All ECG 59
- Atrial fibrillation with an uncontrolled ventricular response
- Intermittent right bundle branch block - rate dependent
This ECG shows atrial fibrillation with an uncontrolled ventricular rate. There are two QRS complexes that become wide in a right bundle branch block pattern. This can occur at fast heart rates when the right bundle has not yet had a chance to recover from it's refractory period. The conduction can be blocked in the right or left bundle resulting in this phenomenon. When this occurs due to a premature atrial contraction causing a right bundle pattern, the term "Ashman beat" is used.
This ECG example is a rate dependent right bundle and not a ventricular couplet (two PVCs in a row) due to the QRS morphology. Recall that the Brugada criteria describe a ventricular origin to a wide QRS beat in a right bundle pattern only if the R is larger than the R' in lead V1. These wide QRS complexes show the R is smaller than the R' favoring a rate dependent right bundle branch block (supraventricular origin).