Introduction: CRT implantation in CHF patients is indicated in patients with wide QRS, low EF <35% and NYHA class 2 and above. This study assessed the acute effects of RV apical pacing and bi-ventricular (Bi-V) pacing on left ventricular (LV) mechanics in chronic heart failure (CHF) patients using speckle tracking echo (STE) techniques.
Methods: 10 patients, ages 63-75 years underwent CRT implantation for CHF according to the standard guidelines. Echocardiographic images were obtained one day after implantation during baseline (BL) with no pacing, during RV pacing only and during Bi-V pacing. Echo studies included standard parasternal short axis imaging and apical 2- and 4-chamber views. Post-processing by STE was then performed to calculate LV ejection fraction (EF), circumferential and longitudinal strain as well as LV segmental rotation and torsion.
Results: Adequate echo images for STE analysis were obtained in 6 patients. ECG analysis showed QRS narrowing from 134±23ms at BL, to 89±30ms with RV pacing (p<0.05) & 85±24ms with Bi-V pacing (p<0.01). Echo analysis showed no acute significant difference in the EF during pacing, 26±9% at BL, 27±1% with RV pacing and 30±6% with Bi-V pacing. Longitudinal global strain was mildly increased during RV pacing and significantly increased during Bi-V pacing: - 5.8±3.8% at BL, -6.1±3.7% with RV pacing and -8.4±4.6% with Bi-V pacing (p<0.01). Segmental analysis showed that circumferential strain (CS) at the mitral valve level was -4.7 ±3.6% at BL, increased to -7.3±3.5% during RV pacing (p=0.14) & further increased to - 7.8±4.8% during RV pacing (p=0.06). At the LV apex, the CS was - 5.9±5.6% at BL, mildly increased to -7.2±6.5% during RV pacing and significantly increased to -11±9.1% during Bi-V pacing, (p<0.05). The LV torsion was 5.1±1.9° at BL; 3.9±2.8° during RV pacing and 4.3±1.8° during Bi-V pacing.
Conclusions: In CHF patients, acute RV pacing had mild effects on the LV function while CRT showed significant improved global longitudinal and segmental circumferential strains, & minimal effect on the torsion. These findings can elucidate the long term reverse remodeling effects of CRT in CHF patients and could serve as predictors for responders versus non responders prior to the improvement of the EF and the clinical tests.
