Conduction Blocks Flashcards by nura souliman

Define Bradycardia?

Bradycardia is defined as a heart rate below 60 beats per minute, which can either be physiological or due to dysfunction of the conduction pathway (sinus node or atrioventricular (AV) node conduction dysfunction).

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What is a heart block?

Heart block block is a cardiac electrical disorder defined as impaired (delayed or absent) conduction from the atria to the ventricles.

The severity of the conduction abnormality is described in degrees.

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What is the aetiology of first degree heart block?

LEV’s disease
- This is the result of proximal bundle branch calcification or fibrosisand is often described as senile degeneration of the conduction system.
Ischaemic heart disease
- scar tissue from myocyte death blocks conduction pathway
Myocarditis
Hypokalaemia

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What is the aetiology of second degree heart block?

Natural aging process.
Damage to the heart from surgery.
Damage to the heart muscle from a heart attack.
Other types of heart disease that damage the heart muscle.
Low thyroid levels.
Electrolyte abnormalities.
Inflammatory or infectious heart conditions.

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What is the aetiology of second degree heart block?

Natural aging process.
Damage to the heart from surgery.
Damage to the heart muscle from a heart attack.
Other types of heart disease that damage the heart muscle.
Low thyroid levels.
Electrolyte abnormalities.
Inflammatory or infectious heart conditions.

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What is the aetiology of third degree heart block?

Coronary heart disease
Infection
Hypertension

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What is the aetiology of third degree heart block?

Coronary heart disease
Infection
Hypertension

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What is the epidemiology of heart block?

The incidence of AV conduction abnormalities increases with age, corresponding with the age-related incidence of ischaemic heart disease.

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What is the pathophysiology of heart block?

A heart block does not mean that the heart stops beating altogether, because other ‘back-up’ systems can take over. However, it can result in an abnormally slow heartbeat (bradycardia), leading to the body’s organs and tissue becoming deprived of oxygen

Asymptomatic bradycardia does not usually require treatment. However, there are several different types of bradycardia which can be categorised as below:

Sinus node dysfunction may be associated with sinus bradycardia, tachycardia-bradycardia, and sick sinus syndrome.

Atrioventricular(AV) conduction disturbances can either be due to poor transmission of atrial depolarisation to the ventricles or a delay in atrial depolarisation.

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What is first degree AV block?

PR interval >0.2s
Can be normal, e.g. in athletes. May represent pathology, e.g. inferior MI
As an isolated finding often has little significance

First-degree AV block: occurs where there is delayed atrioventricular conduction through the AV node but every atrial impulse leads to a ventricular contraction.

Block at the level of the AV node manifesting as first-degree or type I second-degree AV block is usually a function of either high vagal tone or medication.

First-degree heart block; PR interval is approximately 200ms.

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What is second degree AV block?

Second-degree AV block**(failure of conduction from atria to ventricles):

- Mobitz type 1 (Wenckebach)

Increasing PR interval culminating in a dropped QRS complex. The PR interval resets and the cycle repeats

- Due to reversible conduction block at the level of the AV node
- AV nodal cells progressively fatigue until they fail to conduct
- Can be normal, e.g. in athletes. May represent pathology, e.g. inferior MI
- As an isolated finding often has little significance
- Generally caused by AV node block and results in progressive PR interval prolongation until a P wave fails to conduct and a QRS is absent after the first P wave (dropped beat)
- Eventually ventricle’s pacemaker cells kick in
- The PR interval then returns to normal and the cycle repeats itself
- Patient often experiences light headedness, dizziness and syncope

**Mobitz type I / Wenckebach**: atrial inputs becomes gradually weaker until it does not pass through the AV node. After failing to stimulate a ventricular contraction the atrial impulse returns to being strong.

- Mobitz type II:

The PR interval remains constant, but with intermittent dropped QRS complexes (2:1, 3:1, etc)

- Due to disease of the His-Purkinje system → AV depolarisation does not result in appropriate ventricular depolarisation
- Usually due to structural heart damage, e.g. myocardial infarct
- High risk of sudden cardiac death
- Requires treatment
- Caused by a block at an intra-nodal level so the QRS is widened and QRS complexes are dropped without PR prolongation
- Fairly random dropped beats – no PR elongation

**Mobitz type II**: Usually due to disease of the His-Purkinje system which causes intermitted failure or interruption of AV conduction. This results in missing QRS complexes. There is usually a set ratio of P waves to QRS complexes.

Patients often experience chest pain, SOB, syncope and postural hypotension

**Mobitz type I shows an increasing PR interval, followed by a dropped beat. Mobitz type II shows a constant PR interval with an occasional dropped beat.**

**Mobitz type II with 2:1 block, i.e. every other beat is 'dropped'.**

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What is third degree AV block?

Complete absence of AV conduction. None of the supraventricular impulses are conducted to the ventricles
P wave and QRS complex are completely dissociated
Usually due to His-Purkinje disease
High risk of sudden cardiac death
Requires treatment
In third-degree AV block, no atrial impulses could reach the ventricle.
It can occur in the AV node or in the infranodal specialized conduction system.
So it occurs when there is complete dissociation between atrial and ventricular activity. E.g. atrial BPM is 60, ventricular is 30 BPM

Third-degree AV block: complete heart block. This is no observable relationship between P waves and QRS complexes.

Complete heart block: no association between P-waves and QRS complexes.

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What are the symptoms of heart block?

Dizziness
Fatigue
Shortness of breath
Syncope

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What are the symptoms of heart block?

Dizziness
Fatigue
Shortness of breath
Syncope

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What are the symptoms of first degree heart block?

The least serious is 1st-degree heart block, which may not cause any symptoms.
chest pain.
shortness of breath.
feeling very dizzy suddenly when standing up from a lying or sitting position – this is caused by having low blood pressure (hypotension)

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What are the symptoms of second degree heart block?

Dizziness.
Fainting - Syncope
The feeling that your heart pauses for a beat.
Trouble breathing or shortness of breath.
Nausea.
Severe tiredness (fatigue)

What are the symptoms of third degree heart block?

Syncope
Dyspnoea
Chest pain
Confusion

What are the signs of heart block?

Associated with Cushing’s triad:raised intracranial pressure
- Bradycardia
- Hypertension
- Irregular respirations (apnoea)
JVP:cannon A waves
- Occurs in complete heart block due to atrial contraction against a closed tricuspid valve

What are the life threatening features of heart block?

It is important to be aware of the life-threatening features associated with any peri-arrest arrhythmia as the presence of these features guides ongoing management.

Shock: hypotension (systolic blood pressure <90 mm Hg), pallor, sweating, cold, clammy extremities, confusion or impaired consciousness
Syncope: transient loss of consciousness due to a global reduction in blood flow to the brain
Myocardial ischaemia: typical ischaemic chest pain and/or evidence of myocardial ischaemia on 12-lead ECG
Heart failure: pulmonary oedema and/or raised jugular venous pressure (with or without peripheral oedema and liver enlargement)

What are the primary investigations of heart block?

12-lead ECG

First-degree AV block: PR interval >0.2s
Mobitz type I / Wenckebach: increasing PR interval culminating in a dropped QRS complex. The PR interval resets and the cycle repeats.
Mobitz type II: the PR interval remains constant, but with intermittent dropped QRS complexes (2:1, 3:1, etc).
Third-degree AV block: P wave and QRS complex are completely dissociated

What are the other investigations to consider for heart block?

TFTs:hypothyroidism may be responsible for the bradycardia
U&Es and metabolic panel: screen forhyperkalaemia, hypokalaemia, hypercalcaemia, or hypocalcaemia
Serum digoxin level: appropriate for patients on digoxin
Holter monitoring: allows the correlation of symptoms with episodes of bradycardia
Tilt-table testing: to assess forneurocardiogenicsyncope, whereby head-upright tilting causes a sudden drop in blood pressure followed by bradycardia
ECHO: useful if a permanent pacemaker is being implanted in order to assess left ventricular ejection fraction (LVEF)
- LVEF<30%would warrant a pacemakerandan implantable cardioverter-defibrillator

What is the management for heart block?

If stable: observe
If unstable or risk of asystole
- First line: atropine500mcg IV
- If no improvement:
  - Atropine500mcg IV repeated
  - Otherinotropes(such as noradrenalin)
  - Transcutaneous cardiac pacing(using a defibrillator)
In patients with high risk ofasystole
- Temporary transvenous cardiac pacingusing an electrode on the end of a wire that is inserted into a vein and fed through the venous system to the right atrium or ventricle to stimulate them directly
- Permanent implantable pacemakerwhen available
First Degree Heart Block
- Asymptomatic so no treatment required
Second Degree Heart BlockIf you have second-degree heart block and have symptoms, you may need a pacemaker to keep your heart beating like it should.
Third Degree Heart Block
- IV atropine (acute) – increases heart rate
- Permanent pacemaker insertion
  - Third degree heart block is often first discovered during an emergency situation. Treatment almost always includes a pacemaker.

- Syncope
  - An important complication and recognised life-threatening feature of bradycardia.
- Arrhythmias (irregular heartbeat):some patients may go on to develop asystole, ventricular tachycardia or ventricular fibrillation
- Congestive heart failure: due to poor cardiac output
  - A minority of patients with chronic bradycardia may develop congestive heart failure due to poor cardiac output
- Pacemaker infection is common in the elderly, especially with underlying medical conditions.
- Also, sometimes it can be challenging for pacemaker patients who need other studies like MRI for diagnosing other medical conditions such as stroke.
- Sudden cardiac arrest

What are the complications for heart block?

Syncope
- An important complication and recognised life-threatening feature of bradycardia.
Arrhythmias (irregular heartbeat):some patients may go on to develop asystole, ventricular tachycardia or ventricular fibrillation
Congestive heart failure: due to poor cardiac output
- A minority of patients with chronic bradycardia may develop congestive heart failure due to poor cardiac output
Pacemaker infection is common in the elderly, especially with underlying medical conditions.
Also, sometimes it can be challenging for pacemaker patients who need other studies like MRI for diagnosing other medical conditions such as stroke.
Sudden cardiac arrest

What is the differential diagnosis for heart block?

- Once diagnosed, underlying causes should be evaluated that include ischemic workup, autoimmune diseases in young patients that can cause fibrosis of the conducting system, offending medications and electrolyte disturbances such as hyperkalemia.

What are the risk factors for heart block?

You may be at increased risk of a heart block if: - **Increasing age (> 70 years old)**: increases the risk of sinoatrial and AV node dysfunction - You are of older age. Risk of heart block increases with age. - **Endocrine**: hypothyroidism - Your mother has an autoimmune disease, such as lupus. - You have a disease that affects the heart including rheumatic heart disease or sarcoidosis. - **Infections**: e.g. typhoid and diptheria - **Electrolytes**: hyperkalaemia, hypokalaemia, hypercalcaemia, or hypocalcaemia - **Cardiac**: recent myocardial infarction - You have other heart conditions including coronary artery disease, heart valve disease. - **Drugs**: e.g. beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, adenosine and amiodarone - You take medications that slow the conduction of the heart’s electrical impulses. - **Surgery**: intra-operative sinus bradycardia is relatively common - **Hypothermia** - You have birth defects of the heart. - You have an overactive vagus nerve (causes the heart to slow down).

What is the prognosis for heart block?

Bradycardia treated with a pacemaker will typically have a good prognosis.

Where can a block occur?

There are 2 place which can be blocked: - Block in AVN or bundle of His = AV block Block in lower conduction system = Bundle Branch Block (RBBB or LBBB)

What is a Bundle branch block?

a delay or blockage along the pathway that electrical impulses travel to make your heart beat. Complete block of a bundle branch is associated with a wide QRS complex with an abnormal pattern and is usually symptomatic. There are 2 types: LBBB RBBB

What is the aetiology of a BBB?

LBBB —> Cardiac pathology; ischarmic heart disease, left ventricular hypertrophy, aortic valve disease and following cardiac surgery - Causes: ischaemic heart disease, hypertension, cardiomyopathy, idiopathic fibrosis RBBB —> Pulmonary embolus, RV hypertrophy, ischaemic/congenital heart disease - Causes: pulmonary embolism, cor pulmonale, ischaemic heart disease, atrial/ ventricular septal defect

What is the pathophysiology of a BBB?

LBBB —> Left bundle branch no longer conducts an impulse and the two ventricles do not receive an impulse simultaneously (first right then the left). This creates the second R wave in the left ventricular leads (I, AVL and V4-V6) and a slurred S wave (V1 and V2). RBBB—> Right bundle branch no longer conducts an impulse and the two ventricles do not receive an impulse simultaneously (first left then the right). This creates the second R wave (V1) and a slurred S wave (V5 and V6). - RBBB - There is sequential spread of an impulse (i.e. LV then RV) - Results in an R wave in V1 and a slurred S wave in V5/6 (MaRRoW) - Occurs in PE, RV hypertrophy, IDH, congenital heart disease e.g. atrial/ventricular septal defects and Fallot’s Tetralogy - LBBB - Opposite of a RBBB - Slurred S wave in V1 and R wave in V5/6 (WiLLiaM) - Occurs in IHD, aortic stenosis, hypertension, aortic valve disease

What is the detailed pathophysiology of a BBB?

**Physiology:** - The His bundle gives rise to the right and left bundle branches - The left branch subdivides into the anterior and posterior divisions of the left bundle **Pathophysiology:** - **Right bundle branch block (RBBB):** - Right bundle no longer conducts, meaning that the two ventricles do not get impulses at the same time. The impulse therefore spreads from left to right, which produces late activation of right ventricle. - **Left bundle branch block (LBBB):** - Results in late activation of left ventricle - As the left bundle branch conduction is normally responsible for the initial ventricular activation, left bundle branch block also produce abnormal Q waves - **Bifascicular block:** blockage of right bundle branch and left anterior fascicle - **Complete block:** failure of all bundle branches

What are the symptoms of a BBB?

- Usually **asymptomatic** LBBB —> Usually asymptomatic. Possible syncope RBBB —> Usually asymptomatic. Possible syncope

What are the symptoms of a BBB?

- Usually **asymptomatic** LBBB —> Usually asymptomatic. Possible syncope RBBB —> Usually asymptomatic. Possible syncope

What are the signs of a BBB?

- LBBB: **reverse splitting of the second heart sound** - RBBB: **wide physiological splitting of second heart sound**

What are the investigations of a BBB?

- LBBB: - Deep S wave in V1 and a tall late R wave in V6 - WilliaM: QRS looks like a W in V1 and V2, QRS looks like an M in V4-V6 LBBB —> **ECG:** Secondary R in I, AVL, V4-V6. Slurred S in V1 and V2. --- - RBBB: - Wide, slurred S wave in V6 and as a tall late R wave in V1 - MarroW: QRS looks like an M in V1, QRS looks like a W in V5 and V6 RBBB—> **ECG:** Secondary R in V1 and a slurred S wave in V5 and V6

What are the differential diagnosis for a BBB?

AF Cardiac tamponade

What is the management for a BBB?

LBBB—> May require pacemaker. RBBB—> Treat underlying condition

What are the complications for a BBB?

syncope arrhythmias

What are the risk factors for a BBB?

- use of known causative medications - age >70 years - recent myocardial infarction - surgery