Bradycardia and Heart Block The conduc on 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 Bradycardia
• The conduc on 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 conduc on system – SA node
SA node (natural pacemaker) Sinus Bradycardia 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 dysfunc on • If she has lethargy, exercise incapacity, falls or blackouts, refer for considera on 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 arrhythmia: 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 Junc onal ectopics (no p waves visible with the ectopics despite ‘room’ to see them) Profoundly hypothyroid pa ent Junc onal bradycardia The conduc on 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 heart block (conducts none) • If the QRS width is less than 120ms (three small squares), conduc on 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 inves ga on • Anyone old enough for IHD, look for signs of old infarct to explain (par cularly inferior) • Check for drugs that can do this and consider stopping these if alterna ves available • In older person (>70) likely represents beginnings of conduc ons system disease • Look out for symptoms of higher grade block • Don’t treat or inves gate 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 symptoma c
• Refer symptoma c pa ents • Consider referral of asymptoma c pa ents a er 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 indica ons for a temporary pacing wire; • Syncope at rest • End-organ failure • Escape VT • HB with anterior infarct • Acutely alterna ng le and right bundle BB. – Some would include a broad escape, but external pacing is usually adequate for this – Pacing wire complica on rates are significant – Consider carefully before inser on and discuss where possible The conduc on system
Left bundle branch posterior fascicle
Left bundle branch anterior fascicle Right bundle branch
Right Bundle Branch Block: QRS ≥3 squares and V1 points up Right Bundle Branch Block
• Many causes • May be normal variant (3% of popula on) • OPT referral if pa ent 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 inves ga on • Can exacerbate heart failure, but otherwise is asymptoma c Le Anterior Fascicular Block
Left bundle branch posterior fascicle
Left bundle branch anterior fascicle Right bundle branch Le anterior fascicular block = Le axis devia on without cause Le Anterior Fascicular Block
• Part of the le bundle not func oning • Causes le axis devia on on the ECG, but not broadening of the QRS • Other things can cause le axis devia on on an ECG – LVH – Body habitus – Structural heart disease • No LVH, plus le axis devia on, is usually LAFB • The aide memoire is in the le ers: Le Anterior fascicular block = Le Axis devia on Le posterior fascicular block = Right axis devia on without cause Bifascicular Block
Left bundle branch posterior fascicle
Left bundle branch anterior fascicle Right bundle branch Fascicular Block
• Clinically not essen al to understand • However, worth knowing how to spot them as they are a clue as to the extent of your pa ent’s conduc on 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 devia on 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 Trifascicular block
• Badly named • This refers to a situa on where two fascicles are blocked and the remaining fascicle has abnormal conduc on • i.e. bifascicular block plus first degree heart block
The conduc on 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 conduc on system can fail at any point • Conduc on block on a res ng 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 intermi ently occurring that can cause morbidity (CHB) • CHB and Mobitz Type II usually paced