Atrial Bigeminy and Premature Ventricular Contraction
July 1, 2009
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Patient: n/a
ECG description:
- Sinus tachycardia
- Supraventricular bigemeny
- One premature ventricular contraction
Discussion:
There is a baseline sinus tachycardia with a PR interval of 130ms, regularly interrupted by premature atrial contractions (PAC). Each PAC depolarizes the atria and resets the SA node, causing a change in automaticity and a noncompensatory extrasystolic pause. Judging by the PR interval as well as P axis and morphology of the premature beats, the ectopic pacemaker is atrial. The ectopic PR interval is 130ms, and it is plausible to think that the ectopic pacemaker is located near the SA node. The P wave axis is ca. 30 degrees, and the ectopic P wave axis is ca. 60 degrees, which means that the atria are depolarized anterogradely and in almost the same direction as from the SA node. QRS axis and morphology is slightly different in the QRS complex following the first premature beat and the second and third. Looking closely, we can see that P wave axis and morphology slightly differs from the first PAC to the next two. The PR interval however is the same. This could be due to multifocality, but since the PR interval is quite similar, the two foci must be very close to each other. After the third bigeminal beat, a broad QRS occurs. In spite of the aberrantly looking RBBB-like morphology, this is most likely a premature ventricular contraction (PVC). If this was aberrancy, it would be due a refractory right bundle branch that couldn’t cope with the rapid changes in automaticity caused by the PAC’s. However, the coupling interval before the broad complex is similar to the other coupling intervals, and this demonstrates that the RBB in fact handles the rapid changes in automaticity quite well. In the precordial leads, we can see a P wave following the PVC, suggesting that the atrias have been depolarized retrogradely from the PVC.
Filed under: Atrial Bigeminy (PAC bigeminy), Atrial arrhythmias, LAFB (Left Anterior Fasicle Block) or Hemiblock, Left Axis Deviation, Non-compensatory Postextrasystolic Pause, Premature Atrial Contraction (PAC), Premature Beats, Premature Ventricular Contraction (PVC), Ventricular premature beats
2 Comments Leave a Comment
1.
Jonni Cooper | July 30, 2009 at 11:06 pm
The example you show above does not have a diagnosable left anterior hemiblock pattern. In order to diagnose LAH you need consistent voltage criteria in the standard and AV leads, which you hav in some, but not all of these leads; you must also not make the diagnosis until the axis deviation is at least -45 or higher (this QRS axis is only -0 or at most -15. And, finally, there must be an initial small “r” wave followed by a deep “S” wave in leads 2, 3, and aVF, which is not present here. You may be looking at an old evolved inferior MI causing a QS pattern in leads 3 and aVF and a minor left axis deviation. I may be wrong, but I certainly don’t see evidence to call this a left anterior hemiblock according to Rosenbaum and Kulburtis’s criteria for left anterior hemiblock.
2.
PQRST | July 30, 2009 at 11:23 pm
Thanks for your input. You are certainly correct. Looking at this retrospectively, I must admit I’m not sure why I thought this was LAFB. The small r/deep S is not present in the inferior leads, and the axis too is merely deviated leftwards. Thanks for pointing it out, I’ll make sure it gets corrected. I appreciate your comment.
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