Instructors' Collection ECG of the WEEK: Complete AV Block With Junctional Escape Rhythm
This ECG is from a 78-year-old woman. We do not know any clinical details.
We break from our usual habit of removing the ECG machine’s interpretation of the ECG to serve as a reminder that the computer interpretation can be wrong. ECGs should ALWAYS be interpreted by a knowledgeable person. The machine interpretation can serve as a reminder, but should not take the place of human interpretation.
Here is what we DO see: There is a normal sinus rhythm present, as evidenced by the regular P waves that do not change their morphology. Some of the P waves are “buried” behind QRS or T waves. The atrial rate is 95 bpm.
The ventricular rhythm, at 40 bpm, is also regular, but is separate from the atrial rhythm. Even though some of the P waves LOOK like they have conducted to produce QRS complexes, they have not. The PRIs are not all the same. Neither do they “progressively prolong”. There is no irregularity of the QRS rhythm or variation in QRS morphology. We see the classic “AV DISSOCIATION” of complete heart block.
When there is a third-degree AV block with a narrow-QRS escape rhythm, we can assume the block is in the AV node. The junction is the escape focus, producing a narrow-complex rhythm between approximately 40-60 bpm. In this case, the QRS is slightly wide at 112 ms (.11 sec), and the QRS complexes in several leads are fragmented. Some might argue that there is an idioventricular escape mechanism. But, with a normal frontal plane axis, borderline width, and no T wave inversions, the rhythm looks more supraventricular. The R wave progresson on the precordial leads shows a persistently negative QRS with late transition in V5. The QRS complexes in V1 and V2 appear to have pathological Q waves. When R wave progression is not normal, we should also consider electrode misplacement.
The immediate concern for patients with AV dissociation and escape rhythms is the RATE. If the rate becomes very slow, it can have deleterious effects on the patient’s hemodynamic status. The rate can usually be quickly enhanced with the use of a pacemaker – either temporary trans-venous pacing or trans-cutaneous pacing.
Lastly, the ST segments over this entire ECG are flat and horizontal, a possible sign of ischemic disease. It is not localized to a specific part of the heart or coronary artery’s area.
