Bradycardia and Block The conducon system

SA node (natural pacemaker)

AV node (junction box)

Left bundle branch posterior fascicle

Left bundle branch anterior fascicle Right bundle branch The normal ECG

• The conducon system can fail at any point • Bradycardia per se is not a bad thing • Bradycardia without symptoms is usually not an issue, except in select cases The conducon system – SA node

SA node (natural pacemaker) Sinus Bradycardia – a problem?

• Physically fit people have heart rates in the 50s • Athletes can have heart rates as low as 25 without a problem • If this is an 80 yr old lady, chances are this is sinus node dysfuncon • If she has lethargy, exercise incapacity, falls or blackouts, refer for consideraon of pacing Atrial Pacemakers

• Atrial pacemakers can restore exercise capacity • Have not been shown to improve mortality, only morbidity What is happening with the rhythm? Sinus : Sinus arrhythmia

• In itself not an issue • Usually mediated by vagal tone • Common in athletes What is unusual about this rhythm strip? Low atrial rhythm – usually benign Describe the rhythm strip Junconal ectopics (no p waves visible with the ectopics despite ‘room’ to see them) Profoundly hypothyroid paent Junconal bradycardia The conducon system

AV node (junction box)

Left bundle branch anterior fascicle The AV node

• If problems occur within the AV node, they can form one of the three types of HB • First degree (conducts every beat) • Second degree (conducts some beats) • Third degree (conducts none) • If the QRS width is less than 120ms (three small squares), conducon must be coming through the AV node and down both bundles

First degree block, not usually a big deal First degree –what to do?

• In very young person (<45), refer for invesgaon • Anyone old enough for IHD, look for signs of old infarct to explain (parcularly inferior) • Check for drugs that can do this and consider stopping these if alternaves available • In older person (>70) likely represents beginnings of conducons system disease • Look out for symptoms of higher grade block • Don’t treat or invesgate unless you suspect this • Check thyroid Second degree heart block

Mobitz type I (Wenkebach) • Progressive prolongation of the PR interval followed by a non-conducted beat

Mobitz type II with 2:1 block. • Every second beat is non-conducted

Third degree (complete) heart block (for comparison) • No connection at all between p waves and QRS complexes

Wenkebach Wenkebach – what to do

• Usually nothing • Usually due to high vagal tone • Can occur post-infarct like any arrhythmia • Rarely symptomac

• Refer symptomac paents • Consider referral of asymptomac paents aer seeing results of 24 hour tape

Mobitz Type II block Mobitz Type II Heart Block

• Always pathological • Strong possibility of needing paced • Can progress to complete heart block unpredictably • Post-infarct scenario complex and considered separately

Third degree (Complete) Heart Block CHB

• Post-infarct scenario aside, is usually paced • If in context of drugs, thyroid, hyperkalaemia, decision is made case by case • Outside these scenarios untreated CHB has 50% mortality at 1 yr • Sudden death a possibility • Admit

Dual chamber pacing – modern pacing spikes can be very small Temporary pacing • There are five hard indicaons for a temporary pacing wire; • at rest • End-organ failure • Escape VT • HB with anterior infarct • Acutely alternang le and right bundle BB. – Some would include a broad escape, but external pacing is usually adequate for this – Pacing wire complicaon rates are significant – Consider carefully before inseron and discuss where possible The conducon system

Left bundle branch posterior fascicle

Left bundle branch anterior fascicle Right bundle branch

Right : QRS ≥3 squares and V1 points up Right Bundle Branch Block

• Many causes • May be normal variant (3% of populaon) • OPT referral if paent has symptoms to indicate an underlying cause – SOB – Chest pain – Dizzy spells

N.B. RBBB should have a normal axis Le Bundle Branch Block QRS ≥3 squares and V1 points down

Le Bundle Branch Block

• Always pathological • Requires invesgaon • Can exacerbate , but otherwise is asymptomac Le Anterior Fascicular Block

Left bundle branch posterior fascicle

Left bundle branch anterior fascicle Right bundle branch Le anterior fascicular block = Le axis deviaon without cause Le Anterior Fascicular Block

• Part of the le bundle not funconing • Causes le axis deviaon on the ECG, but not broadening of the QRS • Other things can cause le axis deviaon on an ECG – LVH – Body habitus – Structural heart disease • No LVH, plus le axis deviaon, is usually LAFB • The aide memoire is in the leers: Le Anterior fascicular block = Le Axis deviaon Le posterior fascicular block = Right axis deviaon without cause

Left bundle branch posterior fascicle

Left bundle branch anterior fascicle Right bundle branch Fascicular Block

• Clinically not essenal to understand • However, worth knowing how to spot them as they are a clue as to the extent of your paent’s conducon disease • There are three fascicles: – The right bundle – The le anterior fascicle of the le bundle – The le posterior fascicle of the le bundle Fascicular Block

– If the only the right bundle goes, we should see RBBB with a normal axis – If the le anterior and le posterior go we see LBBB – If only one of the le fascicles goes, we only see axis deviaon on the ECG with no broadening of the QRS

Therefore...... – If the right goes and one of the le fascicles goes, we see RBBB with an abnormal axis Bifascicular block – RBBB & Le axis Bifascicular block – RBBB & Right axis

• Badly named • This refers to a situaon where two fascicles are blocked and the remaining fascicle has abnormal conducon • i.e. bifascicular block plus first degree heart block

The conducon system

Left bundle branch posterior fascicle

Left bundle branch anterior fascicle Right bundle branch Trifascicular block – RBBB (one), le axis (two), first degree HB (hence tri-) Summary

• The conducon system can fail at any point • Conducon block on a resng ECG is a pointer that more trouble may lie ahead • First degree, Wenkebach, Bifasc Block, Trifasc Block don’t themselves cause morbidity • They make it more likely that rhythms may also be intermiently occurring that can cause morbidity (CHB) • CHB and Mobitz Type II usually paced