Arrhythmias Flashcards
Arrhythmias are…
disturbances of heart rate (frequency) rhythm (regularity of beats)
Alterations in impulse formation involve….
changes in automaticity (loss of overdrive suppression) or triggered activity
Abnormalities in impulse conduction arise from…
re-entry, conduction block and accessory tracts
The SA node is the _______1______ of the heart, but all components of the cardiac conduction system demonstrate a (slower) spontaneous phase 4 depolarization and thus possess _____2_____
usual physiological pacemaker
automaticity
The SA node possesses overdrive suppression, what does this mean? How does it maintain this?
It has the highest frequency so it supresses the other latent pacemakers. In order for the SA node to exert its normal control of rate and rhythm it must discharge action potentials at a higher, regular, frequency than any other structure in the heart.
What order do latent pacemakers take over and what is the rate of firing?
- If SA node was damaged then first latent pacemaker to take control is AV node 50-60bpm
- Next to take control is Purkinje fibres at 30-40bpm
- Even if all these are broken ventricles can do it on its own but this would be very low
Explain 3 ways loss of overdrive suppression can occur?
1) May occur if the SA node firing frequency is pathologically low, or if conduction of the impulse from the SA node is impaired. A latent pacemaker may initiate an impulse that generates an escape beat (additional cardiac contraction). A run of such impulses may give rise to an escape rhythm, a series of escape beats
2) May occur if a latent pacemaker fires at an intrinsic rate faster than the SA node rate (even if the SA node is functioning normally). Latent pacemaker initiates an ecoptic beat, or a series of such beats generating an ectopic rhythm (i.e. one not generated by the SA node – ectopic meaning in an abnormal place, or position). Ectopic rhythms can result from ischaemia, hypokalaemia, increased sympathetic activity, fibre stretch and other causes
3) Can occur in response to tissue damage (e.g. post myocardial infarction). Even non-pacemaker cells (i.e. myocytes), when partially depolarized, may assume spontaneous activity
Triggered activity occurs when….
- A normal action potential triggers abnormal oscillations in membrane potential termed afterdepolarizations (ADs) that occur during, or after, repolarization
- Can be early depolarisation (EADs) or delayed afterdepolarisations (DADs)
- Repeated after depolarisation of either types may cause sustained depolarisation
- Triggered initially by a normal action potential but do not arrive from activity in the SA node.
Difference between EADs and DADs
EADs= Occur during the inciting action potential within phase 2 mediated by opening of voltage activated calcium channels . Most likely to occur in slow heart rate
DADs= Occurs after complete repolarisation. Most likely to occur in fast heart rate.
Conduction blocks?
1) Partial block- tissue conducts all impulses but more slowly than usual, this is benign and known as First degree AV block, shown as long PR interval
2) Intermittent block- tissue conducts some impulses, but not others- second degree AV block occurring as two types
- Mobitz type I – PR interval gradually increases from cycle to cycle until AV node fails completely and a ventricular beat is missed.
- Mobitz type II –PR interval is constant but every nth. ventricular depolarization is missing.
3) Complete block no impulses are conducted through the affected area- third degree Av block. No relationship between atria and ventricular beats. ventricular pacemaker is now the Purkinje fibres – fire relatively slowly and unreliably – manifest as bradycardia and low cardiac output. Can’t treat with drugs need an intraventricular pace maker
Accessory tract pathways happen when …
individuals possess electrical pathways in parallel to the AV node. A common pathway is the bundle of Kent. The impulse through bundle of Kent is conducted more quickly than that through the AV node. Ventricles receive impulses from both the normal and accessory pathways – can set up the condition for a re-entrant loop predisposing to tachyarrhythmias.
Target for class 1 anti-arrhythmic drugs is?
Voltage-activated Na+ channel and the upstroke of depolarisation
Target for class 2 anti-arrhythmic drugs?
B-adrenoceptor (as antagonists) to decrease rate of depolarization in SA and AV nodes
Target for class 3 anti-arrhythmic drugs?
Voltage-activated K+ channels (plus others) to prolong AP duration increasing refractory period.
Target for class 4 anti-arrhythmic drugs?
Voltage-activated Ca2+ channels to slow conduction in SA and AV nodes. Decrease force of cardiac contraction.
Name seven supra ventricular arrhythmias
Normal sinus arrhythmia Sinus bradycardia Sinus tachycardia Atrioventricular nodal re-entrant tachycardia Atrioventricular re-entrant tachycardia Atrial fibrillation Atrial flutter
Normal sinus arrhythmia is slight variations in heart rate due to _______
reflex changes in vagal tone during the respiratory cycle
Sinus bradycardia can ___1__ or it can be caused by __2___ or ___3____
If it is acute it can be treated with __4_____
If it is chronic and causing haemodynamic compromise then ___5_____
1 physiological 2 drugs 3 ischaemia 4 atropine 5 pacing is required
Sinus tachycardia could be due to __________
You should try and treat the underlying cause but if it is persistent then _______
anxiety, fever, anaemia, hypotension or drugs
beta blockers
ATNRT happens when there are two pathways: __1__and__2__ in AV node
1 fast
2 slow
ATNRT and ATRT present similarly and can both be treated by….
Valsalva manoeuvre (pop ears), right carotid massage, immersion in cold water
If harm-dynamically unstable may require emergency cardioversion
AVRT is due to ___1_____ between the atria and ventricles and results in a macro re-entry circuit where the _2___ are activated after the ___3___
ON ECG P waves are seen ___4____
Accessory pathways that conduct from ventricles to atria are ___5___ on ECG in sinus rhythm.
Those that conduct from atria to ventricles result in _____6______ of the ventricles known as _____7_____
On ECG this is characterised by ___8___
This can be caused by ___9____
1 accessory pathways 2 atria 3 ventricles 4 between QRS and T wave 5 concealed 6 partial depolarisation 7 pre-excitation 8 short PR interval wide QRS and QRS begins with a slurred part known as a delta wave 9 Wolff-Parkinson White syndrome
Is atrial fibrillation common or uncommon?
Common
Causes of atrial fibrillation
rheumatic heart disease, alcohol intoxication, thyrotoxicosis, hyperthyroidism, hypertension and after cardiac surgery. In some patients cause not identified (lone AF)
