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PubMed1998

A new high-resolution esophageal electrocardiography recording technique: an experimental approach for the detection of myocardial ischemia.

UNLABELLED: Criteria for ischemic changes in the esophageal electrocardiograph (E-ECG) have not been standardized and validated. The main goal of this study was to evaluate the experimental esophageal recording of myocardial ischemia and to assess the association between ST segment alternans in the E-ECG and ischemia. Experiments were performed on 18 anesthetized sheep with occlusion of a branch of the left anterior descending artery. The bipolar signals were recorded via an esophageal lead containing three chloridized silver electrodes. Electrical signals were amplified in a self-designed, battery-supported preamplifier (gain 1000, frequency range 0.01-2000 Hz, common mode rejection 140 dB, signal noise 5-7 microV p-p), then sent to a digital oscilloscope for display and to a pulse code-modulated recorder. Surface electrocardiography (S-ECG) data were also recorded. Ischemia E-ECG revealed homogenous ST segments without any beat-to-beat alternans. Two minutes after occlusion, 14 of 15 sheep (93%) showed repetitive beat-to-beat fluctuations within the ST segment on the E-ECG. Of the 15 sheep, 7 (47%) showed ischemia in the S-ECG (P < 0.01). For calculation of the dynamic changes in the ST segment in the E-ECG, the difference in the amplitudes of the ST segment of five successive beats to the next beat, performed for 200 consecutive beats, was calculated. The central tendency of the sum of these values before versus during ischemia was 2000 mV/ms versus 5000 mV/ms (Hodges-Lehmann point estimator) (95% confidence intervals 1700/2500 versus 3350/9250 [lower limit/upper limit]). The authors have established a close temporal relationship between the magnitude of ST segment alternans recorded via E-ECG and myocardial ischemia. IMPLICATIONS: The study presents the use of an esophageal electrocardiograph for detection of progressive changes of myocardial ischemia and infarction. During acute myocardial ischemia and infarction in sheep, the esophageal electrocardiograph has visually apparent ST alternans of amplitude in the millivolt range, in part due to a special amplifier (0.01-2000 Hz). This is therefore one very promising technique for better evaluation of electrocardiographic changes of ischemia.

Animals↗

PubMed1991

The diagnostic and prognostic value of exercise electrocardiography in asymptomatic subjects and stable symptomatic patients.

In asymptomatic patients, the use of exercise ECG testing for the detection of subclinical coronary artery disease has considerable theoretical appeal, but its practical application is severely hampered by the constraints of Bayes' theorem. Serial exercise ECGs do not appear to offer significant improvement in this regard. Thallium-201 perfusion scintigraphy performed in conjunction with an exercise ECG can greatly improve the predictive value of such testing, although at considerable cost. Screening strategies with promise are those that reserve exercise testing for individuals at greater-than-average risk for subclinical coronary artery disease (eg, patients with multiple coronary risk factors) or that prescribe sequential testing, where only those with an abnormal exercise ECG are subjected to thallium-201 scintigraphy. At present, the optimal method of identifying asymptomatic individuals at high risk of a major cardiac event remains undefined. The use of maximal-effort stress testing has stood the test of time in the evaluation of patients with stable symptoms suggestive of coronary artery disease. This is particularly true when variables other than the ECG response to exercise are considered. The independent contribution of exercise angina remains controversial; however, recent studies indicate that it correlates with a more severe symptom pattern and more extensive coronary artery disease. Prognostic stratification in these studies was improved by considering both subjective and objective manifestations of ischemia. Although exercise ECG testing has been shown to have important prognostic value after acute myocardial infarction, exercise thallium-201 scintigraphy offers several potential advantages for asymptomatic post-myocardial infarction patients, several of which this paper reviews. The more optimal prognostic efficiency of thallium-201 scintigraphy is due in part to the fact that the error rate in falsely classifying patients at low risk is substantially smaller with scintigraphy than with stress electrocardiography. Because of this, there appears to be adequate rationale for recommending exercise perfusion imaging, rather than exercise ECG testing alone, as the preferred method for evaluating mortality and morbidity risks after acute myocardial infarction.

Coronary Disease↗

PubMed1980

Contribution of radio-electrocardiography in the rehabilitation of CVA patients.

Seventy-eight patients with cerebrovascular accidents (CVA) underwent radio-electrocardiographic evaluation (RECG) and blood pressure measurements, together with clinical observation during physical therapy and rehabilitation. Twenty-six out of 78 CVA patients had pathological RECG. Of the total, 20 (25.6%) patients had a history of ischemic heart disease prior to CVA, 11 of them manifested abnormalities on the radio-electrocardiography, suggesting myocardial ischemia, arrhythmia, or severe heart rate changes. Out of 58 patients without any cardiac history or complaints before CVA, 15 (25.9%) showed pathological tracings during active therapy. In 20 patients out of 26 with pathological RECG, marked improvement was seen in repeated telemetric evaluation after drug and/or physical therapy was changed. In 42 hypertensive patients, 12 (28,5%) were found to suffer from marked elevation of the diastolic blood pressure during active physical training. Since the energy cost of ambulation in hemiplegics is much higher than in people without motor disabilities, RECG helps us in the detection of cardiac disorders, assessement of myocardial performance, and prescription of optimal physical and/or drug therapy in CVA patients.

Aged↗

PubMedDate not supplied

Comparative study with a moving heart phantom of the impact of temporal resolution on image quality with two multidetector electrocardiography-gated computed tomography units.

OBJECTIVE: The objective of this study was to compare the temporal resolution-related image quality of electrocardiography-gated images acquired with two multidetector computed tomography (CT) units with a moving heart phantom, at similar fixed heart rates, using half-scan and multisector acquisition modes. METHODS: An adjustable moving heart phantom (Limbsandthings, Horfield, Bristol, UK) was used. Specific heart rates (47, 55, 64, 66, 69, and 73 beats per minute [bpm]) were chosen. On a General Electric CT unit (LightSpeed Plus; General Electric Medical Systems, Milwaukee, WI), retrospective half-scan and multisector mode protocols were performed. On a Siemens CT unit (Somatom Volume Zoom; Siemens, Forchheim, Germany), a retrospective half-scan mode was performed at 47, 55, and 64 bpm, and a two-sector mode was performed at 66, 69, and 73 bpm. Reformatted maximum intensity projection images were qualitatively compared and related to their temporal resolution. RESULTS: Half-scan mode protocols provided similar good results with both CT units up to 55 bpm. The two-sector mode improved image quality compared with the half-scan mode. High temporal resolution with the multisector mode provided the best results. CONCLUSION: For coronary artery imaging, acquisition protocols that provide the highest temporal resolution are mandatory. The multisector mode is one technique that allows high temporal resolution but may be clinically inappropriate at heart rates below 65 bpm or when heart rate variation is observed during scan time.

Coronary Angiography↗

PubMed2004

Exercise versus recovery electrocardiography for predicting outcome in hypertensive patients with chest pain.

BACKGROUND: Exercise electrocardiography has limited prognostic accuracy in hypertensives because of unsatisfactory specificity. We prospectively used comparative stress-recovery heart rate-adjusted ST (ST/HR) analysis to predict mortality in a consecutive population of hypertensives with chest pain. METHODS: The stress-recovery index (SRI), defined as the difference between ST/HR areas during exercise and recovery, was derived in 460 hypertensive with known (n=360, 78%) or suspected (n=100, 22%) coronary artery disease. To assess whether it added prognostic information to routinely obtained information, clinical data, the resting ejection fraction, and exercise testing data were entered into a sequential Cox's model; the SRI was entered last. Model validation was performed by bootstrap adjusted by the degree of optimism in estimates. Survival analysis was performed using the product-limit Kaplan-Meier method. RESULTS: During a median follow-up of 28 months (interquartile range, 13-44 months), 32 (7%) patients died, 23 (5%) suffered from acute myocardial infarction and 60 (13%) underwent late (> 3 months) revascularization. Male gender (hazard ratio, 1.53; 95% confidence interval, 1.01-2.34), peak double product (hazard ratio, 0.70; 95% confidence interval, 0.54-0.90) and the SRI (hazard ratio, 0.69; 95% confidence interval, 0.59-0.81 for interquartile difference) were independent predictors of outcome. The SRI increased the prognostic power of the model on top of clinical and exercise testing variables (concordance index, + 10%; discrimination index, + 32%) and showed the widest area under the ROC curve to predict outcome as compared with exercise-only ST analysis and the ST/HR index. Moreover, it provided a significant discrimination of survival. CONCLUSIONS: The SRI predicts all-cause mortality in hypertensive patients with chest pain and provides additional prognostic information over clinical and standard exercise testing data.

Aged↗

PubMed1997

An evaluation of serum troponin T and signal-averaged electrocardiography in predicting electrocardiographic abnormalities after blunt chest trauma.

OBJECTIVE: Despite multiple inquiries, there are no available tests to definitively detect blunt myocardial injury. The evaluation of patients with chest wall injuries without other indications for intensive care unit (ICU) admission has ranged from a single emergency department electrocardiogram (ECG) to 72 hours of continuous electrocardiographic monitoring. Recently, signal-averaged ECG and serum cardiac troponin T have demonstrated clinical utility in the evaluation of ischemic heart disease. The purpose of this study is to determine the ability of these diagnostic tests to predict the occurrence of significant electrocardiographic rhythm disturbances for patients with chest wall injuries and no other indication for ICU admission. METHODS: We prospectively evaluated 71 consecutive adult patients admitted to a regional Level I trauma center with chest wall injuries not requiring ICU admission. We obtained admission signal-averaged ECG, serum troponin T level, standard ECG, and creatine phosphokinase (CPK-MB) level. Patients received continuous electrocardiographic monitoring, follow-up 12-lead electrocardiography, and serial monitoring of troponin and CPK-MB. Echocardiography was performed for patients with abnormal CPK-MB levels. Electrocardiographic events were graded as normal, abnormal but clinically insignificant, or clinically significant. Multiple stepwise logistic regression analysis was used to evaluate predictors for the development of clinically significant electrocardiographic events. RESULTS: On admission, 17 of 71 patients (23.9%) had normal sinus rhythm; 13 (18.3%) had a clinically significant finding. For 50 patients, follow-up ECG was abnormal; for 26, the findings were clinically significant. Of 17 patients with normal initial ECGs, 7 (41%) developed a clinically significant abnormality. Six patients received intervention for ECG findings. Eleven of 71 patients (16%) had positive troponin T; 5 of 71 (7%) had positive CPK-MB; 15 of 71 (21%) had positive signal-averaged ECG; and 4 of 13 had positive echocardiograms. Initial electrocardiographic abnormalities and a troponin T level > 0.20 microg/L were the only variables found to predict clinically significant electrocardiographic events. Sensitivity and specificity of troponin T in predicting clinically significant abnormalities were 27 and 91%, respectively. CONCLUSIONS: 1. The best predictors for the development of significant electrocardiographic changes are an admission ECG abnormality and an elevated serum troponin T level. 2. Both tests have high specificity with low to moderate sensitivity. 3. Patients with normal ECGs may develop clinically significant events. 4. CPK-MB and echocardiograms continue to be poor predictors of significant electrocardiographic events.

Adult↗

PubMed2003

Normal electrocardiography and serum troponin I levels preclude the presence of clinically significant blunt cardiac injury.

BACKGROUND: Uncertainty about the definition and diagnosis of blunt cardiac injury (BCI) leads to unnecessary hospitalization and cost while trying to rule it out. The purpose of this study was to examine whether the combination of two simple tests, electrocardiography (ECG) and serum troponin I (TnI) level, may serve as reliable predictors of BCI or the absence of it. METHODS: Over a period of 30 months (September 1999-February 2002), 333 consecutive patients with significant blunt thoracic trauma were followed prospectively. Serial ECG and TnI tests were performed routinely and echocardiography was performed selectively. Clinically significant BCI (SigBCI) was defined as the presence of cardiogenic shock, arrhythmias requiring treatment, or posttraumatic structural deficits. RESULTS: SigBCI was diagnosed in 44 patients (13%). Of 80 patients with abnormal ECG and TnI, 27 (34%) developed SigBCI. Of 131 with normal serial ECG and TnI, none developed SigBCI. Of patients with abnormal ECG only or TnI only, 22% and 7%, respectively, developed SigBCI. The positive and negative predictive values were 29% and 98% for ECG, 21% and 94% for TnI, and 34% and 100% for the combination of ECG and TnI. The admission ECG or TnI was abnormal in 43 of 44 patients with SigBCI. Only one patient had initially normal ECG and TnI and developed abnormalities 8 hours after admission. Forty-one patients without other significant injuries stayed 1 to 3 days in the hospital only to rule out SigBCI and could have been discharged earlier. Besides ECG and TnI, other independent risk factors of SigBCI were an Injury Severity Score > 15, the presence of significant skeletal trauma, and history of cardiac disease. CONCLUSION: The combination of normal ECG and TnI at admission and 8 hours later rules out the diagnosis of SigBCI. In the absence of other reasons for hospitalization, such patients can be safely discharged.

Adult↗

PubMed2001

Comparison of continuous vectorcardiography and continuous 12-lead electrocardiography of patients with unstable coronary artery disease: do they identify the same population?

BACKGROUND: Continuous vectorcardiography (cVCG) and continuous 12-lead electrocardiography (c12ECG) are important tools for assessing patients with unstable coronary artery disease. OBJECTIVE: To compare the incidences of ischemia detected by the two methods, and examine whether the patients identified belonged to the same population, with respect to various clinical variables. METHODS: Within a randomized prospective trial (FRISC II) including patients with unstable coronary artery disease, ST-segment monitoring was performed either by cVCG or by c12ECG for 24 h after admission for 1016 patients. RESULTS: cVCG and c12ECG were performed for 730 and 286 patients, respectively. Transient ischemic episodes in 253 (34.7%) patients were detected by cVCG and such episodes were detected in 91 (31.8%) patients by c12EGG. When patients in whom transient ischemic episodes had been detected by cVCG and c12ECG were compared, the groups were similar with respect to baseline characteristics, signs of myocardial damage (67.5 versus 70.5%), occurrence of exercise-induced ischemia (59.0 versus 60.0%), and presence of severe coronary lesions (57.0 versus 51.3%). CONCLUSIONS: Results of this study suggest that these two methods identify the same high-risk population, and that these patients can be considered one group when results obtained using either system are analyzed in multicenter studies. This also implies that results concerning the occurrence of episodes of resting ischemia obtained using one system may also be applicable for the other.

Adult↗

PubMed2002

Continuous vectorcardiography is superior to standard electrocardiography in the prediction of long-term outcome after thrombolysis in patients with acute myocardial infarction.

BACKGROUND: Thrombolytic therapy results in reperfusion of the occluded coronary vessel in approximately 75% of treated patients with acute myocardial infarction (AMI). Unsuccessful thrombolysis results in impaired outcome. This study was undertaken to evaluate reperfusion assessments with 12-lead standard static electrocardiography (ECG) and continuous vectorcardiography (VCG) in AMI patients treated with thrombolytic therapy, with particular emphasis on the value of these assessments in relation to long-term outcome. METHODS: ST-recovery analysis 90 and 180 min after the start of thrombolytic therapy was performed by repeated ECG and by VCG in 63 AMI patients. Median follow-up was 255 days. RESULTS: No significant differences in long-term outcome were found between patients with or without obtained reperfusion, as assessed by ECG. For VCG, we found significant elevated relative risks for experiencing death (relative risk = 11.00, confidence interval = 2.70-44.90); P = 0.0008 for the group with ST-vector magnitude recovery of less than 50% at 90 min from start of thrombolytic therapy. CONCLUSION: We demonstrated that early reperfusion assessment with VCG enables the prediction of long-term outcome and is superior to reperfusion assessment with standard static ECG in this regard. We therefore recommend continuous ischemia monitoring of AMI patients treated with thrombolytic therapy as a routine procedure.

Denmark↗

PubMedDate not supplied

Influence of electrolyte abnormalities on interlead variability of ventricular repolarization times in 12-lead electrocardiography.

Increased QT dispersion (QT(d)) has been associated with increased risk for ventricular arrhythmias. Pathologic extracellular electrolyte concentrations may result in ventricular arrhythmias. The aim of this study was to evaluate the effect of electrolyte abnormalities on QT(d). Ten consecutive patients with isolated electrolyte abnormalities were selected for each of the following groups: hypokalemia, hyperkalemia, hypercalcemia, hypocalcemia, hypomagnesemia, and normal controls. Standard 12-lead electrocardiography was performed for each patient and average QT, JT, and RR intervals were calculated for each lead. Dispersion of QT, JT (JT(d)), and QTc (QTc(d)) intervals were calculated as the range between the longest and shortest measurements. Compared with controls, only patients with hypokalemia had a greater QT(d) (115 +/- 31 vs. 49 +/- 15 ms), JT(d) (116 +/- 34 vs. 52 +/- 12 ms), and QTc(d) (141 +/- 40 vs. 58 +/- 1 ms), (P < 0.05). In an experimental substudy, seven rats were maintained on K(+) and seven on Mg(2+)-free diet followed by normal diet. Experimental hypokalemia significantly increased QT(d) (10 +/- 4 to 37 +/- 7 ms), and QTc(d) (32 +/- 6 to 79 +/- 27 ms) (P < 0.05), whereas hypomagnesemia did not. Restoration of serum potassium resulted in normalization of dispersion (QT(d), 14 +/- 2; QTc(d), 34 +/- 6 ms). Hypokalemia increases the dispersion of ventricular repolarization that may be responsible for arrhythmias. Even though hyperkalemia, hypocalcemia, and hypercalcemia are known to affect ventricular repolarization, our study shows that they are not associated with increased dispersion.

Adult↗

PubMedDate not supplied

Use of intracoronary electrocardiography for detecting ST-T, QTc, and U wave changes during coronary balloon angioplasty.

Intracoronary electrocardiography (IC-ECG) is a more sensitive method than surface ECG to detect electrical changes during percutaneous transluminal coronary angioplasty (PTCA). It also provides direct monitoring of ST-T segment, QTc intervals, and U-wave genesis during balloon inflation. These changes are reflective of myocardial ischemia. The authors studied the effect of transient myocardial ischemia on ST-T segment, QTc intervals, and U-wave appearance by comparing standard and perfusion balloon angioplasty. PTCA of left anterior descending artery was performed in 14 patients using the standard balloons and in 11 patients using the perfusion balloons. Patients with perfusion balloon angioplasty had less ST-T elevation (0.15 +/- 0.05 mV versus 1.04 +/- 0.19 mV, P < 0.001), less QTc-shortening intervals (0.01 +/- 0.02 seconds versus -0.05 +/- 0.04 seconds, P < 0.001), and less positive U waves (two versus nine). The authors concluded that balloon angioplasty with perfusion balloons is associated with less ischemia as reflected by ST-T, QTc-shortening intervals, and U-wave changes. There was more positive U-wave appearance with the standard balloon angioplasty, which implies more ischemia. In addition, QTc-shortening intervals are associated with the development of U waves during standard balloon angioplasty. These findings suggest that IC-ECG is a sensitive tool in detecting myocardial ischemia. IC-ECG may also help to clarify the nature of chest pain during PTCA in some patients. Like QT dispersion (QTd), QTc-shortening intervals and new U waves can have prognostic implications and additional studies are needed to define this role.

Aged↗

PubMedDate not supplied

Computer-enhanced frequency-domain and 12-lead electrocardiography accurately detect abnormalities consistent with obstructive and nonobstructive coronary artery disease.

Noninvasive methods of identifying coronary artery disease are not consistently accurate. To identify abnormalities associated with angiographically determined coronary artery disease, the authors sought to quantify the utility of a new device, a digital database-driven multiphase electrocardiograph system (3DMP), which produces a computer-enhanced frequency/time-domain resting electrocardiogram, in conjunction with a 12-lead electrocardiogram. The authors compared resting 3DMP results from those of coronary angiograms to identify abnormalities associated with coronary artery disease in a random sample of 136 patients. Using a discrete-Fourier transform signal-averaging variant and a series of mathematic transformations, the computer-expert system analyzed signals in the 0.1- to 50-Hz range. The system identified abnormalities by comparing results with a 21,000-patient database culled from predicate research. The system detected abnormalities in 96.0% of patients subsequently found to have 70% or greater stenosis by angiography. For patients with a 40% or less times a more than 50% occlusion, the system detected abnormalities in 75% of cases. For patients with a 50% or less times a 70% or less occlusion, it detected abnormalities in 90% of cases. Overall sensitivity for the study was 93.3% (positive predictive value, 91.2%; specificity, 83%; negative predictive value, 86.7%). No gender differences were detected. A 3DMP electrocardiograph system combined with 12-lead electrocardiography appears to have measurable, diagnostic utility in identifying 3DMP abnormalities associated with coronary artery disease, and warrants further study.

Adolescent↗

PubMed2005

The effects of ondansetron and granisetron on electrocardiography in children receiving chemotherapy for acute leukemia.

5-HT3 receptor antagonists, including granisetron and ondansetron, are widely used in the prophylactic treatment of chemotherapy-induced nausea and vomiting. Although the cardiac safety of granisetron and ondansetron has been investigated in several adult studies, there is no report investigating the effects of those agents on electrocardiography (ECG) in children. The effects of intravenously infused (over 30 seconds) 0.1 mg/kg ondansetron and 40 microg/kg granisetron on ECG were assessed in 22 children receiving high-dose methotrexate therapy for acute lymphoblastic leukemia. The ECG recording was obtained at before and just after the infusion, and repeated at 1, 3, 6, and 24 hours of treatment. Granisetron administration resulted in a statistically significant decrease of mean heart rate at 1 and 3 hours, and significant prolongation of mean QT and QTc dispersions at 1 hour of infusion. In patients treated with ondansetron, no meaningful change was observed. In conclusion, intravenous granisetron but not ondansetron causes clinically asymptomatic and transient changes on ECG measurements in children receiving high-dose methotrexate therapy.

Adolescent↗

PubMed1992

The use of temporal information in the regularization of the inverse problem of electrocardiography.

The inverse problem of electrocardiography is solved in order to reconstruct electrical events within the heart from information measured noninvasively on the body surface. These electrical events can be deduced from measured epicardial potentials; therefore, a noninvasive method of recovering epicardial potentials from body surface data is useful in clinical and experimental work. The ill-posed nature of this problem necessitates the use of regularization in the solution procedure. Inversion using Tikhonov zero-order regularization, a quasi-static method, had been employed previously and was able to reconstruct, with relatively good accuracy, important events in cardiac excitation (maxima, minima, etc.). Taking advantage of the fact that the process of cardiac excitation is continuous in time, one can incorporate information from the time progression of excitation in the regularization procedure using the Twomey technique. Methods of this type were tested on data obtained from a human-torso tank in which a beating canine heart was placed in the correct human anatomical position. The results show a marked improvement in the inverse solution when these temporal methods are used, and demonstrate that important physiological events (e.g., right ventricular breakthrough) not detected by the quasi-static approach, are reconstructed using these methods. In addition, the results indicate that as the time interval between sampled maps is reduced, the quality of the solutions that use this temporal regularization is greatly improved.

Action Potentials↗

PubMed1994

Forward and inverse problems of electrocardiography: modeling and recovery of epicardial potentials in humans.

To assess the accuracy of solutions to the inverse problem of electrocardiography in man, epicardial potentials computed from thoracic potential distributions were compared to potentials measured directly over the surface of the heart during arrhythmia surgery. Three-dimensional finite element models of the thorax with different mesh resolutions and conductivity inhomogeneities were constructed from serial computerized tomography scans of a patient. These torso models were used to compute transfer matrices relating the epicardial potentials to the thoracic potentials. Potential distributions over the torso and the ventricles were measured with 63 leads in the same patient whose anatomical data was used to construct the torso models. To solve the inverse problem, different methods based on Tykhonov regularization or regularization- truncation were applied. The recovered epicardial potential distributions closely resembled the epicardial potential distributions measured early during ventricular preexcitation, but not the more complex distributions measured later during the QRS complex. Several problems encountered as the validation process is applied in man are also discussed.

Electrocardiography↗

PubMed1994

A generalized eigensystem approach to the inverse problem of electrocardiography.

We develop a new approach to the ill-conditioned inverse problem of electrocardiography which employs finite element techniques to generate a truncated eigenvector expansion to stabilize the inversion. Ordinary three-dimensional isoparametric finite elements are used to generate the conductivity matrix for the body. We introduce a related eigenproblem, for which a special two-dimensional isoparametric area matrix is used, and solve for the lowest eigenvalues and eigenvectors. The body surface potentials are expanded in terms of the eigenvectors, and a least squares fit to the measured body surface potentials is used to determine the coefficients of the expansion. This expansion is then used directly to determine the potentials on the surface of the heart. The number of measurement points on the surface of the body can be less than the number of finite element nodes on the body surface, and the number of modes employed in the expansion can be adjusted to reduce errors due to noise.

Action Potentials↗

PubMed1995

Removal of power line interference in signal-averaged electrocardiography systems.

A method for line interference reduction to be used in signal-averaged electrocardiography (SAECG) systems is proposed and its performance is analyzed. This new method is an adaptation of a previously reported technique for removal of line interference from conventional electrocardiograms. It involves the recording of a line reference signal simultaneous with the lead signals, so that a shifted and scaled version of it can be used to subtract line interference from the leads. It is shown that this line interference subtraction method can reduce line interference effectively and without introducing any additional noise into the ECG signal. It is also shown that Late Potential diagnostic decisions are not altered when this filter is applied. It is recommended that this technique be used in SAECG when line interference is unavoidable.

Electrocardiography↗

PubMed1995

The effects of errors in assumed conductivities and geometry on numerical solutions to the inverse problem of electrocardiography.

In this paper we used a previously proposed model problem to examine the effects of inhomogeneities on four techniques for numerically solving the inverse problem of electrocardiography. The layered inhomogeneous eccentric spheres system contains three regions representing the lungs, muscle, and subcutaneous fat, and is numerically modeled using finite elements. We simulated both anterior and posterior spherical cap activation fronts. We examined inverse solutions based on zero order Tikhonov regularization, truncated singular value decomposition, our new generalized eigensystem approach, and a modification of the generalized eigensystem approach. The effects on the inverse solutions of geometrical errors, errors in the assumed conductivities, and homogeneous torso assumptions were examined.

Animals↗