Electrical alternans in cardiac tamponade

Abstract

Of 9 patients with pericardial effusion due to various causes, 4 developed cardiac tamponade. Electrical alternans was present in all 4, being total in 3 and ventricular in one. The alternans corresponded very well with the clinical diagnosis of cardiac tamponade and the radiological signs of a large pericardial effusion. In 2 patients alternans was present even with heart rates below 100 per min. Apart from the exact (1:1) type of electrical alternans, 3 new types are described, a 2:1, 3:1, and a varying type. It is concluded that electrical alternans associated with pericardial effusion is strongly suggestive of impending or established cardiac tamponade, and electrical alternans is produced when the heart is oscillating within the pericardial sac distended by fluid with a frequency equal to one half (exact alternans), one third (2:1 alternans), and one quarter (3:1 alternans) of the heart rate. The aetiology and mechanism of electrical alternans are discussed.