Arrhythmias Overview Flashcards
What are the two basic properties of the heart?
- Mechanical
2. Electrical
What electrolytes are found in higher concentrations outside of the myocyte?
Calcium and sodium
What electrolyte is found in a higher concentration inside the myocyte?
Potassium
How many phases are in a normal myocyte action potential?
5 phases
How many phases are in an SA action potential?
3 phases
Describe normal electrical conduction through the heart
- SA node fires a signal
- Travels to AV node
- AV node to bundle of His
- Splits to left and right bundle branches
- Purkinje fibers
What influences the SA node?
autonomic nervous system
Why does conduction slow at the AV node?
To allow the atrial tissue to completely depolarize, contract, and expel blood into the ventricles, and to limit impulses that can activate the ventricle
What happens to the electrical signal after the Purkinje fibers?
It reaches recently excited (refractory tissue) and dies out
What does the p-wave represent on an EKG?
Atrial depolarization in response to firing of the SA node
What does the QRS complex represent on an EKG?
Depolarization of ventricles
What does the t-wave represent on an EKG?
Ventricular repolarization
What does the PR interval represent on an EKG?
The delay of the AV node to allow filling of the ventricles
What does the ST segment represent on an EKG?
The beginning of ventricular repolarization (should be flat)
How long is a normal PR interval on an EKG?
120-200 msec (0.12-0.2 sec)
What is a longer PR interval indicative of?
Heart block
What is a normal QT interval on an EKG?
200-400 msec (0.2-0.4 sec)
What is a higher QT interval indicative of?
A greater risk of ventricular arrhythmias
What are the two types of abnormal conductions?
- Automatic tachycardias
2. Re-entrant tachycardias
Describe the mechanism of an automatic tachycardia
A random cell takes over and beats faster than the SA and creates and ectopic beat
When does an automatic tachycardia usually occur?
When there is a blockage in the AV node
What are some common causes of an automatic tachycardia?
- Digitalis glycosides
- Catecholamines
- Electrolyte abnormalities
- Myocardial fiber stretch
Describe the mechanism of a Re-entrant tachycardia
Conducting pathway is stimulated prematurely by a previously conducted action potential leading to rapid cyclical reactivation
What are examples of Re-entrant tachycardia?
Atrial fibrillation, atrial flutter, AV nodal or AV re-entrant tachycardia, or recurrent VT
How are antiarrhythmic drugs classified?
By where they work in the action potential
What drug is in class 1a?
Procainamide
How does procainamide work?
It blocks sodium in and blocks potassium out, which lowers the conduction velocity and increases the refractory/repolarization period
What are the side effects associated with procainamide?
- Drug-induced lupus
- Agranulocytosis
- QT prolongation
In what population should you monitor procainamide closely?
In patients with renal disease
What drug is in class 1b?
Lidocaine (Xylocaine)
What does lidocaine do?
It has very little effect on sodium and increases potassium efflux which shortens the refractory period
What are the side effects associated with lidocaine?
- Hypotension
2. Seizures at high doses
What is the formulation of lidocaine?
IV only
What drug is in class 1c?
Propafenone
What does propafenone do?
It block sodium entry for a long time and has no effect on potassium which decreases the conduction velocity
What are class 1a drugs used for?
Afib and VT
What are class 1b drugs used for?
VF or VT
What are class 1c drugs used for?
VT or PSVT
What are the class 2 drugs?
Beta-blockers
What do you give a patient with tachycardia after surgery?
Beta-blocker
What is the antiarrhythmic mechanism of a beta-blocker?
It has anti-adrenergic actions so it works against the SA and AV nodes and indirectly effects calcium influx
What effects do beta-blockers have on the conduction velocity and refractory period?
They decrease conduction velocity and shorten refractory period
What are the class 3 drugs?
- Dofetilide
- Sotalol
- Dronedarone
- Amiodarone
What do class 3 drugs do?
They have no effect on sodium and block outward flow of potassium which prolongs the refractory period
What is the danger of having too much potassium blockage?
It can lead to more arrhythmias
What is dofetilide used for?
To convert afib to a normal sinus rhythm and maintenance afterwards
What are the common side effects of dofetilide?
Heart attack, QT prolongation, and bradycardia
What is the the major interaction with dofetilide?
3A4 substrate (black box warning)
What are the clinical pearls of dofetilide?
- renal dose adjustment
2. PharmD/MD must be registered to use
What is propafenone used for?
VT or PSVT
What are the major adverse effects of propafenone?
- Neutropenia
- Agranulocytosis
- New or worsened arrhythmias
- Heart block
- QT prolongation
What are the interactions with propafenone?
1A2, 2D6, and 3A4 substrate P glycoprotein inhibitor
What are the clinical pearls of propafenone?
- PO only
- renal and hepatic dose adjustment
- Worsens HF
What is sotalol used for?
VT, afib, and aflutter
What are the common adverse effects of sotalol?
- QT prolongation
- bradycardia
- N/V/D
- bronchospasms
What are the interactions with sotalol?
Low potassium and HF patients
What is the one clinical pearl of sotalol?
It has a renal adjustment
What is dronedarone used for?
afib and aflutter
What are the common adverse effects of dronedarone?
- Liver failure
- QT prolongation
- HF
- Heart block
What are the interaction with dronedarone?
- 3A4 substrate (black box warning)
- Digoxin - decrease dose by 50%
- Warfarin - start dose at 2.5 mg
What is the clinical pearl associated with dronedarone?
- You must stop all class one and three agents first
2. Similar to amiodarone without iodine
What is the most popular antiarrhythmic?
Amiodarone
What characteristics of the the Vaughan Williams classes does amiodarone have?
Some of all classes. It blocks sodium and potassium, it has noncompetitive, nonselective beta-blocker actions, and has a small degree of calcium antagonist activity
What is the initial action of amiodarone?
Beta-blockade
What is different about amiodarone’s pharmacokinetics?
It has an extremely long half life of 15 to 100 days
What is amiodarone used for?
afib, aflutter, VT, VF, and PSVT
What are the interactions with amiodarone?
- inhibits P-glycoprotein and most CYP-450 enzymes
- Digoxin
- Warfarin
What are the side effects of amiodarone?
- Pulmonary fibrosis
- Hypothyroidism
- Hyperthyroidism
- Optic neuritis
- Increased LFTs
- Bradycardia/HB
- Tremors, ataxia, peripheral neuropathy
- Photosensitivity/blue-gray skin
What do you do in pulmonary fibrosis?
Discontinue amiodarone and start a corticosteroid
What do you do in hypothyroidism?
Start a thyroid hormone supplement
What do you do in hyperthyroidism?
Start an antithyroid drug
What do you do in optic neuritis?
Stop amiodarone
What do you do in increased LFTs?
consider lowering amiodarone dose or discontinue if LFTs> 3x normal
What do you do in bradycardia/HB?
Lower the dose of amiodarone or discontinue if severe
What do you do in tremors, ataxia, or peripheral neuropathy?
Lower the dose of amiodarone or discontinue if severe
What do you do in photosensitivity/blue-gray skin discoloration?
wear sunblock outside
What are your class 4 drugs?
Calcium channel blockers
What do class 4 drugs do?
slow down conduction velocity and prolong repolarization
What are class 4 drugs used for?
SA/AV node automatic or reentrant tachycardias
What is adenosine used for?
PSVT
What are the common side effects of adenosine?
- flushing
- chest burning
- bronchospasms
What are the interactions with adenosine?
None because the half life is less than 10 seconds
What are the clinical pearls of adenosine?
- IV only
2. Will induce asystole momentarily after administration
