Flashcards in Week 6 Deck (49)
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?
1. 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
1. 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?
1. 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
1. Wolf-Parkinson-White, 2. Lown-Ganong-Levine (LGL)
What are the 3 junctional depolarisation sources?
1. 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?
What can WPW and LGL lead to?
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?
Is 1st degree heart block a contra-indication to exercise testing?
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?
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