SM 140 Pharmacology of Antiarrhythmic Drugs Flashcards
What types of arrhythmias are treated with antiarrhythmic drugs?
Tachyarrhythmias
What are the modalities of antiarrhythmic therapy?
Behavior, device-based, and procedural
What is an example of a behavioral antiarrhythmic therapy?
The Valsalva maneuver
How does the Valsalva maneuver exert antiarrhytmic effects?
The Valsalva maneuver results in increased Vagal tone at the AV Node, and can treat AVNRT and AVRT, both of which are subtypes of PVNRT
How do device-based approaches to antiarrhythmic therapy work?
Use an ICD to administer shocks to reset the heart rhythm when an abnormal rhythm is detected
How do procedural approaches to antiarrhythmic therapy work?
Ablate the cells responsible for an abnormal rhythm, such as those that conduct along a slow pathway
What ion is responsible for Phase 0 of the Myocyte AP, and in what direction does it flow?
Sodium is responsible for the Myocyte AP during phase 0, which represents the upshoot due to Sodium influx
What ion is responsible for Phase 2 of the Myocyte AP, and in what direction does it flow?
Calcium is responsible for the Myocyte AP during phase 2, and is responsible for the plateau due to Calcium influx
What ion is responsible for Phase 3 of the Myocyte AP, and in what direction does it flow?
Potassium is responsible for the Myocyte AP during phase 3, which causes repolarization due to Potassium efflux as well as inactivation of the L type Cav
What is significant about Phase 2 during the Myocyte AP?
Ca influx through DihydropyridineR during Phase 2 is responsible for Calcium induced Calcium release from RyanodineR during the Myocyte AP and contraction
What ion is responsible for Phase 4 of the Pacemaker AP, and in what direction does it flow?
Sodium is responsible for the unstable resting membrane potential during Phase 4, and enters via the funny current
What ion is responsible for Phase 0 of the Pacemaker AP, and in what direction does it flow?
Calcium is responsible for Phase 0 of the Myocyte AP, and causes the upshoot
What are the order of phases in Myocyte APs, starting from rest?
Phase 4 -> Phase 0 -> Phase 1 -> Phase 2 -> Phase 3
What are the order of phases in Pacemaker AP’s, starting from rest?
Phase 4 -> Phase 0 -> Phase 3; No Phase 1 or 2
What phases are missing in comparing the Pacemaker AP to the Myocyte AP?
Phase 1 and 2 are missing in the Pacemaker AP, so no brief hyperpolarization and no plateau
What is special about Phase 4 of the Pacemaker AP?
Unstable = automaticity
How do B agonists affect the Pacemaker cells?
Increase the slope of Phase 4 to reach Vt faster = increase Heart Rate
How does the Vagus nerve affect the Pacemaker cells?
Decreases the slope of Phase 4 to reach Vt slower = decrease Heart Rate
Where on the ECG trace does SA Node firing occur, and is it visible?
SA Node fires before the P wave, and is not visible
Where on the ECG trace does Atrial Contraction occur, and is it visible?
Atria contract during the P wave, and is visible
Where on the ECG trace does AV Node firing occur, and is it visible?
AV Node fires during the PR segment, and is not visible
How can SA and AV Node firing be seen on EKG?
Normally not visible because they are so small, but inserting a catheter can visualize them
Where on the ECG trace does the Ventricle depolarize, and is it visible?
Ventricles depolarize during the QRS complex, and is visible
Where on the ECG trace do the Atria repolarize, and is it visible?
Atria repolarize during the QRS complex, and not visible due to being masked by Ventricular depolarization
Where on the ECG trace does the Ventricle repolarize, and is it visible?
Ventricles repolarize during the T wave, and is visible
What phase or interval on the EKG corresponds to SA node firing?
P wave
What phase of the myocyte AP corresponds to the PR Interval?
Phase 4 of the Myocyte AP = PR Interval, waiting for atrial signal
What phase of the Myocyte AP corresponds to the the initiation of the QRS complex?
Phase 0 = initial influx of Sodium = Beginning of QRS on EKG
What phase of the Myocyte AP corresponds to the QT interval?
QT Interval = Calcium influx for contraction = Phase 2
What can cause a narrow QRS complex?
Normal use of the His-P system for Ventricular Contraction
What can cause a wide QRS complex?
Abnormal Ventricular contraction that does not use the His-P system
What are the 2 basic mechanisms of bradyarrhythmias?
Diminished Automaticity and Block
What are the types of SA Node bradyarrhythmias?
Sinus Bradycardia (decreased Automaticity), Sinus Node Exit Block, Tachy-Brady Syndrome
What are the types of AV Node bradyarrhythmias?
First, Second, and Third Degree AV Blocks
What are the mechanisms of tachyarrhythmias?
Enhanced automaticity, reentry, and triggered activity
What can cause enhanced automaticity and what arrhythmia results?
Sharper slope of Phase 4 of the AP + More negative Vt = Tachyarrhythmia
What are the requirements for a reentry arrhythmia to form?
An anatomical barrier, a fast pathway and a slow pathway, and a block
What causes triggered activity and what arrhythmia results?
Defects in calcium balance lead to after depolarizations; Early afterdepolarizations (Phase 3) and Delayed afterdepolarizations (Phase 4) cause triggered activity, which results in tachyarrythmia
What type of depolarization can occur during a prolonged action potential duration?
Prolonged APD = Long QT = Early Afterdepolarization risk
What type of depolarization can occur from Digoxin toxicity?
Delayed Afterdepolarization risk
What are the types of Supraventricular tachyarrhythmias?
Sinus Tachycardia + Paroxysmal Supraventricular Tachycardia (AVNRT + AVRT + AT) + Atrial Flutter + Atrial Fibrillation
What are the types of Ventricular tachyarrhythmias?
Monomorphic Ventricular Tachychardia + Polymorphic Ventricular Tachycardia + Ventricular Flutter + Ventricular Fibrillation
What pathophysiology causes AVNRT?
Reentry within the AV Node using Fast + Slow pathways
What pathophysiology causes AVRT?
Reentry between Atria and Ventricules using the AV Node as a Slow Pathway and an Accessory Pathway as the Fast Pathway
How does Atrial Flutter present on EKG?
Atrial Rate > Ventricular Rate, Sawtooth Pattern of P waves
How does Atrial Fibrillation present on EKG?
Undulating P waves and Irregular Irregular QRS complexes
Does Atrial Flutter use the AV Node?
No, entirely in the R. Atrium
Does Atrial Fibrillation use the AV Node?
No, entirely in the R. Atrium
How does Monomorphic Ventricular Tachycardia present on EKG?
Regular Ventricular rhythm + Monomorphic QRS + Wide QRS
What causes Monomorphic Ventricular Tachycardia?
Reentrant Ventricular rhythm
What causes Polymorphic Ventricular Tachycardia?
Early Afterdepolarization
How does Polymorphic Ventricular Tachycardia present on EKG?
QRS complexes of varying shape
How can enhanced automaticity be treated?
Hyperpolarize resting membrane potential + make the threshold more positive + slow the slope of Phase 4 depolarization = slow heart rate
How can reentry be treated?
Block the slow pathway or suppress premature beats to prevent reentry loops for forming
How can triggered activity be treated?
Modify the milieu/electrolyte balance
Should rational evidence or empirical evidence be trusted more?
Empirical evidence such as Clinical Trials are the gold standard and should be trusted
What are the two ways to treat Atrial Fibrillation?
Rhythm control and Rate control
How does Rhythm control work and what does it treat?
Rhythm control modifies the electrical properties of the Atria to restore sinus rhythm = treat Atrial Fibrillation
How does Rate control work and what does it treat?
Rate control slows the AV node to control the Ventricular rate and does not treat the Atrial dysregulation = treat Atrial Fibrillation
Which form of Atrial Fibrillation treatment does not affect the atrial rhythm?
Rate control does not affect the atrial rhtym and allows for the Atria to continue to fibrillate
How can Ventricular Fibrillation and Ventricular Tachycardia be treated without drugs?
Shock
What effect do Class I antiarrhythmics have?
Block Na channels
What effect do Class II antiarrhythmics have?
Beta blockers
What effect do Class III arrhythmics have?
Block K channels
What effect do Class IV arrhythmics have?
Block Ca channels
What are the activation gates of Nav channels?
M gates = activation
What are the inactivation gates of Nav channels?
H gates = inactivation
How do Na Channel blockers work?
Na Channel blockers bind the active + inactive states of Nav channels to inhibit Na influx
What state can Na Channel blockers not bind?
Na channel blockers cannot bind the resting state of Nav channels