Mapping the repolarization electric field for detecting steep repolarization gradients using clinical mapping arrays
T Subha, S Masse, G Mokhtar-Sasani, Y Abderrahman, P F H Lai, J Asta, K NanthakumarAbstract
Introduction
Conduction slowing is only one half of the driver of arrhythmogenicity. While repolarization (repol) gradients form the other half, they are currently not mapped nor used for clinical benefit. Ambiguous unipolar repol time annotation hinders detection of such gradients for clinical use. A metric of arrhythmogenicity by detection of direction of depolarization (depol) wavefront and its discrepancy with repol direction has been used previously on surface leads. An intra-cardiac mapping metric for detecting such discrepancy in heterogeneities in ventricular activation and repol has not been attempted for clinical use. With intracardiac electrode array technology, intracardiac depol (QRS) and repol (T) electric field (E-field) direction can be derived. The discrepancy detected in these E-fields could allow for regional assessment of repol heterogeneities while bypassing repol time annotations on unipolar electrograms which are affected by far-field contamination.
Objective
We aimed to validate the applicability of QRS and T E-field direction as a means to spatially assess repol heterogeneities as correlated against optical mapping as the gold standard for detecting repol gradients.
Methods
In an isolated rabbit heart model (n = 4), we conducted simultaneous optical and electrical mapping using an equi-spaced grid electrode array following topical application of ibutilide to locally alter repol. Intracardiac QRS and T E-field directions on an intracardiac vector loop were derived using four electrodes arranged in 4mm-by-4mm square configurations. The QRS and T E-field angle discrepancy (QRS-T angle) was measured from long axes of the QRS and T vector loops. The angles were compared to the spatial dispersion of repol (SDR in ms/mm2) from the optical APD80 values within the 4mm-by-4mm electrode clique.
Results
The QRS-T angle discrepancy at baseline was 21.12 degrees and indicated no/less repol gradient in the area mapped by the electrode array. This correlated with a mean optical APD80 gradient value of 0.38 ms/mm2. Following drug intervention, a mean QRS-T angle of 37.45 degrees was observed in recordings with a mean optical APD80 gradient value of 1.41 ms/mm2. Areas of repol gradient were detected using QRS and T E-field vector angles, validated by SDR values from optical APD80 measurements.
Conclusion
Clinical mapping arrays that sample E-field and the discordance between depol/repol can provide spatial assessment of repol gradients. This mapping technique could be developed for clinical use to stratify regions of risks of re-entrant ventricular tachyarrhythmias without the need for ambiguous unipolar repol time annotations. The QRS-T angle described here to assess repol heterogeneities is analogous to that in surface vector cardiography but provides intracardiac regional localization on the mapping surface that is actionable.