Session S83.6

Performance Evaluation of Cardiac Repolarization Markers Detected from Monophasic Action Potentials and Unipolar Electrograms: A Simulation Study

P Colli Franzone, LF Pavarino, S Scacchi*, B Taccardi

Universita' di Pavia
Pavia, Italy

Objectives: Recovery sequences play an important role in the study of the mechanisms underlying the genesis of cardiac arrhythmias, but there are still uncertainties about the best method for determining recovery times (RTs) from extracellular recordings. In terms of transmembrane action potential (TAP), two widely used markers of RT are the instant RTtap of minimum time derivative during the TAP downstroke and the instant RT90tap when the TAP reaches 90% of its resting value. These two transmembrane based markers are considered to be the best standard for comparison with RT markers derived from unipolar electrograms (EGs) and hybrid monophasic action potentials (HMAPs), currently the only extracellular electrical recording techniques for obtaining cardiac recovery maps on large regions of in vivo beating hearts.
Methods: We considered the following electrogram RT markers: the instant RTeg of maximum time derivative during the T wave of the EG; the instant RThmap of minimum time derivative during the downstroke of the HMAP; the instant RTd2eg of minimum second time derivative during the T wave of the EG; the instant RT90hmap when the HMAP reaches 90% of its resting value. The goal of the present work is to provide an extensive quantitative analysis of the accuracy level of the previous markers. The analysis is based on large scale parallel 3D numerical simulations of the action potential propagation in anisotropic and insulated cardiac blocks, modeled by the anisotropic Bidomain system coupled with the Luo-Rudy I membrane model. In order to mimic the experimental setup used in intramural mapping of the extracellular potential, all the RT markers are computed on a grid of 1872 recording sites located on the epicardial and endocardial surfaces and in the thickness of the cardiac wall.
Results: We found a very high correlation (>0.98) between any of the EG or HMAP markers and the associated TAP markers. In addition to this good global matching, our results also show that RTeg (RTd2eg) may fail to provide reliable estimates of RTtap (RT90tap), where e.g. the S-T interval exhibits a linear ramp or at sites located near recovery front-front and front-boundary collisions.
Conclusions: The markers based on monophasic action potential represent a reliable alternative for estimating the transmembrane action potential markers.

(Abstract Control Number: 141)