Intro Flashcards
Meaning of ECG
Electro—- from electric
Cardio—-means heart
Gram—means a drawing
Natureal pacemaker of the heart
SA node
Order of elecrticity transmission in the heart
SA node»_space; AV node»_space; bundle of hiss»_space; purkinje system (fiber)
Three points that must be focused in ECG dx
• Enlargement
• Ischemia
• arrhythmia
Main components of an ECG waveform:
• P wave : atrial depolarization
• QRS complex: ventricular depolarization
• T wave: ventricular repolarization
Any abnormality (ischemia or hypertrophy) in the atrial (R or L) can cause
Abnormality in P wave
ST segment is ischemia of
Ventricle
+++ in MI and —- in angina
Any abnormality in the ventricle can cause abnormality in
QRS and T waves
P R segment is related to
Ischemia in the atrium
SVT (supraventricular tachycardia) (in the atrium) is related to:
P wave or P R segment
Direction of electricity in the heart called
Vector
Main vector of the heart
From SA node to the ventricle
Difference of electricity between two point
Lead
The arrow is rising or depressed according to
Direction of the electric current
What is the global speed of ECG:
25mm/sec
Voltage in heart is called
Amplitude
Which has biggest voltage, atrium or ventricle
Ventricle (more thick)
More squares in the ECG indicates
+++voltage (Enlargement)
Count the squares
Any chamber give 1mv …
it rises 10mm of the wave
Standard ECG Calibration
A standard ECG calibration produces a 1 mV signal, which should result in a 10 mm deflection (1 large box) on the ECG paper.
One large box =
5 small squares (0.5mv)
Can we change the calibration?
Yes, we can make it more sensitivity
• Double calibration (Like making 1mv=20mm in patients with low voltage ecg)
• Half calibration (1mv=5mm)
**•Note: The standard calibration is 1mv=10mm(2 large squares or 10 small)
Causes of low voltage ECG:
Pericardial effusion
Obesity
Hypothyroidism
Cardiac temponade
Pleural effusion
Pneumothorax
Standard speed of ECG recorder
25mm/sec:
• 5 large squares/sec
• 25 small squares/sec
• 300 large squares/min
• 1500 small squares/min
• The large square (5 small) takes 0.20 sec
• The 3 small squares take 0.12 sec
• The small square takes 0.04 sec
Can we change the speed of ECG recorder
Yes, but it can affect the diagnosis, so if you don’t want it, don’t messing with it.
When we need to change the speed of ECG recorder:
We don’t need!
But you can raise the speed to 50m/sec for better visualization to P wave in case of atrial fibrillation or flutter
What are the problems if we change the speed of the ECG recorder
Misdiagnoses of tachycardia or bradycardia
What is the baseline between P wave and QRS complex and T wave of one beat and P wave to another
Isoelectric line (it is called segment)
Difference between interval and segment
• Interval has wave (P-R interval)
• Segment (isoelectric line) has no wave (PR segment: from end of P wave to beginning of QRS)
• PR segment + P wave = PR interval
Segments of ECG
PR (discussed it before)
ST segment: end of QRS to beginning of T wave that represents distance after depolarization and before repolarization of ventricles
QT interval represents
Beginning of depolarization to end of repolarization of ventricles
When the atrium is repolarized
During QRS complex
But the ECG can’t draw due to the existing stronger wave (masked)
U wave is present in
Hypokalemia
Widths of waves
• P wave: 3mm or a little smaller (0.12 sec)
• QRS: 3mm same
• QT interval : half RR
ECG intervals:
PR interval
QRS interval : start of Q, end of S
QT: start of T to end of T wave
RR : peak of one R to the peak of next T wave
ECG waves
Positive waves:
P, R, and T waves
Negative Waves:
Q and S waves
A normal physiological case where all waves appear negative in an ECG:
In Lead aVR (augmented vector right)
How to identify the case is Sinus or A-Sinus
There is P wave? **Sinus
No P wave? A-Sinus
Comes or doesn’t come from SA node
How to identify the heart is regular or irregular:
RR interval is constant? Regular
Not? Irregular
Characteristics of sinus rhythm:
• Each one P wave is followed by QRS
• P waves in lead I & II is upward
• P-R interval is regular
• R-R interval is regular (not always)
Calculation of Heart Rate in case of regular rhythm
300/Number of Large Squares between RR
Calculation of Heart Rate in case of Irregular rhythm
Number of QRS in 15 Large Squares × 20
Normal number of Large Squares between RR
3-5
100b/min - 50b/min
What is Lead Il in an ECG?
A standard limb lead that records electrical activity from the right arm (-) to the left leg (+).
What heart rhythms can Lead ll help diagnose?
Atrial fibrillation, atrial flutter, heart blocks, and sinus arrhythmia,
Why is Lead Il commonly used for rhythm analysis?
Because it provides a clear view of P waves, QRS complexes, and T waves, making it ideal for detecting arhythmias.
What is Lead I in an ECG?
A standard limb lead that records electrical activity from the right arm (-) to the left arm (+)
What does Lead 1 primarily measure
Electrical activity moving horizontally across the heart, from right to left.
How does a normal P wave appear in Lead I?
Upright, indicating normal atrial depolarization.
What is the normal axis of Lead I?
0 degrees, meaning it views the heart’s activity from a leftward perspective
شنو هو الlead
حساب أي فرق في الجهد الكهربائي ما بين نقطتين في جسم الإنسان تسمى lead
What is Lead 1ll in an ECG?
A standard limb lead that records electrical activity from the left arm (-) to the left leg (+).
What are the other leads
These are augmented limb leads, created by combining two limb electrodes as a reference point for the third.
• They provide frontal plane views of the heart.
VR, VL, and VG
What is AVR
Augmented voltage in the right arm
AVL?
Augmented voltage in left
AVF
Augmented voltage in feet
Normal axis of the heart
-30»_space; +110
Detection of axis:
Look to QRS in lead I & AVF
• Normally are positive
• ** Rt Axis > +110: -I + AVF
• ** Lt Axis < -30: +I -AVF
Summary of limb leads
I : RT arm to LT
II : RT arm to LT leg
III: LT arm to RT leg
VR: RT arm to heart
VL: LT arm to heart
VF: heart to the feet
D/D of right axis deviation (+110 to +150)
• In young children and tall adults
• Left posterior hemiblock
• RVH & RBBB
• Anterolateral MI
• Pulmonary embolism
D/D of left axis deviation (-30 to -90)
• Obesity
• Left anterior hemiblock
• LBBB
• Inferior MI
• Emphysema
• Hyperkalemia
Note: Not all left ventricular hypertrophy cause left axis deviation
