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The 12-lead electrocardiogram (ECG) is still the most frequently used diagnostic method in patients with suspected ischemic heart disease (IHD). Practically all patients presenting at the emergency room with chest pain have an ECG recorded to exclude or confirm unstable IHD and ongoing myocardial ischemia. In many regions, ECG is recorded in ambulances on patients with typical or atypical chest pain, dizziness, fainting, irregular heartbeat, and other clinical symptoms or signs. Furthermore, inducible ECG changes found during an exercise or pharmacologic stress test are frequently used to diagnose significant coronary artery stenosis in the situation of stable IHD. The frequent use of ECG as a diagnostic method in suspected IHD worldwide is due to several factors. First, the ECG provides a unique perspective of the condition of the myocardium by exploring its electrical activity, which is not depicted by other imaging modalities of the heart. Second, it is an inexpensive examination that is not associated with any risk for the patient, and it can be performed within a few minutes. Third, the technique is widely available, even in the developing parts of the world. Finally, the medical community has a long experience with the method because it has been around for more than 100 years.

Currently, the standard clinical ECG is displayed in 12 leads, 6 limb leads, and 6 precordial leads. This results in 12 views of the electrical activity of the myocardium. Body surface potential mapping (BSPM) is a method that provides additional views of the body surface potential distribution by performing recordings at multiple sites (24-240 sites) on the body surface. BSPM has evolved from the so-called classical forward and inverse problems of ECG. The former focuses on how the electrical activity from electrical sources present in the heart is propagated to the epicardium (near-field problem) or to the body surface (far-field problem).1 The latter focuses on how the electrical activity recorded at the body surface can be used to derive details about the electrical activity in the heart (ie, epicardial potentials).2 Both problems require high spatial resolution information from the body surface, which can be obtained through BSPM. Thus, BSPM has previously been shown to be useful for detecting myocardial infarction.3-6 BSPM will not be discussed further in this chapter.

Although there are clear advantages to using additional leads in certain circumstances, problems may occur even when using only the 10 electrodes of the standard 12-lead ECG. Multiple electrodes and wires interfere with auscultation, echocardiograms, resuscitation efforts, and chest x-rays. Noise levels due to limb movement detected by multiple leads make interpretation difficult, and the discomfort to patients caused by so many electrodes tends to be high. Additionally, rapid and accurate electrode placement can be difficult in emergency situations. Fewer electrodes placed at more easily accessed locations could facilitate ECG acquisition for both patients and staff. An example of a reduced lead set is the EASI lead system, which uses five torso electrodes, four ...

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