Arrhythmias Flashcards
Diagnosis and treatment of supraventricular tachycardia
What should ECG show?
What is appropriate management and treatment?
ECG should show rate of >100 bpm with QRS complex duration of
Atrial Fibrillation
Symptoms
ECG findings
Irregular pulse & palpitations.
ECG typically shows ABSENT P WAVES; IRREGULAR QRS COMPLEXES; and can occasionally show t wave inversion if fast AF indicating cardiac ischaemia.
Describe the four types of heart block
First degree block - tissue conducts all impulses, but more slowly than usual - seen as PR intervals longer than 0.2s on ECG
Second degree block - tissue conducts some impulses, but nor others. Split into:
Mobitz type I - PR interval gradually increases from cycle to cycle until AV node fails completely and a ventricular beat is missed
Mobitz type II - PR interval is constant but every nth ventricular depolarization is missing
Third (complete) heart block - no impulses are conducted through the affected area, atria and ventricles beat independently, governed by their own pacemakers
Name a common extra conduction pathway which bypasses the AV node
Bundle of Kent -aka the atrioventricular bypass tract, which is the accessory pathway in WPW syndrome
What is the general aim of anti-arrhythmic drugs?
To inhibit specific ion channels with the intention of suppressing abnormal electrical activity
Name the six types of anti-arrhythmic drugs, their target, and give an example of each
1A - voltage activated Na channel e.g. Disopyramide
1B - voltage activated Na channel e.g. Lignocaine
1C - voltage activated Na channel e.g. Flecainide
II - B-ADR (as antagonists) e.g. Metoprolol
III - voltage activated K+ channels (and others e.g. Amiodarone
IV - voltage activated Ca2+ channels e.g. Verapamil
What do class I agents spare? What do they block? What is the difference between the three types of class I anti-arrhythmic drugs?
Class I agents spare normal cardiac rhythm - they don’t affect healthy normal myocardium.
They selectively block impulses from diseased areas of the heart.
The difference is the rate at which they associate and dissociate from Na+ channels at a moderate rate.
A - moderate
B - rapid
C - slow
What three states do voltage activated Na+ channels rotate between?
The time between these depends on firing frequency.
What conditions cause high frequency?
What do class I agents target?
- Open (conducting)
- Inactivated (non-conducting)
- Resting (non-conducting)
Tachyarrhythmias cause high frequency.
Class I agent bind to areas of the myocardium with high frequency and - Block the open (conducting state)
- Stabilize the inactivated (non-conducting) state
Which two classes of drugs act in the atria to control the rate of a supraventricular tachycardia?
Give an example of each
1C e.g. Flecainide
& III e.g. Amiodarone
Which drugs act in the ventricles?
Give an example of each
1A e.g. Disopyramide
1B e.g. Lignocaine
II e.g. Metoprolol
Which drugs act on the AV node? (Thereby controlling rhythm of SVT)
Give and example of each
Adenosine
Digoxin
Class II e.g. Metoprolol
Class IV e.g. Verapamil
Which drugs act on the atria and ventricles/AV accessory pathways?
Give examples of each
Amiodarone
Sotalol
1A e.g. Disopyramide
1C e.g. Flecainide
Adenosine
What receptor?
How is it delivered?
What is it used for?
Activates A1-adenosine receptors
IV bolus
Used to terminate paroxysmal supraventricular tachycardia
Digoxin
What does it stimulate?
Route of administration?
What is it used to treat?
Stimulates vagal activity
IV agent (oral)
Used to treat AF - chaotic re-entrant impulse conduction through the atrium.
Does this by slowing conduction and prolonging refractory period in AV node and bundle of His
Lignocaine
What class of agent?
What channel does it block?
When is it used?
1B
Blocks Na+ channels
Mainly used in the treatment of ventricular arrhythmias following an MI
