for people ages 18-99 (full criteria)
Healthy Volunteers
healthy people welcome
at La Jolla, California
study started
estimated completion
Principal Investigator
by Jonathan Hsu, MD
Photo of Jonathan Hsu
Jonathan Hsu



Dr. Jonathan Hsu and Dr. Eric Adler are conducting a research study to find out more about how implantable cardiac defibrillator (ICD) settings can be adjusted to improve patient cardiovascular health and quality of life. Patients are being asked to participate in this study if they have a history of heart failure and have or are scheduled to be implanted with a BIOTRONIK ICD that is capable of closed loop stimulation (CLS). CLS is a device setting that works with the cardiovascular system to optimize their heart rate during physical activity. This study is comparing BIOTRONIK's CLS setting to a standard accelerometer setting, which also is able to adjust the heart rate by movement sensors, when necessary. This study has been initiated by Dr. Hsu and Dr. Adler and is financially supported by BIOTRONIK, Inc. There will be approximately 15 participants in this trial.

Official Title

Rate Response With CLS Versus Accelerometer and Effect on Both Subjective Symptoms and Objective Outcomes in a Heart Failure Population Implanted With Cardiac Resynchronization With Defibrillator Device: The CLASS Trial


This study is a prospective, randomized, single-blind crossover study intended to enroll patients who are implanted or are scheduled to be implanted with a Biotronik CLS and accelerometer capable CRT-D device. Patients will serve as their own control group with regard to modes of rate-adaptive pacing. Patients with a previously implanted Biotronik CRT-D device with CLS-capability will be recruited from health care institutions in San Diego and all dedicated functional testing will be performed at the University of California, San Diego (UCSD). The goal enrollment target for analysis will be 15 patients, with up to 20 patients enrolled to allow for withdrawals. The purpose of this study is to evaluate whether changes to an implanted ICD can improve the functional status of patients with suspected chronotropic incompetence (CI). CI is a condition in which the heart rate is unable to adequately respond to meet the patient's physical demands, such as walking, climbing stairs, or doing household chores. CI is common in patients with cardiovascular disease, particularly in patients with heart failure. Common clinical management of patients with suspected CI is to activate an accelerometer setting in the cardiac resynchronization therapy with defibrillator (CRT-D) device. An accelerometer will adjust the heart rate to fit the physiological circumstances and needs of the patient based on patient movement only. BIOTRONIK is a company that has developed a novel technology included in the settings for CRT-D devices that offers CLS as an alternative to a standard accelerometer. CLS utilizes sensed electrical properties of the heart in order to assess what may be the best heart rate for both physical and mental demands. This study is designed to compare whether patients will benefit from CLS when compared with standard accelerometer technology.


Heart Failure ICD Chronotropic Incompetence defibrillator CRT-D cardiac resynchronization therapy rate response CLS closed-loop stimulation accelerometer CLS Mode on Biotronik CRT-D Accelerometer Mode on Biotronik CRT-D


You can join if…

Open to people ages 18-99

  • Patients with a BIOTRONIK CRT-D device (capable of CLS and accelerometer rate responsive pacing)
  • Patients at least 18 years old
  • Patients who have plausible symptoms of CI based on previous monitoring and clinical symptoms

You CAN'T join if...

  • Pregnant patients
  • Patients who are unwilling/unable to provide informed consent
  • Patients who are unable to complete study related procedures
  • Current persistent atrial fibrillation


  • Sulpizio Cardiovascular Center
    La Jolla California 92037 United States

Lead Scientist at UCSD

  • Jonathan Hsu, MD
    Associate Professor Of Clinical, Medicine. Authored (or co-authored) 115 research publications. Research interests: Ventricular Tachycardia · Ventricular Arrhythmias · Supraventricular Tachycardia (SVT) · Pacemaker/ICD Implantation · Mechanisms of Arrhythmias · ICDs-Implantable Cardiac Defibrillator · Defibrillator (ICD) · Biventricular Pacemakers · Atrial Flutter


in progress, not accepting new patients
Start Date
Completion Date
University of California, San Diego
Study Type
Last Updated