Electrocardiogram and Heart Function

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Questions and Answers

What is the direction of the instantaneous cardiac vectors in the transverse plane leads?

Right and left

Up and down

Circumferential

Anteriorly and posteriorly (correct)

What is the normal characteristics of the P wave?

Triphasic

Notched and triangular

Smooth and rectangular

Smooth and rounded (correct)

What is the purpose of the PR interval?

To measure the heart rate

To measure the relaxation of the ventricles

To measure the time it takes for the electrical impulse to travel from the SA node to the ventricles (correct)

To measure the contraction of the atria

What is the placement of the electrode for lead V4?

5th ICS, midclavicular line Signup and view all the answers

What is the difference between bipolar limb leads and augmented unipolar leads?

Bipolar leads measure voltage differences, while augmented unipolar leads measure voltage Signup and view all the answers

What type of ECG leads are used to measure the heart's electrical activity in the transverse plane?

Precordial leads Signup and view all the answers

How many unipolar leads are recorded in the transverse plane?

6 Signup and view all the answers

What does the QRS complex represent?

Ventricular depolarization Signup and view all the answers

What is the main function of the cardiac conduction system?

To send signals to the heart muscle causing it to contract Signup and view all the answers

What is the name of the test that records the electric currents produced by the heart?

Electrocardiogram (ECG or EKG) Signup and view all the answers

What are the metallic electrodes placed on the surface of the body for ECG recording called?

ECG leads Signup and view all the answers

How many leads are there in a standard ECG?

12 leads Signup and view all the answers

What is the function of bipolar leads in an ECG?

To record the potential difference between two points Signup and view all the answers

What are the two planes in which recordings are made during a routine ECG examination?

Frontal and transverse planes Signup and view all the answers

What is the name of the node that acts as the pacemaker of the heart?

Sinoatrial node (SA node or pacemaker) Signup and view all the answers

What is the machine used for recording the electrocardiogram called?

Electrocardiograph Signup and view all the answers

At the end of the PR interval, what is happening to the atria and ventricles?

The atria are beginning to repolarize and the ventricles are beginning to depolarize Signup and view all the answers

What is the normal duration of the PR interval?

0.12 to 0.20 seconds Signup and view all the answers

What is the Q wave in the QRS complex?

The first downward stroke Signup and view all the answers

What is the normal width of the QRS complex?

At least 5 mm and not more than 20 mm Signup and view all the answers

What does the ST segment represent?

The period between ventricular depolarization and repolarization Signup and view all the answers

What is the T wave?

The wave of ventricular repolarization Signup and view all the answers

What is the period from the beginning of the T wave to nearly the end called?

The relative refractory period Signup and view all the answers

What is the significance of a deviation of the ST segment from the baseline?

It indicates coronary artery disease Signup and view all the answers

What is the primary function of the heart?

To pump blood throughout the body to deliver oxygen and nutrients Signup and view all the answers

What is the position of the heart in the chest?

2/3 of the heart is on the left side of the chest, rotated and positioned on its side Signup and view all the answers

How many chambers does the heart have?

Four chambers Signup and view all the answers

What is the difference between the left and right ventricular walls?

The left ventricular wall is thicker than the right ventricular wall Signup and view all the answers

What is the function of the right side of the heart?

To deliver deoxygenated blood from the body to the lungs Signup and view all the answers

What is the purpose of the heart conduction system?

To start each heart contraction and rapidly spread excitation Signup and view all the answers

Where does the apex of the heart come into contact with the chest wall?

At the 5th intercostal space in the mid-clavicular line Signup and view all the answers

What is the role of the left side of the heart?

To deliver oxygenated blood from the lungs to the body Signup and view all the answers

What is the normal range of heart rate for an adult?

60-100 bpm Signup and view all the answers

What is the duration of each small horizontal square on an ECG paper?

0.04 second Signup and view all the answers

What is the name of the abnormal cardiac rhythm?

Arrhythmia Signup and view all the answers

What is the step before attaching the electrodes to the chest, arms, and legs during an ECG?

Applying a special gel Signup and view all the answers

What is the normal duration of the R-R interval?

0.8 second Signup and view all the answers

How long does a resting ECG typically take?

5-10 minutes Signup and view all the answers

What is the purpose of the recording machine in an ECG?

To trace a wave pattern for each wire lead Signup and view all the answers

What is the heart rate if the distance between R-R is 18 mm?

83.3 bpm Signup and view all the answers

Study Notes

The Heart

The heart is a muscular organ that functions as the body's circulatory pump.
It is located in the mediastinum, near the midline, and is rotated and positioned on its side, with 2/3 of the heart on the left side of the chest.
The base of the heart faces up and to the right, while the apex faces down, out, and to the left.

Chambers of the Heart

The heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle.
The wall of the left ventricle is thicker than that of the right ventricle.
The function of the right side of the heart is to deliver deoxygenated blood from the body to the lungs.
The function of the left side of the heart is to deliver oxygenated blood from the lungs to the body.

Heart Conduction System

The heart conduction system is a network of specialized cardiac cells designed to start each heart contraction and coordinate the spread of excitation.
The conduction system consists of the sinoatrial node (SA node or pacemaker), atrioventricular node (AV node), atrioventricular bundle (AV bundle or bundle of His), right and left branches, and Purkinje fibers.

Electrocardiogram (ECG)

An ECG is a painless test that records the electric currents produced by the heart and converts them into waveforms that can be seen on a monitor or printed out on paper.
The ECG machine is used to record the electrocardiogram.
The waveforms created by the ECG can be divided into time segments to measure the rate of movement of the heart's electrical impulses.

ECG Leads

ECG is recorded by placing metallic electrodes on the surface of the body in designated anatomical locations.
The standard ECG has 12 leads, which are subdivided into bipolar leads (3) and unipolar leads (9).
The 12 leads provide a comprehensive picture of the electrical activity of the heart.

Routine ECG Examination

The routine ECG examination records from two planes: the frontal plane and the transverse plane.
The frontal plane leads include standard bipolar limb leads and augmented unipolar leads.
The transverse plane leads include precordial leads or chest leads, which are numbered V1-V6.

ECG Components

The ECG is composed of:
- P wave: the wave of atrial depolarization
- QRS complex: the wave of ventricular depolarization
- T wave: the wave of ventricular repolarization
- Related intervals

Intervals and Waves

P wave:
- Is the wave of atrial depolarization
- Normally has a smooth and rounded shape
- Not more than 3 mm tall
- Upright in leads I, II, and aVF
PR interval:
- Includes the P wave and the space up to the beginning of the QRS complex
- Represents the time it takes the electrical impulse to travel from the SA node to the ventricles
- Normally 0.12-0.20 seconds or 120-200 msec
QRS complex:
- Is the wave of ventricular depolarization
- Should be at least 5 mm and not more than 20 mm tall
- Normal QRS duration is 0.06-0.10 seconds
ST segment:
- Is the period of time between the end of ventricular depolarization and the beginning of ventricular repolarization
- Should be isoelectric, or on the baseline
- A deviation of the ST segment from the baseline may be indicative of coronary artery disease
T wave:
- Is the wave of ventricular repolarization
- Normally deflects in the same direction as the QRS complex
- Should be smooth and rounded

ECG Interpretation

Heart rate: normal range is 60-100 bpm
Rhythm: abnormal cardiac rhythms are called arrhythmias
Duration of waves and intervals: should be within normal ranges

Calculating Heart Rate using ECG Paper

Each small horizontal square is 0.04 seconds, and each large horizontal square is 0.2 seconds
Normal duration of R-R interval is 0.8 seconds
Heart rate = 1500 / # of small squares (R-R)

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Description

Learn about the heart's structure, function, and its role in the body's circulatory system. Understand the importance of the heart in delivering oxygen and nutrients to body tissues.