Optical Action Potential Upstroke Morphology Reveals Near-Surface Transmural Propagation Direction

Abstract

Abstract-The analysis of surface-activation patterns and measurements of conduction velocity in ventricular myocardium is complicated by the fact that the electrical wavefront has a complex 3D shape and can approach the heart surface at various angles. Recent theoretical studies suggest that the optical upstroke is sensitive to the subsurface orientation of the wavefront. Our goal here was to (1) establish the quantitative relationship between optical upstroke morphology and subsurface wavefront orientation using computer modeling and (2) test theoretical predictions experimentally in isolated coronary-perfused swine right ventricular preparations. We show in numerical simulations that by suitable placement of linear epicardial stimulating electrodes, the angle of wavefronts with respect to the heart surface can be controlled. Using this method, we developed theoretical predictions of the optical upstroke shape dependence on . We determined that the level V F * at which the rate of rise of the optical upstroke reaches the maximum linearly depends on . A similar relationship was found in simulations with epicardial point stimulation. The optical mapping data were in good agreement with theory. Plane waves propagating parallel to myocardial fibers produced upstrokes with V F *Ͻ0.5, consistent with theoretical predictions for Ͼ0. Similarly, we obtained good agreement with theory for plane waves propagating in a direction perpendicular to fibers (V F *Ͼ0.5 when Ͻ0). Finally, during epicardial point stimulation, we discovered characteristic saddle-shaped V F * maps that were in excellent agreement with theoretically predicted changes in during wavefront expansion. Our findings should allow for improved interpretation of the results of optical mapping of intact heart preparations. Key Words: optical action potential Ⅲ conduction velocity Ⅲ optical mapping Ⅲ voltage-sensitive dye P atterns of electrical activation within the ventricular wall are determined in large part by the specific 3D organization of myocardial fibers. Histological studies of intact hearts from many species have shown conclusively that myocardial fiber orientation rotates significantly across the heart wall. 1 The total angle of rotation across the myocardial wall can reach 180°. 2 Because of the complex transmural organization of myocardial fibers, an excitation wavefront typically assumes a complex 3D profile that, depending on the mode of stimulation, can approach the myocardial surface at a variety of different angles. [3][4][5][6] For this reason, obtaining accurate quantitative information about the wavefront orientation with respect to the surface is quite important for the interpretation of surface recordings, particularly with regard to measurements of conduction velocity.In a recent modeling study, 7 we discovered that the upstroke morphology of optical action potentials (OAPs) was sensitive to the local subsurface orientation of the excitation wavefront. This suggests that analysis of OAP upstroke morphology may prove useful in determini...

Construction and validation of anisotropic and orthotropic ventricular geometries for quantitative predictive cardiac electrophysiology

“…Figure 5c depicts a so-called V F Ã-map, where V F Ã is the fractional level at which the optical upstroke reaches a maximal derivative. As shown in previous studies [54,57,61], V F Ã can be used to infer the average subsurface wavefront orientation shown in figure 5d. The subsurface angle is positive for waves propagating away from the epircardial surface and negative for waves propagating towards the epicardium.…”

“…Signals from 1 mm deep contribute to the optical signal; longer wavelength light (near infrared) is less prone to scattering and absorption, and so novel near-infrared voltage-sensitive dyes [58 -60] with longer excitation wavelengths allow for imaging deeper layers in cardiac tissue [17]. These intramural components to the epi-fluorescence signal can be exploited to provide information about propagation direction within the heart wall [54,61]. The shape of the optically recorded action potential upstroke depends on the orientation of the wavefront: the optical upstroke is fastest near the top of the action potential for waves propagating towards the imaged surface, whereas the faster portion of the upstroke is located near the foot of the action potential when the wave propagates away from the imaged surface.…”

An Experimental Framework to Validate 3D Models of Cardiac Electrophysiology Via Optical Imaging and MRI

“…These findings were validated with other electrical models (i.e. bidomain and Luo-Rudy) [17][18]. It would be very interesting to compare the solution of the Aliev and Panfilov model with the calculated transmembrane potential generated by the flux of photons during the process of illumination and emission.…”

Atria are more susceptible to electroporation than ventricles: Implications for atrial stunning, shock-induced arrhythmia and defibrillation failure

“…These APs had significantly lower amplitudes and two components of upstroke ( Figure 4B) which reflected activation of the deeper layers and scattered light signal from tissue outside of electroporated area ( Figure 4B). We could derive the transmural waveform orientation from the morphology of upstroke of optical AP ( Figure 2A in Online Data Supplement) using the algorithm proposed by Hyatt et al (32) We found increased transmural propagation after shock as a result of the wave front "diving" below the electroporation-induced conduction block and "resurfacing" after passing through the electroporated region (see maps of V max,%APA in Figure 3 and 4).…”