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PubMed2002

Anisotropic conduction properties in canine atria analyzed by high-resolution optical mapping: preferential direction of conduction block changes from longitudinal to transverse with increasing age.

BACKGROUND: Anisotropic conduction properties may provide a substrate for reentrant arrhythmias. We investigated the age-dependent changes of structural and functional anisotropy in isolated right atria from infant (1 to 2 months), young (6 to 12 months), and old (6 to 10 years) dogs. METHODS AND RESULTS: The histology of the mapped atrial tissues (a small subepicardial area, 2.8x4.2 mm) was characterized by an age-dependent increase of myofiber width and fat cell infiltration between myofibers. Cx43 was distributed homogeneously over the entire cell surface in infant dogs, whereas it progressively polarized to the cell termini with increasing age. The activation sequences were analyzed by high-resolution optical mapping using a voltage-sensitive dye. Activation fronts from the pacing site proceeded more rapidly along fiber orientation (longitudinal) than across it (transverse). Infant dogs showed "elliptical" isochrones with a smooth transition between longitudinal and transverse propagation, whereas old dogs had a "square" pattern with a sharp transition. Conduction block occurred predominantly during longitudinal propagation in infant dogs but during transverse propagation in old dogs. The shape of the wave front and the degree of lateral uncoupling seemed to decide the preferential direction of block. A zigzag activation causing an extremely slow transverse conduction was observed only in old dogs. CONCLUSIONS: Along with the age-dependent structural anisotropy, the preferential direction of block changed from longitudinal to transverse in association with a change in the wave front configuration. A zigzag propagation based on lateral uncoupling would predispose the elderly to multiple reentry and a higher incidence of atrial fibrillation.

Action Potentials↗
PubMed2004

Optical mapping of propagation changes induced by elevated extracellular potassium ion concentration in genetically altered mouse hearts.

UNLABELLED: Diabetes is associated with high rates of cardiovascular disease and sudden death. Therefore, dissecting specific mechanisms, such as the effects of impaired insulin signaling on cardiac electrophysiology may lead to better diagnosis and treatment. Lack of insulin receptors in mouse myocytes has been shown to reduce repolarizing potassium currents and prolong action potential duration. We hypothesized that these changes would manifest as rate-related effects on electrical propagation in the intact heart. This study employed optical mapping to characterize propagation changes in intact mouse hearts with cardiomyocyte-restricted knock out of insulin receptors (CIRKO). METHODS: Fluorescent signals emitted from excited Di-4-ANEPPS in isolated Langendorff perfused mouse hearts were recorded from the left ventricular epicardium using an 8 by 8 photo diode array. The study included hearts from 8 CIRKO mice and 8 wild type (WT) littermate controls. Hearts were stimulated from the right atrium or the left ventricle at basic cycle lengths ranging from 160 to 280 ms under normal conditions and then after 5 minutes of perfusion with elevated potassium ion concentration (9.4 mM). RESULTS: None of the 8 CIRKO hearts maintained regular responses to atrial stimulation at the 160 ms cycle length under normal conditions; however, all of the WT hearts were captured at this rate. Total activation time for a 4 mm by 4 mm area was longer for CIRKO hearts when compared with WT. Average epicardial conduction velocity was slower for the CIRKO when compared to WT. Propagation delay due to the presence of high [K+]e was significant in both CIRKO and WT mice, but significantly longer for the CIRKO hearts. CONCLUSIONS: These results show that in addition to reducing repolarization currents, impaired myocardial insulin signaling leads to impaired electrical impulse propagation particularly at increased heart rates. These data suggest a link between impaired myocardial insulin signaling and the increased risk of arrhythmia and sudden death in patients with diabetes.

Action Potentials↗
PubMed2003

Optical mapping of transmural activation induced by electrical shocks in isolated left ventricular wall wedge preparations.

INTRODUCTION: It is believed that electrical shocks interrupt fibrillation by directly stimulating the bulk of ventricular myocardium in excitable states, but how shocks activate intramural tissue layers is not known. In this study, Vm responses and transmural activation patterns induced by shocks during diastole were measured in isolated coronary perfused preparations of porcine left ventricle. METHODS AND RESULTS: Rectangular shocks (duration = 10 ms; field strength, E = 1-44 V/cm) were applied across preparations (thickness = 14.9 +/- 2.5 mm, n = 9) via large mesh electrodes during diastole or action potential (AP) plateau. Vm responses at the transmural surface were measured using optical mapping technique (resolution = 1.2 mm). Depending on shock strength, three types of Vm responses were observed. (1) Weak shocks (E approximately 1-4 V/cm) applied in diastole induced APs with simple monophasic upstrokes. The latency and time of transmural activation (TTA) rapidly decreased with increasing shock strength. Earliest activation occurred predominantly at the cathodal side of preparations in the areas that exhibited maximal DeltaVm during AP plateau. (2) Intermediate shocks (E approximately 4-23 V/cm) induced monophasic and biphasic upstrokes that were paralleled with predominantly negative plateau DeltaVm. Activation was initiated at multiple transmural sites and rapidly spread across the myocardial wall (TTA = 0.6 +/- 0.2 ms). (3) Very strong shocks (E approximately 23-44 V/cm) could cause triphasic upstrokes, likely reflecting occurrence of membrane electroporation, and delayed activation (TTA = 6.7 +/- 3.8 ms) at sites of largest negative plateau DeltaVm. CONCLUSION: Shocks applied during diastole cause direct and rapid (within 1 ms) activation of ventricular bulk over a wide range of shock strengths, supporting the excitatory hypothesis of defibrillation. Very strong shocks can cause multiphasic Vm responses and delayed activation.

Action Potentials↗
PubMed2003

Optical mapping reveals conduction slowing and impulse block in iron-overload cardiomyopathy.

Cardiac disease with arrhythmia or heart failure is the leading cause of death in patients with thalassemia major and a major complication of other forms of iron overload. Current antiarrhythmic treatment does not appear to alter the clinical course. Using a gerbil model of iron-overload cardiomyopathy, we previously observed a reduction in the fast inward sodium current in isolated cardiomyocytes. Electrocardiograms (ECGs) in the same gerbil model indicate PR-interval prolongation, QRS-interval widening, and arrhythmias. We hypothesize that such changes in the ECG in this model are the result of abnormal action-potential conduction at the level of the whole heart. To test this hypothesis, we took ECGs and recorded action potentials using high-resolution optical mapping from the anterior surface of 9 iron-overloaded and 9 age-matched control ventricular-paced, Langendorff-perfused gerbil hearts. The iron-overloaded gerbils received weekly iron-dextran injections of 800 mg/kg for 14 to 18 weeks. ECGs showed QRS- and PR-interval prolongation in iron-treated gerbils compared with that in controls. In addition, atrioventricular block was observed in 2 of 6 iron-treated gerbils but not in controls. Conduction velocity was significantly slower in iron-treated gerbils than in controls. At normal pacing rates, abnormal activation patterns caused by stable regions of conduction block were observed in iron-overloaded gerbils (33%) but not in controls. Such abnormal impulse conduction may be a mechanism of increased arrhythmia vulnerability in iron-overload cardiomyopathy.

Action Potentials↗
PubMed2005

Optical mapping of electrical activation in the developing heart.

Specialized conduction tissues mediate coordinated propagation of electrical activity through the adult vertebrate heart. Following activation of the atria, the activation wave is slowed down in the atrioventricular canal or node, after which it spreads rapidly into the left and right ventricles via the His-Purkinje system (HPS). This results in the ventricles being activated from the apex toward the base, which is a hallmark of HPS function. The development of mature HPS function follows significant phases of cardiac morphogenesis. Initially, the cardiac impulse propagates in a slow, linear, and isotropic fashion from the sinus venosus at the most caudal portion of the tubular heart. Although the speed of impulse propagation gradually increases as it travels toward the anterior regions of the heart tube, the actual sequence of ventricular activation in the looped heart proceeds in the same direction as blood flow. Eventually, the immature base-to-apex sequence of ventricular activation undergoes an apparent reversal, changing to the mature apex-to-base pattern. Using an optical mapping approach, we demonstrate that the timing of this last transition shows striking dependence on hemodynamic loading of the ventricle, being accelerated by pressure overload and delayed in left ventricular hypoplasia. Comparison of chick and mammalian hearts revealed some striking similarities as well as key differences in the timing of such events during cardiac organogenesis.

Action Potentials↗
PubMed2000

High-resolution optical mapping of the right bundle branch in connexin40 knockout mice reveals slow conduction in the specialized conduction system.

Connexin40 (Cx40) is a major gap junction protein that is expressed in the His-Purkinje system and thought to be a critical determinant of cell-to-cell communication and conduction of electrical impulses. Video maps of the ventricular epicardium and the proximal segment of the right bundle branch (RBB) were obtained using a high-speed CCD camera while simultaneously recording volume-conducted ECGs. In Cx40(-/-) mice, the PR interval was prolonged (47.4+/-1.4 in wild-type [WT] [n=6] and 57.5+/-2.8 in Cx40(-/-) [n=6]; P<0.01). WT ventricular epicardial activation was characterized by focused breakthroughs that originated first on the right ventricle (RV) and then the left ventricle (LV). In Cx40(-/-) hearts, the RV breakthrough occurred after the LV breakthrough. Additionally, Cx40(-/-) mice showed RV breakthrough times that were significantly delayed with respect to QRS complex onset (3.7+/-0.7 ms in WT [n=6] and 6.5+/-0.7 ms in Cx40(-/-) [n=6]; P<0.01), whereas LV breakthrough times did not change. Conduction velocity measurements from optical mapping of the RBB revealed slow conduction in Cx40(-/-) mice (74.5+/-3 cm/s in WT [n=7] and 43.7+/-6 cm/s in Cx40(-/-) [n=7]; P<0.01). In addition, simultaneous ECG records demonstrated significant delays in Cx40(-/-) RBB activation time with respect to P time (P-RBB time; 41.6+/-1.9 ms in WT [n=7] and 55.1+/-1.3 ms in [n=7]; P<0.01). These data represent the first direct demonstration of conduction defects in the specialized conduction system of Cx40(-/-) mice and provide new insight into the role of gap junctions in cardiac impulse propagation.

Acetylthiocholine↗
PubMed2003

Optical mapping of the spread of excitation in the isolated rat atrium during tachycardia-like excitation.

Multiple-site optical recording of membrane potential activity, using the voltage-sensitive merocyanine-rhodanine dye NK2761 and a multiple-element photodiode array, was employed to monitor action potentials in an isolated rat atrial preparation. The events of tachycardia-like excitation (TE) were evoked by electrical stimulation. The conduction pattern of excitation was assessed optically by timing the feet of optical action potentials, then maps of excitation spread patterns were made. The excitatory waves often rotated around the blocked area including the ostium of the superior vena cava. Other patterns, such as reentry without anatomical obstacles, ectopic pacemaker and more complex patterns, were sometimes observed. Optical mapping during the initiation phase of TE indicated that the decrease of the conduction velocity and the appearance of blocked areas contributed the establishment of TE. On the basis of the characteristics of TE, it is suggested that TE is a metastable state of atrial rhythm. TE appears to be analogous to atrial flutter.

Action Potentials↗
PubMed1995

Cardiac tissue geometry as a determinant of unidirectional conduction block: assessment of microscopic excitation spread by optical mapping in patterned cell cultures and in a computer model.

OBJECTIVE: Unidirectional conduction block (UCB) and reentry may occur as a consequence of an abrupt tissue expansion and a related change in the electrical load. The aim of this study was to evaluate critical dimensions of the tissue necessary for establishing UCB in heart cell culture. METHODS: Neonatal rat heart cell cultures with cell strands of variable width emerging into a large cell area were grown using a technique of patterned cell growth. Action potential upstrokes were measured using a voltage sensitive dye (RH-237) and a linear array of 10 photodiodes with a 15 microns resolution. A mathematical model was used to relate action potential wave shapes to underlying ionic currents. RESULTS: UCB (block of a single impulse in anterograde direction - from a strand to a large area - and conduction in the retrograde direction) occurred in narrow cell strands with a width of 15(SD 4) microns (1-2 cells in width, n = 7) and there was no conduction block in strands with a width of 31(8) microns (n = 9, P < 0.001) or larger. The analysis of action potential waveshapes indicated that conduction block was either due to geometrical expansion alone (n = 5) or to additional local depression of conduction (n = 2). In wide strands, action potential upstrokes during anterograde conduction were characterised by multiple rising phases. Mathematical modelling showed that two rising phases were caused by electronic current flow, whereas local ionic current did not coincide with the rising portions of the upstrokes. CONCLUSIONS: (1) High resolution optical mapping shows multiphasic action potential upstrokes at the region of abrupt expansion. At the site of the maximum decrement in conduction, these peaks were largely determined by the electrotonus and not by the local ionic current. (2) Unidirectional conduction block occurred in strands with a width of 15(4) microns (1-2 cells).

Action Potentials↗
PubMed2006

Using recurrence quantification analysis determinism for noise removal in cardiac optical mapping.

Selecting signal processing parameters in optical imaging by utilizing the change in Determinism, a measure introduced in Recurrence Quantification Analysis, provides a novel method using the change in residual noise Determinism for improving noise quantification and removal across signals exhibiting disparate underlying tissue pathologies. The method illustrates an improved process for selecting filtering parameters and how using measured signal-to-noise ratio alone can lead to improper parameter selection.

Algorithms↗
PubMed2001

Optical mapping approaches to cardiac electrophysiological functions.

Recently, optical methods for monitoring membrane potential with fast voltage-sensitive dyes have been introduced as a powerful tool for studying cardiac electrical functions. These methods offer two principal advantages over more conventional electrophysiological techniques. One is that optical recordings may be made from very small cells that are inaccessible to microelectrode impalement, and the other is that multiple sites/regions of a preparation can be monitored simultaneously to provide spatially resolved mapping of electrical activity. The former has made it possible to record spontaneous electrical activities in early embryonic precontractile hearts, and the latter has been applied for mapping of the propagation patterns of electrical activities in the cardiac tissue. In this article, optical studies of the electrophysiological function of the vertebrate heart are reviewed.

Animals↗
PubMed2000

Model-based analysis of optically mapped epicardial activation patterns and conduction velocity.

A novel parametric model-based method was developed to quantify epicardial conduction patterns and velocity in an isolated Langendorff-perfused rabbit heart. The method incorporated geometric and anatomical features of the left and right ventricles into the analysis. Optical images of propagation were obtained using the voltage-sensitive dye DI-4-ANEPPS, and a high-speed digital camera. Activation maps were extracted from these images and interpolated onto a three-dimensional finite-element model of epicardial geometry and fiber structure. Activation time was expressed as a function of local parametric coordinates, and a conduction velocity vector field was computed from the gradient of the scalar field. Activation times measured using bipolar electrodes did not differ significantly from times measured using the optical mapping technique. The method was able to detect a 34% decrease in average fiber velocity and a 28% decrease in average cross-fiber velocity following the addition of 0.5 mM heptanol into the perfusate. The combination of optical mapping with a three-dimensional geometric model of the ventricles provides a new tool to quantify wave-front propagation relative to anatomy at a relatively high spatial resolution.

Animals↗
PubMed1984

Analysis of an optical mapping technique for lung function studies.

An optical technique for lung function measurement studies is described and analysed. Procedures which permit the reconstruction of three dimensional data concerning the thoraco-abdominal wall are developed and methods for calculating volumes, surface areas and cross-sections are outlined.

Humans↗
PubMed2006

Synthesis of voltage-sensitive optical signals: application to panoramic optical mapping.

Fluorescent photon scattering is known to distort optical recordings of cardiac transmembrane potentials; however, this process is not well quantified, hampering interpretation of experimental data. This study presents a novel model, which accurately synthesizes fluorescent recordings over the irregular geometry of the rabbit ventricles. Using the model, the study aims to provide quantification of fluorescent signal distortion for different optical characteristics of the preparation and of the surrounding medium. A bi-domain representation of electrical activity is combined with finite element solutions to the photon diffusion equation simulating both the excitation and emission processes, along with physically realistic boundary conditions at the epicardium, which allow simulation of different experimental setups. We demonstrate that distortion in the optical signal as a result of fluorescent photon scattering is truly a three-dimensional phenomenon and depends critically upon the geometry of the preparation, the scattering properties of the tissue, the direction of wavefront propagation, and the specifics of the experimental setup. Importantly, we show that in an anatomically accurate model of ventricular geometry and fiber orientation, the morphology of the optical signal does not provide reliable information regarding the intramural direction of wavefront propagation. These findings underscore the potential of the new model in interpreting experimental data.

Animals↗
PubMed2001

In vivo optical mapping of epileptic foci and surround inhibition in ferret cerebral cortex.

The population of neurons participating in an epileptiform event varies from moment to moment. Most techniques currently used to localize epileptiform events in vivo have spatial and/or temporal sampling limitations. Here we show in an animal model that optical imaging based on intrinsic signals is an excellent method for in vivo mapping of clinically relevant epileptiform events, such as interictal spikes, ictal onsets, ictal spread and secondary homotopic foci. In addition, a decrease in the optical signal correlates spatially with a decrease in neuronal activity recorded from cortex surrounding an epileptic focus. Optical mapping of epilepsy might be a useful adjunct in the surgical treatment of neocortical epilepsy, which critically depends on the precise localization of intrinsically epileptogenic neurons.

Animals↗
PubMed1998

Optical mapping of atrioventricular node reveals a conduction barrier between atrial and nodal cells.

The mechanisms responsible for atrioventricular (AV) delay remain unclear, in part due to the inability to map electrical activity by conventional microelectrode techniques. In this study, voltage-sensitive dyes and imaging techniques were refined to detect action potentials (APs) from the small cells comprising the AV node and to map activation from the "compact" node. Optical APs (124) were recorded from 5 x 5 mm (approximately 0.5-mm depth) AV zones of perfused rabbit hearts stained with a voltage-sensitive dye. Signals from the node exhibited a set of three spikes; the first and third (peaks I and III) were coincident with atrial (A) and ventricular (V) electrograms, respectively. The second spike (peak II) represented the firing of midnodal (N) and/or lower nodal (NH) cell APs as indicated by their small amplitude, propagation pattern, location determined from superimposition of activation maps and histological sections of the node region, dependence on depth of focus, and insensitivity to tetrodotoxin (TTX). AV delays consisted of tau 1 (49.5 +/- 6.59 ms, 300-ms cycle length), the interval between peaks I and II (perhaps AN to N cells), and tau 2 (57.57 +/- 5.15 ms), the interval between peaks II and III (N to V cells). The conductance time across the node was 10.33 +/- 3.21 ms, indicating an apparent conduction velocity (theta N) of 0.162 +/- 0.02 m/s (n = 9) that was insensitive to TTX. In contrast, tau 1 correlated with changes in AV node delays (measured with surface electrodes) caused by changes in heart rate or perfusion with acetylcholine. The data provide the first maps of activation across the AV node and demonstrate that theta N is faster than previously presumed. These findings are inconsistent with theories of decremental conduction and prove the existence of a conduction barrier between the atrium and the AV node that is an important determinant of AV node delay.

Acetylcholine↗
PubMed2003

Simultaneous electrical and optical mapping in rabbit hearts.

Local cardiac excitation is measured from either extracellular voltage (Ve) or optical transmembrane voltage (Vm) with fluorescent dye. We used a transparent electrode array and a laser scanner to test whether Ve and coepicentral optical Vm give equivalent excitation times during epicardial pacing and sinus beats. To help explain time differences, we estimated interrogation width/depth ratios for Ve and optical Vm with dipole and Monte Carlo models. Magnitudes of time differences between excitation measured with Ve and optical Vm during pacing were 1.9 +/- 1.9 ms (n= 1,112 recording pairs). Deeper interrogation for optical Vm vs Ve was indicated with sinus beats that contained a transmural propagation component. When pacing produced propagation along epicardial fibers, excitation time measured from optical Vm was later than excitation time measured with epicardial Ve. When pacing produced propagation across epicardial fibers, excitation time measured from optical Vm was earlier than that measured with epicardial Ve. These time differences could be attributed to deeper optical interrogation and fiber rotation with depth in ventricles.

Action Potentials↗
PubMed1985

Optical mapping of electrical activity in rat somatosensory and visual cortex.

We have investigated the use of optical methods for monitoring neuron activity in mammalian cortex. The cortex was stained with a voltage-sensitive dye and fluorescence was simultaneously measured from 124 areas using a photodiode array. Optical signals were detected in rat somatosensory cortex in response to small whisker movements and in visual cortex in response to light flashes to the eye. Relatively large signals were obtained during focal interictal epileptiform discharges induced by bicuculline. The measuring system had a time resolution of milliseconds and a spatial resolution of a few hundred micrometers. Simultaneous, multi-site optical recordings of activity may provide a new and potentially powerful method for studying function and dysfunction in mammalian cortex.

Animals↗