Objective The objective of this study was to investigate whether epicardial cryoablation could achieve sufficient endocardial hypothermia to create transmural lesions leading to acute and sustained ...pulmonary vein isolation in a normothermic beating-heart model. Methods Thirty-five– to 45-kg pigs underwent median sternotomy. Epicardial cryoablation was performed on the right ventricle after insertion of thermocouples. Endocardial temperatures from thermocouples were recorded continuously and correlated with the thickness of the myocardium. Thirteen animals underwent pulmonary vein isolation as a box lesion by using 5-minute epicardial cryoablation. Endocardial temperatures were measured in 5 of these animals. Ten animals survived for 7 or 30 days. Electrical isolation was tested at the time of surgical intervention and again at death. Hearts were removed en bloc and submitted for gross and microscopic examination. Results Endocardial temperature varied inversely with tissue thickness, ranging from −60°C in 5-mm-thick tissue to staying unchanged in tissue more than 10 mm thick. During pulmonary vein isolation, median endocardial temperatures were between −1°C and −22°C. Acute electrical isolation was achieved in all 13 animals. All except one of the animals maintained electrical isolation long-term. Histologic analysis revealed transmurality in 89% of sections, although none of the box lesions were completely transmural. Conclusion Epicardial cryoablation can produce long-term pulmonary vein isolation in a beating heart. Dose-response studies demonstrate consistent endocardial hypothermia in tissues up to 7 mm thick. To our knowledge, this is the first report documenting endocardial hypothermia during epicardial cryoablation. This technology holds promise for performing the complete maze procedure on a beating heart.
Abstract Objective This study correlates changes in trunk isometric force parameters and trunk muscle recruitment strategies in subjects with low back pain (LBP) and healthy participants. Methods A ...control group study with repeated measures was performed. Study participants included 15 control subjects and 14 patients with LBP. Participants were required to exert 50% and 75% of their maximal trunk flexion and extension. In a learning phase, feedback was provided, after which study participants were asked to perform 10 trials without any feedback. Spatiotemporal parameters of muscular activity and force production were recorded. Dependent variables included time to peak force, peak force variability, absolute error in peak force, electromyogram (EMG) burst duration for agonist muscles, and normalized integrated EMG. Results Average time to peak force was significantly longer for subjects with LBP than for healthy subjects. Subjects with LBP showed longer burst duration for all 4 muscles recorded. No group difference was noted in normalized integrated EMG. Conclusions We suggest that the observed changes in trunk motor control and trunk muscle recruitment strategies are not only mediated by a neurophysiologic adaptation to chronic pain but also by cognitive adaptations modulated by fear of movement and fear of reinjury.
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