Cardiac Arrhythmia 1 Flashcards
How are arrhythmias generally named?
By their anatomical site or chamber of origin
By their mechanism
Where is the origin of a supra-ventricular tachycardia?
Above the ventricle i.e. SAN, atrial muscle, AV node or HIS origin
What is the origin of a ventricular arrhythmia?
The ventricular muscles (common)
Fasicles of the conducting system (uncommon)
What are the SVT’s?
Atrial fibrillation
Atrial flutter
Ectopic atrial tachycardia
What are the different supra-ventricular bradycardias?
Sinus bradycardia
Sinus pauses
What are the different ventricular arrhythmias?
Ventricular ectopics/premature ventricular complexes
ventricular tachycardia
ventricular fibrillation
asystole
What are the AV nodal arrhythmias?
AVN re-entry tachycardia
AV reciprocating or AV reentrant tachycardia
AV block
- 1st degree
- 2nd degree
- 3rd degree
What are the clinical causes of arrhythmia?
Abnormal anatomy ANS Metabolic Inflammation Drugs Genetic
What anatomical abnormalities can cause arrhythmia?
Left ventricular hypertrophy
Accessory pathways
Congenital HD
What ANS causes can result in arrhythmia?
Sympathetic stimulation (stress, exercise, hyperthyroidism)
Increased vagal tone causing bradycardia
What metabolic causes can result in arrhythmia?
Hypoxia: COPD, PE
Ischaemic myocardium: acute MI, angina
Electrolyte imbalances: K+, Ca 2+, Mg2+
What inflammatory cause can result in arrhythmia?
Viral myocarditis
How do drugs cause arrhythmia?
Direct electrophysiologic effects or via ANS
What genetic changes can cause arrhythmia?
Mutations of genes encoding cardiac ion channels e.g. the congenital long QT syndrome
What are the electrophysiological causes of arrhythmia?
Ectopic beats
Re-entry
What are ectopic beats?
Beats or rhythms that originate in places other than the SA node
What are the causes of ectopic beats?
Altered automaticity: e.g. ischaemia, catecholamines
Triggered activity: e.g. digoxin, long QT syndrome
What does re-entrant arrhythmia require?
Requires more than one conduction pathway, with different speed of conduction (depolarisation) and recovery of excitability (refractoriness)
Name some causes of reentrant arrhythmias?
Accessory pathway tachycardia (Wolf Parkinson White Syndrome)
Previous MI
Congenital heart disease
Describe the mechanism of ectopic beats?
The ectopic focus may cause single beats or a sustained run of beats, that if faster than sinus rhythm, take over the intrinsic rhythm
Describe the mechanism of reentry?
Triggered by an ectopic beat, resulting in a self perpetuating circuit
Is tachycardia dangerous?
Depends on the affect on cardiac output
What is altered automaticity?
A change in the conduction of the heart
What is the most common sympathetic mechanism of altered automaticity arrhythmia?
Change in slope (change in depolarisation), resulting in a change in rate
What increases the phase four slope of cardiac myocytes?
Hyperthermia Hypoxia Hypercapnia Cardiac Dilatation Hypokalaemia (prolongs repolarisation)
What does increase in the slope of phase four cause?
Ectopic beats, increase in HR
What causes a decrease in phase four slope of cardiac myocyte action potential?
Hypothermia
Hyperkalaemia
What does a decreased phase four action potential of cardiac myocytes cause?
Bradycardia, heart block
What is triggered activity?
In the terminal phase of the AP (phase 3), a small depolarisation may occur (after depolarisation), and if of sufficient magnitude may reach depolarisation threshold and lead to a sustained train of depolarisations, termed triggered activity
What is the mechanism underlying digoxin toxicity, long QT syndrome, torsades des pointes, hypokalaemia
Triggered activity
What structural abnormalities can result in re-entry?
Accessory pathways
Scar from MI
congenital heart disease
What functional changes can cause re-entry?
Conditions that depress conduction velocity or shorten refractory period promote functional block e.g. ischaemia, drugs
What are the symptoms of arrhythmia?
Palpitations 'pounding heart' Shortness of breath Dizziness Loss of consciousness 'syncope' Faintness 'presyncope' Sudden cardiac death Angina HF
What investigations are done to investigate arrhythmia?
12 lead ECG (in tachycardia, during SR)
CXR
Echocardiogram
Stress ECG
- look for myocardial ischaemia, exercise related arrythmias
24 hour ECG holter monitoring
Event recorder
Electrophysiological (EP) study
-induce clinical arrhythmia to study mechanism and map arrhythmia
What would you look for on the ECG?
Rhythm
Signs of
- previous MI
- pre-excitation (WPW syndrome)
What ECG changes indicate pre-excitation?
Short PR
Delta wave
Wide QRS
Secondary ST-T change
What would you look for on echocardiography?
To assess for structural heart disease e.g.
- enlarged atria in AF
- LV dilatation
- Previous MI scar
- aneurysm
What does an EP study provide?
The opportunity to perform radio-frequency ablation to extra pathway
Describe a normal sinus arrhythmia
Variation in heart rate, due to reflex changes in vagal tone during the respiratory cycle
Inspiration reduces vagal tone and increases HR
What is classified as sinus bradycardia?
<60bpm
What are the causes of sinus bradycardia?
Drugs (B-blocker)
Physiological (athlete)
Ischaemia (common in inferior STEMIs)
What is the treatment of sinus bradycardia?
Atropine (if acute e.g. acute MI)
Pacing if haemodynamic compromise (hypotension, CHF, Angina, collapse)
What is classifies as a sinus tachycardia?
> 100bpm
What are the causes of sinus tachycardia?
Physiological (anxiety, fever, hypotension, anaemia)
Inappropriate (drugs, etc)
What are the treatments for sinus tachycardia?
Treat underlying cause
B-adrenergic blockers
What are the symptoms of atrial ectopic beats?
Asymptomatic
Palpitations
What is the treatment for atrial ectopic beats?
Generally none
B-adrenergic blockers may hekp
What should be avoided in patients with atrial ectopics?
Stimulants- caffeine, cigarettes
What are the causes of a regular supraventricular tachycardia?
AV nodal re-entrant tachycardia
AV reciprocating tachycardia/AV reentrant tachycardia (via an accessory pathway)
Ectopic atrial tachycardia
What is the difference between an AVNRT and AVRT?
AVNRT: circuit within the AV node, micro-rentry
AVRT: circuit using the AVN and AP way, macro-reentry
What will be seen on the ECG in a antegrade AVRT?
Normal QRS
No delta wave
Retrograde P wave after QRS
What will be seen on the ECG in a retrograde AVRT?
Wide QRS with delta wave
P wave rarely seen
If P wave visible it is retrograde and occurs just before the QRS
What is the acute management of a supra-ventricular tachycardia?
-Increase vagal tone: valsalva, carotid massage
-If slow conduction in the AV node;
IV adenosine
IV verapamil
What is the chronic management of supra-ventricular tachycardias?
Avoid stimulants
EP study and radio frequency ablation (first line in young, symptomatic patients)
Beta blockers
Anti-arrhythmic drugs
What is radio-frequency ablation?
Selective cautery of cardiac tissue to prevent tachycardia, targeting either an automatic focus or part of a re-entry circuit
How is radiofrequency ablation performed?
ECG Catheters placed in heart via femoral veins.
Intracardiac ECG recorded during sinus rhythm, tachycardia and during pacing manoeuvres to find the location and mechanism of the tachycardia
catheter placed over focus / pathway and tip heated to 55-65C
What are the causes of AVN conduction disease (Heart block)?
Ageing Acute myocardial Infarction Myocarditis Infiltrative disease (amyloid) Drugs -B-blockers -CCBs Calcific aortic valve disease Post-aortic valve surgery Genetic -lenegre's disease -myotonic dystrophy
Describe 1st degree AV block?
Not really ‘block’- conduction following each P wave but it takes longer
What would you see on the ECG of 1st degree AV block?
PR interval longer than normal (>0.2sec)
What is the treatment of 1st degree AV block?
None
What is the management of 1st degree AV block?
Rule out other pathology
Long term follow up recommended as more advanced block may develop
Describe 2nd degree AV block?
Intermittent block at the AVN (dropped beats)
What are the types of 2nd degree AV block?
Mobitz type I
Mobitz type II
What is mobitz type I?
progressive lengthening of the PR interval, eventually resulting in a dropped beat.
What is the origin of mobitz type I AV block?
Usually vagal in origin
What is mobitz type II?
Pathological, may progress to complete heart block (3rd degree)
How would you identify mobitz type II?
Usually an identifiable pattern
-2:1
-3:1
is variable
What is recommended in mobitz type II?
Permanent pacemaker indicated
What are the types of pacemakers?
Single chamber
(paces the right atria or right ventricle only)
Dual chamber
(paces the RA and the RV)
What does a dual changer pacemaker maintain? When is it used?
Maintains A-V synchrony (preserves atrial kick)
Used in AVN disease
What are the causes of ventricular ectopics?
Structural -LVH, heart failure, myocarditis Metabolic -Ischaemic heart disease, electrolytes Inherited
What would indicate a ventricular ectopic needs to be further analysed?
Worse on exercise
What is the treatment of ventricular ectopics?
B-blockers
Ablation of focus
Describe ventricular tachycardia?
Life threatening- may be haemodynamically stable
Who gets ventricular tachycardia?
Most patients have significant heart disease
- coronary artery disease
- a previous MI
What are the rarer causes of ventricular tachycardia?
Cardiomyopathy
Inherited/familial arrhythmia syndromes
-long QT, brugada syndrome
What ECG changes help identify VTs?
- QRS complexes are rapid, wide, and distorted
- T waves are large with deflections opposite the QRS complexes.
- ventricular rhythm is usually regular.
- P waves are usually not visible.
- PR interval is not measurable.
- A-V dissociation may be present.
- V-A conduction may or may not be present.
Describe ventricular fibrillation?
Chaotic ventricular activity which causes the heart to lose the ability to function as a pump
What is the treatment of ventricular fibrillation?
Defibrillation
Cardiopulmonary resuscitation
What is the acute treatment of VT?
Direct current cardioversion (DCCV) if unstable.
If stable: consider pharmacologic cardioversion with AAD, in meantime prepare for DCCV.
If unsure if VT or something else, consider adenosine to make a diagnosis.
Correct triggers; Look for causes; Electrolytes Ischaemia Hypoxia Pro-arrhythmic medications (eg drugs that prolong the QT interval eg., sotalol).
What is the long-term treatment of VT?
Correct ischemia if possible (revascularisation)
Optimise CHF therapies.
Anti-arrhythmic drugs to date have been shown to be ineffective and are associated with worse outcomes.
Implantable cardiovertor defbrillators (ICD) if life threatening.
VT catheter ablation.
What is a wide QRS complex with a history of CAD/HF until proven otherwise?
VT
Where do most ventricular arrhythmias occur?
In the setting of structural heart disease
-CHF, CAD
What is the optimum management of VT/VF?
treat underlying condition e.g. CHF, CAD are important
