Complete heart block Flashcards
Define heart block
Heart block refers to an obstruction in the electrical conduction system of the heart.
This can occur at various points in the conduction system, incl SAN, AVN, Bundle of His, or bundle branches.
What is first degree heart block, how is it identified on ECG and management?
It is caused by prolonged conduction of electrical activity through AV node. Identified on ECG by finding a PR interval >200ms/0.2s.
Benign, doesn’t need treatment but patho causes should be removed
Define second degree heart block and how it is identified on ECG?
Two types
Mobitz type 1 - due to reversible conduction block at the AV node, progressive lengthening of PR interval until a dropped beat occurs (a missed QRS)
Mobitz type 2 - PR interval is constant but P wave is often not followed by QRS complex. (this is more severe and can lead to complete heart block)
What is the basic management for the two types of second degree heart block?
Mobitz 1 - generally asymptomatic and low risk of complete heart block so doesnt require any specific management
Mobitz 2 - management with permanent pacemaker due to high risk of complete as well as high risk of become haemodyn unstable
Define complete heart block and how its identified on ECG
It is 3rd degree heart block and the most severe type. It is when atrial impulses fail to be conducted to the ventricles. Sufficient cardiac output may be secondary to a ventricular or junctional escape rhythm.
ECG shows severe bradycardia and complete dissociation between the P waves and the QRS complexes.
What are the causes of complete heart block?
Inferior MI
AV nodal blocking drugs e.g. non-DHP CCBs, BB, digoxin, adneosine
Idiopathic fibrosis
What are the risk factors of complete heart block?
Age, male, AVN drugs, cardiomyopathy, MI, CAD, sarcoidosis, lyme disease, hyperkalaemia, Post open heart surgery
Describe pathophys of complete heart block
In 3rd degree, the atria and ventricles beat independently of each other as no impulses get conducted to the vents. The atria are driven by the SAN while the ventricles are driven by a secondary pacemaker creating an escape rhythm (e.g. junctional escape rhythm by AVN, ventricular escape rhythm by vent myocytes) which may allow sufficient CO.
Alternatively, it could go to ventricular standstill and lead to death.
What are the clinical features of complete heart block?
Symptoms often severe and quick onset
Dizzy, Fatigue, syncope, short of breath, chest pain
ECG - severe bradycardia and dissociation between P waves and QRS complexes
What are the investigations for complete heart block?
12 lead ECG showing severe bradycardia and P wave and QRS complex dissociation, serum K/Ca very low/high.
What is the diagnostic criteria for complete heart block?
ECG - Dissociation between the P wave and QRS complexes +syncope + <40bpm heart rate
What are the differentials for complete heart block?
Junctional rhythm, SVT, AF, tachy brady syndrome
What is management of complete heart block?
Management of acute bradycardia:
If there are adverse signs:
- 1st line = Atropine 500mcg IV
If first dose not working or they have a risk of asystole, give additional up to 3mg OR do Transcutaneous pacing.
If still no response or risk of asystol get specialist help to do transvenous pacing.
- Also need Permanent pacemaker due to risk of sudden death.
What types of conduction problems give risk of asystole?
Complete heart block with broad QRS complex, recent asystole, mobitz II, ventricular pause> 3 seconds
What is the emergency/adverse signs presentation of complete heart block?
Syncope, fatigue, chest pain, dyspnea (last two indicate myocardial ischemia and HF respectively)
