Pacing RateOptimal Pacing Rate for Cardiac Resynchronization Therapy

Inclusion Criteria:

1. Age 18 years or older
2. History of persistent or permanent atrial fibrillation
3. Implantation of CRT or conduction system pacing in prior 3 months to 5 years of study start
4. History of intrinsic AVN block or have undergone AVN ablation in prior 3 months to 5 years of study start
5. LVEF ≥ 50%
6. N-terminal pro-B-type natriuretic peptide (NT-proBNP) >400 pg/mL in the last 24 months
7. Clinical HF diagnosis or NYHA class II or higher
8. Able to provide informed consent

Exclusion Criteria:

1. LVEF <50%
2. Wide QRS (greater than 150ms)
3. Isolated RV pacing
4. Severe valvular disease
5. Severe coronary artery disease as defined by one of the following:

1. ACS or PCI within 1 year
2. Any angina (CCS class 1+)
3. Unrevascularizable severe CAD (>70% stenosis in 1+ major vessels and/or based on functional assessment)
6. ESRD
7. Significant primary pulmonary disease on home oxygen
8. Major orthopedic issues, such as being wheelchair bound and/or unable to perform a six-minute walk test
9. Ventricular ectopy >15% premature ventricular contractions (PVC)
10. End stage cancer diagnosis
11. Life expectancy less than one year
12. Palliative or hospice care
13. Hypertrophic cardiomyopathy (HCM)
14. Uncorrected ventricular septal defect
15. Infiltrative cardiomyopathy (CM)
16. Uncontrolled hypertension as defined by blood pressure >160/100 mm Hg on two measurements ≥15 minutes apart
17. Hemoglobin <7 g/dL
18. Age >90 years old
19. Pregnant or intends to become pregnant