Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (44 page)

   Common causes of pericardial inflammation include infection, uremia, trauma, malignancy, hypersensitivity, and autoimmune diseases. Viral infections (coxsackie- and echovirus) are by far the most common and are usually self-limited.

   Cardiac tamponade is more likely to present as dyspnea in its mild form with additional precordial discomfort and hypotension/shock more likely with severe tamponade.

   When presenting as chest pain, myocarditis is often due to concomitant pericarditis. Myocardial involvement alone more often presents as dyspnea and dilated cardiomyopathy (see Dyspnea section), although younger patients are more likely to present.

   Who Should Be Suspected?

   Any recent trauma victim in shock, post-MI patients, patients with comorbid conditions predisposed to effusion (neoplasm, chronic inflammatory disease), patients with chest pain after a viral prodrome.

   Typical signs and symptoms of acute pericarditis include chest pain (often pleuritic and worse with inspiration and supine position), pericardial friction rub (pathognomonic), ECG changes (e.g., ST elevation, PR depression), and pericardial effusion.

   Not all patients will manifest all of these features; the presence or absence of an effusion does not exclude the diagnosis.

   Diagnostic and Laboratory Findings

   
Echocardiography
: Most useful imaging technique for the evaluation of acute pericarditis and is critical for patients if tamponade is suspected. Small pericardial effusions, undetectable by routine examinations, may be detected, providing support for the diagnosis of pericardial disease. Typically >1 cm of effusion is required for safe performance of pericardiocentesis. Dopplerderived flow-velocity measures of mitral and tricuspid flow may assist in diagnosing tamponade, but it is ultimately a clinical diagnosis based on inspiratory decline in systolic arterial pressure exceeding 10 mm Hg (pulsus paradoxus), which can be also seen in COPD and pulmonary embolism. The absence of any chamber collapse on echocardiography has a high negative predictive value for tamponade (92%), although the positive predictive value is low (58%). Abnormalities of right heart venous return (expiratory diastolic reversal) are more predictive but cannot be obtained in one third of patients.

   
Electrocardiography
: ECG abnormalities may support a diagnosis or suggest alternative diagnoses, such as myocardial infarction or early repolarization abnormalities. There are several important distinguishing characters of pericarditis ECGs from that of STEMI patients. There is upward concavity of ST elevations (compared with downward for ischemic) that rarely exceeds 5 mm with PR-segment depression (not in aVR) that is not present with repolarization abnormalities. T-wave inversions may persist with tuberculuous, uremic, or neoplastic pericarditis. Electrical alternans suggests large effusion.

   
Chest x-ray
: Generally normal but may detect specific abnormalities, like increased cardiac silhouette with effusions (water-bottle heart), pleural effusion, or evidence of underlying etiology (TB, fungal disease, pneumonia, neoplasm).