Left ventricular lesions in arrhythmogenic right ventricular dysplasia and 12-lead electrocardiographic findings

Left ventricular lesions in arrhythmogenic right ventricular dysplasia have not been well described, and the relationship between the left ventricular lesions and the 12-lead electrocardiographic findings has not been analyzed. This study examined whether the presence of left ventricular lesions and the extent of right ventricular lesions due to arrhythmogenic right ventricular dysplasia are predictable by 12-lead electrocardiographic findings. The 12-lead electrocardiograms during sinus rhythm and left and right ventriculography were studied in 29 patients (27 males and 2 females, mean age 42.6 +/- 15.5 years) diagnosed by the current criteria for this disease. After evaluation, patients were divided into two groups: those with normal left ventricles (normal group) and those with left ventricular wall motion abnormalities (abnormal group). Seventeen of the 29 patients (59%) were classified into the abnormal group. Left ventricular wall motion abnormalities were located in the posterolateral (4 patients), apical (1), and posterolateral and apical regions (12). QS patterns of abnormal Q waves in lead I, aVL or V5, V6 rS patterns (R/S ratio < 1) in leads I and V6, and/or R or Rs patterns (R/S ratio > 1) in lead V1 were observed in all patients in the abnormal group, but in none in the normal group. There was a positive correlation between the right ventricular end-diastolic volume index and the number of precordial negative T waves (r = 0.746, p < 0.0001), and the time from onset of the QRS to the terminal portion of the epsilon wave in lead V1 (r = 0.627, p < 0.001). The correlation coefficients showed no significant differences between the groups. A left ventricular lesion associated with arrhythmogenic right ventricular dysplasia was not unusual (59%), and our study suggests that the posterolateral and apical regions are the most frequent sites. The presence of these lesions were predictable by the QRS abnormalities. Moreover, regardless of the presence of such a lesion, the extent of the right ventricular lesion is also predictable by the 12-lead electrocardiographic findings.     

Attitudes to female roles, aspects of menstruation and complaining of menstrual symptoms

Mofidied limb electrode positions are often used in studies which require the recording of rest and exercise ECGs, whereby the arm electrodes are placed at the infraclavicular fossae and the left lef electrode on the left lower abdomen. The effect of the modified limb electrode positions on electrocardiographic waveforms was investigated in 68 supine adult male subjects at rest. The modification produced profound amplitude and waveform changes in the frontal plane ECG leads. The QRS axis shifted on the average by 16 degrees towards a more vertical position with considerable individual variation. Concomitant with the QRS axis shift, the R wave amplitude decreased in leads I and a VL and increased in leads II, III, and aVF. The S wave amplitude increased in leads III and aVF and decreased in lead III. The P and T wave amplitude changes were in a direction similar to those observed for the R waves: a reduction of the amplitude in aVL and an increase in II, III and aFV. Of importance to exercise ECG interpretation are the ST segment waveform changes: The ST slope decreased in aVL and increased in leads II, III and aVF. Waveform changes in the chest leads caused by the modification were less important although statistically significant. These systematic changes in recorded ECG waveforms arise from changes directions and strength of the lead vectors of the six frontal plane leads. Large inter-individual variations in the magnitude of the changes produced by modification of the limb electrode positions prevent effective systematic correction of the distortions by means of a universal lead transformation.     

Clinical approach to wide QRS complex tachycardias

Wide QRS complex tachycardia is a frequently encountered arrhythmia in the emergency department and presents a diagnostic challenge to the emergency physician. The history, physical examination, chest radiograph, and electrocardiogram analysis are important in making the correct diagnosis. The diagnosis of ventricular tachycardia is supported by, 1) a history of prior myocardial infarction or congestive heart failure; 2) a physical examination showing cannon A-waves in the jugular venous pulsation or variable heart sounds; 3) a chest radiograph showing cardiomegaly or evidence of prior cardiac surgery; and 4) characteristic ECG features that include AV dissociation, fusion-capture beats, QRS concordance, or, typical morphologic features in leads V1 and V6. This article presents the diagnostic and therapeutic approaches to wide QRS tachycardias.     

Dynamic vectorcardiography for early diagnosis of acute myocardial infarction compared with 12-lead electrocardiogram. BIOMACS Study Group

BACKGROUND: The aim of the study was to assess the diagnostic accuracy of multilead continuous vectorcardiography (VCG) for early diagnosis of acute myocardial infarction (AMI) in patients admitted to hospital because of suspicion of AMI. VCG was compared with resting 12-lead electrocardiogram (ECG) on admission. METHODS: In a multicentre study, 107 patients with chest pain (< or = 12 h) were included. The diagnosis of AMI was on the basis of World Health Organization criteria. Continuous VCG was recorded for 12-24 h and the data were evaluated blindly at 2 and 6 h of recording and after the completion of recording (12-24 h). RESULTS: AMI was diagnosed in 74 patients. The VCG recording had a diagnostic accuracy of 71% after 2 h and 86% after both the 6 h and the completed VCG recording. Compared with ECG on admission, the VCG recording after 6 h showed a significantly greater sensitivity: 86% compared with 62% (P < 0.01). In patients with non-diagnostic ECG on arrival (n = 55), VCG after 6 h had a diagnostic accuracy of 85%, a sensitivity of 82% and a specificity of 89%. CONCLUSIONS: VCG might be useful for early diagnosis of AMI, especially in patients with non-diagnostic ECG.     

Improved detection of coronary artery disease by exercise electrocardiography with the use of right precordial leads

BACKGROUND: Exercise electrocardiography is an perfect test for the detection of coronary artery disease. We attempted to improve the diagnostic accuracy of exercise testing as a noninvasive method for the detection of coronary artery disease by using a combination of the left and right precordial leads. METHODS: We studied 245 patients (218 men and 27 women) ranging from 32 to 74 years of age (mean [+/-SD], 52+/-8) who underwent treadmill exercise testing, thallium-201 scintigraphy, and coronary arteriography. During exercise testing, each patient had one electrocardiogram recorded with the standard 12 leads and 3 right precordial leads (V3R, V4R, and V5R), with the results for each set of leads recorded and analyzed separately. RESULTS: On the basis of coronary arteriography, 34 patients had normal coronary arteries, 85 had single-vessel disease, 84 had two-vessel disease, and 42 had three-vessel disease. The sensitivities of the standard 12-lead exercise electrocardiogram, exercise electrocardiography incorporating right precordial leads, and thallium-201 scintigraphy were 52 percent, 89 percent, and 87 percent, respectively, for the detection of single-vessel disease; 71 percent, 94 percent, and 96 percent for the detection of two-vessel disease; 83 percent, 95 percent, and 98 percent for the detection of three-vessel disease; and 66 percent, 92 percent, and 93 percent for the detection of any coronary artery disease. The specificities of the three methods for the detection of any coronary artery disease were 88 percent, 88 percent, and 82 percent, respectively. CONCLUSIONS: Use of right precordial leads along with the standard six left precordial leads during exercise electrocardiography greatly improves the sensitivity of exercise testing for the diagnosis of coronary artery disease.     

Preparation of antihemophilic factor from indated plasma

The relations of QRS amplitude sums to activation boundary size at two instants was evaluated in five normal subjects. In each subject, QRS amplitude sums from 192 simultaneously recorded torso electrocardiograms and from 35 leads from the precordial area only were obtained 10 and 15 msec after the QRS onset. Activation boundary size at these instants was taken from published studies of ventricular excitation sequence in the human heart. The relative size of electrocargiographically effective boundaries at 10 and 15 msec and the measured QRS amplitude sum at 10 msec were used to predict expected QRS amplitude sums at 15 msec. Differences between the predicted and measured QRS amplitude sums at 15 msec constitute an estimate of error in determining cardiac source size from its expressions in the body surface electrocardiogram (ECG). Results demonstrated a more consistent relation of activation boundary size to QRS sums from the 192 than from the 35 electrode array. Indirectly the results suggest summed ST segment displacement from the larger array of electrodes would be more consistently related to the extent or severity of myocardial injury than an ST segment displacement sum based on 35 precordial leads. Finally, the findings suggested that the absolute sum of an electrocardiographic measurement such as ST segment displacement would provide a better index of lesion size than ST elevation or depression only.     

Diagnosis of diffuse myocardial changes in ischemic heart disease using orthogonal ECG leads

In 100 patients with chronic ischaemic heart disease and diffuse changes in the myocardium the data of 12 common ECG leads indicated that the corrected orthogonal leads according to Mac Fee--Parungao and Frank reflect these changes in all cases. The severity of the diffuse changes reflected in the deviations of the ST segment and the T-wave in the orthogonal leads corresponds to that reflected in the 12 common leads. A mathematical analysis of the waves of the QRS complex in the X, Y and Z leads indicates a growth of the left ventricular potentials with the development of diffuse myocardial changes. The mentioned systems of orthogonal leads can be recommended for wide employment for the diagnosis of diffuse changes in the myocardium in ischaemic heart disease.     

Diagnostic value of ECG patterns of right ventricular hypertrophy in children

OBJECTIVE: To determine the diagnostic value of traditional criteria of right ventricular hypertrophy (RVH) in children. PATIENTS: The electrocardiograms (ECGs) of 1000 consecutive pediatric patients were reviewed. Children under three months old were excluded as were patients with QRS prolongation. RESULTS: Four hundred and thirty-four patients met all inclusion criteria. The medical records were then reviewed for diagnosis. Sixty-seven per cent had a diagnosis compatible with RVH. Of the ECG patterns evaluated, a precociously upright T wave in lead V1 was most predictive with 99% specificity. Presence of a QR complex in lead V1 had a 96% specificity but R:S ratio, voltage criteria and rSR' incomplete right bundle branch block pattern had intermediate specificities of 66%, 66% and 52%, respectively. Sensitivities of 12.6%, 13.2%, 34.0%, 63.3% and 74.2% were calculated for upright T, QR complex, R:S ratio, voltage criteria and rSR', respectively. CONCLUSIONS: An upright T wave or qR pattern are highly specific but insensitive markers of RVH in children. In contrast, when an incomplete right bundle branch block exists, the rSR' pattern is a relatively sensitive but nonspecific predictor of RVH.     

Distortions in infant electrocardiograms caused by inadequate high-frequency response

Frank lead ECG's from infants were studied for frequency content by introducing low-pass filters of 50, 75, 100, and 150 150 Hz bandwidths before obtaining computer measurements. Results indicated that a minimum bandwidth of 100 Hz is required to avoid amplitude error of 10 per cent or greater. This bandwidth requierement is essentially the same as that required for adult ECG's despite the fact that infant QRS durations are usually about half those of adults. Although the average infant ECG spectrum is likely to contain higher frequencies than the average adult ECG spectrum, duration values for Q, R, and S waves overlap in these populations to such an extent that bandwidth requirements are practically identical.     

Elevation of plasma MB creatine kinase and the development of new Q waves in association with pericarditis

A 64-year-old woman with an acute exacerbation of chronic relapsing pericarditis had initial clinical and ECG features that were consistent with an acute anterior myocardial infarction. Transient Q waves were observed in the precordial leads, and she also exhibited elevated plasma MB creatine kinase (MB CK) activity. However, the overall clinical and laboratory data, including angiographic and radionuclide studies, suggest that the myocardial damage was secondary to pericarditis per se, rather than ischemic myocardial infarction. This case emphasizes that Q waves and elevated MB CK activity can be seen in association with pericarditis, and this must be differentiated from myocardial infarction secondary to coronary artery disease.     

Density functional studies on herpes simplex virus type 1 thymidine kinase-substrate interactions: the role of Tyr-172 and Met-128 in thymine fixation

It has been well documented that the prevalence of certain electrocardiographic (ECG) findings among individuals free of coronary heart disease (CHD) differs by race. However, it is not known whether these differences exist independently of CHD risk factors (e.g., hypertension). We examined the ECG tracings of 2,686 apparently healthy, middle-aged African-American and white men and women who participated in the Atherosclerosis Risk in Communities Study and were at low risk of CHD. Using the Minnesota Code, among men, 46% of African-Americans, but only 25% of whites, had a minor ECG finding (p < 0.001). In women, 32% of African-Americans and 23% of whites had a minor ECG finding (p < 0.01). Specifically, the age-adjusted prevalences of high-amplitude R wave, ST elevation, T-wave findings, and prolonged P-R interval were statistically significantly higher in African-Americans. As for continuous ECG measurements, the R wave in leads V5 and V6, the S wave in V1, the J-point amplitude in leads V2 and V5, the P-R interval, and the Cornell voltage (?S V3? + R aVL) for left ventricular hypertrophy were all significantly greater in African-Americans than in whites. However, in both men and women, the heart rate corrected QT interval was shorter in African-Americans than in whites. All of these findings remained statistically significant after further adjustment for traditional CHD risk factors. These results suggest that racial differences in electrocardiograms may not be explained entirely by differences in established CHD risk factors, and because current diagnostic ECG criteria are largely based on data from middle-aged white men and women, race should be considered in the interpretation of ECG findings.     

Evolutive study of the vectorcardiogram from the 14th day to the 6th month of life on the normal infant

With the purpose of a better evaluation of the changes of cardiac potentials during the early hemodynamic arrangement of the normal heart, the authors analyze the VCG of 10 normal children periodically recorded from the 14th day to the 6th month from birth. Rotation of QRS, T and P loops in the three planes, direction and voltage of principal planar and spatial vectors were analyzed. The QRS loop showed a balanced distribution between right and left ventricular forces in the second week and developed a leftward orientation from the 4th week to the 3rd month, as demonstrated both by the loss of clockwise rotation of horizontal QRS loop and by the progressive leftward and backward direction of intermediate vectors. The initial vectors were sketched or absent in the 14th day and increased successively until the typical Q loop. The voltage of terminal vectors did not change in the course of time, but the S loop in the horizontal plane lost its original clockwise rotation and shifted to middle posterior line. The T loop progressively shifted backward so that it was always posterior after the 30th day. The P loop in the frontal plane was similar to the adult's one while in the horizontal plane it often presented a figure-of-eight. The semeiological aspects and the electrogenic considerations of these changes were discussed.     

Quantification of ischaemia induced vulnerability by precordial T wave alternans analysis in dog and human

OBJECTIVE: The aim was to examine the regional specificity of T wave alternans and the value of precordial ECG monitoring for non-invasive tracking of cardiac vulnerability during acute coronary artery occlusion and reperfusion in animals and humans. METHODS: The left ventricular ECG was monitored during two acute occlusions of the left anterior descending coronary artery and subsequent reperfusion in each of 61 chloralose anaesthetised dogs, and over 150,000 beats were analysed. In subgroups of these animals, lead II and precordial lead V5 were monitored or epicardial electrograms were recorded. In seven patients, lead II and precordial leads V1-6 were monitored during angioplasty. T wave alternans magnitude was quantified by complex demodulation. The same recording equipment and analytical methods were used in the clinical and experimental studies. RESULTS: A close temporal correspondence and linear correlation was found between T wave alternans magnitude--but not ST segment depression or ventricular premature beat incidence--and the incidence of spontaneous ventricular tachycardia and fibrillation during acute coronary artery occlusion and reperfusion. Epicardial electrograms showed alternans to be regionally specific, occurring in the ischaemic but not in the normal zones, and to predict spontaneous ventricular fibrillation and ventricular tachycardia (sensitivity = 79%, specificity = 86%). A significant linear relationship (r2 = 0.86, p < 0.01) between alternans magnitude detected in V5 and the left ventricular intracavitary lead indicates that the precordial leads could be used to assess cardiac vulnerability from the body surface. Lead V5 showed greater resolution than lead II. In humans, the precordial leads overlying the ischaemic zone were superior to lead II or Frank leads for alternans detection during both the occlusion and the reperfusion phases. In both animals and humans, alternation invariably occurred during the first half of the T wave, coinciding with the vulnerable period of the cardiac cycle and suggesting an important electrophysiological link to cardiac vulnerability. CONCLUSIONS: Alternans is regionally specific and is linearly projected to the precordium. Quantification of its magnitude in the precordial ECG may provide a non-invasive means for tracking cardiac vulnerability during acute myocardial ischaemia and reperfusion in both animals and humans.     

Magnito-, electro- and echocardiography in detecting symptoms of the "hypertensive heart"

The study compared diagnostic potential of magnetocardiography (MCG), electrocardiography (ECG) and echocardiography (echo-CG) in 18 patients with arterial hypertension (AH). 32 healthy males served as control. Elements of MCG from normal subjects have been analyzed morphologically in 36 points of precordial leads. Left ventricular hypertrophy was registered at echo-CG, MCG, ECG in 11 (61%), 16 (84%) and 7 (34%) of the AH patients, respectively. Left atrial hypertrophy was discovered primarily by echo-CG and MCG. Defects in ventricular repolarization were recorded by MCg in 7 (39%) patients basing on MCG, echo-CG and rarely ECG signs of left ventricular hypertrophy. MCG is recommended as an effective tool in diagnosis of "hypertensive heart".     

Spontaneous angina in the coronary care unit. 2. Electrocardiographic changes during and after chest pain

Serial ECGs of 16 patients with repetitive attacks of spontaneous angina in the CCU were studied from admission to the hospital to the follow-up phase at the cardiac clinic. Transient repolarization ECG changes occurring during unprovoked angina included ST-segment elevation and ST-segment depression, alterations of T-wave amplitude and polarity, and pseudonormalization of previously inverted T-waves. In addition, QRS complexes were altered transiently during chest pain. Such changes comprised augmentation or reduction of amplitude of R and S waves, widening of QRS complexes and a merging of R waves with the elevated ST-segments. Occasionally the ECG during attacks of angina did not show any change. During asymptomatic periods, between attacks of spontaneous angina, the ECG either returned to baseline, or displayed minor ST-segment shifts, and/or T-wave alterations of varying durations. However, such changes became either persistent or were replaced in the late course of hospitalization by ECG alterations diagnostic of transmural or nontransmural myocardial infarction. Twelve patients suffered an acute myocardial infarction. Four patients died within one month of admission. During follow-up of the 12 surviving patients in the cardiac clinic, amelioration of T-wave changes was noted in the ECGs of patients who remained asymptomatic, but new ischemic alterations were seen in the ECG of patients who had recurrent angina, or were readmitted to the hospital for evaluation. Increase in the amplitude of R-waves, disappearance of Q-waves, or reduction of Q-wave depth were noted at follow-up, in comparison with the discharge ECG, in some patients who had suffered primarily an anterior myocardial infarction.     

Hypertrophic myocardiopathy with isoelectric T waves

INTRODUCTION AND OBJECTIVES: The lack of specificity of electrocardiographic (ECG) recording showing isoelectric T-waves often leads to diagnostic doubts. This study attempts to demonstrate that asymptomatic patients who demonstrate benign forms of hypertrophic cardiomyopathy may be identified from a typical ECG pattern showing isoelectric T-waves. METHODS: In 45 out of 5,126 asymptomatic healthy aircrew members, an ECG pattern which showed isoelectric T-waves in all leads, but were normal in V2 and V3, was found. 12 of them had negative T-waves in III and aVF leads. Cardiac echo-Doppler, Bruce test and 24-hour Holter recordings were performed in 29 of the 45 cases; all were males aged 30-55 (43.1 +/- 7.1) without any associated disorder nor engaged in heavy exercise, and a control group of 15 healthy subjects. In each of the 29 cases, 2-21 ECG's (11.1 +/- 6.3) performed over a period of 2 to 20 years (13.0 +/- 5.9) were reviewed. RESULTS: In 23 of the 29 cases (79.3%), echo-Doppler criteria of non obstructive mild hypertrophic cardiomyopathy were found. T-waves became normal during exercise testing, returning to isoelectric during recovery, in 19 of the 23 cases. In 17 of these cases, reversible T-wave changes were observed between successive ECG's; T-wave changes became clearly negative when the level of exercise was increased. Holter recordings did not show pathological findings. CONCLUSIONS: We believe that echo-Doppler studies must be performed in asymptomatic patients showing the ECG pattern described above, because they are strongly suspicious of having mild hypertrophic cardiomyopathy.     

Evaluation of electrocardiographic left ventricular hypertrophy with both QRS voltage and ST-T change using echocardiography

The purpose of the present study is to determine whether electrocardiographic QRS voltage criteria with ST-T change is useful in the diagnosis of left ventricular hypertrophy (LVH) using echocardiography. One hundred men including 59 with hypertension (HT), 9 with hypertrophic cardiomyopathy (HCM), and 32 without any cardiovascular disease were enrolled in this study. All of them had the electrocardiographic evidence of LVH by Sokolow-Lyon voltage criteria (RV5 or RV6 > 2.6 mV, SV1+RV5 or SV1+RV6 > or = 3.5 mV). They were classified into three groups based on ST-T pattern as follows: Normal ST-T (group N): normal ST-T in twelve leads; Early strain ST-T (group ES): ST depression, flat T (T/R < 1/10), diphasic T or T wave inversion < 0.1 mV in V5 or V6; and Strain ST-T (group S): inverted T wave in V5 and V6. Echocardiographic LVH was determined when either interventricular septal thickness (IVST) or left ventricular posterior wall thickness (LVPWT) > or = 12 mm was present. According to this echocardiographic evidence, 31.7%(20/63) of group N, 75.0% (12/16) of group ES, and 100% (21/21) of group S were diagnosed. There were significant correlations between QRS voltage indices (RV5, RV6, SV1+RV5 and SV1+RV6) and IVST, (IVST+LVPWT)/2, and LV mass in group S(r = 0.650 to 0.858, p < 0.05) but not in group N. Values for IVST and LV mass were significantly greater in group S than in group ES or N. The electrocardiographic diagnosis of LVH with both QRS voltage and ST-T change thus appeared to be more useful than that with QRS voltage criteria alone.     

High-fidelity spectrocardiography for the diagnosis of ischemic cardiopathy. The validation of a new method for analyzing the spectral components of the QRS complex

BACKGROUND: Analysis of high-frequency QRS complex envelope has been suggested as a method that could detect myocardial ischemia but the characteristics of the turbulence spectral from an spectral-temporal mapping into the QRS complex has not been studied yet. This is a prospective study of phase I for the validation of a new diagnostic test. AIMS: The aims for this study are: 1) To validate a new method for the detection of transient myocardial ischemia by both, high-frequency QRS and spectral turbulence analysis, which we have named "high-fidelity spectrocardiogram" (HFS). 2) To compare the sensitivity, specificity and accuracy of this HFS versus those obtained from nuclear medicine (NM-MIBI) and a conventional exercise ECG test, in a highly selected population. PATIENTS AND METHODS: Twenty-five patients (P) were studied: 10 P (Group B) with risk factors for coronary artery disease, without previous infarct, who had atypical precordial pain and a conventional ECG considered as "normal" by two cardiologists. The group A was formed by 15 P without risk factors or another kind of heart disease. All patients underwent a conventional surface ECG, which had to be normal in order to be considered for this study. Echocardiogram, exercise testing ECG and a NM-MIBI study were also normal. The HFS recording was taken before and after Dipyridamole testing, similar to the conventional method for the NM-MIBI (dipyridamole 0.25 mg/Kg/doses) studies. Our software for the analysis of QRS-frequencies was constructed from a language Turbo C++. The Fourier's transform allowed the construction of 3-dimensional graphics. After the determination of the best wide band for detecting changes in the frequency contained of QRS, the determination coefficients (r2) were obtained and compared before and after the challenge with dipyridamole. These changes were compared between groups (A vs B) later. RESULTS: The r2 changed more than 30% after dipyridamole in those patients in whom myocardial ischemia was demonstrated later by NM-MIBI. The sensitivity (85%) and specificity (90%) of HFS were similar to the nuclear medicine for identifying myocardial ischemia, but higher than a conventional exercise ECG testing (p.001). The main change in HFS was in the frequency-contained QRS in the 130-260 Hz band. The accuracy of our method was increased when an analysis of each orthogonal lead was made. There was a clear tendency of the group B to increase the QRS duration, while the contrary was found in group A, being the QRS the shorter (p.064). The chronological responses were different in those patients with ischemia. CONCLUSION: This study suggests that an episode of myocardial ischemia is able to change in a dramatic manner the frequency-contained within of the QRS complex, in spite of an unchanged ST segment in the conventional exercise ECG. We suggest that the HFS could be a good method for identifying myocardial ischemia. Its advantages could be important, particularly when the conventional exercise ECG is non informative.     

Beat-to-beat QRS variability in the 12-lead ECG and the detection of coronary artery disease

The aim of this article was to study beat-to-beat QRS variability in patients with ischemia and old myocardial infarction using the 12-lead resting electrocardiogram (ECG). The variability analysis was based on beats that have been synchronized in time with an iterative alignment technique. The QRS variability was measured in patients submitted for myocardial scintigraphy. Those with a normal myocardial scintigraphy (called NO, n = 34, mean age 57 years, 23 women) were compared with a group with both myocardial infarction and exercise-induced ischemia (called ISCINF, n = 27, mean age 57 years, 5 women). The mean QRS variability was somewhat smaller in lead I in ISCINF than in NO, and there was no statistically significant difference in QRS variability among the groups in leads II, III, and V1-V6. Using a multivariate approach, the joint variability in leads I, II, II, and V1-V6 was used for calculating receiver operating characteristics based on a leave-one-out procedure. The sensitivity for detecting coronary artery disease was 75% at a specificity of 50%. It is concluded that beat-to-beat QRS variability in the 12-lead ECG does not discriminate between the presence and absence of coronary artery disease sufficiently well for clinical purposes.     

QRS prolongation measured by a new computerized method: a sensitive marker for detecting exercise-induced ischemia

This study compared thallium stress testing and exercise changes in QRS duration using a computerized 'optic scanner' in three groups. Group 1 consisted of 108 subjects with positive exercise ECG tests by ST-T segment criteria and with proven coronary artery disease. Group 2 included 19 subjects with nondiagnostic exercise ECG ST-T changes and with proven coronary artery disease. Group 3 was formed by 38 healthy controls. Group 1: Mean increase in exercise QRS width of 12.4 +/- 14 ms. Group 3: Mean decrease in exercise QRS width of 4.9 +/- 9.3 ms (p < 0.0001). Group 2: Mean QRS prolongation of 7.8 +/- 9.2 ms, which was significantly different from the controls (p < 0.0001) but not from group 1. When compared to thallium stress testing, exercise QRS prolongation had a sensitivity of 93%, specificity of 71%, relative risk of 5, and positive predictive value of 86%. QRS duration measurement can improve the diagnostic accuracy of the exercise ECG stress test.