Phase Space Approach in Quantification of Arrhythmia Induction Caused by Potassium Heterogeneities in Isolated Rabbit Hearts

ILIJA Uzelac1 and flavio fenton2
1Georgia Institute of Technology, 2georgia tech


Abstract

Although heterogeneities of electrophysiological properties of the cardiac tissue are important in reentry induction, the particular role of ionic imbalances in creating heterogeneities and arrhythmogenesis is poorly understood. The left marginal vein of the isolated rabbit heart was cannulated separately and a potassium heterogeneity was created by regional perfusion (RP) with a Tyrode’s solution containing 6, 8, 10 and 12 mM of K+ concentration. An optical system and the fluorescence dye (di-4-ANEPPS) were utilized to map the transmembrane potential distribution. We tested stimulation rates starting from 200 ms down to 145 ms with steps of 5-10 ms. To assess the vulnerability to arrhythmia induction, the burst pacing protocol was implemented. Increased pacing rate induced action potential (AP) alternans, which gradually increased as electrical waves propagated deeper into the RP region and resulted in 2:1 conduction block and wave breaks appearance. To quantify the region of elevated potassium, phase space maps were created by time embedded methods from transmembrane potential maps. By parametrizing phase space mapping using different threshold values, region of electrophysiological heterogeneities caused by elevated potassium were spatially localized while spatial locations of wavebreaks and waveblocks were assesed calculating phase singularities in the phase maps. The area of electrophysiological heterogeneity expanded as the stimulation rate was increased. The highest rate of arrhythmia induction correlated with RP having 10 mM of K+, while the elevation of K+ to 12 mM caused RP tissue to become unexcitable.