notes by dr Claudio Italiano
In this website we have already outlined how to interpret an ECG
having achieved a unique success, especially among the parasanitary staff who
took advantage of these few standards put on the web good, the result of
personal university notes and lessons for nurses. Here we speak about the cardiac axis,
to detect it.
We all know that before the echocardiographic technique was invented, the
cardiologist used other methods for patient assessment. For example, the "telecuore"
was made, which does not mean the heart on TV, but a particular projection of
rays that allowed a silhouette of the heart, interpreting the profiles to
achieve the diagnosis of hypertrophy of the heart, of the right ventricle (heart
pulmonary) or of the left ventricle (hypertrophy of the myocardium, as organ
damage, for example, of the patient with hypertension).
So knowing how to interpret the cardiac axis or electrical axis of the heart is
essential to recognize the direction of the electrical vector of the heart which
is the result, then, of all the electrical heart forces at the time of systole
and understand the heart in which "direction" proceeds , if towards the left
ventricle which, probably, must be the most powerful and developed and which
works at greater pressure or, rather, abnormally, towards the right ventricle,
therefore, in the conditions of hypertrophy of the same and therefore in the
conditions in which of pathologies determine the commitment of the right
sections of the heart itself.
Another important concept: the electric axis, in case of ischemic heart injury, the axis deviates; if we have an ischemia along the course of the conduction pathways of the electrical signal of the heart, the axis deviates in the opposite direction. In the left anterior emiblock, for example, the aFV electrode that explores from below, from the feet, sees the vector moving away and then registering it negatively, rather than positively. So the electric vector is diverted up and to the left, it does not go down as it should be.
The diagram you see, a circle with degrees, ideally represents a patient, with the center of the circle at the center of the heart and the various electrocardiographic branches, in essence the various electrical points from which the electrodes explore the heart. The figure shows the reference system on the frontal plane of the representation of the bipolar leads (DI-DII-DIII) and unipolori (aVL, aVF, aVR). The bipolar ECG derivations can be represented by the sides of a triangle (Einthoven's triangle) that joins the upper limbs and the left leg. The vector at the center of the triangle represents an electric force that originates at the heart level.
As a rule, since the heart is more developed in its left sections and the left myocardial portion prevails, the average vector axis or QRS in the adult is between -30 ° and + 90 ° on the frontal plane. The figure shows the limits for the diagnosis of axial deviation left (-30 °, -90 °) and of right axial deviation (+ 90 °, + 150 °). The path (ecg), therefore, must be searched for the highest QRS complex in the various derivations to understand where the direction of the cardiac vector falls. Here are some examples of traces with left axial deviation, right axial deviation, extreme deviation and indeterminate axis in the DI and DII branches.
A left axial deviation can usually be caused by blocking the anterior branch of the left bundle of His beam (left anterior left hemiblock); vice versa, a considerable right axial deviation can be correlated to a block of the posterior branch of the left flock (left posterior hernibus). The right axial deviation is usually linked to cardiac overload (pulmonary heart) or malformations. Obviously, having a conduction block could also be an expression of ischemic facts or of injury that is attained by myocardial infarction.
cardiology index