Arrhythmias - Pathophysiology, presentation and investigation Flashcards
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Learning Outcomes for arrhythmias
What is meant by normal sinus rhythm?
Normal heart rhythm with electrical activation beginning in the SA node
Which lead is the best to assess rhythm?
Whichever lead that shows the P wave most clearly, usually limb lead 2 or V1
What is the PR interval?
Time taken for wave of depolarisation to travel from SA node to ventricular muscle
(usually no longer than 220 ms (6 boxes))
What is meant by first degree heart block?
Delay in conduction pathway from SA node to ventricles
Characteristic prolonged PR interval
What are the casues of first degree heart block?
- Coronary artery disease
- acute rheumatic carditis
- digoxin toxicity
- electrolyte disturbances
What is meant by second degree heart block?
On intermittent occasion, excitation completely fails to pass through AV node or bundle of His
What are the three different types of second degree heart block?
Mobitz type 1
Mobitz type 2
2:1 / 3:1 / 4:1 conduction
What is mobitz type 1 heart block?
Progressive lengthening of PR interval, then failure of conduction of an atrial beat
Followed by conducted beat with shorter PR interval then repetition of this cycle
What is mobitz type 2 heart block?
Most beats are conducted with a constant PR interval, occasional atrial depolarisation without subsequent ventricular depolarisation
What is meant by 2:1 / 3:1 / 4:1 conduction?
Alternate conducted and non-conducted atrial beats (or one conducted atrial beat and then two or three nonconducted beats)
Gives twice (three/four times) as many P waves as QRS complexes
‘2:1’ (‘two to one’), ‘3:1’ (‘three to one’) or ‘4:1’ (‘four to one’) conduction
What is meant by third degree heart block?
Complete heart block
Normal atrial contraction but no beats conducted to ventricles
When this occurs ventricles are excited by slow ‘escape mechanism’ from a depolarising focus within ventricular muscle
No relationship between P waves and QRS complexes
Abnormally shaped QRS complexes,
because of abnormal spread of depolarization from a ventricular focus
What is the effect on QRS complexes in third degree heart block
No relationship between P waves and QRS complexes
Abnormally shaped QRS complexes,
Due to abnormal spread of depolarization from a ventricular focus
What causes third degree heart block?
Acute - Patients with MI (when it is usually transient)
Chronic - due to fibrosis around bundle of His
Caused by block of both bundle branches
What are the common causes of heart block?
Where does mobitz 1 and mobitz 2 take place?
Mobitz 1 - AV node, healthy people, no symptoms, rarely needs treatment
Mobitz 2 - below AV node in other conduction tissue
- aging
- Significant heart disease
- Large heart attack
- Lightheadedness, fainting
- May progress to 3rd degree
- Requires pacemaker
What causes third degree heart block?
- Aging
- medicines
- heart attacks
- infiltrative heart diseases (amyloidosis, sarcoidosis)
- infectious diseases (endocarditis, Chagas disease)
- May occur after heart surgery
- Can be present from birth (congenital)
What are the presentations of third degree heart block?
Fainting, light headedness
When is heart rhythm said to be arrhythmia?
Depolarisation sequence begins somewhere out with SA node
What can control the rhythm of contraction in the ventricles?
Most parts of the heart can depolarize spontaneously and rhythmically
Rate of ventricle contraction controlled by part of heart depolarizing most frequently
What makes up suprventricular rhythm?
Sinus rhythm, atrial rhythm and junctional rhythm
Which rhythms have narrow/wide QRS complexes?
What is the rate of contraction in supraventricular / ventricular rhythm?
Atrial muscle or the area around the AV node (the junctional region) have spontaneous depolarization frequencies of 50/min
If these fail, or if conduction through His bundle is blocked, ventricular focus will take over ventricular rate will be 30/min.
Why are escape rhythms called escape rhythms?
Occur when secondary sites for initiating depolarization escape from their normal inhibition by the more active SA node
What does atrial flutter look like on an ECG?
Atrial rate is greater than 250/min, no flat baseline between P waves, ‘atrial flutter’ is present
What is meant by fibrillation?
Individual muscle fibres contract independently
Explain why there are irregular QRS complexes present in atrial fibrillation
Depolarization spreads at irregular intervals down the His bundle
AV node conduction, ‘all or nothing’, depolarization waves passing into His bundle have constant intensity
Waves are irregular, and ventricles contract irregularly
What is meant by supraventricular tachycardia?
Involves, atrial tachycardia, atrial flutter and nodal tachycardia
Why are some of the P waves not followed by a QRS complex in atrial tachycardia?
Atria depolarise faster than 150/min
AV node cannot conduct atrial rates of discharge greater than 200/min
If atrial rate is faster than this, ‘atrioventricular block’ occurs, with some P waves not followed by QRS complexes
Explain the relationship between the P wave and the QRS complex in nodal tachycardia?
If area around AV node depolarises frequently, P waves may be seen very close to QRS complexes, or may not be seen at all
QRS complex has normal shape due to other supraventricular arrhythmias, ventricles are activated by His bundle in normal way
What is the diffrence between atrial tachycardia and heart block?
AV node working properly vs AV node and possible HIS bundle not working properly
What is meant by the Wolff–Parkinson–White syndrome?
‘accessory’ conducting bundle, forms direct connection between atrium and ventricle
Left side of the heart
No AV node to delay conduction. Depolarization wave reaches ventricle early, and ‘pre-excitation’ occurs
PR interval is short, QRS complex shows early slurred upstroke called a ‘delta wave’
Second part of QRS complex is normal, conduction through His bundle catches up with pre-excitation
What is meant by ventricular tachycardia?
If focus in ventricular muscle depolarises with high frequency
What is seen on an ECG of ventricular tachycardia?
Excitation has to spread by abnormal path through ventricular muscle, QRS complex is wide and abnormal
Wide and abnormal complexes are seen in all 12 leads of standard ECG
What is meant by sinus tachycardia?
Asinus rhythm with elevated rate of impulses
Rate greater than 100 beats/min (bpm) in average adult.
Three or less large squares between QRS complexes represents tachycardia on ECG sheet
How do you calculate heart rate in a patient with irregular qrs complexes?
Count number of QRS complexes over 30 large squares (corresponds to 6s) then multiply by 10 to give number of beats per min
Define sinus bradycardia
Sinus rhythm with rate lower than normal
Rate under 60 beats per min
QRS complex present every 5 boxes or more
Define sinus arrest
Sinoatrial node of heart transiently stops generating electrical impulses.
Lasts 2s to several minutes
Since heart has multiple pacemakers, interruption only lasts a few seconds before another part of heart begins pacing and restores heart action
What is meant by extrasytole or ectopic beat?
Premature contraction of heart independent of normal rhythm
Arises in response to impulse in some part of heart other than normal impulse from SA
Extrasystole followed by pause, as heart electrical system “resets”
Contraction following pause is more forceful than normal, frequently perceived as palpitations
What is an atrial extrasystole seen as?
Looks similar to atrial escape beat where abnormal P wave is seen because excitation of atrium has begun somewhere other than SA node
Extrasystole comes early and escape beat comes late
What do junctional extrasystoles look like?
No P wave or P wave appears immediately before or after QRS complex
Describe ventricular extrasystole
Abnormal QRS complexes, typically wide and almost any shape
Common, usually of no importance
If they occur early in T wave of preceding beat they can induce ventricular fibrillation, potentially dangerous
Discuss the prevalence of af in england
1.36 million have AF. 2.4% of population
AF prevalence higher in men than women, 2.8% v 2.0%
AF prevalence increases with age
2.9% of total estimated AF in population likely to occur in people aged under 45, 16.6% aged 45-65 and 80.5% over 65
What are the signs and symptoms of AF?
AF causes ventricles to contract faster than normal
Ventricles can’t completely fill with blood
May not be able to pump enough blood to lungs and body, can lead to signs and symptoms, such as:
Palpitations (feelings that your heart is skipping a beat, fluttering, or beating too hard or fast)
Shortness of breath
Weakness or problems exercising
Chest pain
Dizziness or fainting
Fatigue (tiredness)
Confusion
What is thetreatment for atrial fibrilaltion?
Rule out over active thyroid, medication to treat overactive thyroid may stop af
Medicines - control af (sub divided into medication that can either restore heart rhythm or control the rate at which the heart beats)
Anticoagulation - prevent risk of stroke (warfarin or a newer type of anticoagulant, such as dabigatran, rivaroxaban, apixaban or edoxaban)
Cardioversion (It involves giving the heart a controlled electric shock to try to restore a normal rhythm.)
Pacemaker
Catheter ablation (a procedure that very carefully destroys the diseased area of your heart and interrupts abnormal electrical circuits.)
(Catheters (thin, soft wires) are guided through one of your veins into your heart, where they record electrical activity. When the source of the abnormality is found, an energy source, such as high-frequency radiowaves that generate heat, is transmitted through one of the catheters to destroy the tissue.)
What medications are able to restore normal rhythm?
Flecainide
beta-blockers, particularly sotalol
amiodarone
dronedarone (only for certain people)
What drugs are used to control the rate of heart beat?
Beta blocker (bisoprolol or atenolol)
Calcium channel blocker (verapamil, diltiazem)
Digoxin may be added to help control HR further. In some cases, amiodarone may be tried.
What can cardioversion be used to treat?
Ventricular tachycardia
Supraventricular tachycardia due to re-entry
Atrial fibrillation
Atrial flutter
Atrial tachycardia
Monomorphic VT with pulses
If you’ve had atrial fibrillation for more than two days, cardioversion can increase the risk of a clot forming, how is clot formation avoided?
Anticoagulant for three to four weeks before cardioversion, for at least four weeks afterwards
What are the indications for ICD therapy (implantable cardioverter-defibrillator)?
Cardiac arrest due to VF/VT
Not due to transient or reversible cause eg early phase of acute MI
Sustained VT causing syncope or significant compromise
Sustained VT with poor LV function
What are the indications for temporary pacing?
- Intermittent or sustained symptomatic bradycardia, particularly syncope
- Prophylactic when patient at high risk for development of severe bradycardia eg 2nd or 3rd degree AV block, post anterior MI, even when asymptomatic
(basically if there is bradycardia or risk of bradycardia)
What are the indications for permanent pacing?
- Symptomatic or profound 2nd/3rd degree AV block, particularly when cause unlikely to disappear
- Probably Mobitz type II 2nd/3rd degree AV block even if asymptomatic
- AV block associated with neuromuscular diseases after (or in preparation for) AV-node ablation
- Alternating RBBB/LBBB
- Syncope when bifascicular/trifascicular block and no other explanation
- Sinus node disease associated with symptoms
- Carotid sinus hypersensitivity/malignant vasovagal syncope
What is meant by bifasicular block?
conduction disturbances below AV node
Right bundle branch and one of two fascicles (anterior or posterior) of left bundle branch are involved
Define trifasicular block
Prolongation of PR interval (first degree AV block)
Right bundle branch block
Either left anterior fascicular block or left posterior fascicular block.
What is a bundle branch block?
Abnormal conduction through either right or left bundle branches
Delay in depolarization of part of ventricular muscle
Extra time taken for depolarization of the whole of the ventricular muscle causes widening of QRS complex.
Normal heart, time taken for depolarization wave to spread from interventricular septum to furthest part of the ventricles less than 120 ms, three small squares of ECG paper
If QRS complex duration is greater than 120 ms, then conduction within ventricles must have occurred by an abnormal and slower pathway
What is the approach to assess ECG?
ARIBAR
A - Any electrical activity
R - Rate
I - Irregular or regular
B - QRS complexes Broad or Narrow
A - Atrial activity
R - Relationship between atrial acivity and ventricular activity
What are the four main types of supraventricular tachycardia?
- atrial fibrillation
- paroxysmal supraventricular tachycardia (PSVT)
- atrial flutter
- Wolff-Parkinson-White syndrome
What is the disease mechanism behind paroxysmal supraventricular tachycardia?
Underlying mechanism typically involves accessory pathway that results in re-entry
How is diagnosis of paroxysmal supraventricular tachycardia achieved?
Diagnosis typically by electrocardiogram (ECG) Shows narrow QRS complexes and fast heart rhythm typically between 150 and 240 beats per minute
What is the initial treatment of paroxysmal supraventricular tachycardia?
Vasalva manouvre
