• Acute changes in surface ECG QRS duration and morphology [ Time Frame: Acute change in QRS duration with pacing compared to intrinsic QRS duration, measured during pacing programming protcol at device implant ]
  QRS duration changes with CRT programming optimisation
• Acute change in LV dP/dtmax [ Time Frame: Acute change in LV dP/dtmax with pacing compared to intrinsic rhythm, measured during pacing programming protcol at device implant ]
  Changes in LV contractility as assessed by pressure wire
• Change in exercise capacity by 6MWT distance [ Time Frame: Pre-implant, 3 and 6 months post randomization ]
  6 minute walk test distance
• Change in NYHA functional class [ Time Frame: Pre-implant, 3 and 6 months post randomization ]
  New York Heart Association Functional class

• Acute changes in surface ECG QRS duration and morphology [ Time Frame: At device implant ]
  QRS duration changes with CRT programming optimisation
• Acute change in LV dP/dtmax [ Time Frame: At device implant ]
  Changes in LV contractility as assessed by pressure wire
• Change in exercise capacity by 6MWT distance [ Time Frame: Pre-implant, 3 and 6 months post randomization ]
  6 minute walk test distance
• Change in NYHA functional class [ Time Frame: Pre-implant, 3 and 6 months post randomization ]
  New York Heart Association Functional class

The objective of this clinical investigation is to evaluate the clinical benefits of an MultiSite pacing (MSP) with patient specific left ventricular vector optimization in patients receiving cardiac resynchronization therapy (CRT) after 6 months of therapy.

This clinical investigation is a single-center, prospective, two-arm, randomized 1:1, crossover study designed to evaluate the effectiveness of Optimized MSP CRT compared to conventional bi-ventricular pacing.

Data will be collected at enrolment, CRT implant procedure, hospital pre-discharge, one, three and six months post implant. Enrolment data collection will include demographics, cardiovascular history, medication, echocardiography measurements, heart failure quality of life questionnaire and six minute walk test distance.

CRT implant procedure data collection will include implanted system information, lead location and conduction times. The electrical conduction recording procedure will include surface ECG and device electrogram (EGM) recordings during various MSP vector pacing configurations at the time of CRT device implant.

Patients will also undergo simultaneous invasive pressure measurements using a left ventricular pressure wire to allow haemodynamic measurements (dP/dtmax) during various MSP vector pacing configurations.

Optimal MSP programming settings will be determined by the narrowest QRS duration recorded by 12 lead ECG and the greatest change in dP/dtmax by pressure wires study.

In a subgroup of patients (approximately 25 patients), non-invasive electrical activation data will be collected with electrocardiographic imaging (ECGi) within 45 days of the implant procedure.

Patients will then be randomized 1:1 to receive either standard biventricular pacing or Optimized MSP at their one-month follow-up (± 15 days) visit.

At the 3 months (± 15 days) post randomization follow up visit, data collection will include surface ECG, EGMs, echocardiographic parameters and quality of life questionnaire. The patients will then undergo cross-over to the alternate randomization group with programming adjusted accordingly.

At the final, 6 months (± 15 days) post randomization follow-up visit, data collection will include surface ECG, EGMs, echocardiographic parameters and quality of life questionnaire. This will mark the completion of the study for each patient.

The expected duration of enrolment is 18 months. The total duration of the clinical investigation is expected to be 25 months.

• Heart Failure
• Left Bundle-Branch Block
• Systolic Dysfunction

• Device: Optimised MultiSite Pacing
  The intervention includes using optimal programming settings with MultiSite pacing configurations via the patient's CRT device. The device in use is the same for each arm, the only changes are the programming settings.
• Device: Standard biventricular pacing
  Conventional programming settings using biventricular pacing will be used

• Placebo Comparator: Standard biventricular pacing
  Cardiac resynchronization therapy (CRT) devices will be programmed as per standard biventricular pacing settings
  Intervention: Device: Standard biventricular pacing
• Active Comparator: Optimised MultiSite Pacing (MSP)
  Cardiac resynchronization therapy (CRT) devices will be programmed as per optimal MSP programming settings; determined by greatest change in dP/dtmax and narrowest QRS duration.
  Intervention: Device: Optimised MultiSite Pacing

Inclusion Criteria:

• Symptomatic Heart Failure (NYHA class I-IV) with QRS duration of 150ms or more with left bundle branch block and LVEF of 35% or less despite optimal medical therapy.
• Patients above 18 years of age
• Able to provide informed consent and willing to comply with study requirements
• Intrinsic QRS duration ≥ 150 ms
• Sinus (or atrial paced) rhythm with intact AV conduction (PR interval ≤250 ms)

Exclusion Criteria:

• Resting heart rate > 100 bpm
• High degree AV Block (2nd or 3rd degree AV block)
• Documented persistent atrial arrhythmia at the moment of enrolment or patients not likely to remain in sinus (or atrial paced) rhythm for the duration of the study
• Patients scheduled for AV node ablation to treat atrial arrhythmias
• Recent (< 3 months) myocardial infarction, catheter ablation, electrolyte imbalance, or any condition within the last 90 days that would contraindicate CRT programming changes in the opinion of the investigator
• Women who are pregnant or plan to become pregnant during the study course
• Known left ventricular thrombus