Cardiac tamponade: Dx

Clinical findings consistent with cardiac tamponade include tachycardia, dyspnea, chest pain, diaphoresis, decreased arterial pulsation, muffled heart sounds, elevated jugular venous pressure and pulsus paradoxus. Classically Beck’s triad is used to characterize three signs of cardiac tamponade: hypotension, jugular venous distention and muffled heart sounds.

Diagnosis of cardiac tamponade relies mainly on index of suspicion especially for patients who are at risk for acute cardiac tamponade physiology (those who have recently had cardiac surgical procedures, electrophysiology procedures). Patients also may have large chronically accumulating pericardial effusions. These patients usually present with significant shortness of breath and chest discomfort prior to developing tamponade physiology since the pericardium stretches and grows appreciably with chronic fluid accumulation.

Imaging modalities helpful in the diagnosis of cardiac tamponade include chest X-ray, electrocardiogram, cardiac catheterization and echocardiography. On chest X-ray the patient will have an enlarged, widened mediastinum with the heart appearing enlarged after effusion of > 200mL has accumulated. The heart may appear as a flask or water bottle. The ECG will demonstrate low voltage throughout the leads in addition to electrical alternans which is an alternating normal-large voltage with reduced voltage due to anterior-posterior swinging of the heart in its fluid-filled pericardial sac. On right heart catheterization there will be an attenuated Y-descent on the right atrial waveform with equilibration of central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure. Cardiac catheterization will show elevation and equalization of pressures in all the cardiac chambers in advanced cardiac tamponade along with varying peak aortic pressures by > 10-12 mmHg (due to pulsus paradoxus) as well as decreased cardiac output.

Echocardiography is perhaps the most helpful method of diagnosing pericardial effusions and cardiac tamponade. Echocardiography is relatively easy to perform (as compared to cardiac catheterization) and is minimally invasive. The size of the effusion can be measured by freezing the image and measuring the echo-free pericardial space (which normally is not able to be discerned) with the caliper function. Size of effusion is classified into small (< 9 mm), moderate (10-19 mm) and large (> 20 mm). Several characteristic features of pericardial effusions and cardiac tamponade are evident on echocardiograms, either transthoracic or transesophageal. Chamber collapse is easily visible on echocardiography and the effect of variation with spontaneous respiration may also be visualized. Right atrial collapse is very common (and not specific for cardiac tamponade) but it is a more sensitive sign when it persists for at least 30% of the cardiac cycle. During diastole the right ventricular free wall inverses and the right atrial wall inverses at end diastole. Left atrial collapse is less common in cardiac tamponade, only occurring in 25% of patients, but it is a specific sign for cardiac tamponade. Left ventricular collapse is rare due to muscular left ventricular wall. Left shift of the interventricular septum is a specific sign for cardiac tamponade, visible on echocardiography, and accounts for the clinical sign of pulsus paradoxus.