Left Axis Deviation in Patients with Non-ischemic
Heart Failure and Left Bundle Branch Block is a
Purely Electrical Phenomenon
background Possible mechanisms of left-axis deviation (LAD) in the setting of left bundle branch block (LBBB) include differences in cardiac electrophysiology, structure, or anatomic axis.
objective The purpose of this study was to clarify the mechanism(s) responsible for LAD in patients with LBBB.
methods Twenty-nine patients with nonischemic cardiomyopathies and LBBB underwent noninvasive electrocardiographic imaging (ECGi), cardiac computed tomography, and magnetic resonance imaging in order to define ventricular electrical activation, characterize cardiac structure, and determine the cardiac anatomic axis.
results Sixteen patients had a normal QRS axis (NA) (mean axis 8°±23°), whereas 13 patients had LAD (mean axis –48°±13° P<0.001). Total activation times were longer in the LAD group (112±25 ms vs 91±14 ms; P<0.01) due to delayed activation of the basal anterolateral region (107±10 ms vs 81±17 ms; P<0.001). Left ventricular (LV) activation in patients with LAD was from apex to base, in contrast to a circumferential pattern of activation in patients with NA. Apex-to-base delay was longer in the LA group (95±13 ms vs 64±21 ms; P<0.001) and correlated with QRS frontal axis (R2=0.67; P<0.001). Both groups were comparable with regard to LV end-diastolic volume (295±84 mL vs LAD 310±91 mL; P=0.69), LV mass (177±33 g vs LAD 180±37 g; P=0.83), and anatomic axis.
conclusion LAD in LBBB appears to be due to electrophysiological abnormalities rather than structural factors or cardiac anatomic axis.
This work received financial support from the French Government as part of the "Investments of the Future" program managed by the National Research Agency (ANR), Grant Reference No. ANR-10-IAHU-04. Dr Ramirez is supported by a Canadian Institutes of Health Research Banting Postdoctoral Fellowship.
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