A middle-aged woman presented to the ED with increasing dyspnea on exertion. She had a normal physical exam except for a heart rate slightly over 100. No other history or vitals are provided. This ECG was recorded:
|What do you see? Answer below.|
The patient was admitted to the hospital for rule out MI. A later cardiology read of the ECG identified electrical alternans and the patient was re-examined and found to be hypotensive. An echo confirmed tamponade. Pericardiocentesis was performed and the patient improved.
No more details are available.
Notice that not only does the voltage alternate, but the QRS morphology also alternates, with slight changes in QRS axis, especially in precordial leads (see lead V3).
Electrical Alternans (EA):
Here is a great old review (full text pdf):
EA is relatively rare, and only about 1/3 of EA is associated with pericardial effusion. Total electrical alternans (involvement of both atrial and ventricular components) is diagnostic of tamponade, but only a fraction of tamponade manifests this (low sensitivity, high specificity).
In patients in sinus rhythm, EA is almost never found in simple pericardial effusion (without tamponade: thus, EA in sinus rhythm is almost always due to tamponade).
Patients with PSVT frequently have EA without any effusion or tamponade, so this rule only applies to patients in sinus rhythm.
Bottom line: do an echo whenever you see EA.