Week 6 Flashcards
What does the P-R interval represent?
Atrial depolarisation, AV node excitation, AV node delay - the time between atrial and ventricular depolarisation
In sinus rhythm, what is the duration of the P-R interval?
3-5 small boxes (0.12 - 0.2 seconds). Length should be consistent
Why is a delay between atrial and ventricular depolarisation important?
To allow optimal ventricular filling
What can a slow ventricular rate lead to?
Reduced CO - lightheadedness, hypotension and confusion
When analysing the PR interval, what 3 things should be asked?
- is the PR interval between 3-5 small boxes? 2. does the PR interval vary? 3. can it be measured?
List 4 causes of AV block
- ischemia 2. myocardial infarction (cell death) 3. exaggerated drug response (digoxin, calcium-channel blockers and beta-blockers). 3. congenital anomalies
How does ischemia effect conduction?
cell repolarise more slowly or incompletely.
What are the two main reasons for shortened PR interval?
- AV junctional rhythm (depolarisation spreads to atria and ventricles at the same time). 2. when an accessory pathway is present and bypasses AV junction. This pathway is fast-conduction.
Name the two accessory pathway syndromes
- Wolf-Parkinson-White, 2. Lown-Ganong-Levine (LGL)
What are the 3 junctional depolarisation sources?
- junctional rhythm, 2. junction ectopic, 3. AV re-entry tachycardia
What ECG characteristic signals retrograde conduction in the atria?
Inverted P wave in lead II
What is the accessory pathway in WPW called?
Bundle of Kent - fasting conducting than AV node. It connects the ventricles directly
What wave is seen on an ECG of WPW client?
Shortened PR interval and delta-wave (slurred QRS)
What dose the delta wave represent?
Slow depolarisation (myocyte-myocyte) of the ventricle. The rest of the ventricles depolarise normally shortly after via AV node and bundle branches.
Is WPW a contraindication to exercise testing?
yes
What can WPW and LGL lead to?
Paroxysmal tachycardia
What is the accessory pathway in LGL syndrome called?
Bundle of James
Where does the Bundle of James connect?
Connects the atria to the bundle of His, bypassing the AV node.
What is the characteristics of 1st degree AV block?
Prolonged PR interval (>0.2 seconds), constant delay, each P wave is followed by QRS. May be temporary.
List what may cause slowing of electrical conduction through the AV node.
Ischemia, injury, infarction, drugs (digoxin, calcium-channel blockers, beta-blockers), myocarditis, degenerative changes (fibrosis associated with age), lyme disease, hypokalemia
What is the only substance a health and wellbeing physiologist can administer?
oxygen
Is 1st degree heart block a contra-indication to exercise testing?
no
How is 2nd degree block Type 1 identified?
The length of PR interval increases with each beat until a P wave fails to produce a QRS complex
How is 2nd degree Type II identified?
The length of the PR interval is constant but occasionally P wave fails to produce QRS complex
What is a block where every second P wave doesn’t produce a QRS?
2:1 AV block
How is 3rd degree (complete) AV block distinguished?
If there is no relationship between the P and QRS waves - i.e they are being triggered independently
Is 2nd degree type I block typically temporary?
yes
Causes of 2nd degree type I block
periods of high vagal activity (e.g. during sleep), ischemia, inferior wall MI, rheumatic fever, drugs
What blocks are contraindications to exercise testing?
2nd and 3rd degree
What block is more common, 2nd degree type I or type II?
2nd degree type I
What is the most common cause of 2nd degree type II block?
Inferior wall MI, severe CAD (ischemia), degenerated changes.
Where in the conduction system is 2nd degree type II thought to arise?
at the level of the bundle branches or bundle of His
Where in the conduction system is 2nd degree type I thought to arise?
at the AV node itself
Is 2nd degree Type I or Type II more serious and why?
Type II - ventricular rate tends to be slow (reduce C0) and can progress without warning to 3rd degree block. A ratio of conducted beats less than 2:1 is more likely to be symptomatic.
In 2nd degree heart block, is atrial and ventricular rhythm regular?
Atrial rhythm is regular and ventricular rhythm is irregular
If the block is constant (2:1 or 3:1) is the rhythm regular?
Yes
Do the atria and ventricles work independently in 3rd degree heart block?
Yes
How do the ventricles know the contract in 3rd degree heart block?
They sometimes develop an escape rhythm at the level of the junctional tissue surrounding the AV node. Most commonly, escape rhythm originates at the level of the Purkinji fibres
What is the rate of a junctional escape rhythm?
40-60bpm
What is the rate of escape rhythm at level of Purkinji fibres?
20-40bpm
3rd degree block at the AV node is most commonly caused by what?
Congenital condition
Do clients with 3rd degree heart block lose atrial kick?
Yes (which is reduces blood flow by 30%).
Bradycardia (20-40bpm) and broad QRS complex should alert you to what?
3rd degree heart block
Can individuals with 3rd degree heart block tolerate exercise?
No
What is the main determinant of the severity of symptoms due to heart block?
Ventricular rate - this determines CO.
What may be given is rate is too slow?
Epinephrine, atropine, dopamine
If escape rhythm originates in the Purkinji fibres, will the QRS complex be wide?
Yes
3rd degree block in anterior wall MI is good/bad prognosis?
Bad - suggests extensive damage
When is 1st degree block normal and why?
When it accompanies sinus bradycardia. Vagal tone reduces AV conduction
