Lecture 24: Mechanisms of tachyarrhythmias Flashcards
What are the 3 mechanisms of tachycardias?
- Reentry
- Automaticity
- Triggered activity
What are the two types of AV nodal pathways?
- Slow pathway
2. Fast pathway
What are the characteristics of the fast pathway?
Faster conduction
Slower recovery
Most people have just this
What are the characteristics of the slow pathway?
Slower conduction
Faster recovery
Exists in 1/3 of people
What happens when you have a premature beat timed just right?
Fast pathway is blocked because it is still repolarizing
Atrium becomes activated from bottom to top
When you have a premature beat timed just right that allows slow pathway to conduct all the way around the circuit and cause backward depolarization of the atrium
What does a sinus beat look like in a person with both a fast and a slow pathway?
Fast pathway conducts first
Fast pathway AP cancels out slow pathway on the left side
What are the general principles of reentry tachycardia?
Happens when a premature beat is timed just right
Fast conduction pathway is still repolarizing
Allows slow pathway to control the circuit
Slow pathway will go down its path, half will propagate but half will go back up the fast conduction loop
The AP that goes up the fast conduction loop will then go back to up to the atria and re-stimulate a pwave
What does the p wave look like in AV nodal reentry tachycardia?
Inverted p wave
What are features of normal sinus?
- isoelectric PR segment
2. narrow QRS complex
What are the characteristics of Wolf-Parkinson-White?
- Has an accessory pathway between atria and ventricle that is FAST conducting
- AV node = slow conducting
A type of reentry tachycardia
Leads to ventricular pre-excitation (because does not need to go through AV node to depol ventricle)
What are the ECG features of WPW syndrome?
- Small PR interval (100ms)
Why does WPW have a shortened PR interval?
Because accessory pathway allows conduction to bypass
Slower AV node (so QRS complex comes more quickly)
Why does WPW have a delta wave in QRS complex?
Because you have initial ventricle depol from accessory
Pathway that cause initial slope, then you get the notch
When the His-Purkinje system from slow pathway
Catches up
Why does WPW have a long QRS complex?
Because it starts with accessory pathway ventricle depol and ends with His-Purkinje depol (the time between the two is much longer)
What is an example of the slow pathway?
AV node
How do you initiate supraventricular tachycardia in WPW?
With a closely coupled premature atrial complex (PAC)
A premature beat that blocks the fast pathway conduction
What are the characteristics of atrioventricular reentrant tachycardia (AVRT)?
Initiated by a closely coupled premature atrial complex (PAC)
Block in the accessory pathway (the fast pathway)
The slow pathway conducts RETROGRADE through the accessory pathway
And you get a retrograde p wave with narrow QRS complex
An example of reentry tachycardia
What are the ECG features of supraventricular tachycardia?
- presence of PAC
- narrow QRS complex (because AV node, the slow
Pathway, is dictating conduction) - tachycardic heart rhythm
What is PAC? Significance?
Premature Atrial Complex
Initiates AVReentrant tachycardia
What are the characteristics of reentrant monomorphic ventricular tachycardia?
A type of reentrant tachycardia
Characterized by scar tissue in the myocardium that is now a SLOW pathway
Healthy tissue = fast pathway
What are the ECG characteristics of ventricular tachycardia?
Wide complex tachycardia
Wide because it is not using the His-Purkinje system
Slow cell-to-cell conduction
Due to premature atrial complex that causes fast pathway to be blocked (the healthy tissue) and allows slow pathway (scar tissue) to dictate pace
What are the characteristics of atrial flutter?
A form of reentry/circus tachycardia
Utilizes anatomy of RA to sustain a loop of depolarization
Loop is counterclockwise, from annulus of bicuspid, to atrial septum and then down the crista terminalis
LA is not part of reentry circuit
Characterized by different degrees of AV block but block does not affect flutter mechanism
What are the ECG characteristics of atrial flutter?
Saw-tooth flutter,
Saw toothed shaped P wave
Negative in leads II, III and aVF (because conduction is counterclockwise)