Closed Loop Stimulation

Closed Loop Stimulation

For more than 20 years, patients with pacemakers or defibrillators have benefitted from the Closed Loop Stimulation (CLS) sensor, offered only by BIOTRONIK. This intelligent cardiac sensor can be activated by clinicians to help patients live a normal life during physical and emotional situations.

CLS is available in IPGs and more recently in ICDs as well as CRTs.

From Vision to Impact

One Life. Take Control with CLS


CLS Details



Why would your patients need a comprehensive physiologic sensor, like CLS?

Every person experiences physical and emotional stress during their life. Regular daily activities, sport, or even playing chess or watching a video can result in such stress. If they suffer from chronotropic incompetence (CI), the patient's heart is not able to respond correctly to the stimulus. Studies have shown that CLS can improve the quality of life of CI patients as well as those suffering from vasovagal syncope.¹

Thanks to CLS rate adaptation, pacemaker patients are also supported during emotional stress.

Which patients can benefit from CLS?

CLS is beneficial for patients with CI and VS as well as patients with Atrial Fibrillation (AF). For patients suffering from CI, the PROVIDE study showed that 75% of patients programmed with DDD-CLS experienced significant improvement compared to only 22% of patients programmed in DDDR. ²


For patients suffering from VS, the recurrence of syncope significantly decreases with a CLS system. The randomized, placebo-controlled, double-blinded, multicenter BIOSync CLS study demonstrated a reduction of syncope recurrence rate after two years by 77% with CLS pacing versus placebo³.


For patients burdened with paroxysmal or permanent atrial fibrillation (AF), cardiac output is also of utmost importance when AV synchrony is lost. CLS is able to support these patients through a steady, reliable and flexible algorithm, be it in a single or dual chamber device. CLS has also been shown to reduce the burden for atrial tachycardia patients compared with other modes. The BURDEN study I demonstrated that patients with CLS sensor had on average 0.11 min/day of AT burden while with DDDR mode patients had on average 10.9 min/day of AT burden.⁴ Subsequently, the BURDEN Study II equally showed a lower AT burden with the CLS sensor. ⁵

About 40% of your pacemaker patients between 70 and 80 years old suffer from chronotropic incompetence.⁶ The CLS sensor could help these patients to get back an emotional life!

CLS can adapt to drug therapy and emotional stresses

CLS can be used for patients following drug therapy. If there is ever a need to make adjustments it can be done without changing the CLS settings, as it automatically updates the curves with the new data. In the same way, according to the mental stress and the physical exercise, CLS will automatically adjust the curves with the input data and modulate the heart rate accordingly. ⁷

① CLS delivers gradual rate decrease based on reduction of myocardium contractility

② Only CLS provides physiological rate adaptation during mental stress

③ CLS provides rate adaptation during hemodynamic changes induced by Isoproterenol infusion

Only CLS precisely correlates between the heart rate and the blood pressure during all activities!

Learn more about CLS benefit with Dr. James Kneller here

1 E. Occhetta et al., Closed loop stimulation in prevention of vasovagal syncope. Inotropy controlled pacing in vasovagal syncope (INVASY).

2 Pavri BB et al., An Impedance Sensor (CLS) is Superior to Accelerometer for Chronotropically Incompetent Patients with Sinus Node Dysfunction: Results of a Pilot Study with a Dual Sensor Pacemaker.

3 Brignole M. et al., Cardiac pacing in severe recurrent reflex syncope and tilt-induced asystole

4 Puglisi et al., Impact of Closed-Loop Stimulation, overdrive pacing, DDDR pacing mode on atrial tachyarrhythmia burden in Brady-Tachy Syndrome.

5 Puglisi et al., Overdrive versus conventional or Closed-Loop rate modulation pacing in the prevention of atrial tachyarrhythmias in Brady-Tachy Syndrome.

6 John F. MacGregor et al. Prevalence of Chronotropic Incompetence in a Large Pacemaker Population: Effect of Gender and Age.

7 Zecchi P., A New Philosophy of Pacing.

CLS Details

A new era of physiological rate regulation

The cardiac output is the product of heart rate and stroke volume. In case of sinus node dysfunction, the heart rate cannot be changed by the ANS. However, the ANS can increase the stroke volume by acting on myocardium contractility, but a high stroke volume is deterious for the patient.The CLS sensor measures the contraction dynamics of the myocardium and translates them into proper heart rate adaptation, thus delivering proven physiological therapy.

Easy to use for physicians

CLS is really easy to use for physicians. CLS can simply be switched on and used with default parameters in more than 90% of the cases in the long term.¹CLS mode is simple to find and activate on the Renamic programmer

Additional technical details

Step 1: Creation of the rest curve

  • CLS measures the intracardiac impedance throughout each ventricular contraction. 
  • When the patient is at rest, reference curves are created by using the average of the last 256 curves of the paced and sensed events. This reference is continuously adapted to the actual resting conditions. 

How is the impedance curve created?

The impedance is measured at the tip of the right ventricular lead and it reflects changes seen during systole.

At the beginning of the systole, blood and muscle volume define the impedance value (1). When the contraction starts, the percentage of muscle volume will increase, resulting in a higher impedance value (2) (3) (4).

Step 2: Comparing the rest curve with the load curve

  • For each heartbeat, CLS determines the impedance curve during the ventricular contraction and compares it to its resting reference curve. No special leads or fixation positions are needed for measuring contraction. 
  •  Slight change between curves will result in a minimum change in rate adaption.The same applies to medium and large changes.

Step 3: Automatic adjustements of CLS

  • CLS is initialized during the auto-initialization phase of the cardiac device. 
  •  CLS is self-calibrating and automatically adjusts to the patients’ situation.
  • Changes in patients’ drug therapy or cardiac remodeling does not affect thethe rate adaption as it automatically updates the curves with the new data. 

Giving back an emotional life simply by switching ON CLS!

1 Lindovská et al., Clinical observations with Closed Loop Stimulation pacemakers in a large patient cohort: the CYLOS routine documentation registry (RECORD)


BIOTRONIK Closed Loop Stimulation vs. accelerometer

Unique to BIOTRONIK pacemakers, Closed Loop Stimulation (CLS) sensor technology offers the most physiological rate regulation on the market.

Dr. Prasad's interview: CLS vs accelerometers

Dr Prasad shares her experiences and opinion regarding the BIOTRONIK CLS sensor compared with the accelerometer.

Mark Dayer's interview: CLS vs accelerometers

Based on his experience, Dr Dayer gives his opinion regarding the BIOTRONIK CLS sensor compared with the accelerometer.

Vasovagal syncope

Janine, a 36-year-old teacher, was diagnosed with vasovagal syncope. Thanks to a BIOTRONIK device with CLS, she was able to return to a normal and resume doing what she loves most: teaching.