This is a randomized, prospective, single-blinded, multi-center study involving approximately 1500 patients at 100 centers. The purpose of this study is to demonstrate the effectiveness of Closed Loop Stimulation (CLS) rate adaption technology over both standard rate responsive technology (R) and non-rate responsive mode (DDD) during activities of daily living (ADL).

All patients enrolled in the CLEAR study are implanted with a Cylos pacemaker with Closed Loop Stimulation (CLS) rate adaption technology. Any legally marketed pacing leads may be implanted with the Cylos family of pacemakers.

Prior to enrollment, patients provide written informed consent and are screened to ensure they are eligible to participate in the study. Patients enrolled in the study must have been implanted within 45 days prior to enrollment or are being considered for implant. Once enrolled and implanted with the Cylos pacemaker, the first 500 patients have 45 days to complete an ADL Testing visit. At the Activities of Daily Living (ADL) testing visit, each of the first 500 enrolled patients performs a 6-minute walk test, orthostatic test, and sweep test in three pacing modes, CLS (DDD-CLS or VVI-CLS), standard rate response (DDDR or VVIR) and non-rate responsive mode (DDD or VVI). The order of the pacing modes for testing is randomized in a 1:1:1 ratio. The study primarily analyzes the number of ADL repetitions performed during the 6-minute walk and sweep tests, pulse pressure during the orthostatic test, and secondarily analyzes heart rates during all three tests to compare CLS to both rate responsive and non-rate responsive pacing modes.

For all enrolled patients, the study collects additional data over a 12-month period. Patients are randomized and their pacemaker programmed to one of three pacing modes, CLS, R, or no-rate response in a 2:1:1 ratio, respectively. The patients are then followed for a period of 12 months after the ADL testing (first 500 enrolled patients) or enrollment (patients 501 through 1500). The study collects the following secondary measures to compare CLS to both rate responsive and non-rate responsive pacing modes: changes in 6-minute walk test distance, quality of life, mode reprogramming, atrial fibrillation (AF) burden, cardiac symptoms, and New York Heart Association (NYHA) classification.

Inclusion Criteria:

• Implanted within the last 45 days or being considered for implant with a BIOTRONIK pacemaker utilizing CLS rate adaptation technology (currently the Cylos family of pacemakers).
• Ability to give written informed consent
• Geographically stable and able to return for regular follow-ups for 12 months after ADL testing
• At least 18 years old

Exclusion Criteria:

• Patients physically limited and unable to perform all or parts of the ADL testing
• Currently enrolled in any other clinical study
• Patients with medical reasons that preclude regular participation in the follow-ups