The differential diagnosis on the electrocardiogram between ventricular tachycardia and preexcited tachycardia

The 12-lead surface electrocardiogram is a simple and useful tool for the differential diagnosis of regular wide QRS complex tachycardia. However, criteria do not as yet exist to discriminate between ventricular tachycardia and supraventricular tachycardia with anterograde conduction over an accessory pathway (preexcited tachycardia). Therefore, we designed a new stepwise approach with three criteria for the electrocardiographic differential diagnosis between ventricular tachycardia and preexcited tachycardia and prospectively studied 267 regular tachycardias with electrophysiologically proven mechanism and a wide QRS complex (≥ 0.12 s): 149 consecutive ventricular tachycardias and 118 consecutive preexcited regular tachycardias. Underlying heart disease was old myocardial infarction in 133 of 149 (89%) ventricular tachycardias. The patients presenting with preexcited tachycardia had no additional structural heart disease. Atrial fibrillation with preexcited QRS complex was not included. The criteria favoring ventricular tachycardia were: (1) presence of predominantly negative QRS complexes in the precordial leads V₄ to V₆, (2) presence of a QR complex in one or more of the precordial leads V₂ to V₆, and (3) AV relation different from 1:1 (more QRS complexes than P waves). The final sensitivity and specificity of these three consecutive steps to diagnose ventricular tachycardia were 0.75 and 1.00, respectively. This new stepwise approach is sensitive and highly specific for the differential diagnosis between ventricular tachycardia in coronary artery disease and preexcited regular tachycardia.     

Approach to the diagnosis and initial management of the stable adult patient with a wide complex tachycardia

The initial electrocardiographic evaluation of every tachyarrhythmia should begin by addressing the question of whether the QRS complex is wide or narrow. The most important cause of wide complex tachycardia (WCT) is ventricular tachycardia. However, supraventricular tachycardia can also manifest with a wide QRS complex. The ability to differentiate between supraventricular tachycardia with a wide QRS due to aberrancy or preexcitation and ventricular tachycardia often presents a diagnostic challenge. The identification of whether WCT has a ventricular or supraventricular origin is critical because the treatment for each is different, and improper therapy may have potentially lethal consequences. In conclusion, although the diagnosis and treatment of sustained WCT often arise in emergency situations, this report focuses on a stepwise approach to the management of WCT in relatively stable adult patients, particularly the diagnosis and differentiation of ventricular tachycardia from supraventricular tachycardia with a wide QRS complex on standard 12-lead electrocardiography.     

Comparison of a vectorcardiographically derived 12-lead electrocardiogram with the conventional electrocardiogram during wide QRS complex tachycardia, and its potential application for continuous bedside monitoring.

Previous investigators published conflicting reports comparing a vectorcardiographically derived electrocardiogram (ECGD) with the conventional 12-lead one (ECG). Prior comparisons were obtained in adults during sinus rhythm, but never in patients with wide QRS complex tachycardia. The ECGD was evaluated during baseline rhythms in patients with varying cardiac diagnoses, and the diagnostic accuracy of the 2 methods was compared during 64 episodes of wide QRS complex tachycardia in 49 patients during cardiac electrophysiologic study. All leads of the 12-lead ECGD closely resembled the conventional ECG in baseline and tachycardia tracings, except leads V3 and V4. QRS voltages were less in the ECGD, resulting in an inability to detect left ventricular hypertrophy in one third of patients with that diagnosis. There was excellent agreement between the ECGD and ECG in diagnosing prior myocardial infarction (92%), ventricular preexcitation patterns (100%), bundle branch and fascicular blocks (100%), and axis deviation. The ECGD was equally as valuable as the ECG in the diagnosis of wide QRS complex tachycardia. There was perfect agreement between the 2 lead systems in application of the morphologic criteria differentiating supraventricular tachycardia with aberration from ventricular tachycardia in leads V1, V2 and V6, and for criteria requiring axis determination and measurement of RS intervals in the precordial leads. The ECGD tracings contained less muscle artifact during body movements (e.g., after direct-current defibrillation). In conclusion, the ECGD's close correlation with the ECG, and its technical superiority and simple 5 torso-positioned electrode configuration make it worth pursuing as an option for continuous bedside monitoring.     

Value of electrocardiographic leads MCL1, MCL6 and other selected leads in the diagnosis of wide QRS complex tachycardia

To compare the modified precordial leads MCL1 and MCL6 with the conventional precordial leads V1 and V6 and assess the diagnostic accuracy of selected leads for continuous bedside electrocardiographic (ECG) monitoring, 121 wide QRS complex tachycardias were recorded from 92 patients during cardiac electrophysiologic study. As ascertained from intracardiac recordings, 86 tachycardias were ventricular and 35 were supraventricular with aberrant conduction. Early or late peaking of the predominant QRS deflection in lead MCL6 or V6 proved valuable in diagnosing wide complex tachycardia. An interval of less than or equal to 50 ms from the onset of the QRS complex to the predominant peak (or nadir) indicated supraventricular tachycardia; an interval of greater than or equal to 70 ms indicated ventricular tachycardia. The QRS complexes in leads MCL1 and MCL6 were comparable to those in leads V1 and V6 during sinus rhythm. Significant discrepancies in QRS configuration occurred between the modified and conventional precordial leads during ventricular tachycardia, especially between leads MCL1 and V1; however. these differences did not affect diagnostic accuracy. A single MCL1, V1, MCL6 or V6 lead was equally valuable in the diagnosis of wide complex tachycardia and far superior to a single lead II. A combination of leads (MCL1 + MCL6), (V1 + V6), (V1 + I + aVF) or (V1 + V6 + I + aVF) was superior to a single lead or the routinely monitored lead V1 + II combination.     

鉴别宽QRS心动过速心电图指标对原有束支传导阻滞患者的应用价值

目的　探讨鉴别宽 QRS心动过速心电图指标对原有束支传导阻滞患者的应用价值。方法　以非选择性、连续性 42 0例完全性束支传导阻滞窦性心律患者为研究对象 ,分析以往文献报道鉴别宽 QRS心动过速心电图标准中的 QRS形态指标的特异性。结果　 12个分析指标中 4个指标特异性 >90 % :右束支传导阻滞 V1 呈三相型 (Rsr′,r SR′,RSR′) ;右束支传导阻滞 V6呈 QS或 QR型 ;左束支传导阻滞 V6有 q或 Q波 ;V1 ～ V6无 RS波。其它 8个指标特异性在 45 %～ 87%范围内。结论　有利于室性心动过速诊断心电图标准中的 QRS形态指标对鉴别原有束支传导阻滞的室上性心动过速患者存在局限性     

形态心电图标准在原有束支阻滞伴宽QRS波群心动过速鉴别诊断中的特异性评价

为探讨形态心电图标准是否适用原有束支阻滞（ＢＢＢ）或心肌梗塞患者合并宽ＱＲＳ波群心动过速的鉴别诊断,选择窦性心律呈ＢＢＢ的患者２０５例［左束支阻滞（ＬＢＢＢ）４５例、右束支阻带（ＲＢＢＢ）１６０例］,分析形态心电图标准用于鉴别宽ＱＲＳ波群心动过速的特异性。胸导联ＱＲＳ波群图形一致、胸导联无ＲＳ型;ＲＢＢＢ时任一胸导联ＲＳ时限＞１００ｍｓ,Ｖ１导联单向（Ｒ）或双向（ｑＲ、ＱＲ、ＲＳ）、呈左兔耳征,Ｖ６导联或ａＶＦ导联Ｑ波,Ｖ６导联Ｒ／Ｓ＜１;ＬＢＢＢ时,Ｖ１、Ｖ２导联ｒ波时限＞３０ｍｓ,Ｖ１、Ｖ２导联Ｓ波降支钝挫,Ｖ６导联或ａＶＦ导联ｑ（Ｑ）波等１２条特异性较高。ＱＲＳ波群时限＞１４０ｍｓ;ＲＢＢＢ时电轴重度左、右偏,ａＶＦ导联Ｒ／Ｓ＜１;ＬＢＢＢ时Ｖ１、Ｖ２导联ＲＳ时限＞６０ｍｓ,Ⅰ导联负向ＱＲＳ波群,Ｖ４较Ｖ１导联Ｓ波振幅更深等７条特异性较低。心肌梗死合并宽ＱＲＳ波群心动过速时采用上述标准鉴别诊断有一定局限。     

Multivariate analysis to simplify the differential diagnosis of broad complex tachycardia.

Univariate analysis has identified several criteria that aid the differential diagnosis of broad complex tachycardia. In this study of 102 consecutive patients multivariate analysis was performed to identify which of 15 clinical and 11 electrocardiographic variables were independent predictors of ventricular tachycardia. These were shown to be a history of myocardial infarction, the QRS waveforms in leads aVF and V1, and a change in axis from sinus rhythm to tachycardia of more than 40 degrees. If none of the criteria was met, the diagnosis was almost certainly supraventricular tachycardia. If one criterion was met the diagnosis was probably supraventricular tachycardia. If two criteria were met then the diagnosis was probably ventricular tachycardia. If three or four criteria were met, the diagnosis was almost certainly ventricular tachycardia. The predictive accuracy was 93%. This was increased to 95% by including two other criteria--definite independent P wave activity and ventricular extrasystoles with the same QRS configuration as that in tachycardia. These criteria were not included in the multivariate analysis because though they were 100% specific they were seldom seen. These four criteria can be used as simple rules in determining the origin of a broad complex tachycardia.     

Multivariate analysis to simplify the differential diagnosis of broad complex tachycardia

Univariate analysis has identified several criteria that aid the differential diagnosis of broad complex tachycardia. In this study of 102 consecutive patients multivariate analysis was performed to identify which of 15 clinical and 11 electrocardiographic variables were independent predictors of ventricular tachycardia. These were shown to be a history of myocardial infarction, the QRS waveforms in leads aVF and V1, and a change in axis from sinus rhythm to tachycardia of more than 40 degrees. If none of the criteria was met, the diagnosis was almost certainly supraventricular tachycardia. If one criterion was met the diagnosis was probably supraventricular tachycardia. If two criteria were met then the diagnosis was probably ventricular tachycardia. If three or four criteria were met, the diagnosis was almost certainly ventricular tachycardia. The predictive accuracy was 93%. This was increased to 95% by including two other criteria--definite independent P wave activity and ventricular extrasystoles with the same QRS configuration as that in tachycardia. These criteria were not included in the multivariate analysis because though they were 100% specific they were seldom seen. These four criteria can be used as simple rules in determining the origin of a broad complex tachycardia.     

Regelm??ige Tachykardien mit breitem Kammerkomplex

Differential diagnosis of regular tachycardia with broad QRS complex can be challenging in daily practice. There are four different arrhythmias that have to be taken into account when being confronted with a broad QRS complex tachycardia: (1) ventricular tachycardia (VT); (2) supraventricular tachycardia (SVT) with bundle branch block (BBB); (3) SVT with AV conduction over an accessory AV pathway; (4) paced ventricular rhythm. Due to potentially fatal consequences, the correct diagnosis is important in view of both the acute treatment and the long-term therapy. Since SVT with accessory conduction is rare and a paced ventricular rhythm can be identified easily by stimulation artifacts, in most cases, a VT has to be differentiated from an SVT with BBB. Several ECG criteria can be helpful: (1) QRS complex duration > 140 ms in right BBB tachycardia or > 160 ms in left BBB tachycardia; (2) ventricular fusion beats; (3)“Northwest” QRS axis; (4) ventriculoatrial dissociation; (5) absence of an RS complex or RS interval > 100 ms in leads V₁-V₆; (6) a positive or negative concordant R wave progression pattern in leads V₁-V₆; (7) absence of an initial R wave or an S wave in lead V₁ in right BBB tachycardia; (8) absence of an R wave or an R/S ratio < 1 in lead V₆ in right BBB tachycardia; (9) absence or delay of the initial negative forces in lead V₁ in left BBB pattern (R wave duration > 30 ms in V₁; interval between onset of R wave and Nadir of S wave > 60 ms in V₁); (10) presence of Q wave. Any of these variables favor VT. However, none of the criteria has both a sufficient sensitivity and specificity when utilized on its own. Therefore, various diagnostic algorithms have been proposed using a number of the above criteria consecutively. By doing so, the specificity and sensitivity of correctly identifying a VT or an SVT with BBB can be raised to > 95%.     

Surface electrocardiographic clues suggesting presence of a nodofascicular Mahaim fiber

Standard electrocardiograms from 87 consecutive patients with tachycardia of left bundle branch block configuration were analyzed retrospectively for features that might be characteristic of tachycardia utilizing a nodofascicular Mahaim fiber. The study group consisted of 13 patients with nodofascicular tachycardia, 34 with supraventricular tachycardia and aberrant conduction over the His-Purkinje system, 22 with ventricular tachycardia and 18 with antidromic tachycardia utilizing a right-sided accessory atrioventricular pathway. Six variables present during tachycardia of left bundle branch block configuration were predictive of a nodofascicular fiber: cycle length between 220 and 450 ms, QRS axis of 0 to -75 degrees, QRS duration 0.15 second or less, R wave in lead I, rS wave in precordial lead V1 and a precordial transition from a negative to a positive QRS complex after lead V4. All six criteria were present in 16 of the 87 patients. No patient with ventricular tachycardia satisfied these criteria, whereas 3 of 34 with supraventricular tachycardia, 1 of 18 with antidromic tachycardia and 12 of 13 with tachycardia using a nodofascicular fiber did. It is concluded that analysis of the surface electrocardiogram during tachycardia may suggest the presence of a nodofascicular fiber.     

形态心电图标准在宽QRS波心动过速鉴别诊断中的价值

目的:为评价形态心电图单项标准、多项组合的Brugada标准及Brugada标准联合Steurer标准在宽QRS波心动过速(WRT)鉴别诊断中的应用价值及存在的缺陷。方法:对112例WRT[室性心动过速(VT)64例,室上性心动过速(SVT)48例]发作时的常规12导联心电图进行分析。结果:形态心电图单项标准诊断VT的敏感性不高,但部分单项标准的特异性很强(100%),一旦出现,强烈提示VT;多项组合的Brugada标准可提高VT诊断的敏感性(93.8%)及准确性(86.6%),但特异性较低(77.1%);Brugada标准联合Steurer标准可进一步提高诊断VT的特异性(89.6%)及准确性(92.0%)。进一步分析显示:Brugada标准对器质性原因所致VT、右束支传导阻滞型(RBBB)特发性VT(IVT)、SVT伴室内差异性传导(AC)或原有单侧束支传导阻滞(BBB)者诊断符合率高(96.3%~100.0%);对左束支传导阻滞型(LBBB)特发性VT、SVT伴原有双支阻滞、心肌坏死或心肌梗死伴宽QRS波SVT及预激综合征(WPW)伴旁道前传型SVT(WPW-SVT)诊断的符合率低(0~57.1%)。联合Steurer标准可使WPW-SVT得以明确诊断,但对前三者无鉴别意义,故不适合在前三者中应用。结论:形态心电图单项标准诊断VT的敏感性较低,不能依赖某一单项标准判断VT,多项组合的Brugada标准联合Steurer标准是目前诊断VT敏感性、特异性、准确性较强的方法。     

Diagnostic Clues From the Surfaee ECG to Identify Idiopathic (Fascicular) Ventricular Tachycardia: Correlation with Electrophysiologic Findings

ECG in Idiopathic Fascicular VT. Introduction : An RS interval > 100 msec in precordial leads has been recently described for the diagnosis of ventricular tachycardia (VT). The aim of this study was to assess the value of this criterion when applied to patients with right bundle branch block pattern, left-axis deviation (fascicular) VT sensitive to verapamil.
Methods and Results : Eleven patients (mean age 31 ± 11 years; range 16 to 51) had a mean heart rate of 164 ± 37 beats/min (range 107 to 230) during VT, The QRS complex axis was -92°± -15° (range -80 to -115). The mean QRS duration was 121 ± 9 msec (range 105 to 140). The mean RS interval was 67 ± 9 msec (range 60 to 80). Fusion beats were present in 2 patients (18%), and AV dissociation confirmed by electrophysiologic study was found on ECG in 8 (73%) of 11. During tachycardia, the QRS-H'interval was 19 ± 10 msec (range 10 to 30) in 6 of 11 patients. In seven patients, a fast, unique (or double) presystolic potential lasting 32 msec (range 12 to 40) occurring before the onset of the QRS complex was found at the site of origin of VT, localized in the inferior apical left ventricular septum. In all cases, VT was successfully treated by catheter ablation.
Conclusion : A wide QRS complex tachycardia with right bundle branch block and left-axis deviation sensitive to verapamil observed in a young patient without structural heart disease should not be confused with supraventricular tachycardia with aberrancy but rather suggests the presence of fascicular VT. As opposed to VT associated with structural heart disease, the RS interval is < 80 msec in all precordial leads in all cases. Independent of this parameter, AV dissociation detectable on surface ECG has a sensitivity of 73%, which increases to 82% in the presence of fusion beats.     

Taquicardia de QRS largos – importância eletrocardiográfica no diagnóstico diferencial

Correct diagnosis in wide QRS complex tachycardia remains a challenge. Differential diagnosis between ventricular and supraventricular tachycardia has important therapeutic and prognostic implications, and although data from clinical history and physical examination may suggest a particular origin, it is the 12‐lead surface electrocardiogram that usually enables this differentiation.Since 1978, various electrocardiographic criteria have been proposed for the differential diagnosis of wide complex tachycardias, particularly the presence of atrioventricular dissociation, and the axis, duration and morphology of QRS complexes. Despite the wide variety of criteria, diagnosis is still often difficult, and errors can have serious consequences. To reduce such errors, several differential diagnosis algorithms have been proposed since 1991. However, in a small percentage of wide QRS tachycardias the diagnosis remains uncertain and in these the wisest decision is to treat them as ventricular tachycardias.The authors’ objective was to review the main electrocardiographic criteria and differential diagnosis algorithms of wide QRS tachycardia.     

无人区心电轴在宽QRS波心动过速中的鉴别诊断价值

目的探讨无人区心电轴在宽QRS波心动过速(WCT)中的鉴别诊断价值。方法收集并测量北京大学人民医院2000年1月至2005年10月经心内电生理检查明确诊断的WCT患者窦性心律及心动过速时心电图中Ⅰ、Ⅲ标准导联QRS波振幅的代数和,计算QRS波额面平均心电轴,观察无人区心电轴出现的心律失常类型及规律。结果137例[其中特发性室性心动过速(IVT)65例,室上性心动过速(室上速,SVT)72例]明确诊断的WCT患者中,18例出现无人区心电轴,其中室性心动过速(室速)16例(占室速24.6%,占总病例11.7%),均为左心室特发性室速;宽QRS波室上速2例(占宽QRS波室上速2.8%,占总病例1.5%),均为心房颤动(房颤)伴左侧旁路前传。结论无人区心电轴可以作为鉴别室速与宽QRS波室上速的一项可靠指标。     

aVR导联四步流程在宽QRS波心动过速鉴别诊断中的应用

目的 验证分析aVR导联四步流程对宽QRS波心动过速(WCT)进行鉴别诊断的应用价值.方法 回顾性分析113例患者发生WCT时12导联体表心电图的形态学特征.按aVR导联四步流程分步骤地对113例WCT患者的心电图进行室性心动过速(室速)和室上性心动过速(室上速)的鉴别,将分析的结果与电生理检查结果进行比较,计算每一步...     

A New Classification Algorithm for Discrimination of Ventricular from Supraventricular Tachycardia in a Dual Chamher Implantable Cardioverter Defibrillator

New Atrioventricular Classification Algorithm. Introduction : The high incidence of inappropriate therapies due to supraventricular tachycardia remains a major unsolved problem of implantable cardioverter defibrillators. We report a new detection formula for discrimination of ventricular tachycardia from supraventricular tachycardia in a patient with a dual chamber implantable cardioverter defibritlator and a new atrioventricular classification algorithm.
Methods and Results : The enhanced detection algorithm performs a stepwise arrhythmia analysis. The rhythm is first classified on the basis of cycle length. Each episode is then classified as supraventricular or ventricular on the basis of atrioventricular association, stability of circle length, and origin of acceleration, Sophisticated diagnostic information is provided by atrioventricular markers and electrogram recordings. Successful discrimination of two spontaneous episodes of ventricular tachycardia and supraventricular tachycardia is demonstrated.
Conclusion : This new dual chamber detection algorithm may significantly improve the specificity of tachyarrhythmia detection without sacrificing sensitivity, thereby reducing the number of spurious shocks in patients with recurrent supraventricular tachycardias. Further studies are needed to assess the sensitivity and specificity of this detection atgorithm.     

宽QRS波群心动过速的诊断与鉴别诊断研究进展

宽QRS波群心动过速是临床常见的心血管急症,可见于室性心动过速和室上性心动过速。室性心动过速是一种严重的心律失常,而室上性心动过速一般预后良好。由于二者的治疗原则不同,因此及时和正确地对宽QRS波群心动过速进行鉴别诊断在临床上有十分重要的意义。现对宽QRS波群心动过速的诊断和鉴别诊断予以综述。     

Signal averaging of the electrocardiogram in the remote differential diagnosis of broad complex tachycardias

The diagnosis of the origin of a broad complex tachycardia may be difficult, especially in the absence of a 12-lead electrocardiogram of the tachycardia. This study investigates the value of signal averaging in the differential diagnosis of broad complex tachycardia. Signal averaging during sinus rhythm was performed in 102 consecutive patients who presented with broad complex tachycardia (QRS width greater than 110 ms), in whom a definitive electrophysiological diagnosis was made. The presence of late potentials was determined on the basis of two definitions, the second including total QRS duration. The patients studied included 75 with ventricular tachycardia; 33 of these patients had suffered previous myocardial infarction, five had dilated cardiomyopathy, and 37 had a 'normal' heart. Of the 27 patients with supraventricular tachycardia, 22 had an atrioventricular accessory pathway (seven with a delta wave in sinus rhythm), three had atrioventricular nodal tachycardia and two had atrial tachycardia. The sensitivity of late potentials for the diagnosis of ventricular tachycardia was low utilizing both definitions (28% and 45%) although specificity was high (96% and 95%). The sensitivity for the diagnosis of ventricular tachycardia was higher for patients with ischaemic heart disease (43% and 70%) but very low for patients with ventricular tachycardia and a normal heart (16% and 22%). In conclusion, signal averaging in the remote diagnosis of broad complex tachycardia is specific but not sensitive for ventricular tachycardia, which limits its usefulness in selecting patients for electrophysiological study.     

Brugada法联合Steurer法在宽QRS波心动过速鉴别诊断中的价值

为评价Brugada法联合Steurer法在宽QRS波心动过速 (WRT)鉴别诊断中的应用价值及存在的缺陷。对 1 0 1例WRT[室性心动过速 (VT) 5 8例 ,室上性心动过速 (SVT) 43例 ]进行分析。结果 :Brugada法诊断VT灵敏度、特异度、准确性分别为 85 .7%、89.5 %、87.1 % ;联合Steurer法后灵敏度、特异度、准确性分别升至 91 .5 %、90 .5 %、91 .1 %。进一步分析显示 :Brugada法对器质性原因所致VT、右束支阻滞型 (RBBB)特发性VT(IVT)、SVT伴室内差异性传导 (AC)或原有单侧束支阻滞 (BBB)者诊断符合率高 ( 95 .8%～ 1 0 0 .0 % ) ;对左束支阻滞型 (LBBB)特发性VT、SVT伴原有双支阻滞、心肌坏死或心肌梗死伴宽QRS波SVT及预激综合征伴旁道前传型SVT(WPW SVT)诊断的符合率低 ( 0～ 5 0 .0 % )。联合Steurer法可使WPW伴旁道前传型SVT得以明确诊断 ,但对前三者无鉴别意义 ,故不适合在前三者中应用。结论 :Brugada法联合Steurer法能提高WPW伴旁道前传型SVT的鉴别能力 ,是目前鉴别WRT的重要方法。     

Improving the predictive ability of the signal-averaged electrocardiogram with a linear logistic model incorporating clinical variables

To improve the predictive accuracy of the signal-averaged electrocardiogram, we created a linear logistic model for predicting ventricular tachycardia during electrophysiologic testing. This signal-averaged electrocardiographic model was created from data obtained from 214 patients undergoing electrophysiologic testing (70 had ventricular tachycardia during electrophysiologic testing) by using stepwise logistic regression to rank eight clinical and nine signal-averaged electrocardiographic variables. The best predictors were ejection fraction, history of infarction, ventricular ectopic pairs or nonsustained ventricular tachycardia on Holter monitoring, QRS duration after 25-Hz filtering, and root mean square voltage of the terminal 40 msec of the QRS complex after 40- and 80-Hz filtering. Cross validation (a statistical technique that can be used to accurately evaluate how a predictive model will perform on a prospective patient population) was used to validate the model. After cross validation, the model's sensitivity was 91% and specificity was 59% for predicting ventricular tachycardia during electrophysiologic testing. This model compared favorably with established 25-Hz late-potential criteria (QRS duration of more than 110 msec and root mean square voltage of less than 25 microV of the terminal 40 msec of the QRS complex; sensitivity, 64%; specificity, 85%) and with established 40-Hz late-potential criteria (QRS duration of more than 114 msec or root mean square voltage of less than 20 microV of the terminal 40 msec of the QRS complex or duration of the low-amplitude signal less than 40 microV at the terminal QRS complex that is greater than 38 msec; sensitivity, 84%; specificity, 54%).(ABSTRACT TRUNCATED AT 250 WORDS)