Cardiac resynchronization therapy cures dyssynchronopathy in canine left bundle-branch block hearts

AIMS: We investigated to what extent biventricular pacing (BVP) can normalize LV function and remodeling, induced by isolated left bundle branch block (LBBB). METHODS AND RESULTS: In 16 dogs LBBB was induced. Eight animals were followed for 16 weeks and in 8 animals BVP was started after 8 weeks. LV pressure, LV geometry (2Dechocardiography), systolic circumferential shortening (CSsys, MRI tagging) and myocardial blood flow (MBF, microspheres) was measured. * and # indicate P < 0.05 compared to pre-LBBB and 8 weeks of LBBB, respectively. Data is presented relative to pre-LBBB values (mean +/- SEM). BVP increased LV dP/dt|max from 78 +/- 5%* to 86 +/- 5%*# (immediately) and 89 +/- 6%# (after 8 weeks) and normalized regional differences in CSsys and MBF. After 8 weeks of BVP, LV end-diastolic volume (EDV) was reduced from 123 +/- 3%* to 109 +/- 6%# and LV lateral wall mass was reduced from 128 +/- 5%* to 113 +/- 3%*#. The acute increase in LV dP/dt|max upon BVP correlated with LV EDV and LV wall mass after 8 weeks of BVP. CONCLUSION: In canine hearts with long-term isolated LBBB, BVP largely reverses global and regional functional and structural abnormalities induced by LBBB.