Download المحاضرة 06 حسابات وأرقام زمنية فى رسم القلب

‫دورة مهارات رسم القلب الكهربائى‬
‫‪ECG Teacher‬‬
‫محاضرة رقم ‪6‬‬
‫حسابات وأرقام زمنية فى رسم القلب‬
‫‪Time and ECG 2‬‬
‫أوال‪ :‬الملخص العربى‬
‫نتذكر من الحاضرة السابقة‪:‬‬
‫يلتتطقج اهتتا رستتم رهربائ تتق القلتتب الط تتارات الكهربائ تتق ويو ت لها بلتتي ورت رستتم ب تتا ي ات‬
‫مربعات مطواويق الح م بمعدل منطظم ح ث يحطتي ورت رستم القلتب بلتي مربعتات رو ترة ورت‬
‫مربع رو ر يحطي بلي ‪ 5‬مربعات صغ رة أفق تا و رت مربتع صتغ ر ‪1‬متم يملت ‪ 0.04‬ثا تق‬
‫أفق ا ‪،‬وبالطالي رت مربتع رو تر ‪ 5‬متم يملت ‪ 0.2‬ثا تق أ أ ‪ 5‬مربعتات رو ترة ثملت ثا تق و‬
‫‪ 300‬مربع رو ر يمل دق قق ومن لك‪ ،‬يمكن ا حوب معدل وض القلب فتي الدق قتق فمتلذ ا ا‬
‫واتتد ا دورة القلتتب راملتتق ثطكتترر ر ت ‪ 5‬مربع تات رو تترة أ أ القلتتب ينتتوض بمعتتدل ‪ 60‬دقتتق‬
‫الدق قق و هكذا‬
‫الموافق بى أر )‪(P- R interval‬‬
‫و هي ثودأ من بدايق المياق ‪ P‬الي بدايق م ميبق ر ي أر اس )أ من بدايق لودايق و هي‬
‫ثمل اليقت الموطغرت ال طقال الط ار الكهربائي من العقدة ال ب ا ين ق الي اال ين ن و منه الي‬
‫الوط ن ن و هي ثواو من ‪ 0.20- 0.12‬ثا ق أ من ) ‪ (3-5‬مربعات صغ رة‪.‬‬
‫الجزء األزرق يمثل‪ :‬الوقت الالزم إلزالة اإلستقطاب األذينىى ‪ )Depolarization‬بعى بىروز‬
‫التيار الكهربى من العقى ة االذينيىة ‪ ) SA node‬حتىى يلىل للعقى األذينيىة البطينيىة ‪AV‬‬
‫‪) node‬‬
‫والجىزء األحمىر يمثىل‪ :‬هىو التىيخير اليسىيولوجى الىذ يقىوم بى‬
‫الكهربية للبطين‬
‫‪ ) AV node‬لنقىل اإلاىارة‬
‫والجىىزء األخضىىر يمثىىل‪ :‬الوقىىت الىىالزم لنقىىل راىىارة زالىىة اإلسىىتقطاب لاىىبكة النقىىل الكهربىىى‬
‫بالبطين‪.‬‬
‫المجموعة كيو آر س ‪QRS Complex‬‬
‫‪‬‬
‫الفطرة ‪ :‬ثمل اليقت الموطغرت ال طقال الط ار خذل الوط ن ن‪.‬‬
‫‪‬‬
‫المدة ‪ :‬ثواو = ‪ 0.12‬ثا ق ‪ 3‬مربعات صغ رة‬
‫الموافق ‪QT‬‬
‫ويطلق بلى الفطرة الزمن ق ب ن بدايق إ الق االسطقطاب الوط ني وحطى بيدة االسطقطاب الوط ني‬
‫أى من بدايق م مع ‪QRS‬حطى هايق مياق ‪ T‬والشك إلى اسف ييضح من وخصائص‬
‫الموافق ر ي ثى‬
‫ ااه اليي يو‬:‫ثانيا‬
http://www.youtube.com/embed/6Px9J7gK0Yg
‫ النص اإلنجليز للمحاضرة كامال‬:‫ثالثا‬
In addition to calculating heart rate, the fact of distance on ECG paper
equates to time. We use the readout to time the generation of major
events of cardiac cycle. We've seen that at a standard recording speed
of 25 mm/second, five large squares corresponds to one second,
therefore one big square corresponds to 0.2 second and one small
square corresponds to 0.04 second.
There are a few numbers coming up now which is simply most learn:
- In normal heart the time between the onset of depolarization
(beginning of P wave and the onset of ventricular depolarization
(the beginning of the QRS complex) varies between 0.12 – 0.2
seconds (from 3 – 5 small squares) this is called PR interval. The
PR interval is made of a number of elements, the first
component represents (in Blue) the time taken for the
depolarization wave normally generated from the SA node to
traverse the atria to reach AV node. You will know that the
depolarization wave reach the AV node well before the end of P
wave. However the Av node delays transmitting the impulse to
the ventricles, this physiological delay (in Red) is the second
major component of the PR interval. The third component
shown in green is the time taken by the depolarization wave to
transit through the bundle of His and the branches of
interventricular conducting system.
Many disorders are associated with alterations in components of
PR interval manifested as abnormal shortening or prolongation
in ECG. Analysis of PR interval plays essential role in diagnosing
many disorders of the heart.
- The PR interval ends with the release of current in the muscle
mass of the septum and ventricles from the terminal branches of
the interventricular conducting system. In the ECG this point is
marked with the onset of the QRS complex. So the next key
value we need to learn is the generation of the QRS complex
which represents the time taken for ventricular depolarization to
be completed, following the release of the depolarizing current
from the conducting system. It also includes the time taking for
the recording needle to return to base line when the flow of the
depolarizing current in the ventricles complete. The conducting
system in the ventricles is a highly specialized tissue capable of
transmitting the depolarization wave rapidly around the
chambers. Note that with intact conducting system depolarizing
current is delivered to all sectors of the ventricles in a very short
time and ventricular depolarization of all regions of chambers is
complete in less than 0.12 second (less than 3 small squares) so
normal QRS complex is less than 3 small squares ( range from
0.06 to 0.11 second) We will learn that the width of QRS complex
is extremely important when we shift to life threatening
arrhythmias.
- The duration of ventricular Repolarization is also important. The
time between the onset of ventricular depolarization and end of
ventricular Repolarization (from the beginning of the QRS
complex to the end of T wave) is termed QT interval.
At a heart rate of 60/minute the QT interval should be less than
0.45 seconds in males and less than 0.46 seconds in females. The
upper limit of QT interval is between 11-12 small squares (0.44 –
0.48 second). It is important to know that measures of QT
interval vary with heart rate, becomes shorter when the heart
speeds up and longer when the heart slows down. So particularly
at a higher heart rates it is possible to miss an underlying
prolonged QT interval.
- Abnormally slow ventricular Repolarization evidenced by
prolonged QT interval in the ECG places patients at risk of fatal
arrhythmias when treated with certain commonly used drugs.
The ability to identify prolonged QT interval can save life of
these patients by treating them with alternative medications.
- When faced with ECG with heart rate other than 60
beats/minute to calculate the underline QT interval use
(corrected QT interval) QTc. We use the following formula:
QTC = Bazett's Formula = QT Interval / √ (RR interval)
RR interval is the distance between 2 successive R waves
measured in seconds.
-
-
Example: (in Video)
A male with heart rate 100/minute (RR are 3 big squares) = 0.6
seconds. The observed QT interval at aVL lead is 8 small squares
= 0.32 seconds. What is the corrected QT (QTc)?
Bazett's Formula = QT (0.32) / √ (0.6) = 0.41 second.
So this is patient doesn’t have a prolonged QT.
Disadvantage of Bazett's formula is not giving correct results at
high heart rates.
To give a simple rule of thumb: if the observed QT interval on
the ECG is more than 1/2 half of the RR interval at least
consider the possibility of prolonged QT interval.
It is recommended to observe QT interval in one of the
following leads: aVL – aVR – one right sided chest leads V1-V2
Also QT interval varies with age, gender and time of day and
with different leads.
Minor prolongation of QT interval is hard to access the key is not
to miss marked or gross prolonged QT intervals.
In an area of video we studied the manner of depolarization and
Repolarization. We studied the manner of recording them. We
learned the direction of current a depolarizing or repolarizing
relative to lead is the key determinant of the sign deflection
produced in that lead (above or below isoelectric line) We will
expand on this analysis in future videos however for now:
If a depolarizing or repolarizing current is travelling at 90 degrees
relative to lead it will not be recorded by that lead.
As the ECG leads record electrical events from different prospective , a
lead observing this current from a different angle will record it so some
events will be recorded by some leads but missed by others. For this
and many other reasons the electrical events vary between many ECG
leads. When we calculate the time of QRS we choose the lead with the
widest QRS.
Rmember:
- PR interval = 3-5 small squares (0.12 – 0.2 second)
- QRS = 3 small squares (less than 0.12 second)
- QT = less than 11 small squares (less than half of RR)
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