Flashcards in Lecture 24: Mechanisms of tachyarrhythmias Deck (58):
What are the 3 mechanisms of tachycardias?
3. Triggered activity
What are the two types of AV nodal pathways?
1. Slow pathway
2. Fast pathway
What are the characteristics of the fast pathway?
Most people have just this
What are the characteristics of the slow pathway?
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?
1. isoelectric PR segment
2. narrow QRS complex
What are the characteristics of Wolf-Parkinson-White?
1. Has an accessory pathway between atria and ventricle that is FAST conducting
2. 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?
1. 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
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?
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?
1. presence of PAC
2. narrow QRS complex (because AV node, the slow
Pathway, is dictating conduction)
3. 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 toothed shaped P wave
Negative in leads II, III and aVF (because conduction is counterclockwise)
What are the effects of antiarrhythmic drugs?
1. Can prolong repolarization of the slow pathway to make it less likely to dictate pace
-accomplished by Class III potassium channel blockers
2. Can decrease the velocity of the conduction
-increase the amount of time it takes to do one revolution of the circuit
-reentry still occurs but it is slower so less symptoms
How else can you treat reentry tachycardias?
Get rid of the accessory pathway through catheter ablation
What are the different types of reentry tachycardias?
1. Atrial flutter
2. Ventricular tachycardia
3. Wolff-Parkinson-White syndrome
i. Atrioventricular Reentrant Tachycardia (Supraventricular Tachycardia)
What happens to the ECG after you ablate the accessory pathway?
Loss of delta wave because there is no longer any ventricular pre-excitation
What are latent subsidiary pacemakers?
Tissue with slower intrinsic rates
Atrium > AV junction > ventricle
Sinus node = Na INDEPENDENT = Ca dependent
His purkinje = Na Dependent = Ca independent
What is the general principle behind automaticity tachycardia?
When the pacemaking potential is coming from a place different from the SA node
What are the characteristics of Atrial tachycardia?
Defined by focal tachycardia originating in atrial muscle other than the sinus or AV nodes
May have single or multiple foci
-these foci are capable of autonomous depolarization at rapid rates
What are the ECG features of atrial tachycardia?
1. Pwaves are discernible but looks DIFFERENT because it is at a spot different than SA node
2. PR interval is normal
What are the characteristics of sinus tachycardia?
Upright P waves in lead I, avF and biphasic V1
Basically when the SA node is over stimulated by the Sympathetic Nervous System via the catecholamines
Treatment = address underlying cause
What triggers delayed after-depolarizations (DADs)?
When too much calcium is present in the cell, fucks with SR reuptake, SR then releases boluses of calcium that mess with membrane potential and can lead to ectopic beats or trigeminy
Can be caused by digitalis toxicity or leaky SR
-causes spontaneous Ca release from SR that triggers another AP
-can be caused by leaky ryanodine receptor as well
What are the ECG features of DADs?
Fast depol following action potential caused
By release of calcium bolus from SR
What are early afterdepolarizations?
Depol’s that occur during the plateau phase of ventricular AP
Afterdepol occurs DURING beat instead of directly after beat
Happens when there is Long QT inerval
What is torsades de pointes?
Twisting of the points (QRS looks like it is twisting around the baseline)
Caused by early afterdepolarizations
What is the general principle behind triggered activity tachycardia?
Caused by either DELAYED afterdepolarizations or EARLY afterdepolarizations
What are the two types of tachycardia that does not fit into neat categories?
1. atrial fibrillation
2. ventricular fibrillation
What are the key characteristics of atrial fibrillation?
Rapid, irregular, chaotic form of atrial tachyarrhythmia with irregular ventricular response
Large percentage of patients with atrial fibrillation have rapidly firing ectopic focus located in the left superior pulmonary vein
Characterized by Initiation and Maintenance mechanisms
What are the ECG features of atrial fibrillation?
No organized P waves
Irregular R waves because AV node is blocking the irregular/chaotic atrial tachyarrhythmia from reaching ventricle
Lets waves pass through AV node irregularly so you have irregularly spaced QRS complexes
What are the key characteristics of ventricular fibrillation?
1. multiple wavelet reentry in the ventricle
2. QRS complexes replaced by disorganized chaotic low amplitude activity
3. Associated with absence of pulsatile cardiac output and immediate loss of consciousness
4. causes death in absence of intervention
5. Can complicate acute MI or can occur in setting of other advanced structural heart disease
What are the ECG features of ventricular fibrillation?
Irregularly irregular low amplitude QRS complex
How are tachycardias classified?
Supraventricular vs Ventricular tachycardia
Narrow vs Wide
What are the supraventricular tachycardias?
1. Sinus tachycardia (automatic)
2. AV nodal reentrant tachycardia
3. Atrioventricular reentrant tachycardia
4. Atrial tachycardia (automatic)
5. Atrial flutter (reentrant)
6. Atrial fibrillation (Automatic initiation, then maintenance by multiple wavelet reentry)
What are the types of Ventricular tachycardias?
1. Monomorphic ventricular tachycardia (reentrant) due to scarring
2. Ventricular fibrillation (automatic initiation, then maintenance by multiple wavelet reentry)
3. Torsades des pointes (triggered)
4. early after-depolarizations
What does QRS complex wide mean in the context of tachycardias?
A type of tachycardia classification
Refers to the phenomenon in which the ventricle is activated by slow cell-to-cell conduction
Wide QRS complex
What are types of wide complex tachycardias?
1. Monomorphic QRS
i. SVT with bundle branch block
ii. Ventricular tachycardia
iii. SVT with pre-excitation
2. Polymorphic QRS
i. Ventricular fibrillation
ii. Torsades de pointes
What are the types of monomorphic QRS complex tachycardias?
A type of wide complex tachycardias
1 SVT with bundle branch block
2. Ventricular tachycardia
3. SVT with pre-excitation
What are the types of polymorphic QRS complex tachycardias?
A type of wide complex tachycardia
1. Ventricular fibrillation
2. Torsades de Pointes
Why does bundle branch block lead to wide QRS complex tachycardia?
Because it conducts fast through the unblocked branch but then runs slowly to the area of the heart that was blocked in the first place
What does QRS complex narrow mean in the context of tachycardias?
A type of tachycardia classification
Ventricle is activated by His-Purkinje System
What are the types of narrow complex tahycardias?
1. Regular ventricular rate
2. Irregular ventricular rate
What are the regular vs irregular categories of tachycardias?
The two categories of narrow complex tachycardia
What are the types of regular ventricular rate narrow complex tachycardia?
1. AVNRT (AV nodal reentrant tachy)
2. AVRT/WPW (Atrioventricular reentrant)
3. Atrial tachycardia
4. Sinus tachycardia
5. Atrial Flutter
What are the ECG characteristics of AVNRT?
Negative P waves in inferior leads
In contrast with positive p waves in AVRT
What are the ECG characteristics in Sinus Tachy?
Positive p waves in inferior leads
What are the ECG characterisitcs of atrial flutter?