Identification and treatment of pump thrombosis

Pump thrombosis (PT) is a specific case of a severe equipment failure that may be characterized as either suspected or confirmed. The device is often an implanted blood pump, such as a Left Ventricular Assist Device. The malfunction is a stoppage in the flow of blood anywhere along a vessel (upstream or downstream), and it is caused mostly by the presence of a bio-incompatible mechanical instrument. Pump thrombus is a severe consequence of CF LVAD technology , which might need recurrent surgery to replace the pump or result in death.

In the case of suspected pump thrombus, the clinical patient state or pump parameters point to thrombus on any of the pump’s blood-contacting surfaces (inflow cannula, pump itself, or outflow graft).

Visual examination (during device exchange, transplantation, or autopsy), indisputable radiography evidence, or the lack of Doppler inflow or outflow signals are used to confirm pump thrombus.

Laboratory test for pump thrombosis

Lactate dehydrogenase (LDH)

LDH (8) is the most specific indication for device thrombosis, with baseline levels following device implantation ranging from 250 to 350 IU/L. The current standard of care emphasizes the change in LDH levels rather than the actual values. Levels that are more than 2.5 times higher than the baseline should be explored. If a mechanical defect is discovered that is causing any degree of inflow or outflow blockage, it should be surgically addressed. If no mechanical fault is discovered, device thrombosis should be considered, and these patients should be kept hydrated and on increased anticoagulant doses.

Hemoglobin and hematocrit (Hgb/Hct) levels are reduced during hemolysis and thrombosis. Significant decreases from baseline may indicate hemolysis, although bleeding should always be ruled out.

Haptoglobin

Haptoglobin levels are virtually invariably lower in individuals with a properly functioning CF LVAD owing to subclinical hemolysis. If it is normal or raised, this is pretty rare. Overall, we did not find this test to be useful in the diagnosis of VAD thrombosis.

PFH (plasma free hemoglobin): PFH is frequently high in patients with pump thrombosis and hemolysis, and it may help with the workup. It is, however, less sensitive than LDH levels in detecting device thrombosis (8), with findings requiring several days to arrive.

Total bilirubin (TB) TB is frequently increased in the presence of substantial hemolysis, although other reasons such as liver insufficiency in right heart failure, hepatitis, and cirrhosis must be ruled out. Creatinine levels are often high as a consequence of acute renal damage caused by hemoglobinuria and/or heart failure.

INR

Low INR levels caused by insufficient anticoagulation might result in device thrombosis. However, in LVAD thrombosis, INR is often raised rather than lowered. The higher-than-expected INR is more indicative of inadequate output, as well as simultaneous malnutrition and hepatic dysfunction from right heart failure, than of VAD thrombosis.

Pump thrombosis imaging method

X-ray of the chest 

A CXR is the first step in diagnostic imaging. It is a simple test that may be used to assess changes in pump position, cardiomegaly, and pulmonary edema.

Transthoracic echocardiography (TTE)

The most essential diagnostic imaging modality for pump thrombosis is an echocardiogram. TTE is often insufficient for providing adequate information, and it is generally preferable to get a TEE first. Following LVAD implantation, patients should always have a baseline ramp TEE. It aids in identifying ideal pump speed and has been demonstrated to aid in the identification of device malfunctions (9). During the trial, the pump speed is raised until septal shift is seen, and the patient is then kept at a little lower speed to allow for as much flow as feasible to target LV unloading.

When a patient is suspected of having VAD thrombosis, a TEE should be done and compared to the baseline study. The inflow cannula’s connection to the septum, lateral wall, and mitral valve should be observed. The inflow cannula should ideally be parallel to the LV’s long axis, since alternative angles may cause flow blockage. It is also crucial to recognise reduced or nonexistent cannula diastolic flow velocity, as well as an elevated systolic to diastolic velocity ratio (pulsatility). Both variations have been recognised as reliable indicators of suspected pump thrombosis (10). Finally, the aortic valve’s integrity and function should be evaluated, since valvular insufficiency may result in aberrant flow circuits, resulting in increased flow velocities and turbulence, as well as decreased systemic flow. Aortic valve opening despite ramping to a high VAD speed setting is more essential than aortic insufficiency for diagnosing LVAD thrombosis, particularly if the systolic blood pressure reaches 100 mmHg. This occurrence indicates that the “weaker” thrombosed VAD is unable to empty the ventricle at high aortic pressures. Significant thrombosis is rare if the ventricle can be drained by increasing VAD pace.

CTA (computed tomography angiography) CTA has proved to be effective in improving diagnostic assessment of patients with suspected VAD dysfunction, and it may lead to improvements in patient care (11). A high-quality CTA scan may show kinking of the outflow graft and, with three-dimensional (3-D) reconstruction, can show inflow cannula placement. Furthermore, contrast in the lumen is a sensitive measure for outflow graft patency. It is important to remember that CTA can only identify mechanical abnormalities with the outflow. It is not used to diagnose thrombosis, but it should be evaluated in individuals who have aberrant outflow graft velocities on echocardiography but do not seem to have pump thrombosis.

Catheterization of the heart

Aside from intra-aortic pressures, cardiac catheterization may show any pressure gradient in the outflow graft induced by graft kinking or stenosis. Cardiovascular catheterization, like CTA, can not detect pump thrombosis and is not routinely done, although it might be considered in patients with anomalous (increased or reduced) velocities on echocardiography who do not seem to have pump thrombosis.

Overall, the most significant imaging modality in assessing the pump is an echocardiography. If the LV cannot be unloaded on echocardiography and LDH is significant, the risk of thrombosis is high enough to warrant pump exchange. If the clinical picture is ambiguous, further imaging such as CTA and cardiac catheterization should be undertaken to determine the region of any surgically correctable flow blockages.

In individuals with hemolysis and heart failure symptoms but normal or ambiguous unloading on echocardiography, right heart catheterization may be explored. Right heart catheterization with a lower cardiac index and higher filling pressures despite increased pump speed might indicate pump thrombosis.

Initial non-operative management for pump thrombosis

  • When pump thrombosis or hemolysis is suspected, anticoagulation is started, commonly with intravenous unfractionated heparin infusion, to inhibit clot propagation and allow for clot clearance by fibrinolysis. 
  • Furthermore, to avoid renal harm owing to hemoglobinuria, prudent intravenous hydration, with or without extra forced diuresis, should be employed. Sodium bicarbonate drips may be used to alkalinize the urine. Inotropes are started as needed for heart failure symptoms, and the patient is medically optimized in preparation for pump exchange. 
  • All long-acting anticoagulants are being phased out. Patients with fulminant heart failure should not be fluid overloaded, particularly if they are VAD reliant for flow; in these patients, there may not be enough time for meaningful optimization prior to pump exchange. 
  • Prior to pump exchange, patients with refractory cardiogenic shock and multisystem organ failure should be considered for optimization using an extracorporeal membrane oxygenator (ECMO).

Pump thrombosis: Operative Management

A left upper quadrant or subxiphoid incision may be used for operational VAD pump exchange. Every patient’s pump pocket should be reformed. The majority of patients need a brief period of cardiopulmonary bypass. The individual techniques are detailed below, based on the anticipated issue location.

Isolated subxiphoid approach

This is the major method we use for pump exchange. It provides simple access to the pump as well as sections of the input and outflow cannulas. VADoscopy (12) has shown to be particularly sensitive in ruling out thrombi in the extracardiac region of the inflow cannula that are not visible with standard imaging methods. If no mechanical difficulties or thrombus are discovered following meticulous examination of the inflow and outflow components during both preoperative and intraoperative evaluation, isolated pump thrombus is presumed and the pump is replaced. This is done with extreme caution to prevent dislodging the clot. Controlling the outflow cannula during removal may be accomplished by clamping or occluding using a Fogarty catheter.

Subxiphoid approach with right anterior thoracotomy

If the outflow graft cannot be managed only via a subxiphoid incision, or if the outflow graft or aortic anastomosis requires revision, a right anterior thoracotomy in the third intercostal space may be done. This gives you plenty of space to work on the outflow graft and swap it if required.

Subxiphoid approach with small left anterior thoracotomy

If the inflow graft has to be replaced but the LV apex does not need to be re-covered, the procedure may be performed via a left anterior 4th intercostal incision. This method is less invasive than a complete muscle splitting subcostal incision and works well if LV apex manipulation is not absolutely essential, since the LV apex cannot be adequately moved and raised by this incision.

Full redo sternotomy

If the patient arrives in the operating room with a diagnosed inflow cannula placement issue, a thorough sternotomy is the best method since the apex often has to be re-coring. This method allows for complete mobilisation and elevation of the LV apex, as well as optimum exposure.

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