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y 43 (2010) 640–644www.jecgonline.com

Journal of Electrocardiolog

Poster Session 1

Is the QRS-T angle a more sensitive marker of ischemia thanST-segment deviation?Salah S. Al-Zaiti, James A. Fallavollita, Mary G. CareySchool of Nursing and the Center for Research in CardiovascularMedicine, State University of New York, Buffalo, New York, USA

Background: An abnormal spatial QRS-T angle (QRSTA) has alarger hazard ratio for fatal cardiac events than establishedcardiovascular and ECG risk factors. The spatial angle between theQRS and T axes is the angle between the directions of ventriculardepolarization and repolarization.Purpose: Our hypothesis was that in the presence of an increased heart rate(HR), the QRSTA is a more sensitive marker of myocardial ischemia thanST-segment deviation during continuous monitoring in patients with leftventricular failure.Methods: Twenty-four-hour Holter studies (Mortara, Milwaukee, WI) withnarrow QRS complexes (b120 milliseconds) were evaluated for HR events.An ischemic period was defined as an episode of tachycardia (≥100 beats/min) with an accompanying HR increase of 25 beats/min or greater for morethan 20 minutes. Measurements of the QRSTA were calculated from the12-lead electrocardiogram using the QRS/Tsimple formula. The delta frompre-HR event vs HR event for both QRSTA and max ST-segment deviation(mV) was evaluated.Results: Seventy HR events were identified during 62 Holter studies.Average differences between ischemic events (n = 36, or 51%) vsnonischemic HR events (n = 34, or 49%) was 52 ± 15 vs 27 ± 7 beats/minfor HR, 28° ± 25° vs 24° ± 24° for QRSTA, and 43 ± 30 vs 30 ± 26mV for STdeviation, respectively. The sensitivity and specificity for detecting ischemiaby QRSTA and ST deviation based on certain cut points are illustrated in thetable below.Conclusions: In patients with left ventricular, the traditional standard ST-segment deviation (100 mV) is not sensitive enough to detect ischemia; anapproach that uses a combination of QRSTA changes (20°) and low-threshold ST deviation (50 mV) during tachycardia is more accurate todetect ischemia.

n = 70

0022-0736/$ –

Delta QRSTA

see front matter

Delta ST-segment deviation (mV)

≥10°

≥20° ≥100 ≥75 ≥50

Sensitivity

72.2% 47.2% 8.3% 19.4% 41.6% Specificity 41.2% 61.7% 100% 88.2% 79.4%

doi:10.1016/j.jelectrocard.2010.10.002

Secondary T-wave changes in LVH: a model studyLjuba Bacharovaa, Vavrinec Szathmaryb, Anton MateasikaaInternational Laser Center, Slovak Academy of Sciences Bratislava,SlovakiabInstitute of Normal and Pathological Physiology, Slovak Academy ofSciences Bratislava, Slovakia

Background: In our previous study, we simulated the effects of anatomicaltypes of left ventricular hypertrophy and of altered conductivity of the leftventricular myocardium on the QRS complex pattern and duration usingcomputer modeling. In this study, we present the repolarization changes thatresulted from the above-mentioned changes in depolarization, withoutchanging the model parameters of repolarization—the duration ormorphology of the action potential.

Materials and methods: The model defines the geometry of cardiacventricles analytically as parts of ellipsoids and allows to change the dimensionsof ventricles, as well as the conduction velocity in myocardium. Three typesof anatomical changes were simulated: concentric and eccentric hypertrophy,and dilatation. The conduction velocity was slowed in the inner layer of theleft ventricle representing the Purkinje fiber mesh and in the layers representingthe working myocardium. The outcomes of the model are presented as timecourse of the spatial T-vector magnitude, of the vectorcardiographic T loops,and of derived 12-lead electrocardiograms (ECGs).

Results: The most pronounced changes in repolarization were observed incases of left ventricular hypertrophy that were combined with slowedconduction velocity in the working myocardium and included the increase ofthe spatial T-vector magnitude, the prolongation of the QT interval, and ashift of T loop orientation to the right, anteriorly, and upward, opposite to theorientation of the QRS loop. The rightward and upward shift of the T loopresulted in negative T waves in the left precordial and vertical leads of 12-lead ECG.

Conclusion: We demonstrated that changes in conduction velocity in themodel heart produced changes not only in QRS duration and morphologybut resulted also in spatial T-vector magnitude, orientation of T loop, and QTduration, reflected in corresponding changes of T-wave morphology in the12-lead ECG.

doi:10.1016/j.jelectrocard.2010.10.003

What definition for “prolonged QT”?Robert M. FarrellGE Healthcare, Wauwatosa, WI, USA

The ECG interpretative statement “Prolonged QT” means different things todifferent people. It can be taken as a purely descriptive statement referring tothe QT interval beyond a certain threshold. Alternatively, it could be takento refer to a disease state (eg, congenital long QT syndrome), or some otherabnormality. Attention paid to the QTc measurement and to the presence ofthe “Prolonged QT” statement in the electrocardiogram (ECG) interpretationhas markedly increased in the past few years due to increased awareness ofQT-prolonging drugs and the association between prolonged QT andTorsades de pointes.As a manufacturer of electrocardiographs with a computerizedinterpretation program, we hear conflicting comments regarding the“Prolonged QT” statement in the interpretation, ranging from “too manyECGs say Prolonged QT” to “how could it not say Prolonged QT when

Table 2Mean and 2nd/98th percentile of TNDPV (μV) excluding higher noise cases

Sex Race n 2% Mean 98%

Male African American 420 4.95 7.88 13.4White 1193 4.73 7.12 12.3

Female African American 440 4.50 7.17 13.4White 1213 4.45 6.75 11.1

641Poster Session 1 / Journal of Electrocardiology 43 (2010) 640–644

the QTc is over 500 msec?” There is probably truth to both of thesetypes of comments.It has been suggested that we state “Prolonged QT” whenever theQTc exceeds 460 milliseconds (Bazett correction). Although 460milliseconds is above the 98th percentile of QTc for most age groupsof normal subjects, large numbers of ECGs have QTc more than 460milliseconds for which the mention of prolonged QT is notappropriate. For example, it is generally not useful to mentionprolonged QT in the presence of intraventricular conduction defectssuch as right or left bundle-branch block.In an analysis of 44 896 ECGs representing all adult non–ventricular-pacedECGs in a major hospital ECG database over the course of 1 calendar year,the computerized interpretation program stated “Prolonged QT” on 9.8% ofthe ECGs. However, 36.2% of all ECGs had a QTc more than 460milliseconds. A total of 5059 ECGs (11.3%) exhibited some form ofintraventricular conduction block, 77.3% of those also had QTc more than460 milliseconds.It should be evident that it would not be acceptable to state “ProlongedQT” on over a third of all ECGs. Clearly, exclusionary criteria arerequired so that “Prolonged QT” is stated only when meaningful. Ourcomputerized interpretation program excludes ECGs with ventricularconduction blocks and with ventricular rates greater than 100 beats/min.We also have a tiered threshold that ranges from 460 to 510 millisecondsbased on the presence or absence of infarction, ischemia, or nonspecificT-wave abnormality and on age and sex. Further discussion andstandardization of the specific criteria for statement of “Prolonged QT”are warranted.

doi:10.1016/j.jelectrocard.2010.10.004

Normal reference values for QRS and T-wave non-dipolar componentsfor adult Caucasian and African American men and womenRichard E. Gregga, Sophia H. Zhoua, Pentti Rautaharjub

aAdvanced Algorithm Research Center, Philips Healthcare, Andover, MAbWake Forest University Medical School, Winston-Salem, NC

Background: Previous studies have shown the predictive value of bothQRS and T-wave nondipolar components (R wave nondipolar predictivevalue [RNDPV] and T wave nondipolar predictive value [TNDPV],respectively) for coronary artery disease mortality. The present study wasdesigned to derive normal reference values for these electrocardiogram(ECG) variables by age, sex, and race.

Methods: Statistical distributions for RNDPV and TNDPV values (inmicrovolts) were calculated from the Philips DXL algorithm representativeaveraged QRS and T complexes on a large ECG data set of free-living adults(n = 5451). The subjects were 40 to 90 years old; 53% were women, 75%were white, and 25% were African American. Stepwise linear regressionrevealed that root mean square (RMS) noise was a significant contributor tonondipolar components, so noise quintiles were added to age, sex, and raceas grouping variables in the analysis of variance for RNDP and TNDPV.

Results: Age, sex, and race were significant determinants of RNDPV(Table 1). All pair-wise comparisons of means by age, sex, and race were

Table 1Mean and 2nd/98th percentile of RNDPV (μV) normal values

Group (y) Race n 2% Mean 98%

Male (40-59) African American 365 24.5 58.1 114White 919 20.6 44.8 84.3

Female (40-59) African American 448 17.5 40.9 79.0White 1050 15.3 35.0 69.2

Male (60+) African American 257 22.4 51.9 105White 1003 18.5 41.8 79.7

Female (60+) African American 256 19.1 42.8 82.2White 1103 16.8 37.6 73.8

significant except for age for African American women. For TNDPV, RMSnoise and race were significant factors. To reduce bias due to noise inTNDPV normal values, the higher 2 noise quintiles were excluded (3266subjects remaining, or 60%). Table 2 shows the normal values for TNDPVfor the remaining 3266 subjects in 3 quintiles with higher quality ECGs inwhich the RMS noise did not have a significant impact. Differences ofmeans were significant for all pair-wise comparisons by sex and race.

Conclusions: Normal limits for RNDPV and TNDPV need to be stratifiedby sex, age, and race. In addition, ECG quality needs to be taken intoconsideration when determining and using these ECG parameters,particularly TNDPV.

doi:10.1016/j.jelectrocard.2010.10.005

Electrocardiographic identifying proximal occlusion within leftanterior descending coronary arteryRichard E. Gregg, Kjell Nikus, Leonard S. Gettes, Ronald H. Startt/Selvester,Victoria Barbara, Sophia H. ZhouAdvanced Algorithm Research Center, Philips Healthcare,Thousand Oaks, CACardiology Department, Tampere University Hospital, Tampere, FinlandCardiology Division, University of North Carolina School of Medicine,Chapel Hill, NCHeart Institute, Long Beach Memorial Medical Center, Long Beach, CA

Background: Proximal occlusion within the left anterior descendingcoronary artery (LAD) leads to a higher mortality rate and higher riskof restenosis than middle or distal LAD occlusion in patients withacute myocardial infarction (MI). Identification of proximal LADocclusion would allow early notification to interventionists and gainmore time for reperfusion therapy. Based on previous research inECG identification of culprit artery, we developed a computerprogram to detect proximal occlusion within LAD. This study is toreport the performance of the program.

Methods: The source population was all suspected ACS patientspresenting consecutively to the emergency department of a local hospitalwith a discharge diagnosis of acute MI, and a coronary angiogramconfirmed flow-limiting lesion (n = 711). Excluded were subjects withnon–ST-elevation MI (non-STEMI) and electrocardiogram (ECG) con-founders for STEMI. The ECGs that met the STEMI criteria in theanterior and anterolateral regions with angiographic confirmation ofproximal occlusion within LAD were selected for development of thecomputer program (n = 36). The ECGs in the test set also met the STEMIcriteria in the anterior or anterolateral regions with confirmatoryventriculograms but without coronary angiogram confirmation (n =132). One ECG expert overread for acute MI (R.S.), and 2 experts(K.N., L.G.) overread the proximal sites of occluded LAD. Philips DXLalgorithm was used for ST measurements and STEMI classification. Thebasic ECG criteria for LAD proximal occlusion are based on the latestAHA/ACCF/HRS recommendations.

Results: In the development set, tested against coronary angiogram readingof proximal LAD occlusion, the program has a sensitivity of 89% and aspecificity of 72%. Tested against 2 cardiologist expert readings of proximal