Dysrhythmias Flashcards
What are the 3 different classes of dysrhythmias?
- Abnormal sinus rhythym
- Distirubance to the conduction system
- Abnormal sites of impulse initiation
What is the normal sinus rhythym at rest?
60-100bpm
Describe distinqushing feature of sinus rhythm
In sinus rhythm depolarisation begins at the SA node
- Thus every P wave has a corresponding QRS complex
What is the normal PR interval?
Normal for PR interval is between 0.12 and 0.2 of a seconds
What is the normal QRS duration?
QRS duration should be between 0.04 and 0.1 of a second
What are the 4 different types of abnormal rythyms?
- Sinus tachycardia
- Sinus bradycardia
- Sick sinus syndrom
- Sinus arrest
Describe sinus tachycardia
SA node “pacemaker” depolarises abnormally fast, causing the heart rate to exceed 100bpm (must be 3 or more complexes in a row)
Name 5 cases where sinus tachycardia is often present
- Fever
- Pain
- Hyperthyroidism
- Low BP
- Hypoxia
When is sinus tachycardia a concern?
It is a concern if you push heart rate too high → may be too fast to allow ventricular filling to occur → decreases cardiac output (stroke volume x heart rate)
What are treatments for sinus tachycardia?
- Sympatholytic drugs (block sympathetic tone) i.e. B blockers
- Calcium channel blockers (Ca2+ = contraction)
What are the causes of sinus bradycardia?
- Increased parasympathetic tone
- Sleep
- Anaesthetics
- Acute hypertension
What is sinus bradycardia?
Sinus bradycardia is characterised by a sinus rhythm < 60 bpm
When is sinus bradycardia a problem?
If it results in a decreased CO
CO = HR x SV
What is sinus arrhythmia?
Sinus arrhythmia is a perfectly normal variation in sinus rhythm associated with breathing and fluctuations in the autonomic nervous system (non pathological version of sick sinus syndrome)
What is sick sinus syndrome
Sick sinus syndrome: SA node switches between periods of tachycardia and bradycardia (this illness requires an artificial pacemaker) → compromising cardiac output
What is sinus arrest?
a flat line, with no sinoatrial node activity indicating no electrical activation of the heart
What are the 3 different types of disturbances to the conduction system?
- Escape rhythym
- AV block
- Pre-excitation sydrome
What are the 2 differnt types of escape rhythm?
- Junctional escape rhythm
- Ventricular escape rhythm
What is a junctional escape rhythm and how can it be identified on an ECG?
- Damage to the SA node results in the AV node taking over as the pacemaker
- 40-60bpm
- No P wave but normal QRS complex
What is a ventricular escape rhythm and how can it be identified on an ECG?
- Damage to the SA node and AV node results in the bundle of his, bundle branches or the purkinje fibres taking over as the pacemaker
- 15-40bpm
- No P wave and QRS complex that is abnormally wide
What are the 3 types of AV blocks
- First degree
- Second degree
- Type 1 or Type 2
- Third degree
What are the characteristic ECG features of a 1st degree AV block?
- Damage to the AV node results in a greater delay in conductance
- PR interval that is greater than 0.2 of a second
What are the characteristic ECG features of a 2nd degree Type 1 AV block?
(aka Wenckebach or Mobitz type 1)
Progressively increasing PR interval until finally the P wave is not conducted, and thus the QRS complex does not occur
What are the characteristic ECG features of a 2nd degree Type 2 AV block?
(aka Mobitz type 2)
Consistent PR interval (with no PR prolongation), but with sudden blocked P waves and subsequent loss of QRS complex
(More servere - drop in CO - must be treated with pacemaker)
What are the characteristic ECG features of a 3rd degree AV block?
- Complete block of electrical continuity between the atria and the ventricles (that is, the P waves do not have associated QRS complexes)
- Produces a ventricular escape rhythm
- inherent rhythm of 15 – 40 bpm
- Produces an abnormally wide QRS complex’s will be evident
What are the characteristic ECG features of Pre-Excitation syndrome?
- accessory/abnormal conduction pathway that short circuits the normal conduction pathway
- Wolff-Parkinson-White Syndrome is an example of one of these pre-excitation syndromes
It is characterised by an accessory pathway that passes from the atria to the ventricles without passing through the AV Node, consequently we lose the delay in the AV node that allows time for the atria to contract while the ventricles are relaxed
The QRS complex will be abnormal (slightly wider because of the delta wave), instead of the Q caused by depolarisation of the septum, we get a delta wave
What are the 3 causes of abnormal sites of impulse initiation?
What defines each cause
- Abnormal automaticity
- contractile myocytes that should otherwise lack automaticity spontaneously depolarise and produce action potentials ahead of schedule
- Triggered activity
- Where an extra action potential is triggered spontaneously during, or immediately following repolarisation
- Re-entry
- A loop in the conduction system results in self perpetuating depolarisations
- By the time the wave of deplarisation reaches the end of the loop, the refractory period would have passed, and excitation would be possible
What are 3 causes of abnormal automaticity and how do they work?
-
Ischaemia
- Reduced oxygen levels as a result of ischemia, reduce the ATP levels in the cell, thus disabling the ion pumps and altering the ion gradients
- Eventually this results increased sodium and increased calcium, resulting in a spontaneous depolarisation and inappropriate automaticity in the contractile myocytes
-
Electrolyte imbalances (particularly hypokalaemia)
- can be caused by renal problems, excessive vomiting, diarrhoea
-
Abnormally leaky channels
- The cell’s membrane may be abnormally leaky to Na+ or Ca2+ ions at rest (in Phase 4), producing a spontaneous depolarisation
What are the 2 types of triggered activity and describe them
- Early after depolarisation (EADs)
- Delayed after depolarisation (DADs)
Describe how EADs occur
- Second action potentials are triggered early on in the relative refractory period (phase 3)
- These may occur in patients with abnormally long repolarisation times
- Calcium and sodium channels may recover from inactivation (i.e. inactivation gates open) before the membrane potential is below their threshold of activation (hence both activation and inactivation gates are opened) → influx of Na+/Ca2+ → cell depolarises
- EAD happens in long QT syndrome where there is abnormally long repolarisation time → Q wave and T waves become abnormally long → EADs is more likely to occur
Describe DADs
- Are depolarisations that occur after the repolarisation phase is complete, but ahead of the sinus rhythm
- This occurs during Phase 4
- DADs occur due to high intracellular Calcium and sarcoplasmic reticulum calcium level. When the sarcoplasmic reticulum is overloaded, it releases Ca2+. This trigger calcium to be released from the sarcoplasmic reticulum which evokes an action potential
- DADs can be suggestive of
- Heart failure
- Digitalis (Digoxin) toxicity
- Excessive catecholamines
What are the 2 different types of re-entry loops? Describe them
- Functional re-entry:
- occurs when conduction velocity becomes abnormally slow
- Anatomical re-entry:
- occurs when part of the electrical conduction in the heart is through an unusually long pathway
- E.g. due to hypertrophy
What are the 6 different types of abnormal sites of impulse initiation?
- Premature atrial complexes
- Atrial flutter
- Atrial fibrillation
- Premature ventricular complexes
- Ventricular tachycardia
- Ventricular fibrillation
- What is a Premature Atrial Complex (PAC)
- what are the characteristic features on an ECG
- how is it caused?
- atrial depolarisation is initiated by cells other than the SA node pacemaker cells within the atria
- ECG
- Abnormal P wave
- The timing of these PACs is faster than the normal sinus atrial rhythm
- compensatory pause on the ECG until sinus rhythm can re-establish itself
- Can be caused by inappropriate automaticity, an early afterdepolarisation (triggered activity) or delayed afterdepolarization (triggered activity) in atrial contractile myocytes
- What is a Atrial flutter
- how is it caused?
- what are the characteristic features on an ECG
- characterised by an atrial depolarisation rate of 240 – 350 bpm
- Most often caused by a re entry loop
- This will look like a saw tooth pattern of P waves, however will have a slower rate of ventricular depolarisation
- What is Atrial Fibrilation
- how is it caused?
- what are the characteristic features on an ECG
- characterised by chaotic depolarisation of the atria, which is accompanied by a ventricular depolarisation that is irregular and variable
- Caused by multiple re-entry loops
- Refer to 1
Why can clots occur as a result of Atrial fibrilation
- Atrial muscle contracts randomly and weakly
- Thus blood is static and jiggled -> Coagulation
- What are Premature ventricualr complexes
- how is it caused?
- what are the characteristic features on an ECG
- Spontaneous depolarisation of the ventricles
- usually caused by inappropriate automaticity (associated with ischemia and electrolyte imbalance) or triggered activity (DADs or EADs)
- ECG
- Does not usually feedback into the atria, but rather just encompasses both ventricles, thus sinus rhythm is unaffected
- As repolarisation will obviously follow a different path, the T wave is inverted
- As depolarisation follows an unusual sequence, the QRS complex is usually abnormally long
- The PVC will be ahead of the sinus rhythm, before we get a compensatory pause before the next sinus beat
- What is Ventricular tachycardia
- how is it caused?
- what are the characteristic features on an ECG
- 3 or more consecutive QRS complexes at a rate exceeding 100 bpm
- caused by the formation of a re-entry loop
- ECG
- QRS complexes combine with T waves to form large, wide, undulating waves, with individual parts of the wave form being un recognisable (if the waves look the same they are known as monomorphic)
- As it is unusual for ventricular depolarisation to move retrograde into the atria (it can happen in some situations), sinus rhythm is usually unaffected (P waves will be independent of the QRS)
- However these waves are often not seen
What is torsade de pointes
Polymorphic ventricular tachycardia
especially associated with Long QT syndrome (early afterdepolarisations
What is Ventricular fibrillation
how is it caused?
what are the characteristic features on an ECG
- Characterised by rapid, chaotic electrical rhythm which is completely uncoordinated
- This means that the muscle is depolarising and contracting, and repolarisation and relaxing with no coordination
Ventricular muscle thus quivers rather than contracting in a coordinated manner
* CO significantly diminished 2. Multiple Re-entry loops 3. Look at 1
