Session S32.2

Spatial Properties and Effects of Ajmaline for Epicardial Propagation on Isolated Rabbit Hearts: Measurements and a Computer Study

I Romero Legarreta*, S Bauer, H Koch, M Bär

Physikalisch-Technische Bundesanstalt
Berlin, Germany

Time-resolved surface maps of extracellular bioelectric potentials recorded from isolated rabbit hearts were analysed in order to compare them with corresponding maps generated by a computer model and to reproduce the effect of Ajmaline in the computer simulation.
The electrograms were obtained by a matrix of 8 x 8 electrodes placed on the surface of both the left and the right ventricle epicardium. The hearts were stimulated by a paced pulse in the back of the myocardium. Records were obtained under normal conditions (i.e. before drug administration) and after the administration of the antiarrythmic agent Ajmaline to observe its effect on the electric potential conduction. After filtering to reduce noise, activation maps were computed and subsequently surface propagation speed maps were obtained.
The same observations were reproduced in a computational heart model. The computer model is based on a finite element mesh. It incorporates a rabbit specific anatomy (“San Diego rabbit heart”) and heterogeneity between epicardial, endocardial and M-cells. In addition, it employs a simple realistic ionic model. Activation spread was computed in the monodomain approximation, while the resulting extracellular potential was subsequently obtained via bidomain approach. The effect of the Ajmaline was reproduced by reducing the conductivity of the sodium channels (GNa) in the model. Activation and speed maps were computed in the simulated signals according to the measurements.
From the experimental data it was observed that Ajmaline leads to a 33 % increase of the QRS time from 26 ms to 35 ms in one of the rabbit hearts. We find a decrease of typical velocities in the range 150 to 70 cm/s by about 20-30 % in respect to the non-drug conditions. The velocity speeds obtained were very heterogeneous, ranging from up to 160 cm/s in the left ventricle before drug administration down to 50 cm/s in the right ventricle and after antiarrythmic administration. A velocity decrease of about 20 % was obtained in the computer model by a reduction of the parameter GNa by 50 %. It was also observed a QRS time increase in the model of 25 %. Furthermore, the addition of Ajmaline can lead to a 13 % increase of the basic cycle length from 400 ms to 452 ms.
As a conclusion, our model is able to reproduce the effect of the decrease on the speed epicardial propagation followed by the administration of Ajmaline. The reduction of about 20% observed in experimental data was matched in the model simulations. In addition, an increase of 33 % in the QRS time was also reproduced in simulations that gave an increase of 25 % QRS time.

(Abstract Control Number: 147)