Mode Switch, nominally On, functions when the device is operating in a tracking mode (DDDR, DDD, or VDD). Mode Switch has the following programmable settings: 

• Detect Rate – Specifies at what rates to switch modes.
• Detect Duration – The minimum duration (in seconds) that the atrial tachyarrhythmia must persist above the Detect Rate before the mode switches to DDIR.
• Blanked Flutter Search – Setting that allows device to mode switch if 2:1 blanking of a rapid atrial arrhythmia is detected.

To program Mode Switch in pacemakers, go to Params -> Mode Switch.
To program Mode Switch in ICDs, go to Params -> Pacing -> Mode Switch.

Considerations: 

• Mode Switch can be programmed concurrently with Managed Ventricular Pacing (MVP)™ in the AAIR<=>DDDR and AAI<=>DDD modes. During atrial tachyarrhythmias, the pacemaker switches to DDIR pacing regardless of the current operating MVP mode.
• When Mode Switch is On, several rates, timing intervals, and pacing therapies are limited to certain values (i.e. Mode Switch Detect Rate, Post Mode-Switch Overdrive Pacing (PMOP) Overdrive Rate, Rate Drop Response, PVAB, SAV and PAV intervals, Sensor-Varied PVARP). Please reference device manual for specifics.

When the device detects an atrial tachyarrhythmia, it switches from the programmed atrial tracking mode to a non-atrial tracking mode (DDIR or VDIR) and remains in this mode until the atrial tachyarrhythmia ceases. Then the device switches back to the atrial tracking mode, as shown in the table below, unless PMOP has been programmed.

The device defines an atrial tachyarrhythmia based on the device type and model as described below.

Adapta™, Versa™ and Sensia™: 

• 4/7 detection criteria – 4 out of 7 consecutive A-A intervals ≤ the detection rate
• Arrhythmia confirmation criteria – Atrial rate is equal or greater to detection rate and satisfying duration criteria.

• Blanked flutter search – Monitors for A–A intervals that may indicate 2:1 blanking of atrial events. If certain criteria are met, the device extends PVARP and the VA interval to uncover any blanked AS events. If an A-A interval shorter than the detect rate interval is detected, 2:1 sensing of an atrial tachyarrhythmia is assumed. Otherwise, the pacemaker resumes monitoring for 2:1 sensing of atrial tachyarrhythmias in 90 seconds.
• Detect duration – Required delay for Mode Switch to occur. During this delay, device is monitoring every 8th A-A interval < detection interval.
• End of Mode Switch criteria – 7 consecutive A-A intervals longer than the upper tracking rate OR 5 consecutive atrial paces occur, the pacemaker assumes the atrial arrhythmia has ceased and begins to switch back to the programmed atrial tracking mode (DDDR, DDD, or VDD). 

Advisa DR MRI™, Revo MRI™, EnRhythm™, Consulta™ CRT-P, Syncra™ CRT-P and Medtronic ICDs
Arrhythmia criteria: Mode Switch occurs when the device detects the onset of an atrial tachyarrhythmia episode. The detection of AT/AF onset is based on the programmed AT/AF detection interval and the accumulation of additional evidence of atrial tachyarrhythmia based on the number and timing of atrial events within the ventricular intervals. If the atrial rate is above the AT/AF detection interval and there are more atrial events than ventricular events in three V-V intervals, Mode Switch will occur.

The example below demonstrates the steps of a Mode Switch episode:

Considerations: 

• PMOP allows Mode Switch to provide extended DDIR pacing at a higher rate after the atrial arrhythmia subsides.
• A Mode Switch operation cannot start during an ATP therapy in ICDs. If a Mode Switch episode starts before the ATP therapy begins, the device suspends Mode Switch operation during the therapy and resumes it after the therapy delivery.
• Mode Switch and MVP™ modes (AAIR<=>DDDR or AAI<=>DDD) interact to adjust the pacing mode according to the patient’s atrial rhythm and AV conduction status.
• The Mode Switch parameter should be programmed to On if the patient has a history of atrial arrhythmias or atrial arrhythmias are suspected.