### Make the Diagnosis: Cardiac Tamponade

#### Prior Probability of Cardiac Tamponade

Cardiac tamponade occurs when fluid trapped in the pericardial space (ie, effusion) compresses the heart and compromises cardiac output. Thus, an assessment of tamponade in the nonurgent setting requires (1) knowing the pretest probability of an effusion and (2) knowing the prior probability of tamponade among patients with effusion. Most studies report only retrospective case series of patients with effusion, so the prior probability of cardiac tamponade is not known. However, because tamponade is so infrequent, among all patients the probability is most likely less than 1%. Among case series of patients with effusion, the prior probability cannot be determined with certainty because of patient selection bias. In a study of patients with effusion who were clinically suspected of having hemodynamic compromise, 64% had tamponade.1 Since many patients with pericardial effusions have small inconsequential amounts of fluid, the likelihood of tamponade in all patients with effusion should be much lower than 64%.

#### Population for Whom Cardiac Tamponade Should Be Considered

In the absence of chest trauma, cardiac tamponade should be considered in patients with pericardial effusions identified on echocardiography. Once a pericardial effusion is notified, the most common underlying diagnoses of moderate to large effusions are acute idiopathic pericarditis (20%), iatrogenic effusion (16%), malignancy (13%), chronic idiopathic effusion (9%), acute myocardial infarction (8%), end-stage renal disease (6%), congestive heart failure (5%), collagen vascular disease (5%), and tuberculosis or bacterial infection (4%).2 Pericardial effusions often result from primary cardiac disease, occurring in 14% of patients with congestive heart failure, 21% of patients with valvular heart disease, and 15% of patients with myocardial infarction.3

#### Assessing the Likelihood of Cardiac Tamponade in Patients With a Pericardial Effusion

Dyspnea is the only symptom that is present in more than 50% of patients (Table 64-1).

Table 64-1Sensitivity and Likelihood of Findings for Cardiac Tamponade Among Patients with Pericardial Effusion

The Beck triad was described in surgical patients and consists of decreasing arterial blood pressure, increasing jugular venous pressure, and a small, quiet heart. In medical patients, pericardial effusions develop slowly so that these findings seen in surgical patients may not be present at all. Findings present in more than 50% of patients include cardiomegaly seen ...

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