How transthoracic echocardiography detects cardiac tamponade

Nursing,  Mar 2004  by Shatzer, Melanie,  Castor, Amy

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JEFFREY MOORE, 59, who's in the step-down unit recovering from transvenous pacer wire insertion, calls you into his room, complaining of difficulty breathing. Your assessment reveals a dyspneic, anxious, and diaphoretic patient with cool, clammy skin and distended neck veins.

His vital signs are: temperature, 98° F (36.7° C); BP, 112/88; and respirations, 26. While taking an apical pulse, you note tachycardia and faint heart sounds. A stat portable chest X-ray shows an enlarged cardiac silhouette. A 12-lead ECG reveals sinus tachycardia (118 beats/minute) with nonspecific ST-segment and T-wave changes. However, you also note electrical alternans (a beat-to-beat change in the axis of the ECG that can be caused by a swinging motion of the heart during pericardial effusion).

The cardiologist suspects cardiac tamponade-fluid accumulation in the pericardial space that compromises cardiac function-and orders a transthoracic echocardiogram.

Understanding cardiac tamponade

The pericardium consists of an outer fibrous layer and an inner serous layer. The potential space created by these two layers normally contains up to 50 ml of fluid.

Usually considered a medical emergency, cardiac tamponade is a hemodynamic consequence of blood or excess fluid accumulation in the pericardial space. Common causes include surgical or traumatic injury, cancer, kidney failure, acute myocardial infarction, or infections.

Signs and symptoms depend on the amount of accumulated fluid and the speed at which it accumulates. With an acute increase in fluid, as little as 200 ml of fluid can cause marked increases in pericardial pressure and serious hemodynamic compromise that resembles cardiogenic shock. Signs and symptoms of decreased cardiac output include changes in mental status, narrowed pulse pressure, hypotension, distended neck veins, cool and clammy skin, faint or muffled heart sounds, electrical alternans, low voltage on the ECG, and paradoxic pulse (a decrease of 10 mm Hg or more in systolic arterial pressure with normal inspiration).

With a slow accumulation of fluid, the pericardium can stretch, allowing more than 2 liters of fluid to accumulate without a severe increase in intrapericardial pressure. This may lead to signs and symptoms of rightsided heart failure.

After 200 to 250 ml of fluid accumulates, a chest X-ray may reveal an enlarged cardiac silhouette. However, the cardiac silhouette may be normal when a small amount of fluid rapidly accumulates.

By documenting fluid accumulation and cardiac dysfunction, a transthoracic echocardiogram allows the clinician to definitively diagnose cardiac tamponade. An enlarged space indicates fluid accumulation in the pericardial sac. A sign of cardiac tamponade evident on echocardiogram is right ventricular compression, which disappears following pericardiocentesis and isn't present with pericardial effusion without tamponade.

To treat acute, life-threatening tamponade, the clinician will perform echocardiogram-guided pericardiocentesis with a needle or catheter to remove excess fluid in the pericardial space. Depending on the underlying cause, medications or surgical intervention may also be used. If the condition isn't immediately life-threatening, however, he may opt for conservative treatment, including monitoring, serial echocardiograms, fluid administration, oxygen, and therapy to treat the underlying cause.

Pericardiocentesis successfully drains excess fluid from Mr. Moore's pericardial space, and he's transferred to the step-down unit for further monitoring.

SELECTED REFERENCES

Flounders, J.: "Cardiovascular Emergencies: Pericardial Effusion and Cardiac Tamponade," Oncology Nursing Forum. 30(2):48-55, March-April 2003.

Gercekoglu, H., et al.: "Effect of Timing of Chest Tube Removal on Development of Pericardial Effusion following Cardiac Surgery," Journal of Cardiac Surgery. 18(3): 217-224, May-June 2003.

BY MELANIE SHATZER, RN, CCRN, MSN, AND AMY CASTOR, RN, CCRN, BSN

Melanie Shatzer is a cardiovascular clinical nurse specialist at the University of Pittsburgh (Pa.) Medical Center, and Amy Castor is unit director of the cardiothoracic intensive care unit, University of Pittsburgh Medical Center. This department is coordinated by Frederick J. Tasota, RN, MSN, research project director and clinical instructor at the University of Pittsburgh School of Nursing, and Susan Wesmiller, RN, MSN, director, nursing education and research, at the University of Pittsburgh Medical Center.

Copyright Springhouse Corporation Mar 2004
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