76 Stratos LV/LV-T Technical Manual

2.3.6 Refractory Periods

Sensed events that occur during the refractory period have no effect on pacemaker timing. These atrial or ventricular sensed events are classified as “unused” for normal CRT-P timing.

In the Stratos CRT-Ps, the total atrial refractory period has been subdivided into an atrial refractory period (ARP), atrial far-field protection (FFP) and a PMT protection window (PMT). In terms of priority FFP is first, ARP second and PMT third.

When mode switching is turned ON, the atrial events in the atrial refractory period and the PMT protection window are used as the criteria in order to sense atrial tachyarrhythmias and to ensure high atrial rates are not transmitted to the ventricle.

The behavior of BIOTRONIK CRT-Ps reacts differently depending on the timing interval in which the atrial event occurs. The behavior is summarized in Table 20.

Table 20. Response to Atrial Sense Events in Different

Timing Intervals in Stratos CRT-Ps

Timing Interval

Response

As occurs during

No consequence. As is ignored (unused).

the far-field

Neither the AV delay nor the ARP is

protection (FFP)

started. There is no influence on mode

 

switching.

As occurs during

The event influences mode switching.

the Atrial

 

Refractory

 

Period (ARP)

 

As occurs in the

The AUI (atrial upper interval) starts. The

PMT protection

AV delay is not restarted. Post-AES

window

pacing is started if the atrial sense is

 

classified as an AES.

2.3.6.1Atrial Refractory Period

In all modes in which atrial depolarization can be sensed, the Stratos CRT-Ps will start an atrial refractory period upon each atrial depolarization (programmable: AUTO, 225…(25)…775). In standard “Auto” setting, the atrial refractory period (ARP) is automatically preset to a minimum value of 225 ms and is automatically extended if the AV delay is longer.