Ventricular Capture Management Feature
The device enables VCM once Implant Detection is completed in pacemakers and CRT-Ps, and when detection is turned On in ICDs and CRT-Ds. VCM can be programmed Off, Adaptive (nominal), or Monitor Only. The device must be programmed to a mode that permits pacing and sensing in the ventricle (but not VVT mode) in order to use the Ventricular Capture Management feature.
- 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.
- V. Acute Phase Days Remaining – Time in days during which output settings can be adapted both upward and downward, but not below the permanently programmed ventricular outputs.
- V. Sensing During Search – The polarity used for ventricular sensing during ventricular pacing threshold searches (pacemakers only).
To program VCM in the Adapta™/Versa™/Sensia™ pacemakers, go to Params -> Capture… under the Ventricular Lead or RV.
To program VCM in the Micra™ transcatheter pacing system (TPS), go to Params -> Capture Management...
To program VCM in the Advisa™ family of pacemakers and CRT-P devices, go to Params -> RV Amplitude... -> Capture Management
To program VCM in ICD and CRT-D devices, go to Params -> Pacing… -> RV Amplitude… -> Capture Management
Selecting “Additional Parameters” in the Capture Management screen allows you to program the remaining parameters.
Additional parameters for Adapta/Versa/Sensia pacemakers
Additional parameters for ICD, CRT and Advisa family devices
Capture Management will not program ventricular 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. For Micra TPS, Capture Management will not program Ventricular Amplitude above 5.0 V, and will not modify Pulse Width. There are no additional parameters to program for Micra.
The device performs a ventricular pacing threshold search to determine the ventricular threshold, which is the minimum amplitude that consistently results in capture of the ventricular myocardium.
Scheduling the search – A pacing threshold search is initiated according to the schedule and frequency programmed by the clinician in pacemakers (nominally set to Day at Rest) and at 1:00 am in Advisa DR MRI™, ICDs and CRT devices. The device initiates the first pacing threshold search 12 hours after Implant Detection is complete in pacemakers and CRT-Ps or detection is turned on in ICDs and CRT-Ds. If a search cannot be completed, the device retries after 30 minutes. For Micra, a pacing threshold search is initiated at 12:00 midnight each day and the device retries each hour if a search cannot be completed. Additionally, when Capture Management is programmed to Adaptive, Micra verifies that the ventricular amplitude is safely above the ventricular threshold each hour throughout the day.
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. To make the determination, the device looks for intrinsic or rate related events indicating:
- Out of eight measured V-V intervals, no more than two are faster than:
- 100 bpm if the upper sensor rate and upper tracking rate are ≥ 135 bpm.
- 95 bpm if the upper sensor rate and upper tracking rate are ≥ 125 bpm.
- 90 bpm if the upper sensor rate and upper tracking rate are < 125 bpm.
- The sensor rate, checked at the end of the eight intervals, is at or below the ADL rate.
- In dual chamber modes, at least one valid AV interval (AS-VS, AS-VP, AP-VS, AP-VP) occurred during the eight measured intervals.
The device also looks for automatic feature interaction, including:
- Rate Drop Response is not in an intervention state.
- Mode Switch is not changing between a tracking and a nontracking mode.
- Battery measurements are not being taken.
- Atrial Preference Pacing is not in action.
- Sleep Function is not occurring.
If the stable rhythm check is successful, the pacing threshold search is initiated. If any of the criteria for the stable rhythm check is not met, the pacemaker defers the pacing threshold search until the next scheduled search period.
Conducting the search – The device performs the pacing threshold search at given Amplitude and Pulse Width settings through a series of support cycles and test paces. Each series has three sets of support cycles, with each set followed by a test pace and an automatic backup pace as shown in the diagram below.
- The support cycles are pacing cycles at the programmed Amplitude and Pulse Width that may or may not include ventricular paced events. The pacing threshold search begins with the support cycles.
- A test pace follows each set of support cycles and is delivered at a test Amplitude or Pulse Width. Amplitude and Pulse Width settings above the threshold cause capture of the myocardium; settings below the threshold result in loss-of-capture.
- A backup pace automatically follows each test pace regardless of capture or loss-of-capture for that pace. It is delivered 110 ms after the test pace at the programmed Amplitude and a 1.0 ms Pulse Width setting.
- No backup paces are delivered in Micra. Instead, the pacing interval after a loss-of-capture is overdriven to minimize the pause between heart beats.
Modifying Amplitude and Pulse Width during the search – Adapta/Versa/Sensia pacemakers, when modifying first Amplitude and then Pulse Width during the pacing threshold search, the device is looking for two points that lie on the strength duration curve, as shown in the diagram below. These points define the boundary between settings that capture the myocardium and those that do not. For other devices, only the Amplitude is modified during the pacing threshold search.
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:
- Sensing Assurance
- Rate Drop Response detection
- AV modulation (Search AV™+, Rate Adaptive AV)
- NCAP operation
- Lead Monitor
- Auto PVARP and sensor-varied PVARP operations
- Ventricular Safety Pacing on test paces
- Atrial Preference Pacing
- Sinus Preference
Automatic ventricular output adaptation
Capture Management can be programmed (Adaptive setting) to provide automatic adaptation of ventricular Amplitude and Pulse Width based on pacing threshold search results. Following each search, the device creates a target output by applying a programmable safety margin (Amplitude Margin parameter) to the amplitude threshold determined during the search. The pacemaker’s calculation for the target is always rounded up to the next programmable setting. The pacemaker then adapts outputs toward this target.
Adaptation can take place only within an output range that is defined by a programmable lower limit (Minimum Adapted Amplitude parameter) and the upper threshold limit of 5.0 V @ 1.0 ms. The minimum pulse width for Ventricular Capture Management is 0.4 ms. Ventricular Capture Management for Micra is only able to run if the pulse width is 0.24 ms or 0.4 ms. The pulse width is not modified by VCM for Micra.
Pacing Threshold and Safety Margin for Micra TPS
- Ventricular Capture Management for Micra TPS is only able to run if the pulse width is 0.24 ms or 0.4 ms. The pulse width is not modified by VCM for Micra TPS.
- Amplitude is adapted only when a pacing threshold search is successful; otherwise, it remains as programmed.
- If the operating Amplitude is above the target, the pacemaker adapts the Amplitude downward one programmable setting per successful pacing threshold search. If the target is below the programmed minimum output limit, the adaptation stops at the minimum limit.
- In Micra, the target amplitude is based on the highest pacing threshold recorded in the prior 14 days.
- A High Threshold Condition warning is issued if the amplitude threshold is greater than 2.5 V. The pacemaker responds by adapting to an Amplitude of 5.0 V and Pulse Width of 1.0 ms.
- In Micra TPS, the High Thresholds Condition warning is issued if the amplitude threshold is greater than 5.0 V. Micra responds by adapting to an Amplitude of 5.0 V at the programmed pulse width.
- If the amplitude threshold multiplied by the safety margin indicates an amplitude target greater than 5.0 V, the pacemaker responds by adapting to the highest possible Capture Management settings, an Amplitude of 5.0 V and Pulse Width of 1.0 ms.
- In Micra, a safety margin (acute phase is + 1.5 V and chronic phase, + 0.5 V is nominal) is added to the target threshold to determine the Amplitude. The maximum Amplitude is 5.0 V.
- In the event of partial or complete lead dislodgement, Capture Management may not prevent loss-of-capture.
- If the battery reaches the Elective Replacement Indicator (ERI), the device aborts RVCM. No additional RV pacing threshold searches are conducted.
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.
- Evoked response detection – In rare instances, the pacemaker may not detect the electronic waveform created by the contracting myocardium immediately following a pacing pulse. In such instances, a high threshold measurement may result. Refer to the device manual for more information.
Sources: Medtronic Micra™ Clinician Manual, 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.