IvaBRAdine blocK of Funny Current for Heart Rate Control in permanEnt Atrial Fibrillation. (BRAKE-AF Study).

Inclusion Criteria:

1. Age ≥ 18 years.
2. Permanent Atrial Fibrillation (AF) at the time of randomization, with no prospect ofcardioversion, antiarrhythmic treatment with group I or III drugs, or pulmonary veinablation.
3. Symptoms attributable to AF associated with the presence of at least one of thefollowing inadequate Heart rate (HR) control criteria:
4. HR at rest > 110 bpm (on ECG -electrocardiogram- performed in the 14 days priorto inclusion).
5. HR at rest between 80 and 110 bpm (on ECG performed in the 14 days prior toinclusion) and at least one of the following criteria: i. HR in exercise of moderate intensity > 130 bpm (measured in an ergometry or in aHolter-ECG performed in the 60 days prior to inclusion). ii. Average daytime HR > 80 bpm (measured on a Holter-ECG performed in the 60 daysprior to inclusion).
6. Be receiving treatment with beta-blockers or non-dihydropyridine calcium channelblockers (verapamil or diltiazem) at the maximum dose recommended or tolerated by thepatient.
7. Be able to voluntarily give their informed consent.
8. B|ood test carried out in the 6 months prior to inclusion' including: blood count,thyroid hormones and creatinine, in order to rule out secondary causes of poor HRcontrol. The creatinine figure will be used to calculate the creatinine clearance inorder to adjust the dose of patients who are randomized to the Digoxin group.
9. Transthoracic echocardiogram to rule out, eg, severe valvular heart disease,hypertrophic cardiomyopathy. The one performed in the year prior to inclusion in thestudy will be considered acceptable provided that the patient's clinical situation hasbeen stable in that period of time.

Exclusion Criteria:

1. Previous treatment or patients with a known contraindication to Ivabradine or Digoxinor to any excipient of both drugs.
2. Paroxysmal or intermittent complete atrioventricular (AV) block in patients notcarrying a pacemaker.
3. Decompensated heart failure requiring inotropic and I or intravenous diuretics in theweek prior to randomization or in New York Heart Association (NYHA) functional classIV or on the cardiac transplant waiting list,
4. Acute pericarditis, acute myocarditis or constrictive pericarditis.
5. Obstructive hypertrophic cardiomyopathy.
6. Valvular disease requiring surgical or percutaneous correction.
7. Medical causes that justify poor control of heart rate: fever' anemia,hyperthyroidism, pheochromocytoma' etc.
8. Severe hypotension (blood pressure <90/50 mmHg).
9. Concomitant treatment with potent cytochrome P450 3A4 inhibitors such as azoleantifungals (ketoconazole, itraconazole), macrolide antibiotics (clarithromycin, oralerythromycin, josamycin, telithromycin) HIV protease inhibitors (nelfinavir,ritonavir) and nefazodone.
10. Severe renal insufficiency (CrCl <30 ml/Kg/min) or in a hemodialysis program.
11. Severe hepatic insufficiency.
12. Major surgery (including cardiac surgery) in the month prior to randomization.
13. Severe concomitant illness that supposes a llfe expectancy of less than one year.
14. Impossibility of carrying out scheduled visits to the protocol.
15. Woman of childbearing age (under 50 years of age, except for those who present agynecological report that proves the presence of menopause) and women who arebreastfeeding.
16. Participation in a clinical trial in the previous 6 months.
17. Patients with acute myocardial infarction or unstable angina.
18. Patient with a recent stroke.
19. Patients with congenital long QT syndrome or treated with drugs that prolong thisinterval.