L13: Interpreting ECGs, when things go wrong... Flashcards
What does normal sinus rhythm look like on ECG?
Lead 2 rhythm strip
- Regular rhythm
- Heart rate 60-100bpm
- P waves present
- P waves normal and upright
- PR interval normal (3-5 little squares)
- QRS complex follow P wave
- QRS normal (3 small boxes)
- QT interval corrected prolonged if >44small boxes
What do we mean by atrioventricular conduction block?
Delay/ distrubtion of signals from atria to ventricles
What are the different types of AV conduction block?
Three types
- First degree
- Second degree –> Mobitz Type 1 and 2
- Third degree
What causes heart block?
Degeneration with age
Acute myocardial ischemia
Medication
Valvular heart disease
What is first degree heart block?
Conduction is slowed without skipping a beat
Prolonged PR interval (>0.20s) but always followed by QRS complex
What is second degree heart block?
Two types
Mobitz Type 1 (Wenkebach)
- Sucessively prolonged PR interval followed by sudden drop in QRS complex
- Electrical signal not conducted through ventricles
Mobitz Type 2
- PR interval always same normal length (0.12-0.20s) sudden drop in QRS complex
- Atrial rhythm is regular
- Ventricle rhythm is irregular
What is third degree heart block?
AKA complete heart block
Atria and ventricles depolarise independently
Complete failure of AV conduction
Ventricle pacemaker takes over–> escape rhythm–> slow 20-40bpm
Too slow to maintain BP
Pacemaker required
No evidence of atrial impulse getting to ventricles
What is bundle branch block?
Delayed conduction in the bundle branches
Can be right or left
Wider QRS complex–> ventricle depolarisation takes longer
What are the different types of arrythmias that are possible?
Atria–> above the ventricles so are called supraventricular arrythmias
Can be in sinus node, atrium itself or AV node
Normal narrow QRS complex as depolarisation stays the same across the ventricle, usually increased HR
Ventricles–> Ventricular arrythmias
Wider QRS complex as ectopic pacemaker cells fire randomly –> risk of tipping into ventricular fibrillation
What is atrial fibrillation?
Multiple areas in the atria fire at the same time–> multiple foci
Rapid chaotic impulses
Reach AV node but not all go through–> irregular rate
No P waves, just wavy or flat baseline–> depends on number of foci
Atria ‘quiver’ but don’t contract
When conducted ventricles contract normally so normal QRS complex
What does atrial fibrillation look like on ECG?
Slow--> ventricle response <60bpm Fast--> ventricle response >100bpm Normal--> 61-99bpm Coarse fibrillation with amplitude >0.5mm Fine fibrillation with amplitude <0.5mm Irregularly iregular HR and pulse
What does loss of contraction in atrial fibrillation lead to?
Increase blood stasis–> pooling–> blood clots
Stasis most evident in LA–> risk of stroke
What is premature ventricular ectopic beats (contraction) PVCs?
Ectopic focus in ventricle muscles
Impulse does not spread via fast His- Purkinje fibres
Slower depolaristaion –> Wider QRS complex
Premature–> earlier than expected for next sinus impulse
Assymptomatic or can feel palpitation with out haemodynamic consequence
Risk–> develop into ventricular tachycardia
What is ventricular tachycardia?
Run of more then 3 consecutive premature ventricular ectopic beats (contractions)
Complex tachycardia
Dangerous rhythm require urgent treatment
High risk progression to ventricular fibrillation
What is ventricular fibrillation?
Abnormal, chaotic fast ventricular depolarisation
Ectopic sites
No coordinated contraction
Ventricle ‘quiver’ but no contraction
No cardiac output if sustained–> cardiac arrest
What is the general classification of arrythmias?
Brachycardia (slows heart down) or tachycardia (speeds heart up)
AF can fall into either category
What are the ECG changes in ischaemia and myocardial infarction?
Depends on location of occlusion
And area supplied by that BV
What is ischemia?
Lack of O2 but no necrosis
Blood test negative for markers of necrosis
What is myocardial infarction?
Occlusion of blood supply
Results in area of necrosis
Markers of necrosis will be present
What is STEMI?
ST elevated myocardial infarction Occlusion of coronary artery Full thickness of myocardium involved ST elevation (reason unknown) Behaves as if current coming towards electrode resulting in upward deflection (abnormal) Indication for intervention
What is the ECG like a few weeks after STEMI?
Fibrous tissue–> doesn’t conduct electrical impulse
ST and T wave normal
Q wave persists –> remains deep
What does the pathological deep Q wave persist after STEMI?
Myocardium can’t conduct electricity–> fibrous
Living cells needed for depolarisation
ECG looks ‘through’ dead tissue and picks up signal from the other side of the heart
(Q waves not always pathological–> normal L-R depolarisation)
Are all Q waves a sign of old infarct or depolarisation of septum?
Pulmonary embolism can causes Q wave in Lead III Along with: --> S wave in Lead I --> Q wave Lead III --> Inverted T wave in Lead III
What are the difference between non-STEMI and ischemia?
No myocardial damage in angina (ischaemia)
Non-STEMI–> acute myocardial damage but not full thickness
Differentiated by blood test for necrosis–> troponin
What changes occur in non-STEMI and ischemia?
Same ECG for Non-STEMI and Ishcemia
ST segment depression and T wave inversion
Abnormal current traversing damage tissue goes away from the electrode
How can you tell T wave inversion is pathological?
Normally upright in all ECG Leads (except aVR and V1)
Inversion usually symmetrical and deep
T wave inversion is consistent with anatomical region supplied by the occluded coronary artery
e.g. occlusion in RCA–> T wave inversion in Leads II, III, and aVF
What ECG changes are seen in stable angina?
ST depression during exercise
Changes go away with rest
Exercise: treadmill (exercise stress test) or chemically induced (Dobutamine stress test)
What is hypokalaemia? What are the signs and symptoms?
Potassium level <3.5mmol/L Moderate <3.0mmol/L Severe <2.5mmol/L Decreased extracellular K+--> myocardial hyperexcitability Generalised muscle weakness Respiratory depression Ascending paralysis Ileus, constipation Palpitations, arrhythmia and cardiac arrest
What does an ECG of hypokalaemia look like?
Peaked P waves
T waves flattening and inversion
U waves–> downwards deflection on ECG after QRS complex
What is hyperkalaemia? What happens? What are the signs and symptoms?
K+ above >5mmol/L Problems arise at 6.5- 7mmol/L Resting membrane potential becomes less negative Some Na+ channels inactivated Heart becomes less excitable Conduction problems occur Generalise muscle weakness Respiratory depression Ascending paralysis Palpitations, Arrhythmia and cardiac arrest
What does an ECG of someone with hyperkalaemia look like?
5.5-6.5–> Tall tented T waves
6.5-7.5–> Loss of P waves
7.5-8.5–> Widening QRS complex–> not conducting normally through the ventricles
>8.5–> QRS continues to widen, sine wave appearance–> not depolarising and repolarising properly
