Conduction: Difference between revisions

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  [[Image:QRSwaves.jpg|thumb]]
  [[Image:QRSwaves.jpg|thumb]]


The PQ time indicates how fast the action potential is transmitted through the AV node(atrioventricular) from the atria to the ventricles. Measurement should start at the beginning of the P wave to the beginning of the QRS segment.
The PQ time indicates how fast the action potential is transmitted through the AV node (atrioventricular) from the atria to the ventricles. Measurement should start at the beginning of the P wave to the beginning of the QRS segment.


'''The normal PQ is between 0.12 and 0.20 seconds'''.
'''The normal PQ is between 0.12 and 0.20 seconds'''.


A prolonged PQ time is a sign of a degradation of the conductionysystem. This is called [[Rhtyhmdisturbances#AV-block|1ste, 2nd or 3rd degree AV block]].
A prolonged PQ time is a sign of a degradation of the conduction system. This is called [[Arrhythmias #AV-block|1st, 2nd or 3rd degree AV block]].


A short PQ time can bes een in the [[Rhythmdisturbances#WPW|WPW syndrome]] in which a faster connection exists between the atria and the ventrikels.
A short PQ time can be seen in the [[Arrhythmias#WPW|WPW syndrome]] in which a faster connection exists between the atria and the ventricles.
{{clr}}
{{clr}}


==The QRS duration==
==The QRS duration==
  The QRS duration indicates how fats the ventricles depolarize.  
  The QRS duration indicates how fast the ventricles depolarize.  


The ventricles depolarize  normally within 0.10 seconds. When this is longer than 0.12 seconds, this is a '''[[conductiondelay| conductiondelay (Left budlebranchblock or Right bundlebranchblock]]'''.
The ventricles depolarize  normally within 0.10 seconds. When this is longer than 0.12 seconds, this is a '''[[conduction delay| conduction delay (Left bundlebranchblock or Right bundlebranchblock]]'''.


==The QT time==
==The QT time==
  The QT time indicates how fast the ventricles are repolarized and how fast they are ready for a new heartcycle
  The QT time indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle


The normalvalue for QTc(orrected) is: 440ms for men and 450 ms for women.
The normal value for QTc(orrected) is: 440ms for men and 450 ms for women.


[[Image:QRSinterval.jpg|thumb| The QT interval start at the onset of the Q wave and ends where a line golf en eindigt waar The raaklijn langs het laatste Theel van The T golf The basislijn raakt. Klik op The Image voor een vergroting]]
[[Image:QRSinterval.jpg|thumb| The QT interval start at the onset of the Q wave and ends where a line for the steepest part of the T wave crosses the baseline of the ECG. Click on the image for a bigger image]]
<flash>file=QTc.swf|width=200|height=135|quality=best|align=right|salign=R||bgcolor=#FFF5F5</flash>
<flash>file=QTc.swf|width=200|height=135|quality=best|align=right|salign=R||bgcolor=#FFF5F5</flash>




Het QT-inteval omvat het QRS-complex, het ST-segment, The T-golf en vertegenwoordigd ventriculaire Thepolarisatie en repolarisatie.
The QT-interval comprises the QRS-complex, the ST-segment, and the T-wave.


Bij een (ernstig) verlengThe QT time duurt het lang voordat The hartspiervezels weer klaar zijn voor een nieuwe hartslag. Het can dan voorkomen dat sommige vezels nog niet gerepolariseerd zijn, terwijl er wel al een hartslag 'aankomt' . Theze vezels kunnen vervolgens op een ongecontroleerd moment gaan Thepolariseren en zo aanleiding geven tot een [[Ritmestoornissen#TorsaThe_The_pointes|torsaThe The pointes]], een ventriculaire tachycardie.
In  a (serious) prolonged QT time, is takes longer for the myocardial cells to be ready for a new cardiac cycle. There is a possibility that some cells are not yet repolarized, but that a new cardiac cycle is already initiated. These cells are at risk for uncontrolled depolarization and induce a [[Arrhythmmias#Torsades_de_pointes|torsades de pointes]], a ventricular tachycardia.


Het QT interval is geThefinieerd als volgt: <cite>Lepeschkin</cite> The time tussen het begin van The Q tot het punt waar The steilste raaklijn langs The achtercant van The T top The basislijn raakt.  
The QT interval is defined as follows: <cite>Lepeschkin</cite> The time between the beginning of the Q until the point where the steepest tangent line from the end of the T-wave intersects with the base line of the ECG.  


Het lastige is dat The QT time shortr wordt naarmate The hartslag sneller is. Daarom bestaat bij ieThere hartfrequentie een eigen maximale QT time. Dit probleem is op te vangen door The QT time te corrigeren voor The hartfrequentie (QTc). Dit gaat als volgt:
The difficult part is that the QT interval gets shorter if the heart rate increases. This cab be solved by correcting the QT time for heart rate using the Bazett formula::


[[Image:Formule_QTc.png]]
[[Image:Formule_QTc.png]]


''bij een RR interval van 1 seconThe (hartfrequentie 60/min) is QTc=QT''
''at an RR interval 1 second, the  (heart frequency 60/min) QTc=QT''


Met The QTc calculator hier rechts is The QTc time makkelijk uit te rekenen.
Using the QTc calculator on the right, the QTc is easy extractable.


Op moTherne ECG's staat The QTc aangegeven. Het omrekenen van QT naar QTc gaat altime goed (tenzij The hartfrequentie verkeerd gemeten
On the modern ECG machines, the QTc is given. However, the machines are not always capable of recognizing the correct QT time. Therefore, it is important to check this manually..
wordt). Het apparaat maakt wel vaak fouten bij het bepalen van The QT time. Het is dus belangrijk dit te controleren. Als The QT goed is gemeten door het apparaat, zal The QTc ook goed zijn.


Voor The QT time (dus niet gecorrigeerd voor The frequentie) is het lastig om een normaalwaarThe aan te geven, aangezien die afhankelijk is van The hartfrequentie. The volgenThe formule geeft een indicatie voor The normaalwaarThe:  
The following formula is indicative for normal values of QT time (uncorrected):


[[Image:Formule_QTn_nl.png]]
[[Image:Formule_QTn_nl.png]]
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===Difficult QT times===
===Difficult QT times===
Bij sommige varianten van het QT interval is het soms lastig om The QT time te meten. Hier is een apart hoofdstuk aan gewijd: [[Lastige_QT| Het meten van lastige QT tijThen]].
In some examples of the QT interval it can be difficult to measure a correct QT time. We have made a separate chapter: [[Difficult_QT| Measurement of difficult QT times]].


===Causes of a prolonged QT time===
===Causes of prolonged QT time===
*Medicatie (o.a. anti-arrithmetica, tricyclische antiThepressiva, phenothiazeThes, zie [http://www.torsaThes.org TorsaThes.org]
*Medication (i.e. anti-arrhythmics, tricyclic antidepressants, phenothiazedes, for a complete list look on [http://www.torsades.org Torsades.org]
*Erfelijke [[Lange QT syndroom|lange QT syndroom]] (LQTS)
*Inherited [[Long QT syndrome|long QT syndrome]] (LQTS)
*Cerebraal (subarachnoidale bloeding, CVA, trauma)
*Cerebral (subarachnoid haemorrhage, stroke, trauma)
*Post infarct
*Post infarct


===Short QT syndrome===
===Short QT syndrome===
Er bestaat ook een zeldzame vorm van '''short QT syndroom''', waarbij The QTc < 300ms is. Ook hierbij treed plotselinge hartdood op.<cite>Gaita</cite>
There is also a rare form of the '''short QT syndrome''', in which the QTc < 300ms. This has been associated with sudden cardiac death.<cite>Gaita</cite>


== References ==
== References ==

Revision as of 13:56, 6 May 2007

Accuracy dispute This article or section is currently being developed or reviewed.
Some statements may be disputed, incorrect or biased.

The PQ time

The PQ time starts at the beginning of the atrial contraction and ends at the beginning of the ventricular contraction.
QRSwaves.jpg

The PQ time indicates how fast the action potential is transmitted through the AV node (atrioventricular) from the atria to the ventricles. Measurement should start at the beginning of the P wave to the beginning of the QRS segment.

The normal PQ is between 0.12 and 0.20 seconds.

A prolonged PQ time is a sign of a degradation of the conduction system. This is called 1st, 2nd or 3rd degree AV block.

A short PQ time can be seen in the WPW syndrome in which a faster connection exists between the atria and the ventricles.

The QRS duration

The QRS duration indicates how fast the ventricles depolarize.

The ventricles depolarize normally within 0.10 seconds. When this is longer than 0.12 seconds, this is a conduction delay (Left bundlebranchblock or Right bundlebranchblock.

The QT time

The QT time indicates how fast the ventricles are repolarized and how fast they are ready for a new heart cycle

The normal value for QTc(orrected) is: 440ms for men and 450 ms for women.

The QT interval start at the onset of the Q wave and ends where a line for the steepest part of the T wave crosses the baseline of the ECG. Click on the image for a bigger image

<flash>file=QTc.swf|width=200|height=135|quality=best|align=right|salign=R||bgcolor=#FFF5F5</flash>


The QT-interval comprises the QRS-complex, the ST-segment, and the T-wave.

In a (serious) prolonged QT time, is takes longer for the myocardial cells to be ready for a new cardiac cycle. There is a possibility that some cells are not yet repolarized, but that a new cardiac cycle is already initiated. These cells are at risk for uncontrolled depolarization and induce a torsades de pointes, a ventricular tachycardia.

The QT interval is defined as follows: [1] The time between the beginning of the Q until the point where the steepest tangent line from the end of the T-wave intersects with the base line of the ECG.

The difficult part is that the QT interval gets shorter if the heart rate increases. This cab be solved by correcting the QT time for heart rate using the Bazett formula::

Formule QTc.png

at an RR interval 1 second, the (heart frequency 60/min) QTc=QT

Using the QTc calculator on the right, the QTc is easy extractable.

On the modern ECG machines, the QTc is given. However, the machines are not always capable of recognizing the correct QT time. Therefore, it is important to check this manually..

The following formula is indicative for normal values of QT time (uncorrected):

Formule QTn nl.png

Difficult QT times

In some examples of the QT interval it can be difficult to measure a correct QT time. We have made a separate chapter: Measurement of difficult QT times.

Causes of prolonged QT time

  • Medication (i.e. anti-arrhythmics, tricyclic antidepressants, phenothiazedes, for a complete list look on Torsades.org
  • Inherited long QT syndrome (LQTS)
  • Cerebral (subarachnoid haemorrhage, stroke, trauma)
  • Post infarct

Short QT syndrome

There is also a rare form of the short QT syndrome, in which the QTc < 300ms. This has been associated with sudden cardiac death.[2]

References

  1. LEPESCHKIN E and SURAWICZ B. The measurement of the Q-T interval of the electrocardiogram. Circulation. 1952 Sep;6(3):378-88. DOI:10.1161/01.cir.6.3.378 | PubMed ID:14954534 | HubMed [Lepeschkin]
  2. Gaita F, Giustetto C, Bianchi F, Wolpert C, Schimpf R, Riccardi R, Grossi S, Richiardi E, and Borggrefe M. Short QT Syndrome: a familial cause of sudden death. Circulation. 2003 Aug 26;108(8):965-70. DOI:10.1161/01.CIR.0000085071.28695.C4 | PubMed ID:12925462 | HubMed [Gaita]

  3. Bazett HC. An analysis of the time-relations of electrocardiograms. Heart 1920;7:353-370.

    [bazett]

All Medline abstracts: PubMed | HubMed

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