Cardiology: Bradycardia + Heart Block + Long QT Flashcards
What are the causes of acute bradycardia?
1) Sinus/AV nodal disease
2) Drug induced e.g. beta blockers, calcium channel blockers
3) Electrolyte abnormalities
4) Hypothyroidism
Which drugs can induce bradycardia?
Beta blockers, calcium channel blockers
What are the symptoms of acute bradycardia?
1) Dizziness
2) Syncope
3) Tiredness
How should patients with acute bradycardia be initially assessed (ALS)?
ABCDE, ECG monitoring and identify + treat any reversible causes
How do you manage acute bradycardia with adverse features (shock, syncope, myocardial ischaemia or heart failure) or factors that increase the risk of asystole?
IV atropine 500 micrograms (mcg)
How many boluses of atropine can you give to treat acute bradycardia?
6 boluses - up to 3mg
How does atropine work?
Blocks the vagus nerve activity on the heart, which increases the firing rate of the SA node
What factors increase the risk of asystole in bradycardia?
1) Mobitz type II block
2) Complete heart block + broad QRS
3) Recent asystole
4) Ventricular pause > 3 seconds
Even if there are no adverse features, when should atropine still be given for acute bradycardia?
1) Mobitz type II block
2) Complete heart block + broad QRS
3) Recent asystole
4) Ventricular pause > 3 seconds
What are second line alternative drugs to atropine if there is inadequate response in acute bradycardia?
1) Isoprenaline
2) Adrenaline
3) Dopamine
4) Aminophylline
5) Glucagon (in beta blocker/calcium channel blocker overdose)
6) Glycopyrrolate
What drug do you give in addition to atropine in acute bradycardia due to beta blocker or calcium channel blocker overdose?
Glucagon
How do you manage acute bradycardia after initial medical measures have been attempted?
Transcutaneous pacing - can be used as an interim measure whilst awaiting expert help for transvenous pacing/permanent pacemaker insertion
What is first degree heart block caused by?
Prolonged conduction of electrical activity through the AV node
How do you identify first degree heart block on ECG?
PR interval > 200ms (5 small squares)
What are the causes of first degree heart block?
1) High vagal tone (e.g. athletes)
2) Acute inferior MI
3) Electrolyte abnormalities (e.g. hyperkalaemia)
4) Drugs: NHP-CCBs, beta-blockers, digoxin, cholinesterase inhibitors
Which drugs can cause first degree heart block?
1) NHP-CCBs (verapamil, diltiazem)
2) Beta-blockers
3) Digoxin
4) Cholinesterase inhibitors
How do you manage first degree heart block?
1) Reverse pathological underlying cause
2) First degree heart block itself does not need treating (benign)
What are the two types of second degree heart block?
1) Mobitz type I (Wenckebach)
2) Mobitz type II
Which heart block is Wenckebach?
Second degree - Mobitz type I
What causes Wenckebach/Mobitz type I second degree heart block?
Reversible conduction block at the AV node
What does Wenckebach/Mobitz type I second degree heart block look like on ECG?
Progressive lengthening of the PR interval which results in a P wave that fails to conduct a QRS
What are the causes of Wenckebach/Mobitz type I second degree heart block?
1) MI - mainly inferior
2) Drugs e.g. beta blockers, calcium channel blockers, digoxin
3) Professional athletes due to high vagal tone
4) Myocarditis
5) Cardiac surgery
Which drugs can cause Wenckebach/Mobitz type I second degree heart block?
1) Beta blockers
2) Calcium channel blockers
3) Digoxin
How do you manage Wenckebach/Mobitz type I second degree heart block?
1) Generally asymptomatic and does not require any specific management - risk of high AV block/complete heart block is is low
2) If symptoms arise - ECG monitoring, exclude precipitating drugs and if bradycardic might require atropine
What causes Mobitz type II second degree AV block?
Conduction system failure esp. at the His-Purkinje system
What does Mobitz type II second degree AV block look like on ECG?
1) Intermittent non-conducted P waves - may be no pattern or fixed ratios e.g. 2:1 or 3:1 block
2) PR interval is constant
3) Broad QRS - indicating distal block in His-Purkinje system
4) Pre-existing LBBB/bifascicular block
What are the causes of Mobitz type II second degree AV block?
1) MI - esp. anterior (damages bundle branches)
2) Surgery - mitral valve repair or septal ablation
3) Inflammatory/autoimmune - rheumatic heart disease, SLE, systemic sclerosis, myocarditis
4) Fibrosis - Lenegre’s disease
5) Infiltration - sarcoidosis, haemochromatosis, amyloidosis
6) Medication - beta-blockers, CCBs, digoxin, amiodarone
Which medications can cause Mobitz type II second degree AV block?
1) Beta blockers
2) CCBs
3) Digoxin
4) Amiodarone
What are inflammatory/autoimmune causes of Mobitz type II second degree AV block?
1) Rheumatic heart disease
2) SLE
3) Systemic sclerosis
4) Myocarditis
What are surgical causes of Mobitz type II second degree AV block?
1) Mitral valve repair
2) Septal ablation
Which types of heart block do inferior MIs lead to?
First degree or Mobitz type I (Wenckebach) or complete (third degree)
Which type of heart block do anterior MIs lead to?
Mobitz type II second degree
How do you manage first degree or second degree Mobitz type I (Wenckebach) heart block?
No specific treatment
How do you definitively manage second degree Mobitz type II or complete third degree heart block?
Permanent pacemaker
How do you definitively manage Mobitz type II second degree AV block and why?
Permanent pacemaker - bc these patients are at risk of complete heart block and becoming haemodynamically unstable
Why do you treat Mobitz type II second degree AV block with a permanent pacemaker?
Risk of:
1) Complete heart block
2) Haemodynamic instability
What causes complete (third degree) heart block?
When atrial impulses fail to be conducted to the ventricles
What causes sufficient cardiac output in complete (third degree) heart block?
May be secondary to a ventricular or junctional escape rhythm
How do patients with complete (third degree) heart block present?
1) Syncope
2) Cardiac arrest
What does ECG show in complete (third degree) heart block?
1) Severe bradycardia
2) Dissociation between P waves and QRS complexes
What are causes of complete (third degree) heart block?
1) MI - esp. inferior
2) Drugs acting at the AV node - beta blockers, CCBs
3) Idiopathic fibrosis
Which two drugs can cause any type of heart block?
Beta blockers + calcium channel blockers
What is definitive management of complete (third degree) heart block?
Permanent pacemaker - due to risk of sudden death
Why do you need a permanent pacemaker in complete (third degree) heart block?
Due to the risk of sudden death
What are indications for transcutaneous pacing (temporary) in bradyarrhythmias?
1) Patients unresponsive to medical therapy - e.g. with atropine total dose 3mg + adrenaline
2) After an inferior MI
Why is only transcutaneous pacing needed after an inferior MI?
Unlike with anterior MI, bradycardias are usually temporary and do not require permanent pacing
Which bradyarrhythmias require pacemakers?
1) Complete heart block (whether asymptomatic or symptomatic)
2) Mobitz type 2 heart block (whether asymptomatic or symptomatic)
3) Symptomatic sick sinus syndrome
4) Permanent bradyarrhythmias caused by a myocardial infarct (typically anterior infarcts - arrhythmias caused by inferior infarcts tend to be temporary)
What are the two types of temporary pacing?
Transcutaneous or transvenous
What does ECG look like in a paced rhythm?
Pacing spikes describe vertical short duration (usually 2ms) spikes
The amplitude depends on the type of lead used:
1) In atrial pacing the pacing spike precedes the P wave.
2) In ventricular pacing the pacing spike precedes the QRS complex
3) In RV pacing the QRS morphology is similar to LBBB
4) In LV pacing the QRS morphology is similar to RBBB
5) In dual chamber pacing there may be features of atrial pacing, ventricular pacing, or both
How is transcutaneous pacing used?
It is a bridge to transvenous pacing
1) Often used in emergency situations
2) It can be rapidly administrated via external electrodes but is only a bridge to transvenous pacing
3) Sedation is required due to painful stimulation of skeletal muscles
How is transvenous pacing used?
1) More effective form of continuous temporary pacing than transcutaneous pacing (transcutaneous is only a bridge to transvenous)
2) Complications are common as invasive venous access is required (e.g. heart perforation, thromboembolism, infection) so the therapy should not be used for longer than a few days (at this point need permanent pacemaker)
What are the three main causes of bradycardia?
1) Heart block
2) Medication e.g. beta blockers
3) Sick sinus syndrome
What is sick sinus syndrome?
1) Encompasses many conditions that cause dysfunction in the sinoatrial node (SAN)
2) Often caused by idiopathic degenerative fibrosis of the sinoatrial node
3) Can result in sinus bradycardia, sinus arrhythmias and prolonged pauses
What causes sinus bradycardia or sinus arrythmias?
Sick sinus syndrome
What is pulseless electrical activity (PEA)?
When there’s normal co-ordinated cardiac activity on the ECG monitor, but no pulse is present on the patient
What is asystole?
Absence of QRS complexes (or electrical activity) on the ECG + no pulse
How do you manage PEA or asystole?
1) Start CPR 30:2
2) Give adrenaline 1mg IV as soon as IV access is achieved
3) Give further adrenaline 1mg IV every 3-5 min (during alternate 2-min loops of CPR)
4) No shock
What is the only medication you give in PEA or asystole?
Adrenaline IV 1mg (1:10,000)
What is a normal QT interval?
< 440ms (two large squares)
What is the definition of a prolonged QT?
> 450ms
What is the complication of long QT?
Prolonged ventricular repolarisation which predisposed to malignant ventricular arrhythmias e.g. VT, torsades de pointes
What are drug causes of long QT?
1) Amiodarone
2) TCAs
3) Antibiotics
4) Fluconazole
5) Erythromycin
6) Metoclopramide
7) Haloperidol
8) Ondansetron
9) SSRIs
10) Qunidine
What are genetic causes of long QT?
Sodium or potassium channel mutations
1) Jervell and Lange-Nielson syndrome (associated with deafness)
2) Romano Ward syndrome
What are cardiac causes of long QT?
Myocardial disease
Which electrolyte abnormalities can cause long QT?
1) Hypocalcaemia
2) Hypokalaemia
3) Hypomagnasaemia
What is the first line investigation for long QT?
ECG ± 24h ECG
What other investigations are done in long QT?
Echo - to look for structural heart disease ± genetic testing as required
How do you manage long QT?
1) Beta blockade
2) Cardiac pacing
3) Implantation of ICD
4) Manage underlying cause
