3 - ECGs and Bradyarrhythmias Flashcards
What is the protocol for reading an ECG?
- Confirm patients name and ECG date
2. Rate
3. Rhythm
4. Axis
5. P waves
6. Intervals: PR interval, QRS complex, QT interval, ST segment, T waves
- R wave progression
What time interval does each of the following on an ECG represent:
- 1 small box
- 1 large box
Small box: 0.04 seconds
Large box: 0.2 seconds
1 second is represented by 5 large boxes
How do you calculate the rate on an ECG? (assuming speed is 25mm/s)
Regular: 300 ÷ Number of Big squares between R-R
Irregular: Number of QRS complexes on rhythm strip (10 seconds) x 6
Normal is 60-100bpm
How do you work out the rhythm of an ECG?
Use card method to mark position of 3 successive R waves and see if all intervals equal
Can be irregularly irregular or regularly irregular or sinus arrhythmia (p waves but irregular)
What is sinus rhythm?
- All QRS complexes preceded with a P-wave
- Regular rhythm
- Between 60-100bpm
What is sinus arrhythmia?
Slight but regular lengthening and then shortening of RR intervals. All QRS have P waves so sinus node still working
Common in young people, lengthening and shortening corresponds to breathing
What is the difference between AF and atrial flutter?
AF: has no p-waves and is irregularly irregular
Atrial flutter: sawtooth baseline with no discernible p-waves but it is regular
What is the axis on an ECG and what is a normal axis?
Describes the direction of depolarisation across the heart, should spread from 11 to 5 o clock (-30 and +90)
Need to look at JUST LIMB LEADS/ leads I, II, III
Most positive deflection should be in II and most negative should be aVR
How do you work out axis on ECG easily?
Normal: Lead II or I most positive
Left deviation: aVL/Lead I most positive
Right deviation: Lead III most positive
What are the causes of right and left axis deviation?
Right: right ventricular hypertrophy, PE, anterolateral MI, WPW, left posterior fasicle block
(normal in very tall individuals, associated with pulmonary oedema as RVH)
Left: conduction abnormalities, left anterior hemiblock, inferior MI, WPW, LVH
How can you distinguish right and left axis deviation on an ECG?
Right: lead I becomes negative and lead III/aVF become more positive (Lovers Returning)
Left: lead III and II become negative and lead I more positive (Lovers Leaving)
What are the normal time values for the following and where are these intervals on ECG:
- PR interval
- QRS complex
- QT interval
- ST interval
PR: start of P to start of QRS. 0.12-0.2s (3-5 small squares)
QRS: <0.12S
QT: start of QRS to end of T. Should be 0.38-0.42s
ST interval: end of S to start of T
After looking at rate and rhythm on ECG you look at P waves. What are you looking for?
- Are they present?
- Are they followed by a QRS
- Should be upright in II, III, aVF but upside down in aVR
- Flat, flutter or chaotic baseline?
What is the normal PR interval and what can shorten and lengthen this?
3-5 small squares (0.12-0.2 seconds)
Prolonged: Delayed AV conduction e.g heart block
Shortened: fast AV conduction via accessory pathway e.g WPW or SA node in different place
What is a normal QRS complex like and what can cause changes to the QRS complex?
- Width
- Height
- Morphology
Should be <0.12s with Q waves being <0.04s wide and <2mm deep
Prolonged QRS: bundle branch block, metabolic disturbance, ventricular origin
Tall QRS (>5mm in limb leads, >10mm in chest leads): LVH
Pathological Q-Waves: following MI
What are the QRS complexes on this ECG showing?
Delta wave which is common in Wolf Parkinson White Syndrome
Sign that ventricles are being activated earlier than normal from a point distant to the AV node. Early activation spreads slowly across myocardium causing slurred upstroke of QRS
WPW cannot be diagnosed with the delta wave alone. What other ECG abnormality has to be present?
Tachyarrhythmia + Delta Wave
When is a Q wave pathological?
> 25% the size of the R wave that follows it or > 2mm in height and > 40ms in width.
Single Q wave is ok, need to look for Q in whole territory for evidence of previous MI e.g look at all inferior leads
What is wrong with the QRS complexes in this ECG and why might this have occured?
Poor R wave progression
R wave should go from small to big from V1 to V6. Transition of S>R to R>S should be around V3/V4
Poor lead position or previous MI
What is the J point?
Where the S wave joins the ST segment
What is the Osborn wave (J wave)?
Positive deflection of the J point due to hypothermia, SAH or hypercalcaemia
What is a normal ST segment and what is ST elevation/depression?
Should be isoelectric
ST elevation: greater than 1 mm (1 small square) in 2 or more contiguous limb leads or >2mm in 2 or more chest leads.
ST depression: >0.5mm in >2 contiguous leads
What is the cause of ST elevation and ST depression?
Elevation: full thickness myocardial infarction
Depression: myocardial ischaemia
What do T waves represent and what leads are they normally inverted on?
Ventricular repolarisation
Usually inverted in aVR, V1 and V2 and sometimes V3
Abnormal if inverted in I, II, V4-V6
What are the causes of the following:
- Tall T waves (>5mm in limb leads and >10mm in chest leads)
- Inverted T waves
- Biphasic T waves
- Flattened
Tall: hyperkalaemia or STEMI
Inverted: ischaemia, general illness, bundle branch block, PE
Biphasic: Ischaemia and hypokaelaemia
Flattened: hypokalaemia
What is a U wave and what causes these?
> 0.5mm deflection after the T wave usually in V2 or V3
Seen in electrolyte imbalances, hypothermia and secondary to antiarrhythmic therapy (such as digoxin, procainamide or amiodarone)
Seen larger in slower bradycardias
What leads are the most positive in normal cardiac axis, left axis deviation and right axis deviation?
Normal: II
Left: aVL
Right: III
What does ST elevation across all leads represent?
Pericarditis
Saddle shaped
What are some causes of sinus bradycardia?
- IHD
- Thyrotoxicosis
- Hypothermia
- Increased ICP
- Cholestasis
What are some causes of the following:
- ST elevation
- ST depression
- T wave inversion
What are some ECG changes in a PE?
- Sinus tachycardia
- RBBB
- Right axis deviation
- S1Q3T3
What is the Digoxin effect on ECG?
- Down-sloping ST depression
- Inverted T wave in V5-V6
- Any arrhythmia e.g ventricular ectopics and nodal bradycardia
What heart territory do all of the 12 leads of the ECG cover and what vessel supplies them?
How do hyper and hypokalaemia present on ECG?
Hyper
- Tall tenting T waves
- Widened QRS
- Absent P waves
- Sine
Hypo
- Small T waves
- U waves
- Prominent P waves
How do hypo and hypercalcaemia present on ECG?
HypoCa
- Long QT
- Small T waves
HyperCa
- Short QT
What are some continuous ECG monitoring methods that can be used to diagnose paroxysmal arrhythmias that may be missed on a single ECG?
Telemetry: Inpatient, signals watched by staff on screens so if dangerous arrhytmia can help immediately. Used for those at high risk of arrhythmias e.g post STEMI
Exercise ECG: BP also taken whilst doing standardised exercise
Holter Monitor: Worn for 24h for a week whilst going about normal life
Loop recorder: Placed under the skin (e.g Reveal) and record short period before the event, e.g patient has syncope, can press the button when regains consciousness. Good if events happen months apart
Pacemakers and ICDs
How can we split arrhytmias into different categories?
- Bradycardia
- Narrow complex tachycardia
- Wide complex tachycardia
- AF and Atrial flutter
MEMORISE ALGORITHM ON PHOTO
What are some causes of arrhythmias in general?
Cardiac or Non-cardiac
How do patients with arrhythmias present and what questions do you need to ask in the history?
Presentation: palpitations, chest pain, presyncope/syncope, hypotension, pulmonary oedema, asymptomatic
History: take history of palpitations including onset/offset/nature, associated symptoms (e.g chest pain, breathlessness), drug history, family history of cardiac disease or sudden death
How do you classify bradycardic arrhythmias based on the aetiology? (<60bpm)
IMPORTANT FLASHCARD TO UNDERSTAND BRADYCARDIAS
Based on the pacemaker at fault (sinus node or AV node)
Sinus Node: sinus bradycardia, sick sinus syndrome (tachy-brachy), sinus arrest, vasovagal syncope
AV Node: First degree AV block, Second degree AV block (Mobitz I or II), Complete AV block
What are some causes of sinus bradycardia?
- Drugs (b-blockers, amiodarone, digoxin)
- Hypothyroidism
- Hypothermia
- Sleep Apnoea
- Increased intracranial pressure
- Athletic
- Rare: rheumatic fever, viral myocarditis, amyloidosis, haemochromatosis, pericarditis
Most bradycardias cause by sinus node disease are asymptomatic. If they are symptomatic what is needed?
Pacemaker
What are some symptoms of bradycardia?
- Asympyomatic
- Fatigue
- Nausea
- Dizziness
- Syncope
- Chest pain
- Breathless
What is relative vs absolute bradycardia?
Absolute: any heart rate less than 60bpm, can be normal for sleeping athletes
Relative: a heart rate too slow for the haemodynamic state of the patient, doesn’t have to be below 60bpm. (systolic BP<90, HR<40, poor perfusion, poor urine output)
How is symptomatic bradycardia managed acutely? (especially after MI)
- Do ECG and check electrolytes (K+,Mg2+, Ca2+)
- Connect to cardiac monitor/telemetry
3. Address cause e.g correct electrolytes, give glucagon if cause by B-blocker
- If patient has adverse signs give atropine IV 500mcg every 3-5 minutes up to 3mg
- If atropine not working do transcutaneous pacing
What is sick sinus syndrome caused by and what are the symptoms?
Usually due to sinus node fibrosis, often in the elderly. This can cause sinus bradycardias or tachyarrhythmias like AF
Can get tachy brachy syndrome where they alternate between tachy and bradycardic rhythms
Symptoms: syncope, presyncope, light-headedness, palpitations, breathlessness
How is sick sinus syndrome diagnosed and managed?
- VTE prophylaxis is episodes of AF detected
- Permanent pacemaker if symptomatic bradycardia or sinus pauses
- Hard to treat tachy-brachy syndrome as treating one increases the risk of the other
What are some causes of 1st, 2nd and 3rd degree heart block?
1st and 2nd: normal variant, athletes, sick sinus syndrome, IHD especially inferior MI, acute myocarditis, digoxin, beta-blockers
3rd: IHD especially inferior MI, digoxin toxicity, hyperkalaemia, idiopathic fibrosis, congenital, aortic valve calcification, cardiac surgery infiltration by tumours/granulomas/parasites
How does first degree AV block present on ECG and how do you manage it?
PR interval >0.2 seconds with no missed beats
- Check for toxicity if on digoxin
- No treatment needed unless symptoms of dizziness or syncope then cardiac monitoring should be done to identify higher degrees of heart block
How does second degree AV block Mobitz Type I present on ECG and what type of patients may this present in?
Progressive lengthening of the PR interval followed by drop in QRS then pattern resets
Can occur in young fit patients with high vagal tone during the night. Also often after inferior MI
What is another name for Mobitz Type 1 Second degree AV block?
Wenckeback phenomenom
How do we managed Mobitz Type I Seconda Degree Heart block?
Rarely proceeds to complete heart block so no therapy needed
If syncope or diziness do cardiac monitoring for higher degrees of heart block
How does second degree AV block Mobitz Type II present on ECG and how is it managed?
Constant PR interval but then sudden drop of QRS
Can be defined as ratio, e.g 2:1 would be 2 normal for every 1 dropped
Management: risk of progression to complete heart block so permanent pacing needed if drugs excluded
How does 3rd degree complete AV block present on ECG?
No relationship between P and QRS waves as no conduction between atria and ventricles
Patient is very bradycardic and can develop haemodynamic compromise
Can be broad complex escape rhythm (block below the AV node and not well tolerated) or narrow complex escape rhythm (block above AV node, often congenital, well tolerated)
How is 3rd degree AV block managed?
Urgent permanent pacing within 24 hours, unless they are likely to recover normal conduction such as they have had a recent coronary event
What are the main causes of 3rd degree heart block and what medicaions can you administer for this?
- Digoxin toxicity
- Inferior STEMI (often resolves in hours or days)
- Severe hyperkalaemia
- Give calcium chloride for hyperK to stabilise membrane
- If haemodynamically unstable can give atropine 0.5mg up to 3mg
- Can try isoprenaline if atropine not working
What is a junctional rhythm and how does it present on ECG?
Has regular narrow QRS waves but no P waves or P waves hidden in QRS
Due to electrical activation occuring near to or within the AV node rather than the SA node
What does this ECG show?
Intermittent sinus bradycardia on the rhythm strip
Has a tachycardia on other leads so tachy-brady syndrome
Issue at SA node as when AF it is conducted to ventricles
What does this ECG show?
2:1 heart block (Mobitz Type II)
What does this ECG show?
Complete heart block as no relationship with QRS.
Narrow escape rhythm
What does this ECG show?
Complete AV block with broad escape rhythm
More dangerous than narrow escape rhythm as whole AV node not working!!!!
Shows as a bundle branch block
How do pacemakers show on an ECG?
One pacing wire in ventricle: one spike followed by broad QRS
Two pacing wires: will have spike then p wave and spike followed with broad QRS
Where do you place the ECG leads on a patient?
V7 placed at posterior axillary line
Make sure you clean the skin with wipe and shave if hairy before placing on leads
How does RBBB on ECG appear and what are the causes of this?
Due to right ventricle being activated by the left ventricle
- Prolonged QRS
- M Pattern in V1 and V1 positive
- Bunny ears
- Wide slurred S wave in V6
- T wave inversion V1-V3
- Normal axis
Causes: normal variant, RVH, cor pulmonale, PE
How does LBBB appear on ECG and what are the causes of this?
Causes: if new onset STEMI, HTN, cardiomyopathy, idiopathic fibrosis, aortic stenosis
- Prolong QRS
- V1 QRS negative (look at chest leads to see when positive)
- M pattern in V5
- Dominant S (W) in V1
- Left axis deviation
Cannot comment on ST segment or T waves if LBBB
What is bifasicular block and how does it show on ECG?
Conduction block between AV node and two of the three fasicles
RBBB + left or right axis deviation
What does R wave progression mean and what can late R wave transition indicate?
Transition of more positive R than S should happen in V3
If late:
- Prior anterosepctal MI so infarct
- Inaccurate lead placement
- LVH
- Dilated cardiomyopathy
What is this ECG abnormality?
Looks like ST elevation but it is just high take off
What is the QTc interval?
QT interval corrected for heart rate
What do very tall R waves indicate?
LVH
What are some causes of LVH?
- Hypertension
- Aortic stenosis
- Hypertrophic cardiomyopathy
What do small alternating R waves on an ECG indicate?
Pericardial effusion as the heart is swinging in the sac
What is the normal QT interval and what are some causes of long QT and short QT?
<0.44s or 2 large squares
Long: MI, LVH, HypoK, HypoMg, HypoCa, DKA, Drugs, RBBB/LBBB
Short: HyperCa
What is the treatment algorithm for tachycardias?
