How effectively is your ED using cardiac imaging?
December 1, 1997
How effectively is your ED using cardiac imaging?
Ultrasonography is a cost-effective bedside tool
Cardiac imaging enables emergency department (ED) physicians to provide prompt, cost-effective diagnoses of a number of conditions for which no other practical means is readily available, such as differentiating between causes of shock and assessing pulseless electrical activity.
Cardiac imaging sometimes requires minimal expertise such as when identifying a large pericardial effusion but may require substantial technical skill when assessing wall motion abnormalities in patients with ischemic heart disease or the presence of a thoracic dissection, for example.
Frequently shock patients arrive in the ED with nonspecific cardiograms and inadequate histories. By assessing overall wall motion, chamber size, and pericardial fluid, you can distinguish between the following causes of shock:
• cardiogenic;
• hypovolemic;
• tamponade;
• right ventricular dysfunction.
Therapy can be tailored for each type
Cardiac imaging allows the emergency physician to tailor therapy toward a specific type.
With cardiogenic shock, patients exhibit marked, diffuse wall motion abnormalities. Hypovolemic shock is characterized by a hyperdynamic heart with small, right-sided chambers. The echocardiographic hallmark of a massive right ventricular infarct or pulmonary embolism is a large, thin-walled hypokinetic right ventricle and a vigorously beating left ventricle.
Evaluation for pericardial tamponade remains one of the more important uses for echocardiography in the ED setting. The classic clinical findings such as Beck’s triad, electrical alternans, and pulsus paradoxus are nonspecific and late findings. Pericardial fluid is anechoic, conforms to the heart, and is surrounded by the echogenic pericardial sac. Diastolic collapse of right-sided chambers can be seen.
Ultrasonography is also an invaluable tool for displaying pericardial fluid collections from trauma or secondary to pericarditis. Immediate determination of pericardial fluid allows for a formal study if time permits, notification of surgical consultants, or an emergent pericardiocentesis. Another application is differentiating between cardiac and noncardiac causes of pulseless electrical activity.
The subcostal view is useful in assessing both overall cardiac activity and the presence or absence of an effusion. It is a good all-purpose view for the ED since it can be used for noncompliant patients or for those on backboards, and it doesn’t interfere with any concomitant interventions taking place in the thoracic area. With the subcostal view, the probe is placed in the subxiphoid region with the marker dot pointing toward the patient’s right side. The subxiphoid view is sufficient for determining if poor contractility and valve motion exist. With good cardiac activity, reversible etiologies can be sought.
The left parasternal long and short axis views require a little more technical skill but are easily interpreted. They are good for visualization of the mitral and aortic valves as well as overall global left ventricular function. With the probe in the 2nd to 4th intercostal space (ICS) and the marker dot at the 4 o’clock position, the ascending aorta, left atrium, and left ventricle can be visualized. With the probe in the same ICS, rotation of the marker dot to the 8 o’clock position permits imaging via the short axis view. The probe is placed over the maximal apical impulse to obtain the apical view. Often, multiple views must be attempted to find what meets the needs for that particular clinical scenario.
Some difficulties in cardiac scanning arise if patients are noncompliant, have hyperinflated lungs secondary to chronic obstructive pulmonary disease or have difficulty changing position. Pericardial fat is hypoechoic and can be confused with an effusion. In the absence of diastolic collapse, a formal study might be appropriate. In addition, the effusion can be measured and the patient re-scanned within a short time frame when the study is suboptimal with one view, trying several other views.
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