03382nas a2200349 4500008004100000022001400041245008900055210006900144260001200213300001100225490000700236520236800243653002202611653001502633653001202648653003502660653001602695653002402711653002602735653002102761653004002782653002702822653001002849653002502859653002002884100001702904700001902921700001402940700001702954700001402971856004702985 1997 eng d a0090-696400aTechnical features of a CCD video camera system to record cardiac fluorescence data.0 aTechnical features of a CCD video camera system to record cardia c07/1997 a713-250 v253 a

A charge-coupled device (CCD) camera was used to acquire movies of transmembrane activity from thin slices of sheep ventricular epicardial muscle stained with a voltage-sensitive dye. Compared with photodiodes, CCDs have high spatial resolution, but low temporal resolution. Spatial resolution in our system ranged from 0.04 to 0.14 mm/pixel; the acquisition rate was 60, 120, or 240 frames/sec. Propagating waves were readily visualized after subtraction of a background image. The optical signal had an amplitude of 1 to 6 gray levels, with signal-to-noise ratios between 1.5 and 4.4. Because CCD cameras integrate light over the frame interval, moving objects, including propagating waves, are blurred in the resulting movies. A computer model of such an integrating imaging system was developed to study the effects of blur, noise, filtering, and quantization on the ability to measure conduction velocity and action potential duration (APD). The model indicated that blurring, filtering, and quantization do not affect the ability to localize wave fronts in the optical data (i.e., no systematic error in determining spatial position), but noise does increase the uncertainty of the measurements. The model also showed that the low frame rates of the CCD camera introduced a systematic error in the calculation of APD: for cutoff levels > 50%, the APD was erroneously long. Both noise and quantization increased the uncertainty in the APD measurements. The optical measures of conduction velocity were not significantly different from those measured simultaneously with microelectrodes. Optical APDs, however, were longer than the electrically recorded APDs. This APD error could be reduced by using the 50% cutoff level and the fastest frame rate possible.

10aAction Potentials10aAlgorithms10aAnimals10aBody Surface Potential Mapping10aCalibration10aComputer Simulation10aElectric Conductivity10aFluorescent Dyes10aImage Processing, Computer-Assisted10aModels, Cardiovascular10aSheep10aVentricular Function10aVideo Recording1 aBaxter, Bill1 aDavidenko, J M1 aLoew, L M1 aWuskell, J P1 aJalife, J uhttp://www.ncbi.nlm.nih.gov/pubmed/923698303423nas a2200337 4500008004100000022001400041245009300055210006900148260001200217300001200229490000700241520247800248653001202726653002402738653002602762653001002788653001602798653002802814653001102842653002702853653002902880653001002909653002602919100001202945700001702957700001702974700001902991700001403010700001403024856004703038 1994 eng d a0009-733000aWave-front curvature as a cause of slow conduction and block in isolated cardiac muscle.0 aWavefront curvature as a cause of slow conduction and block in i c12/1994 a1014-280 v753 a

We have investigated the role of wave-front curvature on propagation by following the wave front that was diffracted through a narrow isthmus created in a two-dimensional ionic model (Luo-Rudy) of ventricular muscle and in a thin (0.5-mm) sheet of sheep ventricular epicardial muscle. The electrical activity in the experimental preparations was imaged by using a high-resolution video camera that monitored the changes in fluorescence of the potentiometric dye di-4-ANEPPS on the surface of the tissue. Isthmuses were created both parallel and perpendicular to the fiber orientation. In both numerical and biological experiments, when a planar wave front reached the isthmus, it was diffracted to an elliptical wave front whose pronounced curvature was very similar to that of a wave front initiated by point stimulation. In addition, the velocity of propagation was reduced in relation to that of the original planar wave. Furthermore, as shown by the numerical results, wave-front curvature changed as a function of the distance from the isthmus. Such changes in local curvature were accompanied by corresponding changes in velocity of propagation. In the model, the critical isthmus width was 200 microns for longitudinal propagation and 600 microns for transverse propagation of a single planar wave initiated proximal to the isthmus. In the experiments, propagation depended on the width of the isthmus for a fixed stimulation frequency. Propagation through an isthmus of fixed width was rate dependent both along and across fibers. Thus, the critical isthmus width for propagation was estimated in both directions for different frequencies of stimulation. In the longitudinal direction, for cycle lengths between 200 and 500 milliseconds, the critical width was < 1 mm; for 150 milliseconds, it was estimated to be between 1.3 and 2 mm; and for the maximum frequency of stimulation (117 +/- 15 milliseconds), it was > 2.5 mm. In the transverse direction, critical width was between 1.78 and 2.32 mm for a basic cycle length of 200 milliseconds. It increased to values between 2.46 and 3.53 mm for a basic cycle length of 150 milliseconds. The overall results demonstrate that the curvature of the wave front plays an important role in propagation in two-dimensional cardiac muscle and that changes in curvature may cause slow conduction or block.

10aAnimals10aComputer Simulation10aElectric Conductivity10aHeart10aHeart Block10aHeart Conduction System10aHumans10aModels, Cardiovascular10aMotion Pictures as Topic10aSheep10aStaining and Labeling1 aCabo, C1 aPertsov, A V1 aBaxter, Bill1 aDavidenko, J M1 aGray, R A1 aJalife, J uhttp://www.ncbi.nlm.nih.gov/pubmed/7525101