lecture 5 - bradyarrhythmias

Question 1

what is the bundle of HIS?

Answer 1

the conducting fibre bundle immediately after the AVN. it quickly bifurcates into the LBBB and the RBBB

Question 2

what does the LBBB split into

Answer 2

the left posterior fascicle and the left anterior fascicle. the LPF runs circumferentially around the top of the left vertricle just below the level of the valves. the LAF runs down the septum to the apex and back up a bit

Question 3

what is Wenckebach phenomenon

Answer 3

progressive lengthening of conduction time in any cardiac tissue (most often the AV node or junction) with ultimate dropping of a beat (AV Wenckebach) or reversion to the initial conduction time. in the case where the phenomenon is due to AV block this is mobitz type 1 second degree heart block

Question 4

2:1 AV block

Answer 4

every other P wave not conducted

Question 5

Atrioventricular Block

Causes (1)

Answer 5

• First degree and Mobitz 1 AV blocks can occur in people with high vagal tone, e.g. young people and highly trained athletes

• Structural abnormality of AV node, e.g.
– degenerative fibrosis of conduction tissue
– valve disease, esp. calcific aortic valve disease
– myocarditis, including Lyme disease (Borrelia burgdoferi)
– myocardial infarction, esp. inferior MI
– myocardial infiltration, esp. cardiac sarcoidosis
– after cardiac surgery (esp. aortic valve surgery) and ablation
– penetrating chest injuries

• Ischaemia, esp. PDA (RCA) ischaemia
• Drugs, e.g. beta blockers, calcium antagonists, digoxin, TCAs

• Electrolyte and metabolic imbalance:
– hyperkalaemia
– hypothyrodism

• Congenital third degree AV block:
– neonatal lupus (due to maternal auto-antibodies crossing the
placenta) is the cause of majority of cases of congenital third degree
AV block
– more rarely – association with some congenital heart diseases, e.g.
atrioventricular canal defects and ccTGA

Question 6

Atrioventricular Block

Presentation

Answer 6

• Asymptomatic
• Pre-syncope
• Syncope
• More rarely other symptoms, e.g. breathlessness

Question 7

Atrioventricular Block

Management

Answer 7

• Depends on presentation, severity of AV block and likely cause

• Investigations:
– ECG (± other forms of ECG recording if needed)
– blood tests including U&Es, Mg, Ca, TFTs, FBC
– echocardiogram
– other tests depending on clinical features and suspected cause, e.g.
coronary angiogram

• Always treat underlying cause if possible

• Indications for permanent pacing in AV block:
– complete heart block (unless congenital)
– 2:1 AV block
– Mobitz 2 AV block with broad QRS or bifascicular block
– symptomatic Mobitz 2 AV block
– symptomatic Mobitz 1 AV block (in the absence of other
causes)

Question 8

what are the purkinje fibres?

Answer 8

the terminal branches of the RBB and the LAF and LPF

Question 9

Left anterior fascicular block

Answer 9

LAD + Q in lead I + S in lead III + narrowish QRS

Question 10

Left posterior fascicular block

Answer 10

RAD + S in lead I + Q in lead III + narrowish QRS

Question 11

Bifascicular block

Answer 11

LAD + RBBB

Fascicular Block

Question 12

Trifascicular block

Answer 12

LAD + RBBB + prolonged PR

Question 13

Fascicular Block

• Causes

Answer 13

• Causes are similar to AV block – often degenerative fibrosis of
conduction tissue or post-myocadial infarction

Question 14

• Indications for permanent pacing in fascicular block

Answer 14

• Indications for permanent pacing in fascicular block:
– trifascicular block associated with intermittent Mobitz 2 or
third degree AV block
– symptomatic tri- or bifascicular block in the absence of
other causes
– alternating bundle branch block

Question 15

Emergency
Management of
Brady-arrhythmias

Answer 15

• Cardiac monitor

• Treat reversible causes, e.g.
– Correct electrolyte abnormalities
– Stop ± reverse rate-limiting drugs

• Increase heart rate (if adverse
features present)
– Drugs (e.g. atropine, isoprenaline,
adrenaline)
– Transcutaneous pacing
– Temporary transvenous pacing

• Some patients may need
permanent pacing

Question 16

• Permanent pacing systems for brady-arrhythmias can be:

Answer 16

• Permanent pacing systems for brady-arrhythmias can be:
– single chamber (lead in RV or more rarely RA)
– dual chamber (leads in RA and RV)
• Pacing leads are fixed passively (will eventually be fibrosed
onto endocardium) or actively (screwed into
endo/myocardium)
• Generator and pacing algorithm housed in pacing box

single/dual chamber can be differentiated on CXR by if there is one or two leads.

Question 17

Permanent Pacing for Brady-arrhythmias

Pacemaker codes

Answer 17

Pacemaker codes
• Three letter code for pacemakers introduced in 1974 by
Parsonnet – now four letters in routine use (but more for
some systems):

– First letter = chamber paced
– Second letter = chamber sensed
– Third letter = pacemaker response to sensed impulse
– Fourth letter = programmable functions, e.g. rate-responsiveness
– Fifth letter – tachyarrhythmia functions

• Most frequently used pacemaker is now DDDR

Work out these codes:
VVI, AAI, VOO, AOO

Question 18

Permanent Pacing for Brady-arrhythmias

Adverse effects

Answer 18

• Peri-procedural
– Bleeding and haematoma
– Haemo- and pneumothorax
– Cardiac perforation, including cardiac tamponade
– Lead displacement
– Death (very very rare)

• Long term
– Lead displacement or malfunction, e.g. twiddler’s syndrome
– Infection
– Pain and skin erosion