ECG Flashcards
What are the axis of the ECG leads?
- Axis refers to the overall electrical direction within the heart.
- Electricity moving towards an electrode is POSITIVE
- Electricity moving away from an electrode is NEGATIVE
- If there is a change in the overall direction of the energy, the axis will be described as deviated- left, or right
- Look at leads I and II. If both are positive, the axis is normal
What do the different areas of the ECG mean?
How to calculate rate in ECG?
What is a normal PR interval?
Upright P wave=sinus
What is a normal QRS complex?
What is a normal ST segment?
Depression=angina
What is a normal T wave?
What is a normal QT interval?
Long QT=danger for arrhythmia
How do you read an ECG?
- Is the rhythm regular or irregular?
- Is the heart rate fast or slow?
- Is the axis in Lead I & II positive?
- Ratio; Is there one ‘p’ wave to each QRS?
- Is there any ST elevation or depression?
- Check intervals (PR, QRS, QT)
Appearance of rhythms above vs below AV node
What does a normal sinus rhythm look like?
Normal rate = 60-100
What does atrial fibrillation look like?
What does atrial flutter look like?
What does heart block look like?
What does tachycardia look like?
What does ischaemia look like?
What does a MI look like?
STEMI vs NSTEMI
What are cardiac arrhythmias?
- An abnormality of the cardiac rhythm is called a cardiac arrhythmia.
- Arrhythmias may cause sudden death, syncope, heart failure, chest pain, dizziness, palpitations or no symptoms at all.
- There are two main types of arrhythmia:
• Bradycardia: the heart rate is slow (<60b.p.m. during the day or
<50b.p.m. at night).
• Tachycardia: the heart rate is fast (>100b.p.m.). - Tachycardias are more symptomatic when the arrhythmia is
fast and sustained. - Tachycardias are subdivided into:
• supraventricular tachycardias (SVT), which arise from the atrium
or the AV junction
• ventricular tachycardias, which arise from the ventricles. - Some arrhythmias occur in patients with apparently normal
hearts or originate from diseased tissue (scar) because of
underlying structural heart disease. - When myocardial function is poor, arrhythmias are more
symptomatic and are potentially life-threatening
What are sinus arrhythmias?
- Fluctuations of autonomic tone result in phasic changes of
the sinus discharge rate. - During inspiration, parasympathetic tone falls, and the heart
rate quickens; on expiration, the heart rate falls. - This variation is normal, particularly in children and young adults.
- Typically, sinus arrhythmia results in predictable irregularities of the pulse
What are the mechanisms for arrhythmia production?
What is accelerated automacity?
What is triggered activity?
- Is always preceded by AP
- Caused by afterdepolarizations
- 2 types:
• early afterdepolarizations (EADs)
• delayed afterdepolarizations (DADs) - EADs may appear either at the end of the action potential plateau
(phase 2) or approximately midway through repolarization (phase 3)→ prolonged QT, Torsade’s de pointes - DADs occur near the very end of repolarization or just after full repolarization (phase 4)→ Ectopic beat, VT
What is the aetiology of triggered activities and what are the consequences?
Causes of EADs:
- Slow HR
- Prolonged action potentials.
- Certain antiarrhythmic drugs like quinidine which prolongs the
action potential.
Causes of DADs:
- Increased serum Calcium Activate a 3Na+/Ca2+ exchanger
- Increased Adrenaline
- Drug Toxicity like Digoxin
- Myocardial Infarction
What is re-entry?
- Requirements for re-entry
- Two possible routes for electrical impulse to flow down
• Fast-pathway →Long RP
• Slow-pathway →Short RP - Impulse flows down one pathway, back up the other, and gets caught in a loop.
- Slower pathway/route can be caused by:
1. Central area of block e.g. scar tissue, refractory cells
2. Area/path of variable blocking e.g. dead myocyte, myocytes with
different RP/conduction speed
What is sinus bradycardia and its causes?
Sinus bradycardia
- Sinus bradycardia is due either to extrinsic factors that influence a relatively normal sinus node, or to intrinsic sinus node disease.
- The mechanism can be acute and reversible, or chronic and degenerative.
- Common extrinsic causes:
• hypothermia, hypothyroidism, cholestatic jaundice and raised intracranial pressure
• drug therapy with beta-blockers, digitalis and other antiarrhythmic drugs
• neurally mediated syndromes (carotid sinus syndrome, vasovagal attacks) - Common intrinsic causes:
• acute ischaemia and infarction of the sinus node (as a complication of acute myocardial infarction)
• chronic degenerative changes, such as fibrosis of the atrium and sinus node (sick sinus syndrome)
What is heart block?
- Block in either the AV node or the His bundle results in AV block
- Block lower in the conduction system produces bundle
branch block. - 3 forms:
1. First-degree
2. Second-degree
3. Third-degree
What is first degree heart block?
What is second degree heart block?
Due to a block at an infranodal level, such as the His bundle. Pacing usually indicated.
Type 1 vs 2 second degree heart block
What is third degree heart block?
What is the aetiology of complete block?
- Congenital: transposition of great vessels
- Idiopathic fibrosis: Lev’s disease (older people), Lenegre’s disease (younger people)
- IHD: acute MI, ischaemic cardiomyopathy
- Non-IHD: Calcific aortic stenosis, Idiopathic dilated cardiomyopathy, Infiltrations (e.g. amyloidosis, sarcoidosis, neoplasia)
- Cardiac surgery: Following aortic valve replacement, CABG, VSD repair
- Iatrogenic: Radiofrequency AV node ablation and pacemaker implantation
- Drug-induced: Digoxin, beta-blockers, amiodarone, non-dihydropyridine calcium- channel blockers
- Infection: Endocarditis, lyme disease, chagas’ disease
- Autoimmune: SLE, RA
- Neuromuscular disease: Duchenne muscular dystrophy
What is the pathophysiology of complete block?
- Complete heart block occurs when there is complete dissociation
between atrial and ventricular activity - P waves and QRS complexes occur independently of one another
- Ventricular contractions are maintained by a spontaneous escape
rhythm originating below the site of the block either from:
• His bundle: narrow complex QRS (<0.12 s), rate 50–60 bpm, if due to transient ischaemia, IV atropine (no need for pacing), if chronic then pacing
• His-Purkinje system: broad QRS complex (>0.12 s), rate <40 bpm, associated with dizziness and blackouts (Stokes–Adams attacks), Lev’s disease in elderly and Lenegre’s disease in younger pt., permanent pacemaker indicated
What is bundle branch block?
What are the narrow complex tachycardias?
What is atrioventricular nodal re-entrant tachycardia?
Anterograde re-entry; from atrium to ventricle. Red is delta wave
AVRT vs AVNRT
What is atrial flutter
What is atrial fibrillation?
Atrial fibrillation vs flutter
- Definition:
• Flutter: Regular, rapid atrial contractions at a rate of 250-350
beats per minute.
• Fibrillation: Chaotic, irregular atrial contractions at rates
exceeding 300 beats per minute - ECG:
• Flutter: Sawtooth (F waves), typically in a 2:1, 3:1, or 4:1 conduction ratio.
• Fibrillation: ƒ waves, no P waves, irregularly irregular rhythm. - Symptoms:
• Flutter: palpitations, chest discomfort, and fatigue.
• Fibrillation: palpitations, dyspnoea, dizziness, and fatigue. - Complications:
• Flutter: Less commonly associated with embolic events compared to atrial fibrillation.
• Fibrillation: Higher risk of embolic events and stroke due to blood stasis in the atria. - Management:
• Flutter: rate control medications or rhythm control such as ablation.
• Fibrillation: rate control, anticoagulation, and rhythm control based on patient characteristics. - Prognosis:
• Flutter: Generally considered less severe compared to atrial
fibrillation in terms of thromboembolic risk.
• Fibrillation: Higher risk of complications like stroke and heart
failure compared to atrial flutter.
What part of an ECG refers to which part of conduction?
