Left ventricular torsion analysis using echocardiographic speckle tracking in a canine model of dyssynchrony and cardiac resynchronization therapy predicts global cardiac performance

Introduction

Left ventricular (LV) torsion is a primary mechanism used to eject blood during systole. We hypothesized that LV torsion is impaired during dyssynchronous contractions and restored with cardiac resynchronization therapy (CRT) in proportion to the degree that global LV performance improves.

Methods

Seven anesthetized open-chest dogs had high fidelity pressure and conductance volume catheters to assess LV performance. Basal and apical Grayscale echo images were recorded. Right atrial (RA) pacing served as the control. Right ventricular (RV) outflow tract pacing created a left bundle branch block (LBBB) to simulate dyssynchrony. Simultaneous RV–LV free wall and RV–LV apex pacing were modeled CRT (CRTfw and CRTa). Torsion was estimated as the difference between apical and basal rotation in degrees.

Results

Torsion during RA pacing was 7.0 ± 3.6°. RV pacing decreased torsion (5.1 ± 3.6°, P < 0.05 vs. control), reduced the stroke volume (SV), stroke work (SW), and dP/dt_max compared with RA (21 ± 5 vs. 17 ± 5 ml, 252 ± 61 vs.151 ± 64 mJ, and 2,063 ± 456 vs. 1,603 ± 424 mmHg/s, P < 0.05). CRTa improved torsion, SV, SW and dP/dt_max compared with RV pacing (7.7 ± 4.7°, 23 ± 3 ml, 240 ± 50 mJ and 1,947 ± 647 mmHg/s, respectively, P < 0.05), whereas CRTfw did not (5.1 ± 3.6°, 18 ± 5 ml, 175 ± 48 mJ and 1,699 ± 432 mmHg/s, respectively, P < 0.05) (Figure 1). Changes in torsion compared with RA covaried with changes in SW during RV, CRTa and CRTfw.

Figure 1

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Conclusion

LV torsion, as quantified by speckle tracking echocardiography in an acute canine model, was reduced by dyssynchrony contraction and restored by CRT in proportion to the degree to which global measures of LV performance also improved. Thus, torsion and global LV performance are linked during synchronous, dyssynchronous contractions and CRT.