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Leads

Terms in this set (22)

Lead V₁
-Electrode positioned in fourth intercostal space just to the right of the sternum
-Faces and is close to the right ventricle
-Also has a view of ventricular septum
Lead V₂
-Positioned in 4th intercostal space just to the left of the sternum
-Horizontally, it is at the same level as lead V1 but on the opposite side the sternum
-Just like lead V1, V2 faces and is close to the right ventricle
-Although it has a view of the right ventricle and anterior wall of the heart, it is more recognized for its view of the ventricular septum
Lead V₃
-Located midway between leads V2 and V4
-Views anterior wall of the left ventricle
-Depolarization of the left ventricle moves perpendicular to the positive electrode, resulting in a biphasic waveform
Lead V₄
-Is placed at the 5th intercostal space n the midclavicular line
-Views the anterior wall of left ventricle and is close to the heart's apex
-Depolarization of the left ventricle moves perpendicular to the positive electrode resulting in a biphasic waveform
Lead V₅
-Placed in 5th intercostal space at the anterior axillary line
-Horizontally, it is even with V4 but in the anterior axillary line
-Views lateral wall of the left ventricle
-Depolarization of left ventricle moves toward the positive electrode, producing a tall R wave
Lead V₆
-Located horizontally level with V4 and V5 at the midaxillary line
-Views lateral wall of left ventricle
-Depolarization of left ventricle moves toward the positive electrode producing a tall R wave
12 Lead ECG Waveforms
-Each view provides different information
-When assessing the 12 lead ECG look for characteristic normalcy and changes in all leads
Contiguous Leads
-Each view provides different information
-When assessing the 12 lead ECG look for characteristic normalcy and changes in all leads
Right Ventricular Leads
-View the right ventricle
-Are in addition to the 12 lead ECG and require relocating the precordial ECG electrodes
Posterior Leads
-View the posterior surface of the heart
-Are in addition to the 12 lead ECG and require relocating the precordial electrodes
electrical axis
The 12-lead ECG can measure the axis of the electrical flow of energy during the cardiac cycle
instantaneous vectors
Cardiac cell depolarization and repolarization produces many small electrical currents
-Sum of these currents called instantaneous vectors
-Average of instantaneous vectors called the mean vector
mean electrical axis
-Direction of the mean vector called the mean electrical axis
-Axis is defined in the frontal plane only
ECG deflection
Wave of depolarization and its affect on the ECG
QRS axis
Most important and frequently determined axis
Ventricular Depolarization and Mean QRS Axis
-Interventricular septum depolarization represents the first cardiac vector associated with ventricular depolarization
-A sequence of vectors is produced as the Purkinje fibers carry the impulse from the endocardial lining of the RV and LV through the ventricular wall toward the epicardium
-Completion of right ventricular activation occurs first
-The thinner wall of the RV transmits impulse quicker than the thicker wall of LV
Mean QRS Axis
-The small depolarization vectors of the thicker LV are larger
-Therefore, the mean QRS axis points more to the left
Position of Mean QRS Axis
-Limb leads provide information about the frontal plane and are used to determine the position of the mean QRS axis
-Described in degrees within an imaginary circle drawn over the patient's chest
-AV node is center of circle
-Intersection of all lines divides circle into equal, 30-degree segments
-Lead I starts at +0 degrees and is located at the three o'clock position
-Lead aVF starts at +90 degrees and is located at the six o'clock position
-Mean QRS axis normally points downward and to patient's left (between 0 and +90 degrees)
Determing Electrical Axis
Use leads I and aVF
-These two leads can best detect variations in the heart's electrical axis
-If the mean QRS vector directed anywhere between -90º and +90º, positive QRS complex in lead I
-If mean QRS vector directed between 0º and +180º, positive QRS complex in lead aVF
right axis deviation
An axis between +90 and ±180 degrees indicates right axis deviation
left avis deviation
An axis between 0 and −90 degrees indicates left axis deviation
determining electrical axis
The deflection of the QRS complexes in leads I and aVF help identify electrical axis

Location of axis influenced by:
-Heart's position in the chest
-Heart size
-Patient's body size
-Conduction pathways
-Force of electrical impulses being generated
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