Ultrasound Features of Cardiac Tamponade

Key Echocardiographic Findings

The American College of Emergency Physicians suggests that diastolic collapse of any cardiac chamber in the presence of moderate or large pericardial effusion is a key ultrasound feature of cardiac tamponade, with right atrial collapse being the most sensitive sign and right ventricular diastolic collapse being more specific 1, 2, 3
Pericardial effusion appears as an anechoic or hypoechoic fluid collection within the pericardial space, and may have complex echogenicity with inflammatory, infectious, malignant, or hemorrhagic etiologies 1, 2, 3
The European Society of Cardiology recommends classifying pericardial effusion based on size, with small effusions being <10 mm in diastole, moderate effusions being circumferential with no part greater than 10 mm in width in diastole, large effusions being 10-20 mm in width, and very large effusions being >20 mm and/or evidence of tamponade physiology 1, 2, 3
Right atrial collapse is the most sensitive sign of tamponade, showing cyclic compression or inversion in late diastole persisting into early ventricular systole, while right ventricular diastolic collapse is more specific, visible as inward diastolic motion of the RV free wall 4, 5
The presence of chamber collapse in a patient with moderate to large effusion is indicative of tamponade 1, 2, 3

The American Heart Association notes that hemodynamic instability with moderate or large pericardial effusion, even without identifiable diastolic collapse, should raise suspicion for tamponade physiology 1, 2, 3
The rate of fluid accumulation is more important than the absolute volume, with small effusions that develop rapidly able to cause tamponade, while large effusions that develop slowly may be well tolerated 6, 8
Ultrasound findings correspond to clinical features such as pulsus paradoxus (≥10 mmHg fall in systolic blood pressure with inspiration) 4, 5

The use of a phased array cardiac transducer is optimal for scanning through narrow intercostal windows, although a 2-5 MHz general-purpose curved array abdominal probe with a small footprint can suffice if unavailable 3
Multiple views should be obtained (parasternal, apical, subcostal) to fully evaluate for tamponade physiology 1, 2, 3

Loculated effusions, especially post-surgical, may be missed on standard views, and right heart disease can mimic some tamponade findings 5, 7
Positive pressure ventilation can alter the classic findings, and the magnitude of ultrasound findings depends on the rate of fluid accumulation, pericardial distensibility, and filling pressures of cardiac chambers 4, 6