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Normal 12-lead ECG A 12-lead ECG of a 26-year-old male with an incomplete right bundle branch block (RBBB). The overall goal of performing an ECG is to obtain information about the electrical functioning of the heart.
Normal heart rate (classically 60 to 100 beats per minute for an adult). Regular rhythm, with less than 0.16-second variation in the shortest and longest durations between successive P waves The sinus node should pace the heart – therefore, P waves must be round, all the same shape, and present before every QRS complex in a ratio of 1:1.
If lead I is positive (translating to 0° on the hexaxial reference system) and lead II is positive (translating to 60°), the electrical heart axis is estimated to fall in the left lower quadrant within the normal range. On the other hand, as shown in Figure 2, if lead I is negative (translating to 180°) and lead II is positive, the ...
The standard 12 lead ECG does not directly examine the right ventricle, and is relatively poor at examining the posterior basal and lateral walls of the left ventricle. In particular, acute myocardial infarction in the distribution of the circumflex artery is likely to produce a nondiagnostic ECG. [10]
In the superimposed median beat method, a median ECG complex is constructed for each of the 12 leads. The 12 median beats are superimposed on each other and the QT interval is measured either from the earliest onset of the Q wave to the latest offset of the T wave or from the point of maximum convergence for the Q wave onset to the T wave ...
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 QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. LQTS is suggested if the QTc is longer than these cutoffs. However, as 5% of normal people also fall into this category, some suggest cutoffs of 470 and 480 ms for males and females respectively, corresponding with the 99th centiles of normal values.
The manufacturing industries of ECG machines is now entirely digital, and many models incorporate embedded software for analysis and interpretation of ECG recordings with 3 or more leads. Consumer products, such as home ECG recorders for simple, 1-channel heart arrhythmia detection, also use basic ECG analysis, essentially to detect abnormalities.