pacing in DDD-VIP mode

These tracings illustrate the features of the VIP algorithm and its operation in a patient with atrioventricular conduction disorder. In order to favor the return of intrinsic conduction, the device temporarily extends its AV delay (up to a maximum of 450 ms). If no intrinsic ventricular event is sensed at the end of the prolonged AV period, ventricular pacing is delivered. Hence, there can be no blocked P wave during this search, given that ventricular pacing always occurs at the end of the prolonged AV delay in the absence of ventricular sensing. The main advantage of this algorithm is therefore to permanently maintain a 1:1 activation ratio between atria and ventricles. The search for intrinsic conduction is carried out only for rates below 110 bpm so as to avoid the occurrence of a 2:1 block during exercise in a patient with complete atrioventricular block. Indeed, the 2:1 point is dependent on the total atrial refractory period (AV delay + PVARP) which is substantially prolonged when searching for intrinsic conduction (very long AV delay). The temporary prolongation of the AV period can favor the occurrence of a PMT.

Three parameters are programmable necessitating a balance between effectiveness and risk of induction of a PMT: 1) VIP™ Extension which corresponds to the extension of the AV delay applied to the programmed AV delay (paced or sensed) to search for intrinsic conduction; the total value of the AV delay cannot exceed 450 ms; 2) the search interval corresponding to the time interval between each intrinsic conduction search which can be programmed to 30 seconds, 1, 3, 5, 10 or 30 minutes; increasing this value avoids iterative searches in a patient with permanent atrioventricular block; decreasing the value avoids unnecessary right ventricular pacing in a patient with short-term paroxysmal conduction disorder; 3) the number of consecutive cycles the device extends the AV delay to search for the occurrence of intrinsic conduction is programmable to 1, 2 or 3 cycles.

It is possible to view the atrioventricular conduction histogram in the pacemaker's memory. It is also possible to program a specific remote monitoring alert when the percentage of ventricular pacing exceeds a programmable threshold.