Atrial Capture Management Feature

When Atrial Capture Management™ (ACM) is enabled, the device automatically monitors atrial pacing thresholds at periodic intervals. Once the threshold is determined, the device determines a target output based on the programmable safety margin and programmable minimum amplitude.

This feature can be found in some Medtronic Pacemaker, ICD, CRT-P, and CRT-D devices. Please go to manuals.medtronic.com or consult with your local Medtronic representative regarding device models available in your geography.

The device enables ACM once Implant Detection is completed in pacemakers and CRT-Ps and when Detection is turned On in ICDs and CRT-Ds. ACM can be programmed Off, Adaptive (nominal), or Monitor only. ACM operates in DDDR and DDD modes. If the device is programmed to an MVP mode (AAIR<=>DDDR or AAI<=>DDD), the device changes the mode to DDDR or DDD during ACM operations.

  • If programmed to Adaptive, the device reprograms outputs toward the target.
  • If programmed to Monitor Only, the device does not reprogram outputs.

Additional programming parameters include (nominal settings are shown in image below):

  • Amplitude Margin – The safety margin applied to the pacing threshold search results for Amplitude.
  • Minimum Adapted Amplitude – The lower limit to which the operating Amplitude can be adapted.
  • Capture Test Frequency – Determines how often the pacing threshold search will be initiated.
  • Acute Phase Days Remaining – Time in days during which output settings can be adapted both upward and downward, but not below the permanently programmed atrial outputs.

To program ACM in pacemakers, go to Params -> Capture Management under the Atrium Parameters.

To program ACM in ICDs, go to Params -> Pacing… -> Atrial Amplitude…

Selecting “Additional Parameters” in the Capture Management screen allows you to program the remaining parameters.

Additional parameters for pacemakers

Additional parameters for ICDs (and Advisa DR MRI)

Capture Management will not program atrial outputs above 5.0 V or 1.0 ms. If the patient needs a pacing output higher than 5.0 V or 1.0 ms, program Amplitude and Pulse Width manually.

The device must be programmed to DDDR, DDD, AAIR<=>DDDR, or AAI<=>DDD mode in order to use the Atrial Capture Management feature.

Caution: Epicardial leads have not been determined appropriate for use with ACM operation. Program this feature to Off if implanting an epicardial lead.

The device performs an atrial pacing threshold search to determine the atrial amplitude threshold, which is the minimum amplitude that consistently results in capture of the atrial myocardium.

Scheduling the search – A pacing threshold search is initiated according to the schedule and frequency programmed by the clinician in pacemakers and at 1:00 am in Advisa DR MRI, ICDs and CRT devices. The device initiates the first pacing threshold search after Implant Detection is complete in pacemakers and CRT-Ps and Detection is turned on in ICDs and CRT-Ds. Day at Rest means the pacemaker tries to initiate the first pacing threshold search 12 hours after Implant Detection is complete. It then runs subsequent searches at 24-hour intervals from the last successfully completed search. If a search cannot be completed, the device retries after 30 minutes. The device ensures that false events do not influence the determination of capture and loss-of-capture during the search by aborting the search immediately when the patient’s heart rate or if other device features take precedence over the search.

Checking for stable rhythm – Before a pacing threshold search can be initiated, the device determines if the patient is pacing or sensing at a low rate. A low rate is desirable during the pacing threshold search to reduce the risk of competition from forced pacing with fast intrinsic rhythms. A pacing threshold search is performed when a stable atrial rhythm is observed for eight pacing cycles and the sensor rate is less than the ADL rate.

Considerations: 

  • ACM does not operate during Mode Switch episodes.
  • The sensed atrial rate must not be faster than 87 bpm.
  • The paced atrial rate must be slower than 90 bpm.

Conducting the search – The device performs the pacing threshold search through a series of support cycles followed by a test pace applied at a slightly faster rate. Atrial Capture Management (ACM) observes the timing of sensed P and R waves (not evoked response) to evaluate capture.

ACM automatically selects one of two methods for evaluating atrial capture, based on the patient's rhythm at the time of the pacing threshold search:

  1. If the patient has a stable sinus rhythm, the device selects the Atrial Chamber Reset (ACR) method.
  2. Otherwise, the device selects the AV Conduction (AVC) method.

Because the pacing threshold search operates as the highest priority feature in control of pacing cycle parameters, the following pacing features are disabled during the search:

  1. Atrial Chamber Reset (ACR) method
    Atrial Chamber Reset runs during stable sinus rhythm. It evaluates capture by observing the response of the intrinsic rhythm to the atrial test pace. As shown in the diagram below, if the test pace does not capture, the sinus node is not reset, and an atrial refractory sensed event (AR) is observed after the test pace. If no AR is observed within the AV interval, ACR concludes that the test pace captured the myocardium.

  2. Atrial-Ventricular Conduction (AVC) method
    Atrial-Ventricular Conduction method runs when stable 1:1 AV conduction is observed with atrial pacing. The atrial pacing rate is increased by 15 ppm (but no faster than 101 ppm) and the AV interval is lengthened to try to achieve a stable AP-VS rhythm. AVC evaluates capture by observing the conducted ventricular response to the atrial test pace. Each atrial test pace is followed by a backup atrial pace at programmed amplitude and a 1.0 ms pulse width to maintain rhythm stability during the test. If a conducted VS event is observed at approximately the expected AP-VS interval following the atrial test pace, AVC concludes that the test pace captured the myocardium as shown in the diagram below.

Automatic atrial threshold adaptation
The device applies the programmable amplitude safety margin to the amplitude threshold value measured at a 0.4 ms pulse width to determine the target amplitude. If the operating amplitude is above the target, the device adapts the amplitude down toward the target in one-step decrements. If the operating amplitude is below the target, the amplitude is immediately adapted to the target.

Outputs are not adapted below the programmable minimum amplitude. During the programmable Acute Phase following Implant Detection (nominally 112 days), outputs are not adapted below the programmed outputs or the default shipping settings (3.5 V, 0.4 ms). The acute phase days remaining can be reprogrammed for device replacements with chronic leads.

  • A High Threshold Warning is issued if the amplitude threshold is greater than 2.5 V. The device responds by adapting to an amplitude of 5.0 V and pulse width of 1.0 ms.
  • A High Threshold Warning is issued if the target amplitude is greater than 5.0 V and outputs are adapted to 5.0 V and 1.0 ms.
Note: In the event of partial or complete lead dislodgment, Capture Management may not prevent loss-of-capture.

Considerations
In a small percentage of patients, the following conditions can influence thresholds measured by Capture Management and can lead to possible symptoms:

  • Lead fixation – With poor lead fixation, modulations in pacing timing and rate can influence thresholds.
  • Intrinsic event rejection – In rare instances, combinations of morphology and rhythm may result in a low threshold measurement. This may occur if the pacing threshold search is unable to differentiate between myocardial contractions caused by the pacing pulse and those caused by physiologic means.
  • Atrial Capture Management (ACM) and unipolar sensing – If the atrial sensing polarity is unipolar and Atrial Sensitivity is less than 0.45 mV, ACM does not operate.

References

Sources: Medtronic Adapta/Versa/Sensia Reference Guide; Medtronic Consulta CRT-P Clinician Manual;Medtronic Protecta XT DR Clinician Manual; Medtronic Protecta XT CRT-D Clinician Manual.

Last updated: 
27 Mar 2013