All ECG 66
- Atrial fibrillation with an uncontrolled ventricular response
- Low voltage
- Electrical alternans
This ECG occurred in the setting of a large pericardial effusion causing cardiac tamponade. The pericardial effusion dampens the electrical signal on the ECG causing low voltage to be present (see Low Voltage Review for details). The amplitude of the QRS complex varies at times from beat to beat which is a phenomenon called "electrical alternans" and is due to swaying of the heart back and forth within the large pericardial effusion. During some heart beats the heart is closer to the anterior chest wall and at times it is farther, resulting in a beat-to-beat variation in the QRS amplitude. This should not be mistaken with normal QRS amplitude changes that can occur at times with normal respiration. This is termed "respirophasic variation" in the QRS complex and occurs more slowly over many beats, not on a beat-to-beat basis like in the setting of a large pericardial effusion.