Three-dimensional image of mechanical contraction in the left ventricle based on circumferential strain derived by tagged-MRI analysis. Images are shown for a synchronous (RA-paced) failing left ventricle versus a dyssynchronous (RV-paced) failing heart. End-diastolic (starting reference) strain is coded in red, and shortening depicted by progression to blue while stretch is shown by transition to yellow. The position of the septum is denoted by a green dot. Atrial activation results in near simultaneous contraction of all LV segments with temporal and spatial uniformity of shortening. In contrast, high RV-free wall pacing led to early septal contraction with concomitant stretch of the lateral LV, followed by late lateral wall contraction accompanied by reciprocal stretch of the already-activated septum. While systolic wall stress would be fairly uniform in the synchronous heart, it is predicted as highest in the lateral wall endocardium and lowest in the septal region in the dyssynchronous heart.

Files in this Data Supplement:

• Movie I - (AVI) (2.06 MB). Synchronous heart failure (RA tachypacing).
• Movie II - (AVI) (3.36 MB). Dyssychronous heart failure (RV tachypacing).