CARDIO: Arrythmias Flashcards
What is absolute bradycardia?
HR is <40bpm
What is relative bradycardia?
Where HR is inappropriately slow for the haemodynamic state of the patient.
Oxford clinical handbook definition of bradycardia = <60bpm
Signs that may indicate haemodynamic instability?
Systolic BP < 90mmHg HR <40 Poor perfusion Poor urine output Ventricular arrhythmias that need suppression Heart failure
How can bradycardia be classified?
Based on the pacemaker that is faulty:
- sinus node e.g. sinus bradycardia
- AV node
List some causes of bradycardia
Physiological:
- athletes
Cardiac:
- degenerative changes/fibrosis of conduction pathways in elderly
- post-MI (especially inferior MI (leads II, III, aVF)
- sick sinus syndrome
- iatrogenic —> ablation, surgery
- aortic valve disease e.g. infective endocarditis (rheumatic fever)
- myocarditis, cardiomyopathy, sarcoidosis, SLE
Non-cardiac origin:
- vasovagal
- endocrine = hypothyroidism, adrenal insufficiency
- metabolic = hyperkalaemia, hypoxia
- other = hypothermia, raised ICP (Cushing’s triad - bradycardia, hypertension and irregular breathing), pericarditis, haemochromatosis,
Drug induced:
- Beta blockers
- amiodarone
- verapamil
- diltiazem
- digoxin
Main management for pt with symptomatic sinus node disease (e.g. a sinus bradycardia)?
Pacemaker is indicated
What are categories of sinus node dysfunction?
Sinus bradycardia
Sick sinus syndrome
Sinus arrest
Part of vasovagal syncope
How are AV node bradycardias classified?
According to the degree of nodal dysfunction:
- First degree AV block
- Second degree AV block Mobitz Type I aka Wenckebach
- Second degree AV block Mobitz Type II
- Complete/Third degree AV block
How is First degree AV block characterised?
PR interval >0.2s
Pt has bradycardia. What rate limiting drug should you check pt is on and why?
Digoxin. Why? Digoxin toxicity - can worsen conduction abnormalities and worsen heart block
How is Second degree AV block: Wenckebach/Mobitz Type I characterised?
Lengthening of PR interval. Followed by failure of atrial impulse to conduct to the ventricles.
i.e. QRS is dropped after progressive lengthening of PR interval.
Who is more likely to have Second degree AV block: Wenckebach/Mobitz Type I?
- Young fit patients with a high vagal tone
- Patients after inferior MI
How is Second degree AV block: Mobitz Type II characterised?
Constant PR interval followed by sudden failure of a p wave to be conducted to the ventricles.
i.e. PR length constant, then drop of QRS. 2 p waves for every QRS
How is complete heart block/ Third degree AV block characterised?
No conduction from atria to the ventricles. No relationship between p waves and QRS complexes
What does complete/ third degree heart block look like on ECG?
Rate is slow. Broad complex QRS escape rhythm seen, with no linkage of p waves and QRS - they are both independent.
Sometimes can look intermittent - see trifascicular or bifascicular block (RBBB, with or without prolonged PR interval) and alternating LBBB and RBBB.
Where can complete/third degree block occur?
Either:
- above AV node at the HIS region
- beneath AV node
Causes of complete/third degree AV block?
Anti-arrhythmic drugs - especially digoxin toxicity!!
Post- inferior STEMI (will resolve in hrs-days)
Anterior MI
Severe hyperkalaemia
How to treat severe hyperkalaemia causing. complete/third degree AV heart block?
- IV calcium gluconate/calcium chloride 30ml of 10% solution over 3-5 mins: to stabilise the myocardium
- insulin/dextrose infusion: short-term shift in potassium from ECF to ICF
- other treatments such as nebulised salbutamol may be given to temporarily lower the serum potassium
How to treat a haemodynamically unstable patient with complete/third degree AV heart block?
Atropine - 500micrograme to 3 mg.
Isoprenaline - at rate of 5micrograms/minute
Main management for complete/ third degree AV heart block?
Urgent permanent pacemaker. Within 24hrs unless they are likely to have a recovery of conduction (e.g post inferior STEMI)
Types of tachycardic arrhythmias?
Atrial fibrillation
Supraventricular tachycardia = in atria
Ventricular tachycardia
Presentation of AFib?
Asymptomatic Breathlessness Palpatations Syncope/dizziness Chest discomfort Stroke or TIA
Complications of AFib?
Cardioembolic stroke
Cardiac instability
Death
Increase in healthcare costs
How to diagnose A fib?
Presence of symptoms - palpitations, dizziness/syncope, breathlessness, chest discomfort, stroke, TIA
ECG used to confirm if an irregular pulse is due to A fib.
