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The use of additional ECG leads like right-sided leads V3R and V4R and posterior leads V7, V8, and V9 may improve sensitivity for right ventricular and posterior myocardial infarction. In spite of these limitations, the 12 lead ECG stands at the center of risk stratification for the patient with suspected acute myocardial infarction.
The electrodes that form these signals are located on the limbs – one on each arm and one on the left leg. [41] [42] The limb leads form the points of what is known as Einthoven's triangle. [43] Lead I is the voltage between the (positive) left arm (LA) electrode and right arm (RA) electrode: =
Limb: Limb infarction is an infarction of an arm or leg. Causes include arterial embolisms and skeletal muscle infarction as a rare complication of long standing, poorly controlled diabetes mellitus. [12] A major presentation is painful thigh or leg swelling. [12] Bone: Infarction of bone results in avascular necrosis.
Pain radiates most often to the left arm, but may also radiate to the lower jaw, neck, right arm, back, and upper abdomen. [28] [29] The pain most suggestive of an acute MI, with the highest likelihood ratio, is pain radiating to the right arm and shoulder. [30] [29] Similarly, chest pain similar to a previous heart attack is also suggestive. [31]
The right leg electrode acts to reduce interference, and can be placed anywhere without an effect on the ECG results. [6] Each lead measures the electric field created by the heart during the depolarization and repolarization of myocytes. The electric field can be represented as a vector that changes continuously and can be measured by ...
The ECG should be done as early as practicable, including in the ambulance if possible. [18] ECG changes indicating acute heart damage include: ST elevation, new left bundle branch block and ST depression amongst others. The absence of ECG changes does not immediately distinguish between unstable angina and NSTEMI. [6]
The major tissues affected are nerves and muscles, where irreversible damage starts to occur after 4–6 hours of cessation of blood supply. [4] Skeletal muscle, the major tissue affected, is still relatively resistant to infarction compared to the heart and brain because its ability to rely on anaerobic metabolism by glycogen stored in the cells may supply the muscle tissue long enough for ...
Chest pain due to coronary ischemia commonly radiates to the arm or neck. [7] Certain individuals such as women, diabetics, and the elderly may present with more varied symptoms. [8] If blood flow through the coronary arteries is stopped completely, cardiac muscle cells may die, known as a myocardial infarction, or heart attack. [9]