Computer-assisted ECG interpretation for confirmation of premature atrial complexes.

UNLABELLED: Current programs for computerized ECG analysis are not interactive. We developed custom software for computer-assisted ECG interpretation that functioned interactively with an observer directing the computerized process. The software was first used for recognition of PACs superimposed on ST-T waveforms. The interactive process included 6 steps. 1) The computer displayed the 12-lead ECG and the user selected the most frequent QRS-T waveforms for averaging. 2) The computer generated and displayed the averaged QRS-T waveform. 3) The user selected waveforms suspected to have PACs superimposed on the ST-T segments. 4) The computer generated and displayed the difference waveform by subtracting the average waveform from the suspect waveforms. 5) The user recognized and p-waves in the difference waveform and marked the onset and offset by positioning the cursor and clicking. 6) The computer then measured p-wave amplitudes, durations, and areas and displayed the recognized p-wave. The program was developed using digital data from 2 ECGs and tested on 39 ECGs with suspected PACs and 26 control ECGs. RESULTS: The software and user interaction recognized 79 PACs in the suspect group. Control ECGs were analyzed using 3 complexes with the same leads and onsets as the test group. Of the 79 PACs found in the suspect group, mean values included an area under the curve of 4.0 +/- 3.2 microV-s for the test group versus 0.4 +/- 0.4 microV-s for the control (P < 0.001) and peak-to-trough voltage amplitudes of 104 +/- 66 microV versus 15 +/- 7 microV for the control (P < 0.001). The average time of onset of the premature complexes was 282 +/- 120 msec, and their duration was 100 +/- 28 msec. CONCLUSION: Custom software combined the superior human pattern recognition with the digital signal processing of the computer. This enhanced recognition of ectopic atrial activity.

Importance of accounting for the variability of electrocardiographic data among diagnostically similar patients with inferior wall healed myocardial infarction.

The authors describe a method to account for patient-to-patient variability in electrocardiographic data. The method yielded criteria for healed inferior myocardial infarction with diagnostic performances better than those of traditional electrocardiographic parameters.

NHLBI workshop on the utilization of ECG databases: preservation and use of existing ECG databases and development of future resources.

Baseline examinations and periodic reexaminations in longitudinal population studies, together with ongoing surveillance for morbidity and mortality, provide unique opportunities for seeking ways to enhance the value of the electrocardiogram (ECG) recorded with digital technology as an inexpensive and noninvasive tool for prognosis and diagnosis. Clinicians, epidemiologists, and engineers from industry, government, and academic medical centers gathered at a workshop sponsored by the National Heart, Lung, and Blood Institute (NHLBI) on June 11-12, 1997, to discuss the research potential of ECG databases, their preservation and accession, and standards for recording and storage. Databases considered were those acquired in ongoing and future NHLBI-funded studies and in clinical settings in which the ECG continues to provide valuable information for evaluation and treatment. The accessibility of existing databases, the quality of their data, and the availability of ancillary demographic and clinical information were major themes. Also discussed were appropriate statistical methodologies to be used with these data for developing and testing ECG algorithms. The workshop participants affirmed the value of these databases and urged the establishment of an ECG advisory and review group to (1) resolve technical and proprietary issues for the utilization of currently existing databases; (2) develop standards for recording, storage, and utilization of ECGs in future NHLBI-supported studies; (3) oversee the creation of a national ECG database resource, consisting of an archive of ECG databases from past and ongoing NHLBI-supported studies, and a registry of ECG databases that would eventually include digital ECGs from populations currently underrepresented in the demographic spectrum of the NHLBI databases.

False-positive behavior with the dP/dt sensing pacemaker: a rare complication of a physiological sensor.

As with "nonphysiological" devices, sensors that directly measure physiological variables have the potential to measure unexpected signals and for the physiological parameter being measured to respond in an unexpected manner. We present the case of a dP/dt sensing pacing system that functioned normally for 2 months and then developed upper rate behavior due to the sensing of a high frequency artifact on the pressure recording. Our case and others cited reinforce the need for future physiological rate responsive pacemakers to incorporate a second sensor to provide for backup rate response in cases of inappropriate rate response.

Reprogramming pacemakers enhances longevity and is cost-effective.

BACKGROUND: Historically, the majority of pulse generators implanted in the United States remain at the nominal programmed settings from the time of implant. While these nominal settings typically allow a sufficient safety margin to prevent later loss of capture with potential chronic threshold rise, the pulse generator with significant use would not be expected to last longer than that predicted by the manufacturer. However, improvements in lead technology have resulted in significantly lower chronic capture thresholds, which would permit lower programmable output settings while still allowing acceptable safety margins. Such changes could result in a significant reduction in long-term battery drain and translate into longer generator life. METHODS AND RESULTS: One hundred eighty consecutive patients undergoing implantation of permanent pacemakers at our institution were studied to determine the impact of reprogramming on pulse generator longevity and cost. Of these patients, 122 completed 6 months of follow-up at our institution and had pulse generators implanted that were capable of measuring battery current. We compared the estimated longevity based on battery current at nominal settings with that based on settings achieved in follow-up. The final settings were determined by the patient's physician using standard safety margins. The predicted longevity was 6.95 +/- 1.59 years at nominal implant settings and 11.16 +/- 2.71 years at final programmed settings (P < .001). Therefore, reprogramming extends the estimated pulse generator longevity by 4.25 +/- 2.14 years (64%) at a mean cost of $110 per patient (+37 per year extended). CONCLUSIONS: Reprogramming of permanent pacemakers is efficacious and cost-effective.

Agreement between artificial neural networks and experienced electrocardiographer on electrocardiographic diagnosis of healed myocardial infarction.

OBJECTIVES: The purpose of this study was to compare the diagnoses of healed myocardial infarction made from the 12-lead electrocardiogram (ECG) by artificial neural networks and an experienced electrocardiographer. BACKGROUND: Artificial neural networks have proved of value in pattern recognition tasks. Studies of their utility in ECG interpretation have shown performance exceeding that of conventional ECG interpretation programs. The latter present verbal statements, often with an indication of the likelihood for a certain diagnosis, such as "possible left ventricular hypertrophy." A neural network presents its output as a numeric value between 0 and 1; however, these values can be interpreted as Bayesian probabilities. METHODS: The study was based on 351 healthy volunteers and 1,313 patients with a history of chest pain who had undergone diagnostic cardiac catheterization. A 12-lead ECG was recorded in each subject. An expert electrocardiographer classified the ECGs in five different groups by estimating the probability of anterior myocardial infarction. Artificial neural networks were trained and tested to diagnose anterior myocardial infarction. The network outputs were divided into five groups by using the output values and four thresholds between 0 and 1. RESULTS: The neural networks diagnosed healed anterior myocardial infarctions at high levels of sensitivity and specificity. The network outputs were transformed to verbal statements, and the agreement between these probability estimates and those of an expert electrocardiographer was high. CONCLUSIONS: Artificial neural networks can be of value in automated interpretation of ECGs in the near future.

Defibrillator twiddler's syndrome causing device failure in a subpectoral transvenous system.

Twiddler's syndrome is well described as a complication of cardiac pacing. Defibrillator twiddler's syndrome has been recently reported with abdominal implantations of epicardial and transvenous defibrillator systems. We report a case of a patient with a transvenous defibrillator system implanted with the pulse generator placed in the subpectoral plane. The patient developed twiddler's syndrome, which resulted in retraction of both leads. This caused inappropriate shocks due to sensing both the atrial and ventricular electrograms. While the subpectoral position leaves the generator deeper and more difficult for the patient to access, it may not lessen the chance of twiddler's syndrome. It is possible that the subpectoral position may actually predispose the patient to this malady.

Effects of atrial fibrillation and atrial flutter on the signal-averaged electrocardiogram.

In conclusion, atrial flutter can create significant errors in the automated time-domain analysis of the SAECG that are only apparent when the study is repeated in sinus rhythm, thus lowering the predictive accuracy of the technique in patients with atrial flutter. Atrial fibrillation rarely creates problems with time-domain analysis of the SAECG. These findings suggest that, unless the performance of a specific signal-averaging device has been evaluated in patients with atrial flutter and found to have acceptable error rates, patients with atrial flutter should not have SAECGs performed for postinfarction risk assessment.

P wave morphology during atrial pacing along the atrioventricular ring. ECG localization of the site of origin of retrograde atrial activation.

P wave morphology during atrial pacing along the atrioventricular (AV) ring was evaluated to develop electrocardiographic (ECG) criteria for identifying the site of origin of the atrial activation wave during reentrant supraventricular tachycardia. Because P wave morphology changes as the pattern of atrial activation changes, the P wave should show characteristic morphologies during reentrant supraventricular tachycardia with use of either accessory AV pathways or the AV node for retrograde atrial activation. In 14 patients, 12-lead ECGs were recorded during bipolar atrial pacing at sites in the coronary sinus vein (along the mitral annulus) and along the atrial endocardium of the tricuspid annulus. P wave morphology was graded for each lead at each site. Sensitivity, specificity, and predictive value of ECG criteria for left versus right and anterior versus posterior atrial pacing sites were evaluated. Data were obtained from 14 sites along the AV ring, including 71 recordings at 6 sites in the coronary sinus vein and 94 recordings at 8 sites along the tricuspid annulus. These recordings were further divided into 54 anterior sites and 80 posterior sites, as well as 62 recordings along the right free wall and 32 recordings along the right atrial septum. The predictive value of a positive P wave in lead I indicating right atrial site of origin was 98.9%, and that for a negative or isoelectric P wave in lead I indicating a left atrial site of origin was 94.6%. Negative P wave in leads II, III, and aVF indicated a posterior site of origin, with a predictive value of 91.2%. The predictive value of a negative or isoelectric P wave in lead V1 indicating a right atrial free wall site was 87.5%. Thus, P wave morphology can be used to localize the site of origin of the atrial depolarization wave to a region along the AV ring.

Increased sensitivity for the diagnosis of healed myocardial infarction using vectorial information in the 12-lead ECG.

The aim of this study was to use the vectorial information in the conventional 12-lead electrocardiographic (ECG) recording and to investigate whether this information, in combination with well-known ECG criteria, could increase the diagnostic performance for healed anterior or inferior myocardial infarction. A total of 1,458 subjects were included in the study; 272 patients with anterior myocardial infarction, 356 patients with inferior myocardial infarction, and 830 subjects classified as normal. New 12-lead vectorcardiographic criteria for anterior and inferior myocardial infarction were developed and used in combination with well-known ECG criteria. The combined criteria showed a sensitivity of 80.0% and 72.4% for the diagnosis of anterior and inferior myocardial infarction, respectively. The corresponding sensitivities for the conventional ECG criteria were significantly lower. In conclusion, the addition of vectorial parameters into ECG interpretation programs could be of value.

T wave amplitudes in normal populations. Variation with ECG lead, sex, and age.

Consideration of increased T wave amplitude (tall T waves), either alone or in association with other electrocardiographic (ECG) parameters, may be beneficial for the early detection of acute transmural ischemia, and quantification of the increase might be used in quantifying the ischemic area. The primary purpose of this study was to quantify normal T wave amplitude limits according to ECG lead, sex, and age. One thousand nine hundred thirty-five subjects in two normal populations were analyzed, and the 98th percentile of the positive T wave amplitude for each ECG lead (including -aVR) was considered the upper limit of normal. Normal T wave amplitude was two times greater in the precordial than in the limb leads, and it was approximately 25% greater in men than in women in all leads. There was approximately a 10% decrease in normal T wave amplitude between 18-39- and 40-59-year-old patients and a 15% decrease between 40-59- and 60-79-year-old patients. The upper limit of normal T wave amplitudes identified in this study confirm those developed by Lepeschkin for use as means for each lead when age and sex are not considered. These limits might be incorporated into both normograms and automated ECG analysis systems to determine the presence or absence of tall T waves in patients presenting with symptoms of acute transmural ischemia.

Reconstruction of the standard 12-lead ECG from recordings using nonstandard activity-compatible proximal limb lead positions.

Proximal or torso placement of limb leads in the 12-lead electrocardiogram (ECG) has been shown to influence the appearance of QRS waveforms considerably. A method was developed for computer-based reconstruction of standard-like waveforms from nonstandard torso-recorded waveforms. Reconstruction coefficients required by the method were determined using ECG data obtained from 30 patients. The coefficients were then applied on an independent test set of 100 patients. In 21 of these patients, a second standard EGG was obtained the next day to determine the day-to-day variation in QRS waveforms. R wave amplitudes in leads I and II, and electrical axes in the frontal plane were measured in the standard ECG, the nonstandard ECG, and the reconstructed ECG. It is shown that the reconstruction method yields ECGs that differ less from standard than do two standard ECGs recorded on consecutive days. The performance of the reconstruction method was not influenced by age, sex, height, or weight.

Simultaneous ST-segment measurements using standard and monitoring-compatible torso limb lead placements at rest and during coronary occlusion.

Electrocardiographic recordings used to assess ST-segment deviation are performed using both standard and torso limb lead positions, where bony prominences give more artifact-free signal. Whereas significant QRS artifact can be introduced by such changes in lead location, the impact on ST-segment measurements has never been assessed. Digital electrocardiographic recordings were performed in 29 patients throughout elective angioplasty balloon inflation in the left anterior descending (n = 12), right coronary (n = 14), and circumflex (n = 3) arteries. In all cases, unipolar leads V1, V4, and V6 were affixed to the torso lead positions, allowing reconstruction of simultaneously acquired standard and modified 9-lead electrocardiograms (ECGs). ST levels in the 26 patients who had ST deviation during angioplasty were compared at both baseline and peak ischemia of up to 1,046 microV in the anterior, and 551 microV in the inferior leads. Differences in recorded ST levels for modified versus standard lead locations were all < 100 microV, even at peak ischemia. Although ST-segment elevation in the inferior leads appeared to show slightly more pronounced differences between lead sets than did anterior elevation, all differences were < 100 microV. Thus, measurement of ST-segment levels appears unlikely to be importantly affected by the intermixture of ECGs recorded with standard lead positions and ECGs recorded with monitoring-compatible lead positions on the torso. Recalibration of ST-segment measurements may be necessary for meticulous quantification of ischemia, infarct size, or other measurements that might be affected by variations < 100 microV.

Artificial neural networks for the electrocardiographic diagnosis of healed myocardial infarction.

Artificial neural networks are computer-based expert systems that learn by example, in contrast to the currently used rule-based electrocardiographic interpretation programs. For the purpose of this study, 1,107 electrocardiograms (ECGs) from patients who had undergone cardiac catheterization were used to train and test neural networks for the diagnosis of myocardial infarction. Different combinations of QRS and ST-T measurements were used as input to the neural networks. In a learning process, the networks automatically adjusted their characteristics to correctly diagnose anterior or inferior wall myocardial infarction from the ECG. Two thirds of the ECGs were used in this process. Thereafter, the performance of the networks was studied in a separate test set, using the remaining third of the ECGs. The results from the networks were also compared with that of conventional electrocardiographic criteria. The sensitivity for the diagnosis of anterior myocardial infarction was 81% for the best network and 68% for the conventional criteria (p < 0.01), both having a specificity of 97.5%. The corresponding sensitivities of the network and the criteria for the diagnosis of inferior myocardial infarction were 78% and 65.5% (p < 0.01), respectively, compared at a specificity of 95%. The results indicate that artificial neural networks may be of interest in the attempt to improve computer-based electrocardiographic interpretation programs.

Establishment of signal-averaged electrocardiographic criteria with Frank XYZ leads and spectral filter used alone and in combination with ejection fraction to predict inducible ventricular tachycardia in coronary artery disease.

Signal-averaged electrocardiographic criteria are reported for corrected Frank XYZ leads and a spectral filter. The new criteria were used alone and in combination with ejection fraction to predict inducibility of ventricular tachycardia (VT) at electrophysiologic testing. Signal-averaged electrocardiographic criteria were developed in 87 control subjects and validated in 182 patients (aged 63 +/- 10 years) with coronary artery disease and QRS duration less than 118 ms. Patients underwent electrophysiologic testing in which up to 3 extra-stimuli were used during 2 paced drives from 2 right ventricular sites. A positive finding was monomorphic VT lasting 30 seconds or needing intervention. An ejection fraction less than 40% was considered abnormal. Signal-averaged electrocardiographic variables that best characterized control subjects and separated patients with and without inducible VT were filtered QRS duration less than 120 ms, low-amplitude signal duration less than 38 ms and root-mean-square voltage greater than 20 muv. With these criteria, signal-averaged electrocardiographic and ejection fraction sensitivities were 87 and 45%, respectively, and specificities were 65 and 77%, respectively. Combining signal-averaged electrocardiography with ejection fraction improved the predictive accuracy. In conclusion, diagnostic criteria for signal-averaged electrocardiography with use of Frank XYZ leads and a spectral filter produced results similar to those reported for use of bipolar XYZ leads and a Butterworth filter. Signal-averaged electrocardiography was a better predictor of VT than was ejection fraction.

Performance of the automated complete Selvester QRS scoring system in normal subjects and patients with single and multiple myocardial infarctions.

The automated version of the complete Selvester QRS scoring system for estimation of myocardial infarct size was evaluated in 1,344 normal subjects, 706 patients with a single myocardial infarction (366 with inferior infarction, 277 with anterior infarction and 63 with posterolateral infarction) and 131 patients with combined inferior and anterior infarction. The presence and location were determined by angiographic and ventriculographic criteria. The performance of the overall 32-point system, each of the 19 criteria and the 13 criteria sets and each of the 35 criteria within the 13 sets was examined. The mean point scores were 1.7 for normal subjects, 3.7 for posterolateral infarction, 4.1 for inferior infarction, 6.3 for anterior infarction and 6.9 for multiple infarcts. A score greater than 4 yielded a sensitivity of 67% for anterior infarction, 41% for inferior infarction, 32% for posterolateral infarction and 72% for multiple infarcts. However, 7 of 32 criteria failed to achieve 95% specificity and 10 of 35 criteria in criteria sets had a sensitivity that was even lower than their false positive rate. The automated Selvester QRS scoring system currently has limitations that are attributable to development of the original system, which used manual scoring techniques and established criteria limits from middle-aged men. Future automated analysis should use gender- and age-dependent criteria limits.

Evaluation of changes in standard electrocardiographic QRS waveforms recorded from activity-compatible proximal limb lead positions.

Proximal limb lead positions are currently used for activity-compatible electrocardiographic monitoring of myocardial ischemia. Two previously described systems for alternate limb lead placement were studied in patients with and without QRS evidence of healed anterior or inferior myocardial infarction. An innovative method was used to simultaneously record 6 standard and 6 modified limb leads, and 3 standard and 3 modified precordial leads on a standard digital electrocardiograph. Both alternate lead placement systems showed rightward frontal plane axis shift and diminished Q-wave durations in lead aVF compared with those of their simultaneous standard controls. Furthermore, potential differences between the standard distal limb lead sites and 5 more proximal sites were explored along each limb. Differences along the left arm were accentuated relative to those along the right arm owing to differences in proximity of the arms to the myocardium. Along the lower limb, and anterior site showed less deviation from standard than did a more lateral site. It is imperative that recordings from alternate sites be labeled accordingly so that their output cannot be confused with that obtained from standard sites.

Specificity and sensitivity of QRS criteria for diagnosis of single and multiple myocardial infarcts.

A subset of 3 criteria from the complete Selvester scoring system has been proposed earlier for electrocardiographic screening of healed myocardial infarcts. This subset yielded 95% specificity and high sensitivity for single anterior and inferior infarcts. In the present study, an automated version of these criteria was applied to 1,344 electrocardiograms from normal subjects (473 normal subjects as determined by cardiac catheterization and 871 apparently normal subjects by history and physical examination), to 706 from subjects with single myocardial infarction, and to 131 from subjects with combined anterior and inferior myocardial infarcts. Of the single infarcts, 366 had inferior, 277 anterior and 63 posterolateral locations. Presence and location of infarcts were judged from left ventriculograms and coronary angiograms. Overall specificity was only 86%, whereas overall sensitivity for the infarct population was 77%. Specificity was lower in men than in women; it was also lower in older than in younger subjects. One of the screening criteria (R greater than or equal to 40 ms in V1) may possibly be eliminated to augment specificity; this can be done with only minor loss of sensitivity. Differences in wave form measurements between the manual and computer methods account for a large part of the deterioration of specificity in this study compared with previously published results. Computer application of the screening criteria requires altered criteria limits in comparison with those used in manual application. Probably sex- and age-dependent criteria limits should be used.