Left Ventricular Capture Management Feature
The Left Ventricular Capture Management™ (LVCM) algorithm is an automatic algorithm that monitors the pacing amplitude threshold and adjusts LV outputs to:
- Help ensure delivery of CRT
- Potentially save time in testing and measuring LV pacing thresholds during follow-up1
- Automatically balance patient safety and device longevity
LVCM customizes LV pacing outputs to match the needs of individual patients and analyze LV thresholds over time with trends reports.
This feature can be found in some Medtronic 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.
LVCM is nominally programmed to Adaptive and will conduct its first test the evening after the device is implanted.
LVCM can be accessed by selecting Params -> Pacing -> LV Amplitude. The Capture Management programming screen (shown here) has several programmed parameters:
- Capture Management – Programmable to Adaptive (adjustments made), Monitor (diagnostics collected but no adjustments made), and Off.
- Amplitude Safety Margin – For LVCM, the voltage value (i.e. +1.5V) to add to the calculated threshold.
- Maximum Adapted Amplitude – The highest voltage to program the LV pacing output. This parameter can be used to manage diaphragmatic stimulation which may occur at higher LV pacing outputs.
- Pulse Width – The permanently programmed pulse width to use for the LVCM test and pacing output.
Left Ventricular Capture Management (LVCM) is available when the pacing mode is programmed to DDDR, DDD, or VVIR mode or when the device has mode switched into DDIR mode. When LVCM is programmed to the Monitor or Adaptive setting, the device conducts a pacing threshold search to determine the LV pacing threshold. When LVCM is programmed to the Adaptive setting, the device uses the LV pacing threshold to adjust the pacing amplitude toward the target amplitude. The target amplitude is based on the programmed settings for LV Amplitude Safety Margin and LV Maximum Adapted Amplitude parameters.
The LVCM test occurs every day at 1:00 am if the patient’s rhythm is stable enough to support a pacing threshold search. Conditions such as programmed LV output greater than 6 V, unstable patient rhythm (R-R variability > 200 ms) or arrhythmia, or heart rate greater than 90 bpm are considered unstable.
If stability checks are unsuccessful, the device automatically continues to schedule searches every 30 minutes.
The LVCM test looks for an RV sense in one of two locations to determine capture:
- When an LV-only pace is delivered and an RV sense is detected shortly after the LV pace (V to V conduction), capture is confirmed.
- When an LV-only pace is delivered and a RV sense is detected at the intrinsic AV interval (conduction from atrial pace or sense), noncapture is confirmed.
As a baseline, the LVCM algorithm measures both the AP to RVS conduction time and the LVP to RVS conduction time to determine the windows in which an LV pace will conduct to the RV (capture) and in which the atrial event will conduct to the RV (noncapture).
The device then conducts a pacing threshold search to determine the LV pacing amplitude threshold at the programmed pulse width. LVCM varies the amplitude of test paces (by 0.125 V) to find the lowest amplitude that consistently captures the left ventricular myocardium. The device evaluates capture by observing the timing of sensed RV events following an LV paced event to determine whether test amplitudes result in capture.
In each threshold measurement, three support cycles precede the test pace to maintain pacing support during the pacing threshold search. During the test pace, the ventricular pacing configuration changes to LV-only. If the left ventricle responds to a test pace, the result is “capture.” If no response is detected, the result is “loss-of-capture.” The result of a test pace is ignored if the device cannot determine whether the test pace captures the myocardium. In the graphic below, you can see that during loss of capture, the RV sense occurs later (due to AV conduction) and during capture, the RV sense occurs shortly after the LV pace (due to V-V conduction).
If LVCM is programmed to the Adaptive setting, the device calculates a target amplitude by adding the programmed LV Amplitude Safety Margin to the calculated amplitude threshold. If the target amplitude is lower than the current pacing output, the device reduces the amplitude by 0.25 V every other day until it reaches the target amplitude. There is no programmable lower limit and the pulse width remains at the permanently programmed pulse width. If the current amplitude threshold is higher than the last measured amplitude threshold, the device immediately adjusts the operating amplitude to the target and rounds it up to the nearest 0.25 V.
If the target amplitude is greater than the LV Maximum Adapted Amplitude, the LV Amplitude will be adjusted to the Maximum Adapted Amplitude at the programmed pulse width.
- In the event of partial or complete lead dislodgment, LVCM may not prevent loss of capture.
- When LVCM is programmed to Adaptive or Monitor and the programmed value for LV Amplitude is greater than the LV Maximum Adapted Amplitude, LVCM will not run.
- LVCM will not run if there has been a VT/VF episode or a shock in past 30 or 60 minutes, depending on the device model.
- In Consulta™ CRT-P and Syncra™ CRT-P, LVCM must be programmed to Off if the LV Pace Polarity is programmed either to LVtip to RVring or to LVring to RVring. Anodal stimulation is possible with these pace polarities. Anodal stimulation occurs when an LV pacing pulse results in capture in the right ventricle or simultaneous capture in both ventricles.
- In Amplia™ and Compia™ CRT-D devices, programming the Amplitude Safety Margin to + Auto enables the device to monitor the stability of the pacing thresholds and then optimize the LV pacing amplitude safety margin automatically. The feature sets the safety margin just high enough above the pacing amplitude to maintain capture while preserving battery energy. If the programmed LV Amplitude Safety Margin is set to + Auto, then the added safety margin depends on the stability of the last 14 days of capture threshold measurements:
- If fewer than 5 capture threshold measurements were taken in the previous 14 days, then the safety margin is set to + 1.5 V.
- If the capture threshold range (maximum minus minimum) in the previous 14 days is <0.5 V, then the safety margin is set to + 0.5 V.
- If the capture threshold range (maximum minus minimum) in the previous 14 days is ≥0.5 V and <1.0 V, then the safety margin is set to + 1.0 V.
- If the capture threshold range (maximum minus minimum) in the previous 14 days is ≥1.0 V, then the safety margin is set to + 1.5 V.
Evaluation of LVCM
If there are significant observations about LVCM, they are shown in the Quick Look™ II Observations window. Possible observations include high threshold, high output, and inadequate safety margin.
The Quick Look II screen shows trends of average capture thresholds measured by the LVCM feature. Select the Threshold [>>] button to view the Lead Trends and Capture Threshold diagnostic screens. Trends are displayed for the maximum and minimum LV capture threshold values for the last 80 weeks along with details for the last 15 days. This detail will include the reasoning for any aborted tests.
To evaluate the LVCM results, review the LV Capture Threshold lead trend and any Observations on the Quick Look II screen. In this patient, the LV threshold has risen to 5 V @ 0.8 ms. The Amplitude Safety Margin is +0.5 V and the Max Adapted Amplitude is 6 V. Based on the Observations, the LV threshold has risen to above 6 V at times. The device has programmed the output to 6 V @ 0.8 ms, which is the maximum allowable output based on the current programming.
The LV lead should be evaluated for possible dislodgement. The pulse width could be programmed up to 1.5 ms with LVCM on. If LVCM is turned off, the LV pacing output can be programmed up to 8 V @ 1.5 ms. This high output will reduce the overall device longevity significantly and is not recommended for long-term pacing therapy. Therefore, an LV lead revision may be warranted in this case. All diagnostics and clinical information should be taken into account before determining a treatment path.
Left Ventricular Capture Management has been evaluated for accuracy and clinical utility. A trial was performed prior to the release of this feature to measure the accuracy of LVCM measurements as compared to manual LV threshold tests.2 The proportion of Left Ventricular Capture Management (LVCM) in-office threshold tests within 0.5 V of the manual threshold test was 99.7% (306/307). This study demonstrated that the LVCM algorithm is safe, accurate, and highly reliable.2 LVCM worked with different types of leads and different lead locations. LVCM was demonstrated to be clinically equivalent to the manual LV threshold test. LVCM offers automatic measurement, output adaptation, and trends of the LV threshold and should result in improved ability to maintain LV capture without sacrificing device longevity.2
- Murgatroyd, F. et. al. Manual vs. automatic capture management in implantable cardioverter deﬁbrillators and cardiac resynchronization therapy deﬁbrillators. Europace. 2010;12:811-816.
- Crossley, George M.D, et. al. Automated Left Ventricular Capture Management. Pacing and Clinical Electrophysiology. October 2007; 30(10):1190-1200.
Sources: Medtronic Protecta™ XT DR Clinician Manual; Medtronic Protecta™ XT CRT-D Clinician Manual, Amplia MRI™/Amplia MRI™Quad, Compia MRI™/Compia MRI™Quad CRT-D Reference Manual.