lead II demonstrating dual-chamber pacing.
Top: DVI pacing. There is no atrial sensing and atrial pacing is
committed (the pacemaker fires regardless of the P waves). In this illustration,
there are no spontaneous QRS complexes and ventricular inhibition is not
demonstrated. This example could also be called DOO pacing.
Middle: DDI pacing. Although there is atrial sensing, the pacing
system can only inhibit the next atrial paced beat. Ventricular pacing
will occur after a set period provided ventricular sensing does not occur.
Like DVI, the pacing rate is fixed.
Bottom: DDD pacing. There is normal atrial sensing followed by
ventricular pacing. In this illustration, there is no atrial pacing because
the sinus rate exceeds the atrial pacing escape rate. This example could
also be called VDD pacing. In the abbreviations DVI, DOO, DDI, DDD, the
first letter indicates the chamber paced and D would represent dual chamber
pacing, V (ventricle), A (atrium). The second letter in the abbreviations
refers to the chamber sensed and the same three letters: V, A, and D are
used. When there is no sensing capability the letter O is used. In the
third position of the abbreviation the mode of response to sensing is
documented using four letters: I (inhibited), T (triggered), O (asynchronous),
and D (more than one response).
H.G., MD, Permanent Cardiac Pacemakers: Techniques of Implantation, Testing,
and Surveillance, Hurst's The Heart, 8th ed., p 815-841