The Morphology of the Complexes in Atrial Fibrillation

The QRS Complex in Atrial Fibrillation

The QRS complex is usually a normal width in patients with atrial fibrillation. This is because the conduction of the impulse occurs normally from the AV node and beyond. The conduction down the electrical conduction system leads to nice, tight QRS complexes with normal morphology.

Wide complexes can occur in atrial fibrillation because of an underlying chronic bundle branch block, aberrancy, or electrolyte abnormalities. In addition, we saw how escape rhythms can develop in patients with AV nodal block and how enhanced automaticity of the Purkinje system can normalize the ventricular response. Remember, if the complex originated in a ventricular foci, including the Purkinje system, the result would be an aberrant, wide QRS complex.

QRS morphology may vary slightly throughout a strip of atrial fibrillation because of fusion with the underlying f waves and aberrancy. This problem is especially noticeable in coarse Afib, where the larger vectors produced by larger wavelets will affect the appearance of the complexes.