BIVPACE-AVB

INTERVENTION: two:The eligible patients undergo the CRT (Insync III 8024 or newer, Medtronic Inc.) procedure, and randomize into biventricular pacing (group A) and right verntricular apical pacing (Group B) after one week of procedure. The primary parameters are the left ventricular ejection fraction and left ventricular end‐systolic volume at 12 months; CONDITION: AV block, Heart Failure PRIMARY OUTCOME: The left ventricular ejection fraction (LVEF) and left ventricular end‐systolic volume (LVESV); SECONDARY OUTCOME: left ventricular end‐diastolic volume, LV end‐diastolic and endsystolic diameters, Left atrial diment, NYHA class, 6‐minute walk distance, the Minnesota Heart Failure Quality of life scoring, N‐terminal pro‐B‐type natriuretic peptide original (NT proBNP) and atrial high‐frequency event; INCLUSION CRITERIA: 1. Third degree AV block; 2. Second degree AV‐block; 3. Indication for replacement of pacemaker and the ventricular pacing rate more than 40%; 4. LVEF > 35%; 5. NYHA class I‐III in previou 90 days; 6. Writtern informed consent from patients or their guardians; 7. Life expectancy >12 months.