Search AV+ Feature

The Search AV+ feature is intended to promote intrinsic ventricular activation in patients with intact or intermittent AV conduction and prevent inappropriate therapy in patients without conduction.

The pacemaker searches for the patient’s intrinsic AV conduction time and adjusts the SAV and PAV intervals either longer or shorter to promote intrinsic activation of the ventricles.

This feature can be found in some Medtronic Pacemakers. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

Search AV+ is available when the pacemaker is programmed to the DDDR, DDD, DDIR, DDI, DVIR, DVI, or VDD mode.

Programming Search AV+ to On requires setting the Max Increase to AV parameter. This parameter defines the maximum amount of time (in ms) by which the operating SAV and PAV intervals can be lengthened to allow ventricular sensing to occur. The operating SAV and PAV intervals will adapt to the observed conduction time, but will not exceed the Max Increase to AV parameter.

To program this feature, go to Params -> Intrinsic Activation.

Considerations:

  • Search AV+ cannot be enabled if the pacemaker is programmed to an MVP mode (AAIR<=>DDDR or AAI<=>DDD).
  • Rate Adaptive AV (RAAV) can be enabled while Search AV+ is enabled. Search AV+ will operate using the RAAV-determined AV intervals rather than the programmed AV intervals.

The pacemaker attempts to keep intrinsic conducted events in an “AV delay window” that precedes scheduled paced events. The AV delay window is set to promote intrinsic conduction to the ventricles, but end early enough to avoid fusion or pseudofusion beats if pacing is necessary.

To determine when intrinsic conducted events occur, the pacemaker assesses the 16 most recent AV conduction sequences that start with a nonrefractory atrial sense (when the pacemaker is operating in the DDDR, DDD, and VDD modes) or an atrial pace (when the pacemaker is operating in the DDDR, DDD, DDIR, DDI, DVIR, and DVI modes) and end with a ventricular pace or a nonrefractory ventricular sense.

Search criteria of AV conduction times
As shown in the diagram below, the measured AV conduction times are analyzed and divided into 3 zones: on time, too short or too long.

  • Too long means 8 or more of the last 16 ventricular sensed events occurred within 15 ms of the scheduled ventricular pace, or 8 or more of the last 16 ventricular events were paced events.
  • Too short means 8 or more of the last 16 ventricular sensed events occurred more than 55 ms before the scheduled ventricular pace.

Adjustment of SAV and PAV intervals
If AV conduction times are classified as too long, the pacemaker lengthens the operating SAV and PAV intervals by 62 ms for the next 16 pacing cycles to promote intrinsic conduction. The maximum amount of time by which the SAV and PAV can be lengthened is limited by the Search AV+ Maximum Increase to AV parameter.

If the previous 16 AV intervals are classified as too short, the pacemaker shortens the operating SAV and PAV intervals by 8 ms for the next 16 pacing cycles. The maximum amount of time by which SAV and PAV can be shortened is limited by the programmed SAV and PAV values or the RAAV Maximum Offset parameter, if RAAV is On.

Suspension of Search AV+ operation
Search AV+ promotes conduction in patients with intrinsic conduction and prevents inappropriate therapy for patients without intrinsic conduction. If AV conduction is not found, Search AV+ suspends operation for progressively longer periods: 15 minutes, 30 minutes, 1, 2, 4, 8, and 16 hours. If AV conduction is not found following 10 consecutive 16-hour suspensions (approximate duration 1 week), the device automatically turns Search AV+ to Off.

When RAAV is active, the pacemaker also adjusts the SAV and PAV intervals relative to the rate adaptive values. If the pacemaker does not observe intrinsic ventricular activation during its periodic searches over the course of a week, it turns off the Search AV+ feature.

Considerations:

  • Both Automatic  PVARP and RAAV can shorten the AV intervals at higher rates and potentially lead to ventricular pacing.
  • When Automatic PVARP is active and Search AV+ is set to On, the pacemaker will ignore conduction times that are the result of Automatic PVARP shortening of the SAV interval.
  • Ventricular pacing > 40% of the time in DDDR mode was associated with a 2.6-fold increased risk of heart failure hospitalization as compared with < 40% V-pacing.1
  • The risk of AF increased linearly with increasing cumulative percent V-pacing from 0% pacing up to 80-85% pacing in both DDDR and VVIR pacing modes.1
  • Long-term DDDR pacing induces LA dilation, and a high proportion of RV pacing decreases LV function.2
  • In addition, it has been documented that many pacemaker patients have natural PR conduction intervals that extend into the 300-350 ms range.3,4
 
Danish II Trial2
AAI(R) vs. DDD(R) w/Short AV 
vs. DDD(R) w/Long AV
CTOPP Trial5
DDD(R) or AAI(R)
vs. VVI(R)
DAVID Trial6
DDD(R) vs. AAI(R)
ICDs
MOST Sub-Study1
DDD(R) vs. VVIR
HF Hospitalization Not specifically measured; study indicates that high proportion of RV pacing reduces LV function

Not measured

1 yr event-free rate of composite endpoint (death or HFH) was worse in DDDR group when %V-pacing > 40%

2.6-fold increased risk when %V-pacing > 40% (for DDDR group)

Hemodynamic Performance Long-term DDDR pacing induces LA dilation, and a high proportion of RV pacing decreases LV function

Patients with preserved LV function, no history of MI or CAD, derived most benefit from physiologic pacing

Not measured

Supports conclusion that ventricular dyssynchrony imposed by RV-pacing may be most dramatic in patients with failing left ventricles

Incidence of AF Freedom from AF during follow-up is significantly better with AAIR pacing (p=0.03); 17% RV-pacing in DDDR-long AV group

Physiologic pacing reduces annual rate of development of chronic AF

Not measured

Risk increased linearly by 1% for each 1% increase in V-pacing (up to ~ 85%)

References

  1. Sweeney MO, Hellkamp AS, Ellenbogen KA, et al, for the Mode Selection Trial (MOST) Investigators. Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRS in a clinical trial of pacemaker therapy for sinus node dysfunction. Circulation. 2003; 23: 2932-2937.
  2. Nielsen JC, Kristensen L, Andersen HR, et al. A randomized comparison of atrial and dual-chamber pacing in 177 consecutive patients with sick sinus syndrome: echocardiographic and clinical outcome. JACC2003;42(4);614-623.
  3. Linde C, Nordlander R, Rosenqvist M. Atrial rate adaptive pacing: what happens to AV conduction? PACE. 1994;17(10):1581-1589.
  4. Copeman C. EnRhythm Clinical Study Overview. January 2005. Medtronic, Inc. Data on file.
  5. Connolly SJ, Kerr CR, Gent M et al. Effects of physiologic pacing versus ventricular pacing on the risk of stroke and death due to cardiovascular causes. Canadian Trial of Physiologic Pacing Investigators. N Engl J Med 2002; 342: 1385-91.
  6. Wilkoff BL, Cook JR, Epstein AE, et al; Dual Chamber and VVI Implantable Defibrillator Trial Investigators. Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial. JAMA. 2002;288:3115-3123.

Source: Medtronic Adapta/Versa/Sensia Reference Guide.

Last updated: 
03 Apr 2013