A high-potential therapy for repairing the heart post-myocardial infarction is the implantation of tissueengineered myocardium. While several groups have developed constructs that mimic the aligned structure of the native myocardium, to date no one has investigated the particular functional benefits conferred by alignment. In this study we created myocardial constructs in both aligned and isotropic configurations by entrapping neonatal rat cardiac cells in fibrin gel. Constructs were cultured statically for 2 weeks, and then characterized. Histological staining showed spread cells that express typical cardiac cell markers in both configurations. Isotropic constructs had higher final cell and collagen densities, but lower passive mechanical properties than aligned constructs. Twitch force associated with electrical pacing, however, was 181% higher in aligned constructs, and this improvement was greater than what would be expected from merely aligning the cells in the isotropic constructs in the force measurement direction. Our hypothesis was that this was due to improved gap junction formation=function facilitated by cell alignment, and further analyses of the twitch force data, as well as Western blot results of connexin 43 expression and phosphorylation state, support this hypothesis. Regardless of the specific mechanism, the results presented in this study underscore the importance of recapitulating the anisotropy of the native tissue in engineered myocardium.

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Knowledge of the distributions of temperature in cardiac tissue during and after ablation is important in advancing a basic understanding of this process, and for improving its efficacy in treating arrhythmias. Technologies that enable real-time temperature detection and thermal characterization in the transmural direction can help to predict the depths and sizes of lesion that form. Herein, materials and designs for an injectable device platform that supports precision sensors of temperature and thermal transport properties distributed along the length of an ultrathin and flexible needle-type polymer substrate are introduced. The resulting system can insert into the myocardial tissue, in a minimally invasive manner, to monitor both radiofrequency ablation and cryoablation, in a manner that has no measurable effects on the natural mechanical motions of the heart. The measurement results exhibit excellent agreement with thermal simulations, thereby providing improved insights into lesion transmurality.

Diseases of the cardiac conduction system can be debilitating and deadly. Electronic pacemakers are incredibly effective in the treatment of sinus and AV node dysfunction, yet there remain important limitations and complications. These issues have driven interest in the development of a biological pacemaker. Here, we review experimental progress in animal models and discuss future directions, with a focus on reprogramming endogenous cells in the heart to treat defects of rhythm and conduction.

Background: The purpose of this study was to assess the effect local impedance (LI) has on an ablation workflow when combined with a contact force (CF) ablation catheter.Methods: Left pulmonary vein isolation was performed in an in vivo canine model (N = 8) using a nominal (30 W) or an elevated (50 W) power strategy with a CF catheter. The catheter was enabled to measure LI prior to and during ablation. LI was visible for only one of the vein isolations.Results: Chronic block was achieved in all animals when assessed 30 ± 5 days post-ablation procedure with a median LI drop during RF ranging from 23.0 to 34.0 Ω. In both power cohorts, the median radiofrequency (RF) duration decreased if LI was visible to the operator (30 W only CF: 17.0 s; 30 W CF + LI: 14.0 s, p = 0.009; 50 W only CF: 6.0 s; 50 W CF + LI: 4.0 s, p = 0.019). An inverse relationship between the LI prior to RF delivery and the RF duration required to achieve an effective lesion was observed. There was no correlation between the magnitude of the applied force and the drop in LI, once at least 5 g was achieved.Conclusions: An elevated power strategy with the context of CF and LI led to the most efficient titration of successful RF energy delivery. The combination of feedback allows for customization of the ablation strategy based on local tissue variation rather than a uniform approach that could potentially lead to overtreatment. Higher LI drops were more readily achievable when an elevated power strategy was utilized, especially in conditions where the catheter was coupled against tissue with low resistivity. Clinical study is warranted to determine if there is an additive safety benefit to visualizing the dynamics of the tissue response to RF energy with LI when an elevated power strategy is used.