Estimates of repolarization dispersion from electrocardiographic measurements.

BACKGROUND: Repolarization dispersion (Rd) is frequently mentioned as a predictor of cardiac abnormalities. We present a new measure of Rd based on the root-mean-square (RMS) curve of an ECG lead set and compare its performance with that of the commonly used QT dispersion (QTd) measure with the use of recovery times measured from directly recorded canine electrograms. METHODS AND RESULTS: Using isolated, perfused canine hearts suspended in a torso-shaped electrolytic tank, we simultaneously recorded electrograms from 64 epicardial sites and ECGs from 192 "body surface" sites. RMS curves were derived from 4 lead sets: epicardial, body surface, precordial, and a 6-lead optimal set. Repolarization was altered by changing cycle length, temperature, and activation sequence. Rd, calculated directly from recovery times of the 64 epicardial potentials, was then compared with the width of the T wave of the RMS curve and with QTd for each of these 4 lead sets. The correlation between T-wave width and Rd for each lead set, respectively, was epicardium, 0.91; body surface, 0.84; precordial, 0.72; and optimal leads, 0.81. The correlation between QTd and Rd for each lead set was epicardium, 0.46; body surface, 0.47; precordial, 0.17; and optimal leads, 0.11. CONCLUSIONS: RMS curve analysis provides an accurate method of estimating Rd from the body surface. In contrast, QTd analysis provides a poor estimate of Rd.

Estimates of repolarization and its dispersion from electrocardiographic measurements: direct epicardial assessment in the canine heart.

This study investigates a technique to estimate dispersion based on the root mean square (RMS) signal of multiple electrocardiographic leads. Activation and recovery times were measured from 64 sites on the epicardium of canine hearts using acute in situ or Langendorff perfused isolated heart preparations. Repolarization and its dispersion were altered by varying cycle length, myocardial temperature, or ventricular pacing site. Mean and dispersion of activation and recovery times, and activation-recovery interval (ARI) were calculated for each beat. The waveform was then calculated from all leads. Estimates of mean and dispersion of activation and recovery times and mean ARI were derived using only inflection points from the RMS waveform. QT intervals were also measured and QT dispersion was determined. Estimates determined from the RMS waveform provided accurate estimates of repolarization and were, in particular, a better measure of repolarization dispersion than QT dispersion.

Mechanisms of the spatial distribution of QT intervals on the epicardial and body surfaces.

INTRODUCTION: The role of QT dispersion as a predictor of arrhythmia vulnerability has not been consistently confirmed in the literature. Therefore, it is important to identify the electrophysiologic mechanisms that affect QT duration and distribution. We compared the spatial distributions of QT intervals (QTI) with potential distributions on cardiac and body surfaces and with recovery times on the cardiac surface. We hypothesized that the measure of QTI is affected by the presence of the zero potential line in the potential distribution, as well as the sequence of recovery. We also investigated use of the STT area as a possible indicator of recovery times on the cardiac surface. METHODS AND RESULTS: High-resolution spatial distributions of QTI and potentials were determined on the body surface of human subjects and on the surface of a torso-shaped tank containing an isolated canine heart. Additionally, spatial distributions of QTI, recovery times, and STT areas were determined on the surface of exposed canine hearts. Unipolar electrograms were recorded during atrial and ventricular pacing for normal hearts and cases of myocardial infarction. Regions of shortest QTI always coincided with the location of the zero potential line on the cardiac and body surfaces. On the cardiac surface, in regions away from the zero line, similarities were observed between the patterns of QTI and the sequence of recovery. STT areas and recovery times were highly correlated on the cardiac surface. CONCLUSION: QTI is not a robust index of local recovery time on the cardiac surface. QTI distributions were affected by the position of the zero potential line, which is unrelated to local recovery times. However, similarities in the patterns of QTI and recovery times in some regions may help explain the frequently reported predictive value of QT dispersion. Preliminary results indicate STT area may be a better index of recovery time and recovery time dispersion on the epicardium than QTI.

Noninvasive indices of repolarization and its dispersion.

In experimental studies using Langendorff perfused, isolated canine hearts immersed in a torso-shaped electrolytic tank we studied repolarization and its dispersion using direct epicardial measurements and newly derived, noninvasive body surface indices. Activation recovery intervals (ARIs) measured from 64 epicardial sites based on differences between activation times (ATs) and recovery times (RTs) provided direct measures of repolarization. The indirect, torso surface indices were derived from inflections of the root-mean-square (RMS) voltage of the torso tank surface electrocardiograms recorded simultaneously with the epicardial data. For cycle lengths ranging from 300 to 900 ms, and electrolyte temperatures ranging from 32 degrees C to 40 degrees C we calculated mean, variance, and range of ATs, RTs, and ARIs from the epicardium. From epicardial and torso surface RMS waveforms, we used times of R and T peaks and their differences to estimate mean ATs, RTs, and ARIs, respectively. The RMS T wave width as determined from the second derivative inflections on either side of the T peak served as an estimate of the dispersion of RTs. In parallel studies, we showed that the direct measures of repolarization and its dispersion were reflected in RMS waveforms generated from the epicardial electrograms themselves. In this study, we confirm that the torso and epicardial RMS waveforms reflect comparable information for estimating repolarization and its dispersion. Furthermore, the derived measures provide a method to assess mean ARIs and dispersion of RTs on a beat-to-beat basis and during abnormal (ectopic ventricular) activation sequences.

QT interval dispersion: dispersion of ventricular repolarization or dispersion of QT interval?

The QT interval (QTI) has long been useful as a clinical index of the duration of ventricular repolarization, particularly as a marker of prolonged repolarization and its well-established association with arrhythmogenic cardiac states. Likewise, inhomogeneity (dispersion) of repolarization has been linked definitively to increased susceptibility to reentrant arrhythmias. Recent studies have reported the use of QTI dispersion as a meaningful clinical index to identify patients at risk, but the interpretation of the measurement has been controversial. A Langendorff-perfused, isolated canine heart suspended in a torso-shaped, electrolytic tank filled with NaCl-sucrose solution was used to investigate the relationship between body surface QTIs and ventricular repolarization measured directly from the cardiac surface by using activation-recovery intervals, which have been documented to reflect the duration of local action potentials as well as local refractory periods. The data showed poor correlation between cardiac surface activation-recovery intervals and QTIs, as well as the insensitivity of QTIs to regional repolarization shortening in the presence of prolonged repolarization elsewhere. Furthermore, the data confirmed that torso tank QTI dispersion does not reflect directly the full range of measured ventricular repolarization inhomogeneity. It is concluded that body surface QTI dispersion is not a reliable index of repolarization dispersion.

Isolation and Characterization of an Endopolygalacturonase from Cochliobolus sativus and a Cytological Study of Fungal Penetration of Barley.

ABSTRACT Endopolygalacturonase (EPG) of Cochliobolus sativus was produced in shake culture and purified by high-performance liquid chromatography. The enzyme had a molecular mass of 34,000 Da, an isoelectric point in the range of 9.0 to 9.5, exhibited endo activity, was nongly-cosylated, and was inhibited by polygalacturonase-inhibiting proteins from bean, pear, and tomato. The amino terminus contained a 14 amino acid region homologous to a region at the N terminus of an EPG of C. carbonum. C. sativus EPG-specific monoclonal antibodies (MAbs) were generated. Western blot analysis confirmed the specificity of the antibodies for the EPG and detected the enzyme in an extract from Hordeum vulgare (cv. Golden Promise) leaf segments infected with C. sativus. Using conventional immunogold and enzyme-gold cytochemical methods, homogalacturonan, esterified pectin, and cellulose were localized in healthy and infected barley leaf epidermis at the electron microscope level. Additionally, the leaf cell wall polysaccharides recognized by purified C. sativus EPG were localized at the electron microscope level, using the purified enzyme as a primary cytochemical reagent, followed by a gold-labeled MAb specific for the enzyme. Loss of polygalacturonic acid in the vicinity of the invading pathogen was visualized cytochemically at the electron microscope level. These observations suggest the involvement of EPG during host penetration by the fungus.

Optimal lead selection for detection of ST segment shifts.

A comparison was made to determine the ability of optimal sets of 2-6 unipolar leads and a normal Holter lead set to estimate ST potential distributions changes induced by balloon inflation during angioplasty. The performance of these lead sets was compared to measurements observed in recorded 32-lead body surface maps. Unipolar lead potentials were estimated using a linear, least mean squared error estimator of the total body surface map. The correlation between maximum ST potential change in the body surface map and that predicted by the unipolar lead sets ranged from 0.84-0.93. The correlation between maximum ST segment change measured from the body surface map and measured from the Holter leads was 0.29. Therefore, shifts in ST segment potentials can accurately be estimated from a small number of unipolar leads. In contrast, current bipolar ambulatory recording techniques may introduce significant bias to such estimates.

Developmental and Tissue-Specific Structural Alterations of the Cell-Wall Polysaccharides of Arabidopsis thaliana Roots.

The plant cell wall is a dynamic structure that plays important roles in growth and development and in the interactions of plants with their environment and other organisms. We have used monoclonal antibodies that recognize different carbohydrate epitopes present in plant cell-wall polysaccharides to locate these epitopes in roots of developing Arabidopsis thaliana seedlings. An epitope in the pectic polysaccharide rhamnogalacturonan I is observed in the walls of epidermal and cortical cells in mature parts of the root. This epitope is inserted into the walls in a developmentally regulated manner. Initially, the epitope is observed in atrichoblasts and later appears in trichoblasts and simultaneously in cortical cells. A terminal [alpha]-fucosyl-containing epitope is present in almost all of the cell walls in the root. An arabinosylated (1->6)-[beta]-galactan epitope is also found in all of the cell walls of the root with the exception of lateral root-cap cell walls. It is striking that these three polysaccharide epitopes are not uniformly distributed (or accessible) within the walls of a given cell, nor are these epitopes distributed equally across the two walls laid down by adjacent cells. Our results further suggest that the biosynthesis and differentiation of primary cell walls in plants are precisely regulated in a temporal, spatial, and developmental manner.

Excitotoxic lesions of the rat striatum: different responses of kynurenine pathway enzymes during ontogeny.

Excitotoxic lesions of the adult rat striatum result in reactive gliosis and an associated increase in the activities of the astrocytic enzymes 3-hydroxyanthranilic acid oxygenase (3HAO) and kynurenine aminotransferase (KAT), which are responsible for the biosynthesis of the neurotoxin quinolinic acid and the neuroprotectant kynurenic acid, respectively. Unilateral ibotenate injections were made in the striatum of 7-, 14-, 21- and 28-day- and 2.5-month-old rats to study the reaction of 3HAO and KAT when injury is inflicted during ontogeny. By one week, all lesioned striata showed a > 50 percent decrease in the activity of the neuronal marker enzyme glutamic acid decarboxylase. At this timepoint, lesion-induced elevations in 3HA0 activity increased progressively from 130 to 206, 280, 385 and 456 percent of the contralateral striatum in the five age groups studied. In contrast, in the same animals the respective increases in striatal KAT activity were 601, 350, 312, 259 and 159 percent (n = 6-13 per group). In all age groups, statistically significant lesion-induced increases in 3HA0 and KAT were seen up to 4 weeks after the ibotenate injection. Rats receiving an intrastriatal injection of ibotenate on postnatal day 7 also showed an increase in the striatal tissue level of kynurenic acid 1 week after the lesion. These data demonstrate that substantial qualitative differences exist between the immature and adult rat in the reaction of two glial enzymes to striatal injury. Moreover, the ability of the immature brain to mobilize kynurenic acid production preferentially may play a role in the brain's response to perinatal injury.

Evaluation of novel measurement methods for detecting heterogeneous repolarization.

There exists a well-documented link between heterogeneity of cardiac recovery characteristics and vulnerability to arrhythmia; however, electrocardiographic detection of this heterogeneity remains problematic. The only modalities suitable for measuring variation of repolarization are electrophysiologic in nature, with action potential duration in single cells the most direct method and QT intervals from the body surface electrocardiogram the most common clinical approach. The authors have shown previously, however, that the QT interval is a poor measure of regional change in repolarization, especially when shortening occurs. Here, the authors discuss an experimental preparation based on an isolated canine heart suspended in a human-shaped, instrumented, electrolytic tank and describe a method of applying cold to create local, transient changes in recovery characteristics. The authors have simultaneously recorded epicardial and torso tank surface potentials before, during, and after intervention, and from them have generated isopotential and isointegral maps and computed activation-recovery intervals (ARIs). In all cases, epicardial potentials revealed changes in recovery associated with localized heating and cooling. The changes were visible from tank surface potential distributions in some, but not all, cases. The results also suggest that epicardial ARIs are sensitive to changes in recovery and that, at least for a subset of tank surface leads, ARIs can be used to create noninvasive indices of disparity of repolarization characteristics.

Detection and localization of prolonged epicardial electrograms with 64-lead body surface signal-averaged electrocardiography.

BACKGROUND: Prolonged, fractionated ventricular electrograms often are detectable after myocardial infarction and are a marker for an arrhythmia-prone state. QRS late potentials detected on the body surface with signal-averaged electrocardiography (SAECG) are thought to arise from the diseased tissue that generates prolonged ventricular electrograms and as such are also a marker for arrhythmias. A limitation of the current SAECG technique is that recordings are obtained from only three bipolar lead pairs. Because late potentials probably arise from multiple small sources in the heart, more extensive sampling of the body surface may contribute additional information to the SAECG: The present study investigates the additional sensitivity of SAECG using 64 body surface leads in detecting prolonged epicardial electrograms and examines its use in determining the epicardial location of prolonged electrograms. METHODS AND RESULTS: Dogs were studied before and 5-10 days after either lateral left ventricular (n = 13) or right ventricular (n = 8) myocardial infarction. Greater prolongation of signal-averaged QRS duration was detected with 64-lead SAECG (postinfarction QRS duration, 100.3 +/- 16.3 msec) than with three-lead SAECG (postinfarction QRS duration, 89.4 +/- 10.1, p = 0.0005). Nineteen of the 21 dogs (90%) had prolonged epicardial electrograms detected over the infarct. The correlation between epicardial electrogram duration and signal-averaged QRS duration calculated from individual leads was much better for 64-lead SAECG (r = 0.88, p less than 0.0001) than for three-lead SAECG (r = 0.53, p = 0.01), and the difference was most marked in cases with longer electrogram durations (more than 100 msec). Local late potential maxima on the thorax after lateral left ventricular infarction were located to the left and inferior compared with those after right ventricular infarction (p = 0.006). CONCLUSIONS: SAECG with more extensive recording from the body surface using 64 leads detects greater QRS prolongation than three-lead SAECG, and the longer QRS durations detected correspond to the duration of prolonged epicardial electrograms. Body surface location of late potentials corresponds to the epicardial location of the prolonged electrograms. This application of body surface mapping techniques to SAECG may permit more sensitive detection of arrhythmia-prone states and may aid in identifying arrhythmia sources.

Response of joint capsule neurons to axial stress and strain during dynamic loading in cat.

1. Experiments were conducted to test the hypothesis that the responses of joint capsule mechanoreceptors better encode tissue stress or tissue strain. The experimental model was a small ligament from the cat knee capsule, which was stretched uniaxially in vitro. Experiments were done with either force or displacement as the controlled variable, and with steps, sinusoids, or pseudorandom Gaussian noise (PGN) as the input function. 2. The strength of coupling between neural discharge and both strain and stress was quantified during step experiments using linear correlation coefficients. The correlation between the frequency of neural discharge and stress was 0.93 +/- 0.09 (SD). The correlation between frequency of neural discharge and strain was -0.91 +/- 0.06. The magnitudes of these correlation coefficients were not significantly different. 3. The strength of coupling between neural discharge and both strain and stress during sinusoidal and PGN experiments was quantified by the use of an information theoretic statistic, transinformation. Out of 282 sinusoidal runs, transinformation between neural discharge and stress was significantly greater than transinformation between strain and neural discharge 241 times. Transinformation between strain and neural discharge was significantly greater 15 times. 4. During PGN experiments, transinformation between stress and neural discharge was greater than transinformation between strain and neural discharge in all 19 experimental runs. 5. Conditional transinformation between strain and neural discharge, given stress, was calculated for all sinusoidal and pseudorandom experiments. This statistic was greater than zero in 268 out of 289 experimental runs, indicating that a component of strain independent of stress is being signaled in the neural discharge.

Possible forms for dwell-time histograms from single-channel current records.

Certain macromolecules embedded in the cell membranes of a variety of cells behave as gated ion-selective pores or channels. The length of time that a channel remains open or closed is not deterministic in nature and must be described in terms of relative probabilities. If channels act independently of each other and appropriate experimental conditions can be maintained, the behavior of a channel can be described by a homogeneous Markov process. Using this representation, the relative probability of observing openings (or closings) of various durations can be described by a sum of discrete components which are related to the underlying model of the kinetic behavior of the channel. Generally, these discrete components are taken to be simple decaying exponentials; however, exponentially decaying oscillatory components (as well as certain others which are discussed) are consistent with the Markov process representation. The presence of components other than simple decaying exponentials is shown to imply the violation of detailed balance in the steady-state (which requires energy), and thus, the presence of cyclic pathways in models which accurately represent the kinetic behavior of the channel. Oscillatory components, if present, will in general decay at a faster rate than the slowest decaying component, which, except under a very restricted set of conditions, will be a simple exponential.

Extraction of dolichyl phosphate and its quantitation by straight-phase high-performance liquid chromatography.

A procedure for the rapid quantitation of dolichyl phosphate by high-performance liquid chromatography on silica is described. The compound elutes as a single peak at 6 ml in excellent yield. The method employs isocratic elution and requires no column treatment between runs; the limit of sensitivity is in the nanogram range. Dolichyl-11-phosphate, which elutes at 7 ml, can be used as an internal standard, thereby eliminating the requirement for preparation of [3H]dolichyl phosphate. The procedure was used in development of a facile assay for free dolichyl phosphate in rat liver. For the assay of total dolichyl phosphate (free and chemically bound), it was found that when rat liver is first saponified and then extracted with ethyl ether, the amount of dolichyl phosphate present in the ether extract is significantly greater than the sum of the amounts found in extracts derived by treating the tissue first with chloroform/methanol (2/1) and then with chloroform/ethanol/water (10/10/3). Using these new procedures, the level of total dolichyl phosphate in rat liver was found to be 14.7 +/- 3.5 micrograms g-1 wet wt (n = 28). Levels in six other organs are also reported.

A continuous information theoretic approach to the analysis of cutaneous receptor neurons.

Information theoretic and statistical techniques for determining the number of discernible levels in cutaneous receptor neurons are reviewed. Reasons for the large variance in these results are discussed. A new continuous information theoretic analysis technique is presented that overcomes many of the problems in the other methods of analysis discussed. Comparison of this new method of analysis with a statistical technique developed by Schreiner et al. (1978) clearly shows some of the misconceptions that are associated with statistical analysis techniques, and why these problems cannot arise in the new information theoretic technique discussed here.