Determination of Electrical Axis in ECG

Transcript of the video: When we talk about the electrical axis in the ECG, we usually mean the mean QRS axis. Even though it is possible to calculate the axis of each component of the QRS like the initial activation and later activation, we usually mean the mean QRS electrical axis. And, electrical axis can be calculated for the P wave, PR segment, QRS complex, ST segment and T wave. All can be calculated separately. Modern ECG machines, with in-built computerized diagnostic algorithm, usually display a clock face in the print out, which will indicate the axis of P wave, QRS and T wave. Along with that, the measured axis of each wave will also be displayed, in the printout of the measured values.
Simple method of calculating the QRS axis is by looking at lead I and aVF. The negative waves are subtracted from the amplitude of the positive waves, and the resultant taken, for lead I and aVF. And, lead I is given an axis of zero, and aVF an axis of +90. So, this amplitude, the sum of the amplitudes, negative is subtracted from the positive, is plotted along the graph. Will be plotted here, lead I and aVF will be plotted in this direction. And geometrically you can calculate the resultant. That is what we will get as the mean electrical QRS axis in an ECG. So, if both are positive, you can see that the QRS axis will be between lead I and aVF, 0 to 90 degrees. That is a normal axis, simply, this is the normal axis, if both are positive. If lead I is negative and aVF is positive, t...

Source: Cardiophile MD - March 30, 2024 Category: Cardiology Authors: Johnson Francis Tags: General Cardiology Source Type: blogs