Elevated blood pressure and electrocardiographic frontal T axis and spatial QRS-T angle changes in postmenopausal women

Introduction

Frontal T axis and spatial QRS-T angle are both measures of disturbances in ventricular repolarization and depolarization. We determined whether increased blood pressure is a risk factor for changes in these parameters in postmenopausal women free of left ventricular hypertrophy.

Materials and Methods

This cross-sectional study included 969 women. A standard 12-lead electrocardiogram (ECG) was recorded, and frontal T axes and spatial QRS-T angles were computed from vectorcardiography. Logistic regression analysis was used to assess the relationship between systolic and diastolic blood pressures on the one hand and both ECG parameters on the other.

Results

Odds ratios were 1.08 (95% confidence interval [CI], 0.99-1.18) and 1.12 (95% CI, 1.03-1.23) per 10 mm Hg systolic blood pressure for frontal T axis and QRS-T angle, respectively. These values were 1.05 (95% CI, 0.95-1.16) and 1.12 (95% CI, 1.02-1.23) per 5 mm Hg diastolic blood pressure for frontal T-axis and QRS-T angle, respectively.

Conclusion

Elevated blood pressure may lead to ventricular depolarization and repolarization disturbances before overt ECG left ventricular hypertrophy has developed.     

When deriving the spatial QRS-T angle from the 12-lead electrocardiogram, which transform is more Frank: regression or inverse Dower?

Introduction

Our primary objective was to ascertain which commonly used 12-to-Frank-lead transformation yields spatial QRS-T angle values closest to those obtained from simultaneously collected true Frank-lead recordings.

Materials and Methods

Simultaneous 12-lead and Frank XYZ-lead recordings were analyzed for 100 postmyocardial infarction patients and 50 controls. Relative agreement, with true Frank-lead results, of 12-to-Frank-lead-transformed results for the spatial QRS-T angle using Kors' regression versus inverse Dower was assessed via analysis of variance, Lin's concordance, and Bland-Altman plots.

Results

Spatial QRS-T angles from the true Frank leads were not significantly different than those derived from the Kors' regression-related transformation but were significantly smaller than those derived from the inverse Dower-related transformation (P < .001). Independent of method, spatial mean QRS-T angles were also always significantly larger than spatial “maximum” (“peaks”) QRS-T angles.

Discussion

Spatial QRS-T angles are best approximated by regression-related transforms. Spatial mean and spatial “peaks” QRS-T angles should not be used interchangeably.     

The spatial QRS-T angle in the Frank vectorcardiogram: accuracy of estimates derived from the 12-lead electrocardiogram

Background and Purpose

The spatial QRS-T angle (SA), a predictor of sudden cardiac death, is a vectorcardiographic variable. Gold standard vertorcardiograms (VCGs) are recorded by using the Frank electrode positions. However, with the commonly available 12-lead ECG, VCGs must be synthesized by matrix multiplication (inverse Dower matrix/Kors matrix). Alternatively, Rautaharju proposed a method to calculate SA directly from the 12-lead ECG. Neither spatial angles computed by using the inverse Dower matrix (SA-D) nor by using the Kors matrix (SA-K) or by using Rautaharju's method (SA-R) have been validated with regard to the spatial angles as directly measured in the Frank VCG (SA-F). Our present study aimed to perform this essential validation.

Methods

We analyzed SAs in 1220 simultaneously recorded 12-lead ECGs and VCGs, in all data, in SA-F-based tertiles, and after stratification according to pathology or sex.

Results

Linear regression of SA-K, SA-D, and SA-R on SA-F yielded offsets of 0.01°, 20.3°, and 28.3° and slopes of 0.96, 0.86, and 0.79, respectively. The bias of SA-K with respect to SA-F (mean ± SD, −3.2° ± 13.9°) was significantly (P < .001) smaller than the bias of both SA-D and SA-R with respect to SA-F (8.0° ± 18.6° and 9.8° ± 24.6°, respectively); tertile analysis showed a much more homogeneous behavior of the bias in SA-K than of both the bias in SA-D and in SA-R. In pathologic ECGs, there was no significant bias in SA-K; bias in men and women did not differ.

Conclusion

SA-K resembled SA-F best. In general, when there is no specific reason either to synthesize VCGs with the inverse Dower matrix or to calculate the spatial QRS-T angle with Rautaharju's method, it seems prudent to use the Kors matrix.     

Normal limits of the spatial QRS-T angle and ventricular gradient in 12-lead electrocardiograms of young adults: dependence on sex and heart rate

Background and purpose

Normal limits of the spatial QRS-T angle and spatial ventricular gradient (SVG) are only available from Frank vectorcardiograms (VCGs) of male subjects. We determined normal limits for these variables derived from standard 12-lead electrocardiograms (ECGs) of 660 male and female students aged 18 to 29 years.

Methods

A computer algorithm was used that constructed approximated VCG leads by inverse Dower matrix transformation of the 12-lead ECG and subsequently calculated the spatial QRS-T angle, SVG magnitude, and orientation.

Results

In female subjects, the QRS-T angle was more acute (females, 66° ± 23°; normal, 20°-116°; males, 80° ± 24°; normal, 30°-130°; P < .001), and the SVG magnitude was smaller (females, 81 ± 23 mV·ms; normal, 39-143 mV·ms; males, 110 ± 29 mV·ms; normal, 59-187 mV·ms; P < .001) than in male subjects. The male SVG magnitude in our study was larger than that computed in Frank VCGs (79 ± 28 mV·ms; P < .001).

Conclusions

The spatial QRS-T angle and SVG depend strongly on sex. Furthermore, normal limits of SVG derived from Frank VCGs differ markedly from those derived from VCGs synthesized from the standard ECG. As nowadays, VCGs are usually synthesized from the 12-lead ECG; normal limits derived from the standard ECG should preferably be used.     

Prognostic significance of inverse spatial QRS-T angle circadian pattern in myocardial infarction survivors

Background

We investigated the predictive value of the spatial QRS-T angle (QRSTA) circadian variation in myocardial infarction (MI) patients.

Methods

Analyzing 24-hour recordings (SEER MC, GE Marquette) from 151 MI patients (age 63 ± 12.7), the QRSTA was computed in derived XYZ leads. QRS-T angle values were compared between daytime and night time. The end point was cardiac death or life-threatening ventricular arrhythmia in 1 year.

Results

Overall, QRSTA was slightly higher during the day vs. the night (91° vs. 87°, P = .005). However, 33.8% of the patients showed an inverse diurnal QRSTA variation (higher values at night), which was correlated to the outcome (P = .001, odds ratio 6.7). In multivariate analysis, after entering all factors exhibiting univariate trend towards significance, inverse QRSTA circadian pattern remained significant (P = .036).

Conclusion

Inverse QRSTA circadian pattern was found to be associated with adverse outcome (22.4%) in MI patients, whereas a normal pattern was associated (96%) with a favorable outcome.     

Determinants of the total cosine of the spatial angle between the QRS complex and the T wave (TCRT): implications for distinguishing primary from secondary T-wave abnormalities

Background

Contrary to intuitive expectations and dissimilar from that which occurs in the atria, left ventricular (LV) depolarization and repolarization proceed in opposite directions, creating a concordance of the spatial QRS complex and T-wave angles (QRS-T). By defining the determinants of QRS-T, it might be possible to distinguish a primary (caused by an abnormality of repolarization) from a secondary (caused by a delay in ventricular depolarization) T-wave abnormality.

Methods and Results

From a near-consecutive series of 154 patients (age, 60 ± 16 years; 81 females) in sinus rhythm, Doppler echocardiographic and 12-lead electrocardiogram (ECG) findings were related to the total cosine of the angle subtended by the spatial QRS complex and T wave (TCRT). Using the QRS complex and T-wave angles in the frontal and horizontal planes, TCRT was obtained from the table cited in the article of Helm and Fowler (Am Heart J 1953;45:835). TCRT correlated negatively with age, QRS duration (QRS), interventricular septal thickness (IVS) and posterior wall thickness, LV mass, LV cross-sectional area (CSA), LV relative wall thickness (RWT), left atrial dimension, and atrial velocity time integral (all, P < .001), but it was not related to LV diastolic dimension or systolic function. In multivariate analyses of the entire cohort or of patients without a left bundle branch block, QRS, CSA, RWT, and atrial velocity time integral emerged as independent variables (all, P < .001). When patients with right bundle branch block were also excluded, IVS, instead of CSA and RWT, was significant (P < .001). Overall, TCRT distinguished normal patients from those with heart disease, and patients with diabetes mellitus and hypertension from those not having these conditions. However, residuals of regression, TCRT = (−1.6IVS [cm]) + (−0.01QRS [milliseconds]) + 3, distinguished patients with coronary disease, but not other disorders, from normals, and diabetics, but not patients with hypertension or hyperlipidemia, from those not having these conditions (the regression having adjusted for secondary QRS-T discordance).

Conclusions

The determinants of TCRT can be quantified and expressed as a regression that may be used to distinguish primary from secondary T-wave abnormalities.     

Influence of the vectorcardiogram synthesis matrix on the power of the electrocardiogram-derived spatial QRS-T angle to predict arrhythmias in patients with ischemic heart disease and systolic left ventricular dysfunction

Background and Purpose

Several studies have demonstrated that the spatial mean QRS-T angle (SA) predicts cardiac events and mortality. Spatial mean QRS-T angle is a vectorcardiographic variable. Because in clinical practice, 12-lead standard electrocardiograms (ECGs) are recorded rather than vectorcardiograms (VCGs) according to Frank, VCGs are commonly obtained by synthesizing them from 12-lead ECGs, by using a VCG synthesis matrix. Hence, the thus computed SA is an estimate of the real SA measured in the Frank VCG. Recent studies have shown that Kors VCG synthesis matrix yields better estimates of SA than the inverse Dower VCG synthesis matrix. Our current study aims to compare the predictive power of these SA variants for the occurrence of potentially lethal arrhythmias.

Methods

The study group consisted of patients with ischemic heart disease and left ventricular systolic dysfunction who received an implantable cardioverter-defibrillator (ICD) for primary prevention. During follow-up, the occurrence of appropriate device therapy (occurrence of ventricular arrhythmia) was noted. Alternative SAs were computed in VCGs synthesized from standard 12-lead ECGs by using either the inverse Dower matrix (SA-Dower) or the Kors matrix (SA-Kors). Comparison of the predictive power of SA-Dower and SA- Kors was performed by receiver operating characteristic analysis, by Kaplan-Meier analysis, and by univariate and multivariate Cox regression analysis, using every 10th percentile of SA as a cutoff value.

Results

The study group consisted of 412 patients (361 men; mean ± SD age 63 ± 11 years), in which 56 patients had appropriate ICD therapy during follow-up. Receiver operating characteristic analysis revealed that the area under the curve of SA-Kors was significantly larger than area under the curve of SA-Dower (0.646 vs 0.607, P = .043). The discriminative power of SA-Kors for the absence/presence of appropriate ICD therapy in patients during follow-up was generally superior to SA-Dower over a wide range of cutoff values in the Kaplan-Meier analysis and generally yielded stronger hazard ratios in the univariate and multivariate Cox regression analyses.

Conclusion

If there is no specific reason to use the inverse Dower matrix, VCG synthesis from standard 12-lead ECGs should preferably be done by using the Kors matrix. It is likely to assume that already published studies in which the predictive value of SA-Dower was demonstrated would yield stronger results if the SA-Dower angles were substituted by SA-Kors angles.     

Correlation between vectorcardiographic measures and cardiac magnetic resonance imaging of the left ventricle in an implantable cardioverter defibrillator population

Background

Measures of vectorcardiographic changes and LV remodelling have been associated with arrhythmic risk. However the correlation between the two modalities is not well characterised.

Methods

We correlated spatial QRS-T angle and ventricular gradient with cardiac MRI derived LV global measures and scar pattern in 66 ICD recipients.

Results

Spatial QRS-T angle was significantly larger in patients with ischaemic scar than those without scar (150° ± 22° vs. 119° ± 46°, p = 0.01). Larger spatial QRS-T angle was also correlated with more depressed LV function, more dilated LV and larger LV mass. Ventricular gradient azimuth was significantly different between patients with no scar, non-ischaemic scar and ischaemic scar (20° ± 49° vs. 38° ± 62° vs. 65° ± 48°, p = 0.009), but independent of spatial QRS-T angle and LV structure.

Conclusions

Spatial QRS-T angle and ventricular gradient are partially related to LV structural properties. Further investigation is warranted to examine their comparative and combined prognostic value in risk stratification of ventricular arrhythmias.     

Usefulness of body surface potential mapping for early identification of the intraventricular conduction disorders in young patients with chronic kidney disease

Background

Cardiovascular complications are considered a significant problem in patients with chronic kidney disease (CKD). Body surface potential mapping (BSPM) is a noninvasive method that is useful in detecting early changes involving the heart. The aim of the study was to evaluate possible abnormalities within the cardiac intraventricular conduction system in young patients with CKD using the BSPM method.

Methods

Based on the BSPM registrations, the QRS-T isointegral maps were created in 42 young patients with CKD (on hemodialysis, subgroup Ia; on peritoneal dialysis, subgroup Ib; on conservative treatment, group II) and in 26 healthy subjects. Serum levels of electrolytes, urea, and creatinine were also assessed in the entire study population.

Results

In the healthy subjects, the maximums of the group mean QRS-T isointegral map were located in the left lower anterior part of the thorax, whereas in the Ia patients, the maximums were focused at the medial sternum line. The QRS-T maps, both for Ib and II groups, showed the positive integrals covering the left part of the anterior thorax. In all the patients with CKD, standard 12-lead electrocardiogram (ECG) and echocardiography findings were within the reference range.

Conclusions

In the hemodialyzed patients with CKD, the group-mean QRS-T isointegral map distribution suggested a significant delay of excitation propagation in the left bundle branch, although no abnormalities were found with standard ECG. In the patients with CKD treated with peritoneal dialysis or conservatively, the group-mean QRS-T isointegral maps were characteristic for the early phase of conduction disturbances within the left bundle branch, which again was not observed on the standard ECG recordings.     

ECG-derived spatial QRS-T angle is strongly associated with hypertrophic cardiomyopathy

Introduction

ECG-derived vectorcardiography (VCG) has diagnostic and prognostic value in various diseases. Hypertrophic cardiomyopathy (HCM), a genetic disease with unexplained left ventricular hypertrophy, is one of the most common causes of sudden cardiac death (SCD) in young persons. Genotype positive status is associated with increased risk of systolic dysfunction, heart failure, and (SCD). Herein, we aimed to determine the diagnostic utility of derived VCG parameters in a large cohort of genotyped HCM patients.

Detection of hypertrophic cardiomyopathy is improved when using advanced rather than strictly conventional 12-lead electrocardiogram

Introduction

Twelve-lead electrocardiogram (ECG) is used to screen for hypertrophic cardiomyopathy (HCM), but up to 25% of HCM patients do not have distinctly abnormal ECGs, whereas up to 5% to 15% of healthy athletes do. We hypothesized that an approximately 5-minute resting advanced 12-lead ECG test (“A-ECG score”) could detect HCM with greater sensitivity than pooled conventional ECG criteria and distinguish healthy athletes from HCM with greater specificity.

Materials and methods

Five-minute 12-lead ECGs were obtained from 56 HCM patients, 56 age/sex-matched healthy controls, and 69 younger endurance-trained athletes. Electrocardiograms were analyzed using recently suggested pooled conventional ECG criteria and also A-ECG scoring techniques that considered results from multiple advanced and conventional ECG parameters.

Results

Compared with pooled criteria from the strictly conventional ECG, an A-ECG logistic score incorporating results from just 3 advanced ECG parameters (spatial QRS-T angle, unexplained portion of QT variability, and T-wave principal component analysis ratio) increased the sensitivity of ECG for identifying HCM from 89% (78%-96%) to 98% (89%-100%; P = .025), while increasing specificity from 90% (83%-94%) to 95% (92%-99%; P = .020).

Conclusions

Resting 12-lead A-ECG scores that are simultaneously more sensitive than pooled conventional ECG criteria for detecting HCM and more specific for distinguishing healthy athletes and other healthy controls from HCM can be constructed. Pending further prospective validation, such scores may lead to improved ECG-based screening for HCM.     

Spatiotemporal electrocardiographic characterization of ventricular depolarization and repolarization abnormalities in long QT syndrome

Background and Purpose

If only a standard electrocardiogram (ECG) is available, at least 25% of patients with long QT syndrome (LQTS) may be missed. Our goal is to quantify abnormal electrical activity and to develop an ECG decision rule for the patients with LQTS.

Methods

One hundred forty-one subjects were included in this study (71 patients with LQTS and 70 healthy subjects). A 12-lead digital ECG was recorded for each subject and analyzed using the CAVIAR (comparative analysis of ECG-VCG and their interpretation with auto-reference to the patient) method.

Results

A decision tree involving criteria based on 3 spatiotemporal ECG measurements—the QT interval and the maximum amplitude of the T wave, both corrected from heart rate, and the loss of planarity of the end of QRS—identified patients with LQTS from healthy subjects with a sensitivity of 89%, a specificity of 96%, and a total accuracy of 92%.

Conclusions

This study suggests that 3-dimensional ECG analysis may improve the detection of patients with LQTS.     

Spatial characteristics of atrial fibrillation electrocardiograms

Background

The present study investigates spatial properties of atrial fibrillation (AF) by analyzing vectorcardiogram loops synthesized from 12-lead electrocardiograms (ECGs).

Methods

After atrial signal extraction, spatial properties are characterized through analysis of successive, fixed-length signal segments and expressed in loop orientation, that is, azimuth and elevation, as well as in loop morphology, that is, planarity and planar geometry. It is hypothesized that more organized AF, expressed by a lower AF frequency, is associated with decreased variability in loop morphology. Atrial fibrillation frequency is determined using spectral analysis.

Results

Twenty-six patients with chronic AF were analyzed using 60-second ECG recordings. Loop orientation was similar when determined from either entire 60- or 1-second segments. For 1-second segments, the correlation between AF frequency and the parameters planarity and planar geometry were 0.608 (P < .001) and 0.543 (P < .005), respectively.

Conclusions

Quantification of AF organization based on AF frequency and spatial characteristics from the ECG is possible. The results suggested a relatively weak coupling between loop morphology and AF frequency when determined from the surface ECG.     

Intra-abdominal hypertension increases spatial QRS-T angle and elevates ST-segment J-point in healthy women undergoing laparoscopic surgery

Background

Intra-abdominal hypertension (IAH) impairs cardiovascular function, however an effect of IAH on cardiac electrophysiology has been poorly documented. The aim of this study was to evaluate the effect of IAH following pneumoperitoneum on vectorcardiographic variables reflecting cardiac repolarisation and depolarisation.

Long-term prognosis of asymptomatic individuals with spontaneous or drug-induced type 1 electrocardiographic phenotype of Brugada syndrome

Background

Risk stratification of asymptomatic individuals with type 1 electrocardiogram (ECG) phenotype of Brugada syndrome (BS) still remains controversial. This study investigated the long-term prognosis of asymptomatic subjects with spontaneous or drug-induced type 1 ECG pattern of BS.

Methods and results

Data from 33 apparently healthy individuals (30 males; age, 43.6 ± 13.4 years) with spontaneous (n = 12) or drug-induced (n = 21) type 1 ECG pattern of BS were retrospectively analyzed. Thirteen subjects (39.4%) displayed a positive family history of BS and/or sudden cardiac death. Electrophysiologic study was performed in 16 subjects, and programed right ventricular stimulation induced polymorphic ventricular tachycardia in 9 (56.3%) of them. A cardioverter defibrillator was implanted in 6 cases. During a mean follow-up period of 5.3 ± 2.8 years, all subjects remained asymptomatic. None of them had syncope or cardioverter defibrillator discharges due to ventricular arrhythmias.

Conclusions

Asymptomatic individuals with spontaneous or drug-induced type 1 ECG phenotype of BS display a benign clinical course during long-term follow-up.     

Classification of atrial fibrillation episodes from sparse electrocardiogram data

Background

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. This paper presents the application of the Classification and Regression Tree (CART) technique for detecting spontaneous termination or sustenance of AF with sparse data.

Method

Electrocardiogram (ECG) recordings were obtained from the PhysioNet (AF Termination Challenge Database 2004) Web site. Signal analysis, feature extraction, and classification were made to distinguish among 3 AF episodes, namely, Nonterminating (N), Soon (<1 minute) to be terminating (S), and Terminating immediately (<1 second) (T).

Results

A continuous wavelet transform whose basis functions match the EKG patterns was found to yield compact representation (∼2 orders of magnitude). This facilitates the development of efficient algorithms for beat detection, QRST subtraction, and multiple ECG quantifier extraction (eg, QRS width, QT interval). A compact feature set was extracted through principal component analysis of these quantifiers. Accuracies exceeding 90% for AF episode classification were achieved.

Conclusions

A wavelet representation customized to the ECG signal pattern was found to yield 98% lower entropies compared with other representations that use standard library wavelets. The Classification and Regression Tree (CART) technique seems to distinguish the N vs T, and the S vs T classifications very accurately.     

Maximal increase in sensitivity with minimal loss of specificity for diagnosis of acute coronary occlusion achieved by sequentially adding leads from the 24-lead electrocardiogram to the orderly sequenced 12-lead electrocardiogram

Objectives

This study investigates whether sequential addition of inverted (negative) leads from the 24-lead electrocardiogram (ECG) to the orderly sequenced 12-lead ECG would identify a number of leads with which the sensitivity for diagnosis of acute transmural ischemia is significantly increased with minimal loss of specificity.

Background

Acute transmural ischemia due to thrombotic coronary occlusion typically progresses to infarction. Its recognition is based on currently accepted ST-elevation myocardial infarction (STEMI) criteria with suboptimal sensitivity, which could be potentially increased by consideration of the principle that each of the 12 ECG leads can be inverted to provide an additional lead with the opposite (180°) orientation, generating a 24-lead ECG.

Methods

The study population included 162 patients who underwent prolonged coronary occlusion during elective percutaneous transluminal coronary angioplasty. Balloon occlusion was performed in the left anterior descending coronary artery (51 patients), in the right coronary artery (67 patients), or in the left circumflex coronary artery (44 patients). To be classified as indicative of the epicardial injury current of acute ischemia, the ECGs had to fulfill either the criteria of a consensus document from the American College of Cardiology or the European Society of Cardiology or thresholds for the inverted leads based on a population study from Scotland.

Results

The addition of −V1, −V2, −V3, −aVL, −I, aVR, and −III increased sensitivity from 61% to 78% (P ≤ .01) and decreased specificity from 96% to 93% (P = .06).

Conclusions

Addition of 7 leads from the 24-lead ECG, thus creating a 19-lead ECG, was found optimal for attaining high sensitivity while retaining high specificity when compared with the performance of the standard 12-lead ECG.     

Impact of electrical neurostimulation on persistent ST elevation after successful reperfusion by primary percutaneous coronary intervention

Aims

To study the effect of electrical neurostimulation on the ST segment shift in patients with ST elevation myocardial infarction (STEMI) with residual ST elevation after primary percutaneous coronary intervention (PCI).

Methods

After primary PCI, 38 patients with STEMI were divided into 2 groups. Group 1 received 15 minutes of active neurostimulation after the baseline electrocardiogram (ECG); group 2 received 15 minutes of active neurostimulation after 15 minutes of nonactive neurostimulation.

Results

In group 1, ST elevation decreased with neurostimulation from 0.65 ± 0.56 to 0.55 ± 0.51 (P = .02) and to 0.50 ± 0.52 (P = .01) without electrical neurostimulation. In group 2, ST elevation changed without neurostimulation from 0.37 ± 0.32 to 0.33 ± 0.30 (P = NS) and to 0.28 ± 0.27 (P = .01) with electrical neurostimulation. In a posthoc analysis, 17 responders had higher ST elevation at the ECG before active electrical neurostimulation than 21 nonresponders (P = .001).

Conclusion

Electrical neurostimulation may result in significant additional reduction of ST elevation in STEMI after reperfusion treatment, in particular in patients with marked ST elevation on the first ECG after successful primary PCI.     

Electrocardiography Screening for Cardiotoxicity after Modified Vaccinia Ankara Vaccination

Background

Symptomatic myopericarditis has been described after smallpox vaccination using replication-competent vaccinia strains.

Methods

We examined the incidence of new electrocardiogram (ECG) abnormalities and evaluated the safety and immunogenicity related to vaccination. Volunteer subjects (n = 90) aged 18 to 32 years were enrolled in a National Institutes of Health-sponsored phase I smallpox vaccination trial (Division of Microbiology and Infectious Diseases 02-017) and observed over a 26-week period after 2 injections of IMVAMUNE, Modified Vaccinia Ankara vaccine (Bavarian Nordic A/S, Copenhagen, DK), followed by scarification with Dryvax (Wyeth Laboratories, Marietta, Penn). Diagnostic computer-derived ECG statements were available to the clinical study team and compared with those of a board-certified cardiologist who independently read the ECG tracings.

Results

Serial ECG tracings available for 89 of the subjects revealed new ST-segment abnormalities in 2.2% and new T-wave abnormalities in 15.7%; the majority (71.4%) resolved on subsequent tracings. Cardiologist over-read of computer statements resulted in frequent changes in readings, particularly negation of cardiac arrhythmias. A cardiology consultation was requested in 17 subjects for nonspecific cardiac symptoms or new abnormal ECG findings. Echocardiograms were performed in 12 of the 17 subjects and were normal except for 1 subject with possible myopericarditis after receiving Dryvax.

Conclusion

New minor ECG abnormalities are common in apparently young healthy volunteers considered for smallpox vaccination trials. Cardiologist over-read of computer-generated ECG statements in vaccine trials using ECG as a screening tool for safety can reduce false-positive computer-determined ECG diagnoses and the need for inappropriate cardiology referral and additional noninvasive testing.     

Does modifying electrode placement of the 12 lead ECG matter in healthy subjects?

Background

Limb electrodes for the 12 lead ECG are routinely placed on the torso during exercise stress testing or when limbs are clinically inaccessible. It is unclear whether such electrode modification produces ECG changes in healthy male or female subjects that are clinically important according to the 2009 AHA, ACCF, HRS guidelines. We therefore measured whether ECG modification produced clinically important or false positive ECG changes e.g., appearance of Q waves in leads V_1-3, ST changes greater than 0.1 mV, T wave changes greater than 0.5 mV (frontal plane) or 1 mV (transverse plane), QRS axis shifts or alterations to QTc/P-R/QRS intervals.

Methods

The 12 lead ECG was measured in 18 healthy and semi-recumbent subjects using the standard and Takuma modified limb placements.

Results

In the frontal plane we demonstrate that the modification of limb electrode placement produces small Q, R and T wave amplitude and QRS axis changes that are statistically but not clinically significant. In the transverse plane it produces no statistically or clinically significant changes in the ECG or in ST segment morphology, P-R, QRS or QTc intervals.

Conclusions

We provide better and more robust evidence that routine modification of limb electrode placement produces only minor changes to the ECG waveform in healthy subjects. These are not clinically significant according to the 2009 guidelines and thus have no effect on the clinical specificity of the 12 lead ECG.