Introduction: Thromboembolic events (TE) and gastrointestinal bleeding (GIB) are frequent complications of LVAD implantation. Prevention of these events requires optimization of the anticoagulation regimen based on an individual’s risk. Direct assessment of early pump fibrin accumulation could enhance management but molecular imaging of aged (> 48 hours) thrombus under anticoagulation conditions has not been achieved previously, particularly with blood flows at 5 L/min.
Hypothesis: The objectives were to assess the efficacy of a fibrin specific probe (99mTc-F4A) in excised LVADs derived from patients undergoing pump exchange or heart transplantation and to correlate nuclear image data with clinical suspicion of pump thrombosis.
Methods: Excised HeartMate II LVADs were operated in a 200 ml mock loop of circulating plasma/PBS/heparin at 9400 RPM. The 99mTc-F4A (0.5mCi) was injected, circulated for 30 minutes, then removed and replaced with fresh PBS for 2 minutes. LVADs were imaged with a micro single-photon emission counting tomography with Xray-CT (NanoSPECT) blinded to patient history. Clinical records were independently correlated with the nuclear images.
Results: Twenty-nine HeartMate II LVADs were imaged of which 15 were associated with a clinical suspicion of thrombosis. Average LVAD support was 744.1 ± 538.2 days and did not differ between groups. Mean LDH level in patients suspected of LVAD thrombosis was 2157.0 ± 303.8 versus 684.6 ± 152.8 in those unsuspected of thrombus. (p<0.001). All 15 pumps suspected of pump thrombosis contained fibrin deposits detected with 99mTc-F4A associated with the stators or rotor. Ten of 14 pumps from patients unsuspected of thrombosis also had fibrin deposits but only 1 had clot on the stators or rotor. Thrombus in these pumps occurred almost exclusively in the outflow cannula.
Conclusion: This study highlights the effectiveness of 99mTc-F4A to bind aged, anticoagulated fibrin deposits under high shear conditions and illustrates the potential of this method to identify LVADs at risk for TE complications. Application of this management tool earlier in the clinical course could help refine and personalize anticoagulation goals based on thromboembolic risk.