The direction of an average (mean) vector is called the electrical axisThe direction of an average (mean) vector is called the electrical axis. The overall direction of ventricular depolarization is called the QRS axis. Many novice practitioners of 12 lead ECG interpretation find identifying the QRS axis challenging and somewhat confusing.....
A vector is an arrow that represents the size and direction of a force. The larger the force the larger the arrow. Now take the small vectors from Figure 6.11 that represent the direction and size of the electrical force of ventricular depolarizationThe depolarization of the myocardium is represented on an ECG by a series of waveforms, one for atrial depolarization and soon after a larger waveform for ventricular depolarization. Normal ventricular depolarization begins with the septal fascicle of the left bundle.... When adding these small vectors, the resulting size and direction of the overall ventricular depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... could be represented by the large arrow. The direction of an average (mean) vector is called the electrical axis. The overall direction of ventricular depolarization is called the QRS axis.
With an electrocardiogramThe graphical representation of cardiac electrical activity – voltage (mV – y axis) measured over time (x axis). Figure 4.11 The Scales of the ECG 1. Six Second ECG Guidebook (2012), T Barill, p. 64, 196, the mean vector (QRS axis) of ventricular depolarization is best identified by comparing various QRS complexes. The lead viewsLocating the positive electrode is crucial to determining which area of the heart is viewed electrically. Metaphorically, the positive electrode serves as a mini-video camera aimed at the heart in the direction of the negative electrode. These leads and their... taken from the limb electrodesThe 12-lead ECG provides 12 views of the heart. The 12 views are generated through only 10 electrodes. Four limb electrodes attach to the inner forearms and calves. The remaining 6 electrodes, labelled successively from V1 to V6, are attached... (I, II, III, aVR, aVL, aVF) are particularly useful since together these six leads provide a six point mapping of the frontal planeThe ability to be more specific with QRS axis deviation requires a quick scan of all the limb leads (I, II, III, aVR, aVL, aVF). Using these standard and augmented voltage leads, a closer approximation can be made of the... (see Figure 6.11).
Figure 6.11 illustrates the direction of normal depolarization of the ventriclesThe larger chambers of the heart (3 times the volume and muscle thickness than the atria), responsible for the pumping of blood to the lungs and the rest of the body. from the AV nodeIs located in the inferior aspect of the right atria; functions to slow the conduction speed to allow for atrial conduction prior to ventricular conduction (atrial kick); also serves as a pacemaker if the SA node fails to fire. The... out to the apex of the heart. Strictly speaking, each of the four depolarizing waves move in different directions. The septal fascicleNormal ventricular depolarization begins with the septal fascicle of the left bundle branch (causing a Q wave) followed by a simultaneous depolarization of the remaining ventricular walls via the right and left bundle branches. The left bundle branch splits into... of the left bundle branch depolarizes the septal region from the left septum towards the right ventricleThe right ventricle ejects blood through the main branches of the left and right pulmonary arteries to the lungs. The chambers of the heart are the main drivers within an intricate pathway, delivering blood to the lungs for gas exchange... (#1), away from the positive electrode in lead II. This early depolarizing wave away from the positive electrode produces a small Q waveA Q wave is the first negative deflection of the QRS complex that is not preceded by a R wave. A normal Q wave is narrow and small in amplitude. Note that a wide and/or deep Q wave may signify.... Both ventricles then simultaneously depolarize (#2). While the right ventricle depolarizes away from the positive electrode (in lead II), the electrical current of the much thicker left ventricular myocardiumThe muscle layer of the heart; the middle layer that is responsible for contraction of the heart. The muscular myocardium is the thickest layer and the workhorse of the heart. It is composed of specialized muscle and electrical cells that... dominates the overall direction of ventricular depolarization thus producing an upward QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also....
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 163