how many leads on an ecg?
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The standard ECG has 12 leads. Six of the leads are considered “limb leads” because they are placed on the arms and/or legs of the individual. The other six leads are considered “precordial leads” because they are placed on the torso (precordium).
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The Normal ECG The waves on an ECG include the P wave, Q wave, R wave, S wave, T wave and U wave. Interval: The time between two specific ECG events. The intervals commonly measured on an ECG include the PR interval, QRS interval (also called QRS duration), QT interval and RR interval.
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Occasionally, LQRSV in the ECG may not have an apparent explanation; and thus, in normal subjects, it is considered a normal variant. Low ECG QRS voltage may be noted only in the limb leads (a frequent encounter), the precordial leads, or both.
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A lead composed of two electrodes of opposite polarity is called bipolar lead. A lead composed of a single positive electrode and a reference point is a unipolar lead. For a routine analysis of the heart's electrical activity an ECG recorded from 12 separate leads is used.
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The normal PR interval is 0.12 to 0.20 seconds, or 120 to 200 milliseconds. Multiple abnormalities of the PR interval — including prolongation of the PR interval, shortening of the PR interval and variation from beat to beat — can occur; these are discussed in detail in ECG Reviews and Criteria.
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There are two different rates that can be determined on an ECG. The atrial rate is indicated by the frequency of the P waves. The ventricular rate is indicated by the frequency of the QRS complexes.
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If you use an average of 80 beats per minute, your heart beats about 4,800 times per hour. That's a whopping 115,200 times per day. Over the course of a year, your heart would beat about 42,048,000 times! If you live to be 80 years old, your heart would have beaten approximately 3,363,840,000 times!
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The ECG has a target viewpoint of the left ventricle In precordial leads, the current is flowing toward the active electrode The polarity of the P wave and the QRS complex are positive and upright waveforms in leads: I, II, III, and aVF .
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The 12-lead ECG gives a tracing from 12 different “electrical positions” of the heart. Each lead is meant to pick up electrical activity from a different position on the heart muscle. This allows an experienced interpreter to see the heart from many different angles.
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Bifid P waves (known as P mitrale) indicate left-atrial abnormality - e.g. dilatation or hypertrophy. If at least three different shaped P waves can be seen in a given ECG lead tracing, this implies that even if one of them arises from the SA node, at least two others are arising elsewhere.
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The septum is represented on the ECG by leads V1 and V2, whereas the lateral wall is represented by leads V5, V6, lead I and lead aVL. To make things more complicated, sometimes the LAD “wraps around” the cardiac apex, which is a common anatomic variant.
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Sinus tach and most SVTs have only one P wave for each QRS complex. They may or may not be buried in the preceding T waves. But there are other supra-ventricular tachycardias that have more than one P wave for each QRS or no P waves. Atrial fibrillation has no P waves.
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Two heart beats A Doppler can usually detect a heartbeat(s) between 8-12 weeks. If two heartbeats are detected, there is a good chance that it is because there are two babies!
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The standard 12-lead electrocardiogram is a representation of the heart's electrical activity recorded from electrodes on the body surface. This section describes the basic components of the ECG and the lead system used to record the ECG tracings.
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Heart rate can be easily calculated from the ECG strip: When the rhythm is regular, the heart rate is 300 divided by the number of large squares between the QRS complexes. For example, if there are 4 large squares between regular QRS complexes, the heart rate is 75 (300/4=75).
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To assess the cardiac rhythm accurately, a prolonged recording from one lead is used to provide a rhythm strip. Lead II, which usually gives a good view of the P wave, is most commonly used to record the rhythm strip.
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However, it is important to avoid getting the monitor, leads, or electrodes wet. Otherwise, most people are asked to go about their days as usual while doing the 24-hour Holter test. This includes doing any regular exercises unless they involve sweating profusely or getting the area with the device wet.