Cardiac Resynchronization Therapy Efficacy Enhancements

Inclusion Criteria:

• Subject is willing to sign and date the study patient Informed Consent form.

• Subject is at least 18 years of age (or older, if required by local law).

• Subject is expected to remain available after enrollment to complete follow-up visitsin both arms of the study

• Subject has had a Medtronic Viva or Brava CRT-D device implanted at least 30 daysprior to enrollment.

• Subject has history of AF burden, of at least 6 days of at least 4 hours of AF overany 4 week period within the last 90 days as documented in device diagnostic data ORif subject has no atrial lead (therefore no device diagnostic data) but clinicalevidence of high AF burden.

• Subject has demonstrated history of being able to complete Left Ventricular CaptureManagement (LVCM) documented in device data.

• Subject has a documented % V pacing during AF of less than or equal to 97% within 90days prior to enrollment or within 10 days after enrollment.

Exclusion Criteria:

• Subject has undergone AV node ablation for treatment of AF.

• Subject has complete or 3rd degree AV block.

• Subject has had an MI within 30 days.

• Subject has medical conditions that limit study participation (per physiciandiscretion).

• Subject is enrolled in one or more concurrent studies that could confound the studyresults as determined by Medtronic.

• Subject has a limited life expectancy for non-cardiac causes that would not allowcompletion of the study.

• Subject is pregnant (in the US, all women of child-bearing potential must undergo apregnancy test within seven days prior to CRTee download).

• Subject meets the exclusion criteria required by local law.