ECG Theory (Tachycardia) Flashcards
What are the regular and irregular tachyarrhythmias?
Regular:
Atrial Flutter
SVT (AV rentry tachycardia and AV nodal rentry tachycardia)
Ventricular tachycardia
Irregular:
Atrial fibrilation
Describe the basic management principles of tachyarrhythmias?
Stable: use drugs (rate limiting)
Unstable:
- Shock?
- Cardiac chest pain?
- Pulmonary oedema?
- Syncope?
Then they need DC cardioverting (aka shocking into a normal rhythm)
Describe the pathology of atrial fibrilation?
Disordered atrial activity many blocking each other.
Some impulses are picked up by the AV node and conducted to the ventricles.
As the impulses which are picked up are random the rhythm is irregular.
What are the causes of AF?
PIRATES
Pulmonary (COPD/PE/Pneumonia)
Ischaemia
Rheumatic (mitral stenosis)*
Anaemia
Thyrotoxicosis
Ethanol/electrolytes
Sepsis
Mitral regurgitation can also cause AF
Describe the pathophysiology of atrial flutter?
There is a macro reentry circuit going at 300 bpm.
AV node blocks these and lets through every 2nd 3rd or 4th.
To work out how many are let through claculate the rate and divide 300 by this number.
Aka Ventricular rate = 100
300/100 = 3 therefore conducts every 3rd beat called 3:1
What are the causes of atrial fluter?
Same as in AF
PIRATES
How is atrial fibrillation/flutter managed?
If BP stable use medication.
If BP unstable cardiovert back to a normal rhythm.
Rate control:
Beta blocker
Ca Channel blocker if patient has contraindications to B blocker (aka asthmatic)
Digoxin especially used if patient is in heart failure as it is a positive ianotrope.
Anticoagulation:
Use CHA2DS2VASc score to predict which patients would benefit from oral anticoagulation.
Warfarin or a DOAC (Rivoroxaban, dagibatran)
Describe the mechanism AV nodal entry tachycardia? (draw a diagram)
In the AV node there is a slow and a fast pathway.
The impulse goes down the fast pathway and blocks the slow pathway and is conducted.
The refractory period on the fast pathway is longer than that in the slow rhythm.
If an impulse goes down the slow pathway while the fast pathway is in its refractory period then it will be conducted.
Very occasionally an impulse can go down the slow pathway just as the fast pathway finishes its refractory period, this causes a reentry circuit to occur within the node causing the tachycardia.
What occurs in AV reentry tachycardia?
It is the same as AVNRT except that instead of the process ocurring in the AV node it is occuring in an accessory pathway.
How can you distinguish between AVNRT and AVRT on an ECG?
Very difficult, need to be very specialised.
Most of the time can only say it is an SVT. However AVNRT is much more common (90% of SVTs).
How are SVT’s treated (AVRT/AVNRT)?
Vagal manoeuvres: valsalva or carotid minus massage.
Adenosine: essentially blocks the AV node allowing it to reset. (warn the patient they will feel awful and avoid in asthmatics)
Same principle if unstable cardiovert
What is Wolf Parkinson White Pattern?
It is an ECG pattern caused by an accessory pathway the bundle of kent.
ECG pattern
Short PR (as there is no pause with accessory pathway)
Delta wave (slurred QRS) as the accessory pathway is not through the bundle branches and is therefore slow.
What is Wolf Parkinson White syndrome?
It is WPW pattern + episodes of SVT.
Note if a patient with a known accessory pathway such as in WPW comes in with another arrhythmia such as AF it is important to discuss with cardiology.
Any drugs which interfer with the AV node can send all the atrial contractions down the accessory pathway causing VT.
Describe the pathology of VT and the treatment?
Rentry circuit around an area of myocardial scarring in the ventricles. Can also be caused by electrolyte disturbances.
If the patient is stable:
Amiodarone 300mg IV loading dose, followed by 900mg IV infusion over 24hrs. Cardiac monitoring.
If the patient is unstable:
Cardiovert
If pulseless:
Shock
What is a normal QT interval and what is the significane of a prolonged QT interval?
Normal = 360 to 450 milliseconds
Prolonged intervals paticularly over 500ms can predispose to VT.
Clinically may present as a young patient that has had several episodes of syncope.
