Lecture 6 (Dysarrhythmias)-Exam 2 Flashcards
SA node:
* Where is it?
* What is it?
* What does it control?
- Tiny 1 mm collection of cells in upper R corner of RA
- Primary pacemaker site of heart
- Controls rhythm of heart by having fastest intrinsic rate of depolarization(60-100 beats/min)
SA node:
* Starts what?
* SA node discharges too small to generate what?
* What is inscribed by depolarization of atria?
- Starts cardiac cycle by initiating atrial systole
- SA node discharges too small to generate any deflection on ECG
- P wave inscribed by depolarization of atria
AV node:
* Located where?
* What does it provide?
* What does it protect?
- Located near inferior portion of interatrial septum
- Provides a physiologic conduction delay to allow atria to fill ventricles prior to ventricular systole
- Protects ventricle form excessive stimulation from atria such as in atrial flutter or AF
His-purkinje system
* What does the his bundle divde into?
* Where does the left bundle go into?
* What does the systm provide?
- His Bundle divides into R & L bundles
- Left bundle further divides into L anterior & posterior fascicles
- His-Purkinje system provides for orderly depolarization of ventricles
What are the rates of SA, AV, purkinje fibers?
Farther from SA node, slower intrinsic rate of pacemaker site.
Review of Pertinent Anatomy
- Where is the SA node located? What is the blood supply?
- What is the SA and AV nodal rate?
- What is the blood supply of the AV node?
- SA node is at the junction of the RA and SVC. Its blood supply is from RCA in 55% and LCA in 45% of individuals
- SA nodal rate is 60-90, AV nodal rate is 45-60
- AV node is supplied by RCA in 90%, LCA in 10% (ST elevations in inferior leads, might have bradycardia)
Review of Pertinent Anatomy
- Where are rates slowed? How?
- What does the PR interval indicate?
- What does the QRS and QT intercal represent?
- Rates are slowed though the AV node due to slow ion channels but may be bypassed by accessory pathways, allowing for rapid ventricular rates
- PR interval indicates time it takes to conduct from node to ventricle
- QRS represents ventricular depolarization and QT interval is total ventricular depolarization and repolarization
What contributes the most to the membrane potential in stage 3?
A. Calcium channels close, potassium channels open
B. Calcium channels open, potassium channels close
C. Sodium channels close
D. Sodium channels open
E. Magnesium channels close
A. Calcium channels close, potassium channels open
Sodium channel blockade results in what? What are the examples that can cause this (4)
Sodium channel blockade results in widening of the QRS
* TCAs
* Antidysrhythmics
* Local anesthesics
* Benadryl
Potassium channel blockade causes what? What are the examples (4)
Potassium channel blockade prolongs the QT
* Antipsychotics
* Antidysrhythmics
* Antimalarials
* Macrolide abx
What are the dysrhythmias dx options?
- Monitor
- 12-lead EKG
- Holter Monitor
- Patient-activated Event Monitor
- Implantable event monitor
- Stress testing
What is this?
Holter and event monitors
* Patient has to record it when they are feeling it
What is this?
Implantable loop recorders (subcutaneous)
* Usually for pt for a longer period of time
dysrhythmias dx options:
Invasive electrophysiologic studies (EPS)
* Electodes where?
* Done in patients with what?
* Reproduced what?
* Assess what?
* With electrical current, do what?
* Can also be used to detetmine what?
- Electrodes in RA & ventricular chambers
- Done in patients with documented tachyarrhythmias or syncope suspected to occur with tachyarrhythmias
- Reproduce tachyarrhythmias
- Assess effectiveness of pharm agents
- With electrical current, ablate abnormal focus or pathway
- Can also be used to determine conduction disorders & mechanism of heart block
Things to Consider When Analyzing Dysrhythmias
* What are the different sites of origin?
- Sinus Node (ST)
- Atria (PAC)
- AV junction (junctional escape rhythm)
- Ventricles (PVC)
Things to Consider When Analyzing Dysrhythmias
- What are the different rates?
- Accelerated - faster than expected (accelerated junctional rhythm @ 75 bpm)
- Slower than expected (marked SB @ 40 bpm)
- Normal (junctional escape rhythm)
What are the different Regularity of ventricular or atrial response?
- Regular (PSVT)
- Regular irregularity (atrial/ventricular bigeminy)
- Irregular irregularity (AF or MAT-COPD)
- Irregular (multifocal PVCs)
MAT is sort of like wandering pacemaker with different rate
- All narrow QRS complex arrhythmias originate where?
- Supraventricular arrhythmias can have a wide QRS complex if what?
- Ventricular dysrhythmias can never have what?
- All narrow QRS complex arrhythmias originate above the His bundle & are called supraventricular.
- Supraventricular arrhythmias can have a wide QRS complex if there is a concomitant intraventricular conduction defect or aberrant conduction
- Ventricular dysrhythmias can never have a narrow QRS complex
What are the types of tachycardias?
- Narrow Regular
- Narrow Irregular
- Wide Regular
- Wide Irregular
What are the examples of narrow, regular?
- SINUS TACHYCARDIA
- SVT
- Orthodromic WPW
- Atrial flutter
What are these two examples?
- Top: SVT
- Bottom: A.Flutter
What are the narrow, irregular?
- Atrial Fibrillation
- Aflutter w/variable block
- MAT
What are the wide, regular?
- Ventricular Tachycardia
- SVT w/aberrancy
- Antidromic WPW
What are the wide, irregular?
- Afib w/aberrancy
- Polymorphic VT
- WPW w/afib – essential to review old EKGs if available
What are the different types of bradycardias?
- Sinus bradycardia
- Slow atrial fibrillation
- Junctional rhythm (usually)
- Most AV blocks
- Idioventricular rhythm
- 3rd degree AV block (usually)
What is this?
Sinus brady
* P waves present
* Narrow QRS
What can you give to patients with different heart blocks to increase HR? What heart block will this not work?
Atropine
* 3rd will not work because the drug only works on SA node
What is this?
Idioventricular
What are Dr. Pepe’s ordering package?
What is the most common tachydysrhythmia? How do you treat it?
Sinus tachy
* Treat the underlying cause
Approach to Tachycardia
* Consider treatment of rate once above what? Why?
* Wide complex tachycardia is what?
- Consider treatment of rate once above 140. Above this level, further increase in heart rate is rarely adaptive and helpful. This is because CO falls at this level as there is no longer sufficient filling time in diastole.
- Wide complex tachycardia is VT until proven otherwise and needs to be treated as such
What are the two broad causes of tachycardia?
Medication (usually stable, so have time) and electricity (unstable, looks unwell)
- What is the most common braydysrhythmia? Txt?
- Rarely has what?
- Most common bradydysrhythmia- sinus bradycardia- treat underlying cause
- Rarely with symptoms / instability >50 bpm
What are the broad causes of bradycardia?
Medications and electricitiy
Vaughn Williams Classification
* What are the different classes of sodium channel blockage? What does it reduce?
* What are the other 3 classes?
CAB
What are the classes of flecainide, diliazem, esmolol and sotalol
What are the agents of Class 1?
- Procainamide (IA)
- Lidocaine (IB)
- Flecainide (IC)
- Propafenone (IC)
What are the agents in class 2?
- Esmolol
- Metoprolol
What are the agents in class 3?
- Bretylium
- Amiodarone (MC in ER-> unique because acts like all the classes)
- Ibutilide
- Sotalol
- Dofetilide
- Dronedarone
What are the nonpharmacologic management?
- Direct current cardioversion & defibrillation
- Implanted cardiac defibrillators(ICD)
- Radiofrequency catheter ablation
- Pacemakers
What is cardioversion? What can go wrong?
- Synchronized application of an electric shock to terminate a tachyarrhythmia
- Synchronized to QRS complex
- If administer shock during ventricular repolarization (T wave), can cause VF
R on T: if you shock on rel refract period
What is Defibrillation for?
Asynchronous delivery of shock to terminate VF or pulseless VT
Pacemakers:
* What do they do?
* What can you do temporary?
* ICD’s also have what?
- Pacemakers deliver an electrical impuse to cause an action potential
- Temporary transvenous (IV into right heart). Good for about a week at bedside.
- Permanent
- ICD’s also have pacemaker capability of responding to slow rates
What is this?
Temporary Transvenous Pacemaker Placement
* Place central line in Right internal jugular
* Place a sheath and feed wire and balloon in blood= floats to the heart
What does this show?
Ventricular paced rhythm
QRS are wide due to block. We pace ventricles.
What is this?
Dual Chamber Pacemaker
Implanatable Cardiac Defibrillators(ICD)
* What are they?
* What do they sense?
* What do they deliver?
* Often also have what?
- Implanted defibrillators
- Sense fast rates & responds to them
- Deliver current to try to terminate them
- Often also have pacemaker capability of responding to slow rates
Radiofrequency Catheter Ablation
* What is it?
* What is it used for?
* Can do what?
Application of alternating current electrical energy in radiofrequency range to an arrhythmogenic focus of myocardium to ablate focus
* Increasing use in treatment of AFib, Aflutter, SVT
* Can ablate accessory pathway in WPW or dual pathways in AV node
Burn it off
What is cryoablation?
- Cools tissue instead of heating it
- Similar outcomes
What is this?
Sinus Arrhythmia
* Synchronized with what?
* Faster HR when?
- Synchronized with respiratory cycle
- Faster HR results when there is an inspiratory reflex inhibition of vagal tone
Sinus Bradycardia
* What is the definition?
heart rate of <60 beats/min
What are the sxs of sinus bradycardia?
Many patients can tolerate heart rates of 50 or even 40 beats/min, but at lower rates symptoms are likely to occur:
* Fatigue
* Dizziness (not vertigo) about to pass out
* Near syncope
* Syncope
* Ischemic chest pain
Sinus bradycardia:
* What does not need to be treated?
* What does does need to be treated?
- Asymptomatic bradycardia does not need treatment
- Symptomatic Causes: treat underlying cause
Sinus bradycardia:
* What are the underlying causes that can cause symptomatic bradycardia?
- Acute myocardial infarction
- Drugs—for example: β blockers, digoxin, calcium channel blockers (Verapamil and Diltiazem), amiodarone
- Raised intracranial pressure
- Hypothermia
- Hypothyroidism
What are the different drugs that cause bradycardia?
- alpha 2- agonists
- B-blockers
- CCBs
- Digoxin
- Ach-I
Sinus tachycardia:
* What is the rate?
* What causes catecholamine induced by physiology?
* What are the pharmacologically induced?
Premature Atrial Contractions(PAC’s)
* Premature what?
* What is different?
* Occurs in who?
* Can be precipitated by what?
* Isolated PACs seen in what?
* Asymptomatic patients usually only need what?
- Premature discharge of non-sinus atrial pacemaker
- P waves are different
- Occur in patients of all ages
- Can be precipitated by caffeine, alcohol, smoking
- Isolated PACs seen in patients with healthy hearts are considered insignificant
- Asymptomatic patients usually only require observation
Wandering Atrial Pacemaker
* What are the mechanisms and who is it typically seen in?
- 3 or more ectopic pacemakers in atria
- Typically seen in young healthy persons
Wandering Atrial Pacemaker
* What is the heart rate?
- Atrial rate is 60-100
- Ventricular response is regular
Wandering Atrial Pacemaker
* What is the ECG morphology?
- There are at least three P wave morphologies
- There may be moderate variation in atrial & VR’s
What is this?
Wandering atrial pacemaker
* At least three different P wave configurations (seen in the same lead) are needed to diagnose a dysrhythmia as wandering atrial pacemaker.
SVT:
* Arises from what?
* Generic term referring to what?
* Includes what?
- Arises from above ventricles but cannot be definitively identified as atrial or junctional tachycardia because the P’ waves cannot be seen sufficiently
- Generic term referring to a tachycardia originating in atrium, AV junction area, etc (ABOVE VENTRICLE)
- Includes paroxysmal supraventricular tachycardia, (PSVT), non-paroxysmal atrial tachycardia, MAT
SVT:
* What do the QRS complexes look like?
* What is the rate?
* What is paroxysmal?
* Several types of PSVT depending on what?
- Generally regular & has a narrow QRS complex unless has functional aberrancy (R or L BBB)
- Rates 150-250 BPM
- Onset sudden, usually initiated by a premature beat, & arrhythmia also stops abruptly - which is why they are called paroxysmal.
- Several types of PSVT depending on location of reentry circuit.
SVT:
* What are the mechanisms and causes?
- Most examples due to reentry
- Commonest reentry pathway involves AV node(70%, & called AV nodal reentrant tachycardia[AVNRT])
- Pathway may be intraatrial or may utilize an accessory pathway as part of reentrant loop
- PSVT may occur in otherwise completely normal individuals, or may occur as a result of increased atrial pressure or because of presence of an accessory pathway
What is this?
SVT
What is the acute treatment of SVT? (stable and instability)
- Adenosine(6-12 mg IV) first line medical therapy(successfully terminates most SVTs
- NEW- Ca++ blockers being used more often as a first line treatment
- With non-adenosine sensitive atrial tachycardias, adenosine will increase level of AV block, but atrial tachycardia will persist which allows precise identification of mechanism
- In presence of hemodynamic instability, electrical cardioversion is treatment of choice
What type
SVT then treated with adenosine
Chronic txt of SVT
* What are drugs that slow down AV nodal conduction?
- Beta blocker
- Verapamil
- Diltiazem
- Digoxin will help recurrent AVNRT, AVRT and may have varying effectiveness for atrial tachycardia