Muscle protection in cardiac bioassist: Experimental results with the microstim myosen™ muscle stimulator

Introduction: Since the mid' l980s, muscle powered cardiac assistance is considered as potential surgical treatment options for end-stage heart failure. However, clinical results of the dynamic cardiomyoplasty (DCMP) stayed behind expectations due to lost of muscle strength. A pre- and controlled stimulated Latissimus dorsi muscle (LDM) seems to be powerful and fast contracting enough for an effective cardiac assistance. This study investigates experimentally the effect of Microstim's MyoSen™ muscle protecting myostimulator. Methods: Left LDM of male Bore Goats group A (n5) was control and B (n8) was electrically in-situ pre-stimulated for 2 weeks. LDMs of both groups were wrapped around an intra-thoracic elastic training device and pumped 4- 9 months. Electrical stimulation patterns for too % type I- fibres with a mean stimulation frequency of 3 Hz was applied in group A and those with 4-fold reduced mean stimulation frequency of 0.75 Hz in group B. Blood flow and capillary to fibre ratio were evaluated before and after pre-stimulation. Fluid dynamical power, myosin heavy chain and morphometric muscle analysis were performed. Results: In the pre-stimulated LDM of group B, blood flow while LDM contractions was 31 % higher than in A and capillary to fibre ratio was significantly enhanced by 38%. Group B muscle demonstrated after 4 to 9 months of electrical stimulation a 3 to 6 fold higher contraction velocity and peak power whereas average power per days remains equal between groups. Myosin heavy chain analysis demonstrated in group A only slow type-I muscle fibres and in group B approx. 50% fast- twitching, strong type llA-muscle fibres. Conclusion: A controlled muscle stimulation improves the contraction velocity and peak performance of the LDM. A prestimulation enhances muscular blood flow and capillary density. Thus a clinically pre- and controlled stimulated cardiomyoplasty (pcCMP) with maintained fast-twitching muscle fibres seems a promising treatment option.