Characterization of pacemaker arrhythmias due to normally functioning AV demand (DVI) pulse generators.

Normally functioning DVI pulse generators with different electronic characteristics may cause complex cardiac arrhythmias that must not be interpreted as pacemaker malfunction. When there is no refractory period after the atrial output, a DVI pulse generator may deliver atrial pacemaker impulses at irregularly shortened intervals and produce an increase in the atrial pacemaker rate compared with the programmed free-running AV sequential rate. Theoretically this variation of the atrial cycle length can occur only within a well-defined range that represents the difference between the ventricular and atrial output escape intervals. In reality, the interplay of the spontaneous sinus rate, duration of AV conduction, time of sensing the ventricular electrogram in relation to the surface QRS complex, and the programmed AV sequential time all influence the atrial pacemaker rate. DVI pulse generators may also create interesting arrhythmias such as pseudopseudofusion beats (delivery of an atrial spike within the QRS complex), double pseudofusion beats, and double pacemaker impulses within the QRS complex according to the electrophysiologic circumstances and specifications of the pulse generator.