This study is evaluating how MRI after CRT can provide key insights regarding LV function, structure, and mechanics resulting from CRT in patients with or without LV scar and inform optimal pacing strategies. The expected accurate and reproducible response assessment with cardiac MRI has important implications for evaluating CRT outcomes in clinical trials, and the insights from the post-CRT MRI promise to improve implementation of CRT.

We are performing a study of 40 patients with current accepted indications for CRT and no MRI contraindications. These patients will have a pre-CRT MRI and another post-CRT MRI 6 months after the CRT procedure. Echocardiography, cardiopulmonary exercise testing, symptom assessment, and laboratory testing are also performed before and after CRT. Modifications to the post-CRT MRI protocol include the use of gradient echo cine imaging rather than steady state free precession imaging, application of wideband imaging to the LGE acquisitions, and strain imaging with cine Displacement Encoding with Stimulated Echoes (DENSE) tailored for device patients.

Inclusion Criteria:

• Chronic systolic HF
• LVEF 35% or less
• Guideline-based class I or IIa indication for CRT
• 25 and 85 years old
• Predominantly in sinus rhythm
• GFR ≥ 40 ml/min/1.73m2* *Contrast will not be given for the 6-month follow-up scan if the GFR falls to < 40 ml/min/1.73m2.

Exclusion Criteria:

• Inability to provide informed consent
• Pregnancy
• Presence of metal embedded in the body due to prior accident or injury, as documented by skull films or other imaging
• Preexisting pacemaker or defibrillator prior to enrollment
• Cerebral aneurysm clips; 6) cochlear implants
• Other metallic implants (prior to enrollment) known to be contraindications to MRI
• Severe claustrophobia
• Acute kidney injury
• Acute renal failure or chronic kidney disease with GFR < 40 cc/min
• Liver transplant
• Gadolinium allergy