Primary percutaneous coronary intervention in acute myocardial infarction

Blood coagulation: hemostasis and thrombin regulation

Perioperative bleeding is a major challenge particularly because of increasing clinical use of potent antithrombotic drugs. Understanding current concepts of coagulation is important in determining the preoperative bleeding risk of patients, and in managing hemostatic therapy perioperatively. The serine protease thrombin plays pivotal roles in the activation of additional serine protease zymogens (inactive enzymatic precursors), cofactors, and cell-surface receptors. Thrombin generation is closely regulated to locally achieve rapid hemostasis after injury without causing uncontrolled systemic thrombosis. During surgery, there are major disturbances in coagulation and inflammatory systems because of hemorrhage/hemodilution, blood transfusion, and surgical stresses. Postoperative bleeding often requires allogeneic blood transfusions, which support thrombin generation and hemostasis. However, procoagulant activity and inflammation are increased postoperatively; thus, antithrombotic therapy may be required to prevent perioperative thrombotic complications. There have been significant advances in the management of perioperative hemostasis and thrombosis because of the introduction of novel hemostatic and antithrombotic drugs. However, a limitation of current treatment is that conventional clotting tests do not reflect the entire physiological processes of coagulation making optimal pharmacologic therapy difficult. Understanding the in vivo regulatory mechanisms and pharmacologic modulation of thrombin generation may help control bleeding without potentially increasing prothrombotic risks. In this review, we focus on the regulatory mechanisms of hemostasis and thrombin generation using multiple, simplified models of coagulation.

Usefulness of three posterior chest leads for the detection of posterior wall acute myocardial infarction

A significant proportion of patients with myocardial infarction are missed upon initial presentation to the emergency department. The 12-lead electrocardiogram (ECG) has a low sensitivity for the detection of acute myocardial infarction, especially if the culprit lesion is in the left circumflex artery (LCA). This study was designed to evaluate the benefit of adding 3 posterior chest leads on top of the 12-lead ECG to detect ischemia resulting from LC disease, using a model of temporary balloon occlusion to produce ischemia. We studied 53 consecutive patients who underwent clinically indicated coronary interventions. At the time of coronary angiography, the balloon was inflated to produce complete occlusion of the proximal LCA. We recorded and analyzed the changes noted on the 15-lead ECG, which included 3 posterior leads in addition to the standard 12 leads. In response to acute occlusion of the LCA, the posterior chest leads showed more ST elevation than the other leads, and more patients had ST elevation in the posterior leads than in any other lead. The 15-lead ECG was able to detect>or=0.5 mm (74% vs 38%, p<0.0001) and >or=1 mm (62% vs 34%, p<0.0001) ST elevation in any 2 contiguous leads more frequently than the 12-lead ECG. In conclusion, the 15-lead ECG identified more patients with posterior myocardial wall ischemia because of temporary balloon occlusion of the LC than the 12-lead ECG. This information may enhance the detection of posterior MI in the emergency department and potentially facilitate early institution of reperfusion therapy.

Unresolved issues in myocardial reperfusion injury

While the basic pathobiology of myocardial ischemic injury and reperfusion has been determined over the last 50 years, there are important, unresolved, or at least not completely elucidated, issues in the field. These include the relative contributions of different modes of cell injury and death to evolving myocardial infarcts; interactions of phenomena produced by reperfusion, including stunning and preconditioning; and potential new approaches for successfully combining adjuvant therapy with coronary artery opening. A model of myocardial ischemic and reperfusion injury is proposed involving the potential expression of apoptotic and oncotic pathways in the same perturbed cardiomyocytes. Promising new cardioprotective strategies for reducing lethal reperfusion injury are discussed, including ischemic postconditioning, activators of the reperfusion injury salvage kinase (RISK) pathway, inhibitors of protein kinase c-delta, and inhibitors of the mitochondrial membrane permeability transition pore (PTP). Major outstanding clinical challenges are also discussed, including the development of clinical care systems that can routinely deliver very timely coronary opening and reperfusion, perhaps combined with adjuvant therapy, and the development of strategies to retard adverse remodeling and congestive heart failure in patients with significant myocardial infarction and scarring, perhaps by refinements in stem cell therapy.