ST segment elevation in ECG is seen in all of the following except:

In constrictive pericarditis, ECG does not show ST elevation, it frequently shows low voltage QRS complexes and diffuse flattening or inversion of the T waves. 1/3rd of the patients shows changes consistent with atrial fibrillation. Constrictive pericarditis: Is inflammation of pericardium which leads to the formation of a thickened, fibrotic, adherent pericardium that restricts diastolic filling and produces chronically elevated venous pressures. Clinical features: Patients presents with progressive dyspnea, fatigue, and weakness. On examination: JVP is elevated with a rapid y descent. Kussmaul sign and pulsus paradoxus is present. Apex of hea retract with systole and a pericardial knock may be heard in early diastole. Chest radiograph may show cardiomegaly and pericardial calcification. Echocardiography shows thickened pericardium and septal bounce reflecting the rapid early filling. Reference: 1. Current Medical Diagnosis and Treatment, 2012, Chapter 10 2. Harrison's Internal Medicine, 18th Edition, Chapter 239