AdaptivCRT™ is a dynamic, physiologic pacing algorithm that enhances cardiac resynchronization therapy (CRT) by adjusting CRT parameters automatically with changes in patient activity levels and conduction status. It leverages a patient’s intrinsic RV conduction when possible while still maintaining CRT. AdaptivCRT also provides continuous optimization of AV/V-V timing settings. In addition, the reduction of RV pacing when operating in Adaptive LV results in increased longevity. AdaptivCRT comprises two pacing operations: Adaptive LV and Adaptive Bi-V.
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.
AdaptivCRT is programmed On by selecting either the “Adaptive Bi-V and LV” or the “Adaptive Bi-V” setting. Adaptive Bi-V and LV is the nominal setting, as well as the shipped setting in Amplia™ devices. Standard Bi-V pacing can be programmed by selecting the Nonadaptive CRT setting. To gain optimal effect of the AdaptivCRT algorithm for the patient, it is recommended to program CRT to the Adaptive Bi-V and LV setting. LV lead stability and patient AV conduction status should be considered before programming to Adaptive Bi-V and LV operation.
AdaptivCRT can be accessed by selecting Params -> CRT... The AdaptivCRT screen (shown above) has several parameters. They are automatically programmed when CRT is in Adaptive Bi-V and LV or Adaptive Bi-V. These parameters can be manually programmed in Nonadaptive CRT:
- V. Pacing – Indicates the patient’s current CRT operation (LV for Adaptive LV and LV->RV or RV->LV for Adaptive Bi-V)
- LV for Adaptive LV
- LV->RV or RV->LV for Adaptive Bi-V in Viva™ devices
- LV->RV only for Adaptive Bi-V in Amplia devices
- V-V Pace Delay – The timing between LV and RV pacing
- Paced AV – The timing between a paced atrial event and a paced ventricular event
- Sensed AV – The timing between a sensed atrial event and a paced ventricular event
Note: AdaptivCRT is available when the device is programmed to DDD/R modes only.
Warning: If the patient has persistent AV block and no ventricular escape rhythm, it may not be appropriate to program AdaptivCRT to Adaptive Bi-V and LV operation. Ventricular function may be lost if the device is functioning in LV-only pacing mode and the LV lead fails to capture the heart (for example, due to dislodgement).
AdaptivCRT continuously and dynamically optimizes the CRT pacing method and AV/V-V delays according to their conduction status and level of activity every minute. It leverages a patient’s intrinsic RV conduction when possible while still maintaining CRT. An additional benefit to reducing RV pacing while in Adaptive LV is increased longevity. AdaptivCRT comprises two pacing operations: Adaptive LV and Adaptive Bi-V.
Adaptive LV pacing leverages the patient's intrinsic conduction by pre-pacing the LV to synchronize with intrinsic RV activation. In patients with normal AV conduction, AdaptivCRT will provide primarily Adaptive LV pacing. During this pacing operation, the timing of the LV pace is automatically adjusted based on the intrinsic AV interval measurement that occurs every minute. The goal is for the LV pace to occur at about 70% of the intrinsic AV interval to account for physiologic adjustments by at least 40 ms prior to the intrinsic QRS to ensure CRT is delivered. After the LV pace occurs, the intrinsic RV contraction completes the biventricular activation. Each minute, the AV delays are updated to ensure optimal CRT delivery.
Adaptive LV will be used when CRT is programmed to Adaptive Bi-V and LV, which is only available if the pacing mode is programmed to DDD or DDDR. Once the Adaptive Bi-V and LV setting is programmed, the device uses Adaptive LV pacing when the patient's heart rate is at or below 100, AV conduction is normal, and LV capture is confirmed.
- Normal AV intervals for Viva devices are defined as less than or equal to 200 ms for atrial sensed intervals (SAV) and less than or equal to 250 ms for atrial paced intervals (PAV).
- Normal AV intervals for Amplia devices are defined as less than or equal to 220 ms for atrial sensed intervals (SAV) and less than or equal to 270 ms for atrial paced intervals (PAV).
Note that Adaptive LV is suspended if a tachyarrhythmia or incompatible device operation occurs. Incompatible device operations include capture management test, pacing threshold, etc. CRT will switch to Nonadaptive Bi-V pacing during these times and use the last calculated AV delays, V-V pace delay, and V. Pacing Configuration (chamber paced first). Automatic adjustments will resume when Adaptive Bi-V or LV operation is no longer suspended.
Adaptive Bi-V Pacing
Adaptive Bi-V pacing automatically optimizes AV/V-V delays and ventricular pacing configurations based on changes in patient activity levels and conduction status. This pacing operation is part of the Adaptive Bi-V and LV operation and is also offered as a standalone CRT operation, Adaptive Bi-V. When combined with Adaptive LV, Adaptive Bi-V operates when the patient's heart rate increases or AV conduction is prolonged. Unlike programmer-based algorithms, Adaptive Bi-V pacing provides ongoing optimization of AV/V-V timing settings based on a patient’s conduction status and activity levels. Adaptive Bi-V maximizes CRT benefit by optimizing ventricular filling and ejection and eliminates the need for time-consuming, manual echo optimization.
During Adaptive Bi-V pacing, the AV delays are updated every minute based on AV interval and P wave width measurements. Intrinsic AV intervals are measured every minute, and P wave and QRS widths are measured every 16 hours. The AV delay is adjusted to pace about 30 ms after the end of the P wave but at least 50 ms before the onset of the intrinsic QRS. This provides enough time for atrial contraction, while ensuring biventricular pacing, prior to intrinsic conduction to the ventricles. In addition, the ventricular pacing configuration (RV->LV, LV->RV) and V-V pace delay are updated every minute based on the AV interval and QRS width measurements.
Adaptive Bi-V pacing will operate when AdaptivCRT is programmed to Adaptive Bi-V and LV or Adaptive Bi-V. Programming CRT to the Adaptive Bi-V and LV operation will provide your patient with the fully automated algorithm, but should you choose Adaptive Bi-V, your patient will still receive optimized biventricular pacing.
When programmed to Adaptive Bi-V and LV, Adaptive Bi-V will operate when the patient's heart rate is above 100 bpm (non-arrhythmia), intrinsic AV intervals are prolonged, or loss of LV capture is confirmed by LVCM. Prolonged intrinsic AV intervals are greater than 200 ms for atrial sensed intervals and greater than 250 ms for atrial paced intervals for Viva devices are SAV > 200 ms or PAV > 250 ms, and SAV > 220 ms or PAV > 270 ms for Amplia devices.
Like Adaptive LV, Adaptive Bi-V is suspended if a tachyarrhythmia or incompatible device operation occurs.
Adaptive Bi-V and LV Pacing
The Adaptive Bi-V and LV setting can be summarized as a three step algorithm:
- Step 1: The device assesses intrinsic conduction to determine if a patient's AV interval is normal or prolonged.
- Step 2: The device determines the pacing method to be either Adaptive LV or Adaptive Bi-V.
- Step 3: The device optimizes the timing of the AV and V-V delays, and pacing configuration.
In step 1, the device assesses heart rate and intrinsic conduction every minute and determines if a patient's AV interval is normal or prolonged. The AV interval measurement is performed by extending the AV delay to 300 ms to allow for intrinsic conduction. If the Ventricular Sense Response (VSR) is programmed On, a VSR is triggered after the ventricular sense in the current pacing configuration (LV or BiV). The algorithm also monitors the patient's heart rate each minute. These measured values are used to determine the pacing method (Adaptive Bi-V or Adaptive LV).
If AV block is suspected, the time interval between AV interval measurements doubles (for example, 2 min, 4 min, 8 min and so on until a max of 16 hours is reached) and the device operates in Adaptive Bi-V to provide right ventricular pacing support. If a single measurement ends with a ventricular sense event, the AV interval measurements return to 1-minute intervals.
In step 2, based on the intrinsic conduction assessment, AdaptivCRT determines the pacing method to be either Adaptive LV for normal AV intervals and heart rates, or Adaptive Bi-V for prolonged AV intervals or high heart rates.
In step 3, if the patient is being Adaptive LV paced, the algorithm will determine when to pre-pace the LV to synchronize with the intrinsic RV contraction. If the patient is being Adaptive Bi-V paced, it will optimize AV/V-V delays and the ventricular pacing configuration. These calculations are based on AV interval, P wave and QRS waveform width measurements.
Evaluation of AdaptivCRT
There are two ways to tell immediately whether the device is currently operating in Adaptive Bi-V or Adaptive LV pacing:
- On the running EGM strip, the marker channels will be VP for Adaptive LV pacing and BV for Adaptive Bi-V pacing.
- On the CRT parameter screen, the V. Pacing setting will be:
- LV for Adaptive LV
- LV->RV or RV->LV for Adaptive Bi-V in Viva devices
- LV->RV only for Adaptive Bi-V in Amplia devices (RV->LV is not an available Bi-V setting)
- Note, there is no VV pace delay for Adaptive LV
Beginning with Viva XT™ CRT-D device model, the Total VP and CRT Pacing section is included in the Rate Histogram report. The total ventricular pacing value is key in assessing how much CRT therapy the patient is receiving. The ventricular sense response pace percentage indicates how often a ventricular pace was triggered in response to a ventricular sensed event. The VSR paces are not considered a ventricular sense because the device actually paced; it is not considered a ventricular pace because it is not a true biventricular pace. The percentage of ventricular sensing provides information on how often the patient is losing CRT therapy. The sum of these three percentages represents 100% of the time in the session.
The CRT Pacing section details how often ventricular pacing was delivered in Bi-V and in LV. These percentages are a breakdown of the total ventricular pacing percentage. Typically, Bi-V and LV add up to 100% of the total delivered ventricular pacing. A value less than 100% may occur if right-ventricle-only pacing occurs due to operation of a pacing feature that takes priority over AdaptivCRT, such as Ventricular Safety Pacing, Atrial Capture Management™, Ventricular Capture Management™, or VVI backup. If AdaptivCRT pacing is programmed to Adaptive Bi-V or Nonadaptive CRT, the LV pacing percentage will be zero.
A patient* is implanted with a Viva XT CRT-D device. AdaptivCRT is left at the shipped setting of Adaptive Bi-V after implant. The optimized AV and V-V delays are displayed below.
At the first follow-up visit, the clinician notices that the patient has been pacing most of the time in Adaptive Bi-V and is not leveraging the Adaptive LV operation. Additionally, 8.3% of the time, the patient is ventricular sensing. Investigation of the Cardiac Compass™ reveals that the patient experienced episodes of atrial arrhythmias with fast ventricular conduction causing this ventricular sensing. (Remember that AdpativCRT does not operate during episodes of AF).
After optimizing the patient’s arrhythmia medications and beta blockers, the clinician programs the device to ‘Adaptive Bi-V and LV’. This patient has normal AV conduction and the LV lead impedance and thresholds have been stable since implant. The updated optimized parameters are shown below.
At the next visit, the clinician notes that the patient’s ventricular pacing percentage has risen and that almost all of that pacing is occurring in Adaptive LV. Studies have shown that patients with Adaptive LV pacing may have an increased potential for an improved clinical response.1
*This patient information is fictitious and is displayed for educational purposes to describe a likely clinical scenario.
The safety and efficacy of the AdaptivCRT algorithm was tested in the AdaptivCRT clinical trial. This trial concluded that the algorithm was safe and at least as effective as BiV pacing with comprehensive echo optimization.2,3 Also, in the trial, AdaptivCRT was shown to reduce RV pacing by 44%.2
To look at clinical outcomes, the AdaptivCRT Response Analysis compared the CRT response rate of patients with AdaptivCRT to those in historical trials. A propensity score analysis was used to account for baseline differences in the two groups, and the clinical composite score was used to measure response (standard in historical CRT trials). Patients with AdaptivCRT achieved a 12% absolute higher response rate compared to patients in historical trials.4
Finally, the AdaptivCRT LV analysis investigated whether patients who received primarily synchronized LV pacing demonstrated better clinical outcomes. Patients with a higher percentage of synchronized LV pacing in the AdaptivCRT arm had a lower rate of death and HF hospitalizations.4 AdaptivCRT patients with normal AV conduction, as compared to control arm patients with normal AV conduction, produced mostly synchronized LV pacing (73% +/- 25%) and resulted in better clinical response at 6 months (81% vs. 69%).1
- Birnie D. et al., Improved Clinical Outcomes with Synchronized Left-Ventricular Only Pacing by an Automated Cardiac Resynchronization Therapy Algorithm: Analysis of the Adaptive CRT Trial, Presented at the American Heart Association Scientific Sessions 2012. Abstract #: 11672.
- Martin DO, Lemke B, Birnie D, et al. Investigation of a Novel Algorithm for Synchronized left ventricular pacing and Ambulatory Optimization of Cardiac Resynchronization Therapy. Heart Rhythm. 2012 Nov; 9(11): 1807-14.
- Krum H, Lemke B, Birnie D, et al. A novel algorithm for individualized cardiac resynchronization therapy: rationale and design of the adaptive cardiac resynchronization therapy trial. Am Heart J. May 2012;163(5):747-752.e1.
- Singh JP, Shen J, Chung. ES. Clinical response with Adaptive CRT algorithm compared with echo guided AV optimization: a propensity score analysis of multi-center trials. Presentation at European Society of Cardiology Congress August 2012.
Source: Medtronic Viva™ CRT-D Reference Guide, Amplia MRI™/Amplia MRI™Quad, Compia MRI™/Compia MRI™Quad CRT-D Reference Manual.