Dispersion of QT interval in patients with and without susceptibility to ventricular tachyarrhythmias after previous myocardial infarction

Spatial features in body surface potential maps of patients with ventricular tachyarrhythmias with or without coronary artery disease

Body surface potential maps (BSPM) from patients with coronary artery disease or no structural heart disease were analyzed with respect to their spatial features and QT/QTc dispersion in order to determine whether BSPM allows identification of patients with ventricular fibrillation. QRST integral maps and QT/QTc dispersion were acquired from simultaneous recordings of 62 ECG leads during sinus rhythm in patients with idiopathic ventricular fibrillation (n=13), ventricular fibrillation and coronary artery disease (n=22), coronary artery disease without ventricular fibrillation (n=21) and healthy controls (n=18). The Karhunen-Loeve transformation was applied to reduce the dimensionality of the data matrix of the QRST map to eight coefficients. Linear discriminant analysis allowed discrimination between idiopathic ventricular fibrillation patients and controls with high sensitivity (85%) and specificity (89%). However, discrimination between coronary artery disease patients with or without ventricular fibrillation was poor (68% and 67%, respectively). QTc dispersion calculated from BSPM was longer in idiopathic ventricular fibrillation patients than in controls (99+/-30 ms vs 70+/-14 ms, P=0.009) in contrast to QTc dispersion taken from 12-lead ECG (53+/-21 ms vs. 47+/-12 ms, P=n.s.). No significant difference was noted for coronary artery disease patients with or without ventricular fibrillation. In conclusion, repolarization disturbances detected by BSPM allow identification of ventricular fibrillation patients without structural heart disease. However, our results do not suggest a major impact of QT/QTc dispersion or QRST integral mapping for identification of ventricular fibrillation patients with coronary artery disease.

Unsuitability of corrected QT dispersion as a marker for ventricular arrhythmias and cardiac sudden death after acute myocardial infarction

The present study investigated whether corrected QT (QTc) dispersion could play a role as a marker of ventricular arrhythmias and sudden cardiac death after acute myocardial infarction (MI). The study included 76 males and 24 females with a mean age of 60+/-11 years. Standard 12-lead ECGs were recorded during the recovery phase (15+/-9 days) after the onset of MI. The QTc was calculated according to Bazett's formula and QTc dispersion was calculated as the difference between the maximum and minimum QTc intervals. Patients were divided into 2 groups: 21 patients (group A) had a QTc dispersion of > or =80ms, and the other 79 patients (group B) had a QTc dispersion of <80ms in the recovery stage (15+/-9 days). Clinical, angiographical, and Holter monitoring data, and prognosis (mean follow-up period 29+/-18 months) were compared between these 2 groups. The frequencies of early coronary reperfusion and recanalization of infarct-related vessels during the recovery phase were significantly higher in group B than group A. The left ventricular ejection fraction was also higher in group B than group A (51+/-12 vs 43+/-12%, p=0.0029). There were no significant differences in the number of premature ventricular contractions, the percentage of patients with repetitive ventricular arrhythmias, or in the frequency of sudden cardiac death during the follow-up period between the 2 groups. In summary, QTc dispersion in the recovery stage is not a useful marker for ventricular arrhythmias or sudden cardiac death after acute MI, although increased QTc dispersion may correlate with an ineffective early coronary reperfusion and with the degree of depressed left ventricular function.

Relation of QT dispersion to infarct size and left ventricular wall motion in anterior wall acute myocardial infarction

Previous studies have shown that QT dispersion increases during acute myocardial infarction (AMI). However, the relation of QT dispersion to infarct size and left ventricular (LV) function in AMI has not yet been fully clarified. Accordingly, this study was conducted to elucidate this relation at 1 month after anterior wall AMI. We examined 94 patients with first anterior wall AMI (< or = 6 hours) who underwent coronary arteriography at admission, 1 month, and 6 months after AMI, and left ventriculography at 1 and 6 months after AMI. Mean QT dispersion on the chronic phase (about 1 month after AMI) electrocardiogram was 79 +/- 33 ms. There were no significant correlations between QT dispersion and peak creatine phosphokinase levels, LV ejection fraction, and regional wall motion in the infarct region at 1 month after AMI (r = 0.06, p = 0.57; r = 0.11, p = 0.29; r = -0.05, p = 0.63, respectively). In conclusion, the findings of this study suggest that QT dispersion on the resting electrocardiogram at 1 month after anterior wall AMI is unrelated to infarct size estimated by the peak creatine phosphokinase level and the degree of LV dysfunction.

QT interval dispersion and autonomic modulation in subjects with anxiety

This study was designed to assess Q-T interval dispersion as a marker of electrical instability in subjects with anxiety. Recent observations have shown that the presence of anxiety symptoms increases the risk of sudden death. The Kawachi anxiety questionnaire identified 29 subjects (male/female ratio 13:16) who scored 0, 22 subjects (male/female ratio 14:8) who scored 1, and 37 subjects (male/female ratio 13:24) who scored 2 or more. In all subjects we measured electrocardiographic interlead QT dispersion and autonomic function through spectral analysis of R-R interval and blood pressure variabilities and left ventricular mass. Compared with subjects who scored 0, those reporting 2 or more symptoms showed increased heart rate-corrected QT dispersion (54.9+/-1.7 ms vs. 34.9+/-3.2 ms, P<.001), sympathetic modulation (normal logarithm low-frequency power/high-frequency power 0.59+/-0.1 vs. 0.12+/-0.04, P<.05), and left ventricular mass (120.7+/-3.5 g/m2 vs. 97.9+/-2.8 g/m2, P<.001). Probably because it augments sympathetic activity, anxiety causes left ventricular mass to increase and, like hypertension, increases heart rate-corrected Q-T interval dispersion. The consequent electrical instability could be the substrate responsible for inducing fatal ventricular arrhythmias.

QT dispersion is not related to infarct size or inducibility in patients with coronary artery disease and life threatening ventricular arrhythmias

OBJECTIVE

To relate QT parameters to infarct size and inducibility during electrophysiological studies.

DESIGN

Analysis of a prospective register.

SETTING

University hospital.

PATIENTS

64 patients with coronary artery disease and documented life threatening ventricular arrhythmias.

INTERVENTIONS

Measurements of QT-max, QTc-max, and QT dispersion (QT-d) on a simultaneous 12 lead ECG (50 mm/s). Estimation of myocardial infarct size with radionuclide left ventricular ejection fraction (LVEF), echocardiography (left ventricular end diastolic diameter, LVEDD), and a defect score based on a quantitative stress redistribution 201-thallium perfusion study. Electrophysiological study to assess inducibility.

RESULTS

Mean (SD) QT parameters were: QT-max 440 (50) ms, QTc-max 475 (46) ms, and QT-d 47 (20) ms. Mean (SD) estimates of infarct size were: LVEF 34 (13)%, LVEDD 61 (9) mm, and defect score 18 (11). There was no significant correlation between any index of infarct size and QT parameters. QT parameters were not significantly different between patients with inducible (n = 57) and non-inducible arrhythmias (n = 7) (QT-max: 416 (30) v 443 (51) ms, p = 0.18; QTc-max 485 (34) v 473 (47) ms, p = 0.34; QT-d 47 (12) v 47 (21) ms, p = 0.73). Non-inducible patients had a significant lower defect score: 8 (9) v 19 (11), p = 0.02, but comparable LVEF: 38 (12)% v 34 (12)%, p = 0.58, and LVEDD: 54 (10) v 61 (8) mm, p = 0.13.

CONCLUSIONS

QT parameters are not influenced by infarct size and do not predict inducibility during electrophysiological study in patients with coronary artery disease and malignant ventricular arrhythmias. In contrast, the amount of scar tissue determined by perfusion imaging is strongly correlated with inducibility.

Relation between QT dispersion and adenosine triphosphate stress thallium-201 single-photon emission computed tomographic imaging for detecting myocardial ischemia and scar

It is not known if QT dispersion is useful for detecting coronary artery disease. We investigated whether QT dispersion at baseline and during adenosine triphosphate (ATP) infusion correlate with the imaging patterns obtained from ATP stress thallium-201 single-photon emission computed tomography (ATP-SPECT). QT dispersion was determined in 169 patients who underwent ATP-SPECT from 12-lead electrocardiograms obtained at baseline and 3 minutes after the beginning of ATP infusion. Based on the results of ATP-SPECT, patients were divided into 4 groups: normal (n = 55), ischemia (n = 38), ischemia and scar (n = 42), and scar (n = 34). Baseline QT dispersions (mean +/- SD) in the normal, ischemia, ischemia and scar, and scar groups were 48 +/- 15, 50 +/- 17, 69 +/- 25, and 70 +/- 24 ms, respectively. Baseline QT dispersion was significantly greater in the groups with myocardial scar. QT dispersions during ATP infusion were 43 +/- 16, 63 +/- 20, 76 +/- 20, and 62 +/- 25 ms in the normal, ischemia, ischemia and scar, and scar groups, respectively. QT dispersion increased with ATP infusion in patients with myocardial ischemia. QT dispersion at baseline and during ATP infusion correlated with the ATP-SPECT imaging pattern. These findings suggest that baseline QT dispersion and ATP-induced changes in QT dispersion may help detect the presence of myocardial ischemia and scar.

QT dispersion in patients with Duchenne-type progressive muscular dystrophy

BACKGROUND

A high degree of QT dispersion is a risk factor for arrhythmic sudden death in patients with myocardial infarction and cardiomyopathy. Duchenne-type progressive muscular dystrophy (DMD) is also associated with the development of ventricular arrhythmias. The purpose of this study was to determine the relationship between QT interval dispersion and ventricular arrhythmias in patients with DMD.

METHODS

Sixty-seven patients with DMD were studied. Standard 12-lead electrocardiograms and 24-hour Holter electrocardiograms were recorded, and the QT interval was determined in every lead of the standard electrocardiogram to determine the QT dispersion. QT dispersion was compared with the frequency of ventricular arrhythmias and the severity of skeletal muscle damage on the basis of the Swinyard and Deaver 8-stage scale.

RESULTS

QT dispersion in all 67 patients averaged 54 +/- 18 ms. The QT dispersion was 49 +/- 16 ms in stage 5 patients, 61 +/- 22 ms in stage 6 patients, 52 +/- 17 ms in stage 7 patients, and 56 +/- 17 ms in stage 8 patients. Ventricular arrhythmias of Lown grade III or higher were observed in 3 of 35 patients with QT dispersion <60 ms and in 14 of 32 patients with QT dispersion >/=60 ms. Logistic regression analysis demonstrated that QT dispersion is an independent risk factor for ventricular arrhythmias of grade III or higher in patients with DMD.

CONCLUSIONS

The incidence of ventricular arrhythmias of Lown grade III or higher was greater in patients with QT dispersion >/=60 ms than in patients with QT dispersion >60 ms. QT dispersion therefore is a risk factor for serious ventricular arrhythmias in patients with DMD.

QT dispersion and late potentials during doxorubicin therapy for non-Hodgkin's lymphoma

OBJECTIVES

To investigate effects of doxorubicin therapy on cardiac electrophysiology, with special emphasis on QT dispersion and late potentials, in lymphoma patients.

DESIGN

Prospective study.

SETTING

University hospital.

SUBJECTS

Twenty-eight adult non-Hodgkin's lymphoma patients who received doxorubicin to a cumulative dose of 400-500 mg m-2.

MAIN OUTCOME MEASURES

Standard 12-lead electrocardiogram (ECG) and signal-averaged ECG (SAECG) recordings were performed at baseline and after cumulative doxorubicin doses of 200, 400 and 500 mg m-2.

RESULTS

Heart rate-corrected QT interval (QTc) increased from 402 +/- 4 to 416 +/- 5 ms (P = 0.002) during the study period. QT dispersion (variability in QT interval duration amongst the different leads of the standard 12-lead ECG) increased from 24.1 +/- 2.5 to 35.0 +/- 2.8 ms (P = 0.041) and QTc dispersion increased from 26.5 +/- 2.5 to 39.0 +/- 3.5 ms (P = 0.039). Five patients (18%) developed QT dispersion exceeding 50 ms. In addition, two patients (7%) developed late potentials during doxorubicin therapy. The changes in QTc duration, QT dispersion and late potentials occurred independently of the impairment of left ventricular function.

CONCLUSIONS

Prolongation of QTc, increased QT dispersion and development of late potentials are indicative of doxorubicin-induced abnormal ventricular depolarization and repolarization. QT dispersion and late potentials are both known to be associated with increased risk of serious ventricular dysrhythmias and sudden death in various cardiac diseases. Thus, follow-up of these parameters might also be useful in assessing the risk of late cardiovascular events in cancer patients treated with anthracyclines.

Ramipril reduces QT dispersion in patients with acute myocardial infarction and heart failure

In a cohort of 67 patients from the Acute Infarction Ramipril Efficacy study, we showed that ramipril therapy was associated with a significant reduction in QT dispersion over a 2-month period after acute myocardial infarction. This reduction of ventricular repolarization inhomogeneity indicates an antiarrhythmic effect and may be an important additional mechanism for the reduced all-cause mortality and sudden death incidence achieved with angiotensin-converting enzyme inhibition after acute myocardial infarction.

Which strategy is "best" after myocardial infarction? The Beta-blocker Strategy plus Implantable Cardioverter Defibrillator Trial: rationale and study design

The Beta-blocker Strategy plus Implantable Cardioverter Defibrillator (BEST-ICD) Trial is a multicenter prospective randomized trial that started in June 1998, in 95 centers in Italy and Germany. The trial will test the hypothesis whether, in high-risk post myocardial infarction (MI) patients already treated with beta blockers, electrophysiologic study (EPS)-guided therapy (including the prophylactic implantation of implantable cardioverter defibrillator [ICD] in inducible patients) will improve survival compared with conventional therapy. Patients eligible for the study are survivors of recent MI (> or = 5 and < or = 21 days), aged < or = 80 years, with left ventricular ejection fraction < or = 35% and > or = 1 of the following additional risk factors: (1) ventricular premature beats > or = 10/hour; (2) decreased heart rate variability (standard deviation of unusual RR intervals < 70 msec); and (3) presence of ventricular late potentials. Furthermore, all enrolled patients must be able to tolerate at least 25 mg of metoprolol per day. These patients constitute about 9% of all patients with recent MI and are expected to have a 2-year all-cause mortality > 25% of which 50% is anticipated to be from sudden death. The main criteria of exclusion from the study are (1) a history of sustained ventricular arrhythmia; (2) documentation of nonsustained ventricular tachycardia during the screening phase; and (3) the need for myocardial revascularization and contraindications or intolerance to beta-blocker therapy. Eligible patients will be randomized to 2 different therapeutic strategies: conventional strategy or EPS/ICD strategy. Patients allocated to the EPS/ICD strategy will undergo further risk stratification, and electrophysiologically inducible patients (approximately 35%) will receive prophylactic ICDs, in addition to the conventional therapy, whereas noninducible patients will be only conventionally treated. The primary endpoint of the study will be death from all causes. By hypothesizing a 30% reduction in the 2-year mortality (from 20% to 14%) in the EPS/ICD group compared with conventionally treated patients, 1,200 patients will have to be included. A triangular, 2-sided sequential design with preset boundaries, for a 5% significance level and 90% power to detect a reduction in 2-year mortality from 20% to 14%, will be used to permit early termination of the trial if the strategy is found to be efficacious, no difference, or inefficacious.

QT dispersion in patients with chronic heart failure: beta blockers are associated with a reduction in QT dispersion

OBJECTIVE

To compare QT dispersion in patients with impaired left ventricular systolic function and in matched control patients with normal left ventricular systolic function.

DESIGN

A retrospective, case-control study with controls matched 4:1 for age, sex, previous myocardial infarction, and diuretic and beta blocker treatment.

SETTING

A regional cardiology centre and a university teaching hospital.

PATIENTS

25 patients with impaired left ventricular systolic function and 100 patients with normal left ventricular systolic function.

MAIN OUTCOME MEASURES

QT and QTc dispersion measured by three methods: the difference between maximum and minimum QT and QTc intervals, the standard deviation of QT and QTc intervals, and the "lead adjusted" QT and QTc dispersion.

RESULTS

All measures of QT/QTc dispersion were closely interrelated (r values 0.86 to 0.99; all p < 0.001). All measures of QT and QTc dispersion were significantly increased in the patients with impaired left ventricular systolic function v controls (p < 0.001): 71.9 (6.5) (mean (SEM)) v 46.9 (1.7) ms for QT dispersion, and 83.6 (7.6) v 54.3 (2.1) ms(-1-2) for QTc dispersion. All six dispersion parameters were reduced in patients taking beta blockers (p < 0.05), regardless of whether left ventricular function was normal or impaired-by 9.4 (4.6) ms for QT dispersion (p < 0.05) and by 13.8 (6. 5) ms(-1-2) for QTc dispersion (p = 0.01).

CONCLUSIONS

QT and QTc dispersion are increased in patients with systolic heart failure in comparison with matched controls, regardless of the method of measurement and independently of possible confounding factors. beta Blockers are associated with a reduction in both QT and QTc dispersion, raising the possibility that a reduction in dispersion of ventricular repolarisation may be an important antiarrhythmic mechanism of beta blockade.

QT dispersion and early arrhythmic risk during acute myocardial infarction

It has been suggested that QT dispersion (maximal minus minimal QT interval calculated on a standard 12-lead electrocardiogram) could reflect regional variations of ventricular repolarization and could provide a substrate for reentry ventricular arrhythmias. The present study evaluates QT dispersion in patients with acute myocardial infarction, assessing its relation with early severe ventricular arrhythmias and some clinical features. Three hundred three patients with acute myocardial infarction and a control group of 297 healthy subjects were studied. QT and QTc dispersion were determined on the electrocardiogram taken after 12 hours and on days 3 and 10 after symptoms onset and on the electrocardiogram taken in the control group. The average values of QT and QTc dispersions (ms) were as follows: 70.5 +/- 42.5-87 +/- 45.6 (12th hour), 66.7 +/- 37.6-76.8 +/- 43.6 (day 3), 68.8 +/- 42.7-76.8 +/- 42.8 (day 10), versus 43 +/- 13.2-53.9 +/- 16.2 (control group). There were statistically significant differences between QT and QTc dispersion recorded in normal subjects and in each of the three electrocardiograms taken in patients with infarction. A greater QT dispersion was recorded in patients with anterior infarction (78.9 +/- 38.5 vs 64.9 +/- 42.8 in inferior/lateral infarction). In the first 3 days QT dispersion was not different in patients treated and untreated with thrombolysis, whereas on day 10 it was greater in untreated patients (74.9 +/- 45.3 vs 60.5 +/- 37.2). Creatine kinase peak level did not influence QT dispersion. In the first 72 hours of infarction, 37 patients developed ventricular fibrillation or sustained ventricular tachycardia. Higher early values of QT and QTc dispersion were found in patients who developed severe ventricular arrhythmias (107.8 +/- 62 and 124.8 +/- 67.5 ms) than in patients without serious arrhythmias (62.9 +/- 32.2 and 80.1 +/- 37.9 ms). These data suggest that: (1) QT dispersion increased during acute myocardial infarction. (2) The values were higher in the early hours and fell late after infarction with thrombolysis. (3) Greater QT dispersion is associated with severe ventricular arrhythmias.

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.

Irbesartan reduces QT dispersion in hypertensive individuals

Angiotensin type 1 receptor antagonists have direct effects on the autonomic nervous system and myocardium. Because of this, we hypothesized that irbesartan would reduce QT dispersion to a greater degree than amlodipine, a highly selective vasodilator. To test this, we gathered electrocardiographic (ECG) data from a multinational, multicenter, randomized, double-blind parallel group study that compared the antihypertensive efficacy of irbesartan and amlodipine in elderly subjects with mild to moderate hypertension. Subjects were treated for 6 months with either drug. Hydrochlorothiazide and atenolol were added after 12 weeks if blood pressure (BP) remained uncontrolled. ECGs were obtained before randomization and at 6 months. A total of 188 subjects (118 with baseline ECGs) were randomized. We analyzed 104 subjects who had complete ECGs at baseline and after 6 months of treatment. Baseline characteristics between treatments were similar, apart from a slight imbalance in diastolic BP (irbesartan [n=53] versus amlodipine [n=51], 99.2 [SD 3. 6] versus 100.8 [3.8] mm Hg; P=0.03). There were no significant differences in BP normalization (diastolic BP <90 mm Hg) between treatments at 6 months (irbesartan versus amlodipine, 80% versus 88%; P=0.378). We found a significant reduction in QT indexes in the irbesartan group (QTc dispersion mean, -11.4 [34.5] milliseconds, P=0.02; QTc max, -12.8 [35.5] milliseconds, P=0.01), and QTc dispersion did not correlate with the change in BP. The reduction in QT indexes with amlodipine (QTc dispersion, -9.7 [35.4] milliseconds, P=0.06; QTc max, -8.6 [33.2] milliseconds, P=0.07) did not quite reach statistical significance, but there was a correlation between the change in QT indexes and changes in systolic BP. In conclusion, irbesartan improved QT dispersion, and this effect may be important in preventing sudden cardiac death in at-risk hypertensive subjects.

Relation between QT dispersion and slow intraventricular conduction in patients with acute anterior wall myocardial infarction

BACKGROUND

QT dispersion has been proposed as a simple, noninvasive measure for identifying patients at risk of postinfarction arrhythmia. It is assumed to reflect nonuniform ventricular repolarization, which, in turn, may result from regional differences in repolarization time as well as from localized activation delay. The aim of this study was to examine the relation between QT dispersion and intraventricular conduction abnormalities in patients with acute anterior wall myocardial infarction.

METHODS AND RESULTS

Standard 12-lead electrocardiographic and 12-lead signal-averaged electrocardiographic recordings were performed in 25 patients with a first Q-wave anterior wall myocardial infarction. Measures calculated by using the 6 precordial (V1 through V6) leads for QT dispersion were (1) difference between maximum and minimum QT and QTc intervals and (2) standard deviation of QT and QTc intervals. Measures calculated from the signal-averaged electrocardiogram were (1) maximum filtered QRS duration; (2) mean; and (3) standard deviation of filtered QRS duration. No relation was found between any measure of filtered QRS duration and that of QT dispersion by using linear correlation analysis. Similarly, no significant association was demonstrated between the filtered QRS duration and corresponding QT interval measurements (total 131 leads).

CONCLUSIONS

The lack of correlation between signal-averaged electrocardiogram indexes of slow intraventricular conduction and electrocardiogram variables of QT dispersion suggests an independent predictive value for the 2 methods in identifying patients at risk of postinfarction arrhythmia. This suggestion is further supported by the finding that altered activation sequence is an unlikely mechanism of QT dispersion in patients with acute myocardial infarction, as indicated by the lack of association between the filtered QRS duration and corresponding QT interval measurements.

Using simulated noise to define optimal QT intervals for computer analysis of ambulatory ECG

The ambulatory electrocardiogram (ECG) is an important medical tool, not only for diagnosis of adverse cardiac events, but also to predict the risk of such events occurring. The 24-hour ambulatory ECG has certain problems and drawbacks because the signal is corrupted by noise from various sources and also several other conditions which may alter the ECG morphology. We have developed a Windows based program for the computer analysis of ambulatory ECG which attempts to address these problems. The software includes options for importing ECG data, different methods of waveform analysis, data-viewing, and exporting the extracted time series. In addition, the modular structure allows for flexible maintenance and expansion of the software. The ECG was recorded using a Holter device and oversampled to enhance the fidelity of the low sampling rate of the ambulatory ECG. The influence of different sampling rates on the interval variability were studied. The noise sensitivity of the implemented algorithm was tested with several types of simulated noise and the precision of the interval measurement was reported with SD values. Our simulations showed that, in most of the cases, defining the end of QT interval at the maximum of the T wave gave the most precise measurement. The definition of the onset of the ventricular repolarization duration is most precisely made on the maximum or descending maximal slope of the R wave. We also analyzed some examples of time series from patients using power spectrum estimates in order to validate the low level QT interval variability.

Prognosis in myocardial infarction survivors with left ventricular dysfunction is predicted by electrocardiographic RR interval but not QT dispersion

OBJECTIVES

The aim of the study was to assess if QT dispersion and RR interval on the standard 12-lead electrocardiogram (ECG) predict cardiac death and late arrhythmic events in postinfarction patients with low left ventricular ejection fraction (LVEF). QT dispersion on a standard electrocardiogram (ECG) is a measure of repolarization inhomogeneity, but its prognostic meaning in myocardial infarction (MI) survivors is unclear, especially in patients with left ventricular dysfunction. RR interval has been shown to predict mortality in post-MI patients, but its prognostic power has not been compared with other noninvasive risk factors.

METHODS

Retrospective cohort study. Ninety patients were identified, from a series of 547 consecutive postinfarction patients admitted to our institution for phase II cardiac rehabilitation, as having a LVEF of <0.40 at two-dimensional echocardiography (mean LVEF 0.35+/-0.04; range 0.20-0.39). QT dispersion and RR interval were analyzed on the admission 12-lead electrocardiogram, 20+/-10 (range 8-45) days after MI, using specially designed software. Additional risk markers were collected from clinical variables, signal-averaged ECG and Holter recording.

RESULTS

During 24+/-18 (range 1-63) months of follow-up, 10 of 90 patients (11%) died, all from cardiac causes, and there were 18 late arrhythmic events, defined as sudden death or the occurrence of a sustained ventricular arrhythmia > or =5 days after the index MI. QT interval and dispersion were not significantly prolonged in patients who died compared to survivors and not significantly different between patients with and without arrhythmic events. Mean RR interval from standard ECG was significantly shorter in patients with both cardiac death (682+/-99 vs. 811+/-134 ms; P=0.004) and arrhythmic events (720+/-100 vs. 818+/-139 ms; P=0.006). A Cox proportional hazards model identified RR interval from standard ECG (P<0.001) and a history of more than one MI (P=0.002) as significant predictors of cardiac death independent of thrombolytic therapy, LVEF, filtered QRS complex duration at signal-averaged ECG, mean RR and its standard deviation at 24-h Holter monitoring.

CONCLUSIONS

Measurement of QT interval and dispersion 3 weeks after MI has no prognostic power in patients with LV dysfunction after a recent MI. RR interval on standard 12-lead ECG is as good a prognostic indicator as other, more expensive, noninvasive markers. These findings may be relevant in this era of limited health care resources.

QT dispersion and risk factors for sudden cardiac death in patients with hypertrophic cardiomyopathy

This study examines the relation of QT dispersion (QTd) on a surface electrocardiogram (ECG) to clinical features and established risk factors of sudden cardiac death (SCD) in patients with hypertrophic cardiomyopathy (HC). One hundred fifty-six consecutive patients with HC (91 men, mean age 41+/-15 years, range 7 to 79) and 72 normal subjects (41 men, mean age 39+/-9 years, range 20 to 60) were studied. Standard 12-lead ECGs were recorded from each subject using a MAC VU electrocardiograph. Patients with nonsinus rhythm, atrioventricular conduction block, QRS duration > 120 ms, age < 15 years, and low amplitude T waves were excluded from the analysis (n=51). Another 22 patients who were receiving amiodarone and/or sotalol therapy were also excluded. QT interval and QTd were measured using automated analysis in the remaining 83 patients (46 men, age 40+/-14 years, range 16 to 76). QT interval (406+/-38 ms), QTc interval (432+/-27 ms), and QTd (43+/-25 ms) were significantly greater in patients with HC than in normal controls (386+/-31 ms, 404+/-16 ms, 26+/-16 ms, respectively) (p <0.0001). QTd was significantly greater in patients with HC with chest pain compared with asymptomatic or mildly symptomatic patients (50+/-28 ms vs 37+/-20 ms, p=0.02). Increased QTd was found in patients with dyspnea New York Heart Association functional classes II/III than in those with dyspnea New York Heart Association functional class I (50+/-27 ms vs 38+/-22 ms, p=0.04). QTd was weakly correlated with maximum left ventricular wall thickness (r=0.228, p=0.038). No significant association was found between QTd and any risk factors for SCD. Thus, patients with HC have increased QTd. The QTd correlates with symptomatic status. Assessment of QTd might provide complementary clinical characterization of patients with HC but its relation to SCD remains uncertain.

Long-term outcome and prognostic determinants in children with hypertrophic cardiomyopathy

OBJECTIVES

We sought to determine clinical, angiographic, and echocardiographic predictors of survival in children with isolated hypertrophic cardiomyopathy (HCM) in a large pediatric centre.

BACKGROUND

Sudden death is a catastrophic outcome of HCM in childhood but has been difficult to predict. Current therapies might provide for improved outcome if factors identifying high risk can be identified.

METHODS

Records of 99 patients diagnosed with HCM from 1958 to 1997 at <18 yr were reviewed for clinical, angiographic (n = 62) and echocardiographic (n = 83) predictors of survival outcome. The effects of clinical characteristics on sudden death (including resuscitated sudden death) were individually tested in Cox's proportionate hazard modeling.

RESULTS

Seventy-one subjects were male. Median age at diagnosis was 5.0 yr with a medical follow-up interval of 4.8 yr. Thirty-seven of 97 patients had a family history of HCM. Ambulatory electrocardiograms (ECG) in 78 patients demonstrated supraventricular tachycardia in 16 and ventricular tachycardia in 21. Death or resuscitated sudden death occurred in 18 patients. Sudden death rate was 2.7%/yr after age 8 yr. Cox's proportionate survival modeling revealed increased corrected QT interval (QTc) dispersion on ECG (relative risk [RR] 1.61 per 20 ms increment, p < 0.0003), ventricular tachycardia (VT) on ambulatory ECG (RR 3.75, p < 0.006) and myocardial bridging of the LAD coronary (RR 12.0, p < 0.003) to be associated with reduced time to death or resuscitated sudden death.

CONCLUSIONS

Detailed assessment of ECGs, ambulatory ECGs, and coronary angiography can assist in identifying which children with HCM are at risk for sudden death.

Increased QT dispersion in the absence of QT prolongation in patients with Behcet's disease and ventricular arrhythmias

In Behcet's disease, prominent clinical manifestations include involvement of mucocutaneous, ocular, gastrointestinal, respiratory, neurologic, urogenital, articular and cardiovascular systems. Patients with Behcet's disease have higher incidence of ventricular arrhythmia than healthy subjects. However there is a little information about the mechanism of ventricular arrhythmias in Behcet's disease. The aim of the study was to investigate whether dispersion of ventricular repolarisation was an arrhythmogenic mechanism. QT dispersion parameters were measured in 73 Behcet patients and QT dispersion was defined as the difference between the maximum and minimum QT interval in any of the 12 leads of surface electrocardiogram. Corrected QT dispersion for heart rate was calculated by Bazett's formula. The results were compared with the data from 51 matched controls without a history of cardiac disease. We found QT dispersion was greater in Behcet patients (58+/-12 vs. 37+/-8 ms, P=0.001) as was corrected QT dispersion (81+/-14 vs. 52+/-11 ms, P=0.001). There was no significant difference in minimum or maximum QT intervals between Behcet patients and controls (P>0.05). We found a correlation between QT dispersion and grade of premature ventricular complexes (r=0.7, P=0.002). Our findings suggest that increased dispersion of repolarisation may account for the development of ventricular arrhythmias in Behcet's disease.

Comparison of ECG variables of dispersion of ventricular repolarization with direct myocardial repolarization measurements in the human heart

INTRODUCTION

QT dispersion (QTD) from the 12-lead ECG has been widely adopted as a noninvasive index of dispersion of ventricular repolarization (DVR). QTD, however, has never been validated by direct comparison with myocardial DVR in the human heart.

METHODS AND RESULTS

Monophasic action potential (MAP) recordings obtained in an earlier study were retrospectively matched with 12-lead ECGs available from within 24 hours of the invasive procedure. MAPs were available from an average of 8+/-3 left endocardial sites in 4 patients with left ventricular hypertrophy (LVH) and 7 patients with normal ECGs, and 6+/-2 epicardial sites in 3 patients of each group during normal ventricular activation. Local repolarization time (RT) was determined as MAP duration at 90% repolarization plus the local activation time. Dispersion of RT was calculated as the difference between the earliest and latest RT. ECGs were digitized and analyzed with recently described interactive QTD analysis software. In addition to standard QTD (defined as QTmax-QTmin), all currently proposed ECG dispersion variables were compared and correlated with the invasive measurements of DVR. QTD exhibited a reasonable correlation with dispersion of RT (R = 0.67; P < 0.01). Several other variables designed to measure DVR exhibited a similar, but not better, correlation. Among them, the QT peak/QT end ratio in V3 (R = -0.72; P < 0.01) and averaged over all analyzable leads (R = -0.59; P < 0.01) exhibited a good correlation with dispersion of RT, which was further improved when endocardial measurements were considered alone. T area measures did not correlate with dispersion of RT, but discriminated LVH.

CONCLUSION

DVR can be assessed by means of a 12-lead surface ECG. Several of the variables under study exhibit a similar accuracy in determination of true myocardial dispersion of repolarization. Variables involving the terminal part of repolarization, such as the QT peak/QT ratio, even from a single lead, may add to the determination of DVR from the human heart.

Regression of left ventricular hypertrophy results in improvement of QT dispersion in patients with hypertension

OBJECTIVES

Increased QT dispersion has been considered as predisposing to ventricular arrhythmias in hypertrophic cardiomyopathy, congestive heart failure, and coronary artery disease. An increased QT dispersion has also been found in hypertensive patients with left ventricular hypertrophy (LVH). The data on the effect of LVH regression on QT dispersion are limited.

METHODS AND RESULTS

To assess the relation of LVH regression and QT dispersion decrease, 68 patients (42 men and 26 women, mean age 56.3+/-9.5 years) with uncomplicated essential hypertension were studied. All underwent full electrocardiographic and echocardiographic studies at baseline and after 6 months of monotherapy, 29 with angiotensin-converting enzyme inhibitors and 39 with calcium antagonists. QT dispersion was calculated by subtracting the shortest QT from the longest QT, in absolute value (QTmax - QTmin). It was also corrected with Bazett's formula (QTc dispersion). Left ventricular mass index was assessed according to the Devereux formula. After treatment, LVH decreased with both angiotensin-converting enzyme inhibitors (from 155 to 130 g/m2, P < .001) and calcium antagonists (156 to 133/92/m2, P < .001). QT dispersion decreased both after angiotensin-converting enzyme inhibitor treatment (from 82 to 63 ms) and calcium antagonist treatment (from 77 to 63 ms, both P < .001 ). There was a significant correlation of QT dispersion and left ventricular mass after therapy (r = 0.36, P < .005). There was a correlation of the degree of LVH and QT dispersion decrease (r = 0.27, P < .05).

CONCLUSIONS

It is concluded that LVH regression influences AQT favorably. Its prognostic value has yet to be determined.

Myocardial bridging in children with hypertrophic cardiomyopathy--a risk factor for sudden death

BACKGROUND

Myocardial bridging may cause compression of a coronary artery, and it has been suggested that myocardial ischemia may result. The clinical significance and prognostic value of myocardial bridging of the left anterior descending coronary artery in children with hypertrophic cardiomyopathy are unknown. We sought to determine the prevalence and clinical effects of myocardial bridging in children with hypertrophic cardiomyopathy who underwent cardiac catheterization.

METHODS

Angiograms from 36 children with hypertrophic cardiomyopathy were reviewed to determine whether myocardial bridging was present and, if so, to assess the characteristics of systolic narrowing of the left anterior descending coronary artery caused by myocardial bridging and the duration of residual diastolic compression. We also reviewed clinical data on these patients.

RESULTS

Myocardial bridging was present in 10 (28 percent) of the patients. Compression of the left anterior descending coronary artery persisted for a mean (+/-SD) of 50+/-17 percent of diastole. As compared with patients without bridging, patients with bridging had a greater incidence of chest pain (60 percent vs. 19 percent, P=0.04), cardiac arrest with subsequent resuscitation (50 percent vs. 4 percent, P=0.004), and ventricular tachycardia (80 percent vs. 8 percent, P<0.001). On average, the patients with bridging had a reduction in systolic blood pressure with exercise of 17+/-27 mm Hg, as compared with an elevation of 43+/-31 mm Hg in those without bridging (P<0.001). The patients with bridging also had greater ST-segment depression with exercise (median, 5 vs. 0 mm, P=0.004) and a shorter duration of exercise (mean, 6.6+/-2.4 vs. 9.1+/-1.4 minutes, P=0.008). The degree of dispersion of the QT interval corrected for heart rate on the electrocardiogram was greater in patients with bridging than in those without bridging (104+/-46 vs. 48+/-31 msec, P=0.002). Kaplan-Meier estimates of the proportions of patients who had not died or had cardiac arrest with subsequent resuscitation five years after the diagnosis of hypertrophic cardiomyopathy were 67 percent among patients with bridging and 94 percent among those without bridging (P=0.004).

CONCLUSIONS

Myocardial bridging is associated with a poor outcome in children with hypertrophic cardiomyopathy. Our observations suggest that bridging is associated with myocardial ischemia

Magnetocardiographic QT interval dispersion in postmyocardial infarction patients with sustained ventricular tachycardia: validation of automated QT measurements

QT dispersion is a measure of heterogeneity in ventricular repolarization. Increased ECG QT dispersion is associated with life-threatening ventricular arrhythmias. We studied if magnetocardiographic (MCG) measures of QT dispersion can separate postmyocardial infarction patients with and without susceptibility to sustained VT. Manual dispersion measurements were compared to a newly adapted automatic QT interval analysis method. Ten patients with a history of sustained VT (VT group) and eight patients without ventricular arrhythmias (Controls) were studied after a remote myocardial infarction. Single-channel MCGs were recorded from 42 locations over the frontal chest area and the signals were averaged. QT dispersion was defined as maximum-minimum or standard deviation of measured QT intervals. VT group showed significantly more QT and JT dispersion than Controls. QTapex dispersions were 127 +/- 26 versus 83 +/- 21 ms (P = 0.004) and QTend dispersions 130 +/- 37 versus 82 +/- 37 ms (P = 0.013), respectively. Automatic method gave comparable values. Their relative differences were 9% for QTapex and 27% for QTend dispersion on average. In conclusion, increased MCG QT interval dispersion seems to be associated with a susceptibility to VT in postmyocardial infarction patients. MCG mapping with automated QT interval analysis may provide a user independent method to detect nonhomogeneity in ventricular repolarization.

QT dispersion may be a useful adjunct for detection of myocardial infarction in the chest pain center

BACKGROUND

QT dispersion has been proposed as a noninvasive measurement of the degree of inhomogeneity in myocardial repolarization. Increased QT dispersion has been reported after myocardial infarction. We hypothesized that increased QT dispersion may be a useful adjunct for risk stratification in patients being evaluated in a chest pain center.

METHODS AND RESULTS

Patients were admitted to the chest pain center for evaluation of chest pain. Exclusion criteria included (1) systolic blood pressure <90 mm Hg, (2) ischemia or infarction on the initial electrocardiograph (ECG), (3) elevated creatine kinase or MB fraction, and (4) chest pain associated with cocaine use. Serial creatine kinase and MB levels and ECGs were obtained at 0, 6, and 9 hours. Patients were monitored for (1) creatine kinase and MB rise, (2) ECG changes for infarction, (3) ST-segment changes, and (4) rest angina. A negative evaluation at the chest pain center led to an exercise stress test. Patients with a positive exercise stress test were admitted for further evaluation and patients with a negative exercise stress test result were discharged home. Patients were divided into 3 groups. Group 1 consisted of patients who were found to have an acute myocardial infarction (AMI), group 2 consisted of patients with prior history of coronary artery disease but no evidence of AMI, and group 3 consisted of patients without prior coronary artery disease or AMI. QT dispersion was measured on the initial ECG in all patients. A total of 586 patients were evaluated. Group 1 consisted of 13 patients with mean QT dispersion of 44.6+/-18.5 ms, group 2 consisted of 267 patients with a mean QT dispersion of 10.0+/-13.8 ms, and group 3 consisted of 303 patients with a mean QT dispersion of 10.5+/-10.0 ms. Analysis of variance showed a significantly higher QT dispersion in patients who had AMI compared with other patients with chest pain (P< .001).

CONCLUSIONS

QT dispersion can be a useful diagnostic adjunct for detection of AMI in patients with chest pain with a normal ECG and normal cardiac enzymes.

Increased QT dispersion in patients with vasospastic angina

BACKGROUND

The risk factors for ventricular arrhythmias in patients with coronary vasospasm have not been identified. We evaluated QT dispersion in patients with vasospastic angina and its relation to susceptibility to ventricular arrhythmias during myocardial ischemia and reperfusion.

METHODS AND RESULTS

We assessed the corrected QT (QTc) dispersion before induction of coronary artery spasm by intracoronary injection of acetylcholine (baseline) and 30 minutes after administration of isosorbide dinitrate in 50 patients with vasospastic angina and 50 patients with atypical chest pain. The baseline QTc dispersion was significantly greater in patients with vasospastic angina than in patients with atypical chest pain (mean+/-SD: 69+/-24 versus 44+/-19 ms, 95% confidence interval of mean difference [CI]: 16 to 33 ms; P<0.001). QTc dispersion decreased significantly, to 48+/-15 ms (CI: 15 to 26 ms; P<0.001 versus baseline), after administration of isosorbide dinitrate in patients with vasospastic angina but did not change significantly in patients with atypical chest pain (mean+/-SD: 41+/-17 ms, CI: -3 to 9 ms). During the provocation test, 24 of 50 patients with vasospastic angina experienced ventricular arrhythmias. The baseline QTc dispersion was significantly greater in patients with than without ventricular arrhythmias (mean+/-SD: 77+/-23 versus 61+/-19 ms, CI: 4 to 26 ms; P<0.05).

CONCLUSIONS

Patients with vasospastic angina exhibited an increased baseline QTc dispersion compared with patients with atypical chest pain, which suggests that inhomogeneity of repolarization and susceptibility to ventricular arrhythmias are increased in patients with vasospastic angina, even when asymptomatic. The association between increased QTc dispersion and ventricular arrhythmias during the provocation test suggests that measurement of QT dispersion may help predict which patients with vasospastic angina are at high risk for ventricular arrhythmias during ischemia.

Effects of postmyocardial infarction scar size, cardiac function, and severity of coronary artery disease on QT interval dispersion as a risk factor for complex ventricular arrhythmia

The aim of the study was to determine the relation between QT dispersion and ventricular arrhythmia after myocardial infarction, as well as the effects of postinfarction scar size, cardiac function, and severity of coronary artery disease on QT dispersion. Three hundred three patients, 3 months after myocardial infarction, and a group of 21 healthy subjects were evaluated. QT dispersion was the difference between maximal and minimal QT interval in 12-ECG leads. Postinfarction scar size was determined by Selvester's QRS scoring system. Cardiac function was evaluated by echocardiography and exercise stress test, and the severity of coronary artery disease by the number and degree of coronary artery stenoses. QT dispersion increased significantly in relation to the severity of arrhythmia (< 50 premature ventricular complexes vs ventricular tachycardia; 61.6 [+/- 12.3] vs 84.8 [+/- 16.4] ms, P < 0.001). QT dispersion > 80 ms was associated with ventricular tachycardia with the sensitivity of 68% and specificity of 88%. QT dispersion also increased significantly, dependent on the postinfarction scar size (0% vs > or = 33% of left ventricular myocardium; 61.8 [+/- 16.4] vs 74.7 [+/- 16] ms, P < 0.001), as well as in the case of significantly impaired cardiac function. Although QT dispersion increased with the number of diseased vessels and the degree of stenoses, the differences were not significant (P > 0.05). In conclusion, QT dispersion is a risk marker of complex ventricular arrhythmia in the chronic stage of myocardial infarction. Multiple regression analysis indicates that only the postinfarction scar size has an independent effect on QT dispersion (R2 = 0.39, P < 0.05).

Different Effects of Amiodarone and Quinidine on the Homogeneity of Myocardial Refractoriness in Patients With Intraventricular Conduction Delay

BACKGROUND: Increases in QT and JT dispersion have been suggested as indicative of a proarrhythmic potential as a result of heterogeneity in myocardial refractoriness, the reduction of which by antiarrhythmic agents might be associated with a beneficial effect on the development of serious ventricular arrhythmias. METHODS: To test the hypothesis that amiodarone reduces the heter-ogeneity of ventricular refractoriness to a significantly greater extent than quinidine in patients with intraventricular conduction defects under treatment for ventricular arrhythmias, the corrected and uncorrected QT and JT intervals and dispersions from 12-lead surface electrocardiograms were determined in 120 patients with intraventricular conduction defects with cardiac arrhythmias before and during treatment with amiodarone (n = 60) and quinidine (n = 60). RESULTS: Amiodarone increased QT from 403 +/- 50 ms to 459 +/- 47 ms (P <.001), with a similar increase in the corrected QT interval (QTc) (P <.001). Amiodarone reduced QT dispersion by 40% (P <.001), whereas quinidine increased by 18% (P <.001). The net effects of both drugs were similar for OTc. Amiodarone, but not quinidine, reduced heart rate significantly; amiodarone had no effect on the QRS; but quinidine increased if (P <.001). Quinidine as well as amiodarone increased the JT and JTc intervals significantly, but the effect of quinidine was qualitatively less striking. Amiodarone decreased the JT dispersion by 33% (P <.001) and JTc dispersion by 37% (P <.001). On the other hand, quinidine increased the corresponding values for JT and JTc by 18% (P <.001) and 21% (P <.001), respectively. The overall data on QT and JT dispersion indicate an improvement in the homogeneity of myocardial refractoriness with amiodarone treatment and the converse with quinidine treatment; this observation is consistent with a lower proarrhythmic propensity and mortality with amiodarone than with quinidine. Quinidine increased the QRS interval more than amiodarone, and the data indicate that in patients with intraventricular conduction defects, the monitoring of the JT interval might more accurately reflect changes in myocardial repolarization. CONCLUSIONS: Amiodarone and quinidine both increased the corrected and uncorrected QT and JT intervals; amiodarone decreased and quinidine increased the dispersion of these intervals, and these results suggested an improvement in the homogeneity of myocardial refractoriness as a result of amiodarone treatment and the converse as a result of quinidine treatment. Quinidine increased the QTS interval more than amiodarone, and the data indicate that in patients with intraventricular conduction defects, the monitoring of the JT interval might more accurately reflect changes in myocardial repolarization.

Assessment of QT dispersion for prediction of mortality or arrhythmic events after myocardial infarction: results of a prospective, long-term follow-up study

BACKGROUND

Risk stratification by means of analysis of QT dispersion (QTD) in the 12-lead surface ECG is under intense investigation in various patient populations. The aim of the present prospective study was to evaluate the prognostic value of QTD and other ECG variables reflecting dispersion of ventricular repolarization in comparison with established risk stratifiers during long-term follow-up in a large cohort of post-myocardial infarction patients treated according to contemporary therapeutic guidelines.

METHODS AND RESULTS

In 280 consecutive infarct survivors, the 12-lead ECG was optically scanned and digitized for analysis of QTD (QTmax-QTmin) and 25 other repolarization variables, including recently developed and validated parameters such as the T peak-to-T end interval and the area under the T wave. In addition, a variety of established risk stratifiers were assessed. After a mean follow-up period of 32+/-10 months, 30 patients reached one of the prospectively defined study end points (death, ventricular tachycardia, or resuscitated ventricular fibrillation). Comparisons between event and nonevent patients by means of Kaplan-Meier event probability analyses revealed that none of the ECG dispersion variables were of discriminative value. In contrast, variables such as left ventricular ejection fraction (P=0.007), mean 24-hour heart rate (P=0.022), or heart rate variability (P=0.007) proved to be potentially useful risk stratifiers in this patient population. On multivariate analysis, only LVEF, heart rate variability, and a history of thrombolysis were independent predictors of outcome.

CONCLUSIONS

Determination of QTD from the surface ECG even when performed with the best available methodology failed to predict subsequent risk in this large series of infarct survivors.

Electrocardiographic measures of ventricular repolarisation dispersion in patients with coronary artery disease susceptible to ventricular fibrillation

OBJECTIVE

To study electrocardiographic measures of ventricular repolarisation dispersion in patients prone to ventricular fibrillation compared with controls matched for the extent of coronary heart disease and the use of beta blockers.

DESIGN

A case-control study.

SETTING

Cardiovascular laboratory of a tertiary referral centre.

PATIENTS

Fifty patients with documented ventricular fibrillation not associated with acute myocardial infarction, and their controls matched for sex, age, number of diseased coronary vessels, left ventricular ejection fraction, previous myocardial infarction and its location, and the use of beta blockers.

MAIN OUTCOME MEASURES

Electrocardiographic measures of QT, JT, and Tend interval dispersions in a 12 lead electrocardiogram.

RESULTS

The ventricular fibrillation patients compared to controls showed increased mean (SD) QTapex dispersion (53 (18) ms v 44 (18) ms, respectively; p < 0.01) and mean (SD) Tend dispersion (46 (17) ms v 38 (15) ms, respectively; p < 0.05).

CONCLUSIONS

Increased QTapex and Tend dispersions are associated with a susceptibility to ventricular fibrillation even when the extent of the coronary heart disease and use of beta blockers are taken into consideration. However, because of a considerable overlap between the groups, measures of QT dispersion assessed from a 12 lead electrocardiogram do not provide clinically useful information for identification of patients at risk of sudden cardiac death.

Multivariate associates of QT dispersion in patients with acute myocardial infarction: primacy of patency status of the infarct-related artery. TEAM-3 Investigators. Third trial of Thrombolysis with Eminase in Acute Myocardial Infarction

BACKGROUND

QT dispersion (QTd; QT interval maximum minus minimum) has been shown to reflect regional variations in ventricular repolarization and is increased in patients with life-threatening ventricular arrhythmias.

METHODS

To determine correlates of QTd in patients who had had myocardial infarction (MI), 207 patients (158 men, aged 57 +/- 11 years) with acute MI who were treated with alteplase or anistreplase within 2.7 +/- 0.9 hours of symptom onset were studied. Angiograms at a median of 27 hours after thrombolysis showed reperfusion (Thrombolysis in Myocardial Infarction grade > or =2) in 184 (88%) patients. QT was measured in 10 +/- 2 leads on discharge electrocardiograms with a computerized analysis program interfaced with a digitizer. Associations of QTd with 24 variables related to patient characteristics, acute MI, angiography, interventions, and radionuclide ventriculography were evaluated by univariate and multivariate regression.

RESULTS

Univariate associations with QTd (p < or = 0.10) were Thrombolysis in Myocardial Infarction flow grade 0/1 versus 2/3 (QTd = 75 +/- 33 msec vs 53 +/- 22 msec, p < 0.0001), minimal luminal diameter (p = 0.007), left ventricular ejection fraction at discharge (p = 0.007), reinfarction (p = 0.01), number of leads with ST elevation (p = 0.05), end-systolic volume at discharge (p = 0.04), time to peak creatine kinase (p = 0.06), and YST elevation (p = 0.10). Independent associates of QTd were Thrombolysis in Myocardial Infarction grade 0/1 versus 2/3 (p < 0.0001), reinfarction (p = 0.005), and ejection fraction (p = 0.02).

CONCLUSIONS

Successful thrombolysis is associated with less QTd in patients after acute MI. Our results support the hypothesis that QTd after MI depends on reperfusion status, reinfarction, and left ventricular function. Reduction in QTd may be an additional mechanism by which the benefit of thrombolytic therapy is realized.

QT interval dispersion: dispersion of ventricular repolarization or dispersion of QT interval?

The QT interval (QTI) has long been useful as a clinical index of the duration of ventricular repolarization, particularly as a marker of prolonged repolarization and its well-established association with arrhythmogenic cardiac states. Likewise, inhomogeneity (dispersion) of repolarization has been linked definitively to increased susceptibility to reentrant arrhythmias. Recent studies have reported the use of QTI dispersion as a meaningful clinical index to identify patients at risk, but the interpretation of the measurement has been controversial. A Langendorff-perfused, isolated canine heart suspended in a torso-shaped, electrolytic tank filled with NaCl-sucrose solution was used to investigate the relationship between body surface QTIs and ventricular repolarization measured directly from the cardiac surface by using activation-recovery intervals, which have been documented to reflect the duration of local action potentials as well as local refractory periods. The data showed poor correlation between cardiac surface activation-recovery intervals and QTIs, as well as the insensitivity of QTIs to regional repolarization shortening in the presence of prolonged repolarization elsewhere. Furthermore, the data confirmed that torso tank QTI dispersion does not reflect directly the full range of measured ventricular repolarization inhomogeneity. It is concluded that body surface QTI dispersion is not a reliable index of repolarization dispersion.

Cellular basis for QT dispersion

The cellular basis for the dispersion of the QT interval recorded at the body surface is incompletely understood. Contributing to QT dispersion are heterogeneities of repolarization time in the three-dimensional structure of the ventricular myocardium, which are secondary to regional differences in action potential duration (APD) and activation time. While differences in APD occur along the apicobasal and anteroposterior axes in both epicardium and endocardium of many species, transitions are usually gradual. Recent studies have also demonstrated important APD gradients along the transmural axis. Because transmural heterogeneities in repolarization time are more abrupt than those recorded along the surfaces of the heart, they may represent a more onerous substrate for the development of arrhythmias, and their quantitation may provide a valuable tool for evaluation of arrhythmia risk. Our data, derived from the arterially perfused canine left ventricular wedge preparation, suggest that transmural gradients of voltage during repolarization contribute importantly to the inscription of the T wave. The start of the T wave is caused by a more rapid decline of the plateau, or phase 2 of the epicardial action potential, creating a voltage gradient across the wall. The gradient increases as the epicardial action potential continues to repolarize, reaching a maximum with full repolarization of epicardium; this juncture marks the peak of the T wave. The next region to repolarize is endocardium, giving rise to the initial descending limb of the upright T wave. The last region to repolarize is the M region, contributing to the final segment of the T wave. Full repolarization of the M region marks the end of the T wave. The time interval between the peak and the end of the T wave therefore represents the transmural dispersion of repolarization. Conditions known to augment QTc dispersion, including acquired long QT syndrome (class IA or III antiarrhythmics) lead to augmentation of transmural dispersion of repolarization in the wedge, due to a preferential effect of the drugs to prolong the M cell action potential. Antiarrhythmic agents known to diminish QTc dispersion, such as amiodarone, also diminish transmural dispersion of repolarization in the wedge by causing a preferential prolongation of APD in epicardium and endocardium. While exaggerated transmural heterogeneity clearly can provide the substrate for reentry, a precipitating event in the form of a premature beat that penetrates the vulnerable window is usually required to initiate the reentrant arrhythmia. In long QT syndrome, the trigger is thought to be an early afterdepolarization (EAD)-induced triggered beat. The likelihood of developing EADs and triggered activity is increased when repolarizing forces are diminished, making for a slower and more gradual repolarization of phases 2 and 3 of the action potential, which translates into broad, low amplitude and sometimes bifurcated T waves in the electrocardiogram. Our findings suggest that regional differences in the duration of the M cell action potential may be the basis for QT dispersion measured at the body surface under normal and long QT conditions. The data indicate that the interval delimited by the peak and the end of the T wave represents an accurate measure of regional dispersion of repolarization across the ventricular wall and as such may be a valuable index for assessment of arrhythmic risk. The presence of low amplitude, broad and/or bifurcated T waves, particularly under conditions of long QT syndrome, is indicative of diminished repolarizing forces and may represent an independent variable of arrhythmic risk, forecasting the development of EAD-induced triggered beats that can precipitate torsade de pointes. Although the QT interval, QT dispersion, the T wave peak-to-end interval, and the width and amplitude of the T wave often change in parallel, they contain different information and should not be expected to be e

Dispersions of the QT interval in postmyocardial infarction patients presenting with ventricular tachycardia or with ventricular fibrillation

Increased QT interval dispersion is associated with ventricular arrhythmias. The aim of this study was to examine if in postmyocardial infarction patients with impaired left ventricular function, increased QT dispersion is associated with ventricular tachycardia (VT) and ventricular fibrillation (VF). Measures of QT dispersion, calculated as maximum-minimum (D) and standard deviation (SD) of QTend, QTapex, JTend, JTapex, and Tend intervals in the 12-lead electrocardiogram, were compared in patients who late after myocardial infarction experienced sustained VT (VT group) only, VF (VF group) only, or had no ventricular arrhythmias (controls). The 25 patients in each group were individually matched for age, gender, number of diseased coronary vessels, location of the previous myocardial infarction, and left ventricular ejection fraction. Dispersion measures of QTend, QTapex, and JTapex intervals separated VT group from controls, but none of the measures separated the VF group from controls. QTendD was 49+/-18 ms in controls, 57+/-18 ms in the VF group (controls vs VF group, p = NS), and 65+/-29 ms in the VT group (controls vs VT group, p <0.05). VT group had increased QTapexSD, JTapexSD, and JTapexD compared with the VF group. The cycle length of induced sustained monomorphic VT, present in 19 VT and 19 VF patients, correlated with several dispersion indexes in the VT group, but not with those in the VF group. Thus, in postmyocardial infarction patients with a severely damaged left ventricle, increased QT dispersion is associated with susceptibility to sustained VT, but not to VF.

Increased QT dispersion and other repolarization abnormalities as a possible cause of electrical instability in isolated aortic stenosis

The aim of our study was to analyze the ventricular repolarization phase in patients with isolated aortic stenosis (AS) in order to search for possible abnormalities that might contribute to an explanation of the electrical instability peculiar to this valve disease. We selected a population of 39 patients with isolated AS (25 M and 14 F, mean age 60+/-16 yrs). As controls we considered a group of 31 age-matched healthy subjects 20 M and 11 F, mean age 55+/-14 yrs, P=NS. Disease severity was assessed by echocardiography, calculating the maximum and mean pressure gradients max and mean PG) and the functional valve orifice area. Various electrocardiographic intervals (QT, QT'c, JT, JTc) and indices (QT and QTc dispersion were adopted for a detailed non-invasive evaluation of the ventricular repolarization. In patients with AS, M-QT (391+/-45 ms vs 362+/-25 ms, P=0.002), M=QTc (431+/-29 ms vs 412+/-19 ms, P=0.003), M-JT (290+/-41 ms vs 265+/-26 ms, P=0.003, M-JTc 331+/-29 ms vs 302+/-19 ms, P<0.001, QTD (67+/-34 ms vs 40+/-15 ms, P<0.001), QTcD (77+/-36 ms vs 52+/-23 ms, P<0.001) all resulted significantly greater than in controls. QTD and QTcD both resulted linearly related either to max PCi (r=0.388, P=0.018 and r=0.357, P=0.03) or to mean PG (r=0.513, P=0.004 and r=0.438, P=0.015), while M-JT and M-JTc turned out to be directly related only to mean PG (r=0.436, P=0.016 and r=0.483, P=0.007). Our findings suggest a prolonged duration of ventricular recovery and a greater dispersion of ventricular repolarization in patients with AS and might account for the electrical instability proper to this valve dysfunction. Besides, the existence of a linear direct relation between the severity of AS and the degree of inhomogeneity of left ventricular recovery, together with the correlation found among mean PCr and the total duration of the repolarization phase, expressed by the intervals JT and JTc, strongly suggest the hypothesis that in AS arrhythmogenic substrates development parallels the worsening of the valve defect.

JT dispersion in Wolff-Parkinson-White syndrome: effect of eccentric ventricular depolarization on the dispersion of repolarization

There is much interest in QT dispersion for noninvasive risk stratification of patients at risk of arrhythmias. However, little is known about the genesis of abnormal QT dispersion. In particular, whether eccentric ventricular depolarization, as seen in preexcitation, can lead to abnormal dispersion of repolarization is unknown. We studied 24 children aged 1-19 years (mean +/- SD, 11 +/- 5 years) with manifest preexcitation due to Wolff-Parkinson-White syndrome who had successful catheter ablation. Standard ECGs done preablation, early postablation (< 1 week), mid postablation (> 1 week, < 2 months), and late postablation (> 2 months) were reviewed. The QRS duration prior to ablation ranged from 90-160 ms (mean +/- SD, 123 +/- 21 ms). On the preablation ECG, the JT and JTc dispersions showed no relationship to the QRS duration (r = 0.04 and 0.07, respectively). There was no change in JT dispersion when the preablation (42 +/- 15 ms) ECG was compared to early (43 +/- 15 ms), mid (44 +/- 13 ms), and late postablation (48 +/- 19 ms) ECGs. There was no significant change in JTc dispersion as well. Thus, JT dispersion is unrelated to QRS duration and unaffected by catheter ablation in patients with Wolff-Parkinson-White syndrome. Eccentric ventricular depolarization does not lead to abnormal dispersion of repolarization.

Exercise-induced changes in the QT interval duration and dispersion in patients with sudden cardiac death after myocardial infarction

BACKGROUND

Prolongation of the QT interval and increased QT dispersion have been proposed to be associated with arrhythmic risk after myocardial infarction. However, controversy remains regarding the prognostic value of ventricular repolarization abnormalities in the risk stratification of patients surviving acute myocardial infarction. HYPOTHESIS AND OBJECTIVE: The QT interval is sensitive to myocardial ischaemia, and exercise-induced ischaemia may change the QT interval regionally, resulting in increased QT dispersion. This study examined whether there are abnormalities of ventricular repolarization during exercise and whether assessment of the exercise-induced changes in QT interval duration and dispersion would be able to differentiate patients at high risk from those at low risk of sudden cardiac death after myocardial infarction.

METHODS

Twenty-six post-myocardial infarction patients (mean age 54.5+/-8.9 years, 22 men) were retrospectively studied. Thirteen patients who died suddenly (SCD patients) during a follow-up of 39+/-6 months were compared to 13 patients who remained event-free, i.e. no ventricular tachyarrhythmias, no reinfarction, no by-pass (MI survivors). The two groups were pair-matched for age, gender, site of infarction, left ventricular ejection fraction and use of beta blocker. A further 13 patients with chest pain, normal coronary arteriograms and negative exercise test results were studied as controls. They were age and gender matched with the post-infarction patients. A 12-lead exercise ECG was recorded from each patient before, during and after exercise. QT and RR interval were measured on the exercise ECGs at each stage and QT dispersion was defined as the difference between the maximum and minimum QT intervals across the 12-lead ECG.

RESULTS

There were no significant differences in RR, QT and QTc (Bazett's and Fridericia's correction) intervals, or QT dispersion between any groups before exercise. A significant difference in QT and QT dispersion was found at peak exercise between post-infarction patients and controls (P=0.03 and P=0.0001, respectively), but no difference was observed between SCD patients and MI survivors. The maximum QTc at peak exercise was longer in SCD patients compared with MI survivors (P=0.02) and a maximum QTc>440 ms (Bazett's correction) was common in SCD patients but not in MI survivors or controls (62%, 15%, 15%, P=0.01). The differences in QT, QTc or QT dispersion observed at peak exercise were no longer significant after exercise.

CONCLUSIONS

Exercise-induced prolongation of the QTc interval differentiates patients at high risk of sudden cardiac death from those at low risk, whereas exercise-induced changes in QT dispersion failed to identify patients at high risk of sudden cardiac death after myocardial infarction.

Effect of exercise-induced ischemia on QT interval dispersion

An increased spatial dispersion of ventricular repolarization duration (QT dispersion) is associated with an increased vulnerability to arrhythmias. This study was designed to examine the effect of exercise on QT dispersion in ischemic heart disease (IHD). QT dispersion, corrected QT dispersion, and percentage change in uncorrected and corrected QT dispersion between rest and peak exercise were examined in 14 members of a control group, 17 patients with IHD, and 14 patients with IHD who were receiving beta-blockers (IHD-B). All subjects had undergone a standard Bruce protocol exercise test, and QT intervals were measured at rest and peak exercise with a digitizing tablet interfaced to a personal computer. QT dispersion at rest was markedly increased in the IHD group compared with that in the control and IHD-B groups, respectively (corrected QT dispersion in milliseconds), 74 +/- 7, 40 +/- 4, 49 +/- 5, p < 0.03). The corrected QT dispersion at peak exercise was greater in the IHD group compared with that in the control group (57 +/- 5 vs 26 +/- 3 msec, p < 0.03). The percentage change in QT dispersion with exercise was significantly higher in the IHD group (52% +/- 5%) compared with that in both the control group (28% +/- 4%, p < 0.002) and the IHD-B group (30% +/- 3%, p < 0.01). A larger mean QT dispersion at peak exercise and an increased percentage change in QT dispersion with exercise may help explain the increased susceptibility of the IHD group for arrhythmias. The cardioprotective action of beta-blockers may be explained by their blunting effect on exercise-related changes in QT dispersion.

Occurrence of sustained increase in QT dispersion following exercise in patients with residual myocardial ischemia after healing of anterior wall myocardial infarction

Our objective was to evaluate the effect of exercise on QT dispersion over the next 3 hours, as seen on a standard 12-lead electrocardiogram in patients with healed myocardial infarction with or without residual ischemia. We measured QT and QTc dispersion before, immediately after, and 1 and 2 hours after symptom-limited, dynamic treadmill exercise tests in 28 patients with healed anterior wall myocardial infarction with (group I, n = 18) and without (group II, n = 10) residual ischemia. The same protocol was followed in 5 group I patients after successful performance of coronary angioplasty. QT and QTc dispersion did not change immediately after exercise in group II. These parameters increased in group I (QT dispersion at rest [mean +/- SD] 57 +/- 22 ms, and after exercise 87 +/- 27 ms; QTc dispersion at rest 62 +/- 25 ms, and after exercise 114 +/- 36 ms). The increases in QT and QTc dispersion were sustained for at least 2 hours. After a successful coronary angioplasty in 5 patients, these parameters no longer increased with exercise. Thus, QT dispersion increased for at least 2 hours after exercise in patients who had residual ischemia after healing of myocardial infarction. Data obtained in 5 of these patients after coronary angioplasty support the idea that residual ischemia plays a key role in the sustained increase in QT dispersion after exercise.