The electrocardiographic changes associated with pericardial effusion consist of a triad of findings which are virtually diagnostic if present.


Changes associated with pericardial effusion:

(1) low voltage

(1a) This consists of a generalized decrease in all ECG waveform amplitudes.

(1b) It occurs when significant pericardial effusion or pericardial thickening are present.

(2) total electrical alternans

(2a) Alternation in the configuration of the ECG complexes arising from the same pacemaker and independent of periodic extracardiac phenomena.

(2b) This involves both the P waves as well as the QRS complexes.

(2c) The findings are ascribed to the cyclic motion of the whole heart within the pericardial sac.

(3) ST segment elevation



• A small or moderate effusion may not show all of the classic findings. The presence of electrical alternans tends to be associated with cardiac tamponade.


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