Spatial, temporal and wavefront direction characteristics of 12-lead T-wave morphology

Comparison of Electric- and Magnetic-Cardiograms Produced by Myocardial Ischemia in Models of the Human Ventricle and Torso

Myocardial ventricular ischemia arises from a lack of blood supply to the heart, which may cause abnormal repolarization and excitation wave conduction patterns in the tissue, leading to cardiac arrhythmias and even sudden death. Current diagnosis of cardiac ischemia by the 12-lead electrocardiogram (ECG) has limitations as they are insensitive in many cases and may show unnoticeable differences to normal patterns. As the magnetic field provides extra information on cardiac excitation and is more sensitive to tangential currents to the surface of the chest, whereas the electric field is more sensitive to flux currents, it has been hypothesized that the magnetocardiogram (MCG) may provide a complementary method to the ECG in ischemic diagnosis. However, it is unclear yet about the differences in sensitivity regions of body surface ECG and MCG signals to ischemic conditions. The aim of this study was to investigate such differences by using 12-, 36- ECG and 36-MCG computed from multi-scale biophysically detailed computational models of the human ventricles and torso in both control and ischemic conditions. It was shown that ischemia produced changes in the ECG and MCG signals in the QRS complex, T-wave and ST-segment, with greater relative differences seen in the 36-lead ECG and MCG as compared to the 12-leads ECG (34% and 37% vs 26%, respectively). The 36-lead ECG showed more averaged sensitivity than the MCG in the change of T-wave due to ischemia (37% vs 32%, respectively), whereas the MCG showed greater sensitivity than the ECG in the change of the ST-segment (50% vs 40%, respectively). In addition, both MCG and ECG showed regional-dependent changes to ischemia, but with MCG showing a stronger correlation between ischemic region in the heart. In conclusion, MCG shows more sensitivity than ECG in response to ischemia, which may provide an alternative method for the diagnosis of ischemia.

Global electrical heterogeneity: A review of the spatial ventricular gradient

The ventricular gradient, an electrocardiographic concept calculated by integrating the area under the QRS complex and T-wave, represents the degree and direction of myocardial electrical heterogeneity. Although the concept of the ventricular gradient was first introduced in the 1930s, it has not yet found a place in routine electrocardiography. In the modern era, it is relatively simple to calculate the ventricular gradient in three dimensions (the spatial ventricular gradient (SVG)), and there is now renewed interest in using the SVG as a tool for risk stratification of ventricular arrhythmias and sudden cardiac death. This manuscript will review the history of the ventricular gradient, describe its electrophysiological meaning and significance, and discuss its clinical utility.

Analysis of ECG Measures of Cardiac Repolarization in Relation to Arrhythmic Events in an Implantable Cardioverter Defibrillator Population

BACKGROUND

ECG-derived measures of cardiac repolarization may have utility in risk prediction of future ventricular arrhythmia, and a range of different measures have been proposed. We compared time-based, vectorcardiographic, and singular value decomposition (SVD) derived measures of repolarization to determine which was most predictive of appropriate therapy in an ICD population.

METHODS

We examined the independent prognostic value of a range of repolarization measures derived from 60 second 12-lead ECG recordings in 150 patients receiving new ICD implants in relation to the occurrence of appropriate therapy during follow-up.

RESULTS

Over an average follow-up of 2.15 ± 0.87 years, male gender, presence of premature ventricular complex (PVC), relative T wave residuum (TWR-rel, measures regional repolarization heterogeneity), and TCRT (the total cosine R-to-T, describes the global angle between repolarization and depolarization wavefronts) were the only independent predictors of appropriate therapy. With every 0.01% increase in TWR-rel, there was 2% increased risk of appropriate therapy (HR = 1.02, 95% CI 1.006-1.034, P < 0.001). With every 1° decrease in TCRT, there was an increase in arrhythmic risk of 0.9% (HR 1.009, 95% CI 1.003-1.015, P = 0.003).

CONCLUSIONS

The use of advanced analytic ECG techniques to derive measures of repolarization abnormality might shave utility in risk stratification in an ICD population.

Electrocardiographic T Wave Abnormalities and the Risk of Sudden Cardiac Death: The Finnish Perspective

The identification of patients at risk for sudden cardiac death (SCD) is still a significant challenge to clinicians and scientists. Noninvasive identification of high-risk patients has been of great interest, and several ventricular depolarization and repolarization abnormalities in the standard 12-lead electrocardiogram (ECG) have been associated with increased vulnerability to lethal ventricular arrhythmias. Several benign and pathological conditions can induce changes in repolarization detected as alteration of the ST segment or T wave. Changes in the ST segment and T waves can be early markers of an underlying cardiovascular disease, and even minor ST-T abnormalities have predicted reduced survival and increased risk of SCD in the adult population. In this review, we will discuss the current knowledge of the SCD risk with standard 12-lead ECG T wave abnormalities in the general population, and possible T wave changes in various cardiac conditions predisposing to SCD.

Clinical Utility of Ventricular Repolarization Dispersion for Real-Time Detection of Non-ST Elevation Myocardial Infarction in Emergency Departments

BACKGROUND

A specific electrocardiographic (ECG) marker of ischemia would greatly improve the speed and accuracy of detecting and treating non-ST elevation myocardial infarction (NSTEMI). We hypothesize that ischemia induces ventricular repolarization dispersion (VRD), altering the T-wave before any ST segment deviation. We sought to evaluate the clinical utility of VRD to (1) detect NSTEMI cases in the emergency department (ED) and (2) identify NSTEMI cases at high risk for in-hospital major adverse cardiac events (MACEs).

METHODS AND RESULTS

We continuously recorded 12-lead Holter ECGs from chest pain patients upon their arrival to the ED. VRD was quantified using principal component analysis of the 12-lead ECG to compute a T-wave complexity ratio (ie, ratio of second to first eigenvectors of repolarization). Clinical outcomes were obtained from hospital records. The sample was composed mainly of older males (n=369; ages 63±12 years; 63% males), and 92 (25%) had NSTEMI and 26 (7%) had MACEs. Baseline T-wave complexity ratio modestly correlated with peak troponin levels (r=0.41; P<0.001) and was a good classifier of NSTEMI events (area under the curve=0.70). An increased T-wave complexity ratio on the presenting ECG was strongly associated with NSTEMI (odds ratio [OR]=3.8 [2.1 to 5.8]) and in-hospital MACE (OR=8.2 [3.1 to 21.5]).

CONCLUSIONS

A simple measure of global VRD on the presenting 12-lead ECG correlates with ischemic myocardial injury and can discriminate NSTEMI cases very early during evaluation. Prospective studies should validate these findings and test whether VRD can guide therapy.

Comprehensive T wave morphology assessment in a randomized clinical study of dofetilide, quinidine, ranolazine, and verapamil

BACKGROUND

Congenital long QT syndrome type 2 (abnormal hERG potassium channel) patients can develop flat, asymmetric, and notched T waves. Similar observations have been made with a limited number of hERG-blocking drugs. However, it is not known how additional calcium or late sodium block, that can decrease torsade risk, affects T wave morphology.

METHODS AND RESULTS

Twenty-two healthy subjects received a single dose of a pure hERG blocker (dofetilide) and 3 drugs that also block calcium or sodium (quinidine, ranolazine, and verapamil) as part of a 5-period, placebo-controlled cross-over trial. At pre-dose and 15 time-points post-dose, ECGs and plasma drug concentration were assessed. Patch clamp experiments were performed to assess block of hERG, calcium (L-type) and late sodium currents for each drug. Pure hERG block (dofetilide) and strong hERG block with lesser calcium and late sodium block (quinidine) caused substantial T wave morphology changes (P<0.001). Strong late sodium current and hERG block (ranolazine) still caused T wave morphology changes (P<0.01). Strong calcium and hERG block (verapamil) did not cause T wave morphology changes. At equivalent QTc prolongation, multichannel blockers (quinidine and ranolazine) caused equal or greater T wave morphology changes compared with pure hERG block (dofetilide).

CONCLUSIONS

T wave morphology changes are directly related to amount of hERG block; however, with quinidine and ranolazine, multichannel block did not prevent T wave morphology changes. A combined approach of assessing multiple ion channels, along with ECG intervals and T wave morphology may provide the greatest insight into drug-ion channel interactions and torsade de pointes risk.

CLINICAL TRIAL REGISTRATION

URL: http://clinicaltrials.gov/ Unique identifier: NCT01873950.

Cardiac autonomic changes in middle-aged women: identification based on principal component analysis

The purpose of this study was to investigate the application of the principal component analysis (PCA) technique on power spectral density function (PSD) of consecutive normal RR intervals (iRR) aiming at assessing its ability to discriminate healthy women according to age groups: young group (20-25 year-old) and middle-aged group (40-60 year-old). Thirty healthy and non-smoking female volunteers were investigated (13 young [mean ± SD (median): 22·8 ± 0·9 years (23·0)] and 17 Middle-aged [51·7 ± 5·3 years (50·0)]). The iRR sequence was collected during ten minutes, breathing spontaneously, in supine position and in the morning, using a heart rate monitor. After selecting an iRR segment (5 min) with the smallest variance, an auto regressive model was used to estimate the PSD. Five principal component coefficients, extracted from PSD signals, were retained for analysis according to the Mahalanobis distance classifier. A threshold established by logistic regression allowed the separation of the groups with 100% specificity, 83·2% sensitivity and 93·3% total accuracy. The PCA appropriately classified two groups of women in relation to age (young and Middle-aged) based on PSD analysis of consecutive normal RR intervals.

Repolarisation descriptors and heart rate variability in hemodialysed patients

T wave morphology (TWM) descriptors derived from Holter electrocardiograms during hemodialysis (HD) are of potential value for cardiac risk assessment in HD patients. Our knowledge on autonomic regulation of TWM descriptors is limited. The purpose of this study was to investigate the association between TWM parameters and heart rate variability (HRV) during intradialytic monitoring. In each of 81 patients on maintenance HD, continuous electrocardiograms were recorded 5 times during HD on alternate weeks. TWM descriptors were calculated every 5 s in overlapping 10-s ECG segments and Low Frequency (LF) (0.04 Hz to 0.15 Hz), High Frequency (HF) (0.15 Hz to 0.40 Hz) powers of the spectrum of HRV were calculated every five min. The calculated values of TWM and HRV were averaged during the first hour of the recordings and subsequently over all recordings in each subject. Analyzable data for HRV and TWM were available in 71 HD patients (aged 61+/-15, 36 % diabetics, 32 % females). LF in normalized units correlated positively with Total Cosine R to T (r=0.374, p=0.001) and negatively with T wave morphology dispersion (r=-0.253, p=0.033) after adjusting for heart rate. A heart rate independent association between repolarisation descriptors and HRV exists in HD patients. Autonomic modulation needs to be considered when using TWM characteristics for risk profiling of HD patients.

Electrocardiogram-based predictors of clinical outcomes: a meta-analysis of the prognostic value of ventricular repolarization

OBJECTIVES

To estimate age- and sex-specific prognostic values of eight electrocardiographic repolarization descriptors to predict various mortality endpoints.

BACKGROUND

Using electrocardiographic markers for risk stratification is well studied; however, the prognostic value of many markers is controversial, and their clinical utility remains debatable. No meta-analyses exist that address the prognostic value of ECG markers.

METHODS

Data were synthesized from 106 primary studies using a random-effect variance model. Age and sex subgroups were analyzed using sensitivity analysis.

RESULTS

Four classic (i.e., duration, amplitude, inversion, and ST-T changes) and four novel (i.e., axis, loop, wavefront direction, and waveform complexity) repolarization descriptors were studied. These novel descriptors were particularly useful in predicting sudden death. Abnormal repolarization duration, vectors, and loops have greater impact on negative cardiovascular outcomes in women compared to men; additionally, ischemic repolarization changes have greater impact on negative cardiovascular outcomes in younger versus older adults.

CONCLUSIONS

Assessing repolarization abnormalities is particularly helpful in women and younger adults. Researchers need to further explore the clinical utility of these abnormalities in management algorithms.

The spatial QRS-T angle: implications in clinical practice

The ventricular gradient (VG) as a concept was conceived in the 1930s and its calculation yielded information that was not otherwise obtainable. The VG was not utilized by clinicians at large because it was not easy to understand and its computation time-consuming. The contemporary spatial QRS-T angle is based on the concept of the VG and defined as its mathematical and physiological integral. Its current major clinical use is to assess the cardiac primary repolarization abnormalities in 3-dimensional spatial vectorial plans which are normally untraced in the presence of secondary electrophysiological activity in a 2-dimensional routine electrocardiogram (ECG). Currently the calculation of the spatial QRS-T angle can be easily computed on the basis of a classical ECG and contributes to localization of arrhythmogenic areas in the heart by assessing overall and local heterogeneity of the myocardial ventricular action potention duration. Recent population-based studies suggest that the spatial QRS-T angle is a dominant ECG predictor of future cardiovascular events and death and it is superior to more conventional ECG parameters. Its assessment warrants consideration for intensified primary and secondary cardiovascular prevention efforts and should be included in everyday clinical practice. This review addresses the nature and diagnostic potential of the spatial QRS-T angle. The main focus is its role in ECG assessment of dispersion of repolarization, a key factor in arrythmogeneity.

An analysis of the U-wave and its relation to the T-wave in body surface potential maps for healthy subjects and MI patients

BACKGROUND

The aim of this study was to analyze the U-wave morphology and its relation to the T-wave in one group of healthy subjects and in two groups of myocardial infarction (MI) patients-with and without ventricular tachycardia (VT) episodes. The context of the U-wave origin was also discussed and the U-wave as a potential marker of VT was investigated.

METHODS

The study was carried out on three groups of subjects: 20 healthy subjects, 14 MI patients not at risk of VT, and 22 MI patients at risk of VT. The morphology of the repolarization phase was examined in the high-resolution body surface potential maps recorded from 64 surface ECG leads. The temporal and spatial distributions of several ECG parameters were studied.

RESULTS

The U-wave was present in almost all the studied subjects. The spatial heterogeneity and smooth change in both the T- and U-wave shapes on the entire torso were observed in all the studied groups. The statistical significance of discrimination between the MI patients without VT and MI patients with VT was observed for QRS interval, QT interval, U-wave integral, and normalized U-wave integral.

CONCLUSIONS

High-resolution measurement of body surface potentials and an advanced data analysis allow for a detailed description of U-wave morphology and its relation to the T-wave. This might be of value in discriminating intracardiac repolarization effects, mechano-electrical feedback, and arrhythmia risk stratification.

Evaluation of ventricular repolarization dispersion during acute myocardial ischemia: spatial and temporal ECG indices

In this work, we studied the evolution of different electrocardiogram (ECG) indices of ventricular repolarization dispersion (VRD) during acute transmural myocardial ischemia in 95 patients undergoing percutaneous coronary intervention (PCI). We studied both temporal indices of VRD (T-VRD), based on the time intervals of the ECG wave, and spatial indices of VRD (S-VRD), based on the eigenvalues of the spatial correlation matrix of the ECG. The T-wave peak-to-end interval I(TPE) index showed statistically significant differences during left anterior descending artery and right coronary artery (RCA) occlusion for almost the complete time course of the PCI procedure with respect to the control recording. Regarding S-VRD indices, we observed statistically significant increases in the ratio of second to the first eigenvalue I(T21), the ratio of the third to the first eigenvalue I(T31) and the T-wave residuum I(TWR) during RCA occlusions. We also found a statistically significant increase in the I(T31) during left circumflex artery occlusions. To evaluate the evolution of VRD indices during acute ischemia, we calculated the relative change parameter R(I) for each index I. Maximal relative changes (R(I)) during acute ischemia were found for the S-VRD indices I(T21), the first eigenvalue I(λ1) and the second eigenvalue I(λ2), with changes 64, 57 and 52 times their baseline range of variation during the control recording, respectively. Also, we found that relative changes with respect to the baseline were higher in patients with T-wave alternans (TWA) than in those without TWA. In conclusion, results suggest that I(TPE) as well as I(T21), I(T31) and I(TWR) are very responsive to dispersion changes induced by ischemia, but with a behavior which very much depends on the occluded artery.

Major arrhythmic events and T wave morphology descriptors in hemodialyzed patients

BACKGROUND

Sudden cardiac death is common in patients receiving regular hemodialysis (HD). We recently demonstrated that selected repolarization descriptors calculated from electrocardiographic monitoring during HD demonstrate intra-subject stability. In this study we followed up the initial cohort for major arrhythmic events (MAE).

METHODS

Holter electrocardiograms (ECGs) were recorded during dialysis in 81 HD patients and repeated 5 times at 2 week intervals. The QRS-to-T angle (TCRT), the principal component analysis (PCA) ratio and the T wave morphology dispersion (TMD) were calculated in overlapping 10 second ECG segments and averaged overall recordings in each patient. Patients were followed up for MAE and non-arrhythmic mortality.

RESULTS

During 18 ± 3 months, 3 patients experienced MAE. Compared to others, MAE patients exhibited extreme TCRT and TMD values and minimal intradialytic changes.

CONCLUSION

The prognostic value of repolarization descriptors from intradialytic monitoring should be assessed prospectively.

Predictive value of electrocardiographic T-wave morphology parameters and T-wave peak to T-wave end interval for sudden cardiac death in the general population

BACKGROUND

Previous population studies have found an association between electrocardiographic T-wave morphology parameters and cardiovascular mortality, but their relationship to sudden cardiac death (SCD) is not clear. To our knowledge, there are no follow-up studies assessing the association between electrocardiographic T-wave peak to T-wave end interval (TPE) and SCD. We assessed the predictive value of electrocardiographic T-wave morphology parameters and TPE for SCD in an adult general population sample.

METHODS AND RESULTS

A total of 4 T-wave morphology parameters (principal component analysis ratio, T-wave morphology dispersion, total cosine R-to-T, T-wave residuum) as well as TPE were measured from digital standard 12-lead ECGs in 5618 adults (46% men; mean age 50.9±12.5 years) participating in the Finnish population-based Health 2000 Study. After a mean follow-up time of 7.7±1.4 years, 72 SCDs had occurred. In univariable analyses, all T-wave morphology parameters were associated with an increased SCD risk. In multivariable Cox models, T-wave morphology dispersion and total cosine R-to-T remained as predictors of SCD, with T-wave morphology dispersion showing the highest SCD risk (hazard ratio of 1.4 [95% confidence interval 1.1-1.7, P=0.001] per 1 SD increase in the loge T-wave morphology dispersion). In contrast, TPE was not associated with SCD in univariable or multivariable analyses.

CONCLUSIONS

Electrocardiographic T-wave morphology parameters describing the 3-dimensional shape of the T-wave stratify SCD risk in the general population, but we did not find an association between TPE and SCD.

Sex differences in cardiac autonomic regulation and in repolarisation electrocardiography

The review summarises the present knowledge on the sex differences in cardiac autonomic regulations and in related aspects of electrocardiography with particular attention to myocardial repolarisation. Although some of the sex differences are far from fully established, multitude of observations show consistent differences between women and men. Despite more pronounced parasympathetic cardiac regulation, women have higher resting heart rate and lower baroreflex sensitivity. Of the electrocardiographic phenomena, women have longer QT interval duration, repolarisation sequence more synchronised with the inverse of the depolarisation sequence, and likely increased regional heterogeneity of myocardial repolarisation. Studies investigating the relationship of these sex disparities to hormonal differences led frequently to conflicting results. Although sex hormones seem to play a key role by influencing both autonomic tone and electrophysiological properties at the cellular level, neither the truly relevant hormones nor their detailed actions are known. Physiologic usefulness of the described sex differences is also unknown. The review suggests that new studies are needed to advance the understanding of the physiologic mechanisms responsible for these inequalities between women and men and provides key methodological suggestions that need to be followed in future research.

T-wave alternans search over 24 hour holter ECG recordings based on singular value decomposition

This paper proposes an efficient method to search for T-wave alternans (TWA) over 24 hour Holter ECG recordings. After appropriate pre-processing to remove baseline drift and artifact, data are segmented to 2 minute successive time intervals. For each beat in the segment, singular value decomposition is applied to derive orthogonal characteristic signals. Then two prominent orthogonal signals are used for the TWA search. A pair of alternans indices is defined for each beat as the orthogonal waveform distance between the target beat and the adjacent two beats. When alternans presents, the first index will be larger than the second index. The periodogram of the sequence of alternans indices in each segment yields a useful alternans measure named Alternans Ratio (AR). To show the effectiveness of the measure, the method is applied to 25 control and 24 data from patients with various cardio vascular disorders. AR distribution showed prominent differences among subject groups. It has been demonstrated that the measure AR is not only useful to detect the presence of TWA but the AR distribution can be used for the stratification of the TWA risk.

Proarrhythmic safety of repeat doses of mirabegron in healthy subjects: a randomized, double-blind, placebo-, and active-controlled thorough QT study

Potential effects of the selective β(3)-adrenoceptor agonist mirabegron on cardiac repolarization were studied in healthy subjects. The four-arm, parallel, two-way crossover study was double-blind and placebo- and active (moxifloxacin)-controlled. After 2 baseline ECG days, subjects were randomized to one of eight treatment sequences (22 females and 22 males per sequence) of placebo crossed over with once-daily (10 days) 50, 100, or 200 mg mirabegron or a single 400-mg moxifloxacin dose on day 10. In each period, continuous ECGs were recorded at two baselines and on the last drug administration day. The lower one-sided 95% confidence interval for moxifloxacin effect on QTcI was >5 ms, demonstrating assay sensitivity. According to ICH E14 criteria, mirabegron did not cause QTcI prolongation at the 50-mg therapeutic and 100-mg supratherapeutic doses in either sex. Mirabegron prolonged QTcI interval at the 200-mg supratherapeutic dose (upper one-sided 95% CI >10 ms) in females, but not in males.

Beat-to-beat vectorcardiographic analysis of ventricular depolarization and repolarization in myocardial infarction

Objectives

Increased beat-to-beat variability in the QT interval has been associated with heart disease and mortality. The purpose of this study was to investigate the beat-to-beat spatial and temporal variations of ventricular depolarization and repolarization in vectorcardiogram (VCG) for characterising myocardial infarction (MI) patients.

Methods

Standard 12-lead ECGs of 84 MI patients (22 f, 63±12 yrs; 62 m, 56±10 yrs) and 69 healthy subjects (17 f, 42±18 yrs; 52 m, 40±13 yrs) were investigated. To extract the beat-to-beat QT intervals, a template-matching algorithm and the singular value decomposition method have been applied to synthesise the ECG data to VCG. Spatial and temporal variations in the QRS complex and T-wave loops were studied by investigating several descriptors (point-to-point distance variability, mean loop length, T-wave morphology dispersion, percentage of loop area, total cosine R-to-T).

Results

Point-to-point distance variability of QRS and T-loops (0.13±0.04 vs. 0.10±0.04, p< 0.0001 and 0.16±0.07 vs. 0.13±0.06, p< 0.05) were significantly larger in the MI group than in the control group. The average T-wave morphology dispersion was significantly higher in the MI group than in the control group (62°±8° vs. 38°±16°, p< 0.0001). Further, its beat-to-beat variability appeared significantly lower in the MI group than in the control group (12°±5° vs. 15°±6°, p< 0.005). Moreover, the average percentage of the T-loop area was found significantly lower in the MI group than the controls (46±17 vs. 55±15, p< 0.001). Finally, the average and beat-to-beat variability of total cosine R-to-T were not found statistically significant between both groups.

Conclusions

Beat-to-beat assessment of VCG parameters may have diagnostic attributes that might help in identifying MI patients.

Effect of atorvastatin on dynamic parameters of myocardial repolarization in healthy subjects

BACKGROUND

Antiarrhythmic properties of statins were suggested as a part of their pleiotropic effects. The aim of the present study was to evaluate the effects of atorvastatin on myocardial repolarization as manifested on surface electrocardiograms (ECGs) in healthy subjects.

METHODS AND RESULTS

Forty young healthy volunteers (20 men, 20 women) underwent a single-dose double-blind 3-way crossover study of 20 and 80 mg of atorvastatin and placebo. Long-term 13-hour 12-lead ECGs were obtained in each subject and each study period starting 15 minutes before drug administration. Each study period contained 18 time-points of 5-minute durations when the subjects were in resting supine positions. Digital ECG recordings were analyzed automatically, and the results were completed blindly before statistical analyses. Dynamic parameters of myocardial repolarization and T-wave morphology descriptors were evaluated. Although some trends were observed, no significant drug-related changes in any of investigated ECG repolarization descriptors were found.

CONCLUSION

In comparison with placebo, single doses of atorvastatin had no effect on repolarization heterogeneity in healthy subjects. The observation confirms safe profile of the drug with limited proarrhythmic potential.

Choice of an alternative lead for QT interval measurement in serial ECGs when Lead II is not suitable for analysis

INTRODUCTION

Conventionally, QT interval is measured in lead II. There are no data to select an alternative lead for QT measurement when it cannot be measured in Lead II for any reason.

METHODS AND RESULTS

We retrospectively analyzed ECGs from 1906 healthy volunteers from 41 phase I studies. QT interval was measured on the median beat in all 12 leads. The mean difference in QT interval between lead aVR and in Lead II was the least, followed by aVF, V5, V6 and V4; lead aVL had maximum difference. The T wave was flat (<0.1 mV) in Lead II in 6.9% of ECGs; it was also flat in 20% of these ECGs (1.4% of all ECGs) in Leads aVR, aVF and V5.

CONCLUSIONS

When QT interval cannot be measured in Lead II, the best alternative leads are aVR, aVF, V5, V6 and V4 in that sequence. It differs maximally from that in Lead II in Lead aVL.

Beat-to-beat spatial and temporal analysis for QRS-T morphology

The aim of this study was to investigate beat-to-beat variations of spatial and temporal QRS and T loop morphology for identifying myocardial infarction (MI) patients. We investigated short-term 12-lead ECG recordings of 84 MI patients (22 female, mean age 63 ± 12 years and 62 male, mean age 56 ± 10 years) and 69 healthy control subjects (17 female, mean age 42 ± 18 years and 52 male, mean age 40 ± 13 years). To quantify spatial and temporal variations in QRS complex and T-wave morphology, we defined two descriptor parameters: point-to-point distance variability (DV) and mean loop length (MLL). These parameters were extracted from the reconstructed vector ECG, using singular value decomposition. The results showed that the beat-to-beat spatiotemporal point-to-point distance variability for QRS and T loops (DV(QRS); 0.13 ± 0.04 vs. 0.10 ± 0.04, p < 0.0001 and DV(T); 0.16 ± 0.07 vs. 0.13 ± 0.06, p < 0.05), were significantly higher in MI subjects compared to control subjects. In addition, the mean loop length of QRS and T loops were significantly higher in control subjects than MI (p < 0.001), respectively. In conclusion, the beat-to-beat spatiotemporal DV and MLL may be useful for characterizing conduction and repolarization characteristics in patients with MI.

Advanced electrocardiographic parameters change with severity of mitral regurgitation in Cavalier King Charles Spaniels in sinus rhythm

BACKGROUND

Multiple advanced resting ECG (A-ECG) techniques have improved the diagnostic or prognostic value of ECG in detecting human cardiac diseases even before onset of clinical signs or changes in conventional ECG.

OBJECTIVE

To determine which A-ECG parameters, derived from 12-lead A-ECG recordings, change with severity of mitral regurgitation (MR) caused by myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCSs) in sinus rhythm.

ANIMALS

Seventy-six privately owned CKCSs.

METHODS

Dogs were prospectively divided into 5 groups according to the degree of MR (estimated by color Doppler mapping as the percentage of the left atrial area affected by the MR jet) and presence of clinical signs. High fidelity approximately 5-minute 12-lead ECG recordings were evaluated using custom software to calculate multiple conventional and A-ECG parameters.

RESULTS

Nineteen of 76 ECG parameters were significantly different (P < .05) across the 5 dog groups. A 4-parameter model that incorporated results from 1 parameter of heart rate variability, 2 parameters of QT variability, and 1 parameter of QRS amplitude was identified that explained 82.4% of the variance with a correlation coefficient (R) of 0.60 (P < .01). When age or murmur grade was included in the statistical model the prediction value further increased the R to 0.74 and 0.85 (P < .01), respectively.

CONCLUSION

In CKCSs with sinus rhythm, 4 selected A-ECG parameters further improve prediction of MR jet severity beyond age and murmur grade, although the predictive increment in this study probably is not sufficient to warrant utilization in clinical veterinary practice.

Increased T wave complexity can indicate subclinical myocardial ischemia in asymptomatic adults

BACKGROUND

Altered ventricular repolarization and cardiovascular mortality are closely correlated, and recent novel findings show that a distorted T wave loop morphology is also strongly correlated with subsequent onset of myocardial infarction among patients with stable angina. Therefore, we hypothesized that an abnormal T wave complexity ratio (CR) can indicate vulnerability to myocardial ischemia in asymptomatic, apparently healthy adults.

METHODS

Healthy firefighters were enrolled in the current investigation where they completed symptom-limited, graded exercise treadmill testing (ETT) and 24-hour Holter electrocardiogram recording. The CR was automatically calculated using principal component analysis of the high-resolution Holter electrocardiogram signal then averaged over 24 hours (CR(24h)). End points were manually analyzed from the ETT; recordings revealing horizontal ST-segment depression (≥ 1 mm) in 2 or more leads for at least 1 minute during the peak of exercise were considered indicators of myocardial ischemia.

RESULTS

One hundred four firefighters (age, 44 ± 8 years; 96% men) completed both ETT and Holter recording. Firefighters with positive end points (n = 34, or 33%) had higher CR(24h) compared with those with negative end points (0.14 ± 0.06 vs 0.09 ± 0.04, P < .01); there were no demographic differences between the 2 groups. After controlling for age, smoking status, hypertension, and obesity, an abnormal CR(24h) (≥ 20%) significantly predicted exercise-induced myocardial ischemia (odds ratio, 4.6; P = .01).

CONCLUSIONS

Increased T wave CR(24h) can predict myocardial ischemia in asymptomatic middle-age adults; this suggests that the distorted T wave loop morphology can reflect an altered ventricular repolarization caused by prolonged subclinical myocardial ischemia possibly caused by early coronary artery disease.

Risk assessment of ventricular arrhythmia using new parameters based on high resolution body surface potential mapping

Background

The effective screening of myocardial infarction (MI) patients threatened by ventricular tachycardia (VT) is an important issue in clinical practice, especially in the process of implantable cardioverter-defibrillator (ICD) therapy recommendation. This study proposes new parameters describing depolarization and repolarization inhomogeneity in high resolution body surface potential maps (HR BSPM) to identify MI patients threatened by VT.

Material/Methods

High resolution ECGs were recorded from 64 surface leads. Time-averaged HR BSPMs were used. Several parameters for arrhythmia risk assessment were calculated in 2 groups of MI patients: those with and without documented VT. Additionally, a control group of healthy subjects was studied. To assess the risk of VT, the following parameters were proposed: correlation coefficient between STT and QRST integral maps (STT_QRST_CORR), departure index of absolute value of STT integral map (STT_DI), and departure index of absolute value of T-wave shape index (TSI_DI). These new parameters were compared to known parameters: QRS width, QT interval, QT dispersion, Tpeak-Tend interval, total cosines between QRS complex and T wave, and non-dipolar content of QRST integral maps.

Results

STT_DI, TSI_DI, STT_QRST_CORR, QRS width, and QT interval parameters were statistically significant (p≤0.05) in arrhythmia risk assessment. The highest sensitivity was found for the STT_DI parameter (0.77) and the highest specificity for TSI_DI (0.79).

Conclusions

Arrhythmia risk is demonstrated by both abnormal spatial distribution of the repolarization phase and changed relationship between depolarization and repolarization phases, as well as their prolongation. The proposed new parameters might be applied for risk stratification of cardiac arrhythmia.

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.

QRS-T morphology measured from exercise electrocardiogram as a predictor of cardiac mortality

AIMS

Total cosine R-to-T (TCRT) measured from the standard 12-lead electrocardiogram (ECG) reflects the spatial relationship between depolarization and repolarization wavefronts and a low TCRT value is a marker of poor prognosis. We tested the hypothesis that measurement of TCRT or QRS/T angle from exercise ECG would provide even more powerful prognostic information.

METHODS AND RESULTS

The prognostic significances of TCRT and QRS/T angle were assessed from exercise ECG recordings in 1297 patients [age 56 ± 13 years (mean ± SD), 67% males] undergoing a clinically indicated bicycle stress-test and the subsequent follow-up. During an average follow-up of 45 ± 12 months, 74 patients died (5.7%); 34 (2.6%) were cardiac deaths, and 24 (1.9%) were sudden cardiac deaths. Total cosine R-to-T and QRS/T angle exhibited a correlation with the RR intervals in the total cohort, but the individual responses were variable, e.g. median correlation of TCRT-RR was 0.89 with an inter-quartile range from 0.55 to 0.98. A reduced correlation of TCRT-RR during the recovery phase of exercise ECG predicted cardiac death [adjusted heart rate (HR) 3.5, 95% confidence interval (CI): 1.8-6.8, P= 0.001] similarly as the baseline TCRT measured from ECG at rest (adjusted HR 3.4, 95% CI: 1.4-8.1, P= 0.01). The poor correlation between the TCRT-RR both during the exercise and recovery was specifically related to a risk of sudden cardiac death (adjusted HR 6.2, 95% CI: 2.1-17.8, P< 0.001).

CONCLUSIONS

Loss of rate-adaptation of the spatial relationship between depolarization and repolarization wavefronts is a strong predictor of cardiac death, especially of sudden cardiac death.

Dynamics and rate-dependence of the spatial angle between ventricular depolarization and repolarization wave fronts during exercise ECG

BACKGROUND

QRS/T angle and the cosine of the angle between QRS and T-wave vectors (TCRT), measured from standard 12-lead electrocardiogram (ECG), have been used in risk stratification of patients. This study assessed the possible rate dependence of these variables during exercise ECG in healthy subjects.

METHODS

Forty healthy volunteers, 20 men and 20 women, aged 34.6 +/- 3.4, underwent an exercise ECG testing. Twelve-lead ECG was recorded from each test subject and the spatial QRS/T angle and TCRT were automatically analyzed in a beat-to-beat manner with custom-made software. The individual TCRT/RR and QRST/RR patterns were fitted with seven different regression models, including a linear model and six nonlinear models.

RESULTS

TCRT and QRS/T angle showed a significant rate dependence, with decreased values at higher heart rates (HR). In individual subjects, the second-degree polynomic model was the best regression model for TCRT/RR and QRST/RR slopes. It provided the best fit for both exercise and recovery. The overall TCRT/RR and QRST/RR slopes were similar between men and women during exercise and recovery. However, women had predominantly higher TCRT and QRS/T values. With respect to time, the dynamics of TCRT differed significantly between men and women; with a steeper exercise slope in women (women, -0.04/min vs -0.02/min in men, P < 0.0001). In addition, evident hysteresis was observed in the TCRT/RR slopes; with higher TCRT values during exercise.

CONCLUSIONS

The individual patterns of TCRT and QRS/T angle are affected by HR and gender. Delayed rate adaptation creates hysteresis in the TCRT/RR slopes.

Beat-to-beat three-dimensional ECG variability predicts ventricular arrhythmia in ICD recipients

BACKGROUND

Methodological difficulties associated with QT measurements prompt the search for new electrocardiographic markers of repolarization heterogeneity.

OBJECTIVE

We hypothesized that beat-to-beat 3-dimensional vectorcardiogram variability predicts ventricular arrhythmia (VA) in patients with structural heart disease, left ventricular systolic dysfunction, and implanted implantable cardioverter-defibrillators (ICDs).

METHODS

Baseline orthogonal electrocardiograms were recorded in 414 patients with structural heart disease (mean age 59.4 ± 12.0; 280 white [68%] and 134 black [32%]) at rest before implantation of ICD for primary prevention of sudden cardiac death. R and T peaks of 30 consecutive sinus beats were plotted in 3 dimensions to form an R peaks cloud and a T peaks cloud. The volume of the peaks cloud was calculated as the volume within the convex hull. Patients were followed up for at least 6 months; sustained VA with appropriate ICD therapies served as an end point.

RESULTS

During a mean follow-up time of 18.4 ± 12.5 months, 61 of the 414 patients (14.73% or 9.6% per person-year of follow-up) experienced sustained VA with appropriate ICD therapies: 41 of them were white and 20 were black. In the multivariate Cox model that included inducibility of VA and use of beta-blockers, the highest tertile of T/R peaks cloud volume ratio significantly predicted VA (hazard ratio 1.68, 95% confidence interval 1.01 to 2.80; P = .046) in all patients. T peaks cloud volume and T/R peaks cloud volume ratio were significantly smaller in black subjects (median 0.09 [interquartile range 0.04 to 0.15] vs. median 0.11 [interquartile range 0.06 to 0.22], P = .002).

CONCLUSION

A relatively large T peaks cloud volume is associated with increased risk of VA in patients with structural heart disease and systolic dysfunction.

The time course of new T-wave ECG descriptors following single- and double-dose administration of sotalol in healthy subjects

INTRODUCTION

The aim of the study was to assess the time course effect of IKr blockade on ECG biomarkers of ventricular repolarization and to evaluate the accuracy of a fully automatic approach for QT duration evaluation.

METHODS

Twelve-lead digital ECG Holter was recorded in 38 healthy subjects (27 males, mean age = 27.4 + or - 8.0 years) on baseline conditions (day 0) and after administration of 160 mg (day 1) and 320 mg (day 2) of d-l sotalol. For each 24-hour period and each subject, ECGs were extracted every 10 minutes during the 4-hour period following drug dosage. Ventricular repolarization was characterized using three biomarker categories: conventional ECG time intervals, principal component analysis (PCA) analysis on the T wave, and fully automatic biomarkers computed from a mathematical model of the T wave.

RESULTS

QT interval was significantly prolonged starting 1 hour 20 minutes after drug dosing with 160 mg and 1 hour 10 minutes after drug dosing with 320 mg. PCA ventricular repolarization parameters sotalol-induced changes were delayed (>3 hours). After sotalol dosing, the early phase of the T wave changed earlier than the late phase prolongation. Globally, the modeled surrogate QT paralleled manual QT changes. The duration of manual QT and automatic surrogate QT were strongly correlated (R(2) = 0.92, P < 0.001). The Bland and Altman plot revealed a nonstationary systematic bias (bias = 26.5 ms + or - 1.96*SD = 16 ms).

CONCLUSIONS

Changes in different ECG biomarkers of ventricular repolarization display different kinetics after administration of a potent potassium channel blocker. These differences need to be taken into account when designing ventricular repolarization ECG studies.

The association between T-wave morphology and life-threatening ventricular tachyarrhythmias in patients with congestive heart failure

BACKGROUND

Whether T-wave morphology descriptors on the 12-lead electrocardiogram (ECG) can predict the occurrence of life-threatening ventricular arrhythmia in patients with advanced congestive heart failure is unclear.

METHODS

Standard 12-lead ECGs were photoscanned and digitized for analysis in 27 heart failure patients with ventricular tachycardia/ventricular fibrillation (VT/VF; study group), as well as in 54 age- and sex-matched heart failure patients without life-threatening ventricular arrhythmia as a control group. Novel T-wave morphology descriptors were compared.

RESULTS

The results showed that the temporal descriptor, the lead dispersion (LD; 426.5 +/- 279.8 vs 189.0 +/- 125.7, P < 0.001), was significantly higher in the study than in the control group. The other T-wave morphology parameters, such as the T-wave morphology dispersion (45.7 +/- 20.1 vs 44.9 +/- 18.6), the total cosine between QRS and T wave (TCRT; -0.4 +/- 0.4 vs -0.5 +/- 0.3), and the normalized T-loop area (NTLA; 0.5 +/- 0.1 vs 0.4 +/- 0.1), were not significantly different between the two groups (all P value > 0.05). After an adjustment for other clinical variables, increased LD (odds ratio: 9.9, 95% confidence interval [CI]: 2.9-33.4, P < 0.001) or decreased NTLA (odds ratio: 0.4, 95% CI: 0.1-1.0, P =0.05) was associated with VT/VF.

CONCLUSION

The novel T-wave morphology analysis may help in identifying heart failure patients at high risk for VT/VF.

Assessment of the Spatial QRS-T Angle by Vectorcardiography: Current Data and Perspectives

The concept of the ventricular gradient (VG) was conceived in the 1930s and its calculation yielded information that was not otherwise obtainable. The VG was not utilized by clinicians at large because it was not easy to understand and its computation time-consuming. Spatial vectorcardiography is based on the concept of the VG. Its current major clinical use is to identify primary [heterogeneity of ventricular action potential (VAP) morphology] in the presence of secondary [heterogeneity in ventricular depolarization instants] T-wave abnormalities in an ECG. Nowadays, the calculation of the spatial VG can be computed on the basis of a regular routine ECG and contributes to localization of arrhythmogenic areas in the heart by assessing overall and local VAP duration heterogeneity. Recent population-based studies suggest that the spatial VG is a dominant ECG predictor of future cardiovascular events and death and it is superior to more conventional ECG parameters. Its assessment warrants consideration for intensified primary and secondary prevention efforts and can be included in everyday clinical practice. This review addresses the nature and diagnostic potential of the spatial VG. The main focus is the role of the spatial VG in ECG assessment of dispersion of repolarization, a key factor in arrhythmogeneity.

Risk stratification by T-wave morphology for cardiovascular mortality in patients with systolic heart failure

AIMS

The objective was to investigate the prognostic value of T-wave morphology in systolic heart failure patients. T-wave morphology descriptors on standard 12-lead electrocardiograms (ECG) have been shown to have prognostic importance concerning the arrhythmic susceptibility of patients with previous myocardial infarction. However, these descriptors have not been considered with regard to further risk stratification in patients with systolic heart failure.

METHODS AND RESULTS

Patients with systolic heart failure [defined by a left ventricular ejection fraction (LVEF) <50%] were enrolled. Standard digitized 12-lead ECGs were used for analysis of T-wave morphology descriptors [lead dispersion, T-wave morphology dispersion, percentage of the loop area, percentage of the outer area, and the total cosine between QRS and T-wave (TCRT)]. A total of 650 patients with a mean age of 63 +/- 14 years were enrolled and followed-up for 2.7 +/- 1.8 years. The mean LVEF was 36 +/- 9%. During this study, the total mortality rate was 32.7% and cardiovascular mortality rate was 22.3%. A stepwise backward Cox regression analysis showed that cardiovascular mortality was significantly associated with age (P < 0.001), diabetes mellitus (P = 0.022), haemoglobin (P = 0.001), LVEF (P = 0.001), and TCRT (P = 0.003). On the basis of a median TCRT of -0.473 as a cut-off point, a significant difference in cardiovascular mortality was observed from a Kaplan-Meier survival curve (P = 0.01). Total cosine between QRS and T-wave further stratified the risk of LVEF (P = 0.007), age (P = 0.001), haemoglobin (P < 0.001), and diabetes mellitus (P < 0.001) in cardiovascular mortality for these patients.

CONCLUSION

Total cosine between QRS and T-wave may provide further risk stratification for and therefore impact on the prognosis of patients with systolic heart failure.

Spectral energy of ECG morphologic differences to predict death

Unstable conduction system bifurcations following ischemia and infarction are associated with variations in the electrocardiographic activity spanning the heart beat. In this paper, we investigate a spectral energy measure of morphologic differences (SE-MD) that quantifies aspects of these changes. Our measure uses a dynamic time-warping approach to compute the time-aligned morphology differences between pairs of successive sinus beats in an electrocardiographic signal. While comparing beats, the entire heart beat signal is analyzed in order to capture changes affecting both depolarization and repolarization. We show that variations in electrocardiographic activity associated with death can be distinguished by their spectral characteristics. We developed the SE-MD metric on holter data from 764 patients from the TIMI DISPERSE2 dataset and tested it on 600 patients from the TIMI MERLIN dataset. In the test population, high SE-MD was strongly associated with death over a 90 day period following non-ST-elevation acute coronary syndrome (HR 10.45, p < 0.001) and showed significant discriminative ability (c-statistic 0.85). In comparison with heart rate variability and deceleration capacity, SE-MD was also the most significant predictor of death in the study population. Furthermore, SE-MD had low correlation with these other measures, suggesting that complementary use of the risk variables may allow for more complete assessment of cardiac health.

Predictive value of electrocardiographic QT interval and T-wave morphology parameters for all-cause and cardiovascular mortality in a general population sample

BACKGROUND

The predictive value of ECG QT interval for mortality in the general population has been weak. Only a few population studies on the predictive value of ECG T-wave morphology parameters for mortality have been reported.

OBJECTIVE

The purpose of this study was to examine the predictive value of ECG QT interval and T-wave morphology parameters for all-cause and cardiovascular mortality in the general population.

METHODS

The prognostic values of ECG QT interval and four T-wave morphology parameters (principal component analysis ratio, T-wave morphology dispersion, total cosine R-to-T, T-wave residuum) were assessed in 5,917 adults (45% men; age 52 +/- 14 years) participating in the Finnish population-based Health 2000 Study.

RESULTS

After a mean follow-up of 5.9 +/- 0.8 years, 335 deaths had occurred, including 131 cardiovascular deaths. QT interval and, with a few exceptions, all T-wave morphology parameters were significant univariate mortality predictors. In men, in Cox multivariate analyses, principal component analysis ratio and T-wave morphology dispersion remained as independent predictors of all-cause and cardiovascular mortality, with the above-median T-wave morphology dispersion group showing the highest risk of cardiovascular death (hazard ratio [HR] 4.4, 95% confidence interval [CI] 2.1-9.4). In women, independent mortality predictors were total cosine R-to-T (cardiovascular mortality) and T-wave residuum (all-cause and cardiovascular mortality), with the above-median T-wave residuum group showing the highest risk of cardiovascular death (HR 2.2, 95% CI 1.1-4.2).

CONCLUSION

In the general population, T-wave morphology parameters, but not heart rate-corrected QT interval, provide independent prognostic information on mortality. The prognostic value of T-wave morphology parameters is specifically related to cardiovascular mortality and seems to be gender specific.