Characteristics, Frequency, and Disposition of Patients With a HeartMate II Left Ventricular Assist Device Presenting to the ED

There are, and continue to be, advances in both LVAD design and function. Since the time period of our study, changes have been made in the outflow bend relief (the tube at the junction of the outflow cannula and the pump housing designed to prevent kinking of the outflow cannula) and the LVAD controller. Older controllers have been replaced with newer models, but many of the LVAD pumps in this article remain in service.

Anticoagulation Therapy

Patients who have a CF LVAD require anticoagulation therapy with warfarin to a target international normalized ratio (INR) of 2 to 3, in addition to aspirin therapy of 325 mg daily.^8,9Newer oral anticoagulant drugs are not routinely given to patients who have a CF LVAD.

Cardiopulmonary Evaluation

With CF LVADs, blood is pumped continuously, and a constant, machine-like murmur can be heard on auscultation rather than the typical heart sounds. Patients who have an LVAD may not have palpable arterial pulses. Doppler evaluation of the brachial artery and a manual blood pressure (BP) cuff are used to listen for the start of Korotkoff sounds as the cuff is released. The pressure at which the first sound is heard is used to estimate the patient’s mean arterial pressure (MAP) at the time when there is no pulse; and the systolic BP (SBP) is heard at the time when there is pulse. Patients with a CF LVAD with nonpulsatile flow should have a MAP between 70 mm Hg and 90 mm Hg (HMII), or 70 mm Hg and 80 mm Hg (HVAD). Patients who have a CF LVAD with a palpable pulse should have an SBP less than 120 mm Hg (HMII) or 105 mm Hg (HVAD). Readings outside of these ranges require an adjustment in the patient’s antihypertensive therapy, since high BP increases the risk of stroke and can impair the cardiac support provided by the LVAD.⁸Low BP may be the result of inadequate pump speed, dehydration, inflow cannula obstruction, or pump thrombus.

Bleeding

In our study, bleeding and volume overload were the two most common reasons LVAD patients presented to the ED. Interestingly, in a systematic review of clinical outcomes following CF LVAD implantation, bleeding was the most commonly recorded adverse event.¹²In fact, the majority of patients in all of the studies reviewed experienced at least one bleeding event. In one study of 139 HMII LVAD patients, the risk of bleeding was greatest within the first two weeks, and early bleeding was associated with increased mortality.¹³The most common source of bleeding complications in patients with a CF LVAD are GI, similar to our study.¹⁴

In a review and meta-analysis by Draper et al,¹⁵of GI bleeding in 1,697 patients with CF LVADs, the pooled prevalence was 23%.Subgroup analysis demonstrated an increased risk of bleeding in older patients and in those who had an elevated serum creatinine level.¹⁵ Upper GI bleeding occurred in 48% of patients, lower GI bleeding in 22%, small-bowel bleeding in 15%, and bleeding at an unknown site in 19%. The most common cause of the bleeding was from arteriovenous malformations (AVMs).¹⁵ In their review, Draper et al¹⁵ found a 9.3% prevalence of recurrent GI bleeding and a pooled event rate for an all-cause mortality rate of 23%.

They also noted that the increased risk of GI bleeding in CF LVAD patients is multifactorial. For example, there was decreased activity of type 2 von Willebrand factor multimers in patients with CF LVADs, leading to an acquired von Willebrand syndrome.¹⁵

Another finding seen in this review was that CF devices lead to a low pulse-pressure system, which is thought to cause some degree of intestinal hypoperfusion, potentially leading to vascular dilation and AVM formation.¹⁵ Based on findings, a neurovascular etiology involving increased sympathetic tone resulting in smooth muscle relaxation and AVM formation has been proposed. Lastly, the anticoagulation required with the CF LVADs to prevent pump thrombosis also increases the risk of GI bleeding, especially when combined with aspirin or other antiplatelet agents which are routinely prescribed.¹⁵

Volume Overload

Interestingly, in our study, volume overload as a cause for ED presentation was the same as for bleeding complications. In the systematic review of clinical outcomes in CF LVAD patients, volume overload or ongoing heart failure occurred in 18% of patients 1 year after device implantation.¹²

The clinical presentation of patients experiencing volume overload is typically dyspnea and fatigue; on physical examination they will frequently demonstrate evidence of fluid retention, such as dependent edema and pulmonary congestion.¹⁶Causes of volume overload in the LVAD patient includes medication noncompliance, inadequate pump speed, device malfunction, right ventricular failure, impaired renal function, and cardiac tamponade.¹⁶ These patients will frequently have MAPs greater than 90 mm Hg, and may require treatment with diuretics, calcium channel blockers, beta-blockers, or angiotensin-converting enzyme inhibitors.⁸

Weakness, Lightheadedness, Dizziness, Syncope

In our study, some combination of weakness, lightheadedness, dizziness, and syncope accounted for the third most common cause of ED presentation (9.6%). In the majority of cases, this was due to dehydration. Usually, these patients will have a MAP less than 60 mm Hg. Unfortunately, patients with pump thrombosis, sepsis, or cannula malposition can also present with a low MAP. It is important to differentiate the cause, as the management is quite different, depending on the etiology. Bedside ultrasound can play an important role in evaluating the volume status and cannula position.⁸ In addition, emergent consult with the patients ventricular assist device (VAD) treatment team is critical.⁸ Pump thrombus is a medical emergency and is usually associated with hematuria without red blood cells in the urine, acute kidney injury, and marked elevations in lactate dehydrogenase and serum free hemoglobin.⁸ If not treated promptly, renal failure and death may result. If dehydration is the cause, gentle rehydration with intravenous normal saline and electrolyte replacement may be all that is required.

Device Malfunction

Device malfunction was the next most common reason for ED presentation in our study, at 8.1%. This category included a number of different events, including battery failure, driveline fracture, and pump thrombosis. According to McIlvennan et al,¹² causes of device malfunction include thrombus formation with hemolysis, mechanical failure of the impeller, and driveline lead fractures with electrical failure.Again, the VAD team should be consulted immediately, and the EP should plug the LVAD into a hospital power base, if available, to conserve battery life. If power is interrupted, the pump will stop working. The EP should examine all of the connections from the percutaneous lead to the controller and from the controller to the batteries to ensure they are intact. The exit site for the percutaneous lead should be examined for evidence of trauma or signs of infection. The patient should also be asked about recent trauma to the driveline.

Neurological Events

Interestingly, in other reviews, neurological events, including ischemic stroke, hemorrhagic stroke, and transient ischemic attack occur with higher frequency than was the case in the study, and are relatively common complications that can result in severe morbidity and mortality.¹²In the Interagency Registry for Mechanically Assisted Circulatory Support report, there was a 3% risk of stroke at 1 month, 5% at 3 months, 7% at 6 months, 11% at 12 months, 17% at 24 months, and 19% at 36 months post-implant.^6,12Similarly, the HMII DT Trial demonstrated rates of ischemic and hemorrhagic stroke as high as 8% and 11% respectively, within the first 2 years following LVAD placement.^5,6In our study, neurological events accounted for only six (2.4%) of ED visits. It is unclear why our numbers were less than those reported by others.

Cardiac Events and Management

During the study period, one LVAD patient presented to the ED in cardiac arrest. Patients who have an LVAD and are in cardiac arrest have unique considerations that deserve discussion. If the LVAD pump has stopped functioning, connections between the system controller and the pump and power source must be checked, as loose connections need to be refitted and the pump restarted. It is important to note that when an LVAD ceases operation, blood becomes stagnant in the pump and conduits. Delays of even several minutes pose a significant risk for pump thrombosis, stroke, and thromboembolism when the device is restarted. If the pump does not restart and the patient is connected to batteries, the batteries should be replaced with a new, fully charged pair, or the device should be connected to a base unit.¹⁷

Due to the location of the outflow graft on the aorta and the inflow conduit in the LV apex, external chest compressions pose a risk of dislodging the device and causing fatal hemorrhage. Clinical judgment should be used when deciding to perform external chest compressions. A recent American Heart Association scientific statement concluded that withholding chest compression in a patient with an LVAD who is truly in circulatory failure that is not attributable to a device failure would cause more harm to the patient than the potential to dislodge the device.¹⁸

Direct cardiac massage, performed by a skilled surgeon may be effective in patients that have had recent device implantation, especially if prior to mediastinal healing.¹⁶ If external defibrillation/cardioversion is required, the percutaneous lead should not be disconnected from the system controller and the pump should not be stopped prior to the delivery of a shock.¹⁷

Study Limitations

This was a retrospective study and has the limitations common to all such studies. It is possible that some of the patients in our study sought care at a hospital ED outside of our system, and therefore were not included in our study. This, however, is exceedingly unlikely as the cardiologists and care team continually emphasized and instructed all patients in our study only to present to the study hospital ED for any complaint. Similarly, the various emergency medical services agencies for our region were also instructed to bring all LVAD patients to the study hospital.