Pericardial Tamponade: Electrical Alternans

Report:

Sinus tachycardia 111/min

Small voltage

Electrical alternans

Comment:

Alternate QRS complexes vary in size, in this case due to the heart swinging in the pericardial sac. There is no mechanical counterpart, but there may be alternation of the heart sounds.

At least alternate complexes have absolute small voltage (QRS < 10 mm in the chest leads). This is not particularly diagnostic of tamponade, or even effusion: “dry” pericarditis alone can attenuate the voltages, as can of course a host of other conditions. Tamponade does tend to diminish them; apart from its insulating effect there is an element of compression and angulation of the heart1.

As seen in Fig 1a. after 1.4 litre was drained in ICU the alternans disappeared. It tends to disappear with even a small amount of fluid removal. Conversely, relatively small effusions can result in electrical alternans if there is a thickened parietal pericardium12. Unfortunately, this was the case in this patient, who showed restrictive hæmodynamics (and even a new pericardial knock) after the effusion was drained. She died a week later.