Investigación reciente

J Electrocardiol. 2008 May-Jun;41(3):245-50. Epub 2008 Mar 25.

Mirror image electrocardiograms and additional electrocardiographic leads: new wine in old wineskins?

Kors JA, van Herpen G.
Contact: Department of Medical Informatics, Erasmus University Medical Center, Rotterdam, The Netherlands.

BACKGROUND: Mirror image electrocardiograms (ECGs), obtained by inverting the original signals, and additional precordial leads have been proposed as means to improve ECG diagnosis. The theoretical backgrounds of these proposals are discussed.

METHODS: In 746 body surface potential maps, the mirror areas of the 6 precordial leads, V(3)R, and 2 more leads higher up and 1 lower down the thorax have been determined. The similarity between the original signal and its mirror image was expressed by a similarity index. This was done separately for QRS and ST-T; for the first and second parts of QRS; and for the categories normal, left ventricular hypertrophy, and infarct.

RESULTS: In general, high similarity scores were obtained. The mirror images of V(1) and V(2) are almost diametrically located on the back. Inverting these leads could render the V(8) and V(9) leads. The other mirror areas may deviate considerably from where generally expected.

CONCLUSION: Mirror images can be obtained consistently from all locations, supporting the dipole representation of cardiac electrical activity. Neither mirror image ECGs nor additional chest leads contribute essentially to ECG diagnosis.

J Electrocardiol. 2008 May-Jun;41(3):190-6. Epub 2008 Mar 20.

Intraindividual variability in electrocardiograms.

Schijvenaars BJ, van Herpen G, Kors JA.
Contact: Department of Medical Informatics, Erasmus University Medical Center, Rotterdam, The Netherlands.

The electrocardiogram (ECG) can be affected by intraindividual variations from various sources that may confuse the diagnosis of the underlying cardiac condition and impair the accuracy of ECG interpretation. Intraindividual variability is a hindrance in serial ECG analysis, where ECGs of the same individual, but taken at different times, are compared. Two sources of intraindividual variability can be distinguished as follows: variability related to the technical circumstances during ECG recording (technical sources) and nonpathologic biologic variability (biological sources). Among the technical sources, variation in electrode positioning between recordings is the most confusing. Of the biological sources, respiratory variations are effective at any time scale, but the most important are age and weight that work on prolonged time scales. Technical problems are best prevented by rigorously sticking to a standard acquisition protocol. Criteria can be adapted to changing circumstances (age, weight), and by computer modeling, it may be possible to correct the ECG diagnosis for some sources of intraindividual variability.

Am J Emerg Med. 2008 May;26(4):497-503.

The pediatric electrocardiogram part III: Congenital heart disease and other cardiac syndromes.

O'Connor M, McDaniel N, Brady WJ.
Contact: Department of Pediatrics, Childrens' Medical Center, University of Virginia Health System, Charlottesville, VA, USA.

Approximately 1% of newborns are affected by congenital heart disease (CHD), and although many lesions of CHD have trivial hemodynamic and clinical implications, some clinically significant lesions are asymptomatic in the immediate newborn period and may present after discharge from the well baby nursery. Because of this, CHD should be considered in the differential diagnosis of any ill-appearing newborn, regardless of the presence of cyanosis. In addition, the number of children, adolescents, and adults with surgically repaired or palliated CHD continues to grow within the United States and other developed countries. It is in this population that arrhythmias are particularly prone to develop, and knowledge of the common arrhythmias associated with CHD is mandatory for the acute care provider.

Am J Emerg Med. 2008 May;26(4):506-12. Review.

The pediatric electrocardiogram: part I: Age-related interpretation.

O'Connor M, McDaniel N, Brady WJ.
Contact: Department of Pediatrics, Children's Medical Center, University of Virginia Health System, Charlottesville, VA 22908, USA.

Emergency physicians attending to pediatric patients in acute care settings use electrocardiograms (ECGs) for a variety of reasons, including syncope, chest pain, ingestion, suspected dysrhythmias, and as part of the initial evaluation of suspected congenital heart disease. Thus, it is important for emergency and acute care providers to be familiar with the normal pediatric ECG in addition to common ECG abnormalities seen in the pediatric population. The purpose of this 3-part review will be to review (1) age-related changes in the pediatric ECG, (2) common arrhythmias encountered in the pediatric population, and (3) ECG indicators of structural and congenital heart disease in the pediatric population.

J Emerg Med. 2008 Apr 23 [Epub ahead of print].

Electrocardiographic Manifestations: Pediatric ECG.

Chan TC, Sharieff GQ, Brady WJ.
Contact: Department of Emergency Medicine, University of California San Diego Medical Center, San Diego, California.

Interpretation of pediatric electrocardiograms (ECGs) can be challenging for the Emergency Physician. Part of this difficulty arises from the fact that the normal ECG findings, including rate, rhythm, axis, intervals and morphology, change from the neonatal period through infancy, childhood, and adolescence. These changes occur as a result of the maturation of the myocardium and cardiovascular system with age. Along with these changes, up to 20% of pediatric ECGs obtained in the acute setting may have clinically significant abnormal findings. This article will discuss the approach to the interpretation of ECGs in children, the age-related findings and alterations on the normal pediatric ECG, and those ECG abnormalities associated with pediatric cardiac diseases, including the variety of congenital heart diseases seen in children.

Ann Noninvasive Electrocardiol. 2008 Apr;13(2):145-54.

Development and validation of diagnostic criteria for atrial flutter on the surface electrocardiogram.

Weinberg KM, Denes P, Kadish AH, Goldberger JJ.
Contact: Department of Medicine and the Feinberg Cardiovascular Institute, Northwestern University, Chicago, IL, USA.

BACKGROUND: There are no universally accepted ECG diagnostic criteria for atrial flutter (AFL), making its differentiation from "coarse" atrial fibrillation (AF) difficult.

METHODS: To develop diagnostic criteria for AFL, we examined two sets of ECGs. Set 1 consisted of 100 ECGs (50 AF, AFL) with diagnoses confirmed by intracardiac recordings. Criteria evaluated were presence of F waves in the frontal plane leads, F waves in V(1), sawtooth F waves, rate, and regularity of ventricular response. Set 2 included 200 ECGs taken from the hospital database each of which had already been interpreted by a cardiologist as either AF (n = 100) or AFL (n = 100). Set 2 was blindly read by electrophysiologists whose consensus-diagnoses were compared to the diagnoses made by using the best criteria identified from the Set 1 data.

RESULTS: The criteria of frontal plane F waves, regular or partially regular ventricular response, and their combination had sensitivities of 92%, 98%, and 90% and specificities of 100%, 78%, and 100% in Set 1 for the diagnosis of AFL. In Set 2, concordance of electrophysiologist and cardiologist diagnoses was only 84%. The criteria of frontal plane Fwaves, regular or partially regular ventricular response, and their combination resulted in concordances with the cardiologist diagnoses of 85%, 85%, and 82% and with the electrophysiologist-consensus diagnoses of 90%, 89%, and 94% (P < 0.001).

CONCLUSIONS: The criteria of frontal plane F waves and regular or partially regular ventricular response aid in the proper diagnosis of AFL. Because management strategies may differ for AF and AFL, it is important to adopt a more rigorous diagnostic approach.

J Cardiovasc Electrophysiol. 2008 Mar 26 [Epub ahead of print].

Activation Delay and VT Parameters in Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy: Toward Improvement of Diagnostic ECG Criteria.

Cox MG, Nelen MR, Wilde AA, Wiesfeld AC, Smagt JJ, Loh P, Cramer MJ, Doevendans PA, Tintelen JP, de Bakker JM, Hauer RN.
Contact: Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.

INTRODUCTION: Desmosomal changes, electrical uncoupling, and surviving myocardial bundles embedded in fibrofatty tissue are hallmarks of activation delay in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). Currently, generally accepted task force criteria (TFC) are used for clinical diagnosis. We propose additional criteria based on activation delay and ventricular tachycardia (VT) to improve identification of affected individuals.

METHODS AND RESULTS: Activation delay and VT-related 12-lead electrocardiographic (ECG) criteria were studied, while off drugs, in 42 patients with proven ARVD/C according to TFC, and 27 controls with idiopathic VT from the RV outflow tract. Two of three measured TFC could only be identified in a small minority of ARVD/C patients. Additional ECG criteria proposed in this study included (a) prolonged terminal activation duration, an indicator of activation delay; (b) VT with LBBB morphology and superior axis; and (c) multiple different VT morphologies. These criteria were met in 30 (71%), 28 (67%), and 37 (88%) ARVD/C patients, respectively, and in one control patient (P < 0.001). Electrophysiologic studies contributed importantly to yield different VT morphologies. Pathogenic plakophilin-2 mutations were identified in 25 (60%) of ARVD/C patients and in none of the controls. In ARVD/C patients, parameters measured were not significantly different between mutation carriers and noncarriers, except for negative T waves in V1-3, occurring more frequently in patients with mutation.

CONCLUSIONS: The proposed additional criteria are specific for ARVD/C and more sensitive than the current TFC. Therefore, adding the newly proposed criteria to current TFC could improve ARVD/C diagnosis, independent of DNA analysis.

Ann Emerg Med. 2008 Mar;51(3):240-6, 246.e1. Epub 2007 Jun 7.

Low diagnostic yield of electrocardiogram testing in younger patients with syncope.

Sun BC, Hoffman JR, Mower WR, Shlamovitz GZ, Gabayan GZ, Mangione CM.
Contact: Department of Medicine, West Los Angeles Veterans Affairs Medical Center, Los Angeles, CA 90073, USA.

STUDY OBJECTIVE: Routine ECG testing is recommended in the evaluation of syncope, although the value of such testing in young patients is unclear. For ECG testing, we assess the diagnostic yield (frequency that ECG identified the reason for syncope) and predictive accuracy for 14-day cardiac events after an episode of syncope as a function of age.

METHODS: Adult patients with syncope or near-syncope were prospectively enrolled for 1 year at a single academic emergency department (ED). A 3-physician panel reviewed ED charts, hospital records, and telephone interview forms to identify predefined cardiac events. The primary outcome included all 14-day, predefined cardiac events including arrhythmia, myocardial ischemia, and structural heart disease.

RESULTS: Of 592 eligible patients, 477 (81%) provided informed consent. Direct telephone contact or admission/outpatient records were successfully obtained for 461 (97%) patients, who comprised the analytic cohort. There were 44 (10%) patients who experienced a 14-day cardiac event. Overall diagnostic yield of ECG testing was 4% (95% confidence interval 2% to 6%). For patients younger than 40 years, ECG testing had a diagnostic yield of 0% (95% confidence interval 0% to 3%) and was associated with a 10% frequency of abnormal findings.

CONCLUSION: ECG testing in patients younger than 40 years did not reveal a cardiac cause of syncope and was associated with a significant frequency of abnormal ECG findings unrelated to syncope. Although our findings should be verified in larger studies, it may be reasonable to defer ECG testing in younger patients who have a presentation consistent with a benign cause of syncope.

Heart Rhythm. 2008 Mar;5(3):413-8. Epub 2007 Dec 23.

Interatrial conduction can be accurately determined using standard 12-lead electrocardiography: validation of P-wave morphology using electroanatomic mapping in man.

Holmqvist F, Husser D, Tapanainen JM, Carlson J, Jurkko R, Xia Y, Havmöller R, Kongstad O, Toivonen L, Olsson SB, Platonov PG.
Contact: Department of Cardiology, Lund University Hospital, Lund, Sweden.

BACKGROUND: Different P-wave morphologies during sinus rhythm as displayed on standard ECGs have been postulated to correspond to differences in interatrial conduction.

OBJECTIVE: The purpose of this study was to evaluate the hypothesis by comparing P-wave morphologies using left atrial activation maps.

METHODS: Twenty-eight patients (mean age 49 +/- 9 years) admitted for ablation of paroxysmal atrial fibrillation were studied. Electroanatomic mapping of left atrial activation was performed at baseline during sinus rhythm with simultaneous recording of standard 12-lead ECG. Unfiltered signal-averaged P waves were analyzed to determine orthogonal P-wave morphology. The morphology was subsequently classified into one of three predefined types. All analyses were blinded.

RESULTS: The primary left atrial breakthrough site was the fossa ovalis in 8 patients, Bachmann bundle in 18, and coronary sinus in 2. Type 1 P-wave morphology was observed in 9 patients, type 2 in 17, and type 3 in 2. Seven of eight patients with fossa ovalis breakthrough had type 1 P-wave morphology, 16 of 18 patients with Bachmann bundle breakthrough had type 2 morphology, and both patients with coronary sinus breakthrough had type 3 P-wave morphology. Overall, P-wave morphology criteria correctly identified the site of left atrial breakthrough in 25 (89%) of 28 patients.

CONCLUSION: In the vast majority of patients, P-wave morphology derived from standard 12-lead ECG can be used to correctly identify the left atrial breakthrough site and the corresponding route of interatrial conduction.

Heart Rhythm. 2008 Mar;5(3):406-12. Epub 2008 Feb 5.

Consistency of complex fractionated atrial electrograms during atrial fibrillation.

Lin YJ, Tai CT, Kao T, Chang SL, Wongcharoen W, Lo LW, Tuan TC, Udyavar AR, Chen YJ, Higa S, Ueng KC, Chen SA.
Contact: Division of Cardiology, Department of Medicine, Taipei Veterans General Hospital, Taipei, Taiwan.

BACKGROUND: Temporal variation in complex fractionated atrial electrograms (CFAEs) exists during atrial fibrillation (AF).

OBJECTIVE: This study sought to quantify the variation in CFAEs using a fractionation interval (FI) algorithm and to define the shortest optimal recording duration required to consistently characterize the magnitude of the fractionation.

METHODS: Twenty-seven patients undergoing AF mapping in the left atrium were studied. The FI and frequency analysis were performed at each mapped site for recording durations of 1 to 8 seconds. The magnitude of the fractionation was quantified by the FI algorithm, which calculated the mean interval between multiple, discrete deflections during AF. The results from each duration were statistically compared with the maximal-duration recording, as a standard. The FI values were compared with the dominant frequency values obtained from the associated frequency spectra.

RESULTS: The FIs obtained from recording durations between 5 and 8 seconds had a smaller variation in the FI (P < .05) and, for those sites with a FI < 50 ms, the fractionation was typically continuous. The fast-Fourier Transform spectra obtained from the CFAE sites with recording durations of >5 seconds harbored higher dominant frequency values than those with shorter recording durations (8.1 +/- 2.5 Hz vs. 6.8 +/- 0.98 Hz, P < .05). The CFAE sites with continuous fractionation were located within the pulmonary veins and their ostia in 77% of patients with paroxysmal AF, and in only 29% of patients with nonparoxysmal AF (P < .05).

CONCLUSION: The assessment of fractionated electrograms requires a recording duration of > or =5 seconds at each site to obtain a consistent fractionation. Sites with the shortest FIs consistently identified sites with the fastest electrogram activity throughout the entire left atrium and pulmonary veins.

IEEE Trans Biomed Eng. 2008 Mar;55(3):1243-7.

Automatic detection and imaging of ischemic changes during electrocardiogram monitoring.

Zizzo C, Hassani A, Turner D.
Contact: Computing Department, Anglia Ruskin University, Victoria Road South, Chelmsford CM1 1LL, UK.

A new electrocardiogram (ECG) monitor with automated ST analysis and display capability has been developed to assist healthcare professionals identify the site and severity of acute ischemic changes. The monitor displays the changes as a 3-D image of the heart in real time. The underpinning assumption is that images are easier to interpret than ECG traces. We describe here the features of two functions of the monitor, the ischemia detection and imaging function (IF). The ischemia detection function was validated using the European ST-T database, and was found to have a sensitivity of 85% and positive predictivity of 93%. Fifty doctors took part in the evaluation of the new IF and the results showed an increase in their median proficiency to diagnose ischemia from 50% to 100% and an increase in their certainty of the diagnosis from 65% to 80%. The time to reach a diagnosis for eight ECGs, dropped from 15 to 9 min.

J Cardiovasc Nurs. 2008 Mar-Apr;23(2):169-74.

Electrocardiographic evaluation of cardiovascular status.

Wung SF, Kozik T.
Contact: College of Nursing, The University of Arizona, Tucson, AZ 85721-0203, USA.

The electrocardiogram (ECG) is indispensable for the diagnosis and management of patients with a wide variety of cardiac and noncardiac diseases. The purpose of this paper is focused on recent research that used ECG, specifically the long-QT interval and microvolt T wave alternans, for the evaluation of life-threatening ventricular arrhythmias. Although remaining to be validated, QT prolongation along with other emerging electrocardiographic indices such as T wave morphology, T peak-to-T end time, or beat-to-beat QT variability may be sensitive indicators of malignant polymorphic ventricular tachyarrhythmia, torsade de pointes. Microvolt T wave alternans may provide important information in identifying a low-risk group with left ventricular dysfunction who is unlikely to benefit from unnecessary prophylactic implantable cardioverter defibrillator therapy. These ECG markers have the potential to aid in the safe administration of individualized medications, avoidance of sudden cardiac death, and provision of a noninvasive strategy to identify patients who are most and least likely to benefit from expensive prophylactic implantable cardioverter defibrillator placement.

Med Eng Phys. 2008 Mar;30(2):248-57. Epub 2007 Mar 26.

Assessment and comparison of different methods for heartbeat classification.

Jekova I, Bortolan G, Christov I.
Contact: Centre of Biomedical Engineering, Bulgarian Academy of Sciences, Sofia, Bulgaria.

The most common way to diagnose cardiac dysfunctions is the ECG signal analysis, usually starting with the assessment of the QRS complex as the most significant wave in the electrocardiogram. Many methods for automatic heartbeats classification have been applied and reported in the literature but the use of different ECG features and the training and testing on different datasets, makes their direct comparison questionable. This paper presents a comparative study of the learning capacity and the classification abilities of four classification methods--Kth nearest neighbour rule, neural networks, discriminant analysis and fuzzy logic. They were applied on 26 morphological parameters, which include information of amplitude, area, interval durations and the QRS vector in a VCG plane and were tested for five types of ventricular complexes--normal heart beats, premature ventricular contractions, left and right bundled branch blocks, and paced beats. One global, one basic and two local learning sets were used. A small-sized learning set, containing the five types of QRS complexes collected from all patients in the MIT-BIH database, was used either with or without applying the leave one out rule, thus representing the global and the basic learning set, respectively. The local learning sets consisted of heartbeats only from the tested patient, which were taken either consecutively or randomly. Using the local learning sets the assessed methods achieved high accuracies, while the small size of the basic learning set was balanced by reduced classification ability. Expectedly, the worst results were obtained with the global learning set.

Am J Emerg Med. 2008 Mar;26(3):348-58.

The pediatric electrocardiogram part II: Dysrhythmias.

O'Connor M, McDaniel N, Brady WJ.
Contact: Department of Pediatrics, Children's Medical Center, University of Virginia Health System, Charlottesville, VA 22908, USA.

The following article in this series will describe common arrhythmias seen in the pediatric population. Their definitions and clinical presentations along with electrocardiogram (ECG) examples will be presented. In addition, ECG changes seen in acute toxic ingestions commonly seen in children will be described, even if such ingestions do not produce arrhythmias per se. Disturbances of rhythm seen frequently in patients with unrepaired and corrected congenital heart disease will be more fully discussed in the third article of this series. Numerous classification schemes for arrhythmias exist; in this article arrhythmias will be grouped based upon their major ECG manifestations.

Am J Physiol Heart Circ Physiol. 2008 Feb 29 [Epub ahead of print].

Improved ECG detection of presence and severity of right ventricular pressure load validated with cardiac magnetic resonance imaging.

Henkens IR, Mouchaers KT, Vonk-Noordegraaf A, Boonstra A, Swenne CA, Maan AC, Man SC, Twisk JW, van der Wall EE, Schalij MJ, Vliegen HW.
Contact: Cardiology, Leiden University Medical Center, Leiden, Netherlands.

The study aimed to assess whether the 12-lead electrocardiogram (ECG) derived ventricular gradient, a vectorial representation of ventricular action potential duration heterogeneity directed towards the area of shortest action potential duration, can improve ECG diagnosis of chronic right ventricular (RV) pressure load. ECGs from 72 pulmonary arterial hypertension patients recorded <30 days before onset of therapy were compared with ECGs from matched healthy controls subjects (n=144). Conventional ECG criteria for increased RV pressure load were compared with changes in the ventricular gradient. In 38 patients a cardiac magnetic resonance (CMR) study had been performed within 24 hours of the ECG. By multivariable analysis, combined use of conventional ECG parameters (rsr'or rsR' in V1, R/S>1 with R>0.5 mV in V1, and QRS axis >90 degrees ) had a sensitivity of 89%, and a specificity of 93% for presence of chronic RV pressure load. However, the ventricular gradient not only had a higher diagnostic accuracy for chronic RV pressure load by ROC analysis (AUC=0.993, SE 0.004 vs. AUC=0.945, SE 0.021, P<0.05), but also discriminated between mild to moderate and severe RV pressure load. CMR identified an inverse relation between the ventricular gradient and RV mass, but there was no significant relation with RV volume. In conclusion, chronically increased RV pressure load is electrocardiographically reflected by an altered ventricular gradient associated with RV remodeling related changes in ventricular action potential duration heterogeneity. Using the ventricular gradient allows ECG detection of even mildly increased RV pressure load. Key words: Pulmonary arterial hypertension, right ventricular hypertrophy, diagnosis, ventricular gradient.

Int J Cardiol. 2008 Feb 29;124(2):250-3. Epub 2007 Mar 27.

A novel approach in R peak detection using Hybrid Complex Wavelet (HCW).

Fard PJ, Moradi MH, Tajvidi MR.

In this letter, by design of Complex Morlet Wavelet and Complex Frequency B-Spline Wavelet and linearly combining them, a novel approach, Hybrid Complex Wavelet, has been proposed to identify and detect the components of ECG signal such as QRS complex and R peak. By train and test of implementing the proposed method on both clinically recorded signals from 40 patients and 30 signals of MIT BIH database, we reached better recognition accuracy in comparison to other well-known approaches.

Eur J Pediatr. 2008 Feb 13; [Epub ahead of print].

Are ECG abnormalities in Noonan syndrome characteristic for the syndrome?

Raaijmakers R, Noordam C, Noonan JA, Croonen EA, van der Burgt CJ, Draaisma JM.
Contact: Department of Paediatric Cardiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands,

Of all patients with Noonan syndrome, 50-90% have one or more congenital heart defects. The most frequent occurring are pulmonary stenosis (PS) and hypertrophic cardiomyopathy. The electrocardiogram (ECG) of a patient with Noonan syndrome often shows a characteristic pattern, with a left axis deviation, abnormal R/S ratio over the left precordium, and an abnormal Q wave. The objective of this study was to determine if these ECG characteristics are an independent feature of the Noonan syndrome or if they are related to the congenital heart defect. A cohort study was performed with 118 patients from two university hospitals in the United States and in The Netherlands. All patients were diagnosed with definite Noonan syndrome and had had an ECG and echocardiography. Sixty-nine patients (58%) had characteristic abnormalities of the ECG. In the patient group without a cardiac defect (n = 21), ten patients had a characteristic ECG abnormality. There was no statistical relationship between the presence of a characteristic ECG abnormality and the presence of a cardiac defect (p = 0.33). Patients with hypertrophic cardiomyopathy had more ECG abnormalities in total (p = 0.05), without correlation with a specific ECG abnormality. We conclude that the ECG features in patients with Noonan syndrome are characteristic for the syndrome and are not related to a specific cardiac defect. An ECG is very useful in the diagnosis of Noonan syndrome; every child with a Noonan phenotype should have an ECG and echocardiogram for evaluation.

Am J Cardiol. 2008 Feb 1;101(3):359-63. Epub 2007 Dec 21.

Prognostic value of electrocardiographic measurements before and after cardiac resynchronization device implantation in patients with heart failure due to ischemic or nonischemic cardiomyopathy.

Iler MA, Hu T, Ayyagari S, Callahan TD 4th, Civello KC, Thal SG, Wilkoff BL, Chung MK.
Contact: Cleveland Clinic, Cleveland, Ohio, USA.

Postimplant QRS narrowing may predict clinical response after cardiac resynchronization therapy (CRT), but identification of nonresponders remains difficult. We studied the predictive value of electrocardiographic characteristics for mortality or cardiac transplantation in patients after CRT. Patients who had electrocardiograms available for review from before and after CRT device implantation were identified from a clinical database. Bivariate and multivariate Cox regression analyses were performed for the end point of death or transplantation. Of 337 patients (age 65+/-12 years, 76% men, left ventricular ejection fraction 22+/-12%, pre-QRS 175+/-30 ms), 84 died and 7 underwent transplantation during a follow-up of 27+/-15 months. Variables predictive of death or transplantation included QRS increase after CRT (45% vs 32%, p=0.03), older age, higher New York Heart Association class, lower left ventricular ejection fraction, and higher tertile of postimplant QRS (p=0.04), but not preimplant rhythm, QRS duration, or QRS morphology. After adjusting for confounding variables, independent predictors of mortality were older age (hazard ratio [HR] 1.03, 95% confidence interval [CI] 1.00 to 1.05, p=0.04), lack of angiotensin-converting enzyme inhibitor or angiotensin receptor blocker (HR 2.17, 95% CI 1.16 to 4.08, p<0.02), and longer postimplant QRS by tertile (HR 1.50, 95% CI 1.09 to 2.05, p=0.01). In conclusion, wider QRS after CRT device implantation is an independent predictor of mortality or transplantation. In patients with increased QRS durations despite CRT, closer follow-up or reassessment for alternative management strategies may be warranted.

IEEE Trans Biomed Eng. 2008 Feb;55(2):468-77.

QRS slopes for detection and characterization of myocardial ischemia.

Pueyo E, Sornmo L, Laguna P.
Contact: Communications Technology Group at the Aragón Institute for Engineering Research (I3A), University of Zaragoza, Zaragoza 50015, Spain.

In this study, the upward I(US) and downward I(DS) slopes of the QRS complex are proposed as indices for quantifying ischemia-induced electrocardiogram (ECG) changes. Using ECG recordings acquired before and during percutaneous transluminal coronary angioplasty (PTCA), it is found that the QRS slopes are considerably less steep during artery occlusion, in particular for I(DS). With respect to ischemia detection, the slope indices outperform the often used high-frequency index (defined as the root mean square (rms) of the bandpass-filtered QRS signal for the frequency band 150-250 Hz) as the mean relative factors of change are much larger for I(US) and I(DS) than for the high-frequency index (6.9 and 7.3 versus 3.7). The superior performance of the slope indices is equally valid when other frequency bands of the high-frequency index are investigated (the optimum one is found to be 125-175 Hz). Employing a simulation model in which the slopes of a template QRS are altered by different techniques, it is found that the slope changes observed during PTCA are mostly due to a widening of the QRS complex or a decrease of its amplitudes, but not a reduction of its high-frequency content or a combination of this and the previous effects. It is concluded that QRS slope information can be used as an adjunct to the conventional ST segment analysis in the monitoring of myocardial ischemia.

J Cardiovasc Electrophysiol. 2008 Feb;19(2):224-9. Epub 2007 Oct 24.

ECG clues for diagnosing ventricular tachycardia mechanism.

Riley MP, Marchlinski FE.
Contact: Electrophysiology Section, Division of Cardiology, University of Pennsylvania Health System, Philadelphia, Pennsylvania, USA.

Three mechanisms underlie the initiation and maintenance of ventricular tachycardia: automaticity, triggered activity, and reentry. As straightforward as these mechanisms are, assessing which mechanism is operative in a particular patient's ventricular tachycardia can be difficult. The optimal treatment strategy for ventricular tachycardia in a given patient can be influenced by the mechanism underlying the ventricular tachycardia. Appropriately counseling patients, choosing the optimal pharmacologic agent that maximizes efficacy while minimizing undesirable side effects, risks, and toxicities, as well as recommending and timing ablative therapy all hinge on identifying the probable mechanism of ventricular tachycardia. Much has been published regarding invasive electrophysiologic maneuvers that allow for correct diagnosis of ventricular tachycardia mechanism. The aim of this clinical review is to provide insight into VT mechanisms based on ECG clues of spontaneous arrhythmia events and the response to pharmacologic manipulation prior to invasive electrophysiologic evaluation.

J Clin Nurs. 2008 Feb;17(3):370-7.

A comparison between EASI system 12-lead ECGs and standard 12-lead ECGs for improved clinical nursing practice.

Lancia L, Pisegna Cerone M, Vittorini P, Romano S, Penco M.
Contact: Department of Internal Medicine and Public Health, University of L'Aquila, L'Aquila, Italy.

AIMS AND OBJECTIVES: This study was carried out to verify the accuracy of 12-Lead ECG, obtained through a continuous ECG monitoring system with five cables positioned in EASI mode, to identify basic ECG alterations.

BACKGROUND: This study concerns continuous ECG monitoring systems in Coronary Care Units. Continuous ECG monitoring is an important device for nursing surveillance and is useful in decreasing adverse events.

DESIGN AND METHOD: Thirteen patients admitted consecutively to the Coronary Care Unit for Acute Myocardial Infarction underwent daily and simultaneous recording of a12-lead ECG using both procedures: EASI ECG and STANDARD ECG. A sample of 1,164 ECG leads acquired in EASI mode was compared with a sample of as many ECG leads acquired using the standard procedure with a traditional cardiograph.

RESULTS AND CONCLUSIONS: In the Coronary Care Unit, Continous ECG monitoring with five cables positioned in EASI mode is a valid alternative to the standard 12-lead ECG for cardiac rhythm abnormalities detection and for acute myocardial ischemia and old myocardial infarction assessment. Therefore, the EASI system might be advantageous for long-term patient monitoring.

RELEVANCE TO CLINICAL PRACTICE: The EASI system represents a valid device for the nursing surveillance of patients who need continuous ECG monitoring, improves clinical nursing practice in Coronary Care Units, supports the reduction of adverse events such as cardiac arrest and reduces the hospital costs.

Stroke. 2008 Feb;39(2):480-2. Epub 2008 Jan 3.

Serial electrocardiographic assessments significantly improve detection of atrial fibrillation 2.6-fold in patients with acute stroke.

Douen AG, Pageau N, Medic S.

BACKGROUND AND PURPOSE: Previous studies have reported a low, approximately 1% to 3%, rate of detection of occult atrial fibrillation (AF) with Holter monitor in patients with acute stroke. Furthermore, at least one study has reported that Holter monitoring could not always corroborate initial electrocardiographic (ECG) detection of AF suggesting underestimation of AF by Holter. We compare the detection of new-onset AF by serial ECG assessments and Holter after acute ischemic stroke.

METHODS: One hundred forty-four patients with ischemic stroke admitted to a stroke unit were studied. The number of ECGs conducted within the first 3 days up to the detection of AF as well as the time interval for Holter "hookup" and subsequent reporting of AF was documented.

RESULTS: ECGs were performed in 143 patients with a baseline of 10 (7%) patients having a history of AF. Serial ECGs detected 15 new AF cases in <2 days of admission, thereby increasing the total number of known AF cases to 25 (17.5%), a 2.6-fold increased realization of AF (P=0.011). Holter was also completed in 12 of 15 new cases of AF but surprisingly identified AF in only 50% (6 of 12). Holter monitoring was performed in 126 cases and in this subgroup, there was no statistically significant difference in the rate of AF detection with ECG or Holter.

CONCLUSIONS: Serial ECG assessments within the first 72 hours of an acute stroke significantly improve detection of AF. The discordance regarding the corroboration of AF by Holter in ECG-positive patients with AF supports previous observations and suggests a high incidence of paroxysmal AF as a cause of ischemic stroke.

BMC Med Inform Decis Mak. 2008 Jan 30;8:7.

A new methodology for assessment of the performance of heartbeat classification systems.

Darrington JM, Hool LC.
Contact: School of Computer Science and Software Engineering University of Western Australia Perth, WA, Australia.

BACKGROUND: The literature presents many different algorithms for classifying heartbeats from ECG signals. The performance of the classifier is normally presented in terms of sensitivity, specificity or other metrics describing the proportion of correct versus incorrect beat classifications. From the clinician's point of view, such metrics are however insufficient to rate the performance of a classifier.

METHODS: We propose a new methodology for the presentation of classifier performance, based on Bayesian classification theory. Our proposition lets the investigators report their findings in terms of beat-by-beat comparisons, and defers the role of assessing the utility of the classifier to the statistician. Evaluation of the classifier's utility must be undertaken in conjunction with the set of relative costs applicable to the clinicians' application. Such evaluation produces a metric more tuned to the specific application, whilst preserving the information in the results.

RESULTS: By way of demonstration, we propose a set of costs, based on clinical data from the literature, and examine the results of two published classifiers using our method. We make recommendations for reporting classifier performance, such that this method can be used for subsequent evaluation.

CONCLUSION: The proportion of misclassified beats contains insufficient information to fully evaluate a classifier. Performance reports should include a table of beat-by-beat comparisons, showing not-only the number of misclassifications, but also the identity of the classes involved in each inaccurate classification.

J Cardiovasc Magn Reson. 2008 Jan 25;10(1):7.

Accuracy of electrocardiographic criteria for atrial enlargement: validation with cardiovascular magnetic resonance.

Tsao CW, Josephson ME, Hauser TH, O'Halloran TD, Agarwal A, Manning WJ, Yeon SB.
Contact: Harvard-Thorndike Laboratory and the Department of Medicine, Cardiovascular Division, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts, USA.

BACKGROUND: Anatomic atrial enlargement is associated with significant morbidity and mortality. However, atrial enlargement may not correlate with clinical measures such as electrocardiographic (ECG) criteria. Past studies correlating ECG criteria with anatomic measures mainly used inferior M-mode or two-dimensional echocardiographic data. We sought to determine the accuracy of the ECG to predict anatomic atrial enlargement as determined by volumetric cardiovascular magnetic resonance (CMR).

METHODS: ECG criteria for left (LAE) and right atrial enlargement (RAE) were compared to CMR atrial volume index measurements for 275 consecutive subjects referred for CMR (67% males, 51 +/- 14 years). ECG criteria for LAE and RAE were assessed by an expert observer blinded to CMR data. Atrial volume index was computed using the biplane area-length method.

RESULTS: The prevalence of CMR LAE and RAE was 28% and 11%, respectively, and by any ECG criteria was 82% and 5%, respectively. Though nonspecific, the presence of at least one ECG criteria for LAE was 90% sensitive for CMR LAE. The individual criteria P mitrale, P wave axis < 30 degrees , and negative P terminal force in V1 (NPTF-V1) > were 88-99% specific although not sensitive for CMR LAE. ECG was insensitive but 96-100% specific for CMR RAE.

CONCLUSION: The presence of at least one ECG criteria for LAE is sensitive but not specific for anatomic LAE. Individual criteria for LAE, including P mitrale, P wave axis < 30 degrees , or NPTF-V1 > are highly specific, though not sensitive. ECG is highly specific but insensitive for RAE. Individual ECG P wave changes do not reliably both detect and predict anatomic atrial enlargement.

Anesthesiology. 2008 Jan;108(1):138-48.

Equipment-related electrocardiographic artifacts: causes, characteristics, consequences, and correction.

Patel SI, Souter MJ.
Contact: Department of Anesthesia, Royal Lancaster Infirmary, Lancaster, United Kingdom.

Interference of the monitored or recorded electrocardiogram is common within operating room and intensive care unit environments. Artifactual signals, which corrupt the normal cardiac signal, may arise from internal or external sources. Electrical devices used in the clinical setting can induce artifacts by various different mechanisms. Newer diagnostic and therapeutic modalities may generate artifactual changes. These artifacts may be nonspecific or may resemble serious arrhythmia. Clinical signs, along with monitored waveforms from other simultaneously monitored parameters, may provide the clues to differentiate artifacts from true changes on the electrocardiogram. Simple measures, such as proper attention to basic principles of electrocardiographic measurement, can eliminate some artifacts. However, in persistent cases, expert help may be required to identify the precise source and minimize interference on the electrocardiogram. Technological advancements in processing the electrocardiographic signal may be useful to detect and eliminate artifacts. Ultimately, an improved understanding of the artifacts generated by equipment, and their identifying characteristics, is important to avoid misinterpretation, misdiagnosis, and iatrogenic complication.

Comput Biol Med. 2008 Jan;38(1):1-13. Epub 2007 Jul 31.

ECG signal denoising and baseline wander correction based on the empirical mode decomposition.

Blanco-Velasco M, Weng B, Barner KE.
Contact: Department of Teoría de la Señal y Comunicaciones, Universidad de Alcalá, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain.

The electrocardiogram (ECG) is widely used for diagnosis of heart diseases. Good quality ECG are utilized by physicians for interpretation and identification of physiological and pathological phenomena. However, in real situations, ECG recordings are often corrupted by artifacts. Two dominant artifacts present in ECG recordings are: (1) high-frequency noise caused by electromyogram induced noise, power line interferences, or mechanical forces acting on the electrodes; (2) baseline wander (BW) that may be due to respiration or the motion of the patients or the instruments. These artifacts severely limit the utility of recorded ECGs and thus need to be removed for better clinical evaluation. Several methods have been developed for ECG enhancement. In this paper, we propose a new ECG enhancement method based on the recently developed empirical mode decomposition (EMD). The proposed EMD-based method is able to remove both high-frequency noise and BW with minimum signal distortion. The method is validated through experiments on the MIT-BIH databases. Both quantitative and qualitative results are given. The simulations show that the proposed EMD-based method provides very good results for denoising and BW removal.

Congenit Heart Dis. 2008 Jan;3(1):33-8.

Initial experience with novel mobile cardiac outpatient telemetry for children and adolescents with suspected arrhythmia.

Saarel EV, Doratotaj S, Sterba R.
Contact: Primary Children's Medical Center, Pediatric Cardiology, Salt Lake City, UT 84113, USA.

OBJECTIVES: To report use of a novel mobile cardiac outpatient telemetry (MCOT) system for evaluation of children and adolescents with suspected cardiac arrhythmia.

DESIGN: Prospective data collection and retrospective analysis.

SETTING: All patients who received MCOT from The Children's Hospital at the Cleveland Clinic between 1/14/04 and 2/12/05 were screened. Patients older than 21 years and those with previously documented arrhythmia were excluded.

PATIENTS: Fifty-nine consecutive MCOT studies were performed. Five patients met exclusion criteria leaving 54 subjects (mean age 12.4+/-4.5 years; range 3.2-19.7 years; 46% male) for inclusion.

INTERVENTIONS: The MCOT system (CardioNet, USA) consists of a 3-electrode, 2-channel sensor that transmits wirelessly to a portable monitor. Monitors continuously store, analyze, and transmit the electrocardiogram through cellular and land telephone networks to a central station. MCOT was performed for 9-32 consecutive days (mean 24.5+/-7.4).

RESULTS: Twenty-one subjects (39%) did not experience symptoms during MCOT, yielding a diagnostic rate of 61% (N = 33). Of the 33 diagnostic studies, 9% (N = 3; mean age 16.9+/-0.6 years; range 16.2-17.3 years; 1 male) showed supraventricular tachycardia and 9% (N = 3; mean age 11.1+/-2.7 years; range 8.2-13.5 years; 1 male) showed supraventricular or ventricular ectopy. Minor skin irritation at sites of electrode placement was the only complication of MCOT (N = 5).

CONCLUSIONS: MCOT is safe and useful for evaluation of children and adolescents with suspected arrhythmia, providing a diagnosis in 61% of subjects. The diagnostic yield of MCOT was superior to that expected from traditional event and Holter monitors in this pediatric population.

J Electrocardiol. 2008 Jan-Feb;41(1):8-14.

What is inside the electrocardiograph?

Gregg RE, Zhou SH, Lindauer JM, Helfenbein ED, Giuliano KK.
Contact: Advanced Algorithm Research Center, Philips Medical Systems, 3 Andover, MA 01810, USA.

The details of digital recording and computer processing of a 12-lead electrocardiogram (ECG) remain a source of confusion for many health care professionals. A better understanding of the design and performance tradeoffs inherent in the electrocardiograph design might lead to better quality in ECG recording and better interpretation in ECG reading. This paper serves as a tutorial from an engineering point of view to those who are new to the field of ECG and to those clinicians who want to gain a better understanding of the engineering tradeoffs involved. The problem arises when the benefit of various electrocardiograph features is widely understood while the cost or the tradeoffs are not equally well understood. An electrocardiograph is divided into 2 main components, the patient module for ECG signal acquisition and the remainder for ECG processing which holds the main processor, fast printer, and display. The low-level ECG signal from the body is amplified and converted to a digital signal for further computer processing. The Electrocardiogram is processed for display by user selectable filters to reduce various artifacts. A high-pass filter is used to attenuate the very low frequency baseline sway or wander. A low-pass filter attenuates the high-frequency muscle artifact and a notch filter attenuates interference from alternating current power. Although the target artifact is reduced in each case, the ECG signal is also distorted slightly by the applied filter. The low-pass filter attenuates high-frequency components of the ECG such as sharp R waves and a high-pass filter can cause ST segment distortion for instance. Good skin preparation and electrode placement reduce artifacts to eliminate the need for common usage of these filters.

Pediatr Emerg Care. 2008 Jan;24(1):28-30.

Optimal surface electrocardiogram lead for identification of the mechanism of supraventricular tachycardia in children.

Liberman L, Pass RH, Starc TJ.
Contact: Division of Pediatric Cardiology, Department of Pediatrics, New York Presbyterian Hospital, Columbia University, New York, NY, USA.

OBJECTIVE: Although supraventricular tachycardia (SVT) can be identified from any lead of the bedside monitor, the mechanism of tachycardia is not always obvious. We analyzed the 12-lead electrocardiogram (ECG) in SVT of pediatric patients with different mechanisms of SVT to determine if there is a consistent optimal lead for rhythm identification.

METHODS: Twelve-lead ECGs during SVT were available for retrospective analysis in 54 patients. The tachycardia mechanism was determined either by intracardiac or transesophageal recording, or after cardioversion analysis of atrial flutter or fibrillation. Blinded analysis of each separate lead of the 12-lead ECG was done to determine the best lead to diagnose the mechanism of tachycardia. For statistical analysis, chi(2) or Fisher exact test was used.

RESULTS: From analysis of the surface ECG, the mechanism of SVT could be identified in 49 (91%) of 54 patients. Lead V1 was the most useful lead to determine the tachycardia mechanism. V1 identified the mechanism in 39 (80%) of 49 patients compared with 29 (59%) of 49 in lead III (P < 0.05), 22 (51%) of 49 in lead II (P < 0.01), and 12 (24%) of 49 in V6 (P < 0.001). Lead V1 identified accessory pathway-mediated tachycardia in 15 (68%) of 22 patients, atrial flutter in 12 (87%) of 14 patients, atrial fibrillation in 7 (70%) of 10, and atrioventricular nodal reentrant tachycardia in 5 (62%) of 8 patients. The mechanism of tachycardia was more readily diagnosed using a combination of V1 and lead III (47/49 patients, 96%) compared with V1 alone (P < 0.05).

CONCLUSIONS: A right precordial lead (V1) is the best single lead to diagnose the mechanism of SVT. Furthermore, a combination of V1 and lead III increases the number of patients in whom the mechanism could be identified. Therefore, we recommend that V1 should be combined with an inferior limb lead during cardiac monitoring for optimal identification of the mechanism of SVT in children.