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Magnetocardiography

Multi-channel magnetocardiography (MCG) is potentially useful for noninvasively evaluating cardiac activation with high spatio-temporal resolution. Since 2007, MCG has been introduced into Laboratory of Clinical Physiology in our hospital as an advanced diagnostic modality for heart diseases. However, advantages specific for MCG use remains to be poorly defined. MCG is not yet accepted as a routine diagnostic tool. Our research for a few years has disclosed that MCG enables us to sensitively detect and evaluate cardiac electrophysiologic abnormalities, which is undetectable with use of conventional ECG.

(1) Non-invasive visualization of electrical propagations in left ventricle

We, for the first time, noninvasively visualized two separate electrical propagations in the left ventricle (LV) arising from left anterior and posterior fascicles with MCG sensors placed close to anterior, posterior, and left lateral chest wall. Moreover, we occasionally recognized apparently abnormal conduction and conduction delay by MCG in heart failure patients with severe LV dysfunction but with normal QRS duration on ECG. These findings suggest that MCG can be a powerful tool for assessing intraventricular electrical dyssynchrony and evaluating conduction abnormalities responsible for the genesis of malignant ventricular arrhythmia in patients with heart failure.

References:

  1. Kawakami S, Takaki H, Oishi S, Sato H, Shimizu W, Kamakura S, Sugimachi M. A novel magnetocardiographic approach for estimating the whole ventricular activation with use of 3-directional measurements. Eur Heart J. 2010;31,265 (ESC2010, Abstract)
  2. Kawakami S, Takaki H, Sato H, Shimizu W, Kamakura S, Sugimachi M. A novel magnetocardiographic approach for estimating the whole ventricular activation with use of 3-directional recordings Circulation. 2010;122:A13636 (AHA2010, Abstract)

(2) Detection of"peripheral" intraventricular conduction disturbance in patients with heart failure and with CLBBB on ECG

We can hardly infer how the LV activation proceeds from an ECG showing complete left bundle branch block (CLBBB). Indeed, a substantial number of patients with heart failure exhibit CLBBB, while subjects with normal LV function not uncommonly exhibit CLBBB solely due to the disorder of the conduction system (isolated CLBBB). MCG with high spatio-temporal resolution has enabled us to noninvasively detect abnormal"peripheral" intraventricular conduction accompanied by myocardial damage in patients with LV dysfunction and heart failure, which is not observed in subject with isolated CLBBB and normal LV function.

References:

  1. Oishi S, Takaki H, Hashimoto S, Shimizu W, Sugimachi M, Kamakura S. Magnetocardiography can identify 'Local" ventricular conduction delay in patients with LV dysfunction and CLBBB/IVCD on ECG: Comparison with 'Isolated' CLBBB. J Am Coll Cardiol. 2010;55;A13.E122 (ACC2010, Abstract)

(3) Evaluation of electrical dyssynchrony and prediction of clinical response to cardiac resynchronization therapy (CRT)

Although intraventricular electrical dyssynchrony worsens hemodynamics in heart failure patients, no noninvasive method for its accurate estimation has been established. Furthermore, it is difficult to predict the"responder" to cardiac resynchronization therapy (CRT) that ameliorates the electrical dyssynchrony. Based on MCG findings before CRT implantation, patients with severe heart failure were classified into 2 groups (Group-A: Uni-directional current pattern, Group-B: Multi-directional current pattern). We found 6 responders among 7 Group-A patients and 6 non-responders among 7 Group-B patients, suggesting that the MCG classification is particularly useful for the prediction of clinical response to CRT.

References:

  1. Oishi S, Takaki H, Yamashita E, Hashimoto S, Nakajima I, Tanaka T, Shimizu W, Sugimachi M, Kamakura S. Magnetocardiography (MCG) can predict clinical response to cardiac resynchronization therapy (CRT). Circulation. 2009;120:S647 (AHA2009, Abstract)

(4) Detection and localization of abnormal conduction delay as a cause of lethal ventricular arrhythmias

Arrhymogenic right ventricular cardiomyopathy (ARVC) is a heart muscle disease, characterized by fibro-fatty replacement of the right ventricular myocardium that underlies lethal ventricular arrhythmias. Abnormal local conduction delay within the right ventricle producing ventricular arrhythmias can be expressed as a small notch (ε- wave) on ECG, however, its appearance is often too small to be recognized visually. On the other hand, MCG analysis could clearly reveal such conduction abnormalities with its characteristic QRS multiple-spine (fragmentation) morphology. The ability of MCG to localize abnormal sites using 2-dimensional mapping offers an advantage over conventional ECG modalities such as signal-averaged electrocardiogram (SAECG).

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