Question Of The Day #20

This patient’s EKG demonstrates alternating amplitudes of QRS complexes, a phenomenon known as electrical alternans. This is caused by the heart swinging back and forth within a large pericardial effusion. The patient is tachycardic and borderline hypotensive, which should raise concern over impending cardiac tamponade. The next best investigation to definitively diagnose a large pericardial effusion with possible tamponade would be a cardiac sonogram (Choice B). This investigation could also guide treatment with pericardiocentesis in the event of hemodynamic decompensation and the development of obstructive shock. Other EKG signs of a large pericardial effusion are diffusely low QRS voltages and sinus tachycardia. Chest radiography (Choice C) may show an enlarged cardiac silhouette in this case and evaluate for alternative diagnoses (i.e. pneumothorax, pleural effusions, pneumonia, atelectasis), however, cardiac echocardiography is the best next investigation. CT pulmonary angiography (Choice D) would demonstrate the presence of a pericardial effusion along with differences in cardiac chamber size indicative of tamponade. Still, bedside cardiac sonogram is a faster test that prevents a delay in diagnosis. Sending a potentially unstable patient for a CT scan may also be dangerous. Arterial blood gas testing (Choice A) has no role in diagnosing pericardial effusion or cardiac tamponade. Correct Answer: B