6 Introduction Pericarditis is an important clinical problem and accounts for up to 5% of emergency admissions with acute chest pain. It remains the most common cause of pericardial disease worldwide.1-3 Nevertheless, dedicated pericardial clinics and acute pericardial services are few, and most patients present to and are managed by primary care physicians, emergency physicians or general cardiologists. Most patients respond to first-line treatment and experience a benign disease trajectory with eventual resolution of symptoms and no long-term sequelae. However, approximately 30% of patients can go on to develop recurrent pericarditis, which can have a dramatic deleterious effect on quality of life as well as result in increased utilization of health care resources.4,5 Although many challenges remain, the last decade has witnessed significant advances in our understanding of the pathophysiology of inflammatory pericardial disease as well as several important therapeutic advances. With timely and effective evidence-based initial care, the incidence of recurrent pericarditis can be halved,2 and for those who do go on to develop this complication, newer treatment options are now available.6 The aim of this American Heart Association (AHA) toolkit is to equip all clinicians who may encounter patients with acute pericarditis with the knowledge, skills and practical guidance to manage acute and recurrent pericarditis confidently and effectively. The Recurrent Pericarditis Toolkit has been assembled by an international and multidisciplinary team of experts. It strongly emphasizes practical guidance for issues clinicians are likely to encounter in day-to-day, clinical practice, buttressed where necessary with the theoretical basis for the guidance. Pericardial Anatomy, Structure and Function The pericardium is the outer lining of the heart consisting of an inner double-layered sac called the serous pericardium. The inner layer of the sac is the visceral layer, or epicardium, that lines the heart and proximal great vessels. The visceral layer is reflected to form the parietal pericardium, which lines the fibrous pericardium.7 The pericardial cavity exists between the two layers, which contain approximately 15-50 ml of plasma infiltrate.7 Anchoring the heart in the thorax, the pericardium acts as a mechanical protective layer for the heart against trauma and as an immunologic barrier.1 The pericardial fluid serves as a lubricant to reduce friction between the heart and its surrounding structures and eases movement during the twisting, contracting and relaxation actions. Hemodynamic effects of the pericardium occur in response to changes in intrathoracic pressure, which cause changes in pericardial and intracardiac pressure with slight increases in left ventricular (LV) stroke volume and arterial blood pressure. During inspiration, the negative intrathoracic pressure increases venous return to the right heart and slightly reduces LV filling unrelated to the normal pericardium. The toolkit is supported by a series of four vodcasts and webinars, which in turn build on an extensive library of webinars and podcasts freely available from the AHA Lifelong Learning website (https:// professional.heart.org/en/education/ recurrent-pericarditis-for-professionals). Illustration of the heart showing the pericardial layers. http://www.scientificanimations.com, CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0), via Wikimedia Commons
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