Effects of Upgrading From Right Ventricular Pacing to Cardiac Resynchronization Therapy and Comparison With Dual-Chamber Defibrillator

Inclusion Criteria: De novo CRT group: * Sinus rhythm, * age higher than 18, * EF lower than 35%, * New York Heart Association (NYHA) class II-IV, * QRS \>130 ms, * patients with atrial fibrillation (AF) who converted to sinus rhythm and who remained symptomatic despite 3-6 months of guideline-directed medical therapy. CRT upgrade group: * Sinus rhythm, * age higher than 18, * EF lower than 35%, * NYHA class II-IV, * QRS duration \>130 ms with RV pacing, -\> 20% RV pacing rate, * patients with AF who converted to sinus rhythm, at least 6 months since pacemaker implantation, and symptomatic despite 3-6 months of guideline directed medical therapy. DDDR ICD group: * Sinus rhythm, * age higher than 18, * EF lower than 35%, * QRS ≤120 ms, * NYHA class II-IV, * patients with AF converted to sinus rhythm, * receiving guideline-directed medical therapy. Exclusion Criteria: * patients with atrial fibrillation * LV EF higher than 50 % * NYHA Class 1 * Patients with active infection or cancer