Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC155
Pathological Transmural Electrophysiological Heterogeneity Investigated by Dual Wavelength Optical Mapping
T. Quinn1,2, S. Dutta3, M. J. Bishop3, P. Lee2, P. Kohl1,2, B. Rodriguez3
1. National Heart and Lung Institute, Imperial College London, Middlesex, United Kingdom. 2. Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom. 3. Computing Laboratory, University of Oxford, Oxford, United Kingdom.
Introduction: The depth of myocardium in which voltage-sensitive dyes for optical mapping are excited depends on excitation wavelength, due to differences in tissue penetration. Combined short and long wavelength excitation has been used for imaging transmural electrophysiological properties in intact hearts (Walton et al., 2010). We hypothesized that dual wavelength excitation can be used to reveal pathological transmural electrophysiological heterogeneity, such as occurs with ischaemia. Methods: Langendorff-perfused rabbit hearts (1 kg female, n = 5) were stained with voltage-sensitive dye (20 μM bolus of di-4-ANBDQPQ), excitation-contraction uncoupled (10 μM blebbistatin), paced at the apex, and subjected to global no-flow ischaemia. Fluorescence was excited using camera frame-synchronized LEDs (Lee et al., 2011), alternating 470 ± 10 nm (shallow penetration) and 640 ± 10 nm (deep penetration), and >690 nm emission acquired at 922 Hz (64 x 64 pixel, 16-bit CCD camera). Measurements were made for the first 10 min of ischaemia with pacing at 2 Hz, followed by a progressive increase in pacing rate. Computer simulations, representing both electrophysiological changes during no-flow ischaemia (including epicardial border zone) (Tice et al., 2007) and photon scattering effects (Bishop et al., 2006), were used for experimental data interpretation. Results: Control recordings showed no discernable difference in action potential (AP) morphology between the two excitation wavelengths. However, after 5 min of ischaemia, clear differences appeared, with reduced upstroke velocity and AP duration at 640 nm compared to 470 nm, which increased with the time of ischaemia. Simulations showed a similar effect and revealed that differences are caused by enhanced wavefront curvature due to increased transmural heterogeneity with ischaemia. When pacing rate was increased, further areas of transmural heterogeneities appeared, resulting in the induction of ventricular tachycardia, which was not the case for control. Conclusion: Thus, dual wavelength optical mapping can reveal pathological transmural electrophysiological heterogeneity in the whole heart and may be useful for investigating its role in the initiation and sustenance of arrhythmias.
Where applicable, experiments conform with Society ethical requirements