Biventricular Versus Right Ventricular Pacing in Patients with AV Block (BLOCK HF): Clinical Study Design and Rationale


  • This study is sponsored by Medtronic Inc. Minneapolis, MN.

  • Dr. Curtis is a consultant for Medtronic, St. Jude Medical, and Boston Scientific. She does research for St. Jude Medical and Boston Scientific and serves on speakers bureaus for both institutions. Dr. Chang received honoraria for participating in an advisory committee and for travel to advisory committee meetings. Dr. Worley received compensation for input on the study design. Dr. Adamson received consultation fees and honoraria.

  • Manuscript received 16 January 2007; Revised manuscript received 3 May 2007; Accepted for publication 23 May 2007.

Address for correspondence: Anne B. Curtis, M.D., Professor of Medicine, Chief, Division of Cardiology, University of South Florida, 12901 Bruce B. Downs Blvd., Tampa, FL 33612, USA. Fax: 813-974-8915; E-mail:


Background: Right ventricular (RV) pacing restores ventricular systole in patients with atrioventricular (AV) block, yet recent studies have suggested that in patients with AV block and left ventricular (LV) dysfunction, RV pacing may exacerbate the progression to heart failure (HF). BLOCK HF is a prospective, multi-center, randomized, double-blind, controlled trial designed to determine whether patients with AV block, LV dysfunction (EF ≤ 50%), and mild to moderate HF (NYHA I-III) who require pacing benefit from biventricular (BiV) pacing, compared with RV pacing alone.

Objective: The primary objective of this trial is to determine whether the time to first event (all-cause mortality, heart failure-related urgent care, or a ≥ 15% increase in left ventricular end systolic volume index [LVESVI]) for patients with BiV pacing is superior to that of patients with RV pacing.

Methods: Patients with AV block and LV dysfunction who require permanent pacing and undergo successful implantation of a commercial Medtronic CRT device, with or without an ICD, will be randomized to BiV or RV pacing. Patients are followed at least every 6 months until study closure. Up to 1,636 patients may be enrolled in 150 centers worldwide.

Conclusion: BLOCK HF is a large, randomized, clinical study in pacing-indicated patients with AV block, mild to moderate HF symptoms, and LV dysfunction to determine whether BiV pacing is superior to RV pacing in slowing the progression of HF.