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BACKGROUND: Bivalirudin, a direct thrombin inhibitor, is a widely used adjunctive therapy in patients undergoing percutaneous intervention (PCI). Thrombin is a highly potent agonist of platelets and activates the protease-activated receptors, PAR1 and PAR4, but it is not known whether bivalirudin exerts antiplatelet effects in PCI patients. We tested the hypothesis that bivalirudin acts as an antiplatelet agent in PCI patients by preventing activation of PARs on the platelet surface. METHODS AND RESULTS: The effect of bivalirudin on platelet function and systemic thrombin levels was assessed in patients undergoing elective PCI. Mean plasma levels of bivalirudin were 2.7±0.5 µmol/L during PCI, which correlated with marked inhibition of thrombin-induced platelet aggregation and significantly inhibited cleavage of PAR1. Unexpectedly, bivalirudin also significantly inhibited collagen-platelet aggregation during PCI. Collagen induced a conversion of the platelet surface to a procoagulant state in a thrombin-dependent manner that was blocked by bivalirudin. Consistent with this result, bivalirudin reduced systemic thrombin levels by >50% during PCI. Termination of the bivalirudin infusion resulted in rapid clearance of the drug with a half-life of 29.3 minutes. CONCLUSIONS: Bivalirudin effectively suppresses thrombin-dependent platelet activation via inhibition of PAR1 cleavage and inhibits collagen-induced platelet procoagulant activity as well as systemic thrombin levels in patients undergoing PCI.

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Left ventricular (LV) thrombus is one of the most common complications of myocardial infarction (MI). Contemporary devices for mechanical support during high-risk percutaneous coronary intervention (PCI) include intra-aortic balloon pumps (IABPs) or percutaneous left ventricular assist devices (pVADs). We describe the case of an elderly patient presenting with critical double-vessel disease, severely depressed LV function, and a large LV thrombus in the setting of a mechanical fall causing spinal cord compression. In this report, we describe the use of a TandemHeart pVAD during high-risk PCI in the presence of an unstable LV thrombus.

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Management of right heart failure in acute myocardial infarction (AMI) includes emergent reperfusion of the infarct-related artery, fluid resuscitation, vasopressor and inotropic support, and trans-venous pacing in the presence of high-grade atrio-ventricular conduction block. Historically, mechanical support for right ventricular failure after an AMI has been limited to intra-aortic balloon pump (IABP) counterpulsation or surgically placed ventricular assist devices. Recently, a percutaneous right ventricular assist device (pRVAD, TandemHeart; CardiacAssist Inc., Pittsburgh, Pennsylvania) has offered an intermediate alternative for patients with refractory right heart failure in the setting of AMI. We describe a novel approach to pRVAD implantation via the right internal jugular vein in the setting of cardiogenic shock secondary to an acute inferior myocardial infarction.

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Patients with hypertrophic cardiomyopathy who experience refractory symptoms due to left ventricular outflow tract obstruction are often referred for definitive therapy consisting of either surgical myectomy or alcohol septal ablation (ASA). There currently exists clinical equipoise regarding which therapy is the most efficacious in this challenging patient population. ASA utilizes common interventional techniques usually employed to treat atherosclerotic coronary artery disease to inject small aliquots of ethanol into a branch of the appropriate septal vessel to cause necrosis of the obstructing basal septal tissue. Myocardial contrast echocardiography is used to facilitate location of the most appropriate septal branch with success determined by an acute reduction in the resting and/or provoked gradient. Recent comparative data have suggested similar rates of long and short-term mortality in when comparing patients undergoing ASA and surgical myectomy, with ASA patients experiencing a higher rate of requirement for permanent pacemakers. In addition, patients treated by both techniques appear to have similar gradient reductions and improvement in symptomatic status. Comparisons of these two methods of treatment are limited by the non-randomized nature of the studies, retrospective data collection and the allocation of higher-risk patients to ASA treatment. Concern for the wide-spread adoption of ASA to drug-resistant HCM patients is warranted due to the potential for arrhythmogenesis is a patient population already at risk for life-threatening arrhythmias. There have been case reports of such arrhythmias, however, clinical series to date have not suggested an enhanced risk of sudden cardiac death in patients treated with ASA. Definitive answers concerning which patient subsets with drug-refractory hypertrophic cardiomyopathy would benefit from the two competing therapies can only be answered by a randomized clinical trial. However, for a variety of clinical and logistical factors, such a trial is unlikely to ever be performed. For the foreseeable future, patient-specific therapy will depend on local expertise, patient comorbidities and preferences.

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Efficient induction of apoptosis requires not only the activation of death-promoting proteins but also the inactivation of inhibitors of cell death. ARC (apoptosis repressor with caspase recruitment domain) is an endogenous inhibitor of apoptosis that antagonizes both central apoptosis pathways. Despite its potent inhibition of cell death, cells that express abundant ARC eventually succumb. A possible explanation is that ARC protein levels decrease dramatically in response to death stimuli. The mechanisms that mediate decreases in ARC protein levels during apoptosis and whether these decreases initiate the subsequent cell death are not known. Here we show that endogenous ARC protein levels decrease in response to death stimuli in a variety of cell contexts as well as in a model of myocardial ischemia-reperfusion in intact mice. Decreases in ARC protein levels are not explained by alterations in the abundance of ARC transcripts. Rather, pulse-chase experiments show that decreases in steady state ARC protein levels during apoptosis result from marked destabilization of ARC protein. ARC protein destabilization, in turn, is mediated by the ubiquitin-proteasomal pathway, as mutation of ARC ubiquitin acceptor residues stabilizes ARC protein and preserves its steady state levels during apoptosis. In addition, this degradation-resistant ARC mutant exhibits improved cytoprotection. We conclude that decreases in ARC protein levels in response to death stimuli are mediated by increased ARC protein degradation via the ubiquitin-proteasomal pathway. Moreover, these data demonstrate that decreases in ARC protein levels are a trigger, and not merely a consequence, of the ensuing cell death.

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Death-fold domains constitute an evolutionarily conserved superfamily that mediates apoptotic signaling. These motifs, including CARD (caspase recruitment domain), DD (death domain), and DED (death effector domain), are believed to exert their effects solely through homotypic interactions. Herein we demonstrate that the CARD-containing protein ARC engages in nontraditional death-fold interactions to suppress both extrinsic and intrinsic death pathways. The extrinsic pathway is disrupted by heterotypic interactions between ARC's CARD and the DDs of Fas and FADD, which inhibit Fas-FADD binding and assembly of the death-inducing signaling complex (DISC). The intrinsic pathway is antagonized by ARC-Bax binding, involving ARC's CARD and the Bax C terminus. This inhibits Bax activation and translocation to the mitochondria. Knockdown of endogenous ARC facilitates DISC assembly and triggers spontaneous Bax activation and apoptosis. Conversely, physiological levels of ARC suppress these events. These studies establish a critical role for nonhomotypic death-fold interactions in the regulation of apoptosis.

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