The study will investigate the feasibility of using direct HIS pacing or left bundle branch pacing (LBB pacing) as an alternative to biventricular pacing in patients with symptomatic heart failure and an ECG with a typical left bundle branch block pattern.

Biventricular pacing has for more than a decade been standard of care for patients with HFrEF, LVEF < 35%, NYHA II-IV despite optimal medical treatment and an ECG with left bundle branch block (LBBB). However, it is not always ideal because of several drawbacks such as phrenic nerve capture, inability to reach late activated areas and many more. Direct HIS pacing can in many cases capture the left bundle and provide normal electrical activation of the left ventricle but sometimes with high pacing thresholds. Recently direct left bundle branch pacing has shown promise with synchronous activation of the left ventricle at low pacing thresholds.

In the present study the investigators randomize 125 patients in one center to either conventional CRT (45 patients) or HIS/LBB pacing (80 patients). In the HIS/LBB arm, direct HIS-pacing is attempted first but if its not possible or the pacing threshold for capturing the left bundle branch is > 2.5 V at 1 ms the investigators switch to placing a LBB-lead.

Power calculation for non-inferiority: With the 50 patients in the first His Alternative study (25 Biv-CRT og 25 His-CRT) the investigators observed a fall in systolic volumes of 34% and 46% with a standard deviation of 13-16%. Using these numbers it would take at least 108 patients to be 90% sure that the lower limit of a one-sided 97.5% confidence interval (equal to a 95% two-sided confidence interval) would be over the non-inferiority limit of -10%.

Inclusion Criteria:

• Patients over 18 years of age, ischemic or non-ischemic cardiomyopathy with LVEF ≤ 35% assessed by echocardiography, NYHA class II-IV heart failure symptoms despite optimal medical treatment and

  • Either planned new implantation of a biventricular pacing system (CRT-P or CRT-D), where the ECG is with sinus rhythm and a typical left bundle branch block (see definition below)
  • Or planned upgrade of an existing pacemaker or ICD to a biventricular pacing system (CRT-P or CRT-D), where the ECG is with sinus rhythm and a typical left bundle branch block or there has been> 90% right ventricular pacing from an existing pacemaker for at least 2 months prior to enrollment

• Signed informed consent

• Typical left bundle branch block:

  • QRS width > 130 msec for women and > 140 msec for men QS or rS pattern in leads V1 and V2, and mid-QRS plateau phase with or without extras in at least 2 of leads V1, V2, V5, V6, I, and aVL

Exclusion Criteria:

• Existing biventricular pacing system
• Permanent atrial fibrillation
• Severe renal failure with eGFR < 30 ml/min
• AMI or CABG within the last three months
• The patient does not want to participate

Will share data with international arm of the project NCT04409119

6 months following final recruitment

The patient and the staff performing and evaluating echocardiography and hall-walk tests are blinded to the treatment arm