<title>Torsion of the left ventricle during pacing with MRI tagging</title>

Abstract

Summary of ResultsThe base of the heart rotated in a clockwise direction while the apex rotated counterclockwise during systole withthe net twist being in the counterclockwise direction. This direction of torsion was preserved during pacing. The ventricularpacing protocols reduced the amplitude of the peak twist compared to the RA pacing protocol. During diastolic untwistingthe ventricularly paced hearts consistently overshot the return to zero twist resulting in a second small rotation at end diastole.The regional differences in twist were mostly consistent across all pacing protocols, with the anterior wall having the greatestabsolute magnitude. A significant result was that increasing the synchronization of contraction through Bi-V pacing did notrestore the patterns ofrotation seen in the RA paced hearts. Comparison with other results The bulk rotation of the LV base in the clockwise direction during systole is consistent with the results of Ingels1°who reported that the base and the apex rotated in opposite directions. This result, however, conflicts with the results ofGibbons'3 who reported that the rotation of the LV base was minimal. Though one heart in our studies showed minimalbasal rotation the other four studies had significant clockwise rotation during contraction. To confirm that the rotation wasnot an artifact of the mathematical methods, the raw tagged images of the LV base were examined and the base clearlyrotated in a clockwise direction. It is possible that the thoracotomy and disruption of the pericardium during surgery mayhave affected the direction and freedom of torsion in the heart. However, Rademakers3 found that the peak torsion was thesame in closed chest dogs as in open chest dogs. This study, however did not compare the time evolution of torsion in theopen and closed chest preparations.Buchalter et.