FIG 57.4 Transthoracic echocardiogram in modified parasternal long-axis view showing mild pericardial effusion The accumulation of fluid between cardiac chamber and descending thoracic aorta (DTA) localizes fluid to the pericardium Pericardial fluid compresses cardiac chambers when pressure within the chamber falls below pericardial pressure.54 The collapse of right-sided chambers occurs earlier than the clinical detection of pulsus paradoxus A brief collapse of thin-walled right atrium during late ventricular diastole may be normal Nonetheless, right atrial collapse exceeding one-third of the cardiac cycle is nearly 100% sensitive and specific for cardiac tamponade.3,55 There can be right ventricle collapse during early diastole The duration of right ventricular collapse is proportionate to the severity of tamponade, initially occurring only during inspiration and extending to expiration at later stages.4,54 The collapse of rightsided chambers may be absent in conditions with elevated pressure in the right ventricle as in pulmonary hypertension, pulmonary stenosis, or left ventricular dysfunction.56,57 Conversely, collapse may occur earlier in the setting of hypovolemia.58 In patients with posteriorly loculated pericardial effusion or pulmonary hypertension, there can be collapse of left atrium or left ventricle instead of right-sided chambers.59 A large pericardial effusion may cause beat- to-beat swinging of the heart Doppler interrogation provides direct demonstration of altered ventricular filling Doppler abnormalities are more sensitive than M-mode and twodimensional echocardiographic abnormalities Exaggerated ventricular interdependence on Doppler interrogation manifests as marked respiratory variation in mitral and tricuspid inflow velocities.3,4,6 The mitral inflow velocity, measured at the peak of the E wave, increases greater than 25% during expiration than during inspiration On the other hand, the tricuspid inflow velocity increases during inspiration Reduced filling of the right ventricle during expiration is also reflected as accentuated expiratory diastolic flow reversal in hepatic vein Doppler (Fig 57.5).6,60 FIG 57.5 Hepatic vein Doppler in a child with cardiac tamponade showing prominent expiratory diastolic flow reversal D, Diastolic forward wave; DR, diastolic reversal; S, systolic forward wave; SR, systolic reversal Cardiac computed tomography (CT) and magnetic resonance imaging (MRI) are not required routinely Pericardial thickening and contrast enhancement suggests active inflammation.61–64 Attenuation values of pericardial fluid on CT allows distinction of transudate from exudate.64,65 An attenuation value of less than 10 Hounsfield units (HU) suggests transudate; 20 to 60 HU indicates purulent, malignant, or myxedematous collection; while greater than 60 HU suggests hemopericardium.4,64 Management Established or impending tamponade is an emergency, with most patients requiring urgent pericardial drainage Intravenous hydration with normal saline should be started immediately Inotropic agents should be started in those with hypotension although their efficacy is limited Patients with no or minimal symptoms, even with a large collection, can be carefully observed without pericardial drainage Even if drainage of pericardial effusion is needed, one-time closed pericardiocentesis is generally sufficient.65 The decision of pericardiocentesis must be individualized after careful clinical judgement Medical therapy may be sufficient in some cases For example, an effusion related to acute pericarditis and connective tissue disorder may respond promptly to NSAIDs and corticosteroids, respectively Hypothyroidism-related effusion also responds quickly to thyroid replacement therapy The use of NSAIDs and/or colchicine may be useful in children with recurrent large but asymptomatic pericardial effusion.3 A detailed evaluation for specific etiology helps in disease-specific management However, similar to acute pericarditis, extensive testing is not cost effective.14 The standard technique for closed pericardiocentesis involves subxiphoid insertion of needle into the pericardial space keeping the needle tip toward the left shoulder Alternatively, based on the site of maximum pericardial effusion, an apical or left parasternal approach may be used.65,66 Aspiration of the pericardial fluid confirms correct positioning of the needle Needle position can also be confirmed by echocardiographic visualization of microbubbles in the pericardial space following an injection of agitated saline (Fig 57.6; Video 57.2).67 An injection of iodinated contrast under fluoroscopic vision is also useful for confirmation of needle position Once the position is confirmed, an appropriate-diameter guidewire is placed through the needle over which a pigtail catheter is inserted The catheter is manipulated to achieve the most dependent position for continuous drainage of pericardial fluid The procedural success rate is 97% and major complications are seen in 1% to 2% of cases Typically, the intrapericardial pigtail catheter is left in-situ for a variable period of time, sometimes several days, for continued drainage The frequency of aspiration is dictated by the rate of reaccumulation Open pericardiocentesis and creation of a pericardial window is preferable for refractory, recurrent pericardial effusions and hemopericardium.4,39,65