Refractory periods and PMT in Biotronik pacemakers

Atrial Refractory Period

• the atrial refractory period is set by default to AUTO
• this means that the atrial refractory period is equal to 225 ms; if the AV Delay is programmed longer than 225 ms, the atrial refractory period is extended to match the AV Delay value

Far-Field Protection

• events sensed within this timer are annotated as Ars (FFP) events but are not counted toward Mode Switching
• the programming resolution for Far-Field Protection is 100 ms to 220 ms following a Vs event, and 100 ms to 220 ms following a Vp event

PVARP

• there is a PVARP after VP and a PVC but not after a cycle classified VS
• the PVARP can be programmed on Auto or on a fixed value
• after a PVC, the PVARP is automatically extended to PVARP + 150 ms, up to a maximum of 600 ms
• if the PVARP feature is set to AUTO, the value of PVARP is set to 225 ms and PVARP after PVC is set to 375 ms; once a pacemaker mediated tachycardia is detected, the algorithm automatically extends the PVARP and PVARP after PVC by 50 ms, up to the maximum value of 600 ms

The AV delay defines the interval between an atrial paced or sensed event and the ventricular pacing pulse. If the pacemaker is programmed to dual chamber sensing mode, an intrinsic ventricular event falling within the AV delay inhibits the ventricular pacing pulse.

• the AV delay after atrial pace events can be differentiated from the AV interval after atrial sense events
• the sense compensation can be programmed to OFF and -10…(-5)…-120 ms; when selected, the AV delay after an atrial sense event is the AV delay after an atrial pace minus the sense compensation
• the dynamic AV delays may be programmed individually for each rate range or a fixed AV delay may be programmed for all ranges
• the dynamic AV delay provides independent selection of AV delays from five rate ranges at pre-set AV delay values

AV Hysteresis

• OFF, Positive, Negative and I-Opt
• Positive: Hysteresis – programmable 70, 110, 150 or 200 ms longer than programmed AV delay
• Negative: Hysteresis – 10 … (10) … 150 ms
• AV repetitive/scan cycles: OFF, ON

Positive AV delay hysteresis

• positive hysteresis has been designed to promote intrinsic activity by periodically extending the AV interval to look for intrinsic activity
• if intrinsic activity is present, the AV delay maintains the hysteresis value to promote intrinsic R-waves
• the maximum length the AV delay can be extended is 450 ms
• this will be automatically shortened as the rate increases to ensure appropriate AV conduction

AV Repetitive Hysteresis

When AV Repetitive Hysteresis is enabled, the AV delay is extended by a defined hysteresis value after sensing an intrinsic ventricular event.

• when a ventricular stimulated event occurs, a long AV delay is used for the programmed number of cycles
• if an intrinsic rhythm occurs during one of the repetitive cycles, the long duration AV delay interval remains in effect
• if an intrinsic rhythm does not occur during the repetitive cycles, the original AV delay interval resumes

            AV Scan Hysteresis

• when AV Scan Hysteresis is enabled, after 180 consecutive pacing cycles, the AV delay is extended for the programmed number of pacing cycles
• if an intrinsic rhythm is detected within the extended AV delay, the longer AV delay remains in effect
• if an intrinsic rhythm is not detected within the number of scan cycles, the original AV delay value resumes

            I-Opt

• I-Opt is a one-button feature designed to promote intrinsic activity in the ventricle

• when programmed ON, AV Hysteresis is extended to 400 ms, regardless of the programmed AV Delay
• as the heart rate increases, I-Opt shortens to ensure appropriate conduction is maintained
• a combination of high rate and I-Opt can result in a situation where 2:1 block occurs during repetitive hysteresis function

Negative AV delay Hysteresis

• with Negative AV delay Hysteresis, the AV delay is decreased by a defined value after a ventricular event is sensed, thereby promoting ventricular pacing
• the Negative AV delay Hysteresis is limited to a minimum AV delay of 10 ms
• the normal AV delay resumes after the programmed number of consecutive ventricular paced events (Repetitive Negative AV Delay Hysteresis) elapses

AV Opt. Test

The AV Opt. Test measures P-wave durations for paced and sensed atrial events and provides programming suggestions for the paced and sensed AV-delay. This suggestion attempts to avoid both premature (A-wave truncation; incomplete RV filling) and excessively delayed (E- and A-wave fusion; mitral regurgitation) ventricular pacing following intrinsic and paced atrial events. The system requires bipolar leads to perform the AV Opt. Test. The test cannot be performed if the heart rate is greater than 100 bpm or if the patient is in Mode Switch.

• the AV Opt. Test can be initiated by the user as part of a device follow-up
• this triggers the implant to send IEGMs from the implant to the programmer, first during intrinsic rhythm, followed by atrial paced rhythm
• the programmer analyzes the IEGM signals and extracts the P-wave duration from the different sequences
• based on the measured P-wave durations the software calculates the mean duration, adds 50 ms and displays the result as suggested AV-delay
• if no intrinsic atrial rate is measured, or if the atrial paced rate violates the upper rate limit, the programmer uses the programmed sense compensation to calculate the corresponding AV-delay suggestion
• after the test procedure has been completed, the user has the option to copy the suggested AV-delay parameters over to the main program screen by pressing the “Accept suggestion” button

Ventricular Refractory Period

• the right ventricular refractory period is applied to all ventricular events (Vs, Vp and PVC)
• this parameter is programmable from 200 to 500 ms

Ventricular Blanking After Ap

• the ventricular blanking after Ap is the period after an atrial pacing pulse during which ventricular sensing is deactivated
• this parameter is programmable from 30 to 70 ms

Safety AV Delay

• the safety AV delay is set at 100 ms
• to prevent ventricular pulse inhibition in the presence of crosstalk, a ventricular pulse will be emitted at the end of the safety AV delay when a ventricular signal is sensed in this window (starting at the end of the Ventricular Blanking After Ap)

The PMT detection/termination algorithm consists of 3 components: suspicion, confirmation and termination.

Suspicion

A PMT is suspected when the following criteria are met:

• the heart rate is greater than 100 bpm
• 8 successive V pace-A sense (Vp-As) cycles have occurred with a length shorter than the VA criterion; this VA criterion is programmable between 250 and 500 ms (nominally set to 350 ms)
• the mean deviation of these 8 Vp-As intervals is less than the Stability criterion parameter, defined as less than 25 ms

Confirmation

In order to confirm PMT, one of these two actions is taken:

• if the suspected PMT is occurring at the Upper Tracking Interval, the programmed Upper Tracking Interval is increased to the next programmable length by 50 ms
• if the suspected PMT is occurring at a rate that is slower than the Upper Tracking Interval, the programmed AV delay is shortened to the next programmable length by 50 ms
• in either case, if the measured VA interval remains constant, PMT is confirmed, moving the algorithm to the next phase

Termination

The device extends the PVARP to the VA interval + 50 ms.