A simple analytical model of action potential duration profile in electrotonically-coupled cells

QRS complex and T wave planarity for the efficacy prediction of automatic implantable defibrillators

OBJECTIVE

To test the hypothesis that in recipients of primary prophylactic implantable cardioverter-defibrillators (ICDs), the non-planarity of ECG vector loops predicts (a) deaths despite ICD protection and (b) appropriate ICD shocks.

METHODS

Digital pre-implant ECGs were collected in 1948 ICD recipients: 21.4% females, median age 65 years, 61.5% ischaemic heart disease (IHD). QRS and T wave three-dimensional loops were constructed using singular value decomposition that allowed to measure the vector loop planarity. The non-planarity, that is, the twist of the three-dimensional loops out of a single plane, was related to all-cause mortality (n=294; 15.3% females; 68.7% IHD) and appropriate ICD shocks (n=162; 10.5% females; 87.7% IHD) during 5-year follow-up after device implantation. Using multivariable Cox regression, the predictive power of QRS and T wave non-planarity was compared with that of age, heart rate, left ventricular ejection fraction, QRS duration, spatial QRS-T angle, QTc interval and T-peak to T-end interval.

RESULTS

QRS non-planarity was significantly (p<0.001) associated with follow-up deaths despite ICD protection with HR of 1.339 (95% CI 1.165 to 1.540) but was only univariably associated with appropriate ICD shocks. Non-planarity of the T wave loop was the only ECG-derived index significantly (p<0.001) associated with appropriate ICD shocks with multivariable Cox regression HR of 1.364 (1.180 to 1.576) but was not associated with follow-up mortality.

CONCLUSIONS

The analysed data suggest that QRS and T wave non-planarity might offer distinction between patients who are at greater risk of death despite ICD protection and those who are likely to use the defibrillator protection.

Biowire Model of Interstitial and Focal Cardiac Fibrosis

Myocardial fibrosis is a severe global health problem due to its prevalence in all forms of cardiac diseases and direct role in causing heart failure. The discovery of efficient antifibrotic compounds has been hampered due to the lack of a physiologically relevant disease model. Herein, we present a disease model of human myocardial fibrosis and use it to establish a compound screening system. In the Biowire II platform, cardiac tissues are suspended between a pair of poly(octamethylene maleate (anhydride) citrate) (POMaC) wires. Noninvasive functional readouts are realized on the basis of the deflection of the intrinsically fluorescent polymer. The disease model is constructed to recapitulate contractile, biomechanical, and electrophysiological complexities of fibrotic myocardium. Additionally, we constructed a heteropolar integrated model with fibrotic and healthy cardiac tissues coupled together. The integrated model captures the regional heterogeneity of scar lesion, border zone, and adjacent healthy myocardium. Finally, we demonstrate the utility of the system for the evaluation of antifibrotic compounds. The high-fidelity in vitro model system combined with convenient functional readouts could potentially facilitate the development of precision medicine strategies for cardiac fibrosis modeling and establish a pipeline for preclinical compound screening.

Fitting local repolarization parameters in cardiac reaction-diffusion models in the presence of electrotonic coupling

BACKGROUND

Repolarization gradients contribute to arrhythmogenicity. In reaction-diffusion models of cardiac tissue, heterogeneities in action potential duration (APD) can be created by locally modifying an intrinsic membrane kinetics parameter. Electrotonic coupling, however, acts as a confounding factor that modulates APD dispersion.

METHOD

We developed an algorithm based on a quasi-Newton method that iteratively adjusts the spatial distribution of a membrane parameter to reproduce a pre-defined target APD map in a coupled tissue. The method assumes that the relation between the adjustable parameter and APD is bijective in an isolated cell. Each iteration of the algorithm involved simulating the cardiac reaction-diffusion system with the updated parameter profile for one beat and extracting the APD map. The algorithm was extended to simultaneous estimation of two parameter profiles based on two APD maps at different repolarization thresholds.

RESULTS

The method was validated in 1D, 2D and 3D atrial tissues using synthetic target APD maps with controllable total variation and maximum APD gradient. The adjustable parameter was local acetylcholine concentration. The iterations converged provided that APD gradients were not too steep. Convergence was found to be faster 2-5 iterations) when the maximal gradient was less steep, when APD range was smaller and when tissue conductivity was reduced.

CONCLUSION

This algorithm provides a tool to automatically generate arrhythmogenic substrates with controllable repolarization gradients and possibly incorporate experimental APD maps into computer models.