SM 136 Tachyarrhythmias Flashcards
What are the basic causes of Tachyarrhythmias?
Abnormal Automaticity, Triggered Activity, and Reentry
Which causes of Tachyarrhytmias arise from abnormalities in impulse formation?
Abnormal Automaticity and Triggered Activity = initiated by a focal source
Which cause of Tachyarrhytmias arise from abnormalities in impulse propagation?
Reentry (most common) = initiated from a circuit
What underlies Abnormal Automaticity in Tachyarrhytmias?
Changes in the pacemaker activity of non-sinus node cells, such as an increase in the slope of Phase 4 depolarization or a reduced Vt in Phase 0
What changes result in Abnormal Automaticity?
Changes in electrolyte levels
What underlies Triggered Activity in Tachyarrhytmias?
Increased Ca levels that lead to afterdepolarizations
What is an afterdepolarization?
An abnormal depolarization due to increased calcium levels stemming from gene mutations that alter Ca balance; can trigger an AP if the influx is large enough
During which phases of the AP and in what cells can an afterdepolarization trigger an additional AP?
During Phase 3 and Phase 4, when the cell is relatively refractory
During which phases of the AP and in what cells can an afterdepolarization NOT trigger an additional AP?
During Phase 1 and Phase 2, when the cell is absolutely refractory
What is an Early afterdepolarization?
EAD; occurs in Phase 3
What is a Delayed afterdepolarization?
DAD; occurs in Phase 4
Does Triggered Activity have a focal or circuit source of arrythmia?
Triggered Activity has a focal source of arrythmia
Does Reentry as a cause of Tachyarrhytmia have a focal or circuit source of arrhythmia?
Reentry develops from an extra pathway forming a circuit in the myocardium with premature atrial OR ventricular beats initiating the circuit and cycles of contraction
What is the necessary prerequisite for AVNRT?
A Fast and Slow pathway around the AV Node, which exists in 10% of people
How do Sinus rhythms use the Fast and Slow Pathways?
A normal beat can bifurcate and travel through the Fast pathway to form a normal beat; the end that travels through the Slow pathway arrives at tissue that is already depolarized and has no effect = normal PR
How do Premature Atrial Beats use the Fast and Slow Pathways?
Premature atrial beats arrive at the bifurcation around the AV Node, but find the Fast pathway is in the refractory period and therefor blocked. They travel around the Slow pathway to downstream tissue = elongated PR; they also try to ascend the Fast pathway after causing the long PR, but it is still refractory so the signal dies
How do AV Nodal Echo’s use the Fast and Slow Pathways?
Premature atrial beat arrives at the bifurcation around the AV Node, encounter a blocked Fast pathway due to repolarization. Travel down the Slow pathway to tissue downstream = elongated PR, and travel up the repolarized and unblocked Fast Pathway back to the Atria = inverted P wave after QRS; cannot progress further because the Slow Pathway is still refractory, signal dies
How does AVNRT use the Fast and Slow pathways?
Premature atrial beat arrives at the bifurcation around the AV Node, bypasses blocked Fast pathway due to repolarization and travels down Slow pathway to downstream tissue = long PR; travels back up the Fast pathway which is now repolarized and unbloked to the bifurcation, where the signal splits and travels back to the Atria = inverted P wave after QRS; progresses back down the Slow pathway which is now unblocked and forms a cycle
Describe the conduction and refractory period of the Fast pathway?
Conduction = rapid; Refractory period = long
Describe the conduction and refractory period of the Slow pathway?
Conduction = slow; Refractory period = short
What effect does AVNRT have on the previous sinus rhythm?
AVNRT abolishes the sinus rhythm by suppressing SA Node firing
Where do Supraventricular Tachycardias occur?
SVT occur above the ventricle, and do not include Sinus Tachy
What does AVNRT stand for?
Atrial Ventricular Node Reentrant Tachycardia
How does PSVT present?
Regular, narrow QRS Tachycardia
What are the types of PSVT?
AV Nodal Reentrant Tachycardia (AVNRT), Atrio-ventricular reentrant Tachycardai (AVRT), and Arial Tachycardia (AT)
What is the most common form of PVST?
Of the 3 types of PVST (AVNRT, AVRT, AT), AVNRT is the most common
What is the least common form of PVST?
Of the 3 types of PVST (AVNRT, AVRT, AT), AT is the least common
What symptoms are associated with the 3 types of PVST?
May be asymptomatic, but can involve heart racing, syncope, chest discomfort
What is syncope?
Loss of consciousness
What is necessary for Atrioventricular Reentrant Tachycardias to emerge?
Anomalous bypass tracts aka accessory pathways
How do Accessory Pathways form between the Atria and the Ventricles?
Normally, the AV valves partition the Atria and Ventricles, insulating both anatomically and electrically; when defects occur, bundles of muscle may connect the Atria and Ventricles allowing for conduction of impulses outside the normal cardiac conduction system
How do Accessory Pathways present on EKG?
Preexcitation Delta waves that slur the beginning of the QRS complex
Do Bypass Tracts run Top-Down, Bottom-Up, or bidirectionally between the Atria and Ventricles?
All of the above
Which direction must a Bypass Tract conduct to show up on EKG?
Bypass Tracts must conduct Top-Down to show up on EKG, where they show up as extra QRS complexes; in theory, a Bottom-Up tract could form an inverted P wave
How do Delta waves form during AVRT?
Electrical conduction occurs outside of the AV Node and begins to partially depolarize the ventricles during the PR interval, when the AV Node is normally delayed, forming the Delta wave at the beginning of a QRS complex
What component of the AVRT is the Fast Pathway?
The Bypass Tract is the Fast Pathway, since unlike the AV Node, it does not have a built in delay
What component of the AVRT is the Slow Pathway?
The AV Node, because it has a built in delay
What are the components of the AVRT?
The Bypass Tract (Fast) and the AV Node (Slow), as well as the intervening Atrial and Ventricular Tissue between the two pathways
What are the 2 types of AVRT?
Orthodromic and Antidromic Tachycardia
What is Orthodromic Tachycardia?
A type of AVRT where signal flows from the AV node, down the Ventricles via His-P, and back up the Accessory Pathway = narrow QRS
What is Antidromic Tachycardia?
A type of AVRT where signal flow from through the Accessory Pathway, up the Ventricles via Gap Junctions and up to the AV Node = wide QRS
What would AVRT with Wide QRS complexes indicate and why?
Wide QRS complexes suggest that the signal is passing through the ventricles outside of the His-P system, and points to Antidromic Tachycardia
What would AVRT with Narrow QRS complexes indicate and why?
Narrow QRS complexes suggest that the signal is passing through the ventricles along the His-P system, and points to Orthodromic Tachycardia
How is Atrial Tachycardia treated?
AT is treated with drugs such as Beta Blockers
Does the Valsalva Maneuver work on AT?
No, because the circuit involved in AT is contained in the Atria and increased Vagal stimulation to the AV Node via the maneuver would have no effect
How does the Valsalva Maneuver work?
Block an airway and try to force respiration, results in increased Vagal Tone on the AV Node that can terminate SVT
Which SVT can be terminated by the Valsavla Maneuver?
AVNRT and AVRT, because they involve the AV Node and Vagal Stimulation can inhibit the AV Node
Is Atrial Tachycardia circuit based or focal?
AT is focal and does not require the AV Node
What are the mechanisms underlying AT?
Triggered, automatic, and micro-reentry (a small circuit that appears focal)
When does multifocal AT arise?
3 or more P wave morphologies, irregular, seen in Pulmonary disease
What is the most common arrhythmia?
Atrial Fibrillation
How does Atrial Fibrillation present?
Disorganized atrial activity + irregularly irregular ventricular response
What is a regularly irregular rhythm?
R waves that occur in varying distance with a pattern
What is an irregularly irregular rhythm?
R waves that occur in varying distances without a pattern
How does Fibrillation present?
Irregular and disorganized
What atrial rate is associated with Fibrillation?
Rate > 350bpm
How does Flutter present?
Regular and Organized
What atrial rate is associated with Fibrillation?
240bpm - 350bpm
What are the mechanisms behind Atrial Fibrillation?
Focal, Mother Rotor, and Multiple Wavelets
What is the Focal mechanism of Atrial Fibrillation?
Rapid focal source that conducts throughout the atria in a disorganized fashion to cause AFib
What is the Mother Rotor mechanism of Atrial Fibrillation?
One large functionally reentrant circuit that produces smaller wavelets which cause AFib
What is the Multiple Wavelets mechanism of Atrial Fibrillation?
Many small reentrant circuits in the atria that cause AFib
Define Ventricular Tachycardia?
VT has discrete QRS complexes and Rate > 100bpm
Define Ventricular Fibrillation?
VF has obscured QRS complexes
What are the subtypes of VT?
Monomorphic and Polymorphic
What are the subtypes of Polymorphic VT?
Morphology that changes beat to beat, in the setting of a normal QT interval, and in the setting of a long QT interval
What does Monomorphic VT look like?
A single QRS morphology/shape
What does Polymorphic VT look like?
Varied QRS morphology/shape
What does VFib look like?
Wide QRS complexes
What is non-sustained VT?
VT that lasts less than 3 beats or 30 seconds, hemodynamically tolerated
What is sustained VT?
VT that lasts longer than 30 seconds
Which subtype of VT is more dangerous, and why?
Sustained VT is dangerous because it can progress to VFib
What are the components of arrhythmia pathogensis?
Substrate, triggers, and modulating factors
What factors lead to high risk arrhythmia?
Severe structural heart disease, such as LV dysfunction, and severe arrhythmia, such as VF
Arrange the following arrhythias in order of severity: sustained VT, VF, Premature beats, non-sustained VT
Premature Beats < Nonsustained VT < Sustained VT < VF
What are the general types of Monomorphic VT?
Idiopathic or associated with structural heart disease
What are the characteristics of idiopathic Monomorphic VT?
Normal beats, not associated with sudden death, triggered rhythm
What are the characteristics of the rhythm in Monomorphic VT?
Focal, near the Right Ventricular outflow tract, reentry with the purkinje system
What are the causes of structural heart disease Monomorphic VT?
Can arise from any cardiomyopathy
How can an infarct scar lead to sustained Monomorphic VT?
While the infarct leaves some areas totally unable to conduct electrical current, others can partially conduct at a slower velocity while unaffected areas are fast conducting, setting up a circuit with two pathways
What is the treatment for Ventricular Tachycardia?
Implantable cardioverter defibrillator + adjunctive antiarrythmics
Can antiarrhythmics prevent death from VT?
No
When should ablation be used in VT?
Recurrent VT can be ablated as an adjunt to a defibrillator
What are the subtypes of Polymorphic VT?
Normal QT and Long QT
What is Torsades de Pointes?
Polymorphic VT in the setting of a Long QT interval
Is Long QT syndrome congenital or acquired?
Long QT syndrome tends to be congenital, but may be acquired due to drugs or electrolyte abnormalities
What are the primary causes of VFib?
Non-reversible causes such as cardiomyopathy and congenital electrical disorders
What are the secondary causes of VFib?
Acute MI, ischemia, drugs
What are the symptoms of VFib?
Syncope and Sudden Death
Does VFib self terminate?
No
What is the treatment for VFib?
If secondary VFib, treat cause; use implantable cardioverter device (ICD)
How does cardiomyopathy cause VFib?
Cariomyopathy causes scarring, which predisposes reentry
How do primary electrical abnormalities cause VFib?
They act as functional reentry
What is a substrate in Tachyarrhythmia?
A structural abnormality such as an accessory pathway in AVRT
What is an initiator in Tachyarrhythmia?
Substrate is always present, so an initiator causes the arrhythmia, such as premature atrial or ventricular complexes
What are modulating factors in Tachyarrhythmia?
Things that alter the arrhythmia, such as electrolyte/metabolite abnormalities as well as autonomic tone
What are the 3 requirements for a reentrant arrhythmia to emerge?
A potential circuit around an anatomic obstacle, an area of slow conduction, and a unidirectional block
What is Wolf-Parkinson-White Syndrome?
An accessory pathway that conducts signals from the AV node to the SA Node in AVRT with a distinct ECG trace
How can Wolf-Parkinson-white be lethal?
AFib rapidly conducts over the accessory pathway leading to ventricular fibrillation
