This can be seen in people who are experiencing the classic signs of pericarditis but then show signs of relief, and progress to show signs of cardiac tamponade which include decreased alertness and lethargy, pulsus paradoxus (decrease of at least 10 mmHg of the systolic blood pressure upon inspiration), low blood pressure (due to decreased cardiac index), (jugular vein distention from right sided heart failure and fluid overload), distant heart sounds on auscultation, and equilibration of all the diastolic blood pressures on cardiac catheterization due to the constriction of the pericardium by the fluid.In such cases of cardiac tamponade, EKG or Holter monitor will then depict electrical alternans indicating wobbling of the heart in the fluid filled pericardium, and the capillary refill might decrease, as well as severe vascular collapse and altered mental status due to hypoperfusion of body organs by a heart that can not pump out blood effectively.The diagnosis of tamponade can be confirmed with trans-thoracic echocardiography (TTE), which should show a large pericardial effusion and diastolic collapse of the right ventricle and right atrium. Chest X-ray usually shows an enlarged cardiac silhouette ("water bottle" appearance) and clear lungs. Pulmonary congestion is typically not seen because equalization of diastolic pressures constrains the pulmonary capillary wedge pressure to the intra-pericardial pressure (and all other diastolic pressures). Causes
Infectious
Pericarditis may be caused by viral, bacterial, or fungal infection. In the developed world, viruses are believed to be the cause of about 85% of cases.
In the developing world tuberculosis is a common cause but it is rare in the developed world. Viral causes include coxsackievirus, herpesvirus, mumps virus, and HIV among others.Pneumococcus or tuberculous pericarditis are the most common bacterial forms. Anaerobic bacteria can also be a rare cause. Fungal pericarditis is usually due to histoplasmosis, or in immunocompromised hosts Aspergillus, Candida, and Coccidioides. The most common cause of pericarditis worldwide is infectious pericarditis with tuberculosis. Other
Idiopathic:  No identifiable cause found after routine testing. Autoimmune disease: systemic lupus erythematosus, rheumatic fever, IgG4-related disease
Myocardial infarction
Dresslers syndrome)
Peri-Myocardial Infarction Pericarditis
Trauma to the heart
Uremia (uremic pericarditis)
Cancer
Side effect of some medications, e.g. isoniazid, cyclosporine, hydralazine, warfarin, and heparin
Radiation induced
Aortic dissection
Postpericardiotomy syndrome—such as after CABG surgery
Vaccines-such as smallpox and Covid-19 Vaccines in rare yet documented instances. Diagnosis
Laboratory test
Laboratory values can show increased urea (BUN), or increased blood creatinine in cases of uremic pericarditis. Generally, however, laboratory values are normal, but if there is a concurrent myocardial infarction (heart attack) or great stress to the heart, laboratory values may show increased cardiac markers like Troponin (I, T), CK-MB, Myoglobin, and LDH1 (lactase dehydrogenase isotype 1).The preferred initial diagnostic testing is the ECG, which may demonstrate a 12-lead electrocardiogram with diffuse, non-specific, concave ("saddle-shaped"), ST-segment elevations in all leads except aVR and V1 and PR-segment depression possible in any lead except aVR; sinus tachycardia, and low-voltage QRS complexes can also be seen if there is subsymptomatic levels of pericardial effusion.