This is a paced rhythm (note the verical pacer spikes before each QRS). The intrinsic atrial rate is in the 80's (note the regular P waves), but clearly there is an AV block present, because no QRS complex appears by 0.2 secs following the start of the P wave. When no QRS is sensed, a ventricular lead activates the ventricles. It cannot be said for sure what type of pacer this is. Pacer nomenclature and functioning is very complex, but in general, pacers have a 3 or 4 letter description (the 'NBG' code). Position 1 refers to the chamber(s) paced (A=atrial, V=Ventricular, D=Dual, 0=none), Position 2 the chamber(s) sensed, and Position 3 the response to a sensed native impulse (none, triggered, inhibited, dual). A 4th letter may also be used but is not discussed here.
VVI pacers are classic demand pacers pacing at the programmed rate unless the pacer senses a higher intrinsic ventricular rate. AAI pacers do the same, but sense and pace the atria. DDD pacers pace and sense atria and ventricles, so as not to compete with native rhythms, but to allow coordinated atrial and ventricular contractions in the presence of potential complete block at the AV node.
NOTE: EKG's are for internal educational purposes of the University of Massachusetts Department of Family Medicine. Please do not forward without permission from Dr. Golding!
