Improvement of abnormal systolic motion of the interventricular septum with cardiac resynchronization therapy

Background: There is no consensus in the literature regarding what is the responsible mechanism of left ventricular dyssynchrony; septal dyskinesia or late movement of left ventricle (LV) lateral wall. We aim to evaluate the abnormal systolic motion in each myocardial segment and the improvement of LV systolic function with pulsed tissue Doppler imaging (TDI) in patients undergoing cardiac resynchronization therapy (CRT) with left bundle branch block (LBBB).

Methods: A total of 26 patients undergoing CRT implantation with LBBB, wide QRS duration (≥120 ms), and low ejection fraction (EF) (<35%) were included. Pulsed TDI was taken from apical 4-chamber view and parasternal short axis view (PSAX). All echocardiographic parameters were measured when CRT is on and off.

Results: Systolic ejection time (ET) of anteroseptal and posterolateral wall of LV in PSAX was statistically significantly longer in CRT on group (321.6 ± 62.7 vs 237.5 ± 59.3 ms, P < .001; 323.9 ± 58.0 vs 289.4 ± 43.7 ms, P = .015, respectively). In apical 4-chamber view, septal annulus systolic ET is significantly longer in CRT on group than CRT off group (315.8 ± 57.2 vs 287.3 ± 42.2, P = .014). Also, there was a strong correlation between systolic ET of the septum in PSAX with aortic velocity time integral (VTI), QRS duration and EF (r = .587, P = .002; r = .479, P = .013; r = .440, P = .025; respectively).

Conclusion: Circumferential contraction of septal myocardial fibers is improved with CRT and it is strongly correlated with increase of aortic VTI and shortening of QRS duration. These findings predict the deterioration of septal contraction as the main mechanism in patients with LBBB pattern and, CRT may improves myocardial contraction by correcting septal systolic motion.