Pump thrombosis and stroke are serious complications of left ventricular assist device (LVAD) support. The aim of this study was to test the ability of an accelerometer to detect pump thrombosis and thromboembolic events (TEs) using real-time analysis of pump vibrations. An accelerometer sensor was attached to a HeartWare HVAD and tested in three in vitro experiments using different pumps for each experiment. Each experiment included thrombi injections sized 0.2-1.0 mL and control interventions: pump speed change, afterload increase, preload decrease, and saline bolus injections. A spectrogram was calculated from the accelerometer signal, and the third harmonic amplitude was used to test the sensitivity and specificity of the method. The third harmonic amplitude was compared with the pump energy consumption. The acceleration signals were of high quality. A significant change was identified in the accelerometer third harmonic during the thromboembolic interventions. The third harmonic detected thromboembolic events with higher sensitivity/specificity than LVAD energy consumption: 92%/94% vs. 72%/58%, respectively. A total of 60% of thromboembolic events led to a prolonged third harmonic amplitude change, which is indicative of thrombus mass residue on the impeller. We concluded that there is strong evidence to support the feasibility of real-time continuous LVAD monitoring for thromboembolic events and pump thrombosis using an accelerometer. Further in vivo studies are needed to confirm these promising findings.

We have recently demonstrated that accelerometer-based pump thrombosis and thromboembolic events detection is feasible in vitro. This article focuses on detection of these conditions in vivo. In an open-chest porcine model (n = 7), an accelerometer was attached to the pump casing of an implanted HeartWare HVAD. Pump vibration was analyzed by Fast Fourier Transform of the accelerometer signals, and the spectrogram third harmonic amplitude quantified and compared with pump power. Interventions included injection of thrombi into the left atrium (sized 0.3–0.4 ml, total n = 35) and control interventions; pump speed change, graft obstruction, and saline bolus injections (total n = 47). Graft flow to cardiac output ratio was used to estimate the expected number of thrombi passing through the pump. Sensitivity/specificity was assessed by receiver operating characteristic curve. Graft flow to cardiac output ratio averaged 66%. Twenty-six of 35 (74%) thrombi caused notable accelerometer signal change. Accelerometer third harmonic amplitude was significantly increased in thromboembolic interventions compared with control interventions, 64.5 (interquartile range [IQR]: 18.8–107.1) and 5.45 (IQR: 4.2–6.6), respectively (p < 0.01). The corresponding difference in pump power was 3 W (IQR: 2.9–3.3) and 2.8 W (IQR: 2.4–2.9), respectively (p < 0.01). Sensitivity/specificity of the accelerometer and pump power to detect thromboembolic events was 0.74/1.00 (area under the curve [AUC]: 0.956) and 0.40/1.00 (AUC: 0.759), respectively. Persistent high third harmonic amplitude was evident at end of all experiments, and pump thrombosis was confirmed by visual inspection. The findings demonstrate that accelerometer-based detection of thromboembolic events and pump thrombosis is feasible in vivo and that the method is superior to detection based on pump power.

We have previously demonstrated that accelerometer-based vibration analysis detects thromboembolism and pump thrombosis in HeartWare Left Ventricular Assist Device (HVAD) using the third harmonic frequency (pump_speedx3). Thromboembolism also affected the amplitude of the nonharmonic frequencies. The aim of this study was to determine whether nonharmonic-amplitude (NHA) analysis can improve the diagnosis of thromboembolic complications. An accelerometer was attached to HVAD in three in vitro and seven in vivo experiments. Control interventions, including load and pump speed alternations (n = 107), were followed by thromboembolic events (n = 60). A sliding fast-Fourier-transform was analyzed, and changes in NHAs were quantified in the acute phase and in a steady state. Receiver operating characteristic curves were constructed with cutoff values of NHA to detect thromboembolic events. Positive predictive values were calculated on the basis of a specificity of 1. In the acute phase, NHA change was 6.5 times higher under thromboembolism than under control interventions (p < 0.001). Most thromboembolic events lead to concomitant changes in both NHA and third-harmonic amplitude. Combining the two methods improved the PPV by 8.3%. At steady state, signal changes predominantly demonstrated either NHA or third-harmonic changes. Combined signal analysis improved the PPV by 36%. This method enhanced the detection of thromboembolism and pump thrombosis in the HVAD.