4-(6-(4-dibutylaminophenyl)-1-3-5-hexatrienyl)-1-(4--sulfobutyl)pyridinium and rhod-2

Fluorescence imaging has become a common modality in cardiac electrodynamics. A single fluorescent parameter is typically measured. Given the growing emphasis on simultaneous imaging of more than one cardiac variable, we present an analysis of the potential of dual camera imaging, using as an example our straightforward dual camera system that allows simultaneous measurement of two dynamic quantities from the same region of the heart. The advantages of our system over others include an optional software camera calibration routine that eliminates the need for precise camera alignment. The system allows for rapid setup, dichroic image separation, dual-rate imaging, and high spatial resolution, and it is generally applicable to any two-camera measurement. This type of imaging system offers the potential for recording simultaneously not only transmembrane potential and intracellular calcium, two frequently measured quantities, but also other signals more directly related to myocardial metabolism, such as [K(+)](e), NADH, and reactive oxygen species, leading to the possibility of correlative multimodal cardiac imaging. We provide a compilation of dye and camera information critical to the design of dual camera systems and experiments.

Topics: Algorithms; Animals; Calcium; Computer Simulation; Electrophysiologic Techniques, Cardiac; Heart Ventricles; Heterocyclic Compounds, 3-Ring; Imaging, Three-Dimensional; In Vitro Techniques; Myocardium; NAD; Pyridinium Compounds; Rabbits; Spectrometry, Fluorescence

In the heart, membrane voltage (Vm) and intracellular Ca (Cai) are bidirectionally coupled, so that ionic membrane currents regulate Cai cycling and Cai affects ionic currents regulating action potential duration (APD). Although Cai reliably and consistently tracks Vm at normal heart rates, it is possible that at very rapid rates, sarcoplasmic reticulum Cai cycling may exhibit intrinsic dynamics. Non-voltage-gated Cai release might cause local alternations in APD and refractoriness that influence wavebreak during ventricular fibrillation (VF). In this study, we tested this hypothesis by examining the extent to which Cai is associated with Vm during VF. Cai transients were mapped optically in isolated arterially perfused swine right ventricles using the fluorescent dye rhod 2 AM while intracellular membrane potential was simultaneously recorded either locally with a microelectrode (5 preparations) or globally with the voltage-sensitive dye RH-237 (5 preparations). Mutual information (MI) is a quantitative statistical measure of the extent to which knowledge of one variable (Vm) predicts the value of a second variable (Cai). MI was high during pacing and ventricular tachycardia (VT; 1.13 +/- 0.21 and 1.69 +/- 0.18, respectively) but fell dramatically during VF (0.28 +/- 0.06, P < 0.001). Cai at sites 4-6 mm apart also showed decreased MI during VF (0.63 +/- 0.13) compared with pacing (1.59 +/- 0.34, P < 0.001) or VT (2.05 +/- 0.67, P < 0.001). Spatially, Cai waves usually bore no relationship to membrane depolarization waves during nonreentrant fractionated waves typical of VF, whereas they tracked each other closely during pacing and VT. The dominant frequencies of Vm and Cai signals analyzed by fast Fourier transform were similar during VT but differed significantly during VF. Cai is closely associated with Vm closely during pacing and VT but not during VF. These findings suggest that during VF, non-voltage-gated Cai release events occur and may influence wavebreak by altering Vm and APD locally.

Topics: Animals; Calcium; Cardiac Pacing, Artificial; Electrophysiology; Female; Fluorescent Dyes; Fourier Analysis; Heterocyclic Compounds, 3-Ring; Intracellular Membranes; Male; Membrane Potentials; Models, Cardiovascular; Pyridinium Compounds; Swine; Tachycardia, Ventricular; Ventricular Fibrillation