Electrical Alternans in Tamponade

The electrocardiogram (ECG) in cardiac tamponade most commonly shows sinus tachycardia and diffuse low voltage. If pericarditis is also present, the ECG findings typical of that disorder are seen as well..

Electrical alternans is a broad term that describes alternate-beat variation in the direction, amplitude, and duration of any component of the ECG waveform (ie, P, PR, QRS, R-R, ST, T, U). Electrical alternans must be distinguished from mechanical alternans (eg, pulsus alternans), although both may coexist.

 The pathophysiologic mechanisms that cause electrical alternans can be divided into 3 categories: (1) repolarization alternans (ST, T, U alternans), (2) conduction and refractoriness alternans (P, PR, QRS alternans), and (3) alternans due to cardiac motion.

Electrical alternans associated with cardiac motion is due to the beat to beat swinging or  alternation in  the position of the heart with relation to recording electrodes. The most common underlying disorder is an enlarged pericardial sac; however, not all pericardial effusions cause electrical alternans. Frequently, there is also sinus tachycardia when there is electrical alternans from pericardial effusion. Electrical alternans may also be seen when there is severe cardiomegaly and left ventricular dysfunction, and it may occur with aortic regurgitation.The presence of pericardial disease and total electrical alternans (P, QRS, and T wave) frequently suggests cardiac tamponade, but total electrical alternans is seen in only 5-10% of patients with cardiac tamponade. Heart movement in patients with hypertrophic cardiomyopathy also may result in electrical alternans of this type.

This post courtesy of Dr. Mohammed Sabit