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68  Stratos LV/LV-T Technical Manual   
2.1.6  AAI and VVI  
The pacing modes AAI and VVI provide atrial and ventricular 
demand pacing. The lower rate timer is started by a sense or 
pace event.  A sense event outside of the refractory period 
inhibits pacing and resets the lower rate timer; in the absence of 
a sense event, a pulse generator pulse will be emitted at the end 
of the lower rate interval. 
2.1.7 AAI, VVI 
The AAI and VVI single-chamber pacing modes are used in atrial 
and demand pacing.  In each case, pacing and sensing only 
occur in the atrium (AAI) or the ventricle (VVI). 
The basic interval is started by a sense or pace event.  If the 
sense event occurs before the basic interval has expired, pacing 
is inhibited.  Otherwise, pacing occurs at the end of the basic 
interval. 
2.1.8  AOO, VOO  
In these modes, atrial, ventricular and AV sequential pulses, 
respectively, are emitted asynchronously.  These modes 
primarily serve diagnostic purposes during follow-up.  When 
programming to the VOO or VOO mode, the risks associated 
with asynchronous ventricular pacing should be considered.  
2.1.9 DOO 
Asynchronous, AV sequential pacing pulses are emitted in this 
pacing mode.  When programming DOO mode, the risks of 
asynchronous ventricular pacing should be considered. 
2.1.10 VDI  
The VDI mode corresponds to the VVI mode, with the additional 
function of providing atrial sensing.  However, the timing is the 
same as the VVI mode.  The purpose of the VDI mode is to 
permit the use of the marker function with the IEGM for the atrial 
channel, for example, to measure the retrograde conduction 
time. 
The VA conduction time between a ventricular pace or sense 
event (with marker) and the atrial sense event can be measured 
directly on the display or printout from the programmer or on an 
ECG strip chart recorder (IEGM/marker output function).