Heart blocks and heart failure Flashcards
What is the electrocardiograph?
The machine which produces an ECG recording
What are the standard limb leads used for an ECG?
Right arm, Left arm and left leg
Where is lead 1?
Between the right and left arm?
Where is lead 2?
Between the right arm and left leg?
Where is lead 3?
Between the left arm and the left leg
Which lead shows the biggest deflection?
Lead 2 as depolarisation occurs in this direction
Lead 1 = smallest
How long is the PR interval?
0.12-0.2 seconds
How long is the QRS complex?
0.08-0.1 seconds
How long is the QT interval?
0.4-0.43 seconds
How long is the ST interval on average?
0.32 seconds
What is a high p wave amplitude a result of?
Atrial hypertrophy - more muscle mass = bigger depolarisation = bigger deflection
What does a low T amplitude show?
Ventricular hypoxia - not enough oxygen present for ventricles to contract
What is sinus arrhythmia?
Heart rate increases by 15% during inspiration - seen less in adults
What are first degree heart blocks?
Interruption somewhere between the SA and AV nodes slowing down conduction between the two nodes
Longer PR interval
What is mobitz type 1?
Progressive prelongation of the PR interval culminating in a non-conducted p wave
The PR interval is longest immediately before the dropped beat and shortest immediately after
P waves continue at the same rate
How can you tell the difference between mobitz type 1 and mobitz type 2?
Mobitz 1 = PR intervals change
Mobitz 2 = PR intervals do not change
What is mobitz 2?
Usually due to the failure of conduction at the level of the His purkinje system
More likely to be due to structural damage to the conducting system
How is mobitz 2 all or nothing?
His -purkinje cells suddenly and unexpectedly fail to conduct a supra ventricular impulse
What is a third degree heart block?
Complete absence of AV concution - none of the supraventricular impulses are conducted to the ventricles
The perfusing rhythm is maintained by a junctional or ventricular escape rhythm
Alternatively the patient may suffer ventricular standstill = syncope or sudden cardiac death
Typically the patient will have severe bradychardia with independent atrial and ventricular rates ie AV dissociation
What is sick sinus syndrome?
Impaired SA node firing eg brady or tachycardia
What is happening if the jugular vein is pulsing?
Atria are contracting against a closed tricuspid - sends a cannon wave in the jugular vein
The right atria and ventricle contract at the same time so a pressure wave is sent back up the jugular veins
What can atrial fibrilation cause?
Rapid/irregular heart rates Exercise intolerance Angina Shortness of breath Oedema of the ankles
How can atrial fibrilation be treated?
Flecainide Beta blockers, especially sotalol Amiodamine Dronedarone (only for certain people) Warfarin and other anticoagulants - stop clots forming if the blood is pooling as this could cause a pulmonary embolism
What is a circus movement?
An electrical signal not completing the normal circuit but rather an alternative circuit looping back on itself rapidly
How can refractory muscle become non-refractory?
Unidirectional block
Transient biderectional block
What are the stages in re-entrant excitation?
1) The originating impulse will set up the re-entrant excitement amd the unidirectional conduction block prevents further transmission
2) System behaves as an independent pacemaker with a rate higher than the originating impulse
3) The wave of excitation can travel in the reverse direction
4) The block allows retrograde transmission
