Arrhythmias and Conduction Defects Flashcards
What is an arrhythmia?
- any deviation from the normal cardiac rhythm
- due to abnormal electrical activity of heart
- arise from disturbance of generation or conduction of normal cardiac impulses
- can be intermittent or continuous
What are cardiac causes of arrhythmias?
- Ischaemic heart disease
- Structural changes
- Cardiomyopathy
- Pericarditis
- Myocarditis
- Aberrant conduction pathways
What are non-cardiac causes of arrhythmias?
- Caffeine
- Smoking
- Alcohol
- Pneumonia
- Drugs (beta blockers, digoxin, tricyclics)
- Metabolic imbalance (eg. hyperkalaemia)
- Phaeochromocytoma
What are the various types of ECG monitoring?
- ECG → simple 12-lead, snapshot of heart, may miss
- Telemetry → inpatient, signals shown on screen and watched continuously, reserved for high risk dangerous arrythmias
- Exercise ECGs → pts exercise, BP and ECG monitored looking for changes (eg. delta waves) and arrhythmias
- Holter monitors → pt wears monitor, records rhythm for 24h-7d whilst they go about normal life, analysed later
- Loop recorders → record only when activated, planted under skin and useful in pts w/ infrequent episodes
- Pacemakers & ICDs → record details of cardiac electrical activity, also therapeutic
Disturbances of cardiac rhythm are common, often benign, often intermittent and occasionally severe.
What are the two main types of arrhythmia?
- bradycardia - HR slow, <60 during day or <50 during night
- tachycardia - HR fast, >100
What are the bradycardias?
- Sinus bradycardia
- 1st degree (AV) block
-
2nd degree (AV) block
- Mobitz I / Wenkebach
- Mobitz II
- Complete (AV) heart block
What are causes of sinus bradycardia?
- normal - esp in athletes + elderly
- inc vagal tone - cushing’s reflex*
- drugs - bblockers, ccbs, digoxin, etc
- ischaemia/infarction - right coronary artery
*cushing’s reflex is bradycardia, hypertension and irregular RR - caused by a raised ICP, inc pressure in skull -> inc vagal tone
What is 1st degree heart block?
- prolonged PR interval (> 200ms / 0.2s)
- Every atrial depolarisation is followed by conduction to the ventricles, but with delay
- eg. if AVN or bundle of His damaged -> prolonged PR interval
- common in healthy adults, asymptomatic
- no specific treatment required
What is Mobitz type 1?
- Type 1 (2o) AKA Wenkebach
- Progressive PR interval prolongation, until a P wave fails to conduct
- No treatment required
- Where the QRS is dropped, the PR interval after is short but the one before is much longer
What is Mobitz type 2?
- PR interval is constant but the P wave is often not followed by a QRS complex
- Signifies block at an infranodal level such as the bundle of His
- There is a greater risk of this type to progress into complete heart block
- Consider pacemaker due to risk of developing CHB
What is complete heart block?
- No synchrony between P and QRS AKA complete atrioventricular dissociation
- Regular P waves, regular QRS complexes but NO associated between the two
- By chance, the atria and ventricles may contract at same time → atrial blood occurs against a closed tricuspid → blood refluxes back up the jugular veins → cannon waves
- Ventricles can pace themselves
- Rx: permanent pacemaker
- URGENT specialist referral!
What are the clinical features of complete heart block?
- Syncope
- Heart failure
- Regular bradycardia (30-50 bpm)
- Wide pulse pressure
- JVP: cannon waves in neck
- Variable intensity of S1
What 4 adverse clinical presentations are important to recognise in severe bradycardia and what should be the management if any of these arise?
Manage based on adverse signs:
- shock
- syncope
- myocardial ischaemia
- heart failure
If any of these 4 arise -> TREAT -> atropine 500mcg x 6
- ?betablocker overdose —-> glucagon
The diagram shows typical features of left bundle branch block (LBBB).
What is the most common way to remember the difference (on ECG) between LBBB and RBBB?
WiLLiam vs MaRRow
- LBBB → ‘W’ in V1 and ‘M’ in V6
- RBBB → ‘M’ in V1 and ‘W’ in V6
What are causes of LBBB?
- Ischaemic heart disease
- HTN
- Aortic stenosis
- Cardiomyopathy
- Rare → idiopathic fibrosis, digoxin toxicity, hyperkalaemia
New LBBB is always pathological + may be sign of MI. Diagnosing MI for pts with existing LBBB is tricky. The Sgarbossa criteria can help with this.
What are the causes of RBBB?
- Normal variant - more common w/ increasing age
- Right ventricular hypertrophy
- Chronically increased right ventricular pressure eg. cor pulmonale
- Pulmonary embolism
- Myocardial infarction
- Atrial septal defect
- Cardiomyopathy or myocarditis
Tachyarrhythmias are when the heart is beating >100bpm. How can tachyarrhythmias be classified?
-
Broad complex (QRS >120ms) -> Ventricular tachycardias
- arise from ventricles
- reflect disorganised, delayed depolarisation (hence broad QRS)
-
Narrow complex (QRS <120ms) -> Supraventricular tachycardias
- arise from atrium or atrioventricular junction
- reflect organised efficient electrical activity originating above AV node (hence narrow QRS)
What is atrial fibrillation?
- Technically an SVT
- Characterised by uncoordinated atrial activity on surface eCG
- With fibrillatory waves of varying shapes, amplitudes and timing
- Associated with an irregularly irregular ventricular response when AV conduction is in tact
- Cardiac output drops by 10-20% as ventricles aren’t primed reliably by atria
- AF is common in elderly (~9%)
- Main risk = embolic stroke
What are the cardiac causes of AF?
- Heart failure (24%)
- IHD (33%)
- Hypertension (26%)
- Valvular heart disease (7%)
- MI
- Cardiomyopathy
- Sick sinus syndrome
- Constrictive pericarditis
What are non-cardiac causes of AF?
- Alcohol intoxication or withdrawal
- Hyperthyroidism
- PE
- Electrolyte abnormalities (hypokalaemia)
- Pneumonia
- Caffeine
- Lone AF (no cause, probably genetic)
What are clinical features of AF?
- May be asymptomatic
- Chest pain
- Palpitations
- Dyspnoea
- Faintness
- Signs → irregularly irregular pulse, apical pulse rate greater than radial, signs of LVF (pulm oedema)
What investigations can be done for AF?
- Bedside → ECG looking for absent P waves, irregularly irregular QRS complexes
- Bloods → FBC, U+Es, TFTs, cardiac biomarkers, CRP
- Imaging → CXR (HF, pulm oedema), Echo (left atrial enlargement, mitral valve disease, poor LV function)