CardioSync Optimization Feature

CardioSync™ Optimization, a unique in-office programmer-based algorithm, provides suggested optimized CRT settings to help reduce loss of BiV pacing due to inappropriate AV/VV programming. The CardioSync Optimization Test measures the patient’s intrinsic AV intervals and P and QRS waveform widths. Based on the measurements, the test provides optimized values for the following CRT parameters: V. Pacing configuration, V-V Pace Delay, Paced AV, and Sensed AV. These calculations are comparable to the ambulatory measurements performed by AdaptivCRT, available starting with the Viva XT device model.

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

To run the test:

  1. Select Tests > CardioSync.
  2. Adjust the Sensing Lower Rate, based on the patient’s intrinsic rate, to allow atrial sensed events to occur while considering their pacing needs.
  3. Adjust the Pacing Lower Rate, based on the patient’s intrinsic rate, to cause atrial paced events to occur. This adjustment may not be possible for intrinsic rates of 100 bpm or greater.
  4. Select START Test.
  5. Observe the suggested optimized CRT parameters on the Results screen.
  6. Select PROGRAM to program the pending values, or select Close to exit the test without changing the programmed values.

When CRT is not adaptive (Viva™ S device model or Viva XT in Nonadaptive CRT), running CardioSync optimizes the CRT parameters and makes the resulting parameter values pending.

When AdaptivCRT is adaptive (Viva XT with AdaptivCRT programmed), running CardioSync is not necessary as the device automatically and continuously optimizes the CRT parameters. If the test is run, the device will program the recommended CRT parameters automatically. AdaptivCRT will then continue to update those parameters over time.

Note: There are certain abort criteria that will inhibit the test from being run.

CardioSync In-Office AV/VV Delay optimization enables you to efficiently and effectively optimize both AV/VV timing settings appropriately to maximize CRT benefit for your patients. During the test, the device fixes the ventricular pacing configuration and the V-V pacing delay to the nominal value (LV-RV, 0 ms). The test begins with 10 beats at the Sensing Lower Rate (SLR) to collect measurements during an AS-VS pattern and then 10 beats at the Pacing Lower Rate (PLR) to collect measurements during a AP-VS pattern. During both sequences of the test (SLR and PLR), the AV delay is extended to 300 ms to measure the intrinsic AV, sensed and paced P wave widths, and QRS complex widths. VSR is disabled for the duration of the CardioSync test in order to enable the device to measure the intrinsic (non-paced) QRS complex width without any potential interference from a VSR pace.

When the test is complete, the recommended AV, VV delays and the ventricular pacing configuration (RV->LV, LV->RV) are calculated and displayed in the test results window. The calculations are comparable to the ambulatory measurements performed by AdaptivCRT.

There are certain abort criteria that will inhibit the test from being run:

  • User abort
  • Emergency VVI command
  • HR ≥100 bpm
  • PVCs (one or more)
  • Nonphysiologic AV interval (nonphysiologic meaning a very short AV delay; the limits are SAV <80 ms and for PAV <100 ms)
  • R-R variability
  • Inconsistent atrial events (some AS, some AP; all 10 beats of one sequence need to be either atrial paced or atrial sensed)
  • Prolonged AV (short VA interval as may happen in the case of a PAC or dissociation of the atria from the ventricles; in consequence, the following conduction to the ventricle will be prolonged)

The examples below show the calculated results of a CardioSync Optimization Test. CardioSync Optimization calculates the following optimized CRT settings based on the intrinsic AV interval, P wave width, and QRS width measurements.

  • SAV/PAV Delay
  • V-V Pace Delay
  • V. Pacing configuration

Test results depend on whether CRT is adaptive. If CRT is not adaptive (e.g. Viva S device model or Viva XT in Nonadaptive CRT), the test optimizes the CRT parameters based on the test measurements and makes the resulting parameter values pending. If CRT is not adaptive, the device will only recommend an RV→LV or LV→RV pacing configuration.

Note that if CRT is adaptive, the CRT parameters will continue to adapt over time. Due to this, it is not necessary to run the CardioSync Optimization Test when the device is programmed with AdaptivCRT On.


Suboptimal device timing is one of the potential reasons for reduced CRT response. It has been shown that programmed AV delays are suboptimal in about 45% of CRT nonresponders.Currently, echo optimization is the most common approach to optimizing AV/VV programming, yet echo optimization is costly, time consuming, increases the need for additional resources, and is not always available. Device automated algorithms can provide an additional solution for optimizing your patient’s device timing to potentially increase CRT response.

Contrary to echo optimization, CardioSync provides optimized CRT settings without compromising the percentage of BiV pacing. In a retrospective analysis, using CardioSync settings resulted in no patients with less than or equal to 90% BiV pacing due to inappropriate AV/VV programming. This compares favorably to using echo-optimized settings, which resulted in 5% of patients receiving less than 90% BiV pacing due to inappropriate AV/VV programming.2

CardioSync Optimization is an alternative to timely and traditional echo optimization methods.2,3


  1. Mullens W, Grimm RA, Verga T,et al. Insights From a Cardiac Resynchronization Optimization Clinic as Part of a Heart Failure Disease Management Program. J Am Coll Cardiol. March 3, 2009;53(9):765-773.
  2. Lemke B, Birnie D, Aonuma K. Comparison of Cardiac Resynchronization Therapy Optimization Methods With Respect To Biventricular Pacing Percentage: Sub-analysis of Adaptive CRT trial. J Card Fail. 2012;18:S53-54.
  3. 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: results of the adaptive CRT trial."Heart Rhythm. 2012 Nov: 9(11): 1807-14.

Source: Medtronic Viva CRT-D Reference Guide.

Last updated: 
29 May 2013