Backgroun/Aims: To explore the effect of cardiac contractility modulation (CCM) on myocardial fibrosis in heart failure and to investigate the underlying mechanism. Methods: Rabbits were randomly divided into sham group, HF group and CCM group. A rabbit model of chronic heart failure (CHF) was induced 12 weeks after aortic constriction by pressure unloading. Then cardiac contractility modulation was delivered to the myocardium lasting six hours per day for 4 weeks. Histology examination was carried out to evaluate the myocardial pathological changes. Protein levels of collagen I, collagen III, α-SMA, MMP2, MMP9, TIMP1, TGF-β1 and Smad3 were measured by western blot analysis. Results: Histology examination results showed that CCM therapy attenuated myocardial fibrosis and collagen deposition in rabbits with CHF. In addition, protein levels of collagen I, collagen III, α-SMA, MMP2, MMP9, TIMP1, TGF-β1 and Smad3 were down regulated. Conclusion: CCM therapy exerted protective effects against myocardial fibrosis potentially by inhibiting TGF-β1/Smad3 signaling pathway in CHF rabbits.

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Objective: To compare the effects of biventricular electrical pacing and conventional single-ventricular pacing for cardiac contractility modulation (CCM) on cardiac contractile function and to delineate the underlying molecular mechanisms. Methods: Forty rabbits were divided into four groups before surgery: healthy control, HF sham, HF left ventricular pacing CCM (LVP-CCM), and HF biventricular pacing CCM (BVP-CCM) groups with n=10 for each group. A rabbit model of chronic heart failure was established by ligating ascending aortic root of rabbits. Then electrical stimulations during the absolute refractory period were delivered to the anterior wall of left ventricle in the LVP-CCM group and on the anterior wall of both left and right ventricles in the BVP-CCM group lasting six hours per day for seven days. Changes in ventricular structure, cardiac function and electrocardiogram were monitored before and after CCM stimulation. Results: Compared with the sham-operated group, heart weight, heart weight index, LV end-systolic diameter (LVESD), LV end-diastolic diameter (LVEDD) in the LVP-CCM and BVP-CCM groups were significantly decreased (p<0.05), while LV ejection fraction (LVEF) and fractional shortening fraction (FS) were increased (p<0.05). Notably all these changes were consistently found to be greater in BVP-CCM than in LVP-CCM. Moreover, plasma BNP levels were highest in the HF sham-control group, followed by the LVP-CCM group, and lowest in the BVP-CCM group (p<0.05). Furthermore, sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) protein levels were upregulated by 1.7 and 2.4 fold, along with simultaneous upregulation of a cardiac-enriched microRNA miR-133 levels by 2.6 and 3.3 fold, in LVP-CCM and BVP-CCM, respectively, compared to sham. Conclusions: Biventricular pacing CCM is superior to conventional monoventricular pacing CCM, producing greater improvement cardiac contractile function. Greater upregulation of SERCA2 and miR-133 may account, at least partially, for the improvement by BVP-CCM.

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