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Abstract Background: ChAdOx1 nCoV-19 (AstraZeneca) and Ad26.COV2.S (Janssen Johnson & Johnson) vaccines against COVID-19 have been associated with thrombotic thrombocytopenic reactions referred to as vaccine-induced immune thrombotic thrombocytopenia (VITT) characterized by the presence of platelet-activating, anti-PF4 antibodies. While VITT shares key clinical features with a similar but separate entity, Heparin-induced thrombocytopenia (HIT), there appear to be important differences: 1) VITT patients have extremely high thrombosis rates and are very strongly positive in PF4-polyanion ELISAs, and 2) Many patients with VITT frequently present with refractoriness to therapy or have disease recurrence that suggests distinct antibody characteristics due to a strong autoimmune anti-PF4 response. Aims: The goal of this study was to characterize anti-PF4 antibodies in VITT. Methods: Five VITT patients were studied, one after ChAdOx1 nCoV-19 vaccination and four after Ad26.COV2. Reactivity of VITT anti-PF4 antibodies to uncomplexed PF4, PF4-Polyvinyl sulfonate (PVS), and PF4-heparin targets was evaluated, and the platelet-activating ability of these antibodies was examined in the PF4-dependent P-selectin Expression assay (PEA). Anti-PF4 antibodies were isolated from patient blood samples using PF4-treated heparin sepharose beads, and isolated antibodies were subject to mass spectrometric evaluation (Liquid Chromatography Electrospray Ionization Quadrupole time-of-flight mass spectrometry [LC-ESI-QTOF MS]). Results: Antibodies from all VITT patients recognized both uncomplexed and complexed PF4 (Fig. 1A). Interestingly, recognition of PF4 by VITT antibodies was lower if PF4 targets were complexed with polyanions, PVS, or heparin (Fig. 1A). These results contrasted with those obtained in a "classical" HIT patient which showed reactivity to PF4/polyanion complexes, but not to uncomplexed PF4 (Fig 1A). All samples activated platelets in the PEA (data not shown). Mass spectrometric evaluation of anti-PF4 antibodies isolated from VITT patients demonstrated monoclonal anti-PF4 antibodies in three patients, and bi- and tri-clonal antibodies in one patient each (a representative monoclonal antibody anti-PF4 antibody is shown in Fig 1B). Consistent with current dogma, polyclonal anti-PF4/polyanion antibodies were seen in "classical" HIT (Fig 1C). Evaluation of anti-PF4 antibodies in spontaneous HIT, a type of autoimmune HIT seen in pro-inflammatory milieus such as orthopedic surgery and infectious prodromes also demonstrated monoclonal anti-PF4 antibodies (Fig 1D). Eluates from control heparin-sepharose beads did not reveal any immunoglobulins (data not shown). Conclusion: Although development of platelet-activating anti-PF4 antibodies and the thrombotic thrombocytopenia syndrome seen after ChAdOx1 nCoV-19 and Ad26.COV2.S vaccination resembles HIT, these findings demonstrate that clonally restricted anti-PF4 antibodies mediate VITT while polyclonal anti-PF4 antibodies mediate HIT. In addition, we noted clonally-restricted anti-PF4 antibodies in another condition that does not require proximate heparin exposure, spontaneous ("autoimmune") HIT. In VITT, the strong immune response after vaccine administration may result in the activation of a single or few pre-existing anti-PF4 reactive clones, and development of clonally restricted anti-PF4 antibodies with a similar pathophysiology to Spontaneous HIT. It is also likely that high levels of monoclonal/oligoclonal anti-PF4 antibodies cause the severe thrombotic phenotypes seen in VITT and Spontaneous HIT. The high mortality rate and reports of disease refractoriness to therapy in VITT may warrant consideration of additional therapeutic modalities like rituximab and therapeutic plasma exchange in select cases. Figure Legends: (A): VITT (Patient 1-ChAdOx1 nCoV-19; Patients 2-5, Ad26.COV2.S) patient samples were tested in ELISA against uncomplexed PF4 (white), and PF4 in complex with polyvinyl sulfonate (light grey), or unfractionated heparin (dark gray). (B-D) Mass spectrometric evaluation of anti-PF4 antibodies isolated from VITT (B), HIT (C) and spontaneous HIT patient sera (D). "Relative Intensity" refers to abundance of the Ig light chain relative to the polyclonal background. Numbers above Ig light chain peaks depict mass/charge ratios. NC- Normal control. Figure 1 Figure 1. Disclosures Murray: Mayo Clinic: Other: Has received patents for the Mass-Fix technology which has been licensed to the Binding Site with potential royalties.. Padmanabhan: Veralox Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Abstract Background: COVID-19 vaccinations in the United States (Janssen, Moderna, and Pfizer) have been deemed generally safe and effective. Rare thrombotic events, now termed vaccine-induced thrombotic thrombocytopenia (VITT), have been reported after the Janssen and Moderna vaccinations. With millions of vaccinations being administered to adults, it is expected that some deep vein thrombosis (DVT) will occur coincidentally with vaccination. Whether COVID-19 vaccinations may contribute to DVT risk more generally (outside of VITT) has not been well studied outside of the initial clinical trials. Aims: Evaluate trends in DVT diagnosis before and after COVID-19 vaccination Methods: Vaccinated patients ≥ 18 years between 11/6/2020 through 6/1/2021 were analyzed using electronic medical records across the Mayo Clinic enterprise. Upper and lower DVT venous Duplex ultrasound (DUS) reports occurring 90 days before and after vaccination date (first dose for Pfizer and Moderna vaccines) were extracted and analyzed with a highly accurate, previously validated, Natural Language Processing (NLP) algorithm for acute DVT. Results: 382,527 patients with at least 1 COVID-19 vaccination were identified. The median age was 61 (IQR 44-72) and 55.3% were male. Pfizer was the most common vaccine administered (n=245,572, 64.2%), followed by Moderna (n=120,683, 31.6%) and Janssen (n=16,272, 4.3%). Most patients (91.5%) receiving vaccinations were from states with Mayo Clinic health services (Minnesota, n=197,834; Wisconsin, n=80,720; Florida, n=42,391; Arizona, n=28,882). The mean age at vaccination was 61.0 (SD 17.7), 56.5 (SD 19.1), and 54.7 (SD 16.3) for Moderna, Pfizer, and Janssen vaccines respectively. Women were most likely to receive the Pfizer (56.3%) compared to Moderna (54.1%) and Janssen (49.5%) vaccines. Non-white patients were most likely to receive Janssen (21%) compared to Moderna (7.7%) and Pfizer (8.2%) vaccines. Among all patients, 7,265 upper and lower venous DUS were performed in 5,960 patients. Figure 1 shows the utilization of DUS before and after COVID-19 vaccination and shows that more patients underwent DUS in the 90 days after vaccination compared to 90 days pre-vaccination. Acute DVT was identified by the NLP algorithm in 808 (714 patients) ultrasounds (11.1%); 656 out of 6136 lower extremity DUS (10.7%) and 152 out of 1129 upper extremity DUS (13.5%). The overall rate of acute DVT (upper and lower) was 1.86 per 1000 patients, consistent with the expected background epidemiologic rate. Figure 2 shows the daily probability of acute DVT by ultrasound report in the 90 days before and after vaccination with a linear regression best fit line showing no overall correlation (R 2 = 0.0). Overall acute DVT post-vaccination occurred on 10.8% of DUS compared to 11.6% pre-vaccination (p=0.28). Among ultrasound reports in Janssen vaccinated patients, 7.0% of post-vaccination compared to 18.0% of pre-vaccination were positive for acute DVT (p=0.003). Among ultrasound reports in Moderna vaccinated patients, 11.0% of post-vaccination compared to 12.7% of pre-vaccination were positive for acute DVT (p=0.15). Among ultrasound reports in Pfizer vaccinated patients, 11.0% of post-vaccination compared to 10.4% of pre-vaccination were positive for acute DVT (p=0.56). Using a Cox proportional hazard model, pre vs post-vaccination time among the same patient cohort was compared for each vaccine. The hazard ratio for DVT post-vaccination was 0.68 (95% CI 0.34-1.38) for Janssen, 1.08 (95% CI 0.86-1.35) for Moderna, and 1.20 (95% CI 0.99-1.46) for Pfizer. After adjusting for age and sex, Pfizer and Janssen's vaccines did not have different risks for DVT compared to Moderna in the 90 days post-vaccination (HR 0.80, 95% CI 0.98-1.25 and HR 0.75, 95% CI 0.42-1.32 respectively). Conclusions: In this large cohort of COVID-19 vaccinated patients, no increased risk for acute DVT post-vaccination was identified for any of the approved vaccinations in the United States. Additionally, no significant difference was seen in the risk for DVT post-vaccination when comparing each vaccine to each other. The probability of acute DVT on ultrasounds in the 90 days post-vaccination was lower than the pre-vaccination period with the Janssen vaccine possibly indicating over-testing in this group. These results provide additional reassurance of the safety of approved COVID-19 vaccines. Figure 1 Figure 1. Disclosures Padmanabhan: Veralox Therapeutics: Membership on an entity's Board of Directors or advisory committees. Pruthi: HEMA Biologics: Honoraria; CSL Behring: Honoraria; Genentech: Honoraria; Instrumentation Laboratory: Honoraria; Bayer Healthcare AG: Honoraria; Merck: Honoraria.

Background Most patients with advanced melanomas relapse after checkpoint blockade therapy. Thus, immunotherapies are needed that can be applied safely early, in the adjuvant setting. Seviprotimut-L is a vaccine containing human melanoma antigens, plus alum. To assess the efficacy of seviprotimut-L, the Melanoma Antigen Vaccine Immunotherapy Study (MAVIS) was initiated as a three-part multicenter, double-blind, placebo-controlled phase III trial. Results from part B1 are reported here. Methods Patients with AJCC V.7 stage IIB-III cutaneous melanoma after resection were randomized 2:1, with stage stratification (IIB/C, IIIA, IIIB/C), to seviprotimut-L 40 mcg or placebo. Recurrence-free survival (RFS) was the primary endpoint. For an hypothesized HR of 0.625, one-sided alpha of 0.10, and power 80%, target enrollment was 325 patients. Results For randomized patients (n=347), arms were well-balanced, and treatment-emergent adverse events were similar for seviprotimut-L and placebo. For the primary intent-to-treat endpoint of RFS, the estimated HR was 0.881 (95% CI: 0.629 to 1.233), with stratified logrank p=0.46. However, estimated HRs were not uniform over the stage randomized strata, with HRs (95% CIs) for stages IIB/IIC, IIIA, IIIB/IIIC of 0.67 (95% CI: 0.37 to 1.19), 0.72 (95% CI: 0.35 to 1.50), and 1.19 (95% CI: 0.72 to 1.97), respectively. In the stage IIB/IIC stratum, the effect on RFS was greatest for patients <60 years old (HR=0.324 (95% CI: 0.121 to 0.864)) and those with ulcerated primary melanomas (HR=0.493 (95% CI: 0.255 to 0.952)). Conclusions Seviprotimut-L is very well tolerated. Exploratory efficacy model estimation supports further study in stage IIB/IIC patients, especially younger patients and those with ulcerated melanomas. Trial registration number NCT01546571.

AbstractBackgroundIntracardiac electrogram data remain one of the primary diagnostic inputs guiding complex ablation procedures. However, the technology to collect, process, and display intracardiac signals has known shortcomings and has not advanced in several decades.ObjectiveThe purpose of this study was to evaluate a new signal processing platform, the PURE EP™ system (PURE), in a multi‐center, prospective study.MethodsIntracardiac signal data of clinical interest were collected from 51 patients undergoing ablation procedures with PURE, the signal recording system, and the 3D mapping system at the same time stamps. The samples were randomized and subjected to blinded, controlled evaluation by three independent electrophysiologists to determine the overall quality and clinical utility of PURE signals when compared to conventional sources. Each reviewer assessed the same (92) signal sample sets and responded to (235) questions using a 10‐point rating scale. If two or more reviewers rated the PURE signal higher than the control, it was deemed superior.ResultsA total of 93% of question responses showed consensus amongst the blinded reviewers. Based on the ratings for each pair of signals, a cumulative total of 164 PURE signals out of 218 (75.2%) were statistically rated as Superior for this data set (p < .001). Only 14 PURE signals out of 218 were rated as Inferior (6.4%).ConclusionThe PURE intracardiac signals were statistically rated as superior when compared to conventional systems.

Heparin-induced thrombocytopenia (HIT) is an immune complication of heparin therapy caused by antibodies to complexes of platelet factor 4 (PF4) and heparin. Pathogenic antibodies to PF4/heparin bind and activate platelets to propagate a hypercoagulable state culminating in life-threatening thrombosis. The serotonin-release assay (SRA) is considered the gold-standard test to diagnose HIT. However, the sensitivity of the SRA was questioned with reported cases of clinical diagnosis of HIT and negative SRA. Herein, we present the utility of platelet factor 4-dependent P-selectin expression assay (PEA) in diagnosing HIT in a patient with thrombocytopenia and recurrent thrombosis who repeatedly tested negative with SRA.

Introduction: The availability, national scope and perceived unbiased nature of administrative claims data makes it an attractive choice by health care policy makers for evaluating quality and outcomes. We calculated Ventricular tachycardia (VT) ablation complication rates from national administrative data and compared them with data from randomized trials and prospective studies. Methods: A PUBMED database search was done to identify existing studies of VT ablation. Studies were divided into clinical (randomized controlled trials (RCTs) and prospective studies). Pooled rates of vascular, cardiac, neurological complications and procedure related mortality were computed and compared to reported complication rates from administrative database studies Results: We identified two administrative database studies of VT ablation that included a total of 14,352 procedures and 18 clinical studies with a total of 1,705 procedure. Overall complication rate in administrative studies was higher than in clinical studies (9.39% vs. 7.97%). Rates of cardiac/pericardial (4.47% vs. 2.29%) and vascular access complications (6.9% vs. 3.0%) were higher in real world studies. Neurological complications (1.17% vs. 0.45%) and procedure related mortality (1.53% vs. 1.29%) were higher in clinical studies. Among clinical studies, RCTs had the lowest reported complication rate. Conclusion: Despite substantial improvement, “real-world” complication rates from administrative data remain higher than those reported in RCTs. The discrepancy may be attributable to differences in operator skills, selection bias and variation in data quality. Use of large databases provides an important analytical resource as we embark on improving national health care efficacy and safety in the current challenging environment.

Introduction: One million patients around the world have had total hip arthorplasty with 35% of them having metal-on-metal implants. Although there have been some case reports of cobalt cardiotoxicity from arthroprosthetic cobaltism resulting in dilated cardiomyopathy, incidence of cardiomyopathy and mortality in these patients is unknown. Objective: We therefore sought to determine the incidence of new onset cardiomyopathy (EF <40%) and associated mortality, in patients with metal hip arthroplasty. Methods: We retrospectively examined the records of the patients form our institutional total hip arthroplasty registry (Metal on Metal: MoM, Metal on Polyethylene: MoP, Ceramic on Ceramic: CoC and Ceramic on Polyethylne: CoP). Among 122 patients with baseline and follow up echocardiograms, cobalt and chromium levels were available in 12 patients, none of which developed incident cardiomyopathy. Results: The mean age of the population with metal group (MoM and MoP) was 53 years, predominantly males. During the follow up period of 10 years, the cumulative incidence (KM curve probabilities) of low EF <=40% in our study population was 14% in metal group as compared to 5% in non-metal group (CoC and CoP), (p value 0.51). At 15 years of follow up, among 122 patients, there were16 deaths in the metal group (81) and only 2 deaths in the non-metal group (41) (p value 0.15). Conclusions: In conclusion, although the incidence of cardiomyopathy as well as mortality is low in patients with metal hip arthroplasty and not significantly, further studies maybe needed to assess its effect on diastolic dysfunction.

Background: Worldwide, approximately one million patients have had total hip arthroplasty with 35% being cobalt and chromium Metal-on-Metal (MoM) or Metal-on-Polythelene (MoP) implants. Animal models have suggested that cobalt and chromium can affect all chambers, but there seems to be an atrial predilection. There are several case reports of metal containing hip arthroplasty causing atrial arrhythmias but the true incidence of atrial fibrillation associated with metal hip arthroplasty remains undefined. Objective: We sought to determine the incidence of atrial fibrillation in patients with metal containing hip arthroplasty. We also examined the association between serum cobalt and chromium levels and arrhythmias in this cohort and all cause mortality. Methods: We retrospectively examined the records of patients from the Mayo Clinic total hip arthroplasty registry (Metal group - Metal-on-Metal: MoM and Metal-on-Polyethylene: MoP, Non-Metal group - Ceramic-on-Ceramic: CoC and Ceramic-on-Polyethylne: CoP) to obtain demographic data, comorbidities, laboratory, ECG, and echocardiographic data. Out of a total of 1756 patients, Cobalt and Chromium levels were available in 138 patients. Results: The mean age of patients with metal containing hip replacement was 50 years and were predominantly male. During a follow up period of 10 years, the incidence of atrial fibrillation in our study population was 8% in metal group compared to 2% (p=0.11) in non-metal group. There was no association between cobalt or chromium levels with the incidence of atrial fibrillation. All-cause mortality was significantly higher in metal group versus non-metal group (p=0.005). Conclusion: The incidence of atrial fibrillation was relatively more in patients with metal versus non-metal hip arthroplasty but there was no association of serum cobalt or chromium levels with incidence of atrial fibrillation in the subset of patients. In addition, all-cause mortality was significantly higher in the metal group suggesting potential toxic effects of metal containing hip arthroplasty.