Magnetocardiographic QT dispersion during cardiovascular autonomic function tests (original) (raw)
Journal of Electrocardiology, 2000
Changes in autonomic tone modulate QT interval duration. How cardiovascular autonomic reflexes affect QT dispersion, a suggested marker of arrhythmia risk, is not well established. We studied 10 healthy young adult volunteer men during quiet and deep breathing, the Valsalva maneuver, sustained handgrip, hyperventilation, the cold pressor test, and mental stress. An automated method was used for measurement of QT-peak and QT-end intervals, and QT dispersion was defined as maximum-minimum of the measured intervals. QT-peak dispersion was greater on deep expiration than deep inspiration (49 Ϯ 20 ms vs 37 Ϯ 14 ms, P Ͻ .05). QT-end dispersion decreased in the tachycardia phase of the Valsalva maneuver (45 Ϯ 23 ms vs 35 Ϯ 21 ms, P Ͻ .05), but QT dispersion did not change during the other interventions. Rapid cardiovascular autonomic reflex adjustment does not change QT dispersion in healthy young adult men. However, large intrathoracic volume and intrathoracic pressure changes during forced respiratory movements might confound QT dispersion measurements.
Computers in Cardiology, 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.
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.
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.
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.
Computerised measurements of QT dispersion in healthy subjects
Heart (British Cardiac Society), 1998
To assess the stability and reproducibility of computerised QT dispersion (QTd) measurement in healthy subjects, as this is presently being incorporated into commercial electrocardiographic systems. 70 healthy volunteers (mean (SD) age 38 (10) years, 35 men, 35 women) with a normal 12 lead electrocardiogram (ECG) were studied. From each subject, 70 ECG recordings were taken using the MAC VU ECG recorder (Marquette). In study A, 50 ECGs were recorded in each subject: 10 supine, 10 sitting, 10 standing, 10 holding breath in maximum inspiration, and 10 holding breath in maximum expiration. After a mean interval of 8 (3) days (range 7 to 23), 10 recordings in supine and 10 in the standing position were repeated in each subject (study B). On measurements made using a research version of the commercial software without manual modification, the reproducibility of QTd was assessed by coefficient of variance (CV) and relative error, and comparisons made with other ECG indices. (1) QTd measur...