Mechanical Circulatory Support Devices as Destination Therapy
Pump durability is particularly important for patients assigned to DT. Pump function and reliability are important for patients assigned to DT. This is related to the interaction between implantation techniques and anatomical characteristics of the patient. In addition, the diagnosis of LVAD thrombosis is challenging, as it involves a combination of clinical symptoms, serologic markers, imaging studies and changes in device power consumption. Shah et al. investigated 241 patients with either centrifugal CF-LVAD or axial CF-LVAD, implanted between 2000 and 2012. The results suggested that LDH may be a more sensitive marker for hemolysis than serum free hemoglobin in patients with a continuous flow device, and concluded that LDH is superior in detecting device thrombosis. Boyle et al. reviewed 469 patients enrolled in the BTT arm of the US Heart Mate II pivotal trial and reported a very low incidence of pump thrombosis of only 0.9% in patients who received warfarin and antiplatelet therapy. Although mortality on VAD support continues to decrease, morbidity due to device thrombosis is becoming more apparent, particularly in DT patients as a consequence of long-term support. Furthermore, suspected or confirmed thrombosis was one of the most common indications for device exchange in an analysis of 1,128 patients, of whom 72 underwent pump exchange between 2005 and 2010. Operative mortality for pump exchange at 30 days was 6.5%, and 65% of the patients were alive two years after exchange. However, considering that one-year survival after the first continuous-flow LVAD implant is nowadays about 80%, about 65% after a second implant, and only 50% after a third implant, prevention of pump malfunction and pump thrombosis becomes crucial. In this regard, an interesting observation was reported by Starling et al., who had observed an incremental increase in Heart Mate II pump thrombosis in three large LVAD centers in the US since 2011. Among 895 Heart Mate II patients, 72 confirmed pump thromboses were observed in 66 patients, and additionally in 36 patients a pump thrombosis was suspected. Remarkably, the occurrence of confirmed pump thrombosis increased rapidly after March 2011, from 2.2% at three months after implantation to 8.4% by January 2013. The same trend was observed at all three implanting institutions and for all operating surgeons. Similarly, an INTERMACS database analysis demonstrated an increase in pump thrombosis from 2% before May 2011 to 5% from May 2013 onwards. One critical point was that the anticoagulation protocol was changed during the study and therefore could have resulted in the higher incidence of pump thrombosis. Another explanation may be the deposition of fibrin and denatured protein in the proximity of the inflow bearing, followed by heat generation with increasing shear stress on the red cells. If the deposition of fibrin and denatured protein becomes large enough, this could impair the pump's ability to unload the left ventricle. The "bearing–fibrin" deposition theory could therefore explain the hemolysis that develops as thrombus deposition begins.
Pump Thrombosis and Pump Exchange
Pump durability is particularly important for patients assigned to DT. Pump function and reliability are important for patients assigned to DT. This is related to the interaction between implantation techniques and anatomical characteristics of the patient. In addition, the diagnosis of LVAD thrombosis is challenging, as it involves a combination of clinical symptoms, serologic markers, imaging studies and changes in device power consumption. Shah et al. investigated 241 patients with either centrifugal CF-LVAD or axial CF-LVAD, implanted between 2000 and 2012. The results suggested that LDH may be a more sensitive marker for hemolysis than serum free hemoglobin in patients with a continuous flow device, and concluded that LDH is superior in detecting device thrombosis. Boyle et al. reviewed 469 patients enrolled in the BTT arm of the US Heart Mate II pivotal trial and reported a very low incidence of pump thrombosis of only 0.9% in patients who received warfarin and antiplatelet therapy. Although mortality on VAD support continues to decrease, morbidity due to device thrombosis is becoming more apparent, particularly in DT patients as a consequence of long-term support. Furthermore, suspected or confirmed thrombosis was one of the most common indications for device exchange in an analysis of 1,128 patients, of whom 72 underwent pump exchange between 2005 and 2010. Operative mortality for pump exchange at 30 days was 6.5%, and 65% of the patients were alive two years after exchange. However, considering that one-year survival after the first continuous-flow LVAD implant is nowadays about 80%, about 65% after a second implant, and only 50% after a third implant, prevention of pump malfunction and pump thrombosis becomes crucial. In this regard, an interesting observation was reported by Starling et al., who had observed an incremental increase in Heart Mate II pump thrombosis in three large LVAD centers in the US since 2011. Among 895 Heart Mate II patients, 72 confirmed pump thromboses were observed in 66 patients, and additionally in 36 patients a pump thrombosis was suspected. Remarkably, the occurrence of confirmed pump thrombosis increased rapidly after March 2011, from 2.2% at three months after implantation to 8.4% by January 2013. The same trend was observed at all three implanting institutions and for all operating surgeons. Similarly, an INTERMACS database analysis demonstrated an increase in pump thrombosis from 2% before May 2011 to 5% from May 2013 onwards. One critical point was that the anticoagulation protocol was changed during the study and therefore could have resulted in the higher incidence of pump thrombosis. Another explanation may be the deposition of fibrin and denatured protein in the proximity of the inflow bearing, followed by heat generation with increasing shear stress on the red cells. If the deposition of fibrin and denatured protein becomes large enough, this could impair the pump's ability to unload the left ventricle. The "bearing–fibrin" deposition theory could therefore explain the hemolysis that develops as thrombus deposition begins.