The average time of support was 86.63 hours (± 79.8) with the longest time being 361 hours. After 24 hours of support, the mean hemoglobin (Hb) decreased significantly from 11 to 9.8 mg/dl (p < 0.001), suggesting red blood cell (RBC) loss. Seven of the 40 patients (17%) received blood transfusion during the first 24 hours, and by the time of device removal, 26 of the 40 patients (65%) were transfused to maintain an adequate Hb level, significantly lower when compared with baseline (p = 0.0014) (Figure 2). A total of 205 units of RBCs were used throughout the support, with a mean of 7.5 units per patient transfused.
Hemolysis parameters, including lactate dehydrogenase (LDH), bilirubin, haptoglobin, and plasma free Hb, were evaluated and the results are shown in Figure 3; the LDH increased to 3,595 U/L (n = 21) within the first 24 hours of support. By the time of removal, the LDH increased to 5,201 U/L (n = 22; p = 0.0096), the mean bilirubin was 5.6 mg/dl (p = 0.008), and the haptoglobin level was 15.4 mg/dl (n = 25), suggesting persistent hemolysis.
When hemolysis was retrospectively diagnosed by Hb decrease and/or the need of blood transfusion, plus either increase in LDH or decrease in haptoglobin, the cumulative incidence of hemolysis during the support was 62.5%. When analyzing the patients according to the cause of CS, the patients with AMI had lower rates of hemolysis (4 of 11 patients [36%]) and required the least amount of RBC (18 units) compared with chronic ischemic cardiomyopathy (10 of 13 patients [76%], with 96 units) and nonischemic cardiomyopathy (11 of 16 patients [68.7%], with 91 units); this trend was also seen in patients who underwent PCI with 40% of hemolysis (6 of 15 patients) compared with 76% (19 of 25 patients) in the non-PCI group.
There was no difference at 30 and 90 days of survival in patients with or without hemolysis (Figure 4).
Although no significant increase in creatinine was noted, 42.5% were started or maintained on renal replacement therapy in the form of CVVHD caused by systemic hypotension. A slight but not statistically significant uptrend in creatinine was noted in nondialyzed patients (p = 0.17) (Figure 5).
Historically, CS attributable to AMI carried the highest mortality rate, as high as 80%.9 Furthermore, with early revascularization and wide use of intra-aortic balloon counter pulsation, a class IIa recommendation by the American College of Cardiology/American Heart Association guidelines for the management of AMI patients with CS,10 the mortality remained close to 50%11 and even lower when support with Impella 2.5 was initiated before PCI.2,12
Hemolysis is a common occurrence in patients with long-term Impella support for CS. The EUROSHOCK registry6 reports rates of 7.5% with an average support of 43 hours, 5–10% in Prospective Feasibility Trial Investigating the Use of the Impella 2.5 System in Patients Undergoing High-Risk Percutaneous Coronary Intervention (PROTECT I) trial in the first 24 hours, and 10.3% reported in USpella registry12 with a median duration of support of 23.7 hours. In our sample, hemolysis was evidenced by the persistent decline in Hb and haptoglobin as well as increase in LDH and bilirubin. Our results indicate that hemolysis was present at 24 hours and persisted until the time of removal (Figure 3).
Although patients with post-AMI had the lowest rates of hemolysis and blood transfusion, the small amount of participants in each group and the retrospective nature of the study do not allow us to draw any definitive conclusions. Furthermore, a lower incidence of hemolysis was seen in patients undergoing PCI, and hence, we hypothesize that post-AMI patients tend to receive aggressive anticoagulation, including dual antiplatelet therapy, thus decreasing the possibility of clot formation within the impeller, shear forces and/or device temperature, and lysing the erythrocyte. In this series of patients, a large number of them were started or maintained on renal replacement therapies and probably confounded the outcome while evaluating renal failure.
Longer Impella support is an option in patients with CS as a bridge to decision or recovery,1,13 but strict monitoring of hemolysis parameters at baseline and at frequent intervals is crucial. Although severe anemia secondary to hemolysis can be monitored with serial laboratory tests and treated with blood transfusions, it can also expose transplant candidates to different antigens, elevating the panel-reactive antibodies. Previous studies reported lower incidence of hemolysis with an early increase and subsequent decrease.3 This can be explained on the basis of relatively shorter duration of support and the half-life of the various LDH isoenzymes, which ranges from 6 to 48 hours.
Two recent publications reported decreased rates in mortality when short-term mechanical circulatory support was used in CS.2,12 Although our survival rates are comparable with the current trend, a major limitation to our study is the retrospective analysis of available data. We do not have pump analysis and other data points that may explain higher rate of hemolysis like pump placement signal, flow rate, motor current, and purge pressure alarms. Given that few patients had an Impella 5.0 or CP, we cannot draw conclusions with different devices. Furthermore, the comparison between them is outside the purpose of this study.
Our study highlights a significantly higher incidence of hemolysis in patients undergoing prolonged percutaneous Impella hemodynamic support for CS. To our knowledge, this is the first time effort has been made to quantify the incidence of hemolysis beyond 6 hours. Our observations suggest that higher amount of hemolysis occurring with prolonged Impella support does not affect overall short-term outcomes and can be used as a successful bridge for definitive therapy or recovery. Hemolysis indices, catheter placement, and device alarms should be closely monitored at baseline and at frequent intervals for the duration of support to aid in best patient outcomes.
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Keywords:Copyright © 2016 by the American Society for Artificial Internal Organs
heart failure; shock; hemoglobin; heart-assist device