EKG Tutorial: How the ECG reads cardiac activity

Electrocardiography

How the ECG reads cardiac activity

In the mid-1880's, two fellows named Ludwig and Waller discovered that the electrical activity of the heart could be monitored through the skin. Their device, called a capillary electrometer, used sensor electrodes and magnets to generate an electrical field. A capillary tube with fluid was placed in the field. As current passed through the electrodes, the field increased and decreased causing the fluid in the tube to bounce up and down. This device, as cool as they probably thought it was, was far too crude for clinical use.

It took the genious of Mr. Einthoven to produce a function ECG device. Einthoven devised a clever system for recording the same electrical activity on light-sensitive paper. Noticing a recurring pattern of movement, Einthoven named the prominent waves alphabetically, P, Q, R, S, and T

the P-Wave, representing the impulse across the atria to the A/V Node;

The QRS representing the impulse as it travels across the ventricles;

the T-Wave, representing the repolarization of the ventricles.

Modern ECG devices use more sophisticated techniques like amplification, filtering, and digital signal analysis to more accurately and conveniently measure, display, and analyze ECG data. Many of the high-end machines will perform very detailed interpretation of the ECG thus saving the clinician from the tedious and laborious burden of thinking.

In our analysis of these ECG rhythms, we will examine the shape, consistency, and the time between these waveforms to determine the functionality of the hearts conduction system. Many cardiac conditions have characteristic patterns on the ECG. These dysrhythmias are valuable clues to diagnosing and treating cardiac illnesses - acute and chronic.

Through ECG analysis, it is possible to trace the conduction through the heart, estimate the size and orientation of the heart, and even to locate regions of the heart which have suffered injury, ischemia (oxygen deprivation), or necrosis (tissue death).

This tutorial will focus on Lead II ECGs. Lead II implies that the activity is measured from the right arm to the left leg. The ECG will show activity along the septum of the heart.

Electrocardiography

How the ECG reads cardiac activity

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