To the Editor—Response

Abstract

Scientific progress is achieved with methodologic advances bringing new dimensions to ongoing research. Biophotonic imaging is an example of such a breakthrough, replacing conventional electrode mapping in many electrophysiology research laboratories. As with any new method, optical imaging goes through a long process of validation, clarification of misconceptions, and gradual acceptance. A common misconception about optical recordings is that one can directly compare morphology of optical action potentials with their microelectrode counterparts. Many experimental and theoretical studies 1 Efimov I.R. Sidorov V.Y. Cheng Y. et al. Evidence of 3D scroll waves with ribbon-shaped filament as a mechanism of ventricular tachycardia in the isolated rabbit heart. J Cardiovasc Electrophysiol. 1999; 10: 1452-1462 Crossref PubMed Scopus (90) Google Scholar , 2 Hyatt C.J. Mironov S.F. Wellner M. et al. Synthesis of voltage-sensitive fluorescence signals from three-dimensional myocardial activation patterns. Biophys J. 2003; 85: 2673-2683 Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar , 3 Bishop M.J. Rodriguez B. Eason J. et al. Synthesis of voltage-sensitive optical signals: application to panoramic optical mapping. Biophys J. 2006; 90: 2938-2945 Abstract Full Text Full Text PDF PubMed Scopus (65) Google Scholar have shown that, unlike microelectrode recordings, optical action potentials are generated by scattered light originating from an area that depends on optical magnification and mode of illumination: an optical action potential can be recorded from a micron-size patch of cell membrane or from thousands of cells. Thus, direct comparisons of optical and microelectrode action potential morphologies are not justified. In particular, dV/dtmax of an optical action potential is determined by both rate of rise of cell responses and conduction velocity at the recording site. Thus, it is not surprising to see an optical action potential increase of 30 ms at a site where slow conduction is observed. Our earlier study conducted in collaboration with Dr. Mazgalev used both microelectrodes and optical recordings to demonstrate that complex optical action potentials carry signatures of at least two cell layers, including nodal tissue and atrial transitional myocardium. 4 Efimov I.R. Mazgalev T.N. High-resolution three-dimensional fluorescent imaging reveals multilayer conduction pattern in the atrioventricular node. Circulation. 1998; 98: 54-57 Crossref PubMed Scopus (70) Google Scholar To the EditorHeart RhythmVol. 5Issue 3PreviewWhile acknowledging the difficult task of Hucker et al1 in investigating the important subject of autonomic innervation of the atrioventricular junctional pacemaker reported in the October 2007 issue of Heart Rhythm, we believe that certain methodologic limitations have led the authors to unwarranted categorical conclusions. Full-Text PDF