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

Carbon monoxide intoxication: What we know

Carbon monoxide (CO) is a toxic, color-, taste- and odorless gas with fatal consequences if undetected. Intoxication caused by CO is frequent possibly leading to a high morbidity and mortality. The disease involves multiple organ systems without a typical clinical presentation. The clinical picture is furthermore unrelated to levels of carboxyhemoglobin - the routine biomarker. Therefore the diagnosis and treatment can be very demanding. This article in detail reviews epidemiology, symptoms, diagnosis and the therapy of this multidisciplinary challenge.

Diagnostic value of magnetocardiography in coronary artery disease and cardiac arrhythmias: a review of clinical data

Despite the availability of several advanced non-invasive diagnostic tests such as echocardiography and magnetic resonance imaging, electrocardiography (ECG) remains as the most widely used diagnostic technique in clinical cardiology. ECG detects electrical potentials that are generated by cardiac electrical activity. In addition to electrical potentials, the same electrical activity of the heart also induces magnetic fields. These extremely weak cardiac magnetic signals are detected by a non-invasive, contactless technique called magnetocardiography (MCG), which has been evaluated in a number of clinical studies for its usefulness in diagnosing heart diseases. We reviewed the basic principles, history and clinical data on the diagnostic role of MCG in coronary artery disease and cardiac arrhythmias.

Correction for heart rate is not necessary for QT dispersion in individuals without structural heart disease and patients with ventricular tachycardia

BACKGROUND

It remains controversial whether QT dispersion should be corrected for heart rate, especially when the limitations of rate correction formulae are considered. We investigated whether incremental atrial pacing affects QT dispersion and the rate-corrected values according to Bazett's formula in individuals without structural heart disease and in patients with history of sustained ventricular tachycardia.

METHODS

We studied 32 individuals without structural heart disease (group A), and 16 patients with a history of sustained ventricular tachycardia (group B). QT dispersion and corrected for heart rate QT dispersion using Bazett's formula (QTc dispersion) were calculated in sinus rhythm, and during continuous right atrial pacing for one minute at 100 and 120 beats/min.

RESULTS

Interobserver variability was not significant (P > or = 0.10). QT dispersion did not differ at rest between groups A and B and did not change significantly from baseline at any heart rate in both groups. However, QTc dispersion increased significantly with atrial pacing in a similar manner in group A and group B (42 +/- 19 ms at rest vs 53 +/- 23 ms at 120 beats/min, P < 0.001 for group A, 39 +/- 16 ms at rest vs 60 +/- 19 ms at 120 beats/min, P < 0.001 for group B).

CONCLUSIONS

We conclude that QT dispersion remains unchanged during atrial pacing at heart rates up to 120 beats/min in both individuals without structural heart disease and in patients with a history of sustained ventricular tachycardia. Correction by Bazett's formula results in prolongation of QTc dispersion, yielding values which may be misleading.

Novel indices of ventricular repolarization to screen post myocardial infarction patients

We propose novel indices of ventricular repolarization intervals, the JTp/JT, Tpe/JTp and Tpe/JT ratios. These indices have been compared with the duration of the ventricular repolarization intervals and other ratios in 17 normal subjects and 17 patients with old myocardial infarction. In the intervals and other ratios, the best separation between groups is obtained with the Tpe/QTp and Tpe/QT ratios with 94% sensitivity and 82% specificity, the proposed ratios increased sensitivity to 100% and specificity to 94%. These indices should be further tested to determine their usefulness in discriminating between OMI patients with and without susceptibility to ventricular arrhythmias.

QT dispersion: an electrocardiographic derivative of QT prolongation

BACKGROUND

QT dispersion has been considered a surrogate for heterogeneity of repolarization, leading to ventricular arrhythmias.

METHODS

High-resolution 12-lead electrocardiograms were obtained in 15 patients with a history of ventricular tachycardia or ventricular fibrillation, 15 patients with congestive heart failure, 17 patients with a history of previous Q-wave myocardial infarction without heart failure, and 23 healthy control subjects.

RESULTS

QTc dispersion was prolonged in all 3 patient groups compared with controls (71+/-22, 68 +/-31, 61+/-27 vs 44+/-17 msec, P =. 003), but no difference was seen between heart disease groups. QTc dispersion was strongly correlated with the QTc max (r = 0.73, P<.0001) but did not correlate with the QTc min (r = 0.04, P =.76). QTc dispersion also strongly correlated with the JTc max (r = 0.54, P<.0001) but did not correlate with JTc min (r = -0.007, P =.95). QTc dispersion correlated inversely with T-wave amplitude (r = -0.35, P =.003). When all 876 electrocardiographic signals were considered, a significant negative correlation was present between QTc duration and T-wave amplitude (r = -0.133, P =.0002). Logistic regression analysis failed to demonstrate any independent risk factors that predicted ventricular arrhythmias, including all measures of dispersion.

CONCLUSIONS

The measurement of QT dispersion is strongly influenced by the maximum QT interval, as well as by changes in T-wave amplitude. QT "dispersion" may represent a summary of these changes that reflect the underlying myocardial process but does not represent an accurate quantitative measure of heterogeneity of refractoriness.