ECGs + arrhythmias Flashcards
What does one small square represent?
0.04s
What does one large square represent?
0.2s
How many large squares is 1 second?
5
What are the lateral leads?
I, aVL, V5, V6
What are the inferior leads?
II, III, aVF
What are the anterior leads?
V2, V3, V4
Which is the septal lead?
V1
What vessels correspond to the lateral, anterior and inferior leads?
- Lateral - circumflex artery
- Anterior - LAD artery
- Inferior - RCA
What is a structure for assessing ECGs?
- Name, DOB, clinical context
- Rate (60-100bpm)
- Rhythm strip (regular or irregular and PQ relationship)
- (Axis)
- Parameters - PR, QRS, cQTC
- Morphology:
- Broad/narrow
- BBB?
- ST
- T waves
How can you calculate the rate?
- 300/larges squares between R waves
- QRS complexes in 10 seconds x 6 (useful if irregular rhythm)
What happens in sinus rhythm?
The action potential starts in the sinus node
How do you assess rhythm?
- Assess atrial rhythm:
- See if sinus rhythm…- Is there a +ve P wave in lead II
- Is there a -ve P wave in aVR
- Assess ventricular rhythm
- Look as QRS…- What’s the interval between
- Is it regular/irregular
What leads do you look at to assess axis? When indicates normal axis?
- I and aVF
- Both should be positive
What is the normal cardiac axis?
-30 - 90 degrees
P wave:
1. What does it represent?
2. What do you check?
- Atrial depolarisation
- Present? Height -> tall in RA enlargement
PR interval:
1. What does it represent?
2. What is the normal duration?
3. What do you check?
- Atrial depolarisation and contraction
- 3-5 small squares
- Length -> prolonged = heart block, short = pre-excitation syndrome
Q wave:
1. What do you check?
- Depth -> >1 small square = abnormal. Can be a sign of a previous MI
QRS:
1. What does it represent?
2. What is the normal duration?
3. What do you check?
4. What is indicated by wide QRS complexes?
- Ventricular depolarisation
- 3 small squares
- Width, height -> V hypertrophy
- BBB:
- Look in lead I
- Think about using indicators in a car
- If QRS is -ve = LBBB (indicator down to go L)
- If QRS +ve = RBBB (indicator up to go R)
ST:
1. What does it represent?
2. What do you check for?
- No electrical activity
- Elevation/depression
QT interval:
1. What do you check?
- Width -> if less than 1/2 R-R = normal
T wave:
1. What does it represent?
2. What do you check?
3. What is a key cause of abnormal T waves?
- Ventricular repolarisation
- Where they are +ve/-ve (normally -ve in V1 and aVR), height -> tall in hyperkalemia
- Ischaemia
What are the shockable rhythms?
- VF
- VT
How can VT be classified?
- Narrow complex tachycardia = tachycardia with narrow QRS complexes (<0.12s)
- Broad complex tachycardia = tachycardia with broad QRS complexes (>0.12s)
What’s the management of VT if life threatening features?
- Synchronised DC cardio version under sedation or GA
- IV amiodarone if initial shocks are unsuccessful
What features indicate a pt with tachy/bradycardia is unstable?
- Shock
- LOC
- Heart muscle ischaemia (chest pain)
- Shock/severe HF
Give 4 differentials for narrow complex tachycardia?
- Sinus tachycardia
- SVT
- AF
- Atrial flutter
What can cause sinus tachycardia?What is the management?
- ST occurs in response to an underlying cause e.g. sepsis, pain
- Manage underlying cause
What are the common causes AF?
SMITH:
- Sepsis
- Mitral valve pathology
- Ischaemic heart disease
- Thyrotoxicosis
- Hypertension
What happens in AF?
- Disorganised electrical activity in the atria -> uncoordinated, rapid, irregular atrial contraction
- Chaotic electrical activity passes through to the ventricles -> irregular ventricular contraction
What are the effects of AF?
- Irregularly irregular ventricular contractions
- Tachycardia
- HF due to impaired filling of the ventricle
- Increased risk of stroke
Appearance of AF on ECG?
- Absent P waves
- Narrow QRS complexes
- Irregularly irregular QRS complexes
What causes atrial flutter?
- An extra electrical pathway in either atrium -> re-entrant rhythm
- The signal goes round and round the atrium without interruption -> atrial rate = 300bpm
- The signal does not enter the ventricles every lap which results in two atrial contractions for every one ventricular contraction -> ventricular rate = 150bpm
What is the management of atrial flutter?
- Anticoagulation based on CHA2DS-VASC
- Radio-frequency ablation of re-entrant rhythm can be permanent solution
Appearance of atrial flutter on ECG? What is the atrial rate?
- Regular QRS complexes
- Sawtooth pattern (2 p wave per 1 QRS)
- Rate 300bpm
What is the management of atrial flutter?
- Anticoagulation based on CHA2DS-VASc
- Radio-frequency ablation can be permanent solution
What is SVT?
Supra ventricular tachycardia
Appearance of SVT on ECG?
- Regular QRS complexes
- QRS followed by T wave then QRS etc.
What’s the most common type of SVT? What does this entail?
- Atrioventricular re-entrant tachycardia (aka Wolf-Parkinson White)
- Accessory pathway meaning electrical signals re-enter AV node -> increased ventricular contractions
How can you spot an accessory pathway on ECG (e.g. in WPW)
- Slurred upstroke in QRS
- Also called delta wave
- Will also be a short PR
Stepwise management of SVT in stable patients?
- Valsalva manoeuvre (blow hard into a syringe)
- Carotid sinus massage
- Adenosine
How does adenosine work? How is it given? What do you need to warn patients about?
- Interrupts the AV node/accessory pathways and resets sinus rhythm
- Given as a rapid IV bolus
- Causes brief asystole which can be scary for patients
Management of SVT in unstable patients?
Synchronised cardio version with a defib +/- amiodarone if they need help establishing sinus rhythm
Give 4 differentials for broad complex tachycardia
- Ventricular fibrillation
- Polymorphic VT (aka torsades de pointes)
- AF with BBB
- SVT with BBB
What causes tornadoes de pointes?
- Prolonged QT
- Waiting a long time for repolarisation can result in spontaneous depolarisation in some muscle cells
- These abnormal depolarisations are called afterdepolarisations
- They can spread throughout the ventricles and cause a contraction before repolarisation
- When this leads to recurrent contractions it is called torsades de pointes
What causes prolonged QT?
- Long QT syndrome (inherited condition)
- Meds - antipsychotics, citalopram, flecanide, amiodarone, macrolide abx
- Electrolyte imbalances - hypokalaemia, hypomagnesaemia, hypocalcaemia
What can tornadoes de pointes lead to?
Will either terminate spontaneously and revert to sinus rhythm or progress to ventricular tachycardia. Ventricular tachycardia can lead to cardiac arrest
What’s the management of prolonged QT?
- Stop meds affecting QT
- Correct electrolyte disturbances
- Beta blockers (not sotalol)
- Pacemakers/implantable cardioverter defibrillator
What’s the management of torsades de pointes?
- Correct underlying cause (of prolonged QT)
- Magnesium infusion (even if normal serum Mg)
- Defibrillation in VT occurs
What are ventricular ectopics?
Premature ventricular beats caused by random electrical discharges outside the atria
How do ventricular ectopics appear on ECG?
Isolated, random, abnormal, broad QRS complexes on an otherwise normal ECG
What is bigeminy?
Refers to when every other beat is a ventricular ectopic
Give 3 broad causes of bradycardia?
- Meds (BB)
- Heart block
- Sick sinus syndrome
What happens in heart block?
Impaired electrical conduction between atria and ventricles
What happens in 1st degrees heart block? How does this look on ECG? Presentation and management?
- Delayed conduction through AV node
- PR >0.2s (5 small squares/1 big square)
- P followed by QRS
- Commonly asymptomatic and no treatment required
What happens in 2nd degree heart block?
Some atrial impulses do not make it through AV node
What are two types of 2nd degree heart block? Include the management?
- Mobitz 1: progressive prolongation of PR until a dropped beat occurs. Rx = usually no tx required
- Mobitz 2: PR constant but P wave often not followed by QRS. Rx = usually need pacing
How does 3rd degree heart block look on ECG? What is it also called? What is the management?
- No observable relationship between P and QRS
- Aka complete heart blood
- PPM (permanent pacemaker)
What is sick sinus syndrome?
Encompasses conditions that cause SAN dysfunction
What often causes sick sinus syndrome?
Idiopathic degenerative fibrosis of the SAN
What is asystole?
The absence of electrical activity in the heart (resulting in cardiac arrest)
What increases the risk of asystole?
- Mobitz type 2
- Third-degree HB (complete heart block)
- Previous asystole
- Ventricular pauses longer than 3 seconds
Bradycardia: What is the management of unstable patients and those at risk of asystole?
- IV atropine (first line)
- Inotropes (isoprenaline/adrenaline)
- Temporary cardiac pacing
- Permanent pacemaker
What are options for temporary cardiac pacing?
- Transcutaneous pacing - using pads on the pts chest
- Transvenous pacing - using a catheter through the venous system and simulating the heart directly
