What are the principal diagnostic features of acute pericarditis?

Chest pain (acute infectious pericarditis and HS, severe, retrosternal and left precordial refferred to neck, arms or left shoulder. frequently pleuritic if accompanied with pleural inflammation. relieved by sitting up and leaning forward and intensified by supine position, absent in TB, post-irradiation and neoplastic, uremic, constrictive pericarditis) Pericardial friction rub (Audible 85%, 3 components (high-pitch, rasping/scratching, end-expiration upright pt)) ECG (4 stages, 1: ST elevation widespread and PR depressed, 2: ST normal, 3: T wave inversion, 4:normal) Effusion (short time and may lead to tamponade, fainter sounds with effusion, CXR shows enlargment of cardiac silhoutte watter-bottle configuration, may be normal)