Magnetocardiographic QT Interval Dispersion in Postmyocardial Infarction Patients with Sustained Ventricular Tachycardia: Validation of Automated QT Measurements

Abstract

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.

Ambulatory Electrocardiographic Evidence of Transmural Dispersion of Repolarization in Patients With Long-QT Syndrome Type 1 and 2

“…Before determination of the median TPE values (defined later), signal-to-noise ratio was also improved by continuously averaging 5 successive QRST complexes. By use of an algorithm based on a method originally presented by Simson 8 for QRS onset identification and a previously validated algorithm for determination of T-wave fiducial points, 9 we were able to program computerized calculation of the TPE intervals for each normal-labeled QRS complex in the 24-hour recording. The software first determines the QRS onset as the time instant at which the amplitude of the vector magnitude of the 2 high-pass filtered leads exceeds the predefined noise limit.…”

“…In monophasic T waves, the end of the T wave is defined as the time instant at which the steepest tangent after the T-wave apex and the baseline cross. In complex T waves, the second derivative is also used to detect discontinuities after the peak, 9 and the software excludes U waves using the guidelines presented by Lepeschkin and Surawicz. 10 Bifid T waves exhibiting a time interval Յ0.15 second between first and second components were calculated as T waves; otherwise, the second components were considered U waves.…”

Electrocardiographic assessment of left ventricular hypertrophy with time–voltage QRS and QRST-wave areas

“…23,24 The following BSPM indices were calculated in each lead: (1) QRS area by integrating the absolute value of the BSPM signal over the QRS complex.…”

Single-Lead Electrocardiographic Variables in the Detection of Prior Myocardial Infarction with Respect to Q-Wave Status and Infarct Age

“…QRS was divided into four temporally equal segments, referred to as quartiles. T-wave apex and end were determined automatically, as described earlier [26]. The median T-wave end of all leads was used for calculations.…”