The PR depression is often seen early in the process as the thin atria are affected more easily than the ventricles by the inflammatory process of the pericardium.Since the mid-19th century, retrospective diagnosis of pericarditis has been made upon the finding of adhesions of the pericardium.When pericarditis is diagnosed clinically, the underlying cause is often never known; it may be discovered in only 16–22 percent of people with acute pericarditis. Imaging
On MRI T2-weighted spin-echo images, inflamed pericardium will show high signal intensity. Late gadolinium contrast will show uptake of contrast by the inflamed pericardium. Normal pericardium will not show any contrast enhancement. Classification
Pericarditis can be classified according to the composition of the fluid that accumulates around the heart.Types of pericarditis include the following:
serous
purulent
fibrinous
caseous
hemorrhagic

Acute vs. chronic
Depending on the time of presentation and duration, pericarditis is divided into "acute" and "chronic" forms. Acute pericarditis is more common than chronic pericarditis, and can occur as a complication of infections, immunologic conditions, or even as a result of a heart attack (myocardial infarction), as Dresslers syndrome. Chronic pericarditis however is less common, a form of which is constrictive pericarditis. The following is the clinical classification of acute vs. chronic:
Clinically: Acute (<6 weeks), Subacute (6 weeks to 6 months) and Chronic (>6 months)

Treatment
The treatment in viral or idiopathic pericarditis is with aspirin, or non-steroidal anti-inflammatory drugs (NSAIDs such as ibuprofen).
Colchicine may be added to the above as it decreases the risk of further episodes of pericarditis.Severe cases may require one or more of the following:
antibiotics to treat tuberculosis or other bacterial causes
steroids are used in acute pericarditis but are not favored because they increase the chance of recurrent pericarditis
pericardiocentesis to treat a large pericardial effusion causing tamponadeRecurrent pericarditis resistant to colchicine and anti-inflammatory steroids may benefit from a number of medicines that affect the action of interleukin 1; they cannot be taken in tablet form. These are anakinra, canakinumab and rilonacept. Rilonacept has been specifically approved as an orphan drug for use in this situation. Azathioprine has also been used.Surgical removal of the pericardium, pericardiectomy, may be used in severe cases and where the pericarditis is causing constriction, impairing cardiac function. It is less effective if the pericarditis is a consequence of trauma, in elderly patients, and if the procedure is done incompletely. It carries a risk of death between 5 and 10%. Epidemiology
About 30% of people with viral pericarditis or pericarditis of an unknown cause have one or several recurrent episodes. See also
Myopericarditis
Viral cardiomyopathy

References
External links
Pericarditis — National Library of Medicine
Pericarditis — National Heart Lung Blood Institute