High-pass-filtered magnetocardiogram and cardiomyopathy in patients with type 1 diabetes mellitus

Prolonged and/or fractionated depolarization due to tissue degeneration of the ventricular myocardium is a feature of cardiomyopathy. Signal averaged electrocardiography uses high-pass filters of the Butterworth type to quantify, noninvasively, fractionated high-frequency components at the end of the QRS complex. In this study a finite impulse response high-pass filter of the 90th order (cutoff at 37 Hz) was applied to magnetocardiograms (MCGs) and high-resolution electrocardiograms (ECGs) order to quantify high-frequency components throughout the myocardial depolarization. Additionally, late-potential analysis on the signal-averaged ECG was performed. A prospective investigation was made of 23 cardiologically asymptomatic patients, 11 females and 12 males, with type I diabetes mellitus. Their mean age was 21.7 years (range, 13-34 years). The mean duration of diabetes was 14 years (range, 1-27 years). Data were compared with those of 22 control subjects (12 females, 10 males) of mean age, 23.2 years (range, 11-35 years). The ECGs and MCGs were simultaneously recorded and signal-averaged, digitally filtered, and quantified by a score obtained by multiplying the amplitude variation of the signal by the number of maximal/minimal in the QRS complex. Echocardiograms were used to calculate the left ventricular mass and to document the presence of cardiomyopathy. Scores were higher in the MCGs of with type I diabetes mellitus than in the control subjects (P < .001). High scores correlated with an increased left ventricular muscular mass index (P < .05) and duration of the diabetes (P < .05). The high-resolution ECG, processed analogously, showed similar results in relation to left ventricular mass (P = .06) and duration of diabetes (P = .07), respectively (nonsignificant). No late potentials were found. These findings suggest that using a linear-phase high-pass finite impulse response filter may be useful for the noninvasive identification of patients with cardiomyopathy who exhibit possible disturbances of intraventricular depolarization. Our findings also suggest that analysis using the total QRS complex, rather than the final part of the QRS complex only, may improve identification of patients at risk.