Effect of averaging for the automatic measurement of QT dispersion using multichannel magnetocardiography and 12 Lead ECG (original) (raw)
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Computers in Cardiology, 2004, 2004
Multichannel magnetocardiograms (MCGs) and 12lead ECGs were recorded simultaneously using the PTB multichannel SQUID system from 8 normal volunteers. An automatic method for QT interval measurement was used to determine T wave end with measurements made over 10 consecutive beats in both the MCG and ECG. Channels/leads with small absolute T wave amplitudes and smallest and longest QT measurements were excluded from the analysis. QT dispersion, expressed as the QT interval range, was calculated for a single beat and the average QT interval for each channel/lead over 10 beats. Mean QT dispersion measurement (standard deviation) for the single beat was 44 (26) ms for MCG and 37 (35) ms for ECG over all subjects. Averaging over 10 beats reduced mean QT dispersion to 36.1 (14.6) ms for MCG and 20.9 (13.2) ms for ECG. QT dispersion in the MCG was greater than in the ECG, by 7 ms for the single beat and by 15 ms (p < 0.03) for averaged data over all subjects. Averaging influenced ventricular dispersion measurements in both MCG and ECG waveforms. There were differences in dispersion of ventricular repolarisation time between ECG and MCG, with MCG significantly greater than ECG for averaged data.
Magnetocardiographic QT dispersion during cardiovascular autonomic function tests
Basic Research in Cardiology, 2000
QT dispersion is considered to reflect nonhomogeneity of ventricular repolarization. The autonomic nervous system modulates QT interval duration, but the effect may not be spatially homogenous. Magnetocardiography (MCG) registers the weak magnetic fields generated by myocardial electric currents with high localizing accuracy. We studied the effects of rapid cardiovascular autonomic nervous adjustment on QT dispersion in MCG. Ten healthy male volunteers were monitored during deep breathing, the Valsalva maneuver, sustained handgrip, hyperventilation, the cold pressor test and mental stress. 67 MCG channels and 12 ECG leads were recorded simultaneously. A computer algorithm was used for QT interval measurements. QT dispersion was defined as maximum-minimum or standard deviation of the QT peak and QT end intervals. In MCG the QT end dispersion increased during deep inspiration compared with deep expiration (96 ± 19 ms v 73 ± 27 ms, p = 0.05). Magnetic QT dispersion tended to increase during the bradycardia phase of the Valsalva maneuver, but the change was obvious only for QT end (55 ± 26 ms v 76 ± 29 ms, p < 0.05). Other tests had no significant effect on QT dispersion, not even the cold pressor test, although it causes strong sympathetic activation. Magnetic and electric QT peak and QT end intervals correlated closely (r = 0.93 and 0.91), whereas the QT dispersion measures showed no correlation. In conclusion, magnetic QT dispersion is not modified by rapid changes in autonomic tone, but maneuvers involving deep respiratory efforts and changes in ventricular loading affect QT dispersion measurements.
Journal of Cardiovascular Electrophysiology, 2000
QT dispersion (QTd, range of QT intervals in 12 KCG leads) is thought to reflect spatial heterogeneity of ventricular refractoriness. However, QTd may be largely due to projections of the repolarization dipole rather than "nondipolar" signals. Methods and Results: Seventy-eight normal snhjects (47 ± 16 years, 23 women), 68 hypertrophie cardiomyopathy patients (HCM; 38 ± 15 years. 21 women), 72 dilated cardiomyopathy patients (DCM; 48 ± 15 years, 29 women), and 81 survivors of acute myocardial infarction (AMI; 63 ± 12 years, 20 women) had digital 12-lead resting supine ECGs recorded (10 FXGs recorded in each suhject and results averaged). In each ECG lead, QT interval was measured under operator review by QT Guard (GE Marquette) to ohtain QTd. QTd was expressed as the range, standard deviation, and highest-to-lowest quartile difference of QT interval in all nieasurahle leads. Singular value decompositicm transferred ECGs into a minimum dimensional time orthogonal space. The first three components represented the ECG dipole; other components represented nondipolar signals. The power of the T wave nondipolar within the total components was computed to measure spatial repolarization heterogeneity (relative T wave residuum, TWR). QTd was 33.6 ± 18.
Pacing and Clinical Electrophysiology, 1998
OIKARINEN, L., ET AL.: 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 ECC 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 MCCs 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. QT,,p,.^ dispersions were 127 ± 26 versus 83 ± 21 ms (P = 0.004) and QT^nd dispersions 130 ± 37 versus 82 ± 37 ms (P = 0.013), respectively. Automatic method gave comparable values. Their relative differences were 9% for QTapex anof 27% for QT^^d dispersion on average. In conclusion, increased MCC QT interval dispersion seems to be associated with a susceptibility to VT in postmyocardial infarction patients. MCC mapping with automated QT interval analysis may provide a user independent method to detect nonhomogeneity in ventricular repolarization.
Journal of Cardiothoracic and Vascular Anesthesia, 1999
This study investigated changes in spatial distribution of QT duration in patients with and without coronary artery disease (CAD) using magnetocardiography. Thirty-six-channel magnetocardiograms (MCGs) were registered at rest and under stress in 15 patients with chest pain, seven of whom had significant coronary stenosis. QT dispersion (QTd) was calculated for MCG and 12-lead electrocardiogram (ECG) under both conditions. For MCG, homogeneity of repolarization was measured using a smoothness index (SI). Also, at each registration site, the intraindividual difference between QT at rest and under stress was determined (AQT). QTd values as determined by standard 12-lead configurations were not significantly different between groups. MCG QTd values were significantly higher in the CAD group at rest only when all available channels were taken into consideration (P < .05); SI values differed significantly between groups under both conditions (rest, P < .005; stress, P < .01). Good separation between groups was possible using the range of AQT (P < .05) and SI (AQT) (P < .005). Consideration of the spatial distribution of QTd increases its sensitivity in the detection of CAD, suggesting that CAD involves complex changes in repolarization, not apparent in limited lead sets such as standard 12-lead configurations. Key words: spatial QT dispersion, coronary artery disease, stress, magnetocardiography.
An Overview of QT Dispersion Finding in Cardiac Patients,Review Article
The Egyptian Journal of Hospital Medicine, 2021
Background: QT duration represents the time of the whole summated electric cardiac ventricular activity involving stepwise depolarization followed by repolarization. There has been a long history of using the surface electrocardiogram (ECG) to identify ventricular repolarization problems. The 1960s were a turning point for precise mathematical methodologies. It has been customary in clinical practice to use only the QT interval and the polarity and shape of the T wave when evaluating cardiac repolarization using an electrocardiogram (ECG). This terminology, such as "non-specific ST segment and T wave variations are widely used. An earlier theory on interlead disparities in QTI length was resurrected in a 1990 report by the group led by Professor John Campbell. The "QT dispersion" range of durations was proposed as a measure of ventricular recovery time spatial dispersion. Objective: Determine the relevance of QTd in prediction of myocardial and its severity. Conclusion: For cardiac patients, QTd is an easy-to-use, rapid, affordable, and helpful tool for helping with study interpretation, clinical management, and therapeutic orientation.