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.