Rhythm Strip Bump: P Wave or Artefact?

Report:

Sinus bradycardia 25/min

Junctional escape beats

Escape-capture bigeminy

Right axis deviation

Right bundle branch block

Old anteroseptal infarction

Lateral infarction or ischæmia

Possible right ventricular hypertrophy

Comment:

Congenital heart disease is often indistinguishable from myocardial infarction, especially once surgeons have a go at it. In this case, the repair of the tetralogy of Fallot must have contributed to the appearances; the rest is RVH.

The fourth bigeminal pair is preceded by a bump merging into the junctional QRS complex. It looks like a half-buried P wave. The sinus P wave following the junctional complex is conducted with longer-than-normal PR interval.

I must admit I told every staff member I showed this bump to about the prolonged subsequent PR interval, fearing they may not notice it on their own. I did it to bamboozle them even more into thinking the bump was significant. They all fell for it!

The bump must be an artefact, or else the subsequent P wave would not be there (unless an entrance block is postulated). The PR interval prolongation? Entirely fortuitous: its RP interval is shorter, the AV node more refractory. The RP interval is shorter due to some variation in the junctional escape cycle length (P-P cycles remain constant throughout).