CARDIOLOGY - Junctional & Ventricular Dysrhythmias (Week 7) Flashcards
Types of Junctional Dysrhythmias
- Premature Junctional Complex (not a rhythm - occurs with a rhythm)
- Junctional Escape beat (see sinus arrest)
- Junctional Rhythm
- Junctional Bradycardia
-
Accelerated Junctional Rhythm
- Junctional Tachycardia
Junctional dysrhythmias are rhythms originating in the
in and around the AV node (AV junction)
An impulse originating from the AV junction travels in ______ direction(s). Which directions?
two directions:
1) up the conduction pathway towards the atria (backwards - retrograde motion) to depolarize the atria
2) down the conduction pathway towards the ventricles (forward - antegrade motion) to depolarize the ventricles
AV node and surrounding tissue have an inherent rate of _______ bpm. It is NOT the normal pacemaker of the heart (not as efficienct as SA node) but may assuming pacing responsibility for heart if:
40-60bpm
- SA node fires an impulse, travels through the atria, but is not conducted to the ventricles (AV block)
- SA node fails to fire (sinus arrest)
- Rate of SA node is slower than AV junction (sinus bradycardia)
How does the retrograde motion of an impulse impact the P wave on an ECG tracing?
- P wave changes into 3 different identifiable waves & their morphology is based on where the impulse originated from in the AV junction
- 1) HIGH - impulse generated near the beginning of the AV node
- 2) MIDWAY - impulse generated near the middle of the AV node
- 3) LOW - impulse generated near the end of the AV node
P wave morphology: HIGH origin of impulse at AV node
- impulse generated high in the AV node (close to atria)
- impulse travels in a backwards direction towards atria FIRST before the ventricles SECOND
- P wave will be retrograde and inverted in the QRS complex
P wave morphology: MIDWAY origin of impulse at AV node
- impulse originates midway in the AV node
- impulse travels in a backwards direction towards atria AND towards the ventricles SIMULTANEOUSLY
- because both are the same distance from the AV node, the P wave will be hidden by the QRS and therefore not visible
P wave morphology: LOW origin of impulse at AV node
- impulse generated low in the AV node
- impulse travels forward toward ventricles FIRST and then backwards towards atria SECOND
- Impulse reaches atria second so P wave will be retrograde and inverted to the QRS complex (i.e. inverted P wave AFTER QRS)
Premature Junctional Complex (PJC)
impulse originates from irritable tissue in the AV junction before next sinus beat is due (i.e. PJC occurs EARLY, before the next expected beat). AV node is usurping/taking over the SA node for that beat and therefore interrupting the sinus rhythm
Conduction pathway of Premature Junctional Complex (PJC)
impulse originates in AV junction (higher pacemaker has failed)
heads upwards towards atria (retrograde) and downwards towards ventricles (antegrade) and ultimately depolarizes atria and ventricular muscle
Premature Junctional Complex (PJC)
Rate
Rhythm
P wave
PR Interval
QRS Complex
Rate: can occur at ANY rate
Rhythm: occasionally irregular (remember can also be compensatory or non-compensatory pause but typically non-compensatory) - ALSO REMEMBER: it’s not a rhythm; it is a single beat occuring WITHIN an underlying rhythm (ex. Sinus bradycardia with a PJC (6th complex)
P wave: inverted before or after QRS, or buried in QRS complex (note that inverted P waves are normal in V1)
PR Interval: <0.12 seconds IF the P waves precedes QRS (it’s n/a if the P wave comes after QRS)
QRS Complex: <0.12 (can be >0.12 if BBB exist)
Premature Junctional Complex (PJC)
Causes
Adverse Effects
Treatment
Causes: less common than PACs and PVCs
- Acute coronary syndromes
- Heart disease (i.e. rheumatic, valvular)
- CHF
- Drugs - cocaine, tobacco, caffeine
- Medications - Digitalis toxicity
- Electrolyte imbalance
- Fatigue
Adverse Effects: usually no ill effects
Treatment: None
How to tell the difference between PAC and PJC?
PAC: typically, upright P wave before QRS (in leads II, III, aVF)
PJC: either no P wave present (buried) or inverted (retrograde) AND may or may not precede QRS (in leads II, III, aVF)
When can PJCs often be misdiagnosed?
when the P wave of the PAC is buried in the preceding T wave (looks like a double hump)
Junctional Escape Beat
- predominant pacemaker slows dramatically (or fails) and lower pacemaker takes over at its inherent rate
- initial pacemaker will resume functioning afer missing one/two beats OR
- the other pacemaker may continue as the new pacemaker, and possible creates a new rhythm
- junctional escape beat is an ectopic beat that occurs LATE (i.e. after preceding sinus beat, usually occurs following sinus arrest/block, after premature beats, or during pauses)
- same morphology as PJCs
Conduction pathway of Junctional Escape Beat
impulse originates in the AV junction (the higher pacemaker has failed) → heads upwards (antegrade) and downward (retrograde) → ultimately depolarizes atria and ventricular muscle
Junctional Escape Beat
Rate
Rhythm
P wave
PR interval
QRS Complex
Rate: can occur at any rate
Rhythm: occasionally irregular
P wave: inverted before or after QRS complex or buried in QRS (inverted P waves are notmal in V1)
PR interval: <0.12 seconds IF the P wave precedes the QRS
QRS Complex: <0.12 seconds (can be >0.12 if BBB exist)
Junctional Escape Beat
Causes
Adverse Effects
Treatment
Causes: Typically occurs:
- during episodes of sinus arrest
- in healthy individuals during sinus bradycardia
- Myocardial Infarction
- Heart disease - rheumatic, valvular
- Hypoxia
- Sinus node disease
- Post cardiac surgery
- medications - Digitalis, quinidine, beta blockers, calcium channel blockers
Adverse Effects: usually no ill effects
Treatment: none
True or False. Junctional Escape Beat is not a rhythm.
True. It is single beat occurring within an underlying rhythm (ex. sinus arrest with a junctional escape beat [2nd complex])
for testing purposes - can just write sinus arrest (or sinus arrest with junctional escape beat)
If a junctional escape beat continues as the new pacemaker, it creates:
Junctional Rhythm
Junctional Rhyhtm
several sequential slow and regular junction escape beats (junctional rhythm and junctional escape rhythm used interchangeably)
looks like NSR but is junctional rhythm because of buried P waves
basically it’s the normal rhythm of the AV node (junctional rhythm is at a rate of 40-60, which is the inherent rate of the AV node)
Describe the conduction pathway in junctional rhythm
- Impulse originates in and around the AV node (AV junction) - the higher pacemaker has failed
- travels up the conduction pathway towards the atria and down towards ventricles
- depolarizes both atria and ventricles
Junctional Rhythm
Rate
Rhythm
P wave
PR Interval
QRS complex
Rate: 40-60
Rhythm: Regular
P wave: inverted before or after QRS complex or buried in QRS
PR Interval: <0.12 secs IF the P wave precedes the QRS
QRS complex: <0.12 secs (can be >0.12 if BBB exist)
Junctional Rhythm
Causes
Adverse Effects
Treatment
Causes: Typically occurs
- during episodes of sinus arrest
- in healthy individuals during sinus bradycardia
- Myocardial infarction
- Heart disease - rheumatic, valvular
- Hypoxia
- Sinus node disease
- Post cardiac surgery
- Medications - Digitalis, quinidine, beta blockers, calcium channel blockers
Adverse Effects: often no ill effects; may present with signs of decreased cardiac output it heart rate slow (i.e. ~ 40)
Treatment: None
Junctional Bradycardia
AV junction fires at a slower rate than normal
Describe the conduction pathway in junctional bradycardia.
- Impulse originates in and around the AV node (AV junction) - higher pacemaker has failed
- Travels up conduction pathway towards the atria and down conduction pathway towards ventricles
- Depolarizes both atria and ventricles
Junctional Bradycardia
Rate
Rhythm
P wave
PR interval
QRS complex
Rate: <40
Rhythm: regular
P wave: inverted before or after QRS complex or buried in QRS
PR interval: <0.12 secs IF P wave precedes the QRS
QRS complex: <0.12 (can be >0.12 if BBB exist)
Junctional Bradycardia
Causes
Adverse Effects
Treatment
Causes: Typically occurs
- during episodes of sinus arrest
- in healthy individuals during sinus bradycardia
- Myocardial infarction
- Heart disease - rheumatic, valvular
- Hypoxia
- Sinus node disease
- Post cardiac surgery
- Medications - Digitalis, quinidine, beta blockers, calcium channel blockers
Adverse Effects: decreased cardiac output
Treatment: None
Accelerated Junctional Rhythm
AV junction fires at a faster rate than normal
Describe conduction pathway in accelerated junctional rhythm
- impuulse originates in and around the AV node (AV junction) - higher pacemaker has failed
- travels up conduction pathway towards atria and down conduction pathway towards ventricles
- depolarizes both atria and ventricles
Accelerated Junctional Rhythm
Rate
Rhythm
P wave
PR interval
QRS complex
Rate: 61 - 100
Rhythm: regular
P wave: inverted before or after QRS complex or buried in QRS complex (inverted P wave are normal in V1)
PR interval: <0.12 secs IF the P wave precedes the QRS
QRS complex: <0.12 seconds (can be >0.12 if BBB exist)
Accelerated Junctional Rhythm
Causes
Adverse Effects
Treatment
Causes:
- Myocardial Infarction
- Cardiac surgery
- COPD
- Hypokalemia
- Fever
- Drugs - Digitalis
Adverse Effects: usually asymptomatic because ventricular rate is 61-100 beats/min
Treatment: None
Junctional Tachycardia
3 or more sequential escape beats occuring at a rate of more than 100 beats/min
Describe the conduction pathway in junctional tachycardia
- impulse originates in and around the AV node (AV junction) - the higher pacemaker has failed
- Travels up conduction pathway towards the atria AND down conduction pathway towards to the ventricles
- Depolarizes both the atria and ventricles
Junctional Tachycardia
Rate
Rhythm
P wave
PR Interval
QRS complex
Rate: 101 - 180
Rhythm: Regular
P wave: inverted before or after QRS complex or buried in QRS complex (inverted P wave are normal in V1)
PR Interval: <0.12 seconds if the P wave precedes the QRS
QRS complex: < 0.12 (can be >0.12 if BBB exist)
Junctional Tachycardia
Causes
Adverse Effecs
Treatment
Causes:
- Acute coronary syndromes
- CHF
- Drugs - eg. Digitalis
Adverse Effects: decreased cardiac output (sweaty, confused, SOB)
Treatment: None
Types of Ventricular Dysrhythmias
-
Premature ventricular complex (NOT A RHYTHM)
- ventricular quadrigeminy
- ventricular trigeminy
- ventricular bigeminy
- pairs (with underlying rhythm included)
- Run of V-tach (with underlying rhythm included)
- R on T (with underlying rhythm included)
- Ventricular escape beat (see sinus arrest)
- Idioventricular rhythm
- Accelerated Idioventricular Rhythm
- Agonal Rhythm
- Ventricular Tachycardia
- Torsades de Pointes
- Ventricular Fibrillation
- Asystole
Ventricular dysrhythmias are rhythms originating in the
ventricles (most potentially lethal of all the rhythms)
Slow vs Fast Ventricular Rhythms
Slow Ventricular Rhythms: heart’s last gasp as a pacemaker, kicking in when the higher pacemakers can’t
Fast Ventricular Rhythms: emergency firing rate of 150-250 electrical impulses per minute; can result in decreased cardiac output and ultimately death
Premature Ventricular Complex (PVC)
A PVC can originate from an irritable site within the ventricular tissue before the next sinus beat is due
Describe conduction pathway in premature ventricular complex.
- impulse originates in an automaticity focus (usually in the ventricular wall) - ectopic focus in ventricles
- a small area begins to depolarize, propagating from cell-to-cell through one ventricle and eventually to the next ventricle (normally both ventricles depolarize simultaneously)
- PVCs begin to depolarize the ventricles
- If the higher pacemaker has not failed, the SA node discharges on time (which you can see as the regular P wave within the PVC) BUT the SA node cannot depolarize the entirety of the heart until the ventricles have finished repolarizing
- Once the ventricles have finished repolarizing, a “compensatory pause” occurs making them receptive to the next sinus generated cycle
PVC Classification: Site of Origin
1) Unifocal (monomorphic): when PVCs originate from the same single anatomic foci/location in the ventricle and therefore look alike
2) Multifocal (polymorphic): when PVCS originate from different anatomic foci/location in the ventricle and therefore DO NOT look alike
Quadrigeminal PVCs - Ventricular quadrigeminy
Every 4th complex is a PVC
Trigeminal PVCs - Ventricular Trigeminy
Every 3rd complex is a PVC
Bigeminal PVCs - Ventricular Bigeminy
Every 2nd complex is a PVC
Pairs - Couplet
Two sequential PVCs (could also be unifocal or multifocal)
Runs/Run of V-tach/Bursts
Three or more PVCs in a row at a rate of more than 100 beats/min
R-on-T phenomenon PVC
- occurs when R wave falls on the T wave of the preceding beat (remember that the last half of the T wave is vulnerable to electrical stimulation i.e. relative refractory)
- Dangerous dysrhythmias may result (eg. VT or VF)
Ventricular Escape Beat
Predominant pacemaker slows dramatically (or fails) and lower pacemaker takes over at its inherent rate
either
a) initial pacemaker will resume funcitoning after missing one two beats
or
b) the other pacemaker may continue as the new pacemaker, and possibly create a new rhythm
Accelerated Idioventricular Rhythm (AIVR)
three or more ventricular escape beats occurs in a row at a rate of more than 40 beats/min
Agonal Rhythm (“Dying Heart”)
A very irregular and severely impaired heart is only able to produce an occasional beat
Ventricular Tachycardia (V-tach)
What are the two types?
Three or more PVCs in a row at a rate of more than 100 beats/min (aka monomorphic ventricular tachycardia)
Non-sustained V-tach: V-tach lasting <30 seconds
Sustained V-tach: >30 seconds
Torsades de Pointes (aka TdP)
French for “twisting of the points” which describes the morphology of the QRS
aka polymorphic ventricular tachycardia
Coarse Ventricular Fibrillation (V-Fib)
Waveforms equal or greater than 3mm in amplitude
Fine Ventricular Fibrillation (V-Fib)
Waveforms less than 3mm in amplitude
Asystole (Flat line)
No impulse has originated as all pacemakers have failed
A total absence of cardiac electrical activity
Ventricular Standstill
Occurs as the SA node is still functional, even though there are no impulses passing through to the ventricles
Only atrial depolarization is present and there is no ventricular depolarization (if there is no ventricular depolarization, there is no ventricular contraction and therefore no pulse)
Defibrillation
- A delivery of an unsynchronized electrical current through the myocardium over a very brief period to terminate a cardiac dysrhythmia
- electrical current (shock) attempts to simultaneously depolarize ventricular cells causing momentary asystole, which provides an opportunity for the heart’s natural pacemakers to resume function
- this pacemaker with the highest degree of automaticity should assume repsonsibility for pacing the heart
