Panoramic hyperspectral optical mapping of cardiac membrane potential and tissue type.

Abstract

Significance: Cardiac panoramic optical mapping is a powerful approach for studying action potential dispersion and mapping arrhythmia triggers and propagation pathways over the entire surface of the heart. However, tissue type (muscle, connective tissue, and infarct scar) is also important for interpreting mapping data and is difficult to identify using optical mapping data alone.

Aim: Panoramically map transmembrane potential and tissue type from the surface of infarcted hearts for correlative analysis of cardiac structure and function.

Approach: We developed a multimodal panoramic imaging system to map epicardial tissue type (determined by collagen content) using a line-scan hyperspectral camera and a precision stage to translate and rotate the heart while illuminating the epicardial surface with UV light. Transmembrane potential was subsequently optically mapped by imaging a potentiometric probe with four high speed CMOS cameras position around the heart. The epicardial surface was reconstructed for each heart using images acquired every 3.6 deg of rotation, onto which hyperspectral and optical mapping data were texture mapped. All cameras were registered to one coordinate frame using a calibration procedure.

Results: This system combines, for the first time, high-resolution hyperspectral imaging with optical mapping for quantitative correlative tissue structure-function analyses. It was used to study excitation wave propagation and action potentials across the surface of perfused rat hearts having a four-week-old infarct. The spectral band of collagen fluorescence (400 to 520 nm) revealed infarcted and border zone tissue. PVCs and reentrant activity were observed in 3 of 4 hearts at S1-S2 pacing intervals between 80 and 65 msec (S1 = 150 msec). PVCs originated near the infarct border and propagated around the infarct. Using the integral of spectral intensity from 400 to 435 nm, a k-means clustering algorithm classified each mapped site as either healthy, border zone, or infarcted tissue. Average action potential duration within those tissue types was longest for infarcted tissue, shorter for border zone tissue, and shortest for healthy tissue, a preliminary result that is consistent with the effect of an infarct on ventricular electrophysiology.

Conclusions: This work demonstrates that panoramic hyperspectral mapping of tissue type and transmembrane potential is a powerful approach that enables functional mapping data to be analyzed within the context of local tissue type (healthy, infarct, and border) in living hearts.