Use of lead adjustment formulas for QT dispersion after myocardial infarction

Improving the reproducibility of QT dispersion measures

BACKGROUND

The low reproducibility of the QT dispersion (QTD) method is a major reason why it is not used in clinics. The purpose of this study was to develop QT dispersion parameters with better reproducibility and identification of patients with a high risk of ventricular arrhythmia or death.

METHODS AND RESULTS

Three institutions using different methods for measuring QT intervals provided QT databases, which included more than 3500 twelve-lead surface ECGs. The data represented low and high risk subjects from the following groups: the normal population EpiSet (survivors vs dead from cardiovascular causes), acute myocardial infarction patients AmiSet (survivors vs dead) and remote myocardial infarction patients ArrSet (with vs without a history of ventricular arrhythmia). The EpiSet, AmiSet, and the ArrSet contributed with N = 122, 0, and 110 ECGs for reproducibility analysis, and 3244, 446, and 100 ECGs for the analysis of prognostic accuracy. The prognostic accuracy was measured as the area under the Receiver Operator Curve. The QT intervals were divided into six QT pairs; the longest pair consisted of the longest and the shortest QT intervals etc. The QT dispersion trend (QTDT) was defined as the slope of the linear regression of the N longest QT pairs after estimation of missing QT intervals by interpolation of measured QT intervals. The QTMAD and the QTSTD methods were defined as twice the mean absolute deviation and the standard deviation of the N longest QT pairs. The reproducibility was improved by 27% and 19% in the EpiSet and the ArrSet relative to the reproducibility of QTD. The accuracy improved for the EpiSet and the ArrSet and was maintained for the AmiSet.

CONCLUSIONS

By using the three longest and the three shortest QT intervals in QTDT, QTMAD, or QTSTD, the reproducibility improved significantly while maintaining or improving the prognostic accuracy compared to QTD.

Effect of Physical Training on Corrected QT Dispersion in Patients With Nonischemic Heart Failure

BACKGROUND

The effect of physical training (PT) on QTc dispersion and ventricular tachycardia (VT) remains unclear in patients with nonischemic heart failure.

METHODS AND RESULTS

Eight patients with nonischemic heart failure performed PT using a bicycle ergometer and their exercise tolerance increased (4.9+/-1.8 to 7.0+/-2.5 METs, p<0.05) and QTc dispersion decreased (71+/-22 to 48+/-24 ms, p<0.05). However, PT did not change the frequency of VT.

CONCLUSION

Physical training could improve QTc dispersion in patients with nonischemic heart failure, possibly by improving the autonomic nerve system.

The relation of QT dispersion and localized QT difference to coronary pathology in a population with unstable coronary artery disease

BACKGROUND

QT dispersion (QTd) contains prognostic information in several patient groups. The variable increases in several conditions with ischemia. Originally, it was thought to reflect the local repolarization inhomogeneity. Even though this explanation has been questioned lately, it continues to be put forward. In order to elucidate a possible local mechanism, we investigated the relation between QT dispersion, an ECG parameter reflecting the local dispersion, and angiographical measures in a population with unstable coronary artery disease.

METHODS

The 276 patients were recruited from the FRISC II trial. As the QTd parameter we used the mean value of automatically measured QTd during 27 hours after admission (QTdMean). As a local repolarization measure we used the maximal difference in QT between two adjacent ECG leads (QTdiffMean). The computations were performed on all available ECG leads and on a restricted set without the V1-V2 combination. Previously published angiographic scoring tools were adapted for rating and localizing the coronary pathology by two approaches and applied on 174 patients undergoing angiography.

RESULTS

QTdMean was significantly higher than that reported in previous material with unselected chest pain patients (55 vs 40 ms). QTdiffMean correlated strongly with QTdMean. No differences in QTdMean were detected between patients with different angiographical scores. No relation could be shown between the region with dominating coronary pathology as expressed by the scoring tools and the localization of QTdiffMean.

CONCLUSIONS

QTd in ischemia seems to be increased by a mechanism unrelated to localization and severity of coronary disease.

Discordant iodine-123 metaiodobenzylguanidine uptake area reflects recovery time dispersion in acute myocardial infarction

lodine-123 metaiodobenzylguanidine (MIBG) uptake was reported to be reduced compared to Tl-201 (Tl) in acute myocardial infarction (AMI). Within such an area, degrees of both sympathetic neural function and ischemic myocardial cell damage are considered to be greatly dispersed. These kinds of damage were reported to effect reporalization time in myocardial cells, and we evaluated our hypothesis that extension of the discordant MIBG uptake area correlates with recovery time (RT) dispersion and relate ventricular arrhythmias in AMI. MIBG and Tl images were obtained in AMI patients. Regional Tl or MIBG uptake was estimated in 9 segments of SPECT by using four-point scoring. The total score was the sum of scores in 9 SPECT segments. ATI-MIBG was calculated by subtracting the total MIBG score from the total Tl score. Corrected RT (RTc) was measured as a signal-averaged ECG. RTc dispersion was defined as the difference between maximal and minimal RTc. The patients were assigned to two groups (group A; < or = Lown 4a, group B; > or = Lown 4b) according to the results of 24-hour Holter monitoring. A positive correlation between RTc dispersion and ATI-MIBG was found. ATI-MIBG and RTc dispersion in group B were greater than those in group A. These results suggested that ATI-MIBG could be used to predict the development of malignant ventricular arrhythmias.

[Ischemic sudden death: critical analysis of risk markers. Part VIII]

Coronary artery disease is responsible for approximately 75-80% of sudden cardiac deaths in most industrialized countries. Risk factors can be divided in those which suggest structural heart disease and those reflecting abnormal physiological markers. Therapeutic strategies for primary prevention of sudden cardiac death require careful scrutiny. The systematic use of risk markers to identify and stratify high risk groups may be of help to establish primary prevention measures in daily practice. Different methods to stratify risk factors using ejection fraction, ventricular arrhythmias, heart rate variability, baroreflex sensitivity, and dispersion of repolarization are discussed in this article.

Improvement in corrected QT dispersion by physical training and percutaneous transluminal coronary angioplasty in patients with recent myocardial infarction

The aim of the present study was to assess whether physical training and percutaneous transluminal coronary angioplasty (PTCA) improve the corrected QT (QTc) dispersion in patients with recent myocardial infarction (MI). Twenty-four patients with recent MI were allocated to one of 3 groups: training (n = 8), PTCA (n = 7) or controls (n = 9). Physical training as well as PTCA decreased QTc dispersion, whereas QTc dispersion increased in the control group. Changes in QTc dispersion after physical training or PTCA were inversely correlated with exercise-induced ST depression at the baseline test. These observations suggest that physical training, as well as PTCA, could improve QTc dispersion and electrical instability in patients with recent MI, possibly due to improvement of myocardial ischemia.

Effect of selective versus nonselective beta blockade on QT dispersion in patients with nonischemic dilated cardiomyopathy

We retrospectively examined the electrocardiograms in all of our patients with nonischemic dilated cardiomyopathy and normal sinus rhythm before and after at least 3 months of metoprolol (n = 12), bucindolol (n = 8), carvedilol (n = 6), or no beta blocker (n = 9). Both beta1-selective and nonselective beta-adrenergic blockade reduced QTc dispersion equally in patients with dilated cardiomyopathy.

Determinants of precordial QT dispersion in normal subjects

Dispersion of precordial QT intervals has been attributed to delay in the recovery process in the myocardium under the exploring electrode, a local effect. However, the phenomenon also could be explained by different projections of the heart vector, in which case the 12-lead electrocardiogram (ECG) derived from the heart vector would show similar dispersion that could not be local in nature because the electrical activity of the heart is represented by a single dipole. Using an analog device that switched between the two, conventional and derived ECGs were obtained from 129 normal subjects. Measured as the difference between the longest and shortest precordial QT intervals, QT dispersion from the derived ECGs (mean +/- SD, 40 +/- 20 ms) was nearly identical in magnitude to that from the standard ECGs (41 +/- 18 ms, P = NS). Further analysis of the derived ECGs revealed nonuniform distributions of both the maximal and minimal QT intervals across the precordial leads. In addition, a weak correlation was found between the QT interval and the T wave amplitude in the two precordial leads with the lowest T-wave amplitudes (r = -0.303 in V1, P = .001, and r = 0.253 in V6, P = .005). While findings in patients with disease or with abnormal ECGs may differ and require separate examination, these data suggest that the observed magnitude of precordial QT dispersion in normal subjects can be explained by differences in precordial projection of the end of the T wave rather than by local effect.

QT prolongation and dispersion in myocardial ischemia and infarction

The ability of QT interval dispersion to predict the occurrence of ventricular fibrillation (VF) after acute myocardial infarction treated with thrombolytic therapy is controversial. Continuous 12-lead electrocardiographic (ECG) monitoring for 48 hours or longer provides an opportunity to detect transient changes of QT dispersion and correlate such changes with the clinical outcome. In 543 consecutive patients enrolled in the TAMI-9 and GUSTO I studies, serial changes of the QT dispersion were analyzed in an attempt to predict the occurrence of VF with a system that monitored continuously the 12-lead ECG and stored it at least every 20 minutes. Measurements of QT dispersion were made at a median time of 2.37 hours after the onset of chest pain and at 24- and 48-hour intervals. A total of 43 patients experienced VF during the acute phase of myocardial infarction; of these patients, 33 (77%) had anterior infarcts. However, despite the higher preponderance of anterior myocardial infarcts in the VF group, patients with anterior infarcts did not have longer QT dispersion than those with other infarct locations. Similarly, no significant differences in the QT dispersion were observed at any time between the group with VF and that without. Women had increased QT dispersion in the initial and 24-hour ECG as compared with men (P = .005). However, this normalized at the 48-hour measurements. Despite this difference, there was no higher incidence of VF in female patients. In conclusion, the data suggest that QT dispersion alone is not sufficient to explain the occurrence of VF in the acute phase of myocardial infarction after thrombolytic therapy.

QT dispersion variability and myocardial viability in acute myocardial infarction

The aim of this study was to evaluate QT dispersion in acute and sub-acute stages of myocardial infarction and clarify the relationship between QT dispersion and myocardial viability. We studied 95 patients with acute myocardial infarction. The QT dispersion values were compared to those of a control group of 50 healthy subjects. In the patients with acute myocardial infarction dispersion of ventricular repolarization was evaluated on the standard electrocardiograms obtained at the time of admission and ten days later. Two-dimensional echocardiography examination was performed to assess and compare left ventricular wall motion at different stages. QT dispersion values were increased in patients with acute myocardial infarction and levels were higher in the early than in late phases. A better recovery of QT dispersion was found in those patients who demonstrated improvement of left ventricular contractility. The modifications of QT dispersion can reflect the alterations of myocardial contractility.

Measuring QT dispersion: man versus machine

OBJECTIVE

To compare manual and computer automated techniques for measuring QT dispersion.

DESIGN

Assessment of the ability of manual and automatic measurements of QT dispersion to discriminate between a normal group and two cardiac groups.

SUBJECTS

12 simultaneous electrocardiogram leads were recorded from 25 healthy volunteers, 25 subjects after myocardial infarction, and 25 with cardiac arrhythmias.

MAIN OUTCOME MEASURES

For each subject, QT dispersion was measured as the difference between the maximum and minimum QT from all 12 leads and separately for only those leads with T amplitudes of > 100 microV and for those > 250 microV.

RESULTS

Manual QT dispersion (T > 100 microV) was greater (P < 0.02) in the arrhythmia patients (mean (SD), 45 (21) ms), but not the infarction patients (54 (36) ms), than in the normal subjects (39 (13) ms). There were no significant differences when all T waves were included. QT dispersion was significantly reduced by an average of 30% when T waves < 100 microV were excluded, and by 51% when those < 250 microV were excluded. Automatic techniques gave different measurements for dispersion in comparison with manual measurements. Three of the four automatic techniques detected significant differences between normal and both patient groups when no leads were excluded (P < 0.01) as well as when T waves < 100 microV were excluded (with increased significance, P < 0.002).

CONCLUSIONS

Measurements of QT dispersion from small T waves increases measurement variability and reduces the potential for detecting clinical differences. Automatic measurement of QT dispersion gives different results from manual measurement, but can satisfactorily discriminate between normal and abnormal groups with good quality electrocardiograms.

Computer-assisted study of ECG indices of the dispersion of ventricular repolarization

A new computer-assisted method for the quantitative assessment of the dispersion of ventricular repolarization (DVR) has been developed. Through interactive editing of an averaged QRS-T cycle from a 15-lead electrocardiographic (ECG) record (12-lead ECG + XYZ leads), five ECG indices of DVR are automatically computed: they represent the maximal interlead difference of QT and the intervals from the J point to the T wave end, from the J point to the T wave apex, and from the T wave apex to the T wave end. The standard limits of these indices were then established in six clinical groups, including normal subjects and patients with left ventricular hypertrophy, with myocardial infarction, and with intraventricular conduction defect, all subjects being without ventricular arrhythmias and without interacting drugs. The mean values and percentile ranges of all DVR indices were lower in the normal group than in all pathologic groups. The 97.5th percentiles of the QT end dispersion and the JT end dispersion were, respectively, 65 and 76 ms in normal subjects, 84 and 86 ms in patients with inferior MI; 89 and 100 ms in those with anterior MI; 90 and 98 ms in those with left ventricular hypertrophy; and 94 and 99 ms in those with intraventricular conduction defects. This suggests that increased DVR is associated with the varieties of heart disease represented in this study, even in the absence of ventricular arrhythmias, and also that individual measurements of DVR used as predictors of future arrhythmic events should be referred to the standard range of their own clinical group.