Evaluating a patient for acute thrombosis usually starts with a clinical evaluation but ultimately requires a culmination of laboratory testing in addition to various imaging modalities (Fig. 12.2). One of the primary goals for laboratory testing remains validating the presence of hemolysis. Clinical signs may be present that coincide with lab results suggestive of hemolysis. Patients may describe darkened urine from increased hemoglobin destruction due to active hemolysis from pump thrombosis. When pump thrombosis form s, reduced forward flow develops, preventing adequate unloading of the left ventricle. Soon the patient may experience similar symptoms of decompensated heart failure they felt prior to device implantation. Once these clinical factors are present, active evaluation of pump thrombosis must be performed starting with laboratory analysis. In one retrospective study, hematological markers were a better marker to predict pump thrombosis before imaging or pump parameters were identified [10]. Most advanced heart failure centers routinely screen patients with left ventricular assist devices by checking lactate dehydrogenase (LDH) levels [11]. Long-term monitoring of a patient’s LDH level is key to evaluate trends that may suggest a gradual pump thrombosis versus an acute event. LDH levels tend to remain elevated but stable in the former whereas levels can rise abruptly in the latter. Typically once levels are greater than 2–2.5 times, partial or complete pump thrombus formation should be excluded. Also plasma-free hemoglobin levels are another laboratory test to identify active hemolysis. Typically two separate levels that are greater than 40 mg/dL are suggestive of ongoing hemolysis. Combining an elevated LDH and plasma-free hemoglobin reading with other common markers for hemolysis such as reduced levels of hemoglobin, hematocrit, and haptoglobin and increased indirect bilirubin levels is strongly suggestive of ongoing hemolysis from pump thrombosis.

In addition to laboratory testing for hemolysis , various imaging studies can be utilized to evaluate LVAD positioning and ability to unload the left ventricle. The first imaging study to perform on a patient with a suspected pump thrombosis should be a chest x-ray. The chest x-ray can be useful to not only evaluate pulmonary congestion from decompensated heart failure but also to evaluate any kinking or malposition of the inflow cannula. In addition to the standard chest x-ray, CTA of the chest becomes useful in evaluating the inflow and outflow graft. As mentioned above, positioning of the inflow cannula can be visualized with CT angiography as well as LV cavity size and possible location of pump thrombosis. The outflow graft can also be adequately visualized to determine if any specific segment has thrombus formation or kink present. Most patients with acute pump thrombosis tend to have elevated creatinine levels due to ongoing hemolysis, which can make ordering a CTA difficult due to the need for intravenous contrast. However, the risk of worsening renal perfusion from a low cardiac output state is also an important factor to consider when working up a patient with an acute pump thrombosis.

Two-dimensional echocardiography can be a useful tool when evaluating a patient with suspected pump thrombosis. When pump thrombosis occurs, adequate unloading of the left ventricle becomes difficult. As a result, left ventricular end-diastolic dimensions can increase which is one sign of pump malfunction if the left ventricular size is larger than previous baseline studies at similar speeds. Mitral regurgitation is also a useful parameter seen on 2D echocardiogram which can help in determining if adequate LV unloading is occurring at certain pump speeds. While there may be some mild mitral regurgitation at baseline speeds in a normal functioning LVAD, theoretically increasing the LVAD speed should unload the LV sufficiently to reduce or minimize the presence of mitral regurgitation. Once pump thrombosis occurs, adequate LV unloading is not possible at higher speeds, so severity of mitral regurgitation may persist despite higher VAD settings. The aortic valve can be another structure seen on 2D echocardiography that can assist in determining if adequate LV unloading is occurring at higher speeds. At higher speeds, normal functioning left ventricular assist devices should unload the left ventricle to the point that a majority of blood flow is directed toward the LVAD instead of the left ventricular outflow tract. As a result, minimal aortic valve opening is seen at higher LVAD speeds suggestive of adequate pump function. Caution should be used when performing a ramp study on a patient with suspected pump thrombosis. Depending on the location of thrombus, distal embolization can occur once speed adjustments are made. Usually HeartMate II LVADs are increased by 200 rpm, while HeartWare HVAD speeds are increased by 20 rpm increments. Initial studies reviewing the use of ramp echocardiography evaluation were helpful with HeartMate II LVEDD slope relationships but did not correlate well when extrapolated to HVAD function [12].

In some instances when adequate information is not obtained from CTA or 2D echocardiography, cardiac output and hemodynamics assessed from right heart catheterization can assist in determining if adequate LV unloading is occurring with various pump settings. One advantage to right heart catheterization versus 2D echocardiography or CTA is the ability to measure both left- and right-sided pressures. Specific protocols for ramp right heart catheterization studies may vary from institution to institution; however, similar to ramp echocardiogram study, various measurements such as cardiac outputs, pulmonary capillary wedge pressures, and right-sided filling pressure can be obtained at various speeds. With a normal functioning pump, at higher speeds, cardiac output increases, PCWP decreases, and right-sided filling pressure may increase due to higher preload.

Left ventricular device power surges or changes in pulsatility index can also serve to assist in diagnosing pump thrombosis. Typically pump thrombosis usually causes high power spikes with low a low pulsatility index. Caution should be used in avoiding making clinical decisions based on single pump parameter changes but evaluate changes in LVAD settings compared to a patient’s baseline. Typically pump thrombosis causes elevated power readings >10 W or sustained readings greater than 2 W above a patient’s baseline [13]. Recent studies regarding pump thrombosis recommend identifying multiple factors such as active hemolysis, symptoms of decompensated heart failure, abnormal imaging or ramp studies, and/or abnormal pump readings to help in making the diagnosis.