Showing papers on "QRS complex published in 1987"

Monophasic action potential mapping in human subjects with normal electrocardiograms: direct evidence for the genesis of the T wave.

Abstract: T wave concordance in the normal human electrocardiogram (ECG) generally is explained by assuming opposite directions of ventricular depolarization and repolarization; however, direct experimental evidence for this hypothesis is lacking. We used a contact electrode catheter to record monophasic action potentials (MAPs) from 54 left ventricular endocardial sites during cardiac catheterization (seven patients) and a new contact electrode probe to record MAPs from 23 epicardial sites during cardiac surgery (three patients). All patients had normal left ventricular function and ECGs with concordant T waves. MAP recordings during constant sinus rhythm or right atrial pacing were analyzed for activation time (AT) = earliest QRS deflection to MAP upstroke, action potential duration (APD) = MAP upstroke to 90% repolarization, and repolarization time (RT) = AT plus APD. AT and APD varied by 32 and 64 msec, respectively, over the left ventricular endocardium and by 55 and 73 msec, respectively, over the left ventricular epicardium. On a regional basis, the diaphragmatic and apicoseptal endocardium had the shortest AT and the longest APD, and the anteroapical and posterolateral endocardium had the longest AT and the shortest APD (p less than .05 to less than .0001). RT was less heterogeneous than APD, and no significant transventricular gradients of RT were found. In percent of the simultaneously recorded QT interval, epicardial RT ranged from 70.8 to 87.4 (mean 80.7 +/- 3.9) and endocardial RT ranged from 80 to 97.8 (mean 87.1 +/- 4.4) (p less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of the presence of slow conduction during sustained ventricular tachycardia in man: use of transient entrainment of the tachycardia.

Abstract: To test the hypothesis that an area of slow conduction is present during reentrant ventricular tachycardia in man, and that the earliest activation site during ventricular tachycardia is within or orthodromically just distal to the area of slow conduction in the reentry loop, we studied 12 episodes of ventricular tachycardia (mean rate 185 +/- 32 beats/min) that were induced in nine patients with ischemic heart disease. Rapid ventricular pacing was performed at selected sites during ventricular tachycardia while recording electrograms from an early activation site relative to the onset of the QRS complex (site A) and from a site close to the pacing site (site B). Rapid pacing from the right ventricular apex during ventricular tachycardia with a right bundle branch block pattern and from selected left ventricular sites during ventricular tachycardia with a left bundle branch block pattern (mean pacing rate 202 +/- 38 beats/min) resulted in constant ventricular fusion beats on the electrocardiogram except f...

Detection of transient myocardial ischemia by computer analysis of standard and signal-averaged high-frequency electrocardiograms in patients undergoing percutaneous transluminal coronary angioplasty.

Abstract: Electrocardiographic manifestations of transient myocardial ischemia were studied, in 11 patients undergoing angioplasty (PTCA) of a left anterior descending coronary artery stenosis, by the visual inspection of the standard surface electrocardiogram (S-ECG) and the intracoronary ECG (IC-ECG) as well as computer-assisted analysis of the S-ECG. Cross-correlation analysis (CCA) performed by computer was used to compare beat-to-beat variability in ST-T morphology of the S-ECG during different stages of PTCA. CCA was also applied to the signal-averaged high-frequency QRS (SA-HFQ). All patients developed angina during balloon inflation, accompanied by transient marked ST-T changes in IC-ECG in 10 of 11 patients (90%). Visual inspection of S-ECG revealed transient ST-T changes in only 6 of 11 (54%). In contrast, CCA of the S-ECG revealed transient ST-T changes in 9 of 11 (82%). Analysis of SA-HFQ revealed that balloon inflation was associated with a marked reduction in the calculated root-mean-square (RMS) voltage for such signals (2.31 +/- 1.04 microV) as compared with RMS values before (3.27 +/- 1.12 microV, p less than .05) PTCA or after conclusion of PTCA (3.79 +/- 1.39 microV, p less than .01). Balloon inflation was also accompanied by changes in waveform morphology of the SA-HFQ, including the development of new or more prominent time zones of reduced amplitude in 10 of 11 individuals (90%). Such zones may represent slow conduction in regions of the heart rendered ischemic during PTCA. CCA of the S-ECG and of SA-HFQ appears to detect evidence of transient ischemia with greater sensitivity than simple visual inspection of S-ECG, and may therefore prove to be of use in the evaluation of patients with chest pain of uncertain origin.

Optimal Bandpass Filters for Time-Domain Analysis of the Signal-Averaged Electrocardiogram

Abstract: The optimal bandpass filter for signal averaging of the surface QRS complex to detect late potentials is undefined. A study was conducted in 87 patients; 25 (mean age 34 +/- 10 years) were normal (group I), 29 (60 +/- 20 years) had organic heart disease without ventricular tachycardia (group II) and 33 (62 +/- 15 years) had sustained ventricular tachycardia (group III). In all patients signal-averaged electrocardiography (200 beats) was performed using a sharp, bidirectional filter and data analyzed using the following 7 high-pass filter settings: 10, 15, 20, 25, 40, 80 and 100 Hz. For each filter the duration of the signal-averaged QRS complex, the low-amplitude signals of less than 40 microV and the root-mean-square voltage of the terminal 40 ms (RMS-40) were determined. Normal values for each filter were determined from group I patients. In all 3 groups, quantitative signal-averaged variables were filter dependent. There was a progressive and marked decrease in RMS-40 and a progressive and marked increase in low-amplitude signal duration as the high-pass filtering was increased from 10 to 100 Hz. In contrast, high-pass, filter-dependent changes in signal-averaged QRS duration were less marked. The sensitivity and specificity for each filter using RMS-40 as the index of late potentials in separating group III patients from group II patients were: 10 Hz-64% and 52%; 15 Hz-57% and 72%; 20 Hz-57% and 76%; 25 Hz-42% and 90%; 40 Hz-61% and 83%; 80 Hz-88% and 69%; and 100 Hz-79% and 62%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiologic control of pacemaker rate using pre-ejection interval as the controlling parameter

Abstract: A multi-pole pacing/sensing lead is used to measure the instantaneous impedance in the right ventricle of a patient's heart. The resulting impedance waveform is signal processed to obtain a measure of the time interval beginning with the occurrence of a paced beat or a spontaneous QRS complex (systole marker) and ending with the point where the impedance versus time signal crosses the zero axis in the positive direction following the paced or spontaneous QRS complex initiating the interval or some other predetermined point along the positive-going waveform. The resulting time interval is inversely proportional to the contractility of the heart and is found to decrease with exercise and the introduction of catecholamines. Thus, it can be used as a control parameter for a demand-type cardiac pacemaker. A means for obviating changes in pacing rate due to long-term drift in the impedance sensing circuitry is also disclosed.

Effects of analyzed signal duration and phase on the results of fast fourier transform analysis of the surface electrocardiogram in subjects with and without late potentials

Abstract: A microcomputer-based system capable of performing time- and frequency-domain analysis on the same set of acquired and signal-averaged raw data was used to correlate late potentials detected in the time domain with the results of frequency-domain analysis. Ten patients with spontaneous or inducible sustained ventricular tachycardia (VT) known to have abnormal late potentials in the time-domain signal-averaged electrocardiogram and 10 normal subjects without late potentials were studied. Fast Fourier transform analysis was performed on a segment that comprised the last 40 ms of the QRS and the ST segment up to the onset of the T wave as identified visually. The high-frequency signal content, expressed as the area ratio or the peak magnitude, was found to be markedly dependent on the length of the analyzed QRS-ST segment. A change of as little as 3 ms in the duration of the estimated QRS-ST segment changed the results of the frequency analysis across proposed boundaries of normalcy in normal subjects and in patients with VT. This resulted in both false-negative and false-positive conclusions. Similar results were obtained when the effects of varying analyzed signal length or phase were studied using a pure synthesized sine wave signal. For frequency analysis to be clinically useful and reproducible, standards of normalcy must be established for a signal region of fixed duration or the technique must be modified so as to be insensitive to duration of signal sample.

Effects of coronary occlusion on high-frequency content of the epicardial electrogram and body surface electrocardiogram.

Abstract: The very high-frequency content (150 to 250 Hz) of epicardial electrogram waveforms was studied in 19 anesthetized dogs subjected to occlusion of left anterior descending coronary artery. Computer techniques of digital averaging and digital band-pass filtering were applied. Signals were obtained from epicardial electrodes placed in the ischemic left ventricular region and on the noninjured right ventricular surface, and from the body surface electrocardiogram. All recordings were made simultaneously before, during, and after coronary occlusion and subjected to the same analysis. The waveforms obtained from the ischemic left ventricular region showed a considerable decrease in high-frequency content, while those obtained from the noninjured right ventricular surface remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface high-frequency QRS complex. Therefore, this macroscopic phenomenon measured noninvasively from the body surface is explained by local reduction of high-frequency activity in the ischemic region of the myocardium.

Optimizing electrocardiograph electrode placement for cardiac-gated magnetic resonance imaging.

Abstract: Electrocardiographs recorded in a magnetic field for cardiac-gating in magnetic resonance imaging (MRI) are complicated by blood flow-induced potentials. This study examines which lead of the standard 12-lead ECG maximizes the QRS while minimizing flow-induced interference. Twelve-lead ECGs were performed on normal volunteers (n = 9) and patients (n = 13) in and out of the bore of a 1.5 Tesla imaging magnet. The amplitude of the major flow-induced potentials was measured, and the vectors of largest induced potential and the QRS axis were plotted for each subject. ECGs obtained outside and inside the magnet were digitized and subtracted (in magnet ECG--out of magnet ECG = artifact ECG) and the peaks of the resultant curves measured. Superimposed potentials were largest in the early T wave and late S-T segment in leads I, II, V1, and V2, and smallest in III and AVF. A low-amplitude 7-to 10-Hz signal occurred in most leads. In the frontal plane, QRS axes and flow potential vectors were closely clustered. In the transverse plane, QRS axes generally followed leads V5 or V6, whereas the flow potential vectors followed leads V1, V2, or V3. The normal and patient groups did not differ. Although leads III and AVP showed the smallest superimposed potentials, V5, V6, or a left posterior chest lead may maximize QRS and reduce artifact most consistently. A 7- to 10-Hz frequency filter may help eliminate artifacts in some subjects.

Results of signal-averaged electrocardiography and electrophysiologic study in patients with nonsustained ventricular tachycardia after healing of acute myocardial infarction.

Abstract: Programmed stimulation and signal-averaged electrocardiography were performed in 43 consecutive patients with nonsustained ventricular tachycardia (VT) after healing of inferior (29 patients) or anterior wall (14 patients) acute myocardial infarction. Twenty-two patients had inducible sustained VT. Patients with inferior infarction and inducible sustained VT had significantly longer filtered QRS durations (125 ± 19 vs 112 ± 15 ms, p

Frequency analysis of the surface electrocardiogram for recognition of acute rejection after orthotopic cardiac transplantation in man.

Abstract: Recognition of acute rejection after heart transplantation has been based mainly on invasive methods until now. In this study we analyzed two well-defined surface electrocardiographic recordings by fast Fourier transform (FFT) (Blackman Harris window, 512 points) after low-noise, high-gain amplification (filter setting 0.5 to 300 Hz) each day for 4 weeks after cardiac transplantation in 27 patients. Twenty acute rejection crises requiring treatment were diagnosed by cytoimmunologic monitoring and endomyocardial biopsy. Single-beat analysis of the QRS complex by FFT revealed a progressive change of the spectral morphology (increase of the frequency content between 70 and 110 Hz) on the days of rejection in 19 of 20 patients. At that time there were no visible changes on the electrocardiogram in the time domain in most patients. At the same time, the frequency content of the ST segment decreased between 10 and 30 Hz in 16 of 20 patients. After successful treatment, the frequency spectra of the QRS complex and ST segment returned to control within 1 to 2 weeks in most patients. One false-positive result was seen in a patient with mediastinitis and large pericardial effusion. A drop in QRS amplitude (greater than 20%) occurred in 10 of 20 rejection crises and in 10 patients without rejection. Nine patients after cardiac transplantation without rejection and seven control patients after cardiac surgery (not transplantation) showed stable frequency plots from one day to the other after the first postoperative day, but with considerable changes in QRS amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)

Concordance of distinguishing electrocardiographic features during sinus rhythm with the location of accessory pathways in the Wolff-Parkinson-White syndrome

Abstract: Knowledge of the location of accessory pathways in patients with Wolff-Parkinson-White (WPW) syndrome is pertinent to patient management. Despite the recognition that features of delta waves present during maximal preexcitation reflect ventricular activation at different sites around the anulus fibrosus, the value of electrocardiographic patterns observed during sinus rhythm, when ventricular preexcitation is often not maximal for identifying accessory pathway locations, has not been determined. In this study, 12-lead electrocardiograms recorded during sinus rhythm from 66 patients with WPW syndrome were analyzed for delta-wave polarity, QRS axis in the frontal plane, the pattern of precordial R-wave transition, and concordance between electrocardiographic patterns and the site of the accessory pathway determined using catheter and intraoperative computer mapping. Electrocardiograms from patients with left lateral sites showed negative delta waves in leads I or aVL, a normal QRS axis and early precordial R-wave transition (20 of 24 patients); left posterior sites manifested negative delta waves in II, III and aVF and a prominent R wave in V1 (14 of 16 patients); posteroseptal sites had negative delta waves in II, III and aVF, a superior QRS axis and an R less than S in V1 (all 16 patients); right free wall locations manifested negative delta waves in aVR, a normal QRS axis, and R-wave transition in V3-V5 (6 of 6 patients); and anterior septal sites had negative delta waves in V1 and V2, a normal QRS axis, and R-wave transition in V3-V5 (4 of 4 patients). Characteristic electrocardiographic patterns were not observed in 5 patients because of insufficient preexcitation. Each had a left lateral or left posterior pathway. Overall, the proposed electrocardiographic criteria derived during sinus rhythm identified correctly the accessory pathway location in 60 of 66 patients (91%). Thus, the electrocardiogram provides the physician with a reliable noninvasive means of regionalizing the location of accessory pathways in patients with WPW syndrome.

Value of the 12-lead electrocardiogram in discriminating atrioventricular nodal reciprocating tachycardia from circus movement atrioventricular tachycardia utilizing a retrograde accessory pathway☆

Abstract: The value of the 12-lead electrocardiogram for distinguishing atrioventricular (AV) nodal reciprocating tachycardia from circus movement AV tachycardia utilizing a retrograde accessory pathway was studied in 100 patients with narrow QRS complex tachycardia. Intracardiac electrograms showed AV nodal reciprocating tachycardia in 40 patients and circus movement AV tachycardia in 60. The 12-lead electrocardiograms recorded during tachycardia were randomly sorted and reviewed by 4 experienced cardiac electrophysiologists who were blinded to the diagnosis associated with each tracing, the relative proportion of each arrhythmia and the hypotheses to be tested. Each reviewer was asked to indicate the location of the P wave relative to the QRS complex, electrical axis of the P wave in the frontal and horizontal planes and presence or absence of QRS alternation, and to interpret the most likely mechanism. The performance of published electrocardiographic criteria to differentiate AV nodal reciprocating tachycardia from circus movement AV tachycardia was evaluated. The overall accuracy of the reviewers' interpretations was 75%, similar to the accuracy of the predefined criteria when applied by these observers (71% correct, difference not significant). Interobserver agreement of reviewer interpretations was 76% and the intraobserver agreement was 78%. Features associated with circus movement AV tachycardia by univariable analysis were P waves after the QRS complex, faster tachycardia rates and QRS alternation. Multivariable analysis showed that only the location of the P wave relative to the QRS complex was independently associated with the mechanism of tachycardia (p = 0.002). QRS alternation was found by multivariate analysis to be associated with the rate but not the mechanism of the tachycardia.

Detection and localization of coronary artery disease with body surface mapping in patients with normal electrocardiograms.

Abstract: Patients with clinically significant coronary artery disease often have normal resting electrocardiograms. Clinical and experimental studies have shown that body surface potential maps provide improved recognition of some disease states and more regionally selective information than standard electrocardiograms. Body surface maps were recorded at rest from 41 symptomatic patients with angiographically documented coronary artery disease and normal electrocardiograms. Patient maps were statistically compared with maps recorded from 644 normal subjects with the use of previously reported data representation technique. By this technique, maps from patients with symptomatic coronary artery disease and normal electrocardiograms were separated from maps of normal subjects with a sensitivity and specificity greater than 94%. The majority of discriminating information was present in the QRS interval. Fifteen of the 41 symptomatic patients had documented single-vessel coronary disease and their maps were separately compared with normal maps. Average maps from each of three patient groups with single-vessel disease contained abnormal patterns during the QRS interval that were unique to the vessel affected. In comparison with a average map from normal subjects, the average map from the group with left anterior descending coronary disease showed lower potentials over the anterior and inferolateral thorax during the early to mid QRS interval, the average map from the circumflex disease group showed decreased potentials around the entire inferior thorax in the mid to late QRS interval, and the average map from the right coronary disease group showed decreased potentials over the right anterior thorax during the mid to late QRS interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of late potentials to ejection fraction and wall motion abnormalities in acute myocardial infarction

Abstract: A prospective study was performed to determine the relation between quantitative signal-averaged parameters and ejection fraction (EF) and wall motion abnormalities determined by radionuclide ventriculography in patients with acute myocardial infarction (AMI). In 50 patients with AMI, signal-averaging of the surface QRS complex (200 beats; filter frequencies of 40 to 250 Hz and 80 to 250 Hz) was performed and radionuclide ventriculograms were recorded 8 ± 5 days after AMI. Twenty-five of these patients (50%) had anterior wall AMI, 20 (40%) had inferior wall AMI and 5 (10%) had non-Q-wave AMI. The duration of the low-amplitude signals of less than 40 μV, the signal-averaged QRS complex and the root-mean-square voltage of the terminal 40 ms were determined. In addition to EF determinations, wall motion abnormalities were assessed for the presence or absence of dyskinetic, akinetic and hypokinetic segments. A wall motion score was constructed by separating the left and right ventricles into 21 segments in the anterior, left anterior oblique and lateral views. On the basis of the presence or absence of late potentials, the patients were separated into 2 groups: group I comprised 15 patients (30%) with late potentials and group II 35 patients (70%) without late potentials. The low-amplitude signals (49 ± 12 vs 24 ± 8 ms) and the signal-averaged QRS complex (122 ± 20 vs 96 ± 15 ms) were significantly longer and the root-mean-square voltage (13.8 ± 4.9 vs 54.3 ± 27.4 μV) significantly lower in group I than in group II. However, EF (38 ± 14% vs 36 ± 12%), left and right ventricular wall motion abnormalities and left and right ventricular as well as combined wall motion scores were not significantly different between the groups. Thus, abnormal signal-averaged parameters are seen in 30% of patients with AMI and are independent of EF and wall motion abnormalities, and they may have independent prognostic value in patients who have had infarction.

Proarrhythmic responses during electrophysiologic testing.

Abstract: Antiarrhythmic drugs may worsen ventricular arrhythmias in certain patients. This effect, termed proarrhythmia, aggravation or provocation of arrhythmia, can be investigated with either noninvasive or invasive techniques. Using electrophysiologic study, 160 patients with ventricular tachycardia or ventricular fibrillation were evaluated during treatment with 432 different antiarrhythmic regimens. Proarrhythmic responses were noted in 68 drug trials (16%), and at least 1 event was observed in 51 patients (32%). Nonsustained ventricular tachycardia was converted to sustained ventricular tachycardia in 17% of these studies. Hemodynamically stable ventricular tachycardia was converted to an arrhythmia that required cardioversion for termination in 5% of the studies. Ventricular tachyrhythmia was more easily induced in 12% of trials. These proarrhythmic responses were not related to changes in QRS duration, QT interval or JT interval measured at baseline or to changes produced by antiarrhythmic drugs.