ABC | Volume 115, Nº1, Suplement, July 2020

Case Report Pereira et al. A complicated “one segment” myocardial infarction Arq Bras Cardiol 2020; 115(1Suppl.1):25-30 slow blood accumulation. 2 The latter type corresponds to up to one-third of the cases and can progress to complete rupture or pseudoaneurysm formation. 1-3 In both types, immediate surgery is vital, as FWR has a mortality rate ranging between 60 and 96%. 4 LV pseudoaneurysm formation is an even rarer MC, with a reported prevalence of 0.05%. 5,6 It is a late consequence of an undiscovered or unoperated LV FWR, formed when the myocardial rupture is contained by an adherent layer of pericardium, scar tissue or clot formation. 2 As a result, the initial event is typically self-limited and bleeding causes an hemopericardium not manifested by cardiac tamponade. 2 Urgent surgery is indicated as untreated pseudoaneurysms have a 30 to 45% risk of rupture and a mortality rate of 50%. 3,5 In the reported clinical case, an atypical form of incomplete or subacute LV FWR resulting in both cardiac tamponade and pseudoaneurysm formation was described. Concerning diagnosis, TTE is the cornerstone for the initial evaluation of MC following MI. 2 Pericardial effusion is the main echocardiographic finding in LV FWR. 7 However, in cases of pseudoaneurysm, TTE is diagnostic in only 26% of patients and the gold standard method, for its identification is ventriculography. 8 When pseudoaneurysm diagnosis cannot be established by any of the previous methods, CMR is a reliable alternative, as illustrated by the presented case report. It accurately identifies pseudoaneurysms and distinguishes them from true aneurysms. 9-11 Pseudoaneurysms, or false aneurysms, commonly involve lateral or inferior walls; they have no myocardial elements and are characterized by a narrow neck (ratio of the maximum diameter of the orifice to the maximum internal diameter of the cavity of 0.25-0.5) and an abrupt transition from normal myocardium to the defect. 9-11 True aneurysms are more common in apical, anterior or anterolateral locations; contain elements of myocardium and include a wide neck (diameters ratio of 0.9-1.0) and a smooth transition from normal to thinned myocardium. 9-11 The previous differentiating features presented in the CMR were crucial for the final diagnosis of our patient. Emergency pericardiocentesis also enables the diagnosis of the LV FWR, when an hemopericardium is present. In these cases, spontaneous coagulation of pericardial fluid is usually observed, due to the overwhelming of the fibrinolytic Figure 3 – Cardiac magnetic resonance imaging. (A) Four-chamber and (B) short-axis views, T2-weighted short-tau inversion recovery (STIR) images, showing transmural hyperintense sign of the mid-segment of the lateral wall compatible with oedema; (C) Four-chamber and (D) short-axis views, late gadolinium enhancement images, showing contrast enhancement of the same segment, suggesting myocardial necrosis; (E) End-diastolic and (F) end-systolic phases, steady-state free precession (SSFP) cine images, showing dyskinesia of the mid-segment of lateral wall and a saccular protuberance suggesting a pseudoaneurysm (yellow arrow). 27