EKG of the Week

A 56 yo female dialysis patient complaints of SOB.

Q1. What does the EKG show?

Q2. What is this diagnostic of?

Q3. What is the treatment?

A1. Electrical alternans

A2. Pericardial tamponade

A3. Pericardiocentesis

Electrical alternans has been reported to be a highly specific marker of pericardial tamponade. Electrical alternans is an ECG change in which the morphology and amplitude of the P, QRS, and ST-T waves in any single lead alternate in every other beat. The postulated cause is the mechanical oscillation of the heart in the pericardial fluid, which is called the swinging heart phenomenon. In uncomplicated pericardial effusion, the heart swings back and forth but returns to approximately the same position before the next systole. Electrical alternans does not occur in this situation.

Echocardiographic studies have revealed that when fluid accumulates to a critical extent and cardiac tamponade ensues, the frequency of cardiac oscillation may abruptly decrease to half the heart rate. The cardiac position will alternate, with the heart returning to its original position with every other beat, and electrical alternans may be seen. Electrical alternans, when present, is pathognomonic for tamponade. However, it is much more common in chronic pericardial effusions that evolve into a tamponade, and it is rarely seen in acute pericardial tamponade. However, low amplitude of the QRS complexes may be seen as a result of the presence of pericardial effusion.

Initial treatment includes volume augmentation to the right ventricle with intravenous fluids to increase the filling pressure to overcome the pericardial constriction. Pericardiocentesis or pericardial window is the treatment of choice. Enough fluid should be withdrawn to stabilize the patient. If tamponade recurs, pericardiocentesis may be repeated, or a drainage catheter may be left in the pericardial space. A pericardiectomy ultimately may be necessary. Cardiac tamponade has a high mortality that depends on the severity and nature of the underlying disease, the time course of onset, and the rapidity of diagnosis and intervention.

(Jouriles, Pericardial and Myocardial Disease. In Rosen’s Emergency Medicine, 8th ed. Ch. 82; Eckstein et al, Thoracic Trauma. In Rosen’s Emergency Medicine, 8th ed. Ch.45.)