The electrocardiographic interpretation of pacemaker algorithms enabling minimal ventricular pacing

Abstract Cardiac pacing from the apex of the right ventricle has been shown to result in left ventricular dysfunction, atrial fibrillation and increased mortality. To counter this, one of the strategies developed, is to avoid ventricular pacing when not necessary, using programmable algorithms to minimize ventricular pacing. There are seven algorithms available from five manufacturers. Four of the manufacturers have mode conversion algorithms that pace AAI(R), but in the presence of failed atrio-ventricular (AV) conduction, demonstrate algorithm offset and convert to DDD(R) with ventricular pacing. With three manufacturers, there is no mode conversion, but rather AV extension to encourage AV conduction. Each of these have a unique design and when ventricular pacing is present will regularly schedule conduction testing, to encourage AV conduction and hence algorithm-onset. All of these algorithms appear to violate the rule of AV conduction by allowing the AV delay for sensed ventricular events to be longer than for ventricular paced events. The result are frequently bizarre electrocardiographic (ECG) appearances, often unique to the company algorithm, but also suggesting pacemaker malfunction. This review will highlight and illustrate the features of all these algorithms as the appear on the ECG. The review will also illustrate other situations which result in unintended ventricular pacing.