QRST Interval Research Articles

Abstract 12465: Association of Markers of Electrical Heterogeneity With Premature Ventricular Contractions on 12-Lead Electrocardiogram

Introduction: It was recently shown that independent electrophysiological substrate, quantified by global electrical heterogeneity (GEH) measures on ECG, is associated with Sudden Cardiac Death (SCD). However, mechanisms of GEH development are incompletely understood. Hypothesis: We hypothesized that the presence of premature ventricular contractions (PVCs) on 12-lead ECG is associated with GEH. Methods: We analyzed 20,288 participants from the Atherosclerosis Risk in Communities (ARIC) and Cardiovascular Health Studies (CHS). Linear regression models were adjusted for demographics, structural heart disease and its risk factors to assess the association between PVCs and GEH. In a subsequent analysis, we included only those participants (n =478) who had both (a): monomorphic (if multiple) or single PVCs and (b): normal median sinus beat . The distance between PVC’s QRS vector and sinus T vector was calculated assuming the heart as a global structure. Prematurity index (PI) was defined as coupling interval (CI) divided by mean sinus-beat RR interval. SAI QRST (sum absolute interval of QRST interval) was measured as the arithmetic sum of areas under the QRST curve. Results: After adjusting for structural heart disease and its risk factors, the presence of PVCs was associated with a QRS-T angle widening by 6.9 (95% CI: 4.41-9.41) degrees (p < 0.0001), and SAI QRST increase by 7.03 mV*ms (95% CI: 2.58-11.48, p = 0.002). On comprehensive adjustment using our linear regression model, among those with PVCs, 1 standard deviation of decrease in the distance between PVC’s QRS-vector and sinus beat’s T-vector was associated with spatial QRS-T angle increase by 3.6 (95% CI: 0.3-7.2) degrees (p =0.048). In the same model increase in PI by 10% was associated with spatial QRS-T angle increase by 3.0 (95%CI 0.7-4.9) degrees (P=0.010). Conclusions: The presence of PVCs is independently associated with an increase in the GEH. Better alignment between PVC’s QRS-vector and sinus beat’s T-vector (presumed cardiac memory) and less premature PVC was independently associated with wider spatial QRS-T angle.

Nondipolar content of cardiac magnetic field maps in patients after ST elevation myocardial infarction

Event Abstract Back to Event Nondipolar content of cardiac magnetic field maps in patients after ST elevation myocardial infarction Peter V. Leeuwen1*, Birgit Hailer2, Gregor Eiling2 and Dietrich H. Grönemeyer1 1 University of Witten / Herdecke, Dept. of Radiology / Microtherapy, Germany 2 Philippusstift, Dept. of Internal Medicine, Germany Electrophysiological changes occurring in the context of coronary artery disease (CAD) have been investigated using magnetocardiography. Various approaches have been developed and studied which quantify different aspects of the magnetic signals and reconstructed magnetic field maps (MFM). In this work, we compare the coherence of MFM by determining their relative nondipolar content on the basis of the Karhunen-Loeve transformation in healthy subjects and patients with acute ST elevation myocardial infarction (STEMI). Magnetocardiograms were obtained for 3 minutes in 32 healthy subjects and 75 STEMI patients using a 61 channel biomagnetometer. For each subject, the signals of ~50 beats of similar duration were averaged. Integral maps were calculated for 6 different segments of the QRST interval. For each segment 12 eigenmaps were constructed using Karhunen-Loeve transform. Nondipolar content was determined as percentage of the contribution of all eigenvectors beyond the third. The results showed that the nondipolar content of the MFM was generally increased in the patient group. Discriminatory power of each segment was assessed by the area under the curve (AUC) of the receiver operating characteristic. Results showed that the AUC was highest during repolarization: ST segment 74%, T wave 78% , terminal T wave 77% (p<0.001). Depolarization segments discriminated poorly (QRS, R peak: ~50%). Furthermore, maps with dipolar content (maps 1-3) permitted excellent discrimination with AUCs > 90% for the T wave (p<0.001). The results indicate that the nondipolar content of MFM in patients with acute symptoms of CAD increases particularly during repolarization. However T wave coherence in the dipolar maps differed even more so between healthy subjects and patients with myocardial infarction. Principal component analysis of cardiac MFM using the Karhunen-Loeve transform may thus be helpful in the surveillance of patients with CAD. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Oral Presentation Topic: MCG: Instrumentation, Modeling, Basic and Clinical Studies Citation: Leeuwen PV, Hailer B, Eiling G and Grönemeyer DH (2010). Nondipolar content of cardiac magnetic field maps in patients after ST elevation myocardial infarction. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00309 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Apr 2010; Published Online: 05 Apr 2010. * Correspondence: Peter V Leeuwen, University of Witten / Herdecke, Dept. of Radiology / Microtherapy, Bochum, Germany, sci@van-leeuwen.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Peter V Leeuwen Birgit Hailer Gregor Eiling Dietrich H Grönemeyer Google Peter V Leeuwen Birgit Hailer Gregor Eiling Dietrich H Grönemeyer Google Scholar Peter V Leeuwen Birgit Hailer Gregor Eiling Dietrich H Grönemeyer PubMed Peter V Leeuwen Birgit Hailer Gregor Eiling Dietrich H Grönemeyer Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Identification of Ischemic Lesions Based on Difference Integral Maps, Comparison of Several ECG Intervals

Ischemic changes in small areas of myocardium can be detected from difference integral maps computed from body surface potentials measured on the same subject in situations with and without manifestation of ischemia. The proposed method for their detection is the inverse solution with 2 dipoles. Surface potentials were recorded at rest and during stress on 10 patients and 3 healthy subjects. Difference integral maps were computed for 4 intervals of integration of electrocardiographic signal (QRST, QRSU, STT and STU) and their properties and applicability as input data for inverse identification of ischemic lesions were compared. The results showed that better (more reliable) inverse solutions can be obtained from difference integral maps computed either from QRST or from STT interval of integration. The average correlation between these maps was 97%. The use of the end of U wave instead of the end of T wave for interval of integration did not improve the results. YOCARDIAL ISCHEMIA manifests itself also by a changed shape of action potentials (AP) of myocytes in the ischemic area during the repolarization phase. The idea to find the affected area (lesion) using difference integral maps (DIMs) of the QRST interval and computing the inverse solution to one dipole was introduced in (1). DIMs were computed by subtraction of QRST integral maps obtained under normal conditions from QRST integral maps obtained during the manifestation of ischemia. These maps can be measured on patients in relaxed state and under stress conditions (e.g. physical exercise). In our previous study, an inverse solution with one dipole using DIMs was applied to find the position of a single small local lesion (2). Recently we reported a method for identification of local ischemic lesions by computing an inverse solution with two dipoles (3) for recognition of 1 or 2 simultaneously affected areas on simulated data. The decision to use the whole QRST interval that represents both, depolarization and repolarization of the myocardium (3) was based on the assumption that ischemic changes could affect also the depolarization phase of myocytes' AP by reduced AP amplitude and its rate of rise (4). The other possibility would be to evaluate only the STT interval in electrocardiogram (ECG) reflecting the repolarization phase of the myocardium activation. Another issue when selecting the ECG interval for evaluation of repolarization changes is the determination of the end of repolarization. In many real signals small U wave appears after the T wave in ECG. Although it was observed already by Einthoven, there is no unique (generally acceptable) explanation of its origin. The U-wave is explained in (5) by the presence of after-potentials on the cardiac action potentials (caused by mechanical stress of cardiac cells during systolic phase) associated with ventricular wall motion. According to other studies (6), (7) T and U waves together represent the repolarization period. In such case, inclusion of the U wave into the evaluated interval would be desirable. In (3), only repolarization changes (influencing only STT interval) without the U wave were modeled on simulated data. In the present study the differences between DIMs computed from QRST and STT intervals of real measured data were analyzed and the results obtained for identification of small ischemic lesions were compared. Also the influence of the inclusion of U wave into the evaluated interval representing the myocardium repolarization was investigated. 2. METHODS & MATERIAL

Adaptive singular value cancelation of ventricular activity in single-lead atrial fibrillation electrocardiograms

The proper analysis and characterization of atrial fibrillation (AF) from surface electrocardiographic (ECG) recordings requires to cancel out the ventricular activity (VA), which is composed of the QRS complex and the T wave. Historically, for single-lead ECGs, the averaged beat subtraction (ABS) has been the most widely used technique. However, this method is very sensitive to QRST wave variations and, moreover, high-quality cancelation templates may be difficult to obtain when only short length and single-lead recordings are available. In order to overcome these limitations, a new QRST cancelation method based on adaptive singular value cancelation (ASVC) applied to each single beat is proposed. In addition, an exhaustive study about the optimal set of complexes for better cancelation of every beat is also presented for the first time. The whole study has been carried out with both simulated and real AF signals. For simulated AF, the cancelation performance was evaluated making use of a cross-correlation index and the normalized mean square error (nmse) between the estimated and the original atrial activity (AA). For real AF signals, two additional new parameters were proposed. First, the ventricular residue (VR) index estimated the presence of ventricular activity in the extracted AA. Second, the similarity (S) evaluated how the algorithm preserved the AA segments out of the QRST interval. Results indicated that for simulated AF signals, mean correlation, nmse, VR and S values were 0.945 ± 0.024, 0.332 ± 0.073, 1.552 ± 0.386 and 0.986 ± 0.012, respectively, for the ASVC method and 0.866 ± 0.042, 0.424 ± 0.120, 2.161 ± 0.564 and 0.922 ± 0.051 for ABS. In the case of real signals, the mean VR and S values were 1.725 ± 0.826 and 0.983 ± 0.038, respectively, for ASVC and 3.159 ± 1.097 and 0.951 ± 0.049 for ABS. Thus, ASVC provides a more accurate beat-to-beat ventricular QRST representation than traditional techniques. As a consequence, VA cancelation is optimized and the AA can be extracted more precisely. Finally, the study has proven that optimal VA cancelation is achieved when a number between 20 and 30 complexes is selected following a correlation-based strategy.

Do repolarization abnormalities in hypertrophic cardiomyopathy represent impaired fatty acid utilization?: An observation with QRST isointegral maps

To identify the clinical significance of the isointegral body surface map of the QRST interval (QRST map) and the occurrence of repolarization abnormalities in patients with hypertrophic cardiomyopathy (HCM), the QRST map and signal-averaged electrocardiogram were evaluated in 50 patients with HCM, in 33 of whom the results were compared with nuclear images both for radioiodine-labeled fatty acid metabolism and for radiothallium perfusion. The QRST departure map was used to determine two parameters of difference between patient and control recordings: the subnormal area (the number of lead points at which the departure index values were negative and lay more than 2 SDs from the mean of the normal control group) and the subnormal minimum (the absolute value of the minimum in the departure map). Late potentials were detected in 6 (12%) of the 50 patients; they were observed in 3 of the 5 patients with dilated-phase HCM but in only 3 (7%) of the other 45 patients. The subnormal area and minimum values were lower in nonobstructive HCM than in dilated-phase HCM. Of the 33 patients examined by myocardial imaging, 28 (33%) had a filling defect or decreased uptake, as shown on fatty acid metabolic images, and 10 of the 28 also showed abnormal myocardial perfusion images, while the 18 others showed normal perfusion images. These 28 patients showed significantly larger values of the subnormal area and minimum than patients with normal results in both image tests, regardless of whether or not myocardial perfusion imaging abnormalities were present. The localization of filling defects or of decreased uptake presented in fatty acid metabolic images corresponded to the position of the minimum on the QRST departure map. These results suggest that the QRST map is useful for detection of repolarization abnormalities in HCM and that these abnormalities are highly related to impaired fatty acid utilization of the myocardium.

Discrimination between myocardial infarct and ventricular tachycardia patients using magnetocardiographic trajectory plots and iso-integral maps

Magnetocardiograms were recorded from 30 normal (N) subjects, 15 myocardial infarct (MI) patients, and 15 ventricular tachycardia (VT) patients. Discrimination between the groups was affected by iso-integral magnetic field mapping (MFM) and trajectory plotting of MFM extrema. Iso-integral MFM for the QRST, QRS, and ST-T intervals was created for each test group member. A polarity score, based on the number of extrema features present, was assigned to each iso-integral MFM. Differences in group mean ∫QRST map polarity scores were significant (p < 0.05) between MI and N, between VT and N (p < 0.005), and between MI and VT (p < 0.05) subjects. ∫ST-T map polarity scores were significantly (p < 0.0001) different between VT and N and between MI and VT (p < 0.001) subjects. Discrimination between MI and VT patients, based on polarity score difference, was 56% accurate using ∫QRS maps and 73% accurate using ∫ST-T maps. For each subject, time-normalized MFM was used to construct trajectory plots of the maxima and minima in the QRS and ST-T intervals. Discrimination between MI and VT patients was based upon intergroup differences in fragmented trajectory plots. When the number of discrete trajectories and/or the total number (F) of trajectory points at which discrete trajectories coexist were considered, QRSmin trajectory plots were significantly (p < 0.05) different for VT and N, but not for MI and N subjects. The significant (p < 0.05) difference between MI and VT trajectory plots enabled 76% accuracy for MI and VT identification. ST-Tmax trajectory plots show significantly (p < 0.0001) higher F values for VT patients facilitating accurate (87%) discrimination between MI and VT patients. These results suggest that the abnormalities of repolarization processes, displayed by MFM as multipolar ∫ST-T maps and/or as fragmented trajectory plots of ST-T extrema, may be useful indicators of the arrhythmia substrate/processes that characterize VT and vulnerable MI patients.

Effects of myocardial infarction on cardiac electrical field properties using a numerical expansion technique

This study was undertaken to quantify basic cardiac electrical field properties using the Karhounen-Loeve (K-L) numerical expansion technique after experimental myocardial infarction. Transmural anterior myocardial infarction was produced in seven dogs by injection of liquid latex into the anterior descending artery; posterior myocardial infarction was produced in five dogs by injection of the circumflex artery. Body surface potentials from 84 electrodes were recorded during sinus rhythm prior to and 1 week after infarction. Electrical field properties during the QRS, ST, and QRST intervals were computed by the K-L method based upon areas calculated for each lead. The ratio of the sum of magnitude of the first three eigenvectors to the sum of all computed eigenvectors expressed as a percentage was used as a measure analogous to field dipolarity. Values before infarction were high during the QRS (97.1% +/- 2.0%, mean +/- 1SD), ST (96.0% +/- 5.1%), and QRST (97.7% +/- 2.7%) intervals, with no significant difference between the three periods. After infarction, the ratio during QRS decreased significantly, with lower values after posterior (61.9% +/- 11.7%) than after anterior (91.1% +/- 6.0%) infarction (p less than 0.001). Values during ST and QRST intervals were not significantly changed by infarction. Spatial patterns of the first eigenvector indicated that the derived QRS area electric field is directed away from the myocardial lesion for both anterior and posterior infarcts. Thus, experimental myocardial infarction produces significant changes in cardiac electrical field properties as measured by the K-L technique.

Dispersion of ventricular repolarization in the long QT syndrome

To identify markers of dispersion of the ventricular repolarization in the idiopathic long QT syndrome, body surface potential maps were analyzed in 40 such patients (mean age ± standard deviation 21 ± 11 years) and in 30 healthy control subjects (mean age 24 ± 7 years). In each subject, 117 chest leads were recorded and maps of the integral values of the QRST interval were calculated. A multipolar distribution of the values, a marker of gross electrical inequalities of repolarization, was found only in 4 patients. To detect minor regional disparities of ventricular recovery, all the ST-T waveforms were analyzed in each subject. The ST-T waves were represented by a discrete series of potential values. The “similarity index” was computed by applying a principal component analysis, which represents (in percent) to what extent 1 fundamental pattern of ST-T reproduces all the recorded waveforms. The mean value of the similarity index was significantly lower in patients with long QT syndrome than in control subjects (49 ± 10 vs 77 ± 8%, p < 0.0001). A value <61% (corresponding to 2 standard deviations below the mean value for controls) was found in 35 of 40 patients and in only 1 control subject (sensitivity 87%, specificity 96%). Thus, the similarity index is a more sensitive marker than the multipolar distribution of QRST integral maps in revealing electrical disparities of the ventricular recovery times. The low value of the similarity index found in patients with long QT syndrome indicates a large variety of ST-T waveforms, suggesting a high degree of dispersion of ventricular recovery times, which is a condition of vulnerability to malignant ventricular arrhythmias.

A method to subdivide QRST interval for the time-integral body surface mapping

A method to subdivide QRST interval for the time-integral body surface mapping

Ventricular Repolarization Time - Effect of Chronic Beta Blockade with Class II and/or Class III Properties

A double-blind, crossover study was performed in 20 postinfarction patients to compare the effects of chronic treatment with metoprolol (100 mg twice daily) and sotalol (160 mg twice daily) on the ventricular repolarization time. QRST intervals were measured at a fixed paced cycle length of 800 ms using transesophageal atrial stimulation. Sotalol prolonged the Q-T and J-T intervals 5-8 % more than metoprolol. The prolongation was confined to the J-T interval and thus reflects a change in the repolarization time, since no change was seen in the Q-S interval. The QTT (from the Q wave to the top of the T wave) and QTE (from the Q wave to the end of the T wave) showed consistent changes, which implies that the former may be used with advantage when the end of the T wave is difficult to define. Metoprolol and sotalol in the doses selected were found to be equipotent regarding beta blockade, as judged by the measurements of heart rate and blood pressure at rest and during bicycle exercise tests, respectively. The clinical relevance of the additional effect of sotalol on the ventricular repolarization time regarding ventricular arrhythmias in a postinfarction population is still to be established.

Body surface maps in left bundle branch block uncomplicated or complicated by myocardial infarction, left ventricular hypertrophy or myocardial ischemia

We provided a topographic and quantitative description of body surface maps (BSM) during the entire QRST interval in seven uncomplicated LBBBs and 31 LBBBs complicated by: myocardial infarction (MI, seven cases), left ventricular hypertrophy (LVH, eight cases), myocardial ischemia (IS, seven cases), MI+LVH (six cases) and LVH+IS (three cases). In all patients we observed abnormal map configurations attributable to the LBBB. We were unable to identify consistent effects of the complicating heart condition(s) on the general pattern of chest potentials. Conversely, the surface voltages were generally decreased by MI and IS and increased by LVH. By considering the 38 patients as a preliminary learning set we applied a stepwise discriminant analysis to 77 voltage-related variables derived from BSM to produce a model for discriminating between LBBBs with and without MI. We properly allocated more than 90% of the patients. We also attempted to classify the patients into four groups: pure LBBB, LBBB+MI, LBBB+LVH and LBBB+IS, with a percentage of correct classification of about 80%. The two classifying procedures were applied to ten new LBBB patients with results similar to those obtained in the 38 of the study group.

Evaluation of normal variations in S-T segment patterns by body surface isopotential mapping: S-T segment elevation in absence of heart disease

S-T segment elevation is commonly observed in the electrocardiogram of normal persons. To study the possible origins of such patterns, 45 normal volunteers were examined. Electrocardiographic potentials were registered from 150 torso electrodes and processed to construct iso-potential maps at 2 ms intervals throughout the QRS-T interval. The maximal potentials recorded from any of the 150 electrodes were 198 ± 76.4 and 272.1 ± 84.2 μV at instants 40 and 80 ms into the S-T segment, respectively. Maximal voltages recorded by the six standard precordial V leads at these respective time points were 109.7 ± 57.0 and 163.6 ±66.9 μV. Torso maximal potentials were significantly stronger than were those sensed by V leads; the two were significantly correlated but predictability was limited. The duration of overlap between the onset of ventricular recovery and the end of the excitation was determined from isopotential maps and ranged from 4 to 16 ms. There was no significant correlation (p > 0.05) between these values and either torso or V lead potentials at either 40 or 80 ms into S-T segment. These data suggest that (1) standard precordial leads do not accurately predict maximal torso potentials during the S-T segment, and (2) the degree of overlap between repolarization and depolarization is not a major determinant of precordial voltage. Hence, the rationale for use of the term “early repolarization” to describe this clinical condition is not substantiated.

Body surface distributions of repolarization potentials after acute myocardial infarction. III. Dipole ranging in normal subjects and in patients with acute myocardial infarction

Dipole ranging is a method to determine the location, strength and orientation of the heart vector from body surface measurements. This technique was applied to electrocardiographic data recorded from forty-five normal subjects and from twenty patients suffering an acute myocardial infarction. Moments and locations during the QRST interval were determined by the potential integration formulae of Gabor and Nelson. Results in the normal population showed stability of both variables during cardiac recovery. In subjects with acute infarction, dipole loci were stable during much of the ST-segments of loci compatible with the anatomic positions of the lesions. Thus, dipole ranging methods can provide physiologically relevant information when applied to human electrocardiographic problems.

Isoarea distributions during ectopic stimulation of isolated rabbit hearts

These studies were designed to explore the effects of ectopic left ventricular stimulation on the area distributions recorded during the QRS, ST-T and QRST intervals. Twenty rabbit hearts were suspended in a spherical volume conductor, perfused with an electrolyte solution and stimulated from an anterior and/or a posterior subepicardial left ventricular site. ECG signals were sensed from 32 surface electrodes and were processed to compute areas under the three intervals, to construct area maps and to fit the computed areas to a single moving dipole equivalent cardiac generator model. Results demonstrated that control distributions were overtly nondipolar in 62.5% of cases. Second, ectopic pacing increased the dipolarity of the QRS and ST-T intervals significantly by both dipole ranging and isoarea methods. All area distributions became dipolar. Last, the QRST distribution response to ectopic stimulation varied widely, with major as well as minor changes in patterns occurring with alteration in excitation sequence. Thus, (1) ectopic stimulation changed electrical field properties of mean cardiac forces, and (2) QRST area distributions were dependent upon activation sequence. Each of these observations has direct bearing upon the ventricular gradient concept.

Experimental evaluation of the mean electrical equivalent generator of the isolated rabbit heart

Previous data have documented that the instantaneous cardiac equivalent generator is inadequately modeled as a single dipole. The properties of the mean equivalent generator during the QRS, ST-T and QRST intervals were determined in 22 isolated rabbit heart preparations suspended within a spherical volume conductor and perfused with an electrolyte solution. ECG potentials recorded from 32 surface electrodes were processed to compute instantaneous equivalent generator properties at 0.4 to 2.0 msec intervals during QRS and ST-T. QRS and ST-T areas of each electrode waveform were determined and processed to compute the parameters of the mean generator during QRS, ST-T and QRST intervals. A centric dipole fit 77.96, 71.73 and 67.48 percent of the recorded summed square (SSQ) area during these three intervals. Corresponding values for a single moving dipole model were 86.14%, 87.17% and 86.11%. A four element centric multipole series, in contrast, fit over 98% of SSQ area during each interval. Isoarea maps demonstrated multiple maxima and/or minima in 48% of the studied cases. Thus, mean cardiac forces during activation and recovery, as well as the instantaneous counterparts, are inadequately represented as single dipolar generator sources.

On the cholinergic reactions and sympathoadrenal activity associated with experimental hyperthyroidism in white rats

As demonstrated by this work, thyroxin given in low doses (0.007 mg/100 g of weight) augmented the cholinergic reactions-intensified the negative chrono-and dromotropic effect of acetylcholine and especially of proserine. Threshold doses of proserine become fatal in these conditions. Against the low doses of thyroxin, adrenalin and ephedrine produce a vagal effect-a negative chronotropic effect. High doses of thyroxin (160–220 mg/100 g of weight) caused a rise in sympathicoadrenal activity (tachycardia, shortening of P-Q, QRST intervals, tachypnea, and loss of weight); cholinergic reactions in these conditions are also intensified as compared to control tests but not to such an extent as after low thyroxin doses. The role of increased cholinergic activity as a condition provoking intensification of sympathoadrenal reactions in hyperthyroidism is suggested.