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Stratos LV/LV-T Technical Manual 67
2.1.3 DDI
In contrast to DDD mode, the basic interval in the DDI mode is
not restarted by sensed P-waves, but by ventricular sensed or
paced events. The VA delay is started together with the basic
interval. If atrial or ventricular sensing does not occur during the
VA delay, the atrial pacing occurs at the end of the VA delay.
Atrial pacing starts the AV delay. If atrial sensing occurs outside
of the atrial refractory period (ARP), a PMT safety interval or the
FFP (far-field protection) window, atrial pacing is inhibited.
However, the AV delay does not start with a sense event, but at
the end of the VA interval. Therefore, P-waves in the DDI mode
do not trigger ventricular events.
NOTE:
For additional information on far-field protection window, see
Section 2.3 “Timing Functions”.
An atrial sensed event that occurs during the PMT protection
window starts the atrial upper basic rate to avoid pacing during
the vulnerable phase of the atrium. If the interval of the atrial
upper rate is longer than the basic interval, the AV delay is
shortened by that same amount after atrial pacing, but only until
the end of the safety interval.
2.1.4 DVI
The DVI mode is derived from the DDI mode. In contrast to the
latter, atrial sensing does occur. Therefore, atrial pacing is
delivered at the end of the AV delay. Ventricular sensing within
the AV delay inhibits atrial and ventricular pacing. Ventricular
sensing within the AV delay inhibits ventricular pacing.
2.1.5 VDD
The VDD mode corresponds to the DDD mode with the
exception that it does not provide atrial pacing. In the absence
of a sense event, the basic interval starts with either an atrial
sense event, a ventricular extrasystole or after expiration of the
preceding basic interval.