ECG Flashcards
Why does the trace of atrial fibrillation occur?
When the atrial muscles contract independently to the ventricles, there are no P waves on the ECG, only an irregular line.
The AV node is continuously bombarded with depolarisation waves of varying strength and depolarisation spreads at irregular intervals down the His bundle. The AV node conducts in an ‘all or none’ fashion, so that the depolarisation waves passing into the His bundle are of constant intensity. However, these waves are irregular, and the ventricles therefore contract irregularly. Because the conduction into and through the ventricle is by the normal route, each QRS is of normal shape
List the main features of AF
No p waves
Irregularly irregular rhythm
Normally shaped QRS complexes
Irregular baseline
List the main features of an NSTEMI
ST depression
T wave inversion
List the main features of a STEMI?
ST elevation
Appearance of Q waves
Inverted T waves
List the main features of VT?
Broad complex tachycardia
No P waves or T waves visible
Regular rhythm
List the main features of VF?
Completely irregular rhythm
No discernible P waves, QRS complex or T waves
Describe 1st degree heart block
First degree heart block = delay of conduction between SAN and ventricles. Shown by a prolonged PR interval.
Can be a sign of:
- Coronary artery disease
- Acute rheumatic carditis
- Digoxin toxicity
- Electrolyte disturbances
What are the different types of 2nd degree heart block?
Second degree heart block = excitation intermittently fails to pass through the AV node or the bundle of His.
There are 3 types of 2nd degree heart block:
1) Mobitz type 1
2) Mobitz type 2
3) 2:1, 3:1, 4:1 conduction
Describe mobitz type 1 heart block
Progressive lengthening of the PR interval and then failure of conduction of an atrial beat, followed by a conducted beat with a shorter PR interval.
Describe Mobitz type 2 heart block
Occasionally there is atrial depolarisation without a subsequent ventricular depolarisation
Describe 2:1/3:1/4:1 heart block conducion
There may be alternate conducted and non-conducted atrial beats (or one conduced atrial beat followed by 2 or 3 non-conducted beats). This gives 2 times (or three or four times) as many P waves as QRS complexes
Describe third degree heart block
Complete failure of conduction between atria and ventricles. The P waves bear no relation to the QRS complexes and usually are at a faster rate (AV dissociation). The QRS complexes may be narrow or broad dependent on the site of the pacemaker in the ventricles
Describe bundle branch blocks
The depolarisation wave will reach the interventricular septum normally and the PR interval will be normal but the conduction through the right/left bundle branches will cause a delay in the depolarisation of part of the ventricular muscle. This extra time will be visible as a widened QRS complex. Blockage of both bundle branches has the same effects as a blockage in the bundle of his and will result in third degree heart block.
Describe the appearance of RBBB?
- QRS complex will be prolonged
- Broad S wave in lead V6
- RSR’ complex in lead V1
Describe the appearance of LBBB?
- QRS complex will be prolonged
- ST depression and inverted T waves in leads I, aVL, V5 and V6
