Session S52.4

A Novel Method for Poincaré Plot Shape Quantification Demonstrates Cardiac Tissue Repolarization Inhomogeneities Induced by Drugs

S Mensing, J Limberis, G Gintant, A Safer*

Drug Safety Consultant
Weisenheim am Sand, Germany

Evaluation of effects induced by drug compounds investigates on the monophasic action potentials (MAPs) in isolated cardiac tissues for preclinical cardiac drug safety (ICH S7B).
The use of variable pacing protocols [1] generates Poincaré Plots from the repolarization length (APD90(i) vs APD90 (i+1)) exhibiting a cyclic structure. In order to characterize and quantify the specific shape of the plots a novel method has been developed. The method estimates the medial trajectory and its belief limits, thus allowing a statistical comparison of Poincaré Plots for tissues exposed to different compounds and conditions.
Features to be compared are: (1)median location of APD trajectory (=length of APD), (2)size of APD trajectory (=variability featuring electro-instability) and (3)shape of APD trajectory (a second measure of electro-instability).
A proof of concept study (N=3) has been conducted in order to investigate the repolarization changes induced by Moxifloxacin, an FDA-recommended reference drug. The substrate is a combined heart tissue consisting of Purkinje fiber and papillary muscle. The tissue ensembles were sequentially treated with placebo and drug at concentrations 3µg/ml and 30µg/ml. A pacing protocol derived from an anaesthetized dog has been applied. Due to prominent RR variations during sinus arrhythmia and the correlation of basic cycle length and repolarization duration, the Poincaré Plot of APD90 exhibits the cyclic structure for which we provide a novel method to quantify.
Evaluation of the shape changes of the Poincaré Plot yields evidence, that the repolarization of the two tissue types answers distinctly different to the drug treatment. The median curve perimeter for the papillary muscle was changed to 93% (SD: 2) and 105% (SD: 19) under 3µg/ml and 30µg/ml drug relative to control. The perimeter of the medial curve for the Purkinje fiber trajectory increased to 114% (SD: 5) and 182% (SD: 16) under 3µg/ml and 30µg/ml drug relative to the perimeter of control conditions. Shapes of trajectories were not changed.
We conclude that the use of a variable pacing protocol in combination with our proposed novel method allows the separate quantification of three different features of electro-instability induced by drug substances.
[1] A Safer, G Gintant. “A Modification of the In-Vitro Canine Purkinje Fiber Repolarization Assay using Variable Frequency Pacing”, Computers in Cardiology 2003.

(Abstract Control Number: 210)