FEATURE CARDIAC IMAGING
Emergency Physicians (ACEP) delineates the important role of focused cardiac ultrasound (FOCUS) in patient care and treatment and emphasizes the complementary role of FOCUS to that of comprehensive echocardiography.
CLINICAL INDICATIONS The principal role for FOCUS is the time- sensitive assessment of the symptomatic patient. Primary indications for performing focused echocardiography include; Assessment for the presence of pericardial effusion
Massive pulmonary embolism Estimation of central venous pressure Assessment of left ventricular function Unexplained hypotension Dyspnea Chest pain Cardiac arrest
Other pathologic diagnoses
(intracardiac masses, LV thrombus, valvular dysfunction, regional wall motion abnormalities, endocarditis, aortic dissection) may be suspected on FOCUS, but additional evaluation, including referral for comprehensive echocardiography or cardiology consultation, is recommended.
PERICARDIAL EFFUSION The most straightforward application of bedside echocardiography during cardiac arrest is evaluating for a pericardial effusion. Pericardial effusion presents as an anechoic stripe surrounding the heart. In trauma patients, hemodynamically significant pericardial effusion may be small or focal and the hemorrhage may show evidence of clot formation, yet the degree of hemodynamic instability may be pronounced. If it is large enough to cause cardiac tamponade, the clinician should be prompted to perform an immediate pericardiocentesis using echocardiography guidance. Pericardiocentesis can be life-saving and the removal of just a small amount of fluid may result in significant improvement in cardiac output (see figures 1 and 2). It is important to recognize that
pericardial tamponade is a clinical diagnosis that includes the visualization of pericardial fluid, blood, or thrombus, in addition to clinical signs including hypotension, tachycardia, pulsus paradoxus, and distended neck veins.
The principal role for FOCUS is the time-sensitive assessment of the symptomatic patient
PULMONARY EMBOLISM Right Ventricular Enlargement FOCUS can be used to identify hemodynamically significant pulmonary emboli by observing right ventricular dilatation (>1:1 RV/LV ratio). The normal right ventricular end diastolic diameter is 21 ± 1 mm in a parasternal long axis view. Abnormal values have been described as being greater than 25-30 mm. The normal right to left ventricle ratio, obtained in the apical four-chamber view, is less than 0.5. Abnormal ratios vary by author but have been described as being greater than 0.5 or as high as greater than 1. With massive PE the right ventricle will be round in shape and larger than the left ventricle. There is decreased right ventricular systolic function, or occasionally visualizing free-floating thrombus. An acute pulmonary embolus can result in RV enlargement and dysfunction. Emergency physicians should be aware that an increased RV:LV ratio is not specific for pulmonary embolus and that acute and chronic RV abnormalities may exist in patients with chronic obstructive pulmonary disease, obstructive sleep apnea, pulmonary hypertension, and right-sided myocardial infarction. Massive PE is responsible for about
10% of cardiac arrests in cases where a primary cardiac etiology is clinically suspected. The routine use of bedside echocardiography in cardiac arrest may allow immediate detection of massive PE, even in cases where the diagnosis is not clinically suspected. It is important to immediately recognize that PE is the cause of a cardiac arrest because early thrombolytic therapy has been shown to significantly improve the chance of ROSC (Return of spontaneous circulation). A review of 60 cases of cardiac arrest caused by massive PE found that 81% of patients who received early thrombolysis had ROSC compared with 43% for those
who did not receive the therapy. While direct visualization of a
thrombus may occasionally be seen in the right heart, most echocardiographically detectable changes are indirect indices of right heart strain caused by pumping against a fixed blood clot in the lung. These changes include right ventricular dilatation, right ventricular hypokinesis, tricuspid regurgitation, and abnormal septal motion (see figure 3).
ESTIMATION OF CENTRAL VENOUS PRESSURE Assessment of the size and respiratory variations of the proximal IVC can provide information about Right atrial pressure, which represents the central
FIG 1, 2, 3 1
2
3
FIG 1: Pericardial effusion FIG 2: Chronic Pericardial effusion
FIG 3: RV enlargement, A 4CV, transverse diameter exceeds 2.5cm
Imaging & Diagnostics Issue 3 2011 21
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