Why is ecg called 12 lead

A lead composed of two electrodes of opposite polarity is called bipolar lead. To measure the heart's electrical activity accurately, proper electrode placement is crucial. In a lead ECG, there are 12 leads calculated using 10 electrodes. In this and the other two limb leads, an electrode on the right leg serves as a reference electrode for recording purposes.

Based upon universally accepted ECG rules, a wave a depolarization heading toward the left arm gives a positive deflection in lead I because the positive electrode is on the left arm.

The 12 - lead ECG displays, as the name implies, 12 leads which are derived by means of 10 electrodes. Three of these leads are easy to understand, since they are simply the result of comparing electrical potentials recorded by two electrodes ; one electrode is exploring, while the other is a reference electrode.

What is v1 v2 ECG? Example: V1 is close to the right ventricle and the right atrium. Signals in these areas of the heart have the largest signal in this lead. V6 is the closest to the lateral wall of the left ventricle. Why is a 12 lead called a 12 lead? The lead ECG displays, as the name implies, 12 leads which are derived by means of 10 electrodes. Three of these leads are easy to understand, since they are simply the result of comparing electrical potentials recorded by two electrodes; one electrode is exploring, while the other is a reference electrode.

How do you do a 12 lead? Precordial Lead Placement To locate the space for V1; locate the sternal notch Angle of Louis at the second rib and feel down the sternal border until the fourth intercostal space is found. Next, V4 should be placed before V3. However, V1 and V2 may occasionally display ECG changes indicative of ischemia located in the right ventricle. In such scenarios, it is recommended that additional leads be placed on the right side of the chest.

Considering myocardial ischemia and infarction, elevation of the ST-segment discussed later is an alarming finding as it implies that there is extensive ischemia.

Ischemic ST-segment elevations are often accompanied by ST-segment depressions in ECG leads which view the ischemic vector from the opposite angle. Such ST-segment depressions are therefore termed reciprocal ST-segment depressions, because they are mirror reflections of the ST-segment elevations. Electrical activity emanating from this part of the left ventricle marked with an arrow in Figure 23 cannot be readily detected with the standard leads, but the reciprocal changes ST-segment depressions are commonly seen in V1—V3.

In order to reveal the ST-segment elevations located posteriorly, one must attach the leads V7, V8 and V9 on the back of the patient. Please note that right ventricular infarction and posterolateral infarction will be discussed in detail later on. The conventional placement of electrodes can be suboptimal in some situations. Electrodes placed distally on the limbs will record too much muscle disturbance during exercise stress testing; electrodes on the chest wall may be inappropriate in case of resuscitation and echocardiographic examination etc.

Efforts have been made to find alternative electrode placements, as well as reducing the number of electrodes without loosing information.

In general, lead systems with less than 10 electrodes can still be used to compute the all standard leads in the lead ECG. Such calculated ECG waveforms are very similar to the original lead ECG waveforms, with some minor differences that may affect amplitudes and intervals. As a rule of thumb, modified lead systems are fully capable of diagnosing arrhythmias but one should be cautious when using these systems to diagnose morphological conditions e.

Indeed, in the setting of myocardial ischemia one millimeter may make a life-threatening difference. Lead systems with reduced electrodes are still used daily to detect episodes of ischemia in hospitalized patients. This is explained by the fact that when monitoring continuously — i.

Instead the interest lies in the dynamics of the ECG and in that scenario the initial recording is of little interest. This is used in all types of ECG monitoring arrhythmias, ischemia etc. It is also used for exercise stress testing as it avoids muscle disturbances from the limbs. As stated above, the initial recording may differ slightly in amplitudes so that it is not valid to diagnose ischemia on the initial tracing.

For monitoring ischemia over time, however, Mason-Likar is an effective system. Refer to Figure 24 A. The left and right arm electrodes are moved to the trunk, 2 cm beneath the clavicle, in the infraclavicular fossa Figure 24 A. The left leg electrode is placed in the anterior axillary line between the iliac crest and the last rib.

The right leg electrode can be placed above the iliac crest on the right side. Placement of the chest leads is not changed. As mentioned above, it is possible to construct mathematically a lead system with fewer than 10 electrodes. In general, mathematically derived lead systems generate ECG waveforms that are almost identical to the conventional lead ECG, but only almost. It is generated by means of 7 electrodes Figure 22 B. Using these leads, 3 orthogonal leads X, Y and Z are derived.

These leads are used in vectorcardiography VCG. Orthogonal means that the leads are perpendicular to each other. These leads offer a three-dimensional view of the cardiac vector during the cardiac cycle.

However, the VCG has lost much ground in recent decades as it has become evident that the VCG has very low specificity for most conditions. VCG will not be discussed further here.

Lead X is derived from A, C and I. Lead Y is derived from F, M and H. EASI also provides orthogonal information. The Cabrera format of the lead ECG. Cardiac electrophysiology: action potentials, automaticity, electrical vectors. Video lecture on ECG interpretation. No products in the cart. Sign in Sign up. Search for:. Introduction to ECG Interpretation. Clinical electrocardiography and ECG interpretation. Arrhythmias and arrhythmology. Mechanisms of cardiac arrhythmias: from automaticity to re-entry reentry.

Conduction Defects. Overview of atrioventricular AV blocks. Atrial and ventricular enlargement: hypertrophy and dilatation on ECG. Exercise stress test treadmill test, exercise ECG : Introduction. Section 1, Chapter 3. In Progress. Electrophysiological basis of the ECG leads. The lead ECG. The ECG paper. Derivation of the ECG leads. Anatomical planes and ECG leads.

Principles of the limb leads. Anatomical aspects of the limb leads. Chest leads precordial leads. Presentation of ECG leads. Additional supplementary ECG leads. Alternative ECG lead systems. Mason-Likar ECG lead system. Placement of electrodes. Reduced ECG lead systems. Frank leads. EASI leads. Next chapter. Back to Healio. ECG Basics Save. Introduction to ECG An electrocardiogram is a picture of the electrical conduction of the heart.

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