How do you count Hear rate on an ECG?
1) Count the number of R waves in 30 large squares (6s) and multiply by 10.
2) Count large squares between one QRS to the next. 300/x
How may seconds does 1 large square account for?
1 large square = 0.2s.
30 squares= 6s.
How long is a P wave?
P waves should be no more than 2 small squares long- 0.08s/80ms
What is the PR interval?
It includes the time to cross the AV node and propagate via budge of his
How long is the PR interval?
120-200ms.
A variable PR interval or PR interval over 200ms indicates a form of heart block
What can prolonged PR interval indicate?
Hypokalemia, acute rheumatic fever or carditis
How long should the QRS complex be?
less than 120ms. A long QRS will indicate part of the ventricle not contracting properly
Ventricular tachycardia
Rate 180-190 beats per minute,
Prolonged QRS,
P wave not seen
What is the difference between VT and VF?
In VT the rhythm and amplitude of the QRS complex is regular but much faster
Ventricular fibrillation
Disorganised electrical signals which cause the ventricles to quiver instead of contract in rhythm.
Rhythm- irregular.
Rate- 300+ and disorganised.
P wave- not seen
1st degree heart block
PR interval is a fixed constant. The rate is regular
2nd degree heart block- type 1
Progressively longer PR interval until the P wave is not followed by a QPR
2nd degree heart block- type 2
The AV node randomly fails to respond to atrial impulses- rate is irregularly irregular
3rd degree heart block
The impulses from the atria do not connect with ventricles. The ventricular rhythm is independent of the atrial rhythm ( no relationship between P waves and QRS interval)
Where does the ventricular beats in 3rd degree heart block start?
The ventricles generate their own signal from a focus within the ventricle. These ventricular beats are usually slow so bradycardia is present
Atrial Fibrillation
Many separate sites within the atria generate electrical impulses leading to irregular conduction of impulses by the ventricles.
What are the symptoms of AF?
It may cause no symptoms but is often associated with palpitation, fainting, chest pain or congestive heart failure
AF on a ECG?
Rate- 100-160 bpm.
Rhythm- irregularly irregular.
P wave- no distinguishable.
Atrial flutter
Re-excitation of electrical impulses in the atria cause a high frequency bombardment of AV mode leading to a high regular heart rhythm
What does atrial flutter show on an ECG?
Rate- 110bpm.
Rhythm- regular.
QRS- Normal.
P waves- multiple flutter waves
Junctional rhythm
Damage to the SAN or a block in the conduction pathway in the atria . The AVN takes over the pacemaker
What is junctional rhythm on a ECG?
Rate- 40-60 bpm
Rhythm- regular.
P wave- absent.
Supraventricular Tachycardia
Abnormality in or near the AV node. This creates a high frequency of impulses generated at the AV node (Similar effect to atrial flutter)
Supraventricular Tachycardia on ECGs
Rate- 140-220 bpm.
Rhythm- regular.
P wave- absent or buried in t waves.
AV nodal reentrant tachycardia
The most common supra ventricular tachycardia caused when a reentry circuit forms within or just next to the atrioventricular node so the atrial impulses continues to activate the AV node
Bundle branch block
Abnormal conduction through the bundle branch which causes depolarisation delay of the ventricle. This shows increased QRS complex
What does Right bundle branch block indicate?
Right side heart problems
What does Left bundle branch block indicate?
heart disease
What does bundle branch block show on an ECG?
Normal rate and rhythm.
QRS- prolonged
Everything else- normal.
A notch on the R wave or a double R wave indicates bundle branch block.
What does the ST segment indicate?
It represents the time when both ventricles are fully depolarised (80-120ms)
What does downsloping or depressed ST segments indicate?
Coronary ischemia or hypokalemia
STEMI (ST elevation myocardial infarct)
It is a form of MI where the ST interval is elevated
STEMI on an ECG
ST elevation in 2 or more adjacent ECG leads
Rate- 10bpm
everything- normal
Left axis deviation
If the QRS complex for lead I is +ve but QRS for aVF is -ve. This indicates R ventricular damage
Right axis deviation
If the QRS in lead I and aVF are both negative. This indicates right heart failure
Hyperkalemia
Tented T waves, small/absent P waves, increased PR interval, widened QRS.
PE on ECG
Sinus tachy
T wave inversion V1-3
Right BBB
S1Q3T3 (only 20% of cases!)