Andrew E Pollard

University of Alabama at Birmingham, Birmingham, AL, United States

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Publications (50)180.87 Total impact

  • Charlotte Mae K Waits, Roger C Barr, Andrew E Pollard
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    ABSTRACT: This study was designed to test the hypothesis that a complex composite impedance (uCI) spectra develops when stimulation and recording of cardiac muscle with sufficiently fine spatial resolution in a four-electrode configuration is employed. With traditional (mm scale) separations, the ratio between the recorded interstitial central potential difference and total supplied interstitial current is constant at all frequencies. This occurs because the fraction of supplied current that redistributes to the intracellular compartment depends on effective membrane resistance between electrodes, which is low, to a much greater extent than effective membrane capacitance. The spectra should therefore change with finer separations at which effective membrane resistance increases, as supplied current will remaining primarily interstitial at lower frequencies and redistribute between compartments at higher frequencies. To test this hypothesis, we built arrays with sensors separated (d) by 804 μm, 452 μm and 252 μm, positioned those arrays across myocyte axes on rabbit ventricular epicardium, and resolved spectra in terms of resistivity (ρt) and reactivity (χt) over the 10 Hz to 4000 Hz range. With all separations, we measured comparable spectra to predictions from passive membrane simulations that used a three-dimensional structural framework in which intracellular, interstitial and membrane properties were prescribed based on the limited data available from the literature. At the finest separation, we found mean ρt at 100 Hz and 4000 Hz that lowered from 395 ohm-cm to 236 ohm-cm, with maximal mean χt of 160 ohm-cm.
    AJP Heart and Circulatory Physiology 04/2014; · 4.01 Impact Factor
  • Delilah J. Huelsing, Andrew E. Pollard
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    ABSTRACT: Purkinje-to-ventricular (P-to-V) propagation and electrotonic modulation of repolarization at discrete Purkinje-ventricular junctions (PVJs) depend on differences in the ionic currents and tissue structure of the P network and the V myocardium. We used computer simulations to assess these membrane and tissue level contributions to P-V interactions. At the membrane level, we used the DiFrancesco-Noble membrane equations to model P ionic kinetics and the Luo-Rudy dynamic membrane equations to model V ionic kinetics. At the tissue level, we modeled the P network as a layer of branching cables, and we modeled a single myocardial sheet with an anisotropic layer of excitable cells. P-to-V propagation was enhanced at the tissue level when multiple wavefronts in the branching P network collided at the PVJ. At the membrane level, P-to-V propagation was enhanced by a reduced transient outward current (Ito) in the P layer. Repolarization at the PVJ was also modulated by both membrane and tissue level contributions. Under nominal conditions, action potential duration (APD) shortened in the P layer and prolonged in the V layer. However, when the V mass was reduced, both P and V cell APDs shortened during coupling with nominal Ito. Subsequent Ito inhibition restored coupling-induced prolongation of the V action potential in the reduced V mass. These results suggest that under physiologic conditions, both membrane and tissue level contributions to P-V interactions are important, while membrane level contributions become even more important under pathologies that reduce the difference in P and V tissue size, particularly in the setting of healed myocardial infarction.
    Journal of Biological Systems 11/2011; 07(04). · 0.73 Impact Factor
  • Wei Kong, Andrew E Pollard, Vladimir G Fast
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    ABSTRACT: Intramural measurements of V(m) and Ca(i)(2+) are important in the studies of cardiac arrhythmias and defibrillation. We developed a new design of an "optrode" (bundle of optical fibers) for use in intramural cardiac mapping. The optrodes are made from seven optical fibers with the fiber ends polished at 45° angle and coated with mirror surfaces. The optrodes are enclosed in smooth epoxy resin cast, which protects mirror surfaces from damage and ensures constant optrode diameter along its length. The optrodes are strong enough to be easily inserted into heart muscle, can be reused multiple times, and they may reduce artifacts in the measurements of the effects of defibrillation shocks on V(m).
    IEEE transactions on bio-medical engineering 09/2011; 58(11):3130-4. · 2.15 Impact Factor
  • Source
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    ABSTRACT: We developed a new method for ratiometric optical mapping of transmembrane potential (V(m)) in cardiac preparations stained with di-4-ANEPPS. V(m)-dependent shifts of excitation and emission spectra establish two excitation bands (<481 and >481 nm) that produce fluorescence changes of opposite polarity within a single emission band (575-620 nm). The ratio of these positive and negative fluorescence signals (excitation ratiometry) increases V(m) sensitivity and removes artifacts common to both signals. We pulsed blue (450 ± 10 nm) and cyan (505 ± 15 nm) light emitting diodes (LEDs) at 375 Hz in alternating phase synchronized to a camera (750 frames-per-second). Fluorescence was bandpass filtered (585 ± 20 nm). This produced signals with upright (blue) and inverted (cyan) action potentials (APs) interleaved in sequential frames. In four whole swine hearts with motion chemically arrested, fractional fluorescence for blue, cyan, and ratio signals was 1.2 ± 0.3%, 1.2 ± 0.3%, and 2.4 ± 0.6%, respectively. Signal-to-noise ratios were 4.3 ± 1.4, 4.0 ± 1.2, and 5.8 ± 1.9, respectively. After washing out the electromechanical uncoupling agent, we characterized motion artifact by cross-correlating blue, cyan, and ratio signals with a signal with normal AP morphology. Ratiometry improved cross-correlation coefficients from 0.50 ± 0.48 to 0.81 ± 0.25, but did not cancel all motion artifacts. These findings demonstrate the feasibility of pulsed LED excitation ratiometry in myocardium.
    IEEE transactions on bio-medical engineering 07/2011; 58(7):2120-6. · 2.15 Impact Factor
  • Andrew E Pollard, Roger C Barr
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    ABSTRACT: Alterations to cell-to-cell electrical conductance and to the structural arrangement of the collagen network in cardiac tissue are recognized contributors to arrhythmia development, yet no present method allows direct in vivo measurements of these conductances at their true microscopic scale. The present report documents such a plan, which involves interstitial multisite stimulation at a subcellular to cellular size scale, and verifies the performance of the method through biophysical modeling. Although elements of the plan have been analyzed previously, their performance as a whole is considered here in a comprehensive way. Our analyses take advantage of a three-dimensional structural framework in which interstitial, intracellular, and membrane components are coupled to one another on the fine size scale, and electrodes are separated from one another as in arrays we fabricate routinely. With this arrangement, determination of passive tissue resistances can be made from measurements taken on top of the currents flowing in active tissue. In particular, our results show that measurements taken at multiple frequencies and electrode separations provide powerful predictions of the underlying tissue resistances in all geometric dimensions. Because of the small electrode size, separation of interstitial from intracellular compartment contributions is readily achieved.
    AJP Heart and Circulatory Physiology 06/2010; 298(6):H1699-709. · 4.01 Impact Factor
  • Roger C Barr, Loren W Nolte, Andrew E Pollard
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    ABSTRACT: Bayesian interpretation of observations began in the early 1700s, and scientific electrophysiology began in the late 1700s. For two centuries these two fields developed mostly separately. In part that was because quantitative Bayesian interpretation, in principle a powerful method of relating measurements to their underlying sources, often required too many steps to be feasible with hand calculation in real applications. As computer power became widespread in the later 1900s, Bayesian models and interpretation moved rapidly but unevenly from the domain of mathematical statistics into applications. Use of Bayesian models now is growing rapidly in electrophysiology. Bayesian models are well suited to the electrophysiological environment, allowing a direct and natural way to express what is known (and unknown) and to evaluate which one of many alternatives is most likely the source of the observations, and the closely related receiver operating characteristic (ROC) curve is a powerful tool in making decisions. Yet, in general, many people would ask what such models are for, in electrophysiology, and what particular advantages such models provide. So to examine this question in particular, this review identifies a number of electrophysiological papers in bioengineering arising from questions in several organ systems to see where Bayesian electrophysiological models or ROC curves were important to the results that were achieved.
    IEEE reviews in biomedical engineering. 01/2010; 3:155-68.
  • Raymond E Ideker, Jack M Rogers, Andrew E Pollard
    Heart rhythm: the official journal of the Heart Rhythm Society 08/2008; 5(7):1045-6. · 4.56 Impact Factor
  • Andrew E Pollard, Charles D Ellis, William M Smith
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    ABSTRACT: In this paper, we document a fabrication process that yields linear arrays of rectangular platinum black electrodes spaced 25 mum apart with edge-to-edge separation of 20 microm. The spatial arrangement is therefore sufficiently fine to insure stimulation and recording within cardiac tissue space constants, as six electrodes with dimensions of either 5 x 100 microm2, 5 x 250 microm2, or 5 x 500 microm2 were positioned in a 130-microm2 span in the arrays. Despite the small electrode sizes and available surface areas, favorable impedance characteristics were identifed. Averages ranged from 111 kOmega to 146 kOmega at 0.5 Hz and from 14 kOmega 39 kOmega at 500 Hz. Differences in impedances between the electrode sizes tested were small. Potential differences (deltaphis) recorded using the two central electrodes during stimulation with combinations at separations of only 75 microm, 100 microm, and 125 microm had low signal noise. As a preliminary test of the use of these arrays for possible application to impedance measurements in cardiac tissue, the deltaphis recorded during stimulation were compared to deltaphis obtained from finite-difference simulations using an isotropic volume conductor model. Anticipated decays in deltaphi with widening electrode separation identified in those simulations matched the decays in the recorded deltaphis closely. These findings are significant because they suggest intracellular and interstitial microimpedance mesurements in heart experiments will be straightforward.
    IEEE Transactions on Biomedical Engineering 05/2008; 55(4):1408-14. · 2.35 Impact Factor
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    ABSTRACT: Catecholamines are known to provoke cardiac arrhythmias, but important aspects such as localization of the arrhythmia source in multicellular tissue and exact ionic mechanisms are not well-known. In this work, a multicellular model of arrhythmias caused by local epinephrine application was developed; V (m) and Ca(i)(2+) changes at the arrhythmia source were measured using fluorescent dyes and high-resolution optical mapping. Cultured strands of neonatal rat myocytes (width approximately 0.4 mm) were produced by patterned growth. Epinephrine (1 micromol/l) was applied over an area of 0.3-0.6 mm via two micropipettes, and strands were stimulated by burst pacing. Local epinephrine application caused triggered arrhythmias with cycle lengths of 202-379 ms and duration of >10 s in 9 out of 16 preparations. Optical V(m) mapping demonstrated that in 78% of cases, the source of arrhythmia was located at the boundary of the locally perfused area. Staining with Ca(i)(2+)-sensitive dye Fluo-4 prevented arrhythmia induction in most cases (85%) likely due to Ca(2+) buffering by the dye. Optical Ca(i)(2+) mapping revealed non-propagated Ca(i)(2+) oscillations at the boundary of the locally perfused area in 45% cases. In conclusion, we developed a new model of catecholamine-dependent arrhythmias allowing mapping of V(m) and Ca(i)(2+) at the arrhythmia source with microscopic resolution. The arrhythmias typically originated from the boundary of the epinephrine-perfused area. The location of the arrhythmia source correlated with localized Ca(i)(2+) oscillations suggesting that arrhythmias were caused by Ca(i)(2+) overload at these locations.
    Pflügers Archiv - European Journal of Physiology 04/2007; 453(6):871-7. · 4.87 Impact Factor
  • Source
    Vidya Raman, Andrew E Pollard, Vladimir G Fast
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    ABSTRACT: Responses of Ca(i)2+ to electrical shocks are believed to be important in defibrillation but measurements of shock-induced Ca(i)2+ changes during different phases of the action potential (AP) are lacking. The effects of shocks on Ca(i)2+ and Vm were investigated in geometrically defined cell cultures and in a computer model. Uniform-field shocks (E = 10.4+/-0.9 V/cm) were applied 15-300 ms after AP upstroke in strands of cultured neonatal rat myocytes. Optical mapping was used to measure shock-induced Ca(i)2+ and Vm changes. A rat ionic model was used to elucidate ionic mechanisms of Ca(i)2+ responses. In experiments and simulations, shocks applied with short delays (15-40 ms) caused a transient decrease of Ca(i)2+ at sites of both DeltaV(+)m and DeltaV(-)m. Simulations indicated that the Ca(i)2+ decrease at DeltaV(+)m sites was caused by reversed outward flow of L-type Ca2+ current (I(CaL)), while the Ca(i)2+ decrease at DeltaV(-)m sites was due to the NaCa exchanger (NCX). At intermediate delays (40-150 ms), shocks caused a Ca(i)2+ decrease at sites of DeltaV(-)m and an increase at sites of DeltaV(+)m. Simulations indicated that the Ca(i)2+ increase at DeltaV(+)m sites was caused by transient reactivation of I(CaL) combined with a reverse-mode operation of NCX. Shocks applied at long delays (150-300 ms) caused a Ca(i)2+ increase at DeltaV(+)m and no change at DeltaV(-)m sites. Effects of shocks on Ca(i)2+ depend on the timing of shock application. Shocks applied during the early AP cause a transient Ca(i)2+ decrease, while later in AP shocks induce a Ca(i)2+ increase at sites of DeltaV(+)m. Shock-induced Ca(i)2+ changes in different AP phases are primarily determined by combination of I(CaL) and NCX.
    Cardiovascular Research 02/2007; 73(1):101-10. · 5.81 Impact Factor
  • Roger C Barr, Loren W Nolte, Andrew E Pollard
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    ABSTRACT: The resistivities of microscale components of excitable tissue include the longitudinal intracellular and interstitial resistivities and the membrane resistivity. Measurements of these tissue micro impedances have rarely been obtained, mainly because of the lack of a satisfactory measurement system. Here we evaluate a possible strategy for obtaining such measurements, and begin with a simulation. In the model, a one-dimensional fiber was stimulated with closely space interstitial electrodes at four frequencies, and the voltage differences that occurred in response were recorded. We then considered the inverse question, asking if tissue micro impedances could be found from the voltage measurements plus additive noise. In so doing, we used a Bayesian interpretation of the measured data to find the probability that each of the longitudinal and transmembrane resistivity sets was their origin. The Bayesian procedure proved better suited for interpreting the measurements than was conventional least-squares analysis. It was better because all known data, including realistic noise specifications and a priori probabilities, were included in the defined procedure. The results show that the micro impedances were found satisfactorily using realistic parameters and noise levels. The overall quantitative evaluation is promising for future experimental measurements.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2007; 2007:423-9.
  • Israel A Byrd, Matthew W Kay, Andrew E Pollard
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    ABSTRACT: Interactions between paced wavefronts and monomorphic ventricular tachycardia (VT) dictate antitachycardia pacing outcomes. We used optical mapping to assess those interactions during single and dual site pacing of rabbit ventricular epicardium. Monomorphic VTs were initiated in six isolated rabbit hearts that were endocardially cryoablated to limit viable tissue to visible epicardium and establish apical tissue as the anatomic anchor. Preparations were optically mapped during single (n = 39) and dual (n = 43) site pacing at 50%-90% of VT cycle length (CL) with eight pulses per trial. Overall, we found six pulses that abruptly terminated VT. This occurred because the VT wavefront collided with the antidromic portion of the paced wavefront and the orthodromic portion of paced wavefront blocked in the VT's refractory region. When effective, dual site pacing that captured tissue at both leads simultaneously terminated the VT immediately, while single site pacing or dual site pacing that captured tissue at only one lead terminated the VT after resetting advanced the orthodromic wavefront. We found 12 pulses that induced polymorphic VT, with 11 of those pulses occurring during capture at only one lead. Expansion of the combined antidromic-VT wavefront around one or both ends of the arc of conduction block formed by the interaction of the orthodromic wavefront with the VT's refractory region initiated functional reentry. Six of these polymorphic VTs were nonsustained because the underlying wavefronts self-terminated. The wavefronts did persist for 4.2 +/- 3.5 cycles before self-terminating in these trials, and the post-pacing cycles presented a 146% increase in CL variability, compared with the variability prior to pacing. These temporal characteristics are similar to those of delayed termination in patients with ICDs. The main difference between pulses that terminated abruptly and pulses that induced polymorphic VT was the effective separation of the antidromic and orthodromic portions of the paced wavefront from one another.
    Journal of Cardiovascular Electrophysiology 11/2006; 17(10):1129-39. · 3.48 Impact Factor
  • Andrew E Pollard, Roger C Barr
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    ABSTRACT: We analyzed central interstitial potential differences during multisite stimulation to assess the feasibility of using those recordings to measure cardiac microimpedances in multidimensional preparations. Because interstitial current injected and removed using electrodes with different proximities allows modulation of the portion of current crossing the membrane, we hypothesized that multisite interstitial stimulation would give rise to central interstitial potential differences that depend on intracellular and interstitial microimpedances, allowing measurement of those microimpedances. Simulations of multisite stimulation with fine and wide spacing in two-dimensional models that included dynamic membrane equations for guinea pig ventricular myocytes were performed to generate test data ( partial differentialphio). Isotropic interstitial and intracellular microimpedances were prescribed for one set of simulations, and anisotropic microimpedances with unequal ratios (intracellular to interstitial) along and across fibers were prescribed for another set of simulations. Microimpedance measurements were then obtained by making statistical comparisons between partial differentialphio values and interstitial potential differences from passive bidomain simulations (Deltaphio) in which a wide range of possible microimpedances were considered. Possible microimpedances were selected at 25% increments. After demonstrating the effectiveness of the overall method with microimpedance measurements using one-dimensional test data, we showed microimpedance measurements within 25% of prescribed values in isotropic and anisotropic models. Our findings suggest that development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiological study.
    AJP Heart and Circulatory Physiology 06/2006; 290(5):H1976-87. · 4.01 Impact Factor
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    ABSTRACT: Cardiac electrical activity is significantly affected by variations in the conductance of gap junctions that connect myocytes to one another. To better understand how intrinsic (single cell) electrical activity is modulated by junctional conductance, we used a two-myocyte coupling system in which physically separate cells were electrically coupled via a variable resistance set by the investigator. This brief review summarizes our findings regarding: (1) the effect of the early phase of action potential repolarization (phase 1) and transient outward current (Ito) on action potential conduction, and (2) the effect of coupling on the action potential plateau (late repolarization). We found that inhibition of Ito markedly increased the ability of action potentials to propagate from cell-to-cell when junctional conductance was low. Electrically coupling two myocytes together also suppressed their beat-to-beat variability in action potential duration and contraction. Similarly, early afterdepolarizations (EADS) were readily suppressed by connecting a normal myocyte to one generating EADs. This high sensitivity of the plateau to variations in junctional interactions arises from the large increase in membrane resistance that occurs during this phase of the action potential.
    Journal of Cardiovascular Electrophysiology 04/2006; 17(s1):S8 - S14. · 3.48 Impact Factor
  • Andrew E Pollard, Roger C Barr
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    ABSTRACT: On theoretical grounds, interstitial current injected and removed using electrodes in close proximity does not cross the membrane, while equilibration of intracellular and interstitial potentials occurs distant from electrodes widely separated. Multisite interstitial stimulation should therefore give rise to interstitial potential differences recorded centrally that depend on intracellular and interstitial micro-impedances, allowing independent measurement. We tested the feasibility of completing such measurements using simulations of multisite stimulation with fine and wide spacing in models that included Luo-Rudy dynamic (LRd) membrane equations. Using two-dimensional models, test data (delta phi o) were generated with isotropic interstitial and intracellular micro-impedances prescribed for one set of simulations, and with anisotropic micro-impedances including unequal ratios (intracellular/interstitial) along and across fibers prescribed for another set of simulations. Micro-impedance measurements were then obtained by making statistical comparisons between delta phi o values and interstitial potential differences from passive bidomain simulations (Delta phi o) in which a wide range of possible micro-impedances were considered. Our findings suggest development of microfabricated devices to implement the multisite stimulation procedure would facilitate routine measurement as a component of cardiac electrophysiologic study.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:1572-5.
  • Israel A Byrd, Andrew E Pollard, Matthew W Kay
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    ABSTRACT: Interactions between paced wavefronts and monomorphic ventricular tachycardia (VT) dictate antitachycardia pacing outcomes. Monomorphic VTs were initiated in isolated rabbit hearts (n=6) that were endocardially cryoablated to limit viable tissue to the visible epicardium and the ablated apex served as an anatomic anchor. Preparations were optically mapped during single and dual site pacing at 50% to 90% of VT cycle length with 8 pulses per trial. Of these trials, responses to the 48 single site pulses and to the 172 dual site pulses that captured tissue were analyzed. Overall, we found most pulses reset the VT, and a small number of pulses that abruptly terminated the VT. Of particular interest, we found 12 pulses that shifted the anatomically anchored VT to functionally reentrant wavefronts, and thereby induced polymorphic VT. Delayed termination was observed following 6 of these instances, and the underlying non-sustained polymorphic VT's presented temporal characteristics similar to those presented by delayed termination after antitachycardia pacing in ICD patients.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:3939-42.
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    ABSTRACT: This study was designed to test the feasibility of using microfabricated electrodes to record surface potentials with sufficiently fine spatial resolution to measure the potential gradients necessary for improved computation of transmembrane current density. To assess that feasibility, we recorded unipolar electrograms from perfused rabbit right ventricular free wall epicardium (n = 6) using electrode arrays that included 25-microm sensors fabricated onto a flexible substrate with 75-microm interelectrode spacing. Electrode spacing was therefore on the size scale of an individual myocyte. Signal conditioning adjacent to the sensors to control lead noise was achieved by routing traces from the electrodes to the back side of the substrate where buffer amplifiers were located. For comparison, recordings were also made using arrays built from chloridized silver wire electrodes of either 50-microm (fine wire) or 250-microm (coarse wire) diameters. Electrode separations were necessarily wider than with microfabricated arrays. Comparable signal-to-noise ratios (SNRs) of 21.2 +/- 2.2, 32.5 +/- 4.1, and 22.9 +/- 0.7 for electrograms recorded using microfabricated sensors (n = 78), fine wires (n = 78), and coarse wires (n = 78), respectively, were found. High SNRs were maintained in bipolar electrograms assembled using spatial combinations of the unipolar electrograms necessary for the potential gradient measurements and in second-difference electrograms assembled using spatial combinations of the bipolar electrograms necessary for surface Laplacian (SL) measurements. Simulations incorporating a bidomain representation of tissue structure and a two-dimensional network of guinea pig myocytes prescribed following the Luo and Rudy dynamic membrane equations were completed using 12.5-microm spatial resolution to assess contributions of electrode spacing to the potential gradient and SL measurements. In those simulations, increases in electrode separation from 12.5 to 75.0, 237.5, and 875.0 microm, which were separations comparable to the finest available with our microfabricated, fine wire, and coarse wire arrays, led to 10%, 42%, and 81% reductions in maximum potential gradients and 33%, 76%, and 96% reductions in peak-to-peak SLs. Maintenance of comparable SNRs for source electrograms was therefore important because microfabrication provides a highly attractive methods to achieve spatial resolutions necessary for improved computation of transmembrane current density.
    AJP Heart and Circulatory Physiology 01/2006; 289(6):H2468-77. · 4.01 Impact Factor
  • Article: P4-9
    Vladimir G. Fast, Vidya Raman, Andrew E. Pollard
    Heart Rhythm. 01/2006; 3(5).
  • Stephen B Knisley, Andrew E Pollard
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    ABSTRACT: Biomathematical models and experiments have indicated that passive extracellular conductors influence field stimulation. Because metallic conductors prevent optical mapping under the conductor, we have evaluated a passive translucent indium tin oxide (ITO) thin-film conductor to allow mapping of transmembrane potential (V(m)) and stimulatory current under the conductor. A 1-cm ITO disk was patterned photolithographically and positioned between 0.3-cm(2) mesh shock electrodes on the ventricular epicardium of isolated perfused rabbit hearts stained with 4-{2-[6-(dibutylamino)-2-naphthylenal]ethenyl}-1-(3-sulfopropyl)-, hydroxide, inner salt (di-4-ANEPPS). For a 1-A, 10-ms shock during the action potential plateau, optical maps from fluorescence collected using emission ratiometry (excitation at 488 nm and emissions at 510-570 and >590 nm) indicated that the disk altered V(m) by as much as the height of an action potential. DeltaV(m) became more positive near the edge of the disk, where the ITO conductance gradient was parallel to applied current, and more negative near the opposite edge, where the gradient was not parallel to current. For diastolic shocks, the disk expedited membrane excitation at the sites of positive DeltaV(m) in the heart and in a cardiac model with realistic ITO disk surface and interfacial conductances. Optical maps of ITO transmittance and the model indicated that the disk introduced anodal and cathodal stimulatory current at opposite edges of the disk. Thus ITO allows study of the stimulatory effects of a passive conductor in an electric field.
    AJP Heart and Circulatory Physiology 10/2005; 289(3):H1137-46. · 4.01 Impact Factor
  • Andrew E Pollard, William M Smith, Roger C Barr
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    ABSTRACT: This study was designed to test the hypothesis that analyses of central interstitial potential differences recorded during multisite stimulation with a set of interstitial electrodes provide sufficient data for accurate measurement of cardiac microimpedances. On theoretical grounds, interstitial current injected and removed using electrodes in close proximity does not cross the membrane, whereas equilibration of intracellular and interstitial potentials occurs distant from electrodes widely separated. Multisite interstitial stimulation should therefore give rise to interstitial potential differences recorded centrally that depend on intracellular and interstitial microimpedances, allowing independent measurement. Simulations of multisite stimulation with fine (25 microm) and wide (400 microm) spacing in one-dimensional models that included Luo-Rudy dynamic membrane equations were performed. Constant interstitial and intracellular microimpedances were prescribed for initial analyses. Discrete myoplasmic and gap-junctional components were prescribed intracellularly in later simulations. With constant microimpedances, multisite stimulation using 29 total electrode combinations allowed interstitial and intracellular microimpedance measurements at errors of 0.30% and 0.34%, respectively, with errors of 0.05% and 0.40% achieved using 6 combinations and 10 total electrodes. With discrete myoplasmic and junctional components, comparable accuracy was maintained following adjustments to the junctions to reflect uncoupling. This allowed uncoupling to be quantified as relative increases in total junctional resistance. Our findings suggest development of microfabricated devices to implement the procedure would facilitate routine measurement as a component of cardiac electrophysiological study.
    AJP Heart and Circulatory Physiology 01/2005; 287(6):H2402-11. · 4.01 Impact Factor

Publication Stats

445 Citations
180.87 Total Impact Points

Institutions

  • 1997–2011
    • University of Alabama at Birmingham
      • Department of Biomedical Engineering
      Birmingham, AL, United States
  • 2007–2010
    • Duke University
      • Department of Biomedical Engineering (BME)
      Durham, NC, United States
  • 2008
    • University of Alabama
      Tuscaloosa, Alabama, United States
  • 2005
    • University of North Carolina at Chapel Hill
      • Department of Biomedical Engineering
      Chapel Hill, NC, United States
  • 2000
    • Università degli studi di Parma
      Parma, Emilia-Romagna, Italy
  • 1995–1998
    • Tulane University
      • Department of Biomedical Engineering
      New Orleans, LA, United States
  • 1993
    • University of Utah
      Salt Lake City, Utah, United States