Deja review Cardio/Renal agents - Antiarrhythmics Flashcards
Describe what happens during phase 0
sodium ion channels open (inward) -> leads to depolerization
Describe what happens during phase 1
sodium ion channels are inactivated, potassium ion channels (outward) are activated; chloride ion channels (inward) are activated
Describe what happens during phase 2
Plateau phase; slow influx of calcium ion balanced by outward potassium ion current (delayed rectifier current Ik-funny sodium channel)
Describe what happens during phase 3
Repolarization phase; outward K+ current INC and inward calcium ion current DEC
Describe what happens during phase 4
Membrane returns to resting potential
What phase of cardiac action potential do amiodarone and sotalol work?
phase 0 and 3
What phase of cardiac action potential do lidocaine, flecainide, and quinidine work?
phase 0
What phase of cardiac action potential do ß blockers work?
phase 2 and 4
what is responsible for maintaining the electrochemical gradient at resting membrane potential?
Na+/K+ ATPase
What ion current is responsible for the depolarization of sinoatrial (SA) and atrioventricular (AV) nodal fibers?
Calcium ion (inward)
What ion current is responsible for the repolarization of SA and AV nodal fibers?
Potassium ion (outward)
How does phase 4 of the action potential in slow response fibers (SA and AV nodes) differ from that of fast response fibers?
slow response fibers displays automaticity (ability to depolarize spontaneously); rising phase 4 slope of the action potential = pacemaker potential
What ion current is responsible for the “pacemaker current” (rising slope of phase 4) in slow response fibers?
Sodium ion (inward); calcium ion (inward); potassium ion (outward)
The pacemaker of the heart has the fastest uprising phase 4 slope; where is this pacemaker in nondisease patients?
SA node
Where is the SA node located?
right atrium
How do the effective refractory period (ERP) and relative refractory period (RRP) differ from each other?
No stimulus, no matter the strength, can elicit a response with fibers in the ERP, whereas a strong enough stimulus will elicit a response.
What are the 3 states the voltage gated Na+ channel exists in?
1) Resting state
2) Open state
3) Inactivated state
What state(s) of the voltage gated Na+ channel is/are most susceptible to drugs?
Open state inactivated state
What 2 types of gates does the voltage gated Na+ channel have?
1) M (activating)
2) H (inactivating)
Why is the rate of recovery from an action potential slower in ischemic tissue?
The cells are already partly depolarized at rest
What class of antiarrhythmic agents has membrane-stabilizing effects?
ß-blockers
Antiarrhythmic agents are grouped into 4 classes according to what classification system?
Vaughn-Williams classification
Give the general mechanism of action for ech of the following antiarrythmic drugs classes:
- Class I
- Class II
- Class III
- Class IV
- Class I: Na+ channel blockers
- Class II: ß-blockers
- Class III: K+ channel blockers
- Class IV: Ca2+ Channel blockers
Class I antiarrhythmics are further subdivided into what casses?
1A; 1B; 1C
Give examples of antiarrhythmic drugs in class 1a
“ABBA Performed Dancing Queen”
Quinidine (antimalarial antiprotozoal agent); procainamide; disopyramide
Give examples of antiarrhythmic drugs in class 1b
“Backstreetboys Mainly Lack Talent (and phenytoin)”
-Mexiletine; lidocaine; tocainide; phenytoin
Give examples of antiarrhythmic drugs in class 1c
“Carly (rae jepsen) is Extremely Freaking Painful”
-Encainide; flecainide; propafenone; moricizine
Give examples of antiarrhythmic drugs in class 2
Propranolol; esmolol; metoprolol
Give examples of antiarrhythmic drugs in class 3
Amiodarone; sotalol; ibutilide; dofertilide
Give examples of antiarrhythmic drugs in class 4
Verapamil, diltiazem
Name 3 antiarrhythmic drugs that don’t fit in the Vaughn-Williams classification system
1) Digoxin
2) Adenosine
3) Magnesium
Magnesium is used to treat what specific type of arrhythmia?
Torsades de pointes (polymorphic ventricular tachycardia)
Adenosine is used to treat what types of arrhythmias?
Paroxysmal supraventricular tachycardia (PSVT), specifically narrow complex tachcardia or supraventricular tachycardia (SVT) with aberrancy; AV nodal arrhythmias (adenosine causes transitent AV block).
-Note: synchronized cardioversion and NOT adenosine should be used on symptomatic patients or unstable tachycardia with pulses
Where anatomically should the IV be placed to administer adenosine?
As close to the heart as possible, that is, the antecubital fossa since adenosine has an extremely short half-life. Adenosine rapid IV push should be followed immediately by a 5-10 cc (mL) flush of saline to facilitate its delivery to the heart
What is the mechanism of action of adenosine?
Stimulates α1 receptors which causes a DEC in cyclic adenosine monophosphate (cAMP) (via G2 coupled second messenger system); INC K+ efflux leading to INC hyperpolarizationl INC refractory period in AV node
What are the adverse effects of adenosine?
Flushing, chest pain, dyspnea, hypotension
What 2 drugs can antagonize the effects of adenosine?
Theophylline and caffiene
How is adenosine dosed?
6mg initially by rapid IV push, if not effective within 1-2 minutes, give 12 mg repeat dose (follow each bolus of adenosine with normal saline flush). The 12 mg dose may be repeated once
What is the most deadly ion that can be administered?
Potassium ion
What EKG changes are seen in hyperkalemia?
Flattened P waves, widened QRS complex, peaked T waves, sine waves, ventricular fibrillation
What EKG changes are seen in hypokalemia?
Flattened or inverted T waves, U waves, ST-segment depression
What do class 1a antiarrhythmics do to each of the following?
- Action potential duration:
- ERP:
- Conduction velocity
- Phase 4 slope
- Action potential duration: INC
- ERP: INC
- Conduction velocity: DEC
- Phase 4 slope: DEC
What do class Ib antiarrhythmics do to each of the following?
- Action potential duration:
- ERP:
- Conduction velocity
- Phase 4 slope
- Action potential duration: DEC
- ERP: Little or no change
- Conduction velocity: DEC (primarily in ischemic tissue)
- Phase 4 slope: DEC
What do class 1c antiarrhythmics do to each of the following?
- Action potential duration:
- ERP:
- Conduction velocity
- Phase 4 slope
- Action potential duration: Little or no change
- ERP: Little or no change
- Conduction velocity: DEC
- Phase 4 slope: DEC
Drugs that affect the strength of heart muscle contraction are referred to as what types of agents?
Inotropes (either positive or negative)
Drugs that affect the heart rate are referred to as what types of agents?
Chronotropes (either positive or negative)
Drugs that affect AV conduction velocity are referred to as what types of agents?
Dromotropes (either positive or negative)
QT interval prolongation, and thus torsades de pointes, is more likely to occur with what two classes of antiarrhythmics?
1) class 1a
2) class 3
Which class 1a antiarrhythmic also blocks α-adrenergic and muscarinic receptors, thus potentially leading to INC heart rate and AV conduction?
Quinidine
What are the adverse effects of quinidine?
Tachycardia, proarrhythmic, INC digoxin levels via protein binding displacement, nausea, vomiting, diarrhea, cinchonism
What is cinchonism?
Syndrome that may include tinnitus, high frequency hearing loss, deafness, vertigo, blurred vision, diplopia, photophobia, headache, confusion, delirium
What are the adverse effects of procainamide?
Drug induced lupus (25-30% of patients), pro-arrhythmic, depression, psychosis, hallucination, nausea, vomiting, diarrhea, agranulocytosis, thrombocytopenia, hypotension
What drugs can cause drug induced lupus?
Procainamide, isoniazid (INH), chlorpromazine, penicillamine, sulfasalazine, hydralazine, methyldopa, quinidine, phenytoin, minocycline, valproic acid, carbamazepine, chlorpromazine
Which class 1a antiarrhythmic can cause peripheral vasoconstriction?
Disopyramide
What are the adverse effects of disopyramide?
Anticholinergic adverse effects, such as urinary retention, dry mouth, dry eyes, blurred vision, constipation, sedation
True or false? Lidocaine is useful in the treatment of atrial arrhythmias?
False
True or false? Lidocaine is useful in the treatment of ventricular arrhythmias?
True
True or false? Lidocainse is useful in the treatment of AV junctional arrhythmias?
False
What are the adverse effects of lidocaine?
Proarrhythmic, sedation, agitation, confusion, paresthesias, seizures
What class 1b antiarrhythmic can cause pulmonary fibrosis?
Tocainide
Propafenone, even though a class 1c antiarrhythmic, exhibits what other type of antiarrhythmic activity?
ß-adrenergic receptor blockade
Encainide and flecaininde INC _____ in postmyocardial infarction (MI) patients with arrhythmias?
sudden cardiac death
Sotalol, even though a class III antiarrhythmic, exhibits what other type of antiarrhythmic activty?
ß-adrenergic receptor blockade
Even though this agent is labeled as a class III antiarrhythmic, it displays class I, II, III, and IV antiarrhythmic activity
Amiodarone
What is the 1/2 life of amiodarone?
40-60 days
What are the adverse effects of amiodarone?
Pulmonary fibrosis, tremor, ataxia, dizziness, hyperthyroidism, hypothyroidism, hepatotoxicity, photosensitivity, blue skin discoloration, neuropathy, muscle weakness, proarrhythmic, corneal deposits, lipid abnormalities, hypotension, nausea, vomiting, congestive heart failure (CHF), optic neuritis, pneumonitis, abnormal taste, abnormal smell, syndrome of inappropriate secretion of antiduretic hormone (SIADH)
How should patients on amiodarone therapy be monitored?
EKG thyroid function tests (TFTs), pulmonary function tests (PFTs), liver function tests (LFTs), electrolytes, ophthalmology exam
Verapamil should not be given in what types of arrhythmias?
Wolff-Parkinson-White (WPW) syndrome, ventricular tachcardia
What are the adverse effects of verapamil?
Drug interactions, constipation, hypotension, AV block, CHF, dizziness, flushing
Digoxin is used to control ventricular rate in what types of arrhythmias?
Atrial fibrillation, atrial flutter
Digoxin induced arrhythmias are treated by what drugs?
Lidocaine, phenytoin
Digoxin does what to each of the follow?
- Strength of heart muscle contraction:
- Heart rate:
- AV conduction velocity:
- Strength of heart muscle contraction: INC (positive inotrope)
- Heart rate: DEC (negative chronotrope)
- AV conduction velocity: DEC (negative dromotrope)
What does QTc stand for?
Corrected QT interval
How is QTc calculated?
(QT)/(square root of R to R interval)
Why must the QT interval be corrected?
The QT interval is dependent on heart rate, so higher heart rates will display shorter QT intervals on EKG. It is corrected to remove the variable of the heart rate
What is the normal value for QTc?
Less than 440 milliseconds
What does a long QT interval put a patient at risk for?
Torsades de pointes, a ventricular arrhythmia that can degenerate into ventricular fibrillation
