Several attempts have been made to refine selection criteria for cardiac resynchronisation therapy (CRT) in heart failure patients with reduced ejection fraction (HFrEF). Previously proposed parameters probably do not sufficiently reflect the underlying mechanical dyssynchrony of the left ventricle (LV). Earlier work of our research group suggests that better candidate selection can rely on the direct observation or measurement of this LV mechanical dyssynchrony by means of non-invasive imaging. In this study apical rocking and other non-invasive measures of LV mechanical dyssynchrony will be applied to evaluate regional myocardial workload and metabolism, and determine their predictive value in CRT response.

Inclusion Criteria

Subject is eligible for CRT implantation according to current European Society of Cardiology guidelines of 2013.

• The patient should receive guideline-directed optimal medical therapy for heart failure and left ventricular (LV) function must be severely depressed (LV ejection fraction ≤35%).
• The patients should be in NYHA functional class II, III or ambulatory IV.
• The patient should present a left bundle branch block (LBBB) with QRS duration of >120ms or a non-LBBB with QRS >150ms.
• Also patients with conventional pacemaker in NYHA functional class III and ambulatory IV if high percentage of ventricular pacing, are eligible for CRT implantation.
• Subject is in stable sinus rhythm at the time of CRT implant and during the last 2 weeks prior to inclusion.
• Subject is 18 years or older and able and willing to consent.

Exclusion Criteria:

• Impossible to obtain LV volumes by echocardiography.
• Right bundle branch block.
• Permanent atrial fibrillation, flutter or tachycardia (>100 bpm).
• Recent myocardial infarction, within 40 days prior to enrolment.
• Subject underwent coronary artery bypass graft (CABG) or valve surgery, within 90 days.
• Post heart transplantation, or is actively listed on the transplantation list, or has reasonable probability (per investigator's discretion) of undergoing transplantation in the next year.
• Implanted with a LV assist device (LVAD), or has reasonable probability (per investigator's discretion) of receiving a LVAD in the next year.
• Severe aortic stenosis (with a valve area of <1.0 cm2 or significant valve disease expected to be operated on within study period).
• Complex and uncorrected congenital heart disease.
• Breastfeeding women, women of child bearing potential.
• Enrolled in one or more concurrent studies that would confound the results of this study.