Regular Ventricular Response in Atrial Fibrillation
What happens when you see definite f waves and you have a regular ventricular response? Well, it could be a junctional rhythm (discussed in the next section) with some artifact or it could still be atrial fibrillation. Could Afib be regular? The answer is yes. However, this would not be just simple atrial fibrillation. It would be atrial fibrillation with either pharmacologically, autonomically, anatomically, or ischemically created AV block. We will be addressing the various AV blocks in detail in Chapter 28, Atrioventricular Blocks, but you already possess the knowledge necessary to figure out the problem. Let’s go through it and try to reason out this clinical possibility.
What would happen if the AV node completely shut down conduction and communication between the atria and the ventricles? Some junctional or ventricular pacemaker would take over pacemaking functions and the result would be an escape rhythm. The escape rhythm would have either a junctional or ventricular morphology and would be regular and slow. That is exactly what happens in these patients. You have the presence of f waves and atrial fibrillation with a regular ventricular response due to either a junctional or ventricular escape rhythm.
Figure 20-5 is an example of an atrial fibrillation with a junctional escape rhythm. Note the presence of a coarse atrial fibrillation between the taller QRS complexes. The QRS complexes are less than 0.12 seconds, making them a supraventricular complex. The rate is around 53 BPM, which is compatible with a junctional pacemaker.
Figure 20-5 Atrial fibrillation with a junctional escape rhythm. For this to occur, there has to be no communication present between the atria and the section of the AV node that is acting as the primary pacemaker in this case.
© Jones & Bartlett Learning.
Whenever you see a regular ventricular response in a patient with atrial fibrillation, you need to think of the possible causes for this abnormal response. These include:
We have already reviewed how an AV block can cause normalization of the ventricular response. Now, let’s turn our attention to the other two causes.
If the Purkinje system is stimulated by any means (e.g., sympathetic activity, drugs), the Purkinje system may fire at a rate above the rate at which the atrial fibrillation is being conducted through the AV node. The result would be that the Purkinje system would be faster and would take over the primary pacemaking function for the heart. Now, when an impulse was normally conducted through the AV node, it would find the conduction system and the ventricle in a refractory state and the conducted depolarization wave would simply fizzle out. This “overdrive” by the Purkinje system could normalize the ventricular response in the presence of the atrial fibrillation.
Flutter-fibrillation pattern refers to the fact that atrial flutter will frequently convert spontaneously into atrial fibrillation and vice versa. This is especially true in patients who are having a paroxysmal or persistent pattern of atrial fibrillation. Many strips will show a patient waxing and waning back and forth between the two arrhythmias, with normalization of the regularity during periods of atrial flutter.