Intracardiac light catheter for rapid scanning transmural absorbance spectroscopy of perfused myocardium: measurement of myoglobin oxygenation and mitochondria redox state

Abstract

Absorbance spectroscopy of intrinsic cardiac chromophores provides nondestructive assessment of cytosolic oxygenation and mitochondria redox state. Isolated perfused heart spectroscopy is usually conducted by collecting reflected light from the heart surface, which represents a combination of surface scattering events and light that traversed portions of the myocardium. Reflectance spectroscopy with complex surface scattering effects in the beating heart leads to difficulty in quantitating chromophore absorbance. In this study, surface scattering was minimized and transmural path length optimized by placing a light source within the left ventricular chamber while monitoring transmurally transmitted light at the epicardial surface. The custom-designed intrachamber light catheter was a flexible coaxial cable (2.42-Fr) terminated with an encapsulated side-firing LED of 1.8 × 0.8 mm, altogether similar in size to a Millar pressure catheter. The LED catheter had minimal impact on aortic flow and heart rate in Langendorff perfusion and did not impact stability of the left ventricule of the working heart. Changes in transmural absorbance spectra were deconvoluted using a library of chromophore reference spectra to quantify the relative contribution of specific chromophores to the changes in measured absorbance. This broad-band spectral deconvolution approach eliminated errors that may result from simple dual-wavelength absorbance intensity. The myoglobin oxygenation level was only 82.2 ± 3.0%, whereas cytochrome and cytochrome + were 13.3 ± 1.4% and 12.6 ± 2.2% reduced, respectively, in the Langendorff-perfused heart. The intracardiac illumination strategy permits transmural optical absorbance spectroscopy in perfused hearts, which provides a noninvasive real-time monitor of cytosolic oxygenation and mitochondria redox state. Here, a novel nondestructive real-time approach for monitoring intrinsic indicators of cardiac metabolism and oxygenation is described using a catheter-based transillumination of the left ventricular free wall together with complete spectral analysis of transmitted light. This approach is a significant improvement in the quality of cardiac optical absorbance spectroscopic metabolic analyses.

Intra-cardiac Side-Firing Light Catheter for Monitoring Cellular Metabolism using Transmural Absorbance Spectroscopy of Perfused Mammalian Hearts

“…Using the cyanide data as an estimate of total myoglobin oxygenation and the ischemia data for fully deoxygenated myoglobin, we estimate that under control conditions myoglobin was only 88.2% ± 1.0% (n = 10) oxygenated, consistent with prior studies 20,21,25 . .…”

“…. With the cessation of oxygen consumption, the oxygen tension in the tissue should approach the perfusate and we noted an early increase in oxygenated myoglobin with cyanide consistent with the notion that the saline perfused heart, even in retrograde perfusion modes, is not fully oxygenating myoglobin in the cytosol 19,20,21,36 . Comparing the maximum effect of cyanide on oxygenated myoglobin with the fully deoxygenated spectrum obtained with ischemia reveals a myoglobin oxygenation of only about 88%, consistent with previous studies.…”

“…The VWTOS data is analyzed using full spectral fitting routine based on a reference library of spectra of cardiac chromophores and the spectrum of the light source as previously described 20,22,27,35 with a simple linear least squares approach. This spectral fitting procedure compensated for overlapping absorbance spectrum and does not rely on "isobestic" wavelengths.…”

“…The limitations of reflectance absorption spectroscopy presented above were resolved by introducing an optical catheter into the left ventricle cavity, permitting the collection of transmitted light across the left ventricle free wall 20 . The benefits of transmission spectroscopy for this type of study was appreciated in early invasive studies by Tamura et al 9 The current implementation provides a very robust transmission absorption spectroscopy analysis of the intact heart with regards to cytosolic oxygenation and mitochondria redox state under a variety of conditions 21 .…”

“…This approach allows the use of a wide variety of external light sources including lasers for applications such as Raman scattering spectroscopy. To quantify this data, an online full multicomponent spectral analysis using known reference spectra to improve the accuracy of the spectroscopic determination of cardiac chromophores is presented as previously described 20,22 . The source code for this analysis will be provided by the authors upon request.…”