CARDIOLOGY - Sinus and Atrial Dysrhythmias (Week 5) Flashcards
What are the 6 types of sinus rhythms?
- Normal Sinus Rhythm (NSR)
- Sinus Bradycardia
- Sinus Tachycardia
- Sinus Arrhythmia
- Sinus Block
- Sinus Arrest
Sinus dysrhythmias are rhythms originating from the
SA node
What are two ways in which the sinus node can “relinquish its duty” (i.e. give up its job as primary pacemaker)?
1. illness or death - in which another pacemaker steps in
2. Usurpation - overthrown by another pacemaker (like a king)
True or False. In reality, there is only one “normal” rhythm. What is it?
True. Normal Sinus Rhythm (NSR)
Describe the conduction pathway in NSR.
Impulse originates in sinus node. Heads down normal conduction pathway and ultimately depolarizes into ventricular muscle
Normal Sinus Rhythm (NSR)
Rate
Rhythm
P wave
PR Interval
QRS Complex
Rate: 60 - 100
Rhythm: regular R-R intervals
P wave: present. upright, regular, matching, precedes each QRS complex (may be inverted in V1)
PR Interval: 0.12 - 0.20 secs, constant from beat to beat
QRS Complex: < 0.12 seconds (can be > 0.12 sec if BBB exist)
Normal Sinus Rhythm (NSR)
Causes
Adverse Effects
Treatment
Causes: Normal
Adverse Effects: None
Treatment: None
Sinus bradycardia
looks like NSR but a lot slower (SA node is firing at a slower rate than normal)
Describe the conduction pathway in sinus bradycardia.
Impulse originates in sinus node, heads down normal conduction pathway and ultimately depolarizes into ventricular muscle
Sinus Bradycardia
Rate
Rhythm
P wave
PR Interval
QRS Complex
Rate: < 60 (THIS IS THE ONLY THING THAT IS DIFFERENT when compared to NSR)
Rhythm: regular R-R intervals
P wave: present. upright, regular, matching, precedes each QRS complex (may be inverted in V1)
PR Interval: 0.12 - 0.20 secs, constant from beat to beat
QRS Complex: < 0.12 seconds (can be > 0.12 secs if BBB exist)
Sinus Bradycardia
Causes
Adverse Effects
Treatment
Causes:
- MI (associated with inferior MI)
- vagal stimulation (PNS response) - Vagal maneuveres, Valsalva maneuver, carotid sinus massage)
- Athletes - well conditioned hearts able to pump more blood with each beat and less often
- Increased intracranial pressure - Cushing’s triad
- Medications - calcium channel blockers, beta blockers, Digitalis toxicity
- Disease of the SA node
- Hypoxia
- Post heart transplant
- Hyper/hypokalemia
- Hypothyroidism
- Hypothermia
Adverse Effects:
- Decreased cardiac output
- dizziness
- syncope
- weakness
- hypotension
- pallor
Treatment: correct undelying cause (i.e. provide warmth, hyperventilate, etc.)
Sinus Tachycardia
looks like NSR but a lot faster (SA node firing at a faster rate than normal)
Describe the conduction pathway in Sinus Tachycardia
Impulse originates in sinus node. Heads down normal conduction pathway and ultimately depolarizes into ventricular muscle
Sinus Tachycardia
Rate
Rhythm
P wave
PR interval
QRS complex
Rate: 101 - 180
Rhythm: regular R-R interval
P wave: present, regular, upright, matching, precede each QRS complex (may be inverted in V1) & at very fast rates it may be difficult to differentiate between P waves from T waves (T wave may just look like a double hump because P wave is buried in it)
PR interval: 0.12-0.20 seconds, constant from beat to beat (may shorten with faster rate)
QRS complex: < 0.12 seconds (can be >0. 12 if BBB exists)
Sinus Tachycardia
Causes
Adverse Effets
Treatment
Causes:
- MI (typical with anterior infarctions)
- Sympathetic stimulation - maintaining HR and BP under normal conditions and “fight or flight” response)
- CHF - abnormal condition that reflects impaired cardiac pumping
- Shock - hypovolemic, neurogenic, anaphlyactic, septic, etc.
- Pulmonary embolilsm - blockage of the pulmonary artery by a foreign matter
- Drugs - cocaine, ecstasy, amphetamines, cannabis, nicotine, caffeine, etc.
- Medications - Atropine, epinephrine, dopamine
- Exercise
- Pain
- Fear and Anxiety
- Hpoxia
- Hyperthyroidism
Adverse Effects:
- Decreased cardiac output
- dizziness
- syncope
- weakness
- hypotension
- pallor
Treatment: attempt to correct the underlying cause (pain relief, reducing feer, reliveing anxiety, etc.)
Sinus arrhythmia (Sinus dysrhythmia)
Rhythm where SA node fires irregularly, which is cyclic and usually coincides with respiratory rate/breathing pattern in younger patients
Increases gradually during inspiration (R-R intervals shorten)
Decreases with expiration (R-R interval lengthens)
Physiologically, what is happening during sinus arrhythmia caused by breathing patterns?
RATE increases during inspiration: negative pressure in chest during inspiration sucks up blood from LE (causing more blood to return to RA) which ↑ HR to circulate that increased amount of blood
Describe the conduction pathway in sinus arrhythmia.
Impulse originates in sinus node, heads down the normal conduction pathway. Ultimately depolarizes in ventricular muscle.
Sinus Arrhythmia
Rate
Rhythm
P wave
PR interval
QRS complex
Rate: usually 60 - 100 (can vary due to respiratory pattern)
Rhythm: regularly irregular
- increases during inspirations (R-R interval shortens)
- decreases during expirations (R-R interval lengths)
P wave: present, irregular, upright, matching, precede each QRS complex (may be inverted in V1)
PR interval: 0.12-0.20 seconds (constant from beat to beat)
QRS complex: <0.12 secs (can be > 0.12 if BBB exist)
Sinus Arrhythmia
Causes
Adverse Effects
Treatmnent
Causes:
- respiratory sinus arrhythmia:
- “normal phenomenon” - breathing pattern most commonly seen in children and <30 y.o.
- non-respiratory sinus arrhythmia:
- heart disease
- MI
- Drugs - Digitalis, Morphine
Adverse Effects: None
Treatment: None
Sinus block (Exit Block)
- SA node fires an impulse regularly but it does not conduct (i.e. nothing wrong with the SA node but the impulse is not depolarizing to the atria)
- The impulse is unable to “exit” into surrounding atrial tissue; impulse is NOT conducted anywhere (not to atria, not to ventricles)
- this results in one or more beat sequences missing, creating a “pause” (length of pause will depend on how many beats are blocked)
In sinus block, what is unique about the pause caused by the missed beat?
- The pause caused by the missed beat is the same as (or an exact multiple of) the distance between two P-P intervals of the underlying rhythm (Exactly one or more cycles will fit into the pause)
- When the conduction of the regularly firing sinus impulse resumes, the beat returns on time at the end of the pause
Describe the differences between these two rhythms.
NSR: R-R intervals are exactly equal distances apart
Sinus Block: R-R intervals are exactly equal distance apart EXCEPT for the 6th complex
- the SA node is firing properly but it did not depolarize the atria and therefore did not create a P wave and subsequent QRS complex
When interpreting a sinus block rhythm, what indications on the ECG tracing tell you that the SA node is working properly?
The following P wave and QRS complex after the pause resumes exactly a certain number of cycles apart (depending on pause duration)
Sinus Block
Rate
Rhythm
P wave
PR Interval
QRS complex
Rate: can occur at any rate (usually 60 - 100 BPM)
Rhythm: occasionally irregular (due to pause(s) caused by sinus block); pause is the same distance between two other P-P intervals
P wave: normal sinus P’s before AND after the pause
PR Interval: 0.12-0.20 seconds, constant from beat to beat
QRS complex: <0.12 seconds (can be > 0.12 if BBB exist)
Sinus Block
Causes
Adverse Effects
Treatment
Causes:
- MI
- Vagal stimulation
- CAD (building up atherosclerotic plaque)
- Myocarditis
- CHF
- Hypoxia
- Medications - eg. Digitalis, Quinidine, Procainamide
Adverse Effects: frequent or very long sinus blocks can cause decreased cardiac output
Treatment: attempt to correct the underlying cause
Sinus Arrest (Sinus Pause)
SA node stops firing impulses regularly (aka SA node is not working) and ultimately the heart begins beating after one more missed beats
What’s happening to the SA node in sinus arrest?
- SA node suddenly stops firing for a brief period - result is one or more beat sequences missing, creating a “pause”
- EITHER
- 1) sinus node eventually resumes functioning after missing one or two beats OR
- 2) other pacemaker may continue as the new pacemaker and possibly create a new rhythm
Describe the differences between these two rhythms.
Sinus Block: R-R intervals are exactly equal distance apart EXCEPT for the 6th complex
Sinus Arrest: R-R intervals are exactly equal distance apart EXCEPT for anything after 5th complex
- An ectopic beat follows which confirms another pacemaker (purkinje fibers) assumed responsibility for pacing the heart (heart MUST continue to beat!)
note that the underlying rhythm has to be regular to be able to distinguish between the two
Re-entry
- Reactivation of myocardial tissue for the 2nd or subsequent time by the same impulse
- Occurs when an impulse is DELAYED, BLOCKED or BOTH in one or more segments in the conduction system
- The propagation of the impulse fails to end and continues activating excitable tissue which have just become polarized
Compensatory (complete) pause
- pause is compensatory if the normal beat following PAC occurs WHEN IT IS expected
- if you measure from R wave of complex BEFORE the PAC to the R wave of the complex AFTER the PAC, the period between the complex before and after the premature beat is the same as two normal R-R intervals
Describe the difference between these two rhythms.
NSR: two R-R intervals are exactly equal distance apart
NSR with PAC (3rd complex):
- Two R-R intervals that are unequal distance apart
- The distance before and after the PAC IS equal to two normal R-R intervals and therefore considered compensatory (complete)
Non-compensatory (incomplete) pause
- pause is non-compensatory if the normal beat following the PAC occurs BEFORE it was expected
- Measure from R wave of complex before the PAC to the R wave of the complex AFTER PAC (i.e. the period between the complex before and after the premature beat is less than normal R-R interval)
Describe the difference between these two rhythms.
NSR: Two R-R intervals are exactly equal distance apart
NSR with a PAC (3rd complex): two R-R intervals that are unequal distance apart; the distance before and after the PAC is NOT equal to two normal R-R intervals and therefore considered non-compensatory (incomplete) as it’s actually shorter than two normal R-R intervals
Morphology/signs on rhythm strip where you may suspect non-conducted PAC
- P waves may or may not be followed by a QRS depending on how premature the PAC is (may occur very early and close to the T wave of the preceding beat so only P wave seen)
- always be suspicious when T waves change shape suddently! if one T wave is different, there’s probably a P wave hiding in it
*NOTE: non-conducted PACs may be confused with sinus block or sinus arrest (especially if P wave of PAC happens early enough to be hidden in the preceding T wave)
- to differentiate between the, look and compare T wave contours (in sinus block/arrest, no P wave is producted so the T wave remains the same morphology; in non-conducted PAC, an early abnormal P wave of the PAC will distort preceding T wave)
Wandering Atrial Pacemaker
- Transient pacemaker shifting from SA node to another pacemaker site in the atria or AV junction
- size, shape and direction of P waves vary, sometimes from beat to beat
Describe the conduction pathway of wandering atrial pacemaker.
- impulse originates in at least 3 different foci (location) in the atria (the difference in the look of P waves is the result of pacemaker shifting between the SA node, atria and AV junction)
- heads down the normal conduction pathway and ultimately depolarizes the ventricular muscle
Supraventricular Tachycardia (SVT)
- A fast, regular and narrow dysrhythmia originate somewhere above the ventricles (“supra” meaning above)
- Its exact location of origin can not be identified due to the absence of P waves (P waves may be buried in QRS complex)
- can also be used to describe an “umbrella” of tachycardias that originate above the ventricles in either SA node, atria, or AV junction
- 3 main types of SVT:
- atrial tachycardia (AT)
- AV nodal re-entrant tachycardia (AVNRT)* what paramedics call SVT
- AV re-entrant tachycardia (AVRT)
SVT: Atrial Tachycardia (AT)
- usually caused by altered automaticity (irritable site in the atria fires at a rate of 100-250 times per minute)
- often precipitated by a PAC
- heads down the normal conduction pathway and ultimately depolarizes into ventricular muscle
- typically present when 3 or more PACs occur in a row of >100 BPM
- hard to different between sinus tach and atrial tach (you’d have to see a long ECG tracing and the rhythm that precedes atrial tach to call it atrial tach)
Atrial Tachycardia
Rate
Rhythm
P wave
PR interval
QRS complex
Rate: 100 - 250 beats/min
Rhythm: regular
P wave: upright P wave in Lead II
- if rhythm originated in lower portion of atrium, P’s will be negative in Lead II)
- matching and precede each QRS complex (P wave looks different from those seen when the impulse is initiated from the SA node)
PR interval: may be shorter or longer than normal
QRS complex: <0.12 seconds (can be >0.12 seconds if BBB exists)
SVT: AV nodal Re-entrant Tachycardia (AVNRT)
- most common type of SVT
- impulse originates from an irritable side above the Bundle of His
- exact location of origin CANNOT be identified because P waves are not discernable
- P waves may be hidden in T wave of preceding complex
- heads down normal conduction pathway and ultimately depolarizes in ventricular muscle
- usually caused by a PAC
- impulse is stuck in a re-entry loop as it enters the AV node
- impulse re-enters the normal electrical pathway with each pass of the circuit
Paroxsymal Supraventricular Tachycardia (PSVT)
- SVT that starts and ends suddenly
- “paroxsymal” can describe a rhythm that starts and stops suddenly
- you have to witness the SVT starting to be able to call it PSVT (otherwise it’s just SVT)
Atrial flutter (A flutter) with block ratio
- A rapid re-entry circuit caused by an irritable focus within the atria
- so rapid that “flutter” wave are produced instead of P waves
- usually saw shaped and no P waves
- typically would not see isoelectric line because the flutter waves affect the whole baseline so much
Atrial Fibrillation (A Fib)
- Increased irritability causes many sites/foci in the atria to initiate an electrical impulse at the same time (seen as a wavy line)
- caused by enhanced automaticity or re-entry
Describe conduction pathway of atrial fibrillation.
- atria depolarizes in section instead of a unit causing a “wiggle” or quiver (fibrillate) instead of a contraction - like a bag of worms
- AV node is bombarded with impulses (some are allowed through, but blocks others)
- at irregular intervals, one electrical impulse is conducted
- heads down the normal conduction pathway and ultimately depolarizes into ventricular muscle
