Overview :
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
This consists
of a generalized decrease in all ECG waveform amplitudes.
It occurs
when significant pericardial effusion or pericardial
thickening are present.
(2) total electrical alternans
Alternation
in the configuration of the ECG complexes arising from the
same pacemaker and independent of periodic extracardiac
phenomena.
This involves
both the P waves as well as the QRS complexes.
The findings
are ascribed to the cyclic motion of the whole heart within
the pericardial sac.
(3) ST segment elevation
Limitations:
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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