17 Interpretation of ECG Flashcards
What is a normal sinus rhythm?
60-100 beats /min
RR interval 3-5 large boxes
What is sinus bradycardia?
a slow sinus rhythm; <60/min
(RR interval >5 large boxes).
What is sinus tachycardia?
a fast sinus rhythm; >100/min
RR interval <3 large boxes
What is sinus arrhythmia?
an irregular sinus rhythm; difference between the longest and the shortest PP or RR interval is more than 0.16 s (equivalent to 4 small boxes)]
First method to measure heart rate is by using the RR interval.
How can we obtain the heart rate?
60/ (number of small boxes x 0.04 )
How to derive heart beat by the rule of 300?
Count the number of large boxes between RR intervals and divide it by 300.
e.g. 4 large boxes between 2 RR intervals > 300/4 = 75 beats /min
What is the triplicate method?
Use the heart rate ruler
and sample 3 consecutive RR intervals
What is the 6 second count method?
every 15 large boxes = 3 seconds
30 large boxes = 6 seconds
number of RR intervals in 30 large boxes x 6
How to identify Premature contraction in ECG?
can be ventricular
no P wave/
wider than normal QRS complex
How to identify escape beats in ECG?
T wave is shown late
What is the definition of 1st degree atrioventricular or heart block?
What can be seen in the ECG?
lengthening of PR interval
normal = 0.08-0.12s within a large box!
What is the definition of 2nd degree atrioventricular or heart block?
What can be seen in the ECG?
Intermittent failure of excitation to pass from atria to ventricles
- long PR intervals, disappeared QRS sometimes
What is the definition of 3rd degree atrioventricular or heart block?
What can be seen in the ECG?
Atria and ventricles beat independently
no relationship between P waves and QRS complexes, QRS rate is slower than P rate.
How can a bundle branch block/ aberrant pathway be identified on ECG?
QRS > 0.1s
What is the difference on the ECG of right and left bundle branch block?
right: QRS complex with Bunny ears in V1, V2 leads
left: QRS complex with bunny ears in lead1, V6, and sometimes V1 and V2
____ is defined as additional deflection with inverse
polarity, within the Q, R or S wave of the QRS complex..
Notching
> inverted bunny ears
_____ is a “slight notching”
without change of polarity.
Slurring
> bunny ears
Other than bundle branch block and aberrant pathway of conduction, what else is a possible cause to lengthened QRS complex? > 0.12s
(normal = 0.08-0.12s)
Ventricular hypertrophy
Delay intrinsicoid
deflection means it takes longer time for R
wave to reach its peak as it requires more
time to spread the depolarization through the
thickened ventricular wall.
The cardiac/ QRS axis indicates the direction
of the mean ventricular depolarization vector
in the frontal (vertical)
plane when averaged over time.
What is the normal range of cardiac axis?
0 degree starts at 3 oclock > clockwise
-29 - +90 degrees
lower half positive
upper half negative
What does it mean by right and left axis deviation?
right: > +90 degrees
left: < -30 degrees
What factors will affect the cardiac axis?
A. Age B. Gender C. Body position D. Position of diaphragm (e.g. pregnancy, obesity) E. Anatomical position of heart F. Hypertrophy
All except B
C: Cardiac axis must be determined in supinated position
How can cardiac axis be determined? (using which leads?)
using ANY TWO of the Lead I, II and III.
with larger QRS complex
e.g. Lead I:
R = +16; Q=-2.5
Sum = +13.5 > draw perpendicular line at lead I
A simple way of estimating the electrical axis of the heart is to divide into four quadrants and consider
the positivity and negativity of only ____ and _____.
Lead I and Lead aVF
normal: ++
right axis deviation: -+
left axis deviation: +-
Extreme right axis deviation: –
Rotation of heart: normal should be V3 is the transition zone.
QRS complex can be seen clearly from V3 leads onwards.
If QRS complex can be seen already in V2/ earlier than V3, what does it mean?
Shift to the right.
Counterclockwise rotation
If QRS complex appears in leads from V4 onwards, what does it mean?
Shift to the left
Clockwise rotation.
Where should the 6 chest leads be put?
V1 4th intercostal space at right border of sternum V2 4th intercostal space at left border of sternum V4 5th intercostal space in left mid-clavicular line V3 Midway between V2 and V4 V6 Same level as V4 in midaxillary line V5 Midway between V4 and V6, in anterior axillary line
