Ischemic Heart Disease

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Ischemic heart disease (IHD) is the leading cause of death in adults in industrial countries, where the annual incidence is generally high. For diagnostic purposes, coronary angiography is the current ''gold standard'', but due to a combination of X-ray exposure, adverse side effects and high cost, the method is restricted to those patients with very high pre-test likelihood of IHD. Despite the development of novel noninvasive diagnostic tests, including new imaging technology, 12-lead ECG and echocardiography at rest and under stress remain the most common methods in routine clinical use. Although these are fast and simple diagnostic procedures, their predictive value remains limited. Hence, there is a need for cost-effective diagnostic procedures for IHD that are easy and quick to perform and which deliver a reliable basis for subsequent clinical action.

MCG provides a rapid, noninvasive means of registering cardiac electric activity. Concurrent with the dependable registration of cardiac magnetic fields, a variety of

Fig. 2.38. Magnetocardiogram in a healthy subject.

(a) Signal-averaged traces from a 61-channel prethoracic acquisition.

(b) Magnetic field map at Q onset schematically superimposed on an MR image.

Fig. 2.38. Magnetocardiogram in a healthy subject.

(a) Signal-averaged traces from a 61-channel prethoracic acquisition.

(b) Magnetic field map at Q onset schematically superimposed on an MR image.

data analysis procedures have been developed to examine and quantify cardiac electrophysiological changes. Signal analysis, mapping techniques and the ability to study the three-dimensional localization of cardiac electrical activity have made MCG a potentially useful tool in the early evaluation of the presence and localization of changes related to myocardial ischemia, and have also permitted comparison to ECG procedures. The clinical potential of MCG in the context of IHD may be examined from several aspects:

• Prevention: the ability to identify persons at risk.

• Diagnosis: the early detection of patients with hemodynamically relevant stenoses of the coronary arteries with and without myocardial infarction (MI).

• Follow-up: the post-interventional study of patients and the identification of viable myocardium with the indication for further revascularization procedures.

In the following, an overview of the progress of cardiomagnetism made in the above areas will be outlined with regard to approaches for evaluating magnetic signals recorded from the heart. The different measures are based primarily on the morphology of the MCG signal, the time intervals which can be calculated from it, the reconstruction and analysis of magnetic field maps, and the estimation of current density and current source parameters (Fig. 2.38).

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