Answered: What does an ECG measure? Name the…

Phlebotomy Essentials

6th Edition

ISBN:9781451194524

Author:Ruth McCall, Cathee M. Tankersley MT(ASCP)

Publisher:Ruth McCall, Cathee M. Tankersley MT(ASCP)

Chapter1: Phlebotomy: Past And Present And The Healthcare Setting

Section: Chapter Questions

Problem 1SRQ

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Question

What does an ECG measure? Name the waves and
intervals produced by an ECG, and state what events
occur during each wave and interval.

Expert Solution

Step 1 Introduction

Electrocardiography is the process by which an electrocardiogram is generated. This is a time-dependent voltage graph of the electrical activity of the core by means of electrodes placed on the skin. These electrodes detect small electrical changes that are a consequence of depolarization of the heart muscle followed by repolarisation during each heart cycle.

Step 2

There are three major components to an ECG: the P-wave, which depolarizes the atria; the QRS complex, which depolarizes the ventricles; and the T-wave, which depolarizes the ventricles.
Throughout each pulse, a healthy heart has an orderly depolarization process that begins in pacemaker cells in the SA node, extends throughout the atrium, and travels through the atrioventricular node in its bundle and into the Purkinje fibers, extending across the ventricles and left.
The electrical activity takes place in a small piece of pacemaker cells called the sinus node during a regular heartbeat. This results in a small beep called the P-wave when the pulse stimulates the atria. The PR interval refers to the distance between the appearance of the P-wave and the appearance of the QRS complex. The plane between the end of the P wave and the beginning of the QRS complex is called the PR segment and it reflects the slow impulse conduction through the AV node.
It then activates the main pumping chambers, the ventricles, and produces the large, high-and-low medium, the QRS complex. It shows the reactivation of the ventricles. ST-segment corresponds to an action potential.
The final T-wave is a regeneration period as the pulse reverses on the ventricles and rises.

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