What channel is responsible for the spontaneous depolarization in nodal cells?
If (funny) sodium channels. They open upon cellular repolarization.
What channels and pumps are responsible for the transmembrane potential in cardiac cells?
A patient comes in to see you with a heart rate of 140. He has a previous history of heart attack so you do an EKG and find that he has a ventricular arrhythmia. You prescribe hims sodium channel blockers. Where do these blockers work on his cells? How will this help his arrhythmia?
They bind to the open and inactivated state of the sodium channels. These will help with his arrhythmia because it will make it harder for the cells to depolarize during the relative refractory period.
Why do sodium channel blockers have no effect on the SA or AV node?
Those cells are not voltage dependent. They are only time dependent.
How do beta-1 receptor stimulation, hypokalemia and mechanical stretch affect sinus rhythm by altering the action potential? What about Na+ channel blockers? What about ACh, Adenosine and Digoxin?
What is the difference between triggered and ectopic automaticity?
Triggered automaticity = delayed or early afterdepolarization. Ectopic automaticity = ventricular or atrial origin of automaticity.
What are the two mechanisms for triggered automaticity?
Delayed afterdepolarization and early after depolarization.
Why does vomiting induce arrhythmias?
Vagal stimulation causes a change in action potential slope and baseline. This changes the rate at which the heart contracts.
What is responsible for the majority of tachyarrhythmias?
Reentry caused by a functional or anatomical barrier.
What are the different mechanisms for atrial arrhythmias?
You find a man who died two days ago. He was in his late 40s with no history of health problems. Postmortem examination only revealed puncture in his right forearm. Autopsy showed the heart was in a state of asystole (no cardiac electrical activity). What combination of electrolytes injected could have caused this?
KCl. K+ goes through K+ channels, hyper polarizing the cells and stopping contraction.
What are the four classes of drugs used to treat arrhythmias?
Why would you consider use of class I antiarrhythmatic drugs for someone with an ectopic arrhythmia?
They are sodium channel blockers. Ectopic arrhythmias originate in tissue that utilizes sodium channels to generate action potentials.
A patient comes in with ventricular tachycardia. You prescribe him a drug with a very long half life? What drug did you prescribe him?
A class III K+ channel blocker: Amiodarone. This will increase the QT interval and prevent early depolarization by the ventricle.
What drugs should you not us if you have a patient with a prolonged QT interval?
Drugs that further prolong the QT interval: Sodium channel blockers that also block K+ channels (IA: procainamide and quinidine) and all class III drugs (K+ channel blockers).
A patient with heart failure comes to see you with ventricular arrhythmia. What drugs should you NOT use?
Class IV calcium channel blockers (Verapamil and Diltiazem) and beta blockers. They will decrease contractility of the heart.
You see a patient with WPW syndrome. What drugs do you not want to prescribe to this patient?
Those that block the AV node. (Digitalis, verapamil and diliazem (class IVs).
What drugs should you not prescribe if someone has asthma or diabetes?
What drugs do you use to treat atrial fibrillation and atrial flutter?
You need to control ventricular response if you cannot control sinus rhythm. This can be done with digoxin (slows AV conduction and slows HR).
What drugs do you use to treat supra ventricular tachycardia?
Adenosine or verapamil (IV injection).
What drugs do you use to treat a patient with ventricular tachycardia with MI?
Amiodarone or lidocaine.
What drugs do you use to treat ventricular fibrillation?
Amiodarone or lidocaine.
What do you do to treat digitalis toxicity?
Correct Mg++ and stop digoxin.
When can you use procainamide/ quinidine?
Life-threatening ventricular tachycardia. This is because adverse effects include Lupus and increasing QT interval.
When do you use lidocaine and mexiletine?
To treat and prevent ventricular arrhythmias.
When can you use flecainide?
Life threatening ventricular tachyarrhythmias without ischemic heart disease. They are almost exclusively used for supra ventricular tachycardias.
What are the different generations of beta-blockers?
1: propranolol (blocks beta-1 and beta-2). 2: atenolol, metoprolol (selectively block beta-1). 3: labetalol and carvedilol (blocks beta-1, alpha-1 and agonist for beta-2)