Atrial Refractory Period after Atrial-sensed Event
Atrial refractory is the time period after an atrial-sensed event when additional sensed-atrial events do not initiate timing cycles or inhibit atrial pacing.
- 85 ms (30 ms absolute refractory, 40 ms noise window, 15 ms absolute refractory)
- absolute refractory events are not sensed or marked
- noise events are sensed but not marked
Atrial Refractory after Atrial-paced Event
Atrial refractory is the time period after an atrial-paced event when additional sensed-atrial events do not initiate timing cycles or inhibit atrial pacing.
- 150 ms (110 ms absolute refractory, 40 ms noise window)
- absolute refractory events are not sensed or marked and noise events are marked as [AS]
Cross-chamber atrial blanking windows
Each cross-chamber blanking window may be programmed to a fixed value or to SMART.
SMART Blanking is designed to promote sensing by shortening the blanking period, while rejecting cross-chamber events by automatically adjusting the sensitivity in the following manner:
- shortening the blanked period to an absolute refractory (15 ms for A-blank after V-Sense, and 37.5 ms for A-Blank after V-Pace)
- eliminating the noise portion of the blanking window
- increasing the AGC setting to avoid far-field oversensing of the event in the opposite chamber; the AGC is bumped up to 3/8 of the current peak average
A-Blank after V-Pace
A-Blank after RV-Sense
Post-Ventricular Atrial Refractory Period (PVARP)
PVARP is a programmable period after a ventricular paced or sensed event in which sensed atrial events do not initiate timing cycles or inhibit atrial pacing. PVARP may prevent the tracking of retrograde atrial events initiated in the ventricle that could trigger PMT in a dual chamber device programmed to a tracking mode.
- the initial section of PVARP is the cross-chamber blanking period (composed of absolute refractory and noise window) followed by the fixed refractory period
- events that fall into the absolute refractory window of cross-chamber blanking are not sensed or marked
- events that fall into the noise window are marked as [AS]; there is no noise window for SMART blanking
- events in fixed refractory are marked as (AS), (AF), or (PAC)
- although sensed events in the PVARP fixed refractory window do not initiate timing cycles, they do count toward ATR Entry Counts, AFR, and are included in counters/histograms
The cross chamber blanking period is not shortened by programming dynamic PVARP, only the fixed refractory period. PVARP will decrease linearly between the lower rate limit and maximal tracking rate based on a rolling average of the last four V-V intervals.