ECG Basics Flashcards
Which node is termed the pacemaker node of the heart?
The SA Node
Describe the location of the SA node in the heart?
On the lateral wall of the right atrium
The depolarisation of the purkinje fibres causes which part of the heart to be depolarised?
The ventricles - the perking fibres are embedded within the ventricular wall.
What does the p wave represent?
The p wave represents arterial depolarisation
The QRS complex does not immediately proceed the p wave - why is this?
Following the atrial depolarisation the wave of depolarisation travels to the AV node, Bundle of HIS, Bachman’s Bundle, Bundle branches and purkinje fibres.
What does the QRS complex represent?
Ventricular depolarisation
What does the t wave represent?
Ventricular repolarisation
Ventricular depolarisation is represented by the t wave - which aspect of the ECG tracing represents atrial repolarisation?
The atrial repolarisation is represented within the QRS complex as it occurs simultaneously to ventricular depolarisation.
How many leads are in the normal ECG?
12
Name the 12 leads of a normal ECG tracing.
Lead I, II, III
AVF, AVR, AVL
V1, V2, V3, V4, V5 and V6
From which aspect of the heart does the AVR take electrical information?
The right side of the heart - since electrical activity moves towards the left side of the heart the electrical activity is moving away from the AVR lead - creating a negative or downward deflection.
The net movement of electrical activity is towards the _______(left/right) in the heart.
Left
From which aspect of the heart does lead I and AVL take electrical information?
The left side of the heart - since electrical activity moves towards the left side of the heart the electrical activity is moving towards lead I and AVL - creating a positive or upward deflection.
From which aspect of the heart does lead II, lead III and AVF take electrical information?
Inferior aspect of the heart
From which aspect of the heart does V1-V6 take electrical information?
Across the heart - with V1 most central (right) and V6 most left.
V1 is located on the right side of the heart, as such its deflections will be ______(positive/negative)
Negative - electrical impulses move towards the left side of the heart.
V6 is located on the left side of the heart, as such its deflections will be ______(positive/negative)
positive - electrical impulses move towards the left side of the heart.
List the 5 cardiac pacemakers.
SA node AV node HIS Bundle Branches Purkinje fibers
Describe the pacemaker speed of the 5 cardiac pacemakers.
SA node - 60-100 bpm AV node - 60-80 bpm HIS - 25-40 bpm Bundle Branches - 25-40 bpm Purkinje fibers - 25-40 bpm
Which cardiac pacemaker has the slowest conduction speed?
AV Node- this is important as it allows more time for ventricular filling following atrial depolarisation.
Which cardiac pacemaker has the highest conduction speed?
Purkinje fibers - recall these are responsible fro ventricular depolarisation.
How much time do the “big boxes” represent on the ECG paper?
200 milliseconds
How much time do the “small boxes” represent on the ECG paper?
40 milliseconds
How is heart rate calculated from an ECG tracing?
The number of big boxes between 2 QRS complexes are calculated - 300/#big boxes between QRS complexes.
The normal QRS axis is between _______?
-30 degrees and +90 degrees
Left axis deviation is seen on the QRS axis between _______?
-30 degrees and -90 degrees
Right axis deviation is seen on the QRS axis between _______?
+90 degrees and +180 degrees.
The area of the QRS axis between -90 degrees and +180 degrees is termed what?
No mans land.
Left axis deviation can be caused most commonly by which pathological conditions?
Left bundle branch block
Ventricular rhythm abnormalities - e.g. ventricular tachycardia (impulses are not coming for the node but the ventricle itself).
Right axis deviation can be caused most commonly by which pathological conditions?
Right bundle branch block
Right ventricular hypertrophy
According to the axis quick method, which 2 leads should be used to determine a normal QRS axis and what should these leads show for a normal reading?
Leads I and II
- both leads should be positive for a normal QRS axis.
According to the axis quick method, which 2 leads should be used to determine left axis deviation of QRS axis and what should these leads show for a LAD reading?
Leads I and II
- Lead II (only) should be negative (or downwards) for LAD.
According to the axis quick method, which 2 leads should be used to determine right axis deviation of QRS axis and what should these leads show for a RAD reading?
Leads I and II
- Lead I (only) should be negative (or downwards) for RAD.
Suppose an ECG tracing has a lead II QRS complex that is half above and below baseline (half positive and negative) - what does this indicate?
This indicates a physiologic left axis deviation that is still within normal range.
Where is the PR interval measured from?
The PR interval is measured between the start of the p wave and start of the QRS complex.
What is the normal PR interval?
120-200 milliseconds (a PR interval longer than 1 big box is considered abnormal).
Name a common pathological condition which causes a prolonged PR interval.
First degree AV block
Name a common pathological condition which causes a shortened PR interval.
WPW - Wolf Parkinson White syndrome.
Where is the QRS interval measured from?
The QRS interval is measured between the start of the QRS complex to the end of the QRS complex.
What is the normal QRS interval?
less than 120 milliseconds - (a QRS interval longer than 3 small boxes is considered abnormal).
Name a common pathological condition which causes a prolonged QRS interval.
Bundle branch blocks (right or left bundle branch block)
Where is the Qt interval measured from?
The Qt interval is measured between the start of the QRS complex and END of the t wave
What is the rule of thumb for measuring a normal Qt interval?
The t wave should END before the midway point between 2 QRS complexes.
Name a common pathological condition which causes a shortened Qt interval.
Hypercalcemia - calcium plays an important role in the contractility of the cardiac myocytes. The t wave will IMMEDIATELY follow the QRS complex.
Name a common pathological condition which causes a prolonged Qt interval.
hypocalcemia - calcium plays an important role in the contractility of the cardiac myocytes. Low calcium will mean the time for calcium to be moved back into (repolarise) myocytes increases (represented by the t wave)
drugs (antiarrhythmic drugs)
LQTS (long QT syndrome (a congenital syndrome))
What is a deadly and feared outcome of prolonged Qt intervals?
Torsade de Pointes - a twisting of the points which is where the QRS complex becomes shorter and longer.
What are some causes of Tornado de Pointes?
Hypokalemia
Hypomagnesmia
Hypocalcemia (much less common)
What are some reasons why a patient may have high or peaked t waves?
hyperkalemia
very early in ischemia (often proceed ST segment elevation).
What is a reason why a patient may have u waves present or prominent?
hypokalaemia
What are u waves hypothesised to represent?
Repolarisation of the purkinje fibres.
