Anti-arrhythmicx Flashcards
What two classes of drugs block the inward sodium channel of the ventricular AP, decreasing the slope of phase 0?
Class Ia and Ic agents, which are Na+ channel blockers.
Class Ia: Quinidine, procainamide, disopyramide
Class Ic: Flecanide, propafenone
Class Ia drugs:
What effect does this have on the AP duration?
What effect does this have on refractory period?
What effect does this have on the QT interval?
Class Ia: Quinidine, procainamide, disopyramide
They are Na+ channel blockers that decrease slope of phase 0 of the ventricular AP.
Increase AP duration, which increases refractory period and increases QT interval
The QT interval represents electrical depolarization and repolarization of the ventricles.
Cinchosism is a side effect of which drug?
Quinidine, class Ia sodium channel blocker
cinchosism: blurred vision, headache, tinnitus, psychosis
Lupus-like syndrome (joint pain) is a side effect of which class Ia antiarrythric ?
procainamide
A 60-year-old man comes to the emergency department with severe chest pain. ECG reveals ventricular tachycardia with occasional normal sinus beats, and ST-segment changes suggestive of ischemia. A diagnosis of myocardial infarction is made, and the man is admitted to the cardiac intensive care unit. His arrhythmia should be treated immediately with (A) Adenosine (B) Digoxin (C) Lidocaine (D) Quinidine (E) Verapamil
Lidocaine has limited applications as an antiarrhythmic drug, but emergency treatment of myocardial infarction arrhythmias is one of the most important. Lidocaine is also useful in digoxin-induced arrhythmias.
Which of the following drugs slows conduction through the AV node and has its primary action directly on L-type calcium channels? (A) Adenosine (B) Amiodarone (C) Diltiazem (D) Esmolol (E) Flecainide (F) Lidocaine (G) Mexiletine (H) Procainamide (I) Quinidine
Diltiazem is the calcium channel blocker in this list. (Beta blockers also slow AV conduction but have much smaller effects on calcium channels.)
When working in outlying areas, this 62-year-old rancher is away from his house for 12–14 h at a time. He has an arrhythmia that requires chronic therapy. Which of the following has the longest half-life of all antiarrhythmic drugs? (A) Adenosine (B) Amiodarone (C) Disopyramide (D) Esmolol (E) Flecainide (F) Lidocaine (G) Mexiletine (H) Procainamide (I) Quinidine (J) Verapamil
Amiodarone has the longest half-life of all the antiarrhythmics (weeks).
A 16-year-old girl has paroxysmal attacks of rapid heart rate with palpitations and shortness of breath. These episodes occasionally terminate spontaneously but often require a visit to the emergency department of the local hospital. Her ECG during these episodes reveals an AV nodal tachycardia. The antiarrhythmic of choice in most cases of acute AV nodal tachycardia is (A) Adenosine (B) Amiodarone (C) Flecainide (D) Propranolol (E) Verapamil
Calcium channel blockers are effective in supraventricular AV nodal tachycardias. However, adenosine is just as effective in most acute nodal tachycardias and is less toxic because of its extremely short duration of action.
A 57-year-old man is admitted to the emergency department with chest pain and a fast irregular heart rhythm. The ECG shows an inferior myocardial infarction and ventricular tachycardia. Lidocaine is ordered. When used as an antiarrhythmic drug, lidocaine typically (A) Increases action potential duration (B) Increases contractility (C) Increases PR interval (D) Reduces abnormal automaticity (E) Reduces resting potential
Lidocaine reduces automaticity in the ventricles; the drug does not alter resting potential or AP duration and does not increase contractility.
What drug is preferentially used as emergency TX of VT after and MI?
Lidocaine: Preferentially affects ischemic tissues
With what conditions are class Ic agents contraindicated in?
Class Ic: flecainaide, propafenone
Structure and ischemic heart disease…it is pro-arrhythmic in ischemic tissues
What is the main fcn of class II agents?
Beta blockers: basically try to slow conduction through the AV node
Useful in A-fib and A-flutter
Prevent rapid ventricular response in A-fib and flutter (rate controlled)
What class of drugs are being described:
Indications: SVT, Afib, Atrial flutter, PVCs
Decrease SA node, AV node activity
Suppress ectopic pacemakers
Side effects: bronchospasm, bradycardia, impotence
Beta blockers: esmolol, metoprolol, propranolol, carvedilol
What drug is being described:
Class III agent, but also blocks sodium channels, calcium channels, and alpha and beta-adrenoreceptor blockage
Uses: atrial fibrillation, VT, VF in patients with cardiovascular disease
Very long half life
SE: hepatotoxicity, pulmonary fibrosis, thyroid dysfunction
Check: PFTs, LFTs, TFTs
Amiodarone
What effect does K+ blockade have on the Ventricular AP?
Prolongs refractoriness and therefore repolarization
Which class of antiarrhythmic is being described? Slows depolarization of ventricular AP?
1c>1a>1b
1a: increases QT, QRS, and PR
1b: usually no change
1c: increases PR and QRS
Which class of antiarrhythmic is being described? AV nodal blockade
Class II beta blockers
Class IV Ca2+ Blockers
Decreases HR and increases PR
Which class of antiarrhythmic is being described? Slows repolarization of cell
Class III- K+ channel blockers
Increases QT
What two classes of antiarrhythmics increase QT interval, what does this predispose them to?
Class Ia and Class III
Anytime the AP is prolonged, you can prolong the QT interval and precipitate Torsades de Pointes
Which antiarrhythmic drug is being described? Activates K+ channels in AV node Hyperpolarization of membrane potential Slows conduction through AV node Short half life
Adenosine
Adverse effects: Bronchospasm, Sense of doom, Chest tightness
Which antiarrhythmic drug is being described? Increases inotropy Slows heart rate and AV nodal conduction Many drug-drug interactions Narrow therapeutic index
Digoxin
Anti-arrhythmic mechanism: parasympathomimetic,
decreases conduction velocity through AV node
Side effects: Yellow green visual changes, Anorexia, Nausea, vomiting, diarrhea
A 67-year-old man comes to the physician because of palpitations and fatigue. Further evaluation shows atrial fibrillation, and treatment is begun with a medication that acts by inhibiting sodium-potassium ATPase. Three weeks later he returns to the physician for a follow-up examination with a complaint of yellow/green visual halos, dizziness and abdominal pain. His serum drug levels are well above the therapeutic range. This patient is at highest risk for developing which of the following? A. Acute renal failure B. Cardiac arrhythmia C. Hypokalemia D. Hyponatremia E. Tonic-clonic seizures
B. Cardiac arrhythmia
The drug used is Digoxin, which inhibits cardiac Na+/K+ ATPase, leading to indirect inhibition of the Na+/Ca2+ exchanger, which leads to increased Ca2+ and positive inotropy (contractility). It i used for SVTs (decrease AV conduction and depresses the SA node)
B/c digoxin has a narrow therapeutic window, toxicity can easilydevelop, resulting in the development of any cardiac arrhythmias. The incidence and severity of toxicity is greatly increased when hypokalemia is present
A 69-year-old woman with previously well-controlled atrial fibrillation comes to the physician because of lightheadedness, nausea, vomiting, and blurred, yellow vision. Her temperature is 37.2°C (98.9°F), blood pressure is 110/80 mmHg, and respirations are 18/min. An ECG shows paroxysmal ventricular tachycardia. A drug with which of the following mechanisms of action is most likely responsible for the findings seen in this patient?
A. Inhibits Na+-K+ ATPase
B. Inhibits phosphodiesterase
C. Inhibits transmembrane calcium influx
D. Selectively antagonizes beta-1-adrenergic receptors
E. Stimulates muscarinic cholinergic receptors
F. Stabilizes membranes and decreases the slope of phase 0
A. Inhibits Na+-K+ ATPase
Digoxin directly inhibits the cardiac Na+/K+ ATPase, leading to indirect inhibition of the Na+/Ca2+ exchanger, which leads to increased Ca2+ and positive inotropy.
Digoxin is indicated for heart failure, since it increases contractility and is also indicated in atrial fibrillation by increasing the parasympathetic stimulation of AV and SA nodes (reducing AV and SA node conduction)
An 8-year-old girl is brought to the emergency department after being found unconscious on the playground during school recess. An electrocardiogram shows ventricular tachycardia with a rate of 170/min, and a prolonged QT of approximately 0.5 seconds. When her parents arrive, the mother says that there is a family history of arrhythmias. Which of the following drugs is contraindicated for the treatment of this child? A. Adenosine B. Lidocaine C. Metoprolol D. Procainamide E. Verapamil
D. Procainamide
The child is most likely suffering from long QT syndrome, a family condition assocaited with an increased risk of ventricular arrhythmias. Drugs known to prolong the QT interval (ClassI Ia and III) are contraindicated for use in patients with long QT syndrome.
Procainamide increases AP duration, increases effective refractory period, and increases the QT interval
Nitrates are vasodilators that are used in the tx of stable angina for its anti ischemic effects…they can sometimes cause a decrease in BP, which is sensed by the body and then cause an increase in myocardial O2 demand….why and how do you treat this?
Bopdy senses low BP and causes reflex tachycardia
tx with betablockers
