QT dispersion and components of the QT interval in ischaemia and infarction

New parameters in the interpretation of exercise testing in women: QTc dispersion and QT dispersion ratio difference

BACKGROUND

It has been reported that the increase of QT dispersion (QTD) that occurs due to increased inhomogeneity of the ventricular repolarization because of transient ischemia obtained by standard 12-lead electrocardiogram (ECG), the changes during exercise, and the differences between exercise and rest increase the accuracy of exercise test in the diagnosis of coronary artery disease (CAD).

HYPOTHESIS

This study was designed to investigate the value of QTD parameters, which are reported to increase the diagnostic accuracy of exercise test in women.

METHODS

Ninety-seven women who had undergone coronary angiography and exercise test were evaluated for diagnosis of chest pain. QT dispersion was calculated using the measurements of the highest and lowest values of QT interval obtained by ECG during peak exercise. The QTc using Bazett's equation, and the QTD ratio (QTDR) using QT/RR were calculated, and QTcD and QTD ratios were obtained. The difference between QTcD and QTDR was determined by extracting the rest values from the exercise values.

RESULTS

The groups with normal coronaries (n = 48), single-vessel CAD (n = 24), and multivessel CAD (n = 25) were compared. The obtained QTD parameters at peak exercise and their differences between exercise and rest were found to be significantly increased in patients with CAD (p <0.001). Furthermore, these parameters were found to be higher in the patients with multivessel CAD than in those with single-vessel disease (p < 0.05). With the parameters QTcD > 60 ms and QTDR > 10%, greater sensitivity and specificity were obtained compared with ST-segment depression. The highest diagnostic accuracy was obtained with the QTD parameters calculated from the differences between rest and exercise values. The diagnostic accuracy of the difference of QTcD > 15 ms and the difference of QTDR > 5% was relatively higher than the other parameters (sensitivity, specificity, and negative and positive predictor values are 84, 88, 84, 87% and 84, 96, 85, 95%, respectively).

CONCLUSION

The use of QTD parameters as variables of ECG, which is easily obtainable in the evaluation of exercise ECG in women, increases the diagnostic accuracy of the exercise test. In addition, the evaluation of QTD variables may provide information about the incidence of CAD.

A comparison of the QT and QTc dispersion among patients with sustained ventricular tachyarrhythmias and different etiologies of heart disease

OBJECTIVES

To determine if etiology of heart disease is associated with differences in QT and QTc dispersion among patients with ventricular tachyarrhythmias.

METHODS

This study was undertaken in 145 patients undergoing electrophysiological testing for sustained ventricular tachycardia or ventricular fibrillation. Patients were divided into groups based on etiology of heart disease determined by history, ECG, coronary angiography, and echocardiography. The groups included patients with: dilated cardiomyopathy (n = 29), myocardial infarction (n = 90), established coronary artery disease without a myocardial infarction (n = 11), or hypertension induced left ventricular hypertrophy (n = 15). The QT intervals on a 12--lead ECG were determined and Bazett's formula was used to derive the QTc intervals. The QT and QTc dispersion were determined by subtracting the shortest QT(c) interval from the longest on each 12-lead recording.

RESULTS

The patients with dilated cardiomyopathy had significantly higher QT and QTc dispersion values as compared to any of the other three groups (P < 0.05 for both). No other differences in electrocardiographic variables were found between groups.

CONCLUSIONS

In a group of patients with a history of ventricular tachycardia or ventricular fibrillation, QT and QTc dispersion are significantly greater among patients with dilated cardiomyopathy than for patients with a previous myocardial infarction, established coronary artery disease without a myocardial infarction, or hypertensive left ventricular hypertrophy.

Correlation of QT dispersion with indices used to evaluate the severity of familial ventricular arrhythmias in Boxers

OBJECTIVE

To measure QT interval duration and QT dispersion in Boxers and to determine whether QT variables correlate with indices of disease severity in Boxers with familial ventricular arrhythmias, including the number of ventricular premature complexes per day, arrhythmia grade, and fractional shortening.

ANIMALS

25 Boxers were evaluated by ECG and echocardiography.

PROCEDURE

The QT interval duration was measured from 12-lead ECG and corrected for heart rate (QTc), using Fridericia's formula. The QT and QTc were calculated for each lead, from which QT and QTc dispersion were determined. Echocardiography and 24-hour ambulatory ECG were performed to evaluate for familial ventricular arrhythmias. Total number of ventricular premature complexes, arrhythmia grade, and fractional shortening were determined and used as indices of disease severity.

RESULTS

There was no correlation between any QT variable and total number of ventricular premature complexes, arrhythmia grade, or fractional shortening. No difference between QT dispersion and QTc dispersion was identified, and correction for heart rate did not affect the results.

CONCLUSIONS AND CLINICAL RELEVANCE

QT interval duration and dispersion did not correlate with indices of disease severity for familial ventricular arrhythmias. Heart rate correction of the QT interval did not appear to be necessary for QT dispersion calculation in this group of dogs. QT dispersion does not appear to be a useful noninvasive diagnostic tool in the evaluation of familial ventricular arrhythmias of Boxers. Identification of affected individuals at risk for sudden death remains a challenge in the management of this disease.

Clinical determinants of increased QT dispersion in patients with diabetes mellitus

AIMS

To compare QT dispersion measurements in diabetic patients to control subjects and assess any associations between QT dispersion and diabetic clinical characteristics.

METHODS

A total of 512 diabetics and 50 age and gender matched controls were studied. QT interval was measured manually in 12-lead conventional electrocardiograms, and QT dispersion (QTd), heart rate-corrected QT dispersion (QTcd), number of leads-adjusted QT dispersion (adjuQTd) and adjacent QT dispersion (adjaQTd) were calculated. Demographic, clinical, laboratory and electrocardiographic data were recorded.

RESULTS

Diabetics showed increased QT dispersion compared to controls (QTd: P<0.001, QTcd: P<0.001, adjuQTd: P<0.001), even those with recent diagnosis (less than 2 years) and without arterial hypertension, ECG abnormalities or chronic degenerative complications (QTd: P=0.01, QTcd: P<0.001, adjuQTd: P=0.04). Left ventricular hypertrophy (QTd: P<0.001, QTcd: P<0.001, adjuQTd: P<0.001, adjaQTd: P<0.001) and conduction disturbances (QTd: P=0.002, QTcd: P=0.003, adjuQTd: P=0.003) were the electrocardiographic findings associated with increased QT dispersion in bivariate analysis. Clinical variables were the presence of arterial hypertension (QTd: P=0.004, QTcd: P=0.01, adjuQTd: P<0.001), even without left ventricular hypertrophy (QTd: P=0.01, QTcd: P=0.03, adjuQTd: P=0.003), and the presence of diabetic cardiovascular complications (QTd: P=0.02, QTcd: P=0.01, adjuQTd: P=0.008, adjaQTd: P=0.03). No association between QT dispersion and the presence of diabetic microvascular complications, glycaemic control, age and gender, or cardiovascular drugs was observed. Multivariate regressive statistical analysis confirmed the associations noted in bivariate analysis.

CONCLUSIONS

Diabetic patients have increased QT dispersion compared to non-diabetics even those without arterial hypertension and cardiovascular complications and with recent diagnosis. The presence of arterial hypertension, diabetic cardiovascular complications and electrocardiographic abnormalities of left ventricular hypertrophy and conduction disturbances were associated to increased QT dispersion in diabetes mellitus.

Left ventricular hypertrophy increases transepicardial dispersion of repolarisation in hypertensive patients: a differential effect on QTpeak and QTend dispersion

BACKGROUND

Ventricular arrhythmias in left ventricular hypertrophy (LVH) are related to regional electrical heterogeneity. The significance of noninvasive electrocardiographic indices of electrical heterogeneity in LVH has not been established. The aim of the study was to investigate changes in the Tpeak-Tend interval (an index of transmural dispersion of repolarisation) in addition to other traditional electrocardiographic indices of electrical dispersion in patients with hypertensive LVH.

METHODS

Consecutive patients were screened for the presence of hypertensive echocardiographic LVH and compared with a control group. LVH was identified as left ventricular mass > 134 g m-2 in men and > 110 g m-2 in women. Twelve-lead ECGs were analysed in respect of various indices of electrical dispersion.

RESULTS

Left ventricular mass was greater in the LVH than in the control group (174 +/- 39 vs. 101 +/- 18 g m-2, P < 0.0001). The Tpeak-Tend interval was not affected by LVH. The main effect of LVH was an increase in QTpeak dispersion (40 +/- 13 vs. 53 +/- 21 ms, P < 0.05), which resulted from an increase in the maximum QTpeak interval (337 +/- 24 vs. 358 +/- 30 ms, P < 0.04), without any change in the minimum QTpeak interval. There was a significant correlation between the left ventricular mass index and QTpeak dispersion (r = 0.40; P < 0.01). In contrast, LVH did not exert any effect on QTend dispersion (65 +/- 21 vs. 65 +/- 16 ms, ns), because LVH increased both the maximum QTend interval (430 +/- 30 vs. 449 +/- 28 ms, P < 0.05) and the minimum QTend interval (365 +/- 29 vs. 384 +/- 27 ms, P < 0.04).

CONCLUSIONS

Hypertensive LVH exerts a differential effect on QTpeak and QTend interval dispersion. The most likely explanation is that these changes reflect a nonuniform prolongation of action potential duration across the epicardium, leading to an increase in transepicardial dispersion of repolarisation.

Dispersion of ventricular depolarization-repolarization: a noninvasive marker for risk stratification in arrhythmogenic right ventricular cardiomyopathy

BACKGROUND

We retrospectively investigated the value of clinical and ECG findings as well as QT-QRS dispersion in predicting the risk of sudden death in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC).

METHODS AND RESULTS

Duration and interlead variability of the QT interval and QRS complex were measured manually from standard ECGs in 20 sudden death victims with ARVC diagnosed at autopsy (group I), in 20 living ARVC patients with sustained ventricular tachycardia (group II), in 20 living ARVC patients with </=3 consecutive premature ventricular beats (group III), and in 20 control subjects (group IV). QT and QRS dispersions were greater in group I (77.5+/-10.6 ms for QT and 45.7+/-8.1 ms for QRS) compared with group II (64.5+/-13.9 ms for QT [P=0.001] and 33.5+/-8.7 ms for QRS [P=0.0004]) and in group II compared with group III (48+/-8.9 ms for QT [P<0.0001] and 28+/-5.2 ms for QRS [P<0.0001]) and group IV (33.5+/-4.8 ms for QT [P<0.0001] and 18.5+/-3.6 ms for QRS [P<0.0001]). Negative T wave beyond V(1) and syncope were statistically more frequent in group I (P=0.02 and P=0.007, respectively). On multivariate analysis, QRS dispersion remained an independent predictor of sudden death (P<0.0001), followed by syncope (P=0.09). In assessing risk of sudden death, QRS dispersion >/=40 ms had a sensitivity and specificity of 90% and 77%, respectively; QT dispersion >65 ms, 85% and 75%, respectively; negative T wave beyond V(1), 85% and 42%, respectively; and syncope, 40% and 90%, respectively.

CONCLUSIONS

QRS dispersion (>/=40 ms) was the strongest independent predictor of sudden death in ARVC. Syncope, QT dispersion >65 ms, and negative T wave beyond V(1) refined arrhythmic risk stratification in these patients.

Does the presence of hibernating myocardium in patients with impaired left ventricular contraction affect QT dispersion?

BACKGROUND

Hibernating myocardium is associated with increased cardiovascular events. Increased QT dispersion on the surface electrocardiogram is a marker for serious ventricular arrhythmias. In this study, we determine whether hibernating myocardium is associated with increased QT dispersion in patients with coronary artery disease and impaired left ventricular contraction.

METHODS

Positron emission tomography with (13)N-ammonia and (18)F-fluorodeoxyglucose determined the presence of metabolic-perfusion mismatch defect. QT dispersion was measured by means of a digitizing tablet with validated software. QT intervals were measured on two separate occasions by two investigators blinded to the result of the positron emission tomography scans.

RESULTS

Forty-two patients with impaired left ventricular contraction were studied. They were divided into two groups: group A was made up of patients with mismatch defects (n = 26) and group B was made up of patients with no mismatch defects (n = 16). The mean (SD) QT dispersion measurements were 61.7 +/- 29.8 ms and 70 +/- 24.6 ms for groups A and B, respectively (not significant). When the patients were divided according to the dominant viability status of the impaired myocardial segment, a similar result was found. The patients whose impaired myocardium was dominantly hibernating (n = 19) had a mean QT dispersion of 66.4 +/- 31.9 ms compared with 63.6 +/- 24.8 ms in the patients whose impaired myocardium was mainly scarred (not significant).

CONCLUSIONS

QT dispersion is not affected by the presence of hibernating myocardium and is therefore not clinically useful in identifying patients with this phenomenon. This is in contrast with recent reports by other groups and calls for further investigation of this dichotomy.

Nicorandil, a potent cardioprotective agent, reduces QT dispersion during coronary angioplasty

BACKGROUND

Previous studies have found that ST-segment elevation and QT dispersion are smaller in second coronary occlusions than in first occlusions, a trend that suggests ischemic preconditioning. It has not been established whether nicorandil reduces ST-segment elevation and QT dispersion during coronary angioplasty.

METHODS AND RESULTS

Thirty patients with stable angina undergoing coronary angioplasty in the proximal left anterior descending artery were randomly assigned to one of two groups, receiving either 5 mg oral nicorandil 3 times daily (n = 15) or placebo (n = 15). In the control patients, the total ST-segment elevation decreased from 14 +/- 3 mm during the first inflation to 7 +/- 2 mm during the second inflation (P < .01). In contrast, in the nicorandil-treated patients, the total ST-segment elevation during the second inflation was roughly equivalent to that during the first inflation (8 +/- 3 mm vs 8 +/- 3 mm, P = not significant). After the first reperfusion, a significantly smaller increase in QT dispersion was observed in the nicorandil-treated patients than in the control patients (43 +/- 15 ms vs 54 +/- 15 ms, P < .001). However, after the second reperfusion, QT dispersion was similar for the two groups (32 +/- 15 ms vs 34 +/- 13 ms, P = not significant).

CONCLUSIONS

Nicorandil may precondition the myocardium and may prevent the occurrence of ventricular arrhythmias after coronary reperfusion by suppressing the increase in QT dispersion.

Effect of low estrogen states in healthy women on dispersion of ventricular repolarization

Our data show that although estrogen does not seem to affect the QT interval in healthy women, it significantly decreases the QT dispersion. This finding could provide an explanation to the gender differences in susceptibility to ventricular arrhythmias, besides the difference in the incidence of coronary artery disease.

A new coronary artery disease index of treadmill exercise electrocardiograms based on the step-up diagnostic method

Treadmill exercise electrocardiography (ECG) is one of the most common noninvasive methods for detecting ischemic heart disease. However, this method has problems due to false-positive and false-negative results in a significant number of patients. The aim of this study was to determine whether the diagnostic accuracy of treadmill exercise ECG for detecting significant coronary stenosis can be improved by employing a step-up diagnostic method using multiple diagnostic indicators. We studied 273 consecutive patients (mean age, 56 +/- 9 years; 190 men and 83 women) without a history of myocardial infarction who underwent treadmill exercise ECG and coronary angiography for ischemic chest pain. Of these, 146 patients had no significant coronary stenosis, 61 had single-vessel disease, 56 had multivessel disease, and 10 patients had left main truncus disease. A multivariate logistic regression analysis was used to select 3 treadmill exercise electrocardiographic parameters that were independent predictors of the presence or absence of significant coronary stenosis: exercise-induced maximum ST-segment depression, QT dispersion immediately after exercise, and Athens QRS score. Significant coronary stenosis was diagnosed with a sensitivity of 84% and a specificity of 90% when a step-up diagnostic method using these 3 indicators was employed. These results were better than those obtained for each indicator alone (exercise-induced maximum ST-segment depression: sensitivity, 66%, and specificity, 73%; QT dispersion immediately after exercise [> or =60 ms positive]: sensitivity, 76%, and specificity, 86%; and Athens QRS score [< or =5 mm positive]: sensitivity, 72%, and specificity, 72%). We conclude that this step-up diagnostic method, using multiple diagnostic indicators, is a clinically useful predictor of the presence or absence of significant coronary stenosis.

The Relation Between Early Ventricular Tachycardia and QT Dispersion in Patients with Acute Myocardial Infarction Treated with Thrombolytic Therapy

In this study, we investigated the influence of increased QT dispersion (defined as maximal QT interval minus minimal QT interval) on the occurrence of early nonsustained ventricular tachycardia (NSVT) in patients with acute myocardial infarction (AMI) who received thrombolytic therapy. In the retrospective analysis of 96 patients with clinical reperfusion criteria, 36 had NSVT within the first 12 hours after the onset of thrombolytic therapy (group A), and 60 patients did not have NSVT during the same period (group B). On admission ECG, QT and QT(c) dispersion and the amount of jeopardized myocardial area (Aldrich score) were calculated. In group A, Aldrich score was significantly higher (21.4 +/- 7.2% vs 14.2 +/- 4.9%; p < 0.005). There were significantly higher QT dispersion values on admission (83.3 +/- 23.4 vs 67.5 +/- 23.7 msec; p < 0.005), at 24th hour (87.1 +/- 12.6 vs 72.1 +/- 27.4 msec; p < 0.005) and on the 10th day (63.5 +/- 31.2 vs 49.5 +/- 14.3 msec; p < 0.005) in group A. In subgroup analysis of group A, patients with NSVT between 6-12 hours (group A2) had significantly higher Aldrich score and QT dispersion values at all above time points compared to patients with NSVT between 0-6 hours (group A1) after AMI. In conclusion, in this study we found a strong relation between the occurrence of NSVT within 12 hours and increased QT dispersion on admission ECG in patients with AMI who received thrombolytic therapy. This relation was even stronger for the subgroup of patients with NSVT within 6-12 hours. Thus, these results may indicate that NSVT is related to increased QT dispersion which is secondary to larger jeopardized myocardial area in patients with AMI. </hea

Course and prognostic implications of QT interval and QT interval variability after primary coronary angioplasty in acute myocardial infarction

OBJECTIVES

The aim of this study was to determine the influence of early reperfusion on the course of QT interval and QT interval variability in patients undergoing primary percutaneous transluminal coronary angioplasty (PTCA) in acute myocardial infarction (AMI) and its prognostic implications on major arrhythmic events during one-year follow-up.

BACKGROUND

Although early coronary artery recanalization by primary angioplasty is an established therapy in AMI, a substantial number of patients is still threatened by malignant arrhythmias even after early successful reperfusion, which may be caused by an inhomogeneity of ventricular repolarization despite reperfusion.

METHOD

Temporal fluctuations of ventricular repolarization were studied prospectively in 97 consecutive patients with a first AMI by measurements of QT interval and QT interval variability during and after successful PTCA (Thrombolysis in Myocardial Infarction flow grades 2 and 3). Continuous beat-to-beat QT interval measurement was performed from 24-h Holter monitoring, which was initiated at admission before PTCA.

RESULTS

Reperfusion caused a significant continuous increase of mean RR interval (738 +/- 98 to 808.5 +/- 121 ms; p < 0.001) and a significant decrease of parameters of QT interval (QTc: 440 +/- 32 to 416.5 +/- 37ms; p < 0.001) and QT interval variability (QTcSD: 27.5 +/- 3 to 24.9 +/- 6 ms; p < 0.001) in the majority of patients. However, in patients with major arrhythmic events at the one-year follow-up (sudden cardiac death, ventricular fibrillation or sustained ventricular tachycardia, n = 15), parameters of QT interval remained unaltered after successful reperfusion (QTc: 447.3 +/- 41 to 432.9 +/- 45 ms, p = NS; QTcSD: 35.1 +/- 13.4 to 29.0 +/- 9.1 ms, p = NS).

CONCLUSIONS

Reduction of QT interval and QT interval variability after timely reperfusion of the infarct-related artery may be a previously unreported beneficial mechanism of primary PTCA in AMI, indicating successful reperfusion.

Value of QT dispersion in evaluating spatial dispersion of ventricular repolarization during acute myocardial ischemia

OBJECTIVES

To study the value of epicardial QT interval dispersion in predicting ischemia-induced heterogeneity of ventricular repolarization.

ANIMALS AND METHODS

Ischemia was produced by total occlusion of the obtuse branch of the circumflex coronary artery in seven open-chest sheep. A 64-channel electrocardiogram (ECG) was acquired from the epicardium before and after coronary artery occlusion. Wavelet transformation was used to determine the characteristic points of the epicardial ECGs, and to measure the QT interval and activation-recovery interval (ARI) and their dispersions.

RESULTS

The average QT interval and ARI from the epicardial ECG were not changed by acute myocardial ischemia (P=0.07 and P=0.13, respectively). QT dispersion remained unchanged during ischemia (P=0.17), whereas ARI dispersion was significantly increased by acute ischemia (59.9+/-24.0 ms versus 126.3+/-32.1 ms, P<0.001).

CONCLUSIONS

These findings indicate that epicardial QT dispersion is less sensitive than ARI dispersion in estimating repolarization heterogeneity induced by acute myocardial ischemia.

Usefulness of QT dispersion immediately after exercise as an indicator of coronary stenosis independent of gender or exercise-induced ST-segment depression

Several recent studies suggest that QT dispersion on a standard 12-lead electrocardiogram is a clinically useful indicator of significant coronary stenosis. In this study, we compared the diagnostic accuracy of QT dispersion immediately after exercise as an indicator of coronary stenosis in men and women, and in the presence or absence of exercise-induced significant ST-segment depression. The subjects were 273 consecutive patients (mean age 56 +/- 9 years; 190 men and 83 women) without a history of myocardial infarction who underwent treadmill exercise electrocardiography and coronary angiography for evaluation of angina. Of these, 146 patients had no significant coronary stenosis, 61 had single-vessel disease, 56 had multivessel disease, and 10 had left main coronary artery disease. QT dispersion immediately after exercise was significantly greater in patients with significant coronary stenosis than in those without (64 +/- 14 vs 39 +/- 14 ms, p <0.01). QT dispersion immediately after exercise was significantly more sensitive in men (sensitivity 75%; specificity 85%) and significantly more specific in women (sensitivity 77%, specificity 88%) than exercise-induced significant ST-segment depression (men: sensitivity 62%, specificity 74%; women: sensitivity 81%, specificity 68%) as an indicator of significant coronary stenosis. The addition of factors such as gender and the presence or absence of exercise-induced significant ST-segment depression did not significantly alter the sensitivity and specificity of QT dispersion immediately after exercise for detecting significant coronary stenosis (patients with significant ST-segment depression: sensitivity 77%, specificity 88%; patients without significant ST-segment depression: sensitivity 72%, specificity 86%). In conclusion, QT dispersion immediately after exercise is a clinically useful indicator of significant coronary stenosis independent of gender or the presence or absence of exercise-induced significant ST-segment depression.

Measurement, interpretation and clinical potential of QT dispersion

QT dispersion was originally proposed to measure spatial dispersion of ventricular recovery times. Later, it was shown that QT dispersion does not directly reflect the dispersion of recovery times and that it results mainly from variations in the T loop morphology and the error of QT measurement. The reliability of both automatic and manual measurement of QT dispersion is low and significantly lower than that of the QT interval. The measurement error is of the order of the differences between different patient groups. The agreement between automatic and manual measurement is poor. There is little to choose between various QT dispersion indices, as well as between different lead systems for their measurement. Reported values of QT dispersion vary widely, e.g., normal values from 10 to 71 ms. Although QT dispersion is increased in cardiac patients compared with healthy subjects and prognostic value of QT dispersion has been reported, values are largely overlapping, both between healthy subjects and cardiac patients and between patients with and without adverse outcome. In reality, QT dispersion is a crude and approximate measure of abnormality of the complete course of repolarization. Probably only grossly abnormal values (e.g. > or =100 ms), outside the range of measurement error may potentially have practical value by pointing to a grossly abnormal repolarization. Efforts should be directed toward established as well as new methods for assessment and quantification of repolarization abnormalities, such as principal component analysis of the T wave, T loop descriptors, and T wave morphology and wavefront direction descriptors.

Time dependent variability of QT dispersion after acute myocardial infarction and its relation to ventricular fibrillation: a prospective study

OBJECTIVE

To show whether increased QT dispersion on admission predicts ventricular fibrillation after acute myocardial infarction, and to determine the nature of time related changes in QT dispersion.

DESIGN

Prospective cohort study.

SETTING

Coronary care units of three teaching hospitals in Newcastle-upon-Tyne over an eight month period.

PATIENTS

All had acute myocardial infarction according to World Health Organization criteria.

INTERVENTIONS

For all patients, QT dispersion (QTd) and Bazett rate corrected QTc dispersion (QTcd) were measured from a high quality 12 lead ECG recorded on admission at a paper speed of 50 mm/s. In a subset, serial ECGs were recorded regularly to show time related changes in QTcd following acute myocardial infarction.

MAIN OUTCOME MEASURES

Occurrence of ventricular fibrillation within the first 24 hours after myocardial infarction.

RESULTS

Data collected from 201 patients, 12 of whom (6%) developed ventricular fibrillation within 24 hours. Neither QTd nor QTcd differed between those developing ventricular fibrillation and those who did not: QTd mean (SD), 74 (24) ms (95% confidence interval (CI) 59 to 89) v 66 (24) ms (95% CI 62 to 70), respectively; QTcd, 86 (26) ms(0.5) (95% CI 70 to 102) v 77 (29) ms(0.5) (95% CI 72 to 82), respectively. Significant QTcd changes occurred early after myocardial infarction.

CONCLUSIONS

Admission QTd and QTcd do not predict ventricular fibrillation after acute myocardial infarction. There are significant changes in QTcd with time, which may account for this measured lack of correlation.

Can the assessment of dynamic QT dispersion on exercise electrocardiogram predict sudden cardiac death in hypertrophic cardiomyopathy?

Premature sudden cardiac death (SD) is a critical event in the natural history of hypertrophic cardiomyopathy (HCM), and occurs during or just after physical exertion in approximately 60% of instances. Abnormalities in ventricular repolarization may not be present at rest in some patients but may become apparent under certain conditions. This study was performed to examine whether dynamic QT dispersion during exercise is associated with SD in HCM. Twenty-four HCM patients with catastrophic events (group I; 18 SD, 6 ventricular fibrillation) and 24 event-free survivors (group II) were studied. The two groups were pair-matched for age, gender, and maximum left ventricular wall thickness. QT intervals were manually measured from 12-lead exercise electrocardiogram (ECG) with a digitizing board. A custom-developed program was used to calculate QT and JT dispersion. The QT/RR relationship was evaluated by the slope of linear regression analysis. Before exercise, significant differences in heart rate and JT dispersion were found between group I and II. During exercise, heart rate increased and QT decreased significantly in both groups. QT and JT dispersion decreased in both groups, though the magnitude of reduction was greater in group I than in group II. No significant differences in QTc interval and QT or JT dispersion were found between the groups at any stages. At 3 minutes of recovery, heart rate had decreased but remained higher than before exercise, and all measurements of QT components remained shorter compared with those made before exercise in both groups. There was a strong correlation between QT and RR interval during exercise in all study patients (r = 0.95). No difference in the slope of QT against RR intervals was found between the groups (0.317 vs 0.319). In conclusion, exercise reduced QT dispersion in patients with HCM. The dynamic changes in QT dispersion examined by this method on exercise ECG did not make additional contributions in their risk stratification.

QT dispersion is increased in diabetic patients with foot ulcer

QT dispersion, a measure of inhomogenous ventricular repolarization, was measured in diabetic patients with foot ulcer. We recruited 75 patients with non insulin-dependent diabetes mellitus: patients with neuropathic ulcer (n=15, NU group), with ischemic ulcer (n=20, IU group), with previous myocardial infarction (n=20, MI group) and without any diabetic microangiopathies (n=20, DC group). We also studied normal control subjects (n=15, NC group). The interlead variability of rate corrected QT interval (QTc dispersion) was calculated. QTc interval in the MI group was significantly higher than that in the NC or DC but showed no difference in the NU and IU groups. QTc dispersion in the IU (54+/-15 msec) as well as MI (60+/-21 msec) group were significantly higher than the NC (36+/-18 msec) or DC group (39+/-14 msec). This may be due to complicated coronary artery disease in the IU group. Furthermore, QTc dispersion was also increased (49+/-14 msec) in the NU group in which cardiac autonomic nervous dysfunction was suggested. Patients with both types of diabetic ulcer demonstrated increased QT dispersion due to atherosclerosis or neurological disorder.

The added diagnostic value of automated QT-dispersion measurements and automated ST-segment deviations in the electrocardiographic diagnosis of acute cardiac ischemia

The purpose of this study was to determine the added value of automated QT dispersion and ST-segment measurements to physician interpretation of 12-lead electrocardiograms (ECGs) in patients with chest pain. To date, poor reproducibility of manual measurements and lack of shown added value have limited the clinical use of QT dispersion. Twelve-lead ECGs (n = 1,161) from the Milwaukee Prehospital Chest Pain Database were independently classified by 2 physicians into 3 groups (acute myocardial infarction (AMI), acute cardiac ischemia (ACI), or nonischemic), and their consensus was obtained. QT-end and QT-peak dispersions were measured by a computerized system. The computer also identified ST-segment deviations. Sensitivity, specificity, and positive predictive values (PPVs) and negative predictive values (NPV) for AMI and ACI were evaluated independently and in combinations. For AMI, physicians' consensus classification was remarkably good (sensitivity, 48%, specificity, 99%). Independent classification by QT-end and QT-peak dispersions or ST deviations was not superior to the physicians' consensus. Optimal classification occurred by combining automated QT-end dispersion and ST deviations with physicians' consensus. This combination increased sensitivity for the diagnoses of AMI by 35% (65% vs 48%, P < .001) and ACI by 55% (62% vs 40%, P < .001) compared with physicians' consensus, while maintaining comparable specificity. This study supports a potential clinical role for automated QT dispersion when combined with other diagnostic methods for detecting AMI and ACI.

QT interval dispersion: non-invasive marker of ischemic injury in patients with unstable angina pectoris?

Prognostic assessment of unstable angina pectoris is a common clinical problem for physicians. Markers of myocardial cell injury, serial electrocardiographic findings and ST segment monitoring are mainly studied for prognosis. We investigated the relation between myocardial injury and the value of cardiac troponin T and QT interval dispersion in hospitalized unstable angina patients. This is a prospective study that includes adult patients admitted to an emergency department with Braunwald class IIIB unstable angina pectoris. Eighty-six patients were enrolled in the study (mean age of 57 +/- 12 years, 63 males and 23 females). Cardiac troponin T was assayed and QT dispersion calculated from surface ECG. Fifty-eight patients with troponin T < 0.1 ng/ml and 28 patients with troponin T levels > or = 0.1 formed group 1 and group 2, respectively. There were no significant differences in sex, age, history of coronary revascularization or ECG findings such as ST depression and T inversions between the two groups. The QT dispersion was significantly greater in patients with elevated cardiac troponin T levels (77 +/- 18 msec vs 38 +/- 13 mse; p < 0.014). Because QT interval dispersion exhibited an association with cardiac troponin T levels, it may be used as a non-invasive marker of ischemic injury in patients with unstable angina.

Dispersion of QT intervals: a measure of dispersion of repolarization or simply a projection effect?

QT interval dispersion may provide little information about repolarization dispersion. Some clinical measurements demonstrate an association between high QT interval dispersion and high morbidity and mortality, but what is being measured is not clear. This study was designed to help resolve this dilemma. We compared the association between different clinical measures of QT interval dispersion and the ECG lead amplitudes derived from a heart vector model of repolarization with no repolarization dispersion whatsoever. We compared our clinical QT interval dispersion data obtained from 25 subjects without cardiac disease with similar data from published studies, and correlated these QT dispersion results with the distribution of lead amplitudes derived from the projection of the heart vector onto the body surface during repolarization. Published results were available for mean relative QT intervals and mean differences from the maximum QT interval. The leads were derived from Uijen and Dower lead vector data. Using the Uijen lead vector data, the correlation between measurements of dispersion and derived lead amplitudes ranged from 0.78 to 0.99 for limb leads, and using the Dower values ranged from 0.81 to 0.94 for the precordial leads. These results show a clear association between the measured QT interval dispersion and the variation in ECG lead amplitudes derived from a simple heart vector model of repolarization with no regional information. Therefore, measured QT dispersion is related mostly to a projection effect and is not a true measure of repolarization dispersion. Our existing interpretation of QT dispersion must be reexamined, and other measurements that provide true repolarization dispersion data investigated.

Effects of metabolically ischemic, but viable, myocardium on QT dispersion in patients with acute myocardial infarction: a study with resting I-123-BMIPP/thallium-201 myocardial single-photon emission computed tomography

In chronic Q-wave myocardial infarction, QT dispersion is closely correlated with infarct size, but this correlation has not been evaluated for acute myocardial infarction (AMI). The effects of abnormal fatty acid metabolism on QT dispersion were examined in 123 patients with AMI who underwent resting iodine-123-15-iodophenyl 3-methyl pentadecanoic acid (BMIPP)/thallium-201(201Tl) myocardial single photon emission computed tomography (SPECT) and electrocardiographic analysis in the subacute phase. The relationship between BMIPP and 201Tl was defined as match when the total defect score for BMIPP was equal to or smaller than that for 201Tl, and as mismatch when the total defect score for BMIPP was larger than that for 201Tl. Twenty-six patients (21%) demonstrated BMIPP-201Tl match and 97 (79%) demonstrated mismatch. Infarct size was closely correlated with QT dispersion (r=0.67, p<0.001) in patients with BMIPP-201Tl match, but weakly correlated (r=0.30, p<0.005) in patients with BMIPP-201Tl mismatch. For small infarctions, QT dispersion was significantly larger in patients with BMIPP-201Tl mismatch than in those with BMIPP-201Tl match (62+/-24 ms vs 41+/-18 ms, p=0.03), but did not differ between the 2 groups for large infarctions. This study shows that QT dispersion is influenced by infarct size and by the presence of metabolically ischemic but viable myocardium in patients with AMI.

Application of noninvasive and invasive tests for risk assessment in patients with ventricular arrhythmias

Sudden cardiac death remains a major public health problem in western society. Because most patients who experience cardiac arrest are not successfully resuscitated, primary prevention of sudden death remains an important challenge. A number of noninvasive risk stratification techniques have been suggested as providing useful information in patients with underlying structural heart defects. Unfortunately, the positive predictive value of most of these techniques has been limited. Left ventricular ejection fraction, the presence of nonsustained ventricular tachycardia on Holter monitoring, and inducible sustained ventricular tachycardia at electrophysiologic testing in patients with coronary artery disease remain the best established prognostic test. However, with the exception of two ICD studies using the combination of these markers, prospective studies have not yet completely validated the use of these and other prognostic markers. Further understanding of the pathophysiology of ventricular fibrillation and other risk stratification techniques will be necessary before a clear algorithm can be developed for application to patients at risk for sudden death.

Value of QT dispersion in the interpretation of treadmill exercise electrocardiograms of patients without exercise-induced chest pain or ST-segment depression

It has recently been reported that increased QT dispersion seen on standard 12-lead electrocardiograms (ECGs) reflects transient myocardial ischemia. The present study investigates whether increased QT dispersion induced by exercise is a useful indicator for detecting significant coronary stenosis in patients who do not have chest pain or significant ST-segment depression in response to exercise. We studied 135 consecutive patients (mean age +/- SD, 55 +/- 9 years; 97 men and 38 women) who complained of anginal chest pain and who did not have exercise-induced chest pain or significant ST-segment depression during treadmill exercise electrocardiography. Coronary angiography was performed in all of patients. Of the 135 patients, 97 had no significant coronary stenosis, 25 had 1-vessel coronary artery disease (CAD), and 13 had multivessel CAD. QT dispersion immediately after exercise was significantly greater in the group with significant coronary stenosis than without significant coronary stenosis (62 +/- 13 vs 40 +/- 14 ms, p <0.0001). When QT dispersion >/=60 ms immediately after exercise was considered a positive result, this indicator had a sensitivity of 74%, a specificity of 85%, and an accuracy of 81% for the diagnosis of significant coronary stenosis. In conclusion, we have shown that QT dispersion immediately after exercise is useful for detecting significant CAD in patients who do not have exercise-induced chest pain or significant ST-segment depression.

Beat-to-beat QT interval variability in coronary patients

Changes in ventricular repolarization have been described in patients after myocardial infarction, whereas data for coronary patients without prior myocardial infarction are lacking. This study was designed to evaluate ventricular repolarization in coronary patients with effort angina pectoris. Beat-to-beat QT interval variability (QTV) using 5-minute resting high-resolution ECG recordings was measured in 26 men (mean age 62.1 years) with effort angina pectoris and without prior myocardial infarction, and in 30 age-matched men without clinically evident coronary heart disease (controls). To evaluate the degree of coronary artery disease in coronary patients, coronary angiography was performed. Coronary patients displayed significantly higher values of QTV compared with the control patients (P < .001). Rate adaptation of QT interval correlated significantly with the degree of coronary artery disease in the study group patients (P < .05). The significant association between QTV and coronary heart disease suggests altered ventricular repolarization in coronary patients without prior myocardial infarction.

Estimates of repolarization and its dispersion from electrocardiographic measurements: direct epicardial assessment in the canine heart

This study investigates a technique to estimate dispersion based on the root mean square (RMS) signal of multiple electrocardiographic leads. Activation and recovery times were measured from 64 sites on the epicardium of canine hearts using acute in situ or Langendorff perfused isolated heart preparations. Repolarization and its dispersion were altered by varying cycle length, myocardial temperature, or ventricular pacing site. Mean and dispersion of activation and recovery times, and activation-recovery interval (ARI) were calculated for each beat. The waveform was then calculated from all leads. Estimates of mean and dispersion of activation and recovery times and mean ARI were derived using only inflection points from the RMS waveform. QT intervals were also measured and QT dispersion was determined. Estimates determined from the RMS waveform provided accurate estimates of repolarization and were, in particular, a better measure of repolarization dispersion than QT dispersion.

QT dispersion from body surface ECG does not reflect the spatial dispersion of ventricular repolarization in sheep

The correlation between the QT dispersion on body surface ECG and the dispersion in ventricular repolarization from the cardiac surface was studied in six sheep anesthetized with pentobarbital. The standard 12-lead body surface ECG and multiple ventricular epicardial ECGs were simultaneously recorded. The activation-recovery interval (ARI) was measured from the unipolar epicardial ECGs. The pooled QT dispersion from the six animals was significantly smaller than the pooled ARI dispersion (22.7 +/- 2.6 vs 33.0 +/- 6.9 ms, P < 0.01). There was no correlation between the QT and ARI dispersion. The unipolar epicardial ECGs were then converted into bipolar ECGs and epicardial QT intervals were subsequently acquired from these ECGs. The average value of epicardial QT dispersion from the six animals was similar to that of body surface ECG, but was less than the ARI dispersion (27.5 +/- 6.8 vs 33.0 +/- 6.9, P < 0.01). A good correlation between the epicardial QT dispersion and ARI dispersion was identified (r = 0.84, P < 0.05). In addition, a prolongation in ventricular repolarization, induced by an increase in coronary flow, elicited a pooled ARI dispersion of 62.3 +/- 6.2 ms (n = 6), which was larger than the simultaneously recorded body surface QT dispersion (28.3 +/- 9.8 ms, n = 6, P < 0.01). No correlation between the ARI and QT dispersion was found in the presence of the prolonged ventricular repolarization. In conclusion, QT dispersion from a 12-lead body surface ECG seems to underestimate the spatial dispersion of ventricular repolarization acquired from sheep epicardium.

QT interval and mortality from coronary artery disease

Abnormalities in the QT interval can be divided into 3 types, prolongation of the QT interval, increases in the dispersion of the QT interval, and abnormalities in the heart rate dependent behavior of the QT interval. Abnormalities may be found in short or long-term recordings. Prolongation of the QT interval may reflect factors associated with an adverse prognosis in coronary disease and may in itself be arrhythmogenic. The data to date suggest that there is an association between adverse prognosis and QT interval prolongation in coronary disease, both before and after acute myocardial infarctions. This relationship is weak, however, and is not clinically useful. The data as to whether increased QT dispersion postmyocardial infarction relates to adverse prognosis is weak because there is no convincing evidence yet. If there is a relationship it is weak. Abnormalities in the rate dependent behavior of the QT interval are widely found, but as no large scale prospective study with mortality as an endpoint has yet been undertaken the significance of rate dependent abnormalities is uncertain. The widespread introduction of beat-to-beat QT analysis of 24 hour Holter tapes may take QT intervalology into the realm of clinical practice.

Effect of coronary ischemia on QT dispersion

Over the last 5 to 8 years, numerous clinical studies have been conducted evaluating the effects of coronary ischemia on disparity of ventricular repolarization (VR) as assessed by determination of QT dispersion from the surface electrocardiogram. From findings in patients with acute myocardial infarction, stable coronary disease, and vasospastic angina there is convincing evidence that acute coronary ischemia augments inhomogeneity in VR. In some studies, this was associated with the occurrence of ventricular arrhythmias. In general, therefore, these clinical observations confirm previous experimental work. One should keep in mind, however, various problems inherent to the current technology used to determine QT dispersion from the surface electrocardiogram. Whereas some of these technological limitations can be overcome in carefully designed and conducted clinical studies, these methodological shortcomings have so far precluded the routine use of QT dispersion in taking care of patients with acute coronary syndromes. It remains to be seen whether further refinements in technology will enable clinicians to incorporate assessment of disparity of VR in daily practice in an attempt to further improve care of patients with acute coronary syndromes.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

[QT dispersion in premature beats produced by extrastimuli from the right atrium and right ventricle]

The difference between the maximum and minimum QT interval measured from a 12-lead electrocardiogram was defined as an index of spatial inhomogeneous repolarization of the ventricular myocardium. The causal relationship between QT dispersion and incidence of ventricular arrhythmias has been pointed out in various heart diseases, but until now it was discussed mainly related to sinus rhythm. QT dispersion in extrasystole may be more important in the development of arrhythmias. We examined 5 cases (mean age 34 +/- 12 years) with a history of paroxysmal supraventricular tachycardia, who underwent electrophysiologic study. Both atrial and ventricular premature stimuli were given at a basic cycle length of 600 msec respectively. The QT interval and the ventricular activation time (VAT) (period from premature test stimulus to the summit of QRS) of the premature beats were measured in a simultaneously recorded 12-lead electrocardiogram. QT dispersion (the difference between the longest QT interval and the shortest QT interval) and VAT dispersion (the difference between the longest VAT and the shortest VAT) were measured. In atrial premature beats, there were no significant changes in the QT dispersion or VAT dispersion when the coupling interval of the premature beats was shortened. In the ventricular premature beats, however, both the QT dispersion and the VAT dispersion tended to increase with the shortening of the coupling interval. We concluded that only a short coupled ventricular premature beat induces greater QT and VAT dispersion. A ventricular couplet with short coupling interval may contribute to the development of ventricular tachyarrhythmias.

Mechanisms of the spatial distribution of QT intervals on the epicardial and body surfaces

INTRODUCTION

The role of QT dispersion as a predictor of arrhythmia vulnerability has not been consistently confirmed in the literature. Therefore, it is important to identify the electrophysiologic mechanisms that affect QT duration and distribution. We compared the spatial distributions of QT intervals (QTI) with potential distributions on cardiac and body surfaces and with recovery times on the cardiac surface. We hypothesized that the measure of QTI is affected by the presence of the zero potential line in the potential distribution, as well as the sequence of recovery. We also investigated use of the STT area as a possible indicator of recovery times on the cardiac surface.

METHODS AND RESULTS

High-resolution spatial distributions of QTI and potentials were determined on the body surface of human subjects and on the surface of a torso-shaped tank containing an isolated canine heart. Additionally, spatial distributions of QTI, recovery times, and STT areas were determined on the surface of exposed canine hearts. Unipolar electrograms were recorded during atrial and ventricular pacing for normal hearts and cases of myocardial infarction. Regions of shortest QTI always coincided with the location of the zero potential line on the cardiac and body surfaces. On the cardiac surface, in regions away from the zero line, similarities were observed between the patterns of QTI and the sequence of recovery. STT areas and recovery times were highly correlated on the cardiac surface.

CONCLUSION

QTI is not a robust index of local recovery time on the cardiac surface. QTI distributions were affected by the position of the zero potential line, which is unrelated to local recovery times. However, similarities in the patterns of QTI and recovery times in some regions may help explain the frequently reported predictive value of QT dispersion. Preliminary results indicate STT area may be a better index of recovery time and recovery time dispersion on the epicardium than QTI.

Use of QT dispersion measured on treadmill exercise electrocardiograms for detecting restenosis after percutaneous transluminal coronary angioplasty

BACKGROUND

Treadmill exercise electrocardiography (ECG) has been used to detect restenosis in patients following percutaneous transluminal coronary angioplasty (PTCA). However, the level of sensitivity achieved using conventional criteria of ST-segment depression is too low to be clinically useful in this population.

HYPOTHESIS

QT dispersion is a sensitive method for detecting myocardial ischemia and may improve the accuracy of treadmill exercise ECG testing for detecting restenosis after PTCA.

METHODS

We evaluated 104 patients who underwent PTCA for the treatment of single-vessel coronary artery disease and who had no history of myocardial infarction. Treadmill exercise ECG and coronary angiograms were performed 3 months after PTCA to determine the accuracy of diagnosis restenosis based on standard ST-segment depression and QT dispersion criteria.

RESULTS

Restenosis was observed in 37 of the 104 patients (36%) 3 months after PTCA. QT dispersion immediately after exercise was significantly greater in patients with than in those without restenosis, as was the difference in QT dispersion before and immediately after exercise. The sensitivity, specificity, and accuracy of ST-segment depression criteria were 59, 64, and 63%, respectively. Measurements of QT dispersion immediately after exercise (> or = 50 ms: positive, < 50 ms: negative) improved the sensitivity, specificity, and accuracy of treadmill ECG for predicting restenosis to 81, 87, and 85%, respectively.

CONCLUSIONS

This novel diagnostic method using QT dispersion-based criteria significantly improves the clinical usefulness of treadmill exercise ECG for detecting the presence of restenosis after PTCA.

Relation of ventricular repolarization to cardiac cycle length in normal subjects, hypertrophic cardiomyopathy, and patients with myocardial infarction

BACKGROUND

Prolonged QT interval and QT dispersion have been reported to reflect an increased inhomogeneity of ventricular repolarization, which is believed to be responsible for the development of arrhythmic events in patients with long QT syndrome, coronary heart disease, and myocardial infarction, congestive heart failure, and hypertrophic cardiomyopathy (HC).

HYPOTHESIS

This study was undertaken to determine whether an abnormal QT/RR dynamicity may reflect autonomic imbalance and may contribute to arrhythmogenesis in patients with heart disease.

METHODS

The relation between QT, QTpeak (QTp), Tpeak-Tend (TpTe) intervals and cardiac cycle length was assessed in 70 normal subjects, 37 patients with HC, and 48 survivors of myocardial infarction (MI). A set of 10 consecutive electrocardiograms was evaluated automatically in each subject using QT Guard software (Marquette Medical Systems, Milwaukee, Wisc.).

RESULTS

In patients with HC, all intervals were significantly prolonged compared with normals (p < 0.001 for QT and QTp; p < 0.04 for TpTc); in survivors of MI, this was true for the maximum QT and QTp intervals (p < 0.05). A strong linear correlation between QT, QTp, and RR intervals was observed in normals and in patients with MI and HC (r = 0.65-0.59, 0.82-0.77, 0.79-0.74, respectively, p < 0.0001). TpTe interval only showed a weak correlation with heart rate in normals (r = 0.24, p < 0.05) and was rate-independent in both patient groups (p = NS). Compared with normals, the slopes of QT/RR and QTp/RR regression lines were significantly steeper in patients with MI and HC (0.0990-0.0883, 0.1597-0.1551, 0.1653-0.1486, respectively). Regression lines were neither parallel nor identical between normals and patients (T > 1.96, Z > 3.07). There was no difference in steepness for TpTeR/RR lines between groups (0.0110, 0.0076, 0.0163, respectively). TpTe/QTp ratio was similar in normals and in patients with MI and HC (0.30 +/- 0.03, 0.31 +/- 0.07, 0.30 +/- 0.04, respectively), in the absence of any correlation between QTp and TpTe intervals, suggesting disproportional prolongation of both components of QT interval.

CONCLUSION

Compared with normals, a progressive increase in QT and QTp intervals at slower heart rates in patients with MI and HC may indicate an enhanced variability of the early ventricular repolarization and may be one of the mechanisms of arrhythmogenesis.

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

Three new approaches for the analysis of ventricular repolarisation in 12-lead electrocardiograms (ECGs) are presented: the spatial and temporal variations in T-wave morphology and the wavefront direction difference between the ventricular depolarisation and repolarisation waves. The spatial variation characterises the morphology differences between standard leads. The temporal variation measures the change in interlead relationships. A minimum dimensional space, constructed by ECG singular value decomposition, is used. All descriptors are measured using the ECG vector in the constructed space and the singular vectors that define this space. None of the descriptors requires time domain measurements (e.g. the precise detection of the T-wave offset), and so the inaccuracies associated with conventional QT interval related parameters are avoided. The new descriptors are compared with the conventional measurements provided by a commercial system for an automatic evaluation of QT interval and QT dispersion in digitally recorded 12-lead ECGs. The basic comparison uses a set of 1100 normal ECGs. The short-term intrasubject reproducibility of the new descriptors is compared with that of the conventional measurements in a set of 760 ECGs recorded in 76 normal subjects and a set of 630 ECGs recorded in 63 patients with hypertrophic cardiomyopathy (ten serial recordings in each subject of both these sets). The discriminative power of the new and conventional parameters to distinguish normal and abnormal repolarisation patterns is compared using the same set. The results show that the new parameters do not correlate with the conventional QT interval-related descriptors (i.e. they assess different ECG qualities), are generally more reproducible than the conventional parameters, and lead to a more significant separation between normal and abnormal ECGs, both univariately and in multivariate regression models.

Long-term effect of endoscopic transthoracic sympathicotomy on heart rate variability and QT dispersion in severe angina pectoris

We evaluated short and long-term effects on QT dispersion and autonomic balance after endoscopic transthoracic sympathicotomy (ETS). Heart rate variability (HRV) reflects autonomic balance of the heart. QT dispersion is a marker of cardiac electrical instability in patients with ischemic heart disease. Holter recordings for 24 h and a twelve-lead ECG were made prior to, 1 month, 1 year and 2 years after ETS. HRV was analysed in time domain and spectral analysis was performed during controlled respiration in supine position and during head up tilt. Dispersion of QT time and QTc were calculated. Of 88 patients, 62 (60) were eligible for HRV (QT-dispersion) analysis after 1 month, 39 (38) patients after 1 year and 23 (24) patients after 2 years. The HRV analysis showed a significant change of indices reflecting sympatho-vagal balance indicating significantly reduced sympathetic (LF) and increased vagal (HF, rMSSD) tone. These changes still persisted after 2 years. Global HRV increased over time with significant elevation of SDANN after 2 years. QT dispersion was significantly reduced 1 month after surgery and the dispersion was further diminished 2 years later.

CONCLUSION

ETS changed HRV and QT dispersion which could imply reduced risk for malignant arrhythmias and death after ETS.

Coronary arterial involvement and QT dispersion in Kawasaki disease

For the early detection of myocardial ischemia in patients with severe involvement of the coronary arteries after Kawasaki disease, a method with high sensitivity and low cost is desirable because these patients require frequent follow-up and diagnostic tests. For this purpose, electrocardiographic, echocardiographic, Holter, and stress testing or angiography are repeated. However, these tests have some limitations due to cost, convenience, or sensitivity. It is uncertain that increased QT dispersion would exactly indicate progression of myocardial ischemia after Kawasaki disease, but this is the first study to present that QT dispersion of > or = 60 ms had higher sensitivity for detection of severe involvement of coronary artery after Kawasaki disease. This study is limited due to the small number of patients; larger prospective studies are required to clarify the usefulness of QT dispersion analysis in detecting the progression of myocardial ischemia after Kawasaki disease.

QT dispersion as a predictor of long-term mortality in patients with acute myocardial infarction and clinical evidence of heart failure

BACKGROUND

QT interval dispersion is a marker of inhomogeneous ventricular repolarization, and therefore has the potential to predict re-entry arrhythmias. Following acute myocardial infarction, increased QT dispersion has been associated with a higher risk of ventricular arrhythmias. However, whether or not QT dispersion predicts prognosis post-acute myocardial infarction is not clear. We addressed this issue by analysing the AIREX study registry.

METHODS

AIREX was a follow-up study of 603 post-acute myocardial infarction patients who exhibited clinical signs of heart failure and were randomly allocated to ramipril or placebo. An interpretable 12-lead ECG obtained between day 0 and day 9 after the index infarction (median time 2 days) was available in 501 patients. We examined whether QT dispersion was a predictor of all-cause mortality in the AIREX study registry (mean follow-up 6 years).

RESULTS

QT dispersion measurements were significantly increased in patients who subsequently died (QT dispersion: 92.0 +/- 38.5 ms vs 82.7 +/- 34.3 ins. P=0.005; rate corrected QT dispersion: 105.7 +/- 42.7 ms vs 93.1 +/- 35.9 ms, P<0.001). Univariate analysis showed that QT dispersion as a predictor of all-cause mortality risk (QT dispersion: hazard ratio per l0 ms 1.05, [95% CI 1.02 to 1.09]. P= 0.004; rate corrected QT dispersion: 1-07 [1.03 to 1.10], P<0.001): an increase of 10 ms added a 5-7%, relative risk of death. QT dispersion remained an independent predictor of all-cause mortality risk on multivariate analysis (QT dispersion: 1.05 [1.01 to 1.09], P=0.027; rate corrected QT dispersion: 1.05 [1.01 to 1.09]. P=0.022).

CONCLUSION

QT dispersion. measured from Li routine 12-lead ECG following acute myocardial infarction complicated by heart failure provides independent information regarding the probability of long-term survival. However. the low sensitivity of this electrocardiographic marker limits its usefulness for risk stratification if used in isolation.

Evaluation of autonomic influences on QT dispersion using the head-up tilt test in healthy subjects

Our objective was to examine the autonomic influence on QT interval dispersion using the head-up tilt test in healthy subjects. RR and QT intervals, heart rate variability, and plasma norepinephrine concentration were measured in the supine position and tilting to 70 degrees for 20 minutes using a footboard support in 15 healthy male volunteers (mean age +/- SD: 28.0 +/- 4.5 years). The rate-corrected QT interval (QTc) was calculated using Bazett's formula, and QT and QTc dispersions were defined as the maximum minus minimum values for the QT and QTc, respectively, from the 12-lead ECG. Spectral analysis of the heart rate variability generated values for the low- and high-frequency powers (LF and HF) and their ratio (LF/HF). Compared with values obtained in the supine position, tilting significantly increased QT (P < 0.05) and QTc dispersion (P < 0.01), the LF/HF ratio (P < 0.0001), and plasma norepinephrine concentration (P < 0.0001), and significantly decreased HF (P < 0.0001). QTc dispersion was positively correlated with the LF/HF ratio and plasma norepinephrine concentration, and negatively correlated with HF. These results suggest that head-up tilt testing increases QT dispersion by increasing sympathetic tone and/or decreasing vagal tone in healthy subjects.