• Performance of Activities of Daily Living Tests (6-minute Walk and Sweep) [ Time Frame: within 45 days of enrollment ] [ Designated as safety issue: No ]
  Six-minute walk test and sweep test results for subjects completing tests in all three pacing modes and requiring at least 80% pacing during both tests in the CLS and R pacing modes. The mean composite of repetitions (six minute walk plus sweep) are presented.
  
  
• Pulse Pressure During Activities of Daily Living Tests (Orthostatic Test) [ Time Frame: within 45 days of enrollment ] [ Designated as safety issue: No ]
  Patients completing the orthostatic test in all three pacing modes and that had at least 80% pacing during the test in the CLS and R pacing modes are included in the analysis. The mean pulse pressure is provided.
  
  

• Change in Quality of Life [ Time Frame: baseline and 12 months ] [ Designated as safety issue: No ]
  Change in Quality of life (QOL) score was determined from baseline to the 12 month follow-up visit. The QOL utilized the physical functioning scale of the SF-36 v2, in which a higher score indicates a better health perception. Best possible score was 57.03 while the worst possible score was 14.94.
  
  
• Mode Reprogramming [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  Number of subjects with device reprogramming from dual (atrial and ventricular pacing) to single chamber (ventricular pacing only) or from single (ventricular pacing only) to dual chamber (atrial and ventricular pacing) during the 12 month follow-up.
  
  
• Atrial Fibrillation (AF) Burden [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  AF burden was measured at 12 months as the percentage of total atrial beats that are at or above 160 bpm.
  
  
• Cardiac Symptoms [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  Number of subjects exhibiting each cardiac symptom was determined at the 12 month follow-up visit.
  
  
• Change in New York Heart Association (NYHA) Class [ Time Frame: baseline and 12 months ] [ Designated as safety issue: No ]
  Number of subjects with improved, no change, or worsened NYHA classification at the 12-month visit, as compared to baseline. NYHA classifications (I to IV) are used to assess the various stages of heart failure, with Class I relating to mild heart failure and Class IV relating to severe heart failure.
  
  
• Change in 6-minute Walk Test Distance [ Time Frame: baseline and 12 months ] [ Designated as safety issue: No ]
  Change in number of 10 foot repetitions between baseline and 12-month visit were examined.
  
  

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.