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J Thorac Cardiovasc Surg 2004;128:619-621
© 2004 The American Association for Thoracic Surgery
Brief communication |
a Department of Surgery, Duke University Medical Center, Durham, NC, USA
b Department of Medicine, Duke University Medical Center, Durham, NC, USA
Received for publication December 22, 2003; accepted for publication January 28, 2004.
* Address for reprints: Carmelo A. Milano, MD, Department of Surgery, Box 3043, Duke South, Durham, NC 27710, USA
milan002{at}mc.duke.edu
The implantation of a left ventricular assist device (LVAD) provides a clinically meaningful survival benefit and better quality of life compared with medical therapy in patients with advanced heart failure.1 Malfunction of the LVAD, however, might significantly reduce the survival benefit it incurs. Seven of 41 deaths in patients with LVADs in the REMATCH trial (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure) were attributed to device malfunction.1 We present the case of a patient who had an unusual device complication. Fluid was aspirated into the vent port, resulting in the malfunction of the device and a clinical emergency. A treatment algorithm for this challenging problem is described.
Clinical summary
A 55-year-old man (6'5'', 183 lb) with idiopathic dilated cardiomyopathy had a HeartMate XVE (Thoratec Corp, Pleasanton, Calif) LVAD system implanted. He was convalescing on a step-down ward 3 weeks postoperatively, with stable LVAD flows of between 5 and 6 L/min. The patient was incontinent of urine at 5 AM on the day of the event. Urine was aspirated into the LVAD vent port. The low flow and power limit advisory alarms of the LVAD activated. The low flow persisted, and the patient became hemodynamically unstable. The vent filter was immediately removed, and the patient was placed on his right side, enabling fluid drainage from the vent port. A dry towel was also used to absorb the remaining fluid at the vent port. After several minutes in this position, the alarms stopped, and the LVAD flow returned to previous levels. A new vent filter was placed, and the patient's condition remained stable.
The patient experienced the same malfunction again at 9 AM. The device then stopped, and hand pumping was initiated. Electrical activation was not possible. The patient was systemically anticoagulated. He was transferred to the intensive care unit, and arterial line and pulmonary artery catheters were placed for monitoring. The system controller and power source were removed, and the LVAD was successfully activated with the older pneumatic HeartMate driver. This driver was used with a pressure-limiting device on the pneumatic driveline to avoid injury to the electric pump, as recommended by the company. The pneumatic driver rate was increased to 90 beats/min. The patient, however, remained in shock, and respiratory distress ensued. He was mechanically ventilated, and inotropic infusions were initiated to enhance native ventricular function. Despite these maneuvers, the patient was hypotensive, with a central venous pressure of 22 mm Hg and a cardiac output of 2.3 L/min, as measured with the pulmonary artery catheter and the thermodilution method. Metabolic acidosis was present on the arterial blood gases. The arterial pressure tracing suggested poor LVAD stroke volume, and native ventricular ejection confirmed incomplete ventricular unloading by the pneumatically driven HeartMate LVAD.
A decision was made to replace the LVAD surgically at 11 AM given the patient's persistent shock state. At this point, a final attempt was made to reactivate the pump electrically. Fortunately, the pump could be electrically activated and subsequently functioned without alarms. The patient's hemodynamics rapidly normalized: central venous pressure was 8 mm Hg, and cardiac output increased to 5.3 L/min. The need to surgically replace the pump was averted. The device continued to function electrically without any further events. The patient is in stable condition with good functional status 3 months postoperatively, having undergone successful cardiac transplantation.
Discussion
Pusher plate design implanted LVADs use external venting for air, which is displaced as the pump fills and aspirated during pump systole. The HeartMate XVE has a percutaneous driveline, which consists of the electrical lead and the vent port (Figure 1). Particulate matter is prevented from entering the vent port by a filter at the skin. Fluid, however, can pass through the filter into the port and cause device failure, as experienced in our patient.
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Notably for this patient, the pneumatic driver failed to achieve adequate hemodynamics. This is explained by the fact that the pump stroke volume is significantly reduced if the electric pump is driven by the old pneumatic driver. Furthermore, excursion of the pusher plate might be compromised after such fluid aspiration into the vent port. In fact, on the basis of the cardiac output and pneumatic driver rate, which was set at 90 beats/min, the pump stroke volume when driven by the pneumatic driver was only 26 mL. Therefore use of the pneumatic driver might only be a short-term or incomplete solution. Furthermore, incomplete emptying of the pump with the pneumatic driver might pose a risk of thromboembolism, emphasizing the need for anticoagulation. Nevertheless, in this case support with the pneumatic driver for 2 hours resulted in elimination of vent port obstruction, such that the pump could again function electrically. This averted the need for surgical replacement of the pump. Through this experience, we propose an algorithm, which might help caregivers with this difficult situation (Figure 2).
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