ASSESSMENT OF SKELETAL-MUSCLE VENTRICLE FUNCTION USING TISSUE VELOCITY IMAGING

Background and Aims: Skeletal muscle ventricles (SMVs) are a potential power source for circulatory assistance. Noninvasive assessment of SM Vs is desirable in long-term studies of SMV function. This study evalu ated whether tissue velocity imaging (TVI) indices of function correla te with invasive measurements of output and pressure generation and ex amined the potential of TVI to provide information about SMV geometry and wall Contraction characteristics. Methods: SMVs were constructed i n six sheep. After electrical conditioning, SMVs were connected to a m ock circulation and stimulated with supramaximal 30-Hz and 50-Hz burst s to contract 35 times/min. The SMVs were tested over a range of prelo ads, and afterload was adjusted to simulate systemic (80 mmHg) and rig ht ventricular (30 mmHg) loading conditions. Stroke volume and pressur e were measured invasively, and stroke work was calculated. TVI was us ed to measure velocities in two opposing SMV walls, providing a simple wall motion score (WMS). This was evaluated against stroke volume, st roke work, and pressure development. Results: 50-Hz stimulation freque ncy and high preload optimized SMV performance. Optimal SMV performanc e indices (mean at 50 Hz) were as follows: (a) right ventricular loadi ng conditions (preload 30 mmHg), stroke volume 17.6 mt (SEM 3.2), peak pressure over afterload 44.2 mmHg (10.9), stroke work 0.05 J (0.02); (b) systemic loading conditions (preload 60 mmHg), stroke volume 10.1 mt (3.2), peak pressure over afterload 58 mmHg (14.6), stroke work 0.0 8 J (0.03). With low preloads, geometric anomalies were noted in the S MVs using TVI. Collapse of the SMVs and dyskinesis were observed, whic h normalized with higher preloads. Persistent dyskinesis was noted in one SMV and was associated with poor performance. Correlations (at opt imal loading and stimulation settings) were as follows: systemic loadi ng conditions, stroke volume versus WMS, 0.92 (p =0.026); peak pressur e versus WMS 0.89 (p = 0.045); stroke work versus WMS, r = 0.91 (p = 0 .046). Right ventricular loading conditions were as follows: stroke vo lume versus WMS, 0.63 (p = 0.25); peak pressure versus WMS, 0.66 (p = 0.22); stroke work versus WMS, 0.45 (p = 0.39). Conclusion: Under syst emic loading conditions, TVI indices of SMV wall motion mirror invasiv e indices of performance, suggesting TVI may be a useful tool for long -term noninvasive monitoring of SMV function.