20 mm during diastole and a large effusion as an echo

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20 mm during diastole and a large effusion as an echo-free space of more than 20 mm [ 4 ]. Figure 3.22 demonstrates pericardial effusions in three differ- ent cardiac views. Occasionally, either intra-abdominal fluid or pleural effusions may be confused with pericardial effusions. Therefore, it is absolutely necessary to visualize the hyperechoic image of the pericardium to ensure that the anechoic fluid is indeed intrapericardial. In addition, when visualizing the descending thoracic aorta via a parasternal long-axis window, one will observe that pleural effusions do not cross the aorta, whereas pericardial effusions will. This makes anatomic sense, because pleural effusions will stop at the insertion of the pleura, whereas pericardial effusions will cross the midline ( Figure 3.23 ). Another pitfall can be the mistaken impression that an echo-free collection anterior to the right ventricle is fluid. Many patients have an “epicardial fat pad” that will appear as an anechoic area anterior to the heart. Because most patients have their ultrasounds in a relatively supine position you would expect fluid to collect posteriorly, and thus fluid seen only anteriorly should be suspect. A fat pad will not exert pressure on the right ventricle causing deformation. Cardiac tamponade Cardiac tamponade is the compression of the heart caused by blood or fluid accumulation in the space between the myocardium and the pericar- dium. It is less dependent on the amount of fluid, but rather on the rate of fluid collection within the pericardial sac. It is important to remember that although pericardial effusions are a diagnosis made by ultrasound, tamponade is a clinical diagnosis based on a patient’s hemodynamics and clinical picture. Ultrasound may be useful in confirming the diagnosis in a patient with the classic triad of muffled heart tones, hypotension, and jugular venous distension. More importantly, ultrasound may demonstrate early warning signs of tamponade before the patient becomes hemodynami- cally unstable. Several sonographic signs suggestive of tamponade physiology have been described, although appreciation of these may be subtle [ 4 ]. The most import- ant finding is a circumferential pericardial effusion with a hyperdynamic heart that 78 Diagnostic ultrasound Cardiac ultrasound
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(A) (B) (C) Figure 3.22 Pericardial fluid (*) in three different views. ( A ) Subxiphoid view, with right ventricle (RV) and left ventricle (LV) visible. ( B ) Parasternal long-axis view, with fluid surrounding the left ventricle (V). ( C ) Parasternal short-axis view, with fluid surrounding the left ventricle (V). Diagnostic ultrasound 79 Cardiac ultrasound
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demonstrates diastolic collapse of the right ventricle or right atrium – also referred to as “scalloping” of the right ventricle ( Figures 3.24 and 3.25 ). Left atrial or left ventricular collapse can occur in localized left-sided compressions. Finally, a dilated inferior vena cava (IVC) without inspiratory collapse (plethora) is highly suggestive of tamponade [ 4 ]. Remember that these findings should be taken in light of the patient’s overall clinical picture. Cardiac tamponade
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