Electrocardiographic criteria for detecting coronary artery disease in hypertensive patients with ST-segment changes during exercise testing

Purpose

It is well known that patients with arterial hypertension frequently present with ischemic electrocardiographic changes during exercise testing without actually having coronary artery disease (CAD). The purpose of this study was to establish additional electrocardiographic criteria during exercise testing for detecting CAD in hypertensive patients with ischemic ST-segment response.

Methods

Three hundred eighty-two consecutive hypertensive patients (224 males, 58 ± 8 years) who presented with ischemic electrocardiographic changes during exercise testing and agreed to undergo coronary arteriography were included in the study.

Results

From 382 hypertensive patients undergoing coronary angiography, only 76 (20%) had significant coronary stenosis, whereas 306 (80%) had normal coronary arteries. From 382 patients, 287 (75%) (group A) presented with ST-segment depression during exercise in leads II-III-aVF-V₆, 271 (94%) of which had normal arteries at the angiography. The remaining 95 patients (25%) (group B) of the studied patients presented with ST-segment depression in II-III-aVF and/or V₄ through V₆, 60 (63%) of which had CAD. Furthermore, 251 patients of group A presented with ST-segment depression during the fourth to sixth minute of the recovery period in V₄ through V₆, 247 (98%) of which had normal arteries. Another 28 patients from group B presented with ST-segment depression during the fourth to eighth minute of the recovery period in V₄ through V₆, 22 (79%) of which had significant coronary artery stenosis.

Conclusions

Hypertensive patients who present with ST-segment depression during exercise in leads II-III-aVF and/or V₄ through V₆ and with a prolonged duration of this depression at the recovery phase (fourth to eighth minute) are more likely to have CAD. Absence of ST-segment depression in V₄ and V₅ at the end of exercise or during the seventh and eighth minute of recovery favors a false-positive result.     

Exercise-induced QRS prolongation in patients with mild coronary artery disease: Computer analysis of the digitized multilead ECGs

Although exercise-induced QRS prolongation has been reported as a possible marker for inducible ischemia, subtleness of the prolongation makes it unidentifiable from standard, chart-recorded electrocardiograms (ECGs). To overcome such a limitation, we measured the QRS width using high-resolution ECGs and examined the diagnostic value of the exercise-induced QRS prolongation in patients before and after percutaneous transluminal coronary angioplasty (PTCA). In 16 patients with single- (n = 12) or double-vessel disease (n = 4), treadmill exercise ECG tests were performed before and after PTCA, while continuously recording 8-lead ECGs at 500 Hz. The onset of the QRS complexes was defined by the earliest deflection, and the end was defined as the latest deflection among 8 leads with the use of algebraic sum of the absolute voltage and their time derivatives (dV/dt) from all 8 leads. We compared QRS complexes before and 1 minute after exercise. Before PTCA, exercise prolonged the QRS width in all but 3 patients (unchanged in 2, decreased in 1) (84 ± 7 to 87 ± 8 ms, P < .005). After PTCA, it decreased in 4, was unchanged in 5, and increased in 7 (83 ± 7 to 83 ± 6 ms, not significant). PTCA shortened postexercise QRS width in all but 3 (unchanged in 2, increased in 1: 83 ± 6 to 87 ± 8 ms, P < .001). High-resolution ECGs enabled us to measure subtle QRS prolongation induced by mild ischemia. Because the QRS prolongation and ST-segment changes would reflect different aspects of myocardial ischemia, incorporating this measure into ST segment criteria might significantly improve the diagnostic accuracy for coronary artery disease.     

Exercise-induced QRS amplitude changes in patients with isolated myocardial bridging: a marker of myocardial ischemia

Myocardial bridging (MB) of coronary arteries has been considered as an incidental angio-graphic finding; however, several reports suggest its association with angina pectoris, myocardial ischemia, and even infarction. In this study the authors aimed to assess exercise-induced QRS changes in patients with isolated MB and to compare those with coronary artery disease (CAD) and healthy subjects. The study population consisted of 17 patients with angiographically proven MB (group 1), 16 patients with left anterior descending (LAD) artery stenosis (group 2), and 14 healthy subjects (group 3). Each subject underwent treadmill exercise testing according to Bruce protocol. In each subject amplitude of the Q, R, and S waves in leads aVF and V(5) was measured manually before and immediately after exercise. The Athens QRS score was calculated by subtracting the Q-, R-, and S-wave differences in leads aVF and V(5). Baseline characteristics of each group were similar. There was no difference among the groups with respect to exercise testing parameters (peak heart rate, blood pressure, test duration, etc). In group 1, ST-segment depression ratio was found to be higher than that of group 3 but lower than that of group 2. In group 1, exercise QRS score was found to be lower than that of group 3 while it was higher than that of group 2 (2.9 +/- 2.3 vs 6.5 +/- 3.2 p = 0.001 and 2.9 +/- 2.3 vs 2.6 +/- 2.4 p = 0.001, respectively). In patients with MB exercise, QRS score was significantly lower than in those with normal coronary flow while it was higher in those with CAD. This may result from exercise-induced ischemia at the area perfused by the bridged artery.     

Addition of right-sided and posterior precordial leads during stress testing

Background

Exercise treadmill testing has limited sensitivity for the detection of coronary artery disease, frequently requiring the addition of imaging modalities to enhance the predictive value of the test. Recently, there has been interest in using nonstandard electrocardiographic (ECG) leads during exercise testing.

Methods

We consecutively enrolled all patients undergoing exercise myocardial imaging with four additional leads recorded (V₄R, V₇, V₈, and V₉). The test characteristics of the 12-lead, the 15-lead (12-lead, V₇, V₈, V₉), and the 16-lead (12-lead, V₄R, V₇, V₈, V₉) ECGs were compared with stress imaging in all patients. In the subset of patients who underwent angiography within 60 days of stress testing, these lead arrays were compared with the catheterization findings.

Results

There were 727 subjects who met entry criteria. The mean age was 58.5 ± 12.3 years, and 366 (50.3%) were women. Pretest probability for disease was high in 241 (33.1%), intermediate in 347 (47.7%), and low in 139 (19.1%). A total of 166 subjects had an abnormal 12-lead ECG during exercise. The addition of 3 posterior leads to the standard 12-lead ECG resulted in 7 additional subjects having an abnormal electrocardiographic response to exercise. The addition of V₄R resulted in only 1 additional patient having an abnormal ECG during exercise. The sensitivity of the ECG for detecting ischemia as determined by stress imaging was 36.6%, 39.2%, and 40.0% (P = NS) for the 12-lead, 15-lead, and 16-lead ECGs, respectively. In those with catheterization data (n = 123), the sensitivity for determining obstructive coronary artery disease was 43.5%, 45.2%, and 45.2% (P = NS) for the 12-lead, 15-lead, and 16-lead ECGs, respectively. The sensitivity of imaging modalities was 77.4% when compared with catheterization.

Conclusions

In patients undergoing stress imaging studies, the addition of right-sided and posterior leads did not significantly increase the sensitivity of the ECG for the detection of myocardial ischemia. Additional leads should not be used to replace imaging modalities for the detection of coronary artery disease.     

Exercise electrocardiographic mapping in normal subjects

To investigate the spectrum of change in multiple-lead exercise electrocardiograms, 120-lead body surface potential maps (BSPM) in normal adult subjects during upright, graded, submaximal exercise testing were recorded. Results showed that in the normal group, exercise was associated with substantial electrocardiographic changes on the body surface, many of which persisted during early recovery. The QRS waveform was minimally altered during exercise. Despite, however, no change in QRS duration, there was significant reduction in QRS potential range with consequent reduction QRS integral value. The ST waveforms changed markedly with exercise, showing abbreviated duration and increased slope. This was reflected by significantly increased ST potential range from rest to immediate cessation of exercise, which returned towards resting value during recovery. The effect of the altered ST-segment waveform was also reflected in torso potential distributions at two time instants during the ST-segment. When a spatially-fixed position on the ST-T waveform was evaluated (ST-segment offset), exercise resulted in small potential changes, especially over the torso area occupied by the standard V1 to V6 chest leads. However, when a temporally-fixed point (80 ms after QRS offset) was evaluated, there were large increases in potential over the precordium with exercise. Isointegral ST-segment maps, which reflect both spatial and temporal ST properties, showed that exercise was associated with substantial decreases in values over the precordium and inferior torso, and although diminished, they tended to persist through five minutes of recovery. Thus, electrocardiographic repolarization parameters are particularly affected by physiological exercise and, although the underlying causes of these changes remain undefined, they should be taken into account when evaluating the population at risk.     

Fragmented Left Sided QRS in Absence of Bundle Branch Block: Sign of Left Ventricular Aneurysm

Background: A left ventricular aneurysm (LVA) occurs between 3.5% and 9.4% of all cases of acute myocardial infarction. A fragmented left sided QRS (RSR` pattern or its variant RSr`, rSR`, or rSr`) without evidence of bundle branch block (QRS duration ≤120 ms) on the ECG may be associated with a significant myocardial scar, which is the characteristic of a LVA. We, therefore, postulate that fragmented QRS (RSR` pattern or its variant) in the left sided leads (I, aVL, V₃ to V₆) may be a useful sign of LVA. Methods: ECGs of 110 consecutive patients with LVA documented by left ventricular angiography (30° right anterior oblique view) was compared with 220 patients without LVA (110 patients with and 110 patients without coronary artery disease (CAD)), who were evaluated for CAD by symptoms and signs. Results: The sensitivity of the fragmented QRS for identification of LVA was 50% (55 of 110 patients) and specificity was 94.6% (209 of 220). Within the study population, the positive predictive value of the fragmented QRS for LVA was 83.3% (55 of 66) and the negative predictive value was 79.2% (209 of 264). Based on the range of prevalence of LVA in postmyocardial infarction population (3.5–9.4%) and on observed sensitivity and specificity, the positive predictive value of fragmented QRS for LVA after infarction can be estimated at 29–53% and the negative predictive value can be estimated at 95–98%. Conclusion: The sensitivity of fragmented QRS in left precordial leads for LVA was only 50%, whereas the specificity was 94.5%. It has a relatively low to moderate positive predictive value and high negative predictive value.     

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

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, V₃R, 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 V₁ and V₂ are almost diametrically located on the back. Inverting these leads could render the V₈ and V₉ 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.     

Interlead Difference in QT Interval Rate Adaptation During Exercise in Coronary Artery Disease Patients Susceptible to Ventricular Fibrillation

Background: Nonhomogeneity in ventricular repolarization predisposes to ventricular tachyarrhythmias. Rate adaptation of the QT interval parallels rate adaptation of the action potential, both of which reflect the repolarization phase in ventricular myocardium. The aim of this study was to examine in patients with coronary artery disease (CAD) the relation of interlead differences in QT interval rate‐adaptation to arrhythmia vulnerability. Methods: We studied 29 CAD patients with a history of ventricular fibrillation (VF) not associated with acute myocardial infarction (VF group), and their 29 individually matched CAD controls without arrhythmic events (controls). Rate adaptation of the QT intervals in the 12 leads of the electrocardiogram were determined from QT intervals measured at rest and at the end of each 3 minute load step during exercise test. The relation between heart rate (HR) and QT interval (QT/HR slope) was calculated separately in each lead by the linear regression equation. The slopes of these equations were used to characterize spatial QT interval rate adaptation. Results: The steepest QT_apex/ HR slopes in any lead were (mean ±mD SD) ?2.45 ± 0.63 in the VF group and ‐1.97 ± 0.45 in controls (P = 0.008), whereas the smallest slopes showed no difference (P = NS). The standard deviations of QT_apex/ HR slopes were 0.48 ± 0.23 in the VF group and 0.33 ± 0.12 in controls (P = 0.012). Conclusions: Rate adaptation of the QT_apex interval is locally exaggerated, resulting in nonhomogenous exercise response of the QT_apex intervals in CAD patients susceptible to life‐threatening ventricular arrhythmias. A.N.E. 2000;5(4):346–353     

Where do derived precordial leads fail?

A 12-lead electrocardiogram (ECG) reconstructed from a reduced subset of leads is desired in continued arrhythmia and ST monitoring for less tangled wires and increased patient comfort. However, the impact of reconstructed 12-lead lead ECG on clinical ECG diagnosis has not been studied thoroughly. This study compares the differences between recorded and reconstructed 12-lead diagnostic ECG interpretation with 2 commonly used configurations: reconstruct precordial leads V₂, V₃, V₅, and V₆ from V₁,V₄, or reconstruct V₁, V₃, V₄, and V₆ from V₂,V₅. Limb leads are recorded in both configurations.A total of 1785 ECGs were randomly selected from a large database of 50000 ECGs consecutively collected from 2 teaching hospitals. ECGs with extreme artifact and paced rhythm were excluded. Manual ECG annotations by 2 cardiologists were categorized and used in testing. The Philips resting 12-lead ECG algorithm was used to generate computer measurements and interpretations for comparison. Results were compared for both arrhythmia and morphology categories with high prevalence interpretations including atrial fibrillation, anterior myocardial infarct, right bundle-branch block, left bundle-branch block, left atrial enlargement, and left ventricular hypertrophy. Sensitivity and specificity were calculated for each reconstruction configuration in these arrhythmia and morphology categories.Compared to recorded 12-leads, the V₂,V₅ lead configuration shows weakness in interpretations where V₁ is important such as atrial arrhythmia, atrial enlargement, and bundle-branch blocks. The V₁,V₄ lead configuration shows a decreased sensitivity in detection of anterior myocardial infarct, left bundle-branch block (LBBB), and left ventricular hypertrophy (LVH).In conclusion, reconstructed precordial leads are not equivalent to recorded leads for clinical ECG diagnoses especially in ECGs presenting rhythm and morphology abnormalities. In addition, significant accuracy reduction in ECG interpretation is not strongly correlated with waveform differences between reconstructed and recorded 12-lead ECGs.     

Clinical Significance of QS Complexes in V1 and V2 without Other Electrocardiographic Abnormality

Background: In the absence of other electrocardiographic (ECG) abnormalities, QS deflections simultaneously in both of the leads V₁–V₂ may have multiple possible causes. Despite much information in the literature indicating that this is an unlikely pattern for pure septal infarction, such an ECG diagnosis is frequently given. Methods: Ninety‐nine cases having QS deflections in both leads V₁ and V₂ but no other ECG abnormality were compared to 99 other patients with entirely normal ECGs, to whom they were matched by age, gender, and the presence or absence of septal Q waves. Retrospective analysis of medical records was performed to determine the nature of any cardiovascular disease in these two groups, and to find a possible explanation for the ECG abnormality. Results: Because of its intermittence in subjects with multiple ECGs, QS deflections in leads V₁–V₂ appeared most often to be an artifact of precordial lead placement. Prior myocardial infarction, or presence of clinical coronary disease was present in only about 20% of the cases. Neither the intermittence of Q wave in V₂ on repeated ECGs nor the absence of septal Q waves was useful in distinguishing between those with and without coronary heart disease. Conclusions: This ECG pattern is a sign of prior myocardial infarction in only a minority of cases, and in the latter, infarction limited to the interventricular septum is exceptional. This ECG finding should be interpreted as a nonspecific QRS abnormality with multiple possible causes. Clinical correlation and repeat tracings with attention to lead placement will help to clarify its significance.     

Diagnostic value of exercise-induced S-T segment depression in patients with right bundle branch block

The sensitivity of submaximal exercise testing in detecting coronary artery disease in patients with right bundle branch block is not known. Thirty patients were identified who had right bundle branch block, submaximal treadmill exercise tests and selective coronary angiography. Eighteen of these patients were found to have significant coronary artery disease. Treadmill exercise testing was associated with S-T segment depression limited to leads V₁ to V₃ in three patients with coronary artery disease, whereas S-T segment depression was noted in leads V₄ to V₆ in eight patients, all of whom had multivessel coronary artery disease. Among patients without significant coronary artery disease, six had S-T segment depression limited to leads V₁ to V₃ during exercise testing.In this patient population, composed predominantly of men with symptoms of ischemic heart disease, the 12 lead submaximal treadmill exercise test had a sensitivity rate of 69 percent and a specificity rate of 45 percent in detecting coronary artery disease in the presence of right bundle branch block. The specificity of the treadmill test appears to be greater if S-T depression is recorded in leads V₄ to V₆. S-T segment depression limited to leads V₁ to V₃ often represents a false positive exercise test.     

Cardiopulmonary determinants of functional capacity in patients with chronic heart failure compared with normals

Background: Patients with chronic heart failure (CHF) are characterized by abnormal gas exchange and ventilatory responses to exercise. Hypothesis: This study compares variables obtained from cardiopulmonary exercise testing in 35 patients with CHF with 35 age- and weight-matched healthy subjects. A second goal was to obtain cardiopulrnonary variables measured at ventilatory threshold to distinguish patient changes from those of healthy subjects. Methods: Exercise testing was carried out using bicycle ergometry with ramplike protocol (work rate increments 12.5 W/min). Gas exchange and ventilation were measured breath by breath. Results: Compared with healthy subjects, the VO₂ in patients was lower at identical work rates (p<0.004) and at ventilatory threshold (p<0.0001), and the slope of the VO₂ curve during incremental exercise was flatter (p<0.05). With the exception of heart rate, the variables for VO₂, VCO₂, ventilation, O₂ pulse, ventilatory equivalents for O₂ and CO₂, and V_d/V_t (physiologic deadspace to tidal volume ratio), as well as lactate differed significantly at identical work rates. With the exception of V_d/V_t, all cardiopulmonary variables showed significant differences in their slopes during exercise. By means of a discriminant analysis, VCO₂ and ventilation proved to be the most distinguishing variables at ventilatory threshold between patients with CHF and healthy subjects. Conclusions: These results indicate the clinical usefulness of cardiopulmonary exercise testing when assessing functional impairment due to CHF. For treatment evaluation, not only VQ₂ but also VCO₂ and ventilation responses to exercise should be considered.     

Right Precordial Leads and Lead aVR at Exercise Electrocardiography: Does It Change Test Results?

Background: A recent study on exercise testing (ET) suggested that ST‐segment changes in the right precordial leads (RPL) may increase its sensitivity substantially. However, this study looked at a highly selected population of patients who all underwent thallium‐201 scintigraphy and coronary angiography. The present study evaluated the clinical utility of ST‐segment changes in the RPL and lead aVR in an unselected population of patients undergoing ET. Methods: A total of 906 consecutive patients who received ET were included in the study. ET was done using the Bruce Protocol with a 12‐lead electrocardiogram (ECG) substituting V₄R and V₆R for V₁ and V₆. Leads V₁ and V₆ were selected for omission as these two leads hardly ever manifest changes in isolation. Substituting two leads would obviate the need for a more complex recording system, thus improving clinical utility. Results: On the basis of horizontal/downsloping ST‐segment depression (STD) of 1.0 mm or more (the usually accepted criterion for a positive ET), 159 (17.5%) patients had a positive ET. In those patients with a negative ET (545 patients), 4 patients (0.7%) manifested STD and 5 patients (0.9%) manifested ST‐segment elevation (STE) in leads V₄R and/or V₆R, respectively. Of note, 44.7% of the positive ET group had STE in lead aVR. Conclusion: The use of ST‐segment changes in RPL during exercise stress testing does not appreciably change the test results of a standard ET. If one was to consider an additional marker, STE in aVR may be more useful, as it shows a stronger correlation with positive tests and does not require the recording of additional leads.     

Electrocardiography to define clinical status in primary pulmonary hypertension and pulmonary arterial hypertension secondary to collagen vascular disease

STUDY OBJECTIVES: To determine the utility of the ECG for predicting clinical status in adults with primary pulmonary hypertension (PPH) or pulmonary arterial hypertension (PAH) secondary to collagen vascular disease. DESIGN: Retrospective study. SETTING: Outpatient clinic in a tertiary referral center. PATIENTS: Adult outpatients with PPH or PAH secondary to collagen vascular disease who underwent electrocardiography within 30 days of undergoing right-heart catheterization, echocardiography, and 6-min walk testing. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: The following measurements were recorded from each ECG: P-wave amplitude in lead II; mean frontal QRS axis; QRS duration; R-wave and S-wave deflections in leads I and V6; and the T-wave configurations in the precordial leads. These ECG variables were correlated with hemodynamic variables, RV size, and exercise capacity. Of the 61 patients included in this study, 56 (92%) were women. Eight of 61 patients (13%) had normal findings on ECGs. There was no significant difference in the demographics or hemodynamics when comparing groups with normal vs abnormal ECGs. All ECG parameters had no more than moderate correlation with hemodynamic variables, ventricular size measured by echocardiogram, and exercise capacity as measured by a 6-min walk. The best correlation was between mean the frontal QRS axis and cardiac index (r = -0.46). CONCLUSIONS: The ECG is an inadequate screening tool to rule out the presence of clinically relevant pulmonary hypertension, either primary or secondary to collagen vascular disease. The mean frontal QRS axis correlated best with the severity of hemodynamic impairment.     

Ventricular activation during ventricular endocardial pacing: I. Electrocardiographic patterns related to the site of pacing

The QRS configuration produced by pacing at multiple left ventricular endocardial sites was evaluated in eight patients with (group 1) and six patients without (group 2) left ventricular wall motion abnormalities. Pacing was performed at a total of 122 sites, 4 to 13 sites in each patient. The QRS configuration resulting from apical pacing locations was compared with that at basal, septal to lateral and inferior to superior locations. Significant differences in QRS configuration during pacing from apical and basal locations were observed in electrocardiographic leads I, V₁, V₂ and V₆ (probability [p] < 0.01). Specifically, a QS pattern in leads I, V₂ and V₆ was more characteristic of an apical pacing location (p < 0.001), and a monophasic R wave in leads V₁ and V₂ was more characteristic of a basal pacing location (p < 0.01). Significant differences in leads V₁ and V₂ were observed when septal and lateral pacing sites were compared (p < 0.001). A monophasic R wave in leads V₁ and V₂ was more characteristic of a lateral pacing location (p < 0.01); a QS complex in lead V₂ was more characteristic of a septal pacing location (p < 0.001). Pacing at superior sites usually produced an inferior axis and vice versa (p < 0.001). The electrocardiographic patterns produced by pacing at similar sites in patients in group 1 were less consistent than those in patients in group 2. The QRS complex during ventricular pacing was wider in patients in group 1 (159 ± 30 ms) than in patients in group 2 (132 ± 18 ms) (p < 0.001).It is concluded that the QRS configuration recorded with 12 lead electrocardiography during endocardial pacing can help locate the region of the pacing site in patients with and without organic heart disease, although precise localization is not possible.     

The Role of the ECG in Diagnosis,Risk Estimation,and Catheterization Laboratory Activation in Patients with Acute Coronary Syndromes: A Consensus Document

The electrocardiogram (ECG) is the most widely used imaging tool helping in diagnosis and initial management of patients presenting with symptoms compatible with acute coronary syndrome. Acute ischemia affects the configuration of the QRS complexes, the ST segments and the T waves. The ECG should be read along with the clinical assessment of the patient. ST segment elevation (and ST depression in leads V₁–V₃) in patients with active symptoms usually indicates acute occlusion of an epicardial artery with ongoing transmural ischemia. These patients should be triaged for emergent reperfusion therapy per current guidelines. However, many patients have ST segment elevation secondary to nonischemic causes. ST depression in leads other than V₁–V₃ usually are indicative of subendocardial ischemia secondary to subocclusion of the epicardial artery, distal embolization to small arteries or spasm supply/demand mismatch. ST depression may also be secondary to nonischemic etiologies, such as left ventricular hypertrophy, cardiomyopathies, etc. Knowing the clinical scenario, comparison to previous ECG and subsequent ECGs (in cases that there are changes in the quality or severity of symptoms) may add in the diagnosis and interpretation in difficult cases. This review addresses the different ECG patterns, typically seen in patients with active symptoms, after resolution of symptoms and the significance of such changes when seen in asymptomatic patients.     

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, III, 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.     

Three-Lead Measurement of QTc Dispersion

QTc Dispersion. Introduction: QTc dispersion has traditionally been calculated from all 12 leads of a standard electrocardiogram (ECG). It is possible that alternative, quicker methods using fewer than 12 leads could be used to provide the same information. Methods and Results: We have previously shown a difference in QTc dispersion from ECGs recorded at least 1 month after myocardial infarction between patients who subsequently died and long-term survivors. In the current study, we recalculated QTc dispersion in these ECGs using different methods to determine if the observed difference in QTc dispersion measurements between the two groups, as calculated from 12-lead ECGs, persisted when using smaller sets of leads. QTc dispersion was recalculated by four methods: (1) with the two extreme QTc intervals excluded: (2) from the six precordial leads; (3) from the three leads most likely to contribute to QTc dispersion (aVF, V₁V₄); and (4) from the three quasi-orthogonal leads (aVF, I, V). For each of the 270 12-lead ECGs examined, a mean of 9.9 leads (SD 1.5 leads) had a QT interval analyzed; the QT interval could not be accurately measured in the remaining leads. Using the standard 12-lead measurement of QTc dispersion, there was a difference in the fall in QTc dispersion from early to late ECG between the groups: 9.1 (SD 60.8) msec for deaths versus 34.4 (55.2) msec for survivors (P = 0.016). This difference in QTc dispersion between early and late ECGs was maintained using either three-lead method (quasi-orthogonal leads: -2.6 [56.2] msec for deaths vs 26.9 [54.3] msec for survivors [P = 0.003]; “likeliest” leads: 8.6 [64.9] msec vs 29.5 [50.2] msec [P = 0.05]), but not when using the other two methods (precordial leads: 19.1 [55.5] msec vs 22 [50.8] msec [P = 0.76]; extreme leads removed: 9.2 [50.1] msec vs 21.8 [42] msec [P = 0.13]). Conclusion: QTc dispersion calculated from three leads may be as useful a measurement as QTc dispersion calculated from all leads of a standard ECG. Its advantages over the standard measurement are its simplicity and the lack of problems with lead adjustment.     

Marked exercise‐induced T‐wave heterogeneity in symptomatic diabetic patients with nonflow‐limiting coronary artery stenosis

Background

T‐wave heterogeneity (TWH) independently predicted cardiovascular mortality in Health Survey 2000 based on 12‐lead ECGs recorded at rest. We investigated whether TWH is elevated during exercise tolerance testing (ETT) in symptomatic diabetic patients with nonflow‐limiting coronary artery stenosis compared to control subjects without diabetes.

Methods

Cases were all patients (n = 20) with analyzable ECG recordings during both rest and ETT who were enrolled in the Effects of Ranolazine on Coronary Flow Reserve (CFR) in Symptomatic Patients with Diabetes and Suspected or Known Coronary Artery Disease (RAND‐CFR) study (NCT01754259); median CFR was 1.44; 80% of cases had CFR <2. Control subjects (n = 9) were nondiabetic patients who had functional flow reserve (FFR) >0.8, a range not associated with inducible ischemia. TWH was analyzed from precordial leads V₄, V₅, and V₆ by second central moment analysis, which assesses the interlead splay of T‐waves about a mean waveform.

Results

During exercise to similar rate‐pressure products (p = .31), RAND‐CFR patients exhibited a 49% increase in TWH during exercise (rest: 49 ± 5 μV; exercise: 73 ± 8 μV, p = .003). By comparison, in control subjects, TWH was not significantly altered (rest: 52 ± 11 μV; ETT: 38 ± 5 μV, p = .19). ETT‐induced ST‐segment depression >1 mm (p = .11) and T_peak‐T_end (p = .18) and QTc intervals (p = .80) failed to differentiate cases from controls.

Conclusions

TWH is capable of detecting latent repolarization abnormalities, which are present during ETT in diabetic patients with nonflow‐limiting stenosis but not in control subjects. The technique developed in this study permits TWH analysis from archived ECGs and thereby enables mining of extensive databases for retrospective studies and hypothesis testing.

     

A new ECG algorithm for the localization of accessory pathways using only the polarity of the QRS complex

A new algorithm is proposed for localization of accessory atrioventricular pathways by use of a 12-lead electrocardiogram (ECG). The polarity of the QRS complex in leads III, V₁, and V₂ from 102 patients with Wolff-Parkinson-White syndrome with manifested preexcitation who underwent successful radiofrequency catheter ablation was analyzed. Accessory pathways on the right side of the heart were localized to three regions around the tricuspid annulus, and left-sided pathways were localized to two regions around the mitral valve annulus. In 42 of 46 patients (91%) with left posterolateral accessory pathways, a common characteristic of the ECG was a positive QRS complex in leads III and V₁ (sensitivity 91%, specificity 95%). Of 19 patients with left inferior paraseptal or inferior accessory pathways, 16 (84%) had a negative QRS complex in lead III and a positive QRS complex in lead V₁ (sensitivity 84%, specificity 98%). All six patients with right anterosuperior paraseptal accessory pathways had a positive QRS complex in lead III but a negative QRS complex in lead V₁ (sensitivity 100%, specificity 97%). The 25 patients with right inferior paraseptal or inferior accessory pathways had a negative or isodiphasic QRS complex in leads III and V₁, but the QRS complex was positive in lead V₂ in 21 (84%) of these patients (sensitivity 84%, specificity 100%). Finally, five of the six patients (83%) with right anterior accessory pathways had a negative QRS complex in leads III, V₁, and V₂ (sensitivity 83%, specificity 96%). With the algorithm, the localization of accessory pathways was thus identified in 90 of the 102 patients (88%).