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ECG Waves, Intervals, and Segments

ECG waves, intervals and segments

Electrical Vector
Depolarization and Repolarization
Interval
Segment
Waves and Deflections
PQ Interval
RR Interval
QRS Complex
QT Interval
ST Segment
T Wave
U Wave

Electrical Vector

Limb leads with mechanism of formation q wave, r wave, s wave during depolarization and repolarization

On the ECG, we only see

Limb leads
Electrical vectors during ventricular depolarization

The ventricles depolarize progressively

Ventricular septum (V_S - Septal vector)
Ventricles (V_M - Main vector)
Apex of the left ventricle (V_T - Terminal vector)

QRS complex looks differently in each lead
Because each lead "views" the vectors from a different angle
If the vector points

Toward the lead - a positive deflection occurs
Away from the lead - a negative deflection occurs

Electrical vectors are generated

in the atria and ventricles
during depolarization and repolarization

Depolarization and Repolarization

ECG records and displays

only the electrical activity of the myocardium
not mechanical activity
not the electrical activity of the conduction system

ECG mechanism p wave (atrial depolarization), qrs complex (ventricular depolarization), t wave (ventricular repolarization), u wave

P wave

represents the depolarization of the atria

Ta wave

represents the repolarization of the atria
it is usually not visible, hidden within the QRS complex

QRS complex

represents ventricular depolarization

T wave

represents ventricular repolarization

Interval

ECG intervals: RR interval, QRS interval, QT interval, isoelectric line

An interval is a segment that includes waves or complexes

Segment

ECG segment

A segment is a section that contains only the isoelectric line

Waves and Deflections

ECG waves: P wave, Q wave, R wave, S wave, T wave, U wave

Wave

is rounded

Deflection

has a sharp peak

Wave

In English, both waves and deflections
are referred to as wave

PQ Interval

PR (PQ) interval begins at the onset of the P wave and ends at the QRS complex

Begins at the start of the P wave (atrial depolarization)
Ends at the start of the QRS complex (ventricular depolarization)
PQ interval is sometimes referred to as PR interval

Because sometimes the QRS complex starts with the R wave

Duration is 0.12 - 0.2 seconds

It is the time during which the impulse travels from the SA node to the ventricles

It is mainly used in the diagnosis of AV blocks

RR Interval

RR interval is the interval between two peak R waves

Peak of the R wave

Is the moment

when the ventricles are fully depolarized

Depolarized ventricles create

the main cardiac vector

Used to calculate heart rate

QRS Complex

ECG QRS interval represents the duration of ventricular depolarization, contains Q wave, R wave, S wave

Is sometimes referred to as the QRS interval
The QRS complex represents ventricular depolarization
Ventricular depolarization has 3 electrical vectors

Each vector has a different direction

Ventricular depolarization

is always referred to as the QRS complex
Even though it has a different QRS configuration (RS, qR, Rs, R, rSR)

The ventricles have a more massive myocardium than the atria

This is why the amplitude of the QRS complex is larger

than the amplitude of the P wave (atrial depolarization)

Ventricular depolarization (QRS complex) lasts 0.06s - 0.1s

QT Interval

ECG QT interval represents the duration from depolarization to repolarization of the ventricles. It is the duration of the action potential

Starts with ventricular depolarization (QRS complex)
Ends with ventricular repolarization (end of the T wave)
The QT interval represents the duration of the action potential of the ventricles
Has a duration of 0.35 - 0.44s
Varies with frequency, so the corrected QT interval is calculated
Prolongation risks ventricular arrhythmia Torsades de Pointes

ST Segment

ECG ST segment is normally isoelectric

Is the segment between the end of the QRS and the beginning of the T wave
During the ST segment

No electrical activity is present in the ventricles
The atria are relaxed
The ventricles are contracted

Preparing for repolarization

The ST segment is a major marker for ischemia and infarction

T Wave

ECG T wave corresponds to phase 3 of the action potential. Represents the repolarization of the ventricles

Represents repolarization of the ventricles
Is wide and low

Because repolarization is slower and more asynchronous

Compared to depolarization

The T wave is the most variable part of the ECG curve
Normal T wave is concordant

Has the same direction as the QRS complex

U Wave

ECG U wave is associated with metabolic disturbances - hypokalemia

The U wave follows the T wave
The mechanism of its formation is uncertain

It is probably due to delayed repolarization of the ventricular septum

Not always present

Often appears in cases of hypokalemia

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers

ECG Waves, Intervals, and Segments

ECG waves, intervals and segments

Electrical Vector
Depolarization and Repolarization
Interval
Segment
Waves and Deflections
PQ Interval
RR Interval
QRS Complex
QT Interval
ST Segment
T Wave
U Wave

Electrical Vector

On the ECG, we only see

Limb leads
Electrical vectors during ventricular depolarization

The ventricles depolarize progressively

Ventricular septum (V_S - Septal vector)
Ventricles (V_M - Main vector)
Apex of the left ventricle (V_T - Terminal vector)

QRS complex looks differently in each lead
Because each lead "views" the vectors from a different angle
If the vector points

Toward the lead - a positive deflection occurs
Away from the lead - a negative deflection occurs

Electrical vectors are generated

in the atria and ventricles
during depolarization and repolarization

Limb leads with mechanism of formation q wave, r wave, s wave during depolarization and repolarization

Depolarization and Repolarization

ECG records and displays

only the electrical activity of the myocardium
not mechanical activity
not the electrical activity of the conduction system

P wave

represents the depolarization of the atria

Ta wave

represents the repolarization of the atria
it is usually not visible, hidden within the QRS complex

QRS complex

represents ventricular depolarization

T wave

represents ventricular repolarization

ECG mechanism p wave (atrial depolarization), qrs complex (ventricular depolarization), t wave (ventricular repolarization), u wave

Interval

An interval is a segment that includes waves or complexes

ECG intervals: RR interval, QRS interval, QT interval, isoelectric line

Segment

A segment is a section that contains only the isoelectric line

ECG segment

Waves and Deflections

Wave

is rounded

Deflection

has a sharp peak

Wave

In English, both waves and deflections
are referred to as wave

ECG waves: P wave, Q wave, R wave, S wave, T wave, U wave

PQ Interval

Begins at the start of the P wave (atrial depolarization)
Ends at the start of the QRS complex (ventricular depolarization)
PQ interval is sometimes referred to as PR interval

Because sometimes the QRS complex starts with the R wave

Duration is 0.12 - 0.2 seconds

It is the time during which the impulse travels from the SA node to the ventricles

It is mainly used in the diagnosis of AV blocks

PR (PQ) interval begins at the onset of the P wave and ends at the QRS complex

RR Interval

Peak of the R wave

Is the moment

when the ventricles are fully depolarized

Depolarized ventricles create

the main cardiac vector

Used to calculate heart rate

RR interval is the interval between two peak R waves

QRS Complex

Is sometimes referred to as the QRS interval
The QRS complex represents ventricular depolarization
Ventricular depolarization has 3 electrical vectors

Each vector has a different direction

Ventricular depolarization

is always referred to as the QRS complex
Even though it has a different QRS configuration (RS, qR, Rs, R, rSR)

The ventricles have a more massive myocardium than the atria

This is why the amplitude of the QRS complex is larger

than the amplitude of the P wave (atrial depolarization)

Ventricular depolarization (QRS complex) lasts 0.06s - 0.1s

ECG QRS interval represents the duration of ventricular depolarization, contains Q wave, R wave, S wave

QT Interval

Starts with ventricular depolarization (QRS complex)
Ends with ventricular repolarization (end of the T wave)
The QT interval represents the duration of the action potential of the ventricles
Has a duration of 0.35 - 0.44s
Varies with frequency, so the corrected QT interval is calculated
Prolongation risks ventricular arrhythmia Torsades de Pointes

ECG QT interval represents the duration from depolarization to repolarization of the ventricles. It is the duration of the action potential

ST Segment

Is the segment between the end of the QRS and the beginning of the T wave
During the ST segment

No electrical activity is present in the ventricles
The atria are relaxed
The ventricles are contracted

Preparing for repolarization

The ST segment is a major marker for ischemia and infarction

ECG ST segment is normally isoelectric

T Wave

Represents repolarization of the ventricles
Is wide and low

Because repolarization is slower and more asynchronous

Compared to depolarization

The T wave is the most variable part of the ECG curve
Normal T wave is concordant

Has the same direction as the QRS complex

ECG T wave corresponds to phase 3 of the action potential. Represents the repolarization of the ventricles

U Wave

The U wave follows the T wave
The mechanism of its formation is uncertain

It is probably due to delayed repolarization of the ventricular septum

Not always present

Often appears in cases of hypokalemia

ECG U wave is associated with metabolic disturbances - hypokalemia

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers