, functional status, allergies), Table 5.2 outlines specific areas of focus and consideration during the preanesthetic assessment of a VAD-supported patient, and key areas are discussed in more detail later. I

Planning Appropriate Perioperative Anticoagulation Preoperative planning by the anesthesiologist, surgeon, and cardiologist managing the VAD must determine how anticoagulation will be managed for the perioperative period. An INR of approximately two to three times normal is required for both the HM II and the HVAD to prevent thrombus formation and potential thromboembolism. Maintenance is usually with warfarin and aspirin (and antiplatelet agents in some patients). In elective cases in which bleeding risk is substantial, warfarin can be discontinued or the patient bridged to surgery with heparin, but it would be imprudent to automatically “discontinue heparin on call to the operating room (OR)” or advise a patient to stop warfarin without preoperative discussion with the physician managing the VAD. In general, the amount of anticoagulation can be safely reduced for the immediate perioperative period to the lower limits of manufacturers’ recommendations (which may allow for brief periods without any), but most semi-invasive procedures (e.g., endoscopies) and many general surgical procedures can be safely performed with mild levels of anticoagulation (exceptions include ophthalmologic procedures, neurosurgery, and spine surgery). When needed, infusions of fresh-frozen plasma (FFP), cryoprecipitate, or platelets may be guided by point-of-care (POC) tests (e.g., partial thromboplastin time, INR, thromboelastography, rotational thromboelastometry) 108

Area of Focus

Rationale

End-organ insufficiency

Even seemingly uncompromised VAD-supported patients may exist with varying degrees of renal, hepatic, pulmonary, or CNS insufficiency. The pathophysiology of the current surgical disease and any coexisting disease states must be taken into account when planning the optimization of the VAD-supported patient for surgery. It is common for LVAD-supported patients to have an ICD or a pacemaker. Perioperative management of pacemakers and ICDs is the same as for any other patient undergoing the same procedure (discussed further in the text). Preoperative discussions about the appropriate level of anticoagulation for the case must take place in advance with the physician managing the VAD-supported patient and the surgeon (discussed further in the text). The name of the LVAD present must be known, especially if seeking advice from knowledgeable colleagues about planned management. Perioperative changes to VAD settings are rarely needed in a VAD-supported patient who was optimized on these settings when not anesthetized, so it is helpful to make note of the stable baseline settings and parameters of VAD function before altering the sympathetic tone and volume status with the delivery of an anesthetic because some of the baseline parameters potentially serve as targets during optimization. The clinical control screens of the HM II and the HVAD are depicted in Figs. 5.2 and 5.4. Appropriate anesthesia staffing for these procedures (e.g., cardiac vs. noncardiac trained personnel) is based on the status of the patient, the nature of the procedure, and the culture and resources of the institution and surgical venue (discussed further in the text).

Presence of a CIED Anticoagulation

Type of LVAD present Baseline LVAD settings and parameters of function

Staffing

CIED, Cardiac implantable electronic device; CNS, central nervous system; HM, HeartMate; ICD, implantable cardioverter-defibrillator; LVAD, left ventricular assist device; VAD, ventricular assist device.

to achieve goals. The administration of vitamin K or factor concentrates to reverse anticoagulation is not recommended.

Management of a Cardiac Implantable Electronic Device Pacemakers and implantable cardioverter-defibrillators (ICDs) should be managed in the same fashion as for any other patient undergoing the same procedure. It is critical to understand that a cardiac implantable electrical device (CIED) is either a pacemaker or an ICD. Whereas pacemakers provide pacing, ICDs provide antitachycardia therapies (e.g., shocks and antitachycardia pacing). However, ICDs (with the exception of the recently introduced subcutaneous ICD) have potential backup pacing settings in case defibrillation results in bradycardia or asystole. ICDs can also be programmed 109

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

Table 5.2  Specific Areas of Preanesthetic Inquiry and Consideration for Ventricular Assist Device–Supported Patients

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to provide full-time pacing as needed (e.g., for pacemaker-dependent patients who also have an indication for an ICD; see Chapter 4). Preoperatively, for the highest level of patient safety, it must be ascertained what device is present, programmed settings, level of device dependency, and confirmed that the device is functioning as intended. A review of the chest radiograph can easily establish lead locations (e.g., right atrium, right ventricle, coronary sinus) and if a device is a pacemaker or an ICD. A 12-lead electrocardiogram can help to establish pacemaker dependency because the presence of pacemaker spikes before every P-wave or QRS complex suggests dependency. However, the actual percentage paced can only be established by formal device interrogation. The risk of electromagnetic interference (EMI) during the procedure should be assessed, bearing in mind that EMI (e.g., from the surgical electrocautery unit) will most likely inhibit or otherwise interfere with the intended function of a pacemaker or trigger the delivery of antitachycardia therapies from an ICD. Electrocautery grounding pads should always be positioned distal to the site of surgery with respect to the CIED so that current does not cross the device. Although there is some controversy surrounding cases in which the potential source of EMI is sufficiently far away from the CIED (e.g., >15 cm), current recommendations still hold that ICD therapies should be disabled and pacing settings reprogrammed to an asynchronous (nonsensing) mode for pacemaker-dependent patients. There is no reason to empirically reprogram nondependent patients to an asynchronous mode, and in fact, this could cause harm if pacing impulses compete with a spontaneous rhythm (e.g., R-on-T phenomenon resulting in ventricular fibrillation). Temporary reprogramming of a CIED for the perioperative period can be accomplished with a manufacturer-specific programmer and/or a magnet. Magnet application effectively disables the primary sensing function(s) of a CIED; however, what exactly will be disabled depends on what device is present. Magnet application to the vast majority of pacemakers should cause the pacemaker to pace asynchronously, which will protect the patient from EMI. Pacemakers with adequate battery longevity will pace asynchronously at higher rates than pacemakers with little remaining battery life (e.g., 85–100 beats/min vs. 65 beats/min, respectively). Magnet application to an ICD should disable the antitachycardia therapies but will have no effect on any pacing settings. Therefore magnet application to an ICD in a pacemaker-dependent patient will not protect the pacing settings from interference, and the patient will require formal reprogramming of at least the pacing settings preoperatively. (A magnet could be used intraoperatively to disable the ICD therapies.) When feasible, it is likely safer and more convenient to use a magnet to control the behavior of a CIED intraoperatively because magnet removal will restore the behavior of the device to the preoperative baseline settings. An ICD that was temporarily disabled by magnet application will again be “live” when the magnet is removed and thus enable rapid defibrillation if needed intraoperatively. Reliance on a magnet also permits discharge from the monitored recovery setting without the need for formal interrogation and reprogramming. Removal of a magnet from a pacemaker will restore the baseline “sensing” mode (e.g., DDD, VVI). Although not routinely warranted, there are some clinical situations in which a formal device interrogation is recommended postoperatively, including: 1. Patients who had formal reprogramming of their device preoperatively 2. Patients who underwent “hemodynamically challenging” procedures involving large fluid shifts or transfusions that may have resulted in altered lead impedances 3. Patients who experienced a cardiac arrest intraoperatively requiring resuscitation, defibrillation, and so on 110

Perioperative decision-making algorithms exist in the peer-reviewed published literature and practice advisories, but key to the use of such an algorithm is an understanding of what device is present, how it is programmed (including the magnet response; usually it is programmed “on”), the level of CIED dependency, and that it is functioning as intended.

Baseline Parameters of Ventricular Assist Device Function Figs. 5.2 and 5.4 depict the clinical control screens of the HM II and the HVAD, and the figure legends discuss various aspects of those parameters.

Appropriate Staffing of the Case Even though cardiac-trained personnel still staff all noncardiac cases and procedures on VAD-supported patients in some institutions, it has been demonstrated in experienced, high-volume centers that noncardiac trained anesthesiologists can safely and confidently provide anesthetic care to VAD-supported patients after a period of education and experience. Certainly, minor cases or procedures (e.g., endoscopies, computed tomography scans, cystoscopies) on baseline stable VAD patients who are not on any pharmacologic support and lack other major comorbidities can be safely performed by most board-certified noncardiac anesthesiologists. One factor that has facilitated this culture change in certified VAD centers is the requirement by the CMS for the involvement of a VAD team not only for transport to and from the procedure, but that a “VAD-certified person” must be in the room for the duration of the procedure. Ideally, these cases would be scheduled during daylight hours and can safely take place in their usual locations (e.g., procedural suites). From the standpoint of the anesthesia provider, if questions or concerns exist after appropriate preanesthetic assessment, consultation with cardiac colleagues and discussions with the physician managing the VAD should precede OR entry. However, if the patient at baseline requires pharmacologic support, has major comorbidities, or if the case involves predicted large fluid shifts or potential periods of hemodynamic upheaval or is urgent or emergent, the case should ideally be done by a cardiac-trained anesthesiologist. Even so, the perioperative involvement of the VAD team must be assured as for any other case regardless of the anesthesia team being “VAD knowledgeable” as mandated by CMS.

INTRAOPERATIVE ANESTHETIC MANAGEMENT The vast majority of the time, clinicians must simply ensure continued optimization of the usual determinants of hemodynamics (preload, afterload, heart rate, and contractility) during the anesthetic, just as they would for any patient. In general, maintaining adequate volume status is likely the key to maintaining hemodynamic stability, although assuring adequate right ventricular contractility and avoidance of increased pulmonary vascular resistance (PVR) are important as well. That said, the basis of the safe and effective perioperative anesthetic management of the VAD-supported patient is a working understanding of the physiology of the VAD-supported state and how all the various aspects come together. 111

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

4. Patients who underwent cardiac or thoracic surgery, during which the leads may have been dislodged or damaged, or the device affected by high levels of EMI in close proximity to the device

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Key Points of Physiology There are three essential points of physiology and three intrinsic myocardial mechanisms that must be understood (or can be manipulated) to maintain optimal hemodynamics perioperatively: • • • • • •

Ventricular interdependence Series circulatory effects Ventriculoarterial coupling The Frank-Starling mechanism The Anrep effect The Bowditch effect

Ventricular Interdependence Both ventricles are bounded by, and exist within, the pericardium. Thus geometric changes of one ventricle (e.g., caused by volume or pressure overload) necessarily affect the geometry of the other, and geometrical changes of a ventricle decrease the effectiveness of its contractility. The continuous nature of the muscle fibers between the free wall of the right ventricle (RV) and the left ventricle (LV), as well as the sharing of a common interventricular septum (IVS), results in mechanical interactions between the ventricles and an anatomic coupling of their respective contractility. It is known that leftward septal shift (e.g., caused by excessive decompression of the LV by LVAD action or overfilling of the RV) has a deleterious effect on RV contractility; however, when clinically significant decreases in RV output occur, it is on account of an alteration of muscle fiber orientation and not simply the change in position of the IVS (i.e., leftward shift). In fact, it has long been demonstrated that as long as septal function is unimpaired, the RV free wall is dispensible where overall RV pressure development and volume outflow are concerned because it is really the contraction of the IVS that “wrings” blood out from the RV. I

Series Circulatory Effects The output of the RV fills the LVAD, and the LVAD output subsequently becomes the preload of the RV. Thus optimal LVAD function requires at least adequate RV “function” (which conceptually includes adequate RV preload, adequate RV contractility, or a pulmonary vascular resistance that permits blood to move from the right side to the left).

Ventriculoarterial Coupling No matter how depressed the intrinsic systolic function of a ventricle, the ability of a ventricle to function as a pump can be improved by decreasing the afterload against which it must pump. This is ventriculoarterial coupling. Thus, afterload reduction (as tolerated) is a key principle in the modern management of both left- and right-sided ventricular failure and has applications during both acute and chronic situations. Acute RV dysfunction, for example, responds particularly well to selective pulmonary vasodilatation, and chronic LV dysfunction is routinely managed with inodilators. Acute LV dysfunction, on the other hand, is often accompanied by significant hypotension, limiting the use of systemic afterload reduction. 112

The Frank-Starling law holds that increased stretch on the myocytes (to a point) increases the force of their contraction. As the ventricle fills, the potential force of the myocardial contraction increases because stretching of the muscle fibers increases the affinity of troponin C for calcium, causing a greater number of actin–myosin cross-bridges to form within the muscle fibers. The force that any single cardiac muscle fiber generates is proportional to the initial sarcomere length (also known as preload), and the stretch on the individual fibers is related to the end-diastolic volume of the left and right ventricles. In the human heart, maximal force is generated with an initial sarcomere length of 2.2 µm, a length that is rarely exceeded in the normal heart. Initial lengths longer or shorter than this optimal value will decrease the force the muscle can achieve. At longer sarcomere lengths, there is less overlap of the thin and thick filaments, and at shorter sarcomere lengths, the myofilaments exhibit a decreased sensitivity for calcium.

Anrep Effect The Anrep effect is an intrinsic myocardial reflex, or an autoregulation mechanism, maintained even in the denervated heart, in which myocardial contractility increases with increasing afterload. Initially, acutely increased aortic resistance to ejection results in a decreased stroke volume (and therefore an increased end-diastolic volume) that increases the force of contraction through the Frank-Starling mechanism. However, it has been demonstrated that contractility continues to increase starting around 10 to 15 minutes after the initial sudden stretch through the Anrep effect. Without the Anrep effect, an increase in aortic pressure would result in a sustained decrease in stroke volume, which might compromise cardiac output. This effect was originally described in 1912 by the Russian physiologist Gleb von Anrep, details of the mechanism were further elucidated from 1950 to 1980, and sophisticated investigations into this mechanism continue to the present time. Modern investigations have revealed the Anrep effect to be a very complex mechanism involving angiotensin II, endothelin, the mineralocorticoid receptor, the epidermal growth factor receptor, mitochondrial reactive oxygen species, redox-sensitive kinases upstream myocardial Na+/H+ exchanger (NHE1), NHE1 activation, increase in intracellular Na+ concentration, and increase in Ca2+ transient amplitude through the Na+/Ca2+ exchanger.

Bowditch Effect The prime manner by which the heart achieves an increased contractility in response to increased metabolic demand is via an increase in heart rate. This is the Bowditch effect. Effectively, increases in heart rate result in an increase in contractility and an increase in cardiac output. The putative mechanism underlying the Bowditch effect is similar to the mechanism by which digoxin acts. Increased heart rates challenge the efficiency of the Na+/K+-ATPase, and calcium builds up (which is inotropic in myocardial tissue). The Bowditch effect also reportedly exerts a lusitropic effect, whereby increases in heart rate increase relaxation, improving diastolic function.

Specific Intraoperative Actions Table 5.3 outlines specific intraoperative actions, the anesthetic management, and monitoring of a VAD-supported patient. Key areas are discussed in more detail in the next sections. 113

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Frank-Starling Mechanism

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Table 5.3  Specific Intraoperative Actions and Considerations for Ventricular Assist Device–Supported Patients Intraoperative Intervention Plug it in!

Prophylactic antibiotics Anticoagulation Anesthetic agents and techniques Monitoring

Displayed parameters of LVAD function

Rationale A low battery situation will not occur if the device is kept plugged in. Furthermore, the full control console can only be used (and the displayed parameters of device function to aid optimization) when the device is plugged in. Appropriate antibiotics must be used because VADs are large foreign bodies that cannot be adequately sterilized if infected. The anticoagulation strategy that was determined in advance should be adhered to, but further manipulations may be required if significant surgical bleeding is encountered. No specific sedatives or anesthetic agents are contraindicated because of the presence of a VAD (but the unsupported, potentially dysfunctional RV should be taken into account), and the required anticoagulation often precludes major regional techniques. Standard ASA monitors should always be used. Because baseline pulsatility may decrease with anesthetic induction, a noninvasive blood pressure cuff and pulse oximetry may become unreliable, suggesting the need for an invasive arterial monitoring catheter and cerebral oximetry for cases involving large fluid shifts or if pulsatility is low at baseline or cannot be maintained. The need for central venous access should be considered on a case-by-case basis. Perioperative changes to VAD settings are rarely needed in a VAD-supported patient who was optimized on these settings when not anesthetized. As discussed in the text, the preoperative baseline parameters (noted at the preanesthetic assessment) can help to serve as targets during intraoperative optimization. Optimization will more often require compensation with volume infusion and manipulations of afterload during an anesthetic than changes to previously stable VAD settings.

I ASA, American Society of Anesthesiologist; LVAD, left ventricular assist device; RV, right ventricle; VAD, ventricular assist device.

Plug It In! Transport to the OR will be on battery power. A pair of wearable, rechargeable modern LVAD batteries last for 4 to 8 hours (depending on the charge status, the number of previous charging cycles, and the hemodynamic condition of the patient). Similar to all other critical, life-support, and lifesaving equipment in the OR, whenever feasible, the device should be kept plugged in and the backup batteries charged. Additionally, the full control console and the reported parameters of VAD function used to guide optimization can only be used when the device is plugged in. Appropriate Antibiotic Coverage Preoperative antibiotic coverage for most procedures often includes broad-spectrum coverage, taking local flora into account. Coverage for gram-negative organisms and anaerobes is prudent for intraabdominal procedures. Antifungals should be considered 114

Anticoagulation As already discussed, when needed, POC and standard laboratory testing of the parameters of coagulation and hemostasis can be used to achieve the preoperatively determined goals for intraoperative anticoagulation or further refinements as warranted during the case. Infusions of FFP, cryoprecipitate, or platelets may sometimes be needed if significant surgical bleeding is encountered, but the administration of vitamin K or factor concentrates to acutely and completely reverse anticoagulation is not recommended. As needed, consultation with the physician managing the VAD is encouraged. Anesthetic Agents and Techniques No specific anesthetic agents are contraindicated because of the presence of a VAD, and the choice of agents and dosages used should be appropriate for the procedure, but should take into account the potentially dysfunctional unsupported right ventricle, as well as any other existing comorbidities. Most VAD-supported patients receive a general anesthetic because of the requisite anticoagulation, but in selected cases, superficial regional blocks under ultrasound guidance or a regional intravenous technique (e.g., a Bier block) may be appropriate. Major conduction anesthetics (e.g., spinals and epidurals) are generally contraindicated. Intubation and extubation criteria are the same as for any patient. In fact, early (if not immediate postoperative) extubation is desirable because prolonged intubation predisposes to pulmonary infection and requires prolonged sedation. There is no reason for patients to remain intubated just because they are supported by a VAD. As well, the miniaturized nature of the modern devices currently in use (and the fact that they are no longer implanted in a preperitoneal location) no longer relegates the LVAD-supported patient to “full stomach” status, as was the case with the large, pulsatile first-generation devices. Monitoring Standard ASA monitors should always be used, but the potential loss of pulsatility portends the unreliability of a noninvasive blood pressure (NIBP) cuff and pulse oximetry. Pulsatility of the circulation in a VAD-supported patient refers to contractility of the LV forcing an increased systolic velocity of blood either through the LVAD, out the aortic valve, or both. Although most patients with a modern nonpulsatile LVAD do exhibit pulsatility of their circulation when the LV partially recovers after VAD implantation, they can lose this pulsatility after induction because of the relative hypovolemia and vasodilation that accompany an anesthetic induction. Furthermore, VAD patients always lose pulsatility if they get significantly hypovolemic from blood loss or major fluid shifts. An NIBP cuff and pulse oximeter will work as long as sufficient pulsatility is maintained through optimization of the volume status presented to the LV (or optimization of RV function and pulmonary vascular resistance). Figs. 5.2 and 5.4 show and discuss the clinical control screens of the HM II and the HVAD from which information is obtained to assist with optimization and maintenance of pulsatility. An arterial line catheter often needed for cases with anticipated major 115

Left Ventricular Assist Device–Supported Patient Presenting for Noncardiac Surgery

in patients who may be at higher risk, which may include recent treatment with an antibiotic course or multiple indwelling catheters. Most infections associated with VADs tend to occur in the percutaneous tract through which the driveline exits, but it must be appreciated that VADs are large foreign bodies that when infected may not be adequately treated. The VAD driveline itself should not be prepped with povidone iodine–containing solutions because these can result in breakdown of the plastic. When necessary, drivelines can be draped out of the field or covered temporarily with a sterile drape.

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fluid shifts and can also be used to assess oxygenation when needed. Cerebral oximetry is increasingly being used when the pulse oximeter becomes unreliable. Transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) is not generally necessary unless clinical management questions arise. The VAD console already describes the cardiac output and LV volume status (see Figs. 5.2 and 5.4), so the actual utility of a central venous access or a pulmonary artery (PA) catheter should be carefully assessed for a given patient, particularly for minor procedures and procedures not expected to result in large volume shifts. The risks of line sepsis, arrhythmias, and pneumothorax from central catheter placement must be weighed against the potential utility, which include following the trends of cardiac output and derived hemodynamic indices to help guide fluid management and inotropic support, the ability to measure SVO2, the ability to assess the efficacy of interventions to lower PA pressures, and the ability to provide pacing. Echocardiography, especially TEE, is likely to be the most helpful monitor if a management dilemma arises.

PUTTING IT ALL TOGETHER: OPTIMIZATION DURING THE INTRAOPERATIVE PERIOD

I

A consideration of the physiology of the VAD-supported state, the principles outlined in the earlier sections, and the parameters of VAD function displayed on the clinical control screen provide a clear management strategy for VAD-supported patients who present for NCS. Volume status must be maintained and optimized for the LVAD patient for the same reasons as any other patient receiving an anesthetic and is often the key to maintaining pulsatility of the circulation (through optimization of Starling’s forces and the Anrep effect to optimize contractility). As discussed earlier, the pulsatility index of the HM II, and the information presented on the HVAD clinical screen (e.g., the diastolic baseline and the pulse pressure displayed) can be of assistance in optimizing and maintaining volume status. The goal for perioperative fluid management is to maintain a euvolemic, if not slightly hypervolemic state (assuming the unsupported and potentially dysfunctional RV is able to handle the volume load). The effect of surgical positioning or retractors must be considered as they may influence preload to the RV and high intrathoracic pressure (e.g., from excessively large tidal volumes) should be avoided because it impedes venous return to the heart. An “empty” LV also shifts the interventricular septum (IVS) to the left, which will decrease RV function through the principle of ventricular interdependence and the septal architectural disadvantage that comes from the change of IVS position, which reduces IVS contractility. A relative state of hypovolemia may occur in the LV if the RV fails to get blood across the pulmonary circulation for any reason, and sometimes there is a need to decrease pulmonary vascular resistance (the principle of ventriculoarterial coupling) or support RV contractility. Apart from usual small boluses of vasoconstrictors at the time of induction, significant compensation for anesthetic effects on vasomotor tone is infrequently needed as long as volume status is kept optimized. Judiciously raising the heart rate can also assist contractility (the Bowditch effect). When all this is taken into account, changes to previously stable VAD settings are the least likely initial maneuver undertaken to correct hemodynamic instability resulting from vasodilation and loss of sympathetic tone after anesthetic induction or blood loss. Instead, systemic vasodilatation should be corrected with judicious manipulations of vascular resistance and the correction of hypovolemia. If the amount of blood removed from the LV by continuous VAD action exceeds the amount of blood present, a “suckdown” can occur. A decreasing pulsatility index of the HM II or a decreasing 116

POSTOPERATIVE CONSIDERATIONS Table 5.4 outlines the postanesthetic considerations for VAD-supported patients presenting for NCS. Table 5.4  Specific Postanesthetic Considerations for Ventricular Assist Device–Supported Patient Area of Focus

Rationale

Appropriate recovery setting

The location of patient recovery (e.g., PACU vs. ICU vs. VAD floor, if available) may bear discussion in advance to ensure the receiving staff on duty are able to care for an LVAD patient. Excessive anxiety on the part of the nursing or other receiving staff is not in the best interest of the patient but is generally amenable to education and experience over time. The patient will be transported on battery power from the OR to the recovery location, and it is prudent to reconnect the VAD to A/C power and the system base unit on arrival. Backup batteries should be maintained in their chargers. Optimization of all parameters of hemodynamics must continue into the postoperative period. Volume status must be maintained and all factors avoided that could contribute to elevated PVR (e.g., hypercarbia, hypoxia, hypothermia, acidemia, pain). Effective pain management is essential not only for patient comfort but also to avoid increases in the PVR that may strain the potentially dysfunctional, unsupported RV. Baseline pacemaker or ICD settings should be restored before discharge from a monitored setting. If a magnet was used to keep an ICD inactive intraoperatively, removal of the magnet will reactivate the ICD. Similarly, magnet removal from a pacemaker will restore baseline programming. Any CIED settings that were formally reprogrammed with a manufacturer-specific programming device will need to be similarly restored. Device interrogation will not routinely be necessary except as discussed in the text. Perioperative changes to VAD settings are rarely needed in a VAD-supported patient who was optimized on these settings when not anesthetized, so it is helpful to make note of the stable baseline settings and parameters of VAD function before altering the sympathetic nervous system tone and volume status with the delivery of an anesthetic because some of the baseline parameters potentially serve as targets during optimization. The clinical control screens of the HM II and the HVAD are depicted in Figs. 5.2 and 5.4.

Plug it in!

Continued optimization

CIEDs

Baseline LVAD settings and parameters of function

Continued

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diastolic flow baseline of the HVAD (as well as the suction alarm of the HVAD) can herald an impending suction event. Assuming the volume status is adequate, a suction event will be a rare occurrence, but the usual initial management of such an event would entail volume infusion. If RV dysfunction is suspected, then inotropic support, selective pulmonary vasodilatation, or both would be used. Again, TEE or TTE could assist with a determination of the etiology of the problem. Theoretically, a temporary decrease in VAD speed could help to break the suction event, but caution is advised in this regard unless performed by an experienced VAD operator.

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Table 5.4  Specific Postanesthetic Considerations for Ventricular Assist Device–Supported Patient—cont’d Area of Focus

Rationale

Coordination with knowledgeable VAD personnel

The transportation of the VAD-supported patient from one location to another should be coordinated with and assisted by knowledgeable personnel who can ensure the batteries are correctly connected and that the system is functioning as intended before and after transport.

CIED, Cardiac implantable electronic device; HM, HeartMate; ICD, implantable cardioverterdefibrillator; ICU, intensive care unit; LVAD, left ventricular assist device; OR, operating room; PACU, postanesthesia care unit; PVR, pulmonary vascular resistance; RV, right ventricle; VAD, ventricular assist device.

SUGGESTED READING

Heart Failure and VAD Statistics

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Heidenreich PA, Albert NM, Allen LA, et al; on behalf of the American Heart Association Advocacy Coordinating Committee; Council on Arteriosclerosis, Thrombosis and Vascular Biology; Council on Cardiovascular Radiology and Intervention; Council on Clinical Cardiology; Council on Epidemiology and Prevention; Stroke Council. Forecasting the impact of heart failure in the United States: a policy statement from the American Heart Association. Circ Heart Fail. 2013;6:606–619. Kirklin JK, Naftel DC, Pagani FD, et al. Seventh INTERMACS annual report: 15,000 patients and counting. J Heart Lung Transplant. 2015;34:1495–1504. Mozzafarian D, Benjamin EJ, Go AS, et al; on behalf of the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics—2016 update: a report from the American Heart Association. Circulation. 2016;133:e38–e360.

Devices Mathis M, Sathishkumar S, Kheterpal S, et al. Complications, risk factors, and staffing patterns for noncardiac surger in patients with left ventricular assist devices. Anesthesiology. 2017;126:450–460. Mehra MR, Naka Y, Uriel N, et al; for the MOMENTUM 3 investigators. A fully magnetically levitated circulatory pump for advanced heart failure. N Engl J Med. 2017;376(5):440–450. Rogers JG, Pagani FD, Tatooles AJ, et al; for the ENDURANCE Trial investigators. Intrapericardial left ventricular assist device for advanced heart failure. N Engl J Med. 2017;376(5):451–460. Rose EA, Gelijns AC, Moskowitz AJ, et al. Long-term use of a left ventricular assist device for end-stage heart failure. N Engl J Med. 2001;345(20):1435–1443. Schmitto JD, Hanke JS, Rojas SV, Avsar M, Haverich A. First implantation in man of a new magnetically levitated left ventricular assist device (HeartMate III). J Heart Lung Transplant. 2015;34:858–860. Stoicea N, Cardozo F, Joseph N, et al. Pro: Cardiothoracic anesthesiologists should provide anesthetic care for patients with VADs undergoing noncardiac surgery. J Cardiothorac Vasc Anesth. 2017;31:378–381. (For “Con,” see pp 382–387.) Stone ME, Hinchey J, Sattler C, Evans A. Trends in the management of patients with left ventricular assist devices presenting for non-cardiac surgery—a ten year institutional experience. Semin Cardiothorac Vasc Anesth. 2016;20(3):197–204. Stulak JM, Davis ME, Haglund N, et al. Adverse events in contemporary continuous-flow left ventricular assist devices: A multi-institutional comparison shows significant differences. J Thorac Cardiovasc Surg. 2016;151:177–189.

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VAD Physiology

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