[Magnetcardiographic detection of abnormal intraventricular activation in patients with ischemic heart disease with and without tachycardia]

Fragmented and delayed activation of ventricular myocardium can cause malignant tachyarrhythmias. By detection of ventricular late potentials only a severely delayed depolarisation is registered, but not the intra QRS-activation. The aim of this study was to examine the complete phase of ventricular depolarisation, to detect and to quantify abnormal electrical activation by magnetocardiography and to estimate in a small group of patients with coronary heart disease the prognostic significance.In 26 healthy subjects, 32 patients after myocardial infarction without malignant ventricular arrhythmias and 10 patients with coronary heart disease and a history of sustained, monomorph ventricular tachycardia magnetocardiography was performed in a magnetically shielded room. To quantify the fragmentation of QRS a fragmentation-index (FI) was calculated. Besides signal averaged ECG, in patients with coronary heart disease cardiac catheterisation and in patients with arrhythmias electrophysiological testing was performed. The FI for the three groups was significantly different (p<0,005). The mean FI in the group of healthy subjects was 20,4+/-5,4, in the group of postinfarction-patients without arrhythmias 27+/-12,1 and in the group of patients with coronary heart disease and ventricular arrhythmias 49,5+/-17,9. Dichotomized at 36 the sensitivity was 80%, the specifity 93%, the positive predictive value was 66% and the negative predictive value 96%. The FI was correlated to the extent of regional wall-motion-irregularity and global ejection fraction.Analyzing late potentials, the values for sensitivity and positive predictive value were surprisingly low (20% and 50%, respectively). The specifity was 96%, the negative predictive value was 88%. Calculating the FI on the basis of electrical signals only an insufficient discrimination of the groups was possible.In the follow-up period of two years one post-infarctional patient was resusciated because of ventricular fibrillation. The FI of this patient was 17.One patient with coronary 3-vessel-disease and left ventricular ejection fraction of 50% died due to acute myocardial infarction, his FI was 39.

CONCLUSION

By means of magnetocardiography fragmented ventricular activation in patients with coronary heart disease was demonstrated even within the QRS-complex and could be correlated to ventricular tachyarrhythmias.

Magnetocardiographic mapping of QRS fragmentation in patients with a history of malignant tachyarrhythmias

BACKGROUND

The identification of patients at increased risk for ventricular tachycardia or ventricular fibrillation (VT/VF) and sudden cardiac death has consequences for therapeutic options and thus may reduce mortality in patients with coronary artery disease (CAD).

HYPOTHESIS

We hypothesized that the intra-QRS fragmentation in magnetocardiographic recordings is increased in patients with CAD and with a history of VT/VF.

METHODS

Multichannel magnetocardiography (MCG) was carried out in 34 healthy controls, 42 patients with CAD without a history of VT/VF, and 43 patients with CAD and with a history of VT/VF. The intra-QRS fragmentation was quantified by a new fragmentation score. Its spatial distribution was investigated using two-dimensional (2-D) contour maps according to the sensor position of the 49-channel magnetogradiometer.

RESULTS

Patients with CAD and with a history of VT/VF had significantly increased QRS fragmentation compared with patients with CAD without VT/VF or controls (72.9+/-37.5, 48.5+/-14.3, and 42.5+/-7.8, respectively: p <0.05). The area of high fragmentation in 2-D contour maps was twice as large in patients with than in those without a history of VT/VF (represented by the number of MCG channels with high fragmentation: 26.3+/-15.5 vs. 12.4+/-9.9, p<0.0001). Patients prone to VT/VF could be identified with a sensitivity of 64% and a specificity of 90%.

CONCLUSION

In patients with CAD and with a history of VT/VF, intra-QRS fragmentation is increased and the area of high fragmentation in 2-D contour maps is enlarged. These findings may be helpful in identifying patients with CAD at risk for malignant tachyarrhythmias.

Localization of a ventricular tachycardia-focus with multichannel magnetocardiography and three-dimensional current density reconstruction

The objective of this case report is to determine the accurate localization of a malignant ventricular tachycardia (VT) focus by combining multichannel magnetocardiographic (MCG) information with morphologic data. The localization was obtained by calculating the three-dimensional current density distribution (3D-CDD) on the left ventricular surface. To estimate the accuracy of this localization technique, examinations of a healthy volunteer were additionally performed. The MCG-signals were recorded in a magnetically shielded room by a 49-channel magnetogradiometer. The corresponding morphologic information was recorded by magnetic resonance tomography (MRT). The coordinate systems were matched with the help of markers. The 3D-CDD was calculated by the Philips CURRY software package. The origin of a malignant VT determined by X-ray images of the ablation catheter position during the electrophysiological examination (EPE), was used as the gold standard. This was then compared with the localization results obtained by the 3D-CDD. It was found that the localization coordinates showed a difference of less than 10 mm.

Magnetocardiographic analysis of the two-dimensional distribution of intra-QRS fractionated activation

The spatial distribution of high-frequency components in magnetic signals during the QRS complex of the human heartbeat was investigated. Cardiomagnetic signals were recorded simultaneously using 49 first-order magnetogradiometer channels of a multi-SQUID system with a low noise power density. The QRS fragmentation score S, as a measure of the fragmentation of the bandpass-filtered QRS complex, was examined for its sensitivity and specificity to discriminate 34 healthy volunteers, 42 post-myocardial infarction patients and 43 patients with coronary heart disease and with a history of malignant sustained ventricular tachycardia or ventricular fibrillation. The multichannel information was visualized by two-dimensional mapping of the score values of the single channels. By averaging the score values for the seven central channels, S7, the score values of all 49 channels, S49, and calculating the standard deviation for all 49 channels, D49, a higher sensitivity and specificity for detecting patients with ventricular tachycardia (VT) or ventricular fibrillation (VF) was reached than by analysis of a single channel. Combination of these parameters furnishes a sensitivity of 90% and a specificity of 70% for identifying patients prone to VT/VF. The results were compared with diagnostic information obtained from the QRS duration of the signal as well as with results obtained by modified QRS integral mapping.