Practice ECG 20
This patient is very tachycardic, over 150 BPM to be exact. So let's start out by concentrating on the rhythm. First, answer the rhythm questions we gave you in Chapter 17.
1. Is the rhythm fast, slow or normal?Fast
2. Do I see P waves? Are they the same?Yes, Yes
Yes, we do see P waves. Look at V1, which is usually the best place to see P waves. Do you see that peak right after the QS wave? Those are the P waves. Now, look at the other leads and see if you find a notch or some other irregularity at the same location on the complexes. Leads II, aVF, V2, and V3 definitely show a notch in the area consistent with the location of the P waves in V1. The P waves all look alike, even though they are abnormally located.
Can the P waves be causing the ventricular depolarization represented by the QRS complexes on the ECG? No, the P waves originate after the depolarization of the ventricles have begun. The P waves in this case are formed when a secondary pacemaker fires and the atrial depolarization occurs in a retrograde fashion. In other words, the atria are being depolarized in the opposite direction.
3. Are the complexes narrow or wide?Narrow
4. Is the rhythm regular or irregular?Regular
5. Do I see any pauses?No
6. What is the relationship of the waves P waves are after the QRSs
and the complexes?
7. How can I put it together?See discussion below
We have a narrow-complex tachycardia with P waves that are conducted in a retrograde fashion. The QRS complexes are narrow, so we know that the impulses originate in the AV node and they are conducted normally through the ventricles. Putting it together is now simpler. We have a junctional rhythm with retrograde P waves. Is this the final answer? Not entirely. What is the normal rate for a junctional rhythm? The normal junctional rate is around the 40 to 45 BPM range. This ECG shows a rate over 150 BPM. The correct answer is, therefore, that this is an accelerated junctional rhythm with retrograde P waves.
Finally, the patient shows evidence of LVH with strain and has a prolonged QT despite the tachycardia. Remember, you can talk about hypertrophy and bundle branch blocks in a junctional rhythm because the impulse travels through the normal pathways in the ventricle. You cannot talk about hypertrophy if the ectopic pacemaker is in the ventricle, as occurs in ventricular tachycardia or other ventricular rhythms. Depolarization of the ventricles, in these cases, occurs by abnormal pathways involving direct, cell-to-cell transmission of the impulse. These abnormal pathways change the axis and the duration of the complex, causing changes in the QRS complex that are impossible to interpret.
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