Conducted AF Response (CAFR) Feature
Conducted AF Response (CAFR) adjusts the ventricular pacing rate to help promote regularity within ventricular intervals during AT/AF episodes. It modifies the ventricular pacing rate to be faster when ventricular sensed events occur, and slower when ventricular pacing pulses occur during periods of AT/AF. Conducted AF Response increases the percent of ventricular pacing without significantly raising the average pacing rate.
For ICD patients, Conducted AF Response helps promote a regular ventricular rate that can prevent symptoms such as palpitations or chest pain resulting from short-long intervals during conducted AT/AF episodes.
For CRT patients, Conducted AF Response is designed to promote delivery of BiV pacing during conducted AT/AF episodes. Conducted AF Response works in conjunction with Ventricular Sense Response (VSR) to achieve 100% BiV pacing during AT/AF.
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.
Conducted AF Response is nominally On in Medtronic CRT devices and nominally Off in Medtronic ICD devices. For ICD patients, the algorithm should be used at the discretion of the physician as it may increase the percentage of unnecessary ventricular pacing, which is not desirable in most ICD patients.1-2
To program this feature in ICDs, go to Params -> Pacing... -> Arrhythmia/Post Shock... -> Additional V Settings…
To program this feature in pacemakers, go to Params -> Interventions.
Note that V. Sense Response will not appear in ICD models.
Additional programmable parameters for this feature include:
- Maximum Rate – Increases to the pacing rate caused by Conducted AF Response are limited by the programmed Maximum Rate.
- Response Level – A higher Response Level value results in a higher percentage of ventricular pacing and faster alignment with the patient’s own ventricular response rate. Response Level is not programmable in pacemakers.
Conducted AF Response operates only in nontracking modes. Therefore, when DDD or DDDR mode is programmed, Mode Switch must be programmed On to program Conducted AF Response On.
The following diagram displays the logical operation of Conducted AF Response. For each beat, the ventricular pacing rate may adjust slightly upward or downward.
- If the current interval ends in a V-pace, the device will start to decrease the pacing rate.
- If the interval ends in a V-sense, the device will start to increase the pacing rate.
The result is a higher percentage of ventricular pacing at an average rate that closely matches the patient’s ventricular response to the AT/AF episode.
The CAFR feature provides low, medium, and high response values to adjust the amount by which the pacing rate is increased, beat by beat. The maximum rate is programmable and is set to a nominal value of 110 ppm. Depending on the programmed Response Level value, the device adds up to 3 bpm in response to a sensed event, and subtracts 1 bpm in response to a pacing pulse. By dynamically matching the patient’s response to AT/AF, the device can increase the percentage of ventricular pacing with little or no increase in the average heart rate.
Conducted AF Response operates only in nontracking modes (DDIR or VVIR). It is typically applied during a mode switch brought about by the onset of an atrial tachyarrhythmia.
- CAFR operates only in nontracking modes.
- When DDD or DDDR mode is programmed, Mode Switch must be programmed to On in order to program CAFR to On; in the nontracking modes of VVI(R) and DDI (R), CAFR can programmed to On or Off.
- Note that CAFR promotes more ventricular pacing. In nonCRT patients, its benefits should be weighed against the potential risks that accompany increased unnecessary ventricular pacing.
- Conducted AF Response operation is suspended during tachyarrhythmia therapies, system tests, EP study inductions, manual therapies, and emergency fixed burst, cardioversion, and defibrillation therapies.
- Note: In older pacemaker models, this feature was named Ventricular Response Pacing (VRP).
Evaluation of Conducted AF Response
The device reports ventricular rates during AT/AF episodes in the Rate Histrograms and Cardiac Compass™ trends reports. This information may help you decide which Response Level and Maximum Rate values to select for Conducted AF Response.
The example below shows marker channels for a CRT device operating in VVI mode. Two BiV paces at 800 ms intervals are followed by three ventricular senses, each of which triggers a Ventricular Sense Response pace. The device uses Conducted AF Response to increase the pacing rate, as seen on the next interval (770 ms). Over time, CAFR will continue to adapt the pacing rate as the patient’s sensed ventricular rate decreases and increases (up to the programmed Maximum Rate) to increase the percentage of biventricular pacing.
In both paroxysmal and permanent/persistent AF patients, CAFR significantly increases the percentage of V-pacing without significantly increasing the mean heart rate.3
- Wilkoff BL, Cook JR, Epstein AE, et al; Dual Chamber and VVI Implantable Defibrillator Trial Investigators. Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial. JAMA. 2002;288:3115-3123.
- Sweeney MO, Hellkamp AS, Ellenbogen KA, et al, for the Mode Selection Trial (MOST) Investigators. Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRS in a clinical trial of pacemaker therapy for sinus node dysfunction. Circulation. 2003; 23: 2932–2937.
- Ellenbogen, K.A., Tse, H.F., Lau, C.P., et al. (2003) Outcomes of Adaptive Regularization During Atrial Fibrillation [Abstract]. PACE. 26(4 Part 2): 934.
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.