Postoperative Thrombotic Thrombocytopenic Purpura After Open Heart Operations

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1 Postoperative Thrombotic Thrombocytopenic Purpura After Open Heart Operations Darin J. Saltzman, MD, PhD, Jae C. Chang, MD, Juan C. Jimenez, MD, John G. Carson, MD, Amir Abolhoda, MD, Richard S. Newman, MD, and Jeffrey C. Milliken, MD Department of Surgery and Division of Vascular Surgery, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, and Division of Hematology/Oncology, Division of Cardiothoracic Surgery, and Department of Pathology, University of California Irvine Medical Center, Orange, California Background. Postoperative thrombotic thrombocytopenic purpura (pttp) after cardiovascular operations has an alarmingly high mortality rate if untreated. Five patients after coronary artery bypass graft (CABG) procedure were diagnosed with pttp when they were observed to have a persistent thrombocytopenia associated with symptoms of fever, renal insufficiency, thromboembolic events, or altered mental status in conjunction with a microangiopathic hemolytic anemia (MAHA). A guideline for early diagnosis, followed by timely treatment in these cases, is reviewed. Methods. A retrospective record review of postoperative patients with thrombocytopenia identified 5 patients that met the criteria for pttp from 2004 to We examined these 5 cardiovascular surgical patients in terms of clinical presentation, laboratory data, and outcomes. Results. All patients had the combination of an unexplained thrombocytopenia (platelets < 50,000 mm 3 )in conjunction with a MAHA as determined by the presence of schistocytes. Symptoms of neurologic dysfunction and renal insufficiency developed in all patients. Thromboembolic events were noted in 1 patient. All patients underwent plasmapheresis. In 3 patients, response time to clinical recovery and normalization of hematologic laboratory values after plasmapheresis was 3, 4, and 8 days. Two patients did not recover and died. One patient had a clinical and laboratory recovery after 19 days of plasmapheresis; however, after 11 days, thrombocytopenia with MAHA developed and he died on day 53 from complications related to the operation. Conclusions. Postoperative TTP should be recognized as a possible pathophysiologic mechanism for unexplained postoperative thrombocytopenia and treatment should be initiated once the diagnosis is established. (Ann Thorac Surg 2010;89:119 24) 2010 by The Society of Thoracic Surgeons Thrombocytopenia after cardiothoracic operations often resolves with conservative medical management [1]. Persistent thrombocytopenia, unresponsive to treatment, is associated with high patient morbidity and mortality, especially when thromboembolic events occur [2]. Recently, postoperative thrombocytopenia associated with thrombosis after cardiac operations has been described as postoperative thrombotic thrombocytopenic purpura (pttp) a clinical entity different from other postoperative thrombocytopenias such as heparininduced thrombocytopenia (HIT), disseminated intravascular coagulation (DIC), infection, drug-induced thrombocytopenia, posttransfusion thrombocytopenia, and antibody-mediated TTP seen in the nonoperative medical patient [3 6]. Because HIT is a much more common cause of thrombocytopenia than pttp, it is important to distinguish Accepted for publication Sept 10, Address correspondence to Dr Saltzman, Department of Surgery, David Geffen School of Medicine at UCLA, CHS , Le Conte Ave, Los Angeles, CA 90095; dsaltzman@mednet.ucla.edu. between these two pathologic processes. A distinct feature of pttp, which is not common in HIT, is the presence of microangiopathic hemolytic anemia (MAHA) that is identified by the finding of schistocytes on blood smears [2]. Hemolysis, a clinical feature of pttp and not routinely associated with HIT, releases free hemoglobin that will be bound by haptoglobin. Therefore, a critical step to differentiate pttp from HIT is the determination of plasma haptoglobin, which should be nearly undetectable in pttp but present in HIT [5]. Also helpful in distinguishing pttp from HIT is an elevated level of lactate dehydrogenase (LDH), and reticulocytosis, again not seen with HIT [7]. The best test to confirm a diagnosis of HIT in patients undergoing operations is the heparinassociated platelet antibody by serotonin release assay. DIC, another disease process that can share many of the same characteristics of pttp, including evidence of schistocytes on blood smear, is almost always secondary to an already present condition such as massive hemorrhage, infection, or malignancy [8]. Laboratory values of prothrombin time and partial prothrombin time are rarely abnormal in pttp but are elevated in most patients with DIC [8, 9]. Decreased levels of fibrinogen, factor V, and VIII, with a 2010 by The Society of Thoracic Surgeons /10/$36.00 Published by Elsevier Inc doi: /j.athoracsur

2 120 SALTZMAN ET AL Ann Thorac Surg POSTOPERATIVE THROMBOTIC THROMBOCYTOPENIA 2010;89: Table 1. Patient Characteristics Alive/Dead Dialysis Rx (No.) Days in ICU Plasma Exchanges (No.) Rx Initiation Time to Diagnosis Features of pttp Comorbidities (EuroSCORE) Operation Pt Age Sex Race CABG 4 A, I, K, M, T Died (29) 1 70 F White CAD, 2THY, TIA ( 15.60%) A, K, M, T Died (24) CABG 2, AAA, AVR, 2 76 M White CAD, COPD, DMII, 1LIP, TOB, ETOH ( 51.02%) CABG 1, AAR A, K, M, T Alive 3 64 F White CAD, HTN, ASTM ( 32.71%) 4 77 M Jpn CAD, NHL, BMT ( 21.40%) CABG 3, AVR A, K, M, T Died (53) 5 49 M Chn CAD ( 1.51%) CABG 4, AVR/ A, K, M, T Alive MVR A microangiopathic hemolytic anemia; AAA abdominal aortic aneurysm repair; AAR aortic aneurysm repair; ASTM asthma; AVR aortic valve repair; BMT bone marrow transplant; CABG coronary artery bypass graft; CAD coronary artery disease; COPD chronic obstructive pulmonary disease; DMII type II diabetes mellitus; ETOH heavy alcohol use; EuroSCORE European System for Cardiac Operative Risk Evaluation; HTN hypertension; I peripheral digit ischemic syndrome; ICU intensive care unit; K renal failure; 1LIP hyperlipidemia; M altered mental state; MVR mitral valve repair; NHL non-hodgkin lymphoma; POD Postoperative day; pttp postoperative thrombotic thrombocytopenic purpura; T thrombocytopenia; 2THY Hypothyroidism; TIA transient ischemic attack; TOB tobacco use. significant increase in D-dimer levels (40- to 50-fold), will further support the diagnosis of DIC [8]. Therefore, because many of their clinical and laboratory features will have common characteristics, it is important that the physician not rely on just the clinical, hematologic, or laboratory findings by themselves to distinguish pttp from other postoperative thrombocytopenias [10]. This report reviews 5 patients with postoperative thrombocytopenia not responsive to traditional treatment, with specific attention to the hematology, pathology, and antibody assay of ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) to identify pttp. Patients and Methods This study was approved by the Institutional Review Board. At our institution, the occurrence of thrombocytopenia in 45 patients that resolved with standard therapy and thrombotic thrombocytopenia resistant to conventional treatment in 5 patients was identified in 535 patients undergoing coronary artery bypass grafting (CABG) from 2004 through Patients selected for review had (1) an unexplained postoperative thrombocytopenia (platelets 50,000 mm 3 ), (2) unexplained hemolytic anemia, (3) presence of schistocytes in the blood smear, and (4) neurologic manifestation without focal central nervous system findings [4 5]. The evaluation included a review of drug history, clinical examination, and laboratory testing as previously described [2], including testing for HIT, consumption coagulopathy, and laboratory and imaging studies for systemic infection. Coombs negative hemolytic anemia established on the basis of negative antiglobulin tests, reticulocytosis, increased LDH level, and undetectable haptoglobin level were also used to support the diagnosis of pttp. Presence of significant number of schistocytes was evaluated on the blood smears, and two criteria were met to confirm the diagnosis of MAHA: (1) less than 1% of schistocytes preoperatively and (2) more than 1% of schistocytes on postoperative smears [11]. A European System for Cardiac Operative Risk Evaluation (EuroSCORE) was determined for each patient. Neurologic changes were evaluated with computed tomography (CT) or magnetic resonance imaging (MRI), or both. As soon as pttp was first suspected, a collagenbinding affinity assay (Blood Center of Wisconsin, Milwaukee, WI) for degraded von Willebrand factor (vwf) was used to determine ADAMTS-13 activity, and if present, the antibody inhibitor titer against ADAMTS-13 protein [12]. Patients with the diagnosis of pttp underwent plasmapheresis. Results Table 1 includes the demographic, diagnostic, and therapeutic data of the 5 pttp patients, and the postoperative

3 Ann Thorac Surg SALTZMAN ET AL 2010;89: POSTOPERATIVE THROMBOTIC THROMBOCYTOPENIA Table 2. Postoperative Hematologic Data Pt Lab Data Measured Hgb (g/dl) HCT (%) Platelet Count ( 10 3 / L) At Diagnosis At Lowest Level Reticulocytes (%) Schistocytes LDH (U/L) 121 Haptoglobin (mg/dl) Control values: hemoglobin, g/dl (male), g/dl (female); hematocrit, (male), (female); platelets, / L; reticulocyte, 0.5% 1.5%: schistocytes: 0, 1%; 1, 1% 2%; 2, 2% 5%; 3, 5% 10%; 4, 10%; LDH, U/L; haptoglobin, mg/dl. Hgb hemoglobin; HCT hematocrit; LDH lactate dehydrogenase; POD postoperative day. hematologic data are presented in Table 2. All patients platelet levels dropped to their lowest value within 3 days postoperatively except for patient 1, whose lowest value appeared postoperative day 6. All patient s D-dimer and factor V/VIII values were nondiagnostic for DIC. Severe, intraoperative thrombocytopenia ( 24,000) developed in patient 1, who had been exposed to heparin 1.5 months prior. Repeated, strongly positive serotonin release assays for heparin-associated antibody were initially indicative of HIT, but symptoms of hemolysis indicative of pttp developed. In the course of her postoperative recovery, bilateral patchy foot gangrene developed that progressed to bilateral lower limb gangrene. The remaining patients had a negative history of hematologic disorders before diagnosis, and all had normal hematology values preoperatively. Evidence of hemolysis eventually developed in all patients, which was further evident by the mild to moderate degree of schistocytosis observed in the peripheral blood smear. Fever and neurologic changes were documented in all patients, including unexplained confusion, disorientation, lethargy, and coma. No focal central nervous system abnormality was noted in CT scans or MRI. Renal insufficiency (creatinine increase 0.5 over baseline) developed in all patients. No patients had evidence of a paraprosthetic leak. Plasmapheresis was required in all patients and was discontinued when platelet levels were brought back close to the patient s baseline level and when stable hemoglobin and LDH levels suggested that hemolysis had ceased. Two deaths occurred without hematologic or clinical recovery. Patient 4 had a complete laboratory and clinical Table 3. Activity and Antibody Against ADAMTS-13 Pt ADAMTS-13 Activity (%) ADAMTS-13 Antibody (IU) (Normal: ) (Normal: 0.4) ND ND ADAMTS-13 a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13; ND not done. response to plasma exchange, but signs of hemolysis and thrombocytopenia later developed as a result of a secondary infection related to the operation and he died on postoperative day 53. All families declined autopsy. Complete neurologic and renal recovery was noted in the surviving patients. The measured level of ADAMTS-13 activity and its antibody are recorded in Table 3. These studies were performed in 4 of the 5 patients and the ADAMTS-13 activities were diminished, but none of the 4 patients had any detectable level of antibodies against ADAMTS-13. Comment Thrombocytopenia after surgical intervention is common and often normalizes spontaneously. When it persists after platelet transfusion, attention is required to avoid potentially serious morbidity. Clinical manifestations of pttp may be variable and can present as peripheral ischemia that leads to limb loss, sepsis, renal failure, stroke, myocardial infarction, and death [13]. Thrombocytopenia with unexplained progressive neurologic and hematologic pathology has also been observed after transplantation, gastrointestinal, hepatobiliary, and orthopedic operations [4, 14 17]. TTP after endothelial injury has been recognized for more than 20 years; however, pttp has only recently been appreciated as a distinct clinical syndrome in the surgical field [4 6, 10, 18, 19]. This may be a result of clinicians failing to recognize pttp if high numbers of schistocytes are not seen, which is commonly present with TTP. Therefore, although TTP and pttp are both treated in the same manner, with plasma exchange, the typical absence of an abundant amount of schistocytes in pttp (unlike TTP) makes this condition much more likely to be missed [11]. Needless to say, recognition of pttp and treatment with exchange plasmapheresis may minimize severe postoperative complications. Organ dysfunction as a result of pttp, as similarly seen in nonsurgical patients with TTP, is triggered by the formation of platelet aggregates on the endothelium that disseminate microthrombi obstructing arterioles and capillaries [20, 21]. These aggregates occlude the microvessels and create shear trauma to erythrocytes as they traverse through the microcirculation, resulting in

4 122 SALTZMAN ET AL Ann Thorac Surg POSTOPERATIVE THROMBOTIC THROMBOCYTOPENIA 2010;89: fragments that are observed as schistocytes on light microscopy, a key component for the diagnosis of pttp [22, 23]. Subsequent microaggregation leads to disseminated microthrombi, resulting in vascular occlusion, tissue ischemia, and end-organ damage [24 26]. This pathology has been attributed to decreased levels of ADAMTS-13, a vwf-cleaving protease; when present in normal levels, ADAMTS-13 prevents platelet clumping and its sequelae after endothelial injury [19]. Evidence suggests that there is an inefficient cleavage of vwf multimers secondary to decreased levels of ADAMTS-13 [19] and it has been extensively reviewed in the pathogenesis of TTP [27]. This pathway is distinct from TTP in nonsurgical patients, where the depletion of this vwf-cleaving protease is considered to be autoimmune-mediated, a consequence of autoantibodies against ADAMTS-13 [26]. Decreased ADAMTS-13 activity and the lack of its antibody in our patients suggests a nonimmune-mediated mechanism, which is in agreement with previous investigations that demonstrated a reduced ADAMTS-13 activity level of about 50% after postoperative day 1 in cardiac operations [28, 29]. These reduced levels in ADAMTS-13 activity have been observed in other surgical procedures and serious medical conditions as well [30]. Plasma exchange is believed to reverse this sequence of events by removing the antibody inhibitor of ADAMTS13 or infusing functional ADAMTS-13, or both [8]. A high suspicion of pttp favors a rapid assessment of this distinct clinical entity. Delay in recognition of pttp has been associated with an increased morbidity, as evidenced by other investigations [7]. This may result when more common causes for thrombocytopenia or pancytopenia are pursued, which may take more than a week to evaluate by laboratory studies. The small number of schistocytes seen on a blood smear can contributed to the delay or even a missed pttp diagnosis [11]. Similar to previous studies, the number of schistocytes in our patients was substantially less than what is observed in nonsurgical patients diagnosed with TTP [4, 5]. The detection of schistocytes in the absence of other clinical or laboratory data supporting other causes of thrombocytopenia, however, was instrumental for the diagnosis of pttp for which immediate treatment was rendered. For this reason, thrombocytopenia with a persistent platelet count of less than 50,000/ L should initiate the investigation for a consumptive process. Common causes must be addressed and include HIT, DIC, posttransfusion thrombocytopenia, drug induced, infectious, poor nutrition, and bone marrow and oncologic disorders. Heparin or other drugs known to induce platelet destruction need to be discontinued and blood clotting studies initiated immediately when proceeding to test for postoperative thrombocytopenias. Although testing for vwf cleaving protease and antibodies against vwf is useful for diagnosing TTP in nonsurgical patients, its usefulness in diagnosing patients with pttp is still under investigation. In addition, the clinician should not wait for the determination of ADAMTS-13 activity to make the diagnosis of pttp because this could take several days and could delay the initiation of plasma exchange therapy. Other studies that should be sent include fibrinogen levels, fibrin degradation products, factor V and VIII, and D-dimers because these will aid in the differentiation of DIC vs pttp. Normal levels of these studies and the absence of another explanation for the observed thrombocytopenia in the presence of the above clinical findings would further support the diagnosis of pttp [5]. The definitive cause is not always clear, especially when confounding clinical signs overlap. This was observed in our first patient, who had an initial positive serotonin release assay for heparin-associated antibody, suggestive of HIT, but hemolysis later developed. This has also been observed in other patients after cardiac operations [31]. All of our patients, however, had undetectable haptoglobin at the time of diagnosis, with schistocytes noted on blood smear, both of which are indicative of hemolysis. Once pttp is established, plasmapheresis should be initiated. Delay in treatment has been linked to increased morbidity [32]. Prognosis is not associated with neurologic symptoms or platelet count at initiation of treatment [32]. Platelet transfusion has been traditionally associated with worse outcomes [33], although a recent review of platelet transfusion in patients with TTP suggested that the evidence for this might be uncertain [34]. Platelet transfusion should be reserved for those where a risk of serious bleeding is imminent or present, although this practice may evolve depending on the results of future clinical studies [34]. Plasmapheresis should be implemented daily while monitoring platelet count and LDH levels for signs of improvement. The clinician should realize that although treatment may be initiated promptly, the overall survival of thrombotic thrombocytopenia is only about 80% [32]. Once the process is reversed, as determined by normalization of hematologic values and return of organ function, the treatment is terminated and the patient continues the expected postoperative recovery. Questions still remain if these patients are susceptible to a relapse during the same period or with future surgical procedures. In conclusion, pttp should be recognized as a possible cause of thrombocytopenia after cardiac operations. Presenting symptoms often include an unexplained platelet count of less 50,000 mm 3, signs of neurologic or renal compromise, or both, and fever. When pttp is suspected, a peripheral blood smear should be sent for evaluation as soon as possible, because time will often have elapsed before results have returned. Antibodies may be sent as an adjunct to confirm the diagnosis of pttp. In addition, LDH, reticulocytes, and haptoglobin are used to monitor the progression of the disease. Fibrinogen levels, fibrin degradation products, factor V and VIII, and D-dimers are useful to rule out other causes of thrombocytopenia, such as DIC. Once pttp is confirmed, plasma exchange should be initiated to avoid the morbidity and mortality associated with this rare postoperative syndrome.

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Transfusion 2009;49: INVITED COMMENTARY Saltzman and colleagues [1] have carried out a retrospective study that describes 5 patients with postoperative thrombotic thrombocytopenia purpura (PTTP), which has been considered to be a rare disorder, but its true incidence is not known. However, it is generally considered as life threatening, as confirmed by the death of 3 of the 5 patients described. Moreover, prompt treatment of thrombocytopenia purpura (TTP) with plasmapheresis results in a decrease in mortality from 80% to 20% if the cause is not an immunosuppressive drug. Therefore, this article deals with a significant and possibly undiagnosed condition. Is PTTP a distinct entity differing from TTP by fewer schistocytes? The fact that the schistocytes are usually not accurately quantified (because of the variation of blood smear quality), which make this claim hard to objectively verify. As the authors point out, increased awareness of this entity as a form of TTP should lead to exchange plasmaphoresis, which will result in lower mortality by The Society of Thoracic Surgeons /10/$36.00 Published by Elsevier Inc doi: /j.athoracsur