QRS axis: Difference between revisions

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|mainauthor= [[user:Vdbilt|I.A.C. van der Bilt, MD]]
|mainauthor= [[user:Vdbilt|I.A.C. van der Bilt, MD]]
|advisor=
|moderator= [[T.T. Keller]]
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|supervisor=  
|moderator= [[user:Vdbilt|I.A.C. van der Bilt, MD]]
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==What is the electrical heartaxis?==
[[Image:hartas2.jpg|thumb|The heartaxis indicates the average direction of the depolarization wave. A normal heartaxis, the picture shows an example, is between -30 and +90 degrees. In this example, the heartaxis is +45 degrees.]]
[[Image:einthhartas.png|thumb|Heartaxis from the original publication of Einthoven. Reprinted from The Lancet, March 30 1912, Einthoven W.,
''The Different Forms of The Human Electrocardiogram and Their Signification'', 853-861, 1912, with permission from
Elsevier]]
The electrical heartaxis is an average of all depolarizations in the heart. The depolarization wave begins in the right atrium and proceeds to  the left and right ventricle. Because the left ventricle wall is thicker than the right wall, the arrow indicating the direction of the depolarization wave is directed to the left.
For a lot of people, this is a difficult concept. The theoretic part seems difficult but by doing it a lot, it will become clear.
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'''''Click and drag the arrow in the above animation to change the heart axis and see how the ECG changes.'''''
The electrical heart axis is an average of all depolarizations in the heart. The depolarization wave begins in the right atrium and proceeds to  the left and right ventricle. Because the left ventricle wall is thicker than the right wall, the arrow indicating the direction of the depolarization wave is directed to the left.


==How do you determine the electrical heartaxis==
For a lot of people, this is a difficult concept. The theoretical part seems difficult, but in working with it, the reader will find it becoming clearer.
==How do you determine the electrical heart axis==
[[Image:ECG_lead_angulation.png|500px|left]]
[[Image:hartas2.jpg|thumb|The heart axis indicates the average direction of the depolarization wave. A normal heart axis, the picture shows an example, is between -30 and +90 degrees. In this example, the heart axis is +45 degrees.]]
[[Image:hart_axis.png|thumb]]
[[Image:hart_axis.png|thumb]]
[[Image:hartasroset.png|thumb]]
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When you average all electrical signals from the heart, you can indicate the direction of the average electrical depolarization with an arrow (vector). This is the heart axis. A change of the heart axis or an extreme deviation can be an indication of pathology. To determine the heart axis you look at the extremity leads only (not V1-V6). If you focus especially on leads I, II, and AVF you can make a good estimate of the heart axis. An important concept in determining the heart axis is the fact that electricity going towards a lead yields a positive deflection in the electric recording of that lead. Imagine the leads as cameras looking at the heart. Lead I looks horizontally from the left side. Lead II looks from the left leg. Lead III from the right leg and lead AVF from below towards the heart. A positive deflection here is defined as the QRS having a larger 'area under the curve' above the baseline than below the baseline. With these basics in mind, one can easily estimate the heart axis by looking at leads I and AVF:
*Positive (the average of the QRS surface above the baseline) QRS deflection in lead I: the electrical activity is directed to the left (of the patient)
*Positive QRS deflection in lead AVF: the electrical activity is directed down.
This indicates a normal heart axis. Usually, these two leads are enough to diagnose a normal heart axis! A normal heart axis is between -30 and +90 degrees.


When you average all electrical signals from the heart, you can indicate the direction of the average electrical depolarization with an arrow (vector). This is the heartaxis. Especially a change of the heartaxis or an extreme deviation can be an indication for pathology.
*A '''left heart axis''' is present when the QRS in lead I is positive and negative in II and AVF. (between -30 and -90 degrees)
*A '''right heart axis''' is present when lead I is negative and AVF positive. (between +90 and +180)
*An '''extreme heart axis''' is present when both I and AVF are negative. (axis between +180 and -90 degrees). This is a rare finding.


<i>For example:</i>
The largest vector in the heart is from the AV-node in the direction of ventricular depolarization. Under normal circumstances, this is directed left and down.(towards leads I and AVF). The position of the QRS vector is given in degrees. See the figure. A horizontal line towards the left arm is defined as 0 degrees.


*Biggest QRS deflection in lead I: the electrical activity is directed to the left (of the patient)
An iso-electric lead can help estimate the heart axis more precisely:
*Biggest QRS deflection in lead AVF: the electrical activity is directed down.
;Iso-electric
 
:When the depolarization is perpendicular on the lead, this is called '''iso-electric'''. The QRS is neither positive nor negative.  
This indicates a normal heartaxis. Usually, these two leads are enough to diagnose a normal heartaxis!
 
The biggest vector in the heart is from the AV-node in the direction of the ventricular depolarization. Under normal circulstances, this is directed left and down.(towards leads I and AVF). The position of the QRS vector is given in degrees. See the figure, the middle of the figure is the AV-node. A horizontal ine towards the left arm id defiuned as 0 degrees.
 
A normal heartaxis is between -30 and +90 degrees.
 
'''Rule:''' biggest QRS deflection in I and II is an intermediate = normal heartaxis.
So positive deflections in I and II indicates a normal heartaxis.


;Undetermined axis
:When all extremity leads are biphasic, the axis is directed to the front or back, in a transverse plane. The axis is than '''undetermined'''.
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====Interpretation====
De interpretatie van de elektrische hartas kent een aantal makkelijk te onthouden regeltjes:
* Ten eerste, beweegt een positieve depolarisatiegolf naar een positieve elektrode, dan wordt er een positieve, naar boven gerichte uitslag op het ECG geregistreerd.
*Ten tweede zijn er 4 gebieden waar de QRS-vector naar kan wijzen:
**linksboven --> linker asdraaing (tussen -30º en -90º)
**linksonder --> normaal gebied (tussen -30º en 90º)
**rechtsonder en rechts--> rechter asdraaing (tussen 90º en -150º)
**rechtsboven --> extreme as (tussen -90º en -150º, dit is zeldzaam)
''Bijvoorbeeld'':
Het QRS in afleiding I zal bij een rechter asdraaing naar rechtsonder een negatieve uitslag registreren. De vector wijst namelijk niet in de richting van van de electrode. Bekijk je het QRS echter in de AVF afleiding dan zal deze positief zijn. Hier wijst de vector wel in de richting van de electrode.
====Heart-axis Simulator====
Om goed te begrijpen hoe het ECG verandert bij een asdraai kun je de hart-as simulator gebruiken: http://www.blaufuss.org/ECGviewer/indexFrame2.html
====Iso-electrical====
'''NB:''' Verloopt de depolarisatie loodrecht op de stand van de afleiding dan noemt men dit
'''iso-electrisch'''. Dit kan handig zijn om de as nauwkeurig te bepalen. Is afleiding AVF bijvoorbeeld iso-electrisch en I positief, dan is er sprake van een horizontale hartas.
====Undetermined axis ====
Ook kan het zijn dat alle extremiteitsafleidingen min of meer bifasisch zijn. De hartas staat dan vaak naar voren of achteren en de hartas is dan '''niet te bepalen'''.
==Anbormal heartaxis==
[[Image:left_axis_dev.jpg|thumb| Hartasdraai naar links bij een onderwandinfarct. Linker anterior hemi-blok is ook een veel voorkomende oorzaak. Een linker hartas ligt tussen de -30 en -90 graden. Hier is de hartas ongeveer -30 graden.]]
[[Image:right_axis_dev.jpg|thumb| Hartasdraai naar rechts bij rechtsbelasting, zoals bij longembolie en COPD. Een rechter hartas ligt tussen de +90 en +180 graden. Hier is de hartas ongeveer +135 graden]]
De richting van de vector kan onder verschillende omstandigheden veranderen:
#Is het hart fysiek gedraaid en wijst deze dus niet meer naar linksonder dan draait de hartas in dezelfde richting als het hart mee. Bijv. het hart wijst naar rechts dan is de ORS-vector ook naar rechts gelocaliseerd.
#In het geval van een hypertrofisch hart, zal door grotere elektrische activiteit de vector in die richting meedraaien (naar hypertrofisch weefsel toe).
#Het omgekeerde geldt voor weefsl dat is geinfarceerd. Hier worden namelijk geen elektrische prikkels meer voortgeleid. Dit weefsel draagt niet meer bij aan het ontstaan van vectoren. De QRS-vector draait dan van het geinfarceerde weefsel af.
#Bij geleidingsproblemen draait de hartas ook vaak. Stel dat de rechter kamer, later depolariseert dan de linker door een vertraging in het geleidingsweefsel van de rechter kamer. Als de linker kamer klaar is met contraheren is de rechter nog bezig. Het signaal van de linker kamer maskeert nu niet meer dat van de rechter. Alle nog aanwezige electrische activiteit gaat naar rechts en de hartas draait dus ook naar rechts.


==Abnormal heart axis==
<div style="float:right">
<gallery>
Image:left_axis_dev.jpg| Heart axis deviation to the left in case of an inferior infarct. Left anterior hemiblock is a common cause. A left axis is between -30 and -90 degrees. The axis is -30 degrees.
Image:right_axis_dev.jpg| Heart axis deviation to the right in right ventricular load, as in COPD or pulmonary embolism. A right axis is between +90 and +180 degrees. In this case the axis is +135 degrees
</gallery>
</div>
The direction of the vector can changes under different circumstances:
#When the heart itself is rotated (right ventricular overload), obviously the axis turns with it.
#In case of ventricular hypertrophy, the axis will deviate toward the greater electrical activity and the vector will turn toward the hypertrophied tissue.
#Infarcted tissue is electrically dead. No electrical activity is registered and the QRS vector turns away from the infarcted tissue
#In conduction problems, the axis deviates too. When the right ventricle depolarizes later than the left ventricle, the axis will turn to the right (RBBB). This is because the right ventricle will begin the contraction later and therefore will also finish later. In a normal situation the vector is influenced by the left ventricle, but in RBBB only the right ventricle determines it.
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==Left axis deviation==
==Examples of a left heartaxis==
[[Image:LHA.png|thumb| Left heart axis]]
[[Image:LHA.png|thumb| Linker hartas]]
[[Image:LAHB.png|thumb| Left anterior hemiblock]]
[[Image:LAHB.png|thumb| Linker anterior hemiblok]]
Causes of left axis deviation include:
*Normal variation (physiologic, often with age)
*Mechanical shifts, such as expiration, high diaphragm (pregnancy, ascites, abdominal tumor)
*[[Hypertrophy|Left ventricular hypertrophy]]
*[[LBBB|Left bundle branch block]]
*[[Conduction delay#LAFB| left anterior fascicular block]]
*[[Conduction delay#LAFB| left anterior fascicular block]]
*Congenital heart disease (e.g. atrial septal defect)
*Emphysema
*[[Hyperkalemia]]
*Ventricular ectopic rhythms
*[[WPW|Preexcitation syndromes]]
*[[Ischemia#Inferior|Inferior myocardial infarction]]
*[[Ischemia#Inferior|Inferior myocardial infarction]]
*[[Hypertrophy|Left ventricular hypertrophy]]
*Pacemaker rhythm
*Pacemakerritme
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== Examples of a right heartaxis ==
== Right axis deviation==
[[Image:rightaxis.jpg|thumb| Rechter hartas]]
[[Image:rightaxis.jpg|thumb| Right heartaxis]]
*[[Ventrikelhypertrofie| Rechter ventrikelhypertrofie]]
[[File:E000604.png|thumb|Another example of an ECG with a right heart axis]]
*Rechter ventrikelbelasting, bijvoorbeeld bij [[Overigen#Longembolie|longembolien]] of cor pulmonale (zoals bij COPD)
Causes of right axis deviation include:
*Atriumseptumdefect, ventrikelseptumdefect
*Normal variation (vertical heart with an axis of 90º)
*Mechanical shifts, such as inspiration and emphysema
*[[Hypertrophy| Right ventricular hypertrophy]]
*[[RBBB|Right bundle branch block]]
*[[LPFB|Left posterior fascicular block]]
*Dextrocardia
*Ventricular ectopic rhythms
*[[WPW|Preexcitation syndromes]]
*Lateral wall myocardial infarction
*Right ventricular load, for example [[Pulmonary_Embolism|Pulmonary Embolism]] or Cor Pulmonale (as in COPD)
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<analytics uacct="UA-807577-6"></analytics>
[[Category:ECG Course]]

Latest revision as of 21:12, 14 January 2021

«Step 3: Conduction (PQ, QRS, QT, QTc) Step 5: P wave morphology»


Author(s) I.A.C. van der Bilt, MD
Moderator T.T. Keller
Supervisor
some notes about authorship



Click and drag the arrow in the above animation to change the heart axis and see how the ECG changes. The electrical heart axis is an average of all depolarizations in the heart. The depolarization wave begins in the right atrium and proceeds to the left and right ventricle. Because the left ventricle wall is thicker than the right wall, the arrow indicating the direction of the depolarization wave is directed to the left.

For a lot of people, this is a difficult concept. The theoretical part seems difficult, but in working with it, the reader will find it becoming clearer.

How do you determine the electrical heart axis

ECG lead angulation.png
The heart axis indicates the average direction of the depolarization wave. A normal heart axis, the picture shows an example, is between -30 and +90 degrees. In this example, the heart axis is +45 degrees.
Hart axis.png

When you average all electrical signals from the heart, you can indicate the direction of the average electrical depolarization with an arrow (vector). This is the heart axis. A change of the heart axis or an extreme deviation can be an indication of pathology. To determine the heart axis you look at the extremity leads only (not V1-V6). If you focus especially on leads I, II, and AVF you can make a good estimate of the heart axis. An important concept in determining the heart axis is the fact that electricity going towards a lead yields a positive deflection in the electric recording of that lead. Imagine the leads as cameras looking at the heart. Lead I looks horizontally from the left side. Lead II looks from the left leg. Lead III from the right leg and lead AVF from below towards the heart. A positive deflection here is defined as the QRS having a larger 'area under the curve' above the baseline than below the baseline. With these basics in mind, one can easily estimate the heart axis by looking at leads I and AVF:

  • Positive (the average of the QRS surface above the baseline) QRS deflection in lead I: the electrical activity is directed to the left (of the patient)
  • Positive QRS deflection in lead AVF: the electrical activity is directed down.

This indicates a normal heart axis. Usually, these two leads are enough to diagnose a normal heart axis! A normal heart axis is between -30 and +90 degrees.

  • A left heart axis is present when the QRS in lead I is positive and negative in II and AVF. (between -30 and -90 degrees)
  • A right heart axis is present when lead I is negative and AVF positive. (between +90 and +180)
  • An extreme heart axis is present when both I and AVF are negative. (axis between +180 and -90 degrees). This is a rare finding.

The largest vector in the heart is from the AV-node in the direction of ventricular depolarization. Under normal circumstances, this is directed left and down.(towards leads I and AVF). The position of the QRS vector is given in degrees. See the figure. A horizontal line towards the left arm is defined as 0 degrees.

An iso-electric lead can help estimate the heart axis more precisely:

Iso-electric
When the depolarization is perpendicular on the lead, this is called iso-electric. The QRS is neither positive nor negative.
Undetermined axis
When all extremity leads are biphasic, the axis is directed to the front or back, in a transverse plane. The axis is than undetermined.


Abnormal heart axis

  • Heart axis deviation to the left in case of an inferior infarct. Left anterior hemiblock is a common cause. A left axis is between -30 and -90 degrees. The axis is -30 degrees.

    Heart axis deviation to the left in case of an inferior infarct. Left anterior hemiblock is a common cause. A left axis is between -30 and -90 degrees. The axis is -30 degrees.

  • Heart axis deviation to the right in right ventricular load, as in COPD or pulmonary embolism. A right axis is between +90 and +180 degrees. In this case the axis is +135 degrees

    Heart axis deviation to the right in right ventricular load, as in COPD or pulmonary embolism. A right axis is between +90 and +180 degrees. In this case the axis is +135 degrees

The direction of the vector can changes under different circumstances:

  1. When the heart itself is rotated (right ventricular overload), obviously the axis turns with it.
  2. In case of ventricular hypertrophy, the axis will deviate toward the greater electrical activity and the vector will turn toward the hypertrophied tissue.
  3. Infarcted tissue is electrically dead. No electrical activity is registered and the QRS vector turns away from the infarcted tissue
  4. In conduction problems, the axis deviates too. When the right ventricle depolarizes later than the left ventricle, the axis will turn to the right (RBBB). This is because the right ventricle will begin the contraction later and therefore will also finish later. In a normal situation the vector is influenced by the left ventricle, but in RBBB only the right ventricle determines it.


Left axis deviation

Left heart axis
Left anterior hemiblock

Causes of left axis deviation include:


Right axis deviation

Right heartaxis
Another example of an ECG with a right heart axis

Causes of right axis deviation include:


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