a case of missing P waves

Does it make sense.  A person can probably ask that on any number of levels in life, but it applies to this EKG.

~75 y.o. man with weakness, family concerned for urosepsis

As always, have a system.  We can see immediately that it’s on the slow side.  With 9 QRS complexes spread over the 10 second EKG we multiply 9×6 and get a rate in the mid 50’s.  What is the rhythm?  Typically the first step is to look for P waves in assessing rhythm, but a person could probably also start with the width of the QRS.  A narrow complex QRS is from the atria (or the junction), a wide complex originates below the junction (unless of course the patient has LBBB in which case they’ll be wide no matter where the electricity originates).  This EKG is narrow complex.  We know therefore that the QRS needs to originate either in the atria or the junction.  We return to the question of Are there P waves … let’s zoom in.

20170904_junctional zoom

Almost everyone agreed there’s no clear P waves before the QRS.  However, are there P waves at all?  Many people questioned a complete heart block, and I think they were interpreting the EKG this way, with the blue line the QT segment and the green line the PR:

20170904_junctional zoom color

Have you ever seen a repolarization cycle that was completed inside of one big box (the blue line)?  That doesn’t make sense.  The second bump (that starts at the green line) is more likely the T wave.  That would mean we need an alternate explanation for the inflection points highlighted by the blue line.  Extra inflection points oftentimes imply lost P waves.  In this case however they occur following every QRS, and only follow the QRS.  These are retrograde P waves that depolarize from the junction.  They therefore follow, rather than precede, the QRS; and are mostly downward deflected since the electricity is moving up the atria (and away from the electrodes) instead of down the atria (and toward the electrodes).  This patient has a Junctional Bradycardia.  Generally this is a sign of an aging heart, though it can occur in very well-conditioned athletes as well.  It doesn’t necessitate a pacemaker per se, though if it turns into a sick sinus syndrome equivalent and is associated with syncope that may need consideration.

A number of people questioned if this could be a digoxin-induced arrhythmia.  I agree the extra inflection points of the retrograde P waves do somewhat resemble some of the changes that can occur with Digoxin.  A good thought, though wasn’t present in this case.

Some people questioned posterior ischemia based on possible STD in V1 and V2, again mostly what you’re seeing is the retrograde P wave.  There is a small amount of STD in V5 and V6, this is likely old.


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