Tachycardia lecture and module Flashcards
What causes a wide tachycardia?
Electrical signal has to travel through the slowly conducting ventricular cells, which takes a longer time
How does increased automaticity work?
Decreased parasympathetic drive
Increased phase 4 slope
The threshold is more negative, and the resting membrane potential is more positive – more easy to get an AP
Atrial fibrillation
Most common sustained arrhythmia
Atria depolarize at 400-600 BPM with irregular conduction to the ventricles
Irregular RR intervals
No P waves (can’t see atrial activity)
What is triggered activity
During the partial refractory period, oscillations in the membrane potential can trigger abnormal APs which can lead to a tachy
Atrial flutter
Re-entry circuit that occurs entirely in the R atria
Around 300 BPM
Can be regular or irregular (usually conducts about 2:1)
Sawtooth pattern
Characteristics: > 100BPM, regular rhythm, sawtooth P waves
Orthodromic vs antidromic
Ortho: conduction down the AV node is normal
Anti: conduction is backwards through the AV node
Wolf-Parkinson-White
Palpitations + pre-excitation
Congenital accessory path (antegrade AV conduction) and tachycardia episodes
Accessory pathway is the Bundle of Kent (antegrade and retrograde)
Pre-excitation
Presence of an antegradely conducting accessory path that can pre-depol the ventricles
Will see a delta wave on ECG
Shortened PR interval and widened QRS complex
Pre-excited atrial fibrillation
Atrial rate 400-600 BPM
Ventricular rate dictated by the refractory period of the accessory path
Can be so fast that it results in cardiac risk
Symptoms associated with tachycardia
Palpitations Pre-syncope Syncope Fatigue Poor exercise tolerance Chest pain Sweating (diaphoresis) Shortness of breath
Everyone with SVT should have what investigation?
Echocardiogram
Want to rule out mitral valve prolapse and congenital valve abnormalities
5 waves to evaluate/measure tachycardia
ECG Holter monitor Event monitor Implantable cardiac monitors Echocardiogram
Treatment during a tachy episode
Valsalva Carotid sinus massage Diving reflex (face in cold water) Adenosine IV AV nodal blocker (beta blocker, calcium channel blocker) Cardioversion (extreme circumstances)
How to prevent tachy episodes
Nothing and treat as they come
AV nodal blocker (beta blocker, calcium channel blocker)
Ablation
3 general mechanisms of tachycardia
Re-entry
Automaticity
Triggered activity
Where is the origin of impulse in
1. Narrow
2. Wide
QRS complexes?
- Supraventricular
2. May be ventricular
3 types of supraventricular tachycardias
Ectopic atrial tachycardia
AVNRT
AVRT
Ectopic atrial tachycardia
A form of tachyarrhythmia originating from within the atria, but outside of the SA node
Usually due to a single ectopic focus
Characteristics: HR > 100, regular rhythm, abnormal P wave morphology (not from the SA node)
Multifocal atrial tachycardia
More than one ectopic focus of automaticity outside the SA node
At least 3 ectopic foci of automaticity evident on ECG
Characteristics: HR > 100, irregular rhythm, 3 or more unique P waves
AVNRT
Both the slow and fast pathways are located in the AV node
Only the AV node is an obligate part of the circuit
AVRT
2 arms of the re-entry circuit
One is the AV node, the other is an accessory pathway
The AV node, atrium, and ventricles are all a part of the pathway
P waves can be buried in the QRS complexes (atria being depolarized at the same time as the ventricles)
What does it mean if P waves come after the QRS
They are retrograde P waves that come from the bottom of the atrium (not the SA node)
