Lecture 13 Flashcards
How do you determine normal sinus rhythm?
Look at lead 2
- is rhythm regular
- regular HR (60-100 bpm)
- p waves present and upright, followed by QRS complex
- is PR interval normal
- is QRS width normal
- is corrected QT interval normal
What is an atrioventricular conduction block?
Delay/failure of conduction of impulses from atria to ventricles via AVN and Bundle of His
What are the 3 types of atrioventricular heart block?
- first degree heart block
- second degree heart block (Mobitz type1/2)
- third degree heart block
What are some causes of heart block?
- degeneration of electrical conducting system with age (sclerosis/fibrosis)
- medications
- valvular heart disease
- acute myocardial ischaemia (blood flow to heart is disrupted)
What is sclerosis?
Abnormal hardening of body tissue
What is a first degree AV block?
Conduction is slowed without skipped beats
- all p waves are followed by QRS complexes
- PR interval is longer than normal (>0.2s)
What is second degree AV blockand the two types?
Mobitz type 1/Wenkebach
- successively longer PR intervals until one QRS is dropped (electrical signal not conducted through to ventricles)
- cycle starts again
Mobitz type 2
-PR intervals do not lengthen
-sudden drop of QRS complex with no prior changes to PR
-atrial rhythm is regular (p waves)
-ventricular rhythm is irregular
HIGH RISK PROGRESSION TO COMPLETE HEART BLOCK
Which block is high risk to progress to complete heart block?
Mobitz type 2 (second degree)
What is a third degree AV block?
Atria and ventricles are depolarising independently (complete failure of AV conduction)
-ventricular pacemaker takes over which is slow (20-40 bpm)
-too slow to maintain blood pressure
-wide QRS complex
URGENT PACEMAKER REQUIRED
-random p waves being fired off without QRS following
What heart block requires a pacemaker urgently?
Third degree heart block
What is a bundle branch block?
Delayed conduction within bundle branches
(LBBB/RBBB)
-p waves and PR intervals are normal
-wide, notched QRS complex because ventricular depolarisation takes longer
What is a symbol of heart disease?
LBBB
left bundle branch block
What is arrythmia?
Abnormal rhythms from the heart
What are the types of arrythmia?
Atria (above ventricles and therefore called SUPRAVENTRICULAR arrythmia)
- SAN
- atrium
- AVN
Ventricular arrythmia
Difference between supraventricular and ventricular arrythmias:
Supraventricular -normal QRS complex -HR is altered Ventricular -wide/bizarre QRS complexes (ectopic beats)
What is an ectopic beat?
When a beat comes too early/there is an extra beat
-beat is out of place
=palpitations
What is atrial fibrillation?
A type of supraventricular arrythmia
Atria quiver but you still get blood into ventricles
-arises from many atrial foci (fire in an uncoordinated manner)
-no p waves
-wavy baseline (atria quiver- still get blood to ventricles)
-irregular R-R intervals
-impulses reach AVN at rapid irregular rate- not all conducted
-normal QRS as when conducted, ventricles depolarise normally
What are ectopic foci?
Abnormal pacemaker sites in the heart which display automacity (activity normally supressed by SAN)
-in both atria and ventricles
What are the atrial fibrillation variations?
SLOW
FAST
Normal rate
Coarse (>0.5mm) vs Fine fibrillation (<0.5mm)
What is tachy brady syndrome?
Sometimes the heart is tachycardiac and then bradycardic
Whats an issure with course fibrillation?
It may be mistaken for p waves
What are the haemodynamic effects of atrial fibrillation?
- atria quiver
- ventricles contract normally
- HR and pulse are IRREGULARLY IRREGULAR
- loss of atrial contraction leads to increased blood stasis, especially in left atria
What does blood stasis in the atria cause?
Flow and velocity reduced leading to small clots in LA therefore could lead to ischaemic stroke
What are premature ventricular ectopic beats?
PVC’s
Impulse does not spread via fast His-Purkinje system
-ectopic focus in ventricles leading to slower depolarisation of ventricles = Wider QRS
-premature as it occurs earlier than would be expected for next sinus impulse
-may cause palpitations without haemodynamic consequences
What is ventricular tachycardia?
Run of >3 consequetive PVC’s
- dangerous requiring urgent treatment
- high risk of developing into ventricular fibrillation
What is ventricular fibrillation?
- abnormal fast ventricular depolarisation
- impulses from numerous ectopic sites in ventricle
- no coordinated contraction
- ventricles quiver
- no cardiac output so if sustained it lead to CARDIAC ARREST=MEDICAL EMERGENCY
What does coronary artery narrowing/occlusion lead to?
Ischaemia/infarction of area supplied by that artery
can be viewed by leads facing the affected areas
What is released when myocytes die?
Troponin
Released in MI due to cardiac muscle necrosis= STEMI/NSTEMI
What is myocardial ischaemia?
Lack of oxygen, but no muscle necrosis
-blood tests negative for cardiac troponins
What is myocardial infarction?
Muscle necrosis so blood tests will be positive for cardiac troponins
What is a STEMI?
ST segment elevation myocardial infarction
- complete occlusion of coronary artery
- full thickness of myocardium involved
- ST elevation (cause unknown) but is the earliest sign of a STEMI
How does scar tissue lead to pathologic Q waves?
Following STEMI pathological Q waves develop
No electrcial activity in dead tissue
What is the heart rate described as in atrial fibrillation?
Irregularly irregular
Why does atrial fibrillation lead to ischaemic stroke?
Loss of atrial contraction leads to increased blood stasis.
Stasis most evident in left atrium
=leading to small clots in LA
=ischaemic stroke
WHy learn about premature ventricular ectopics?
Sustained series can lead to ventricular tachycardia and then ventricular fibrillation
Will troponin be positive in ischaemia?
No, because ischaemia is different from infarction. There is lack of oxygen but no muscle necrosis, so no dead cardiomyocytes to release troponin
Where are normal Q waves seen in an ECG?
Small Q waves: LATERAL leads: 1 and aVL, V5-V6
Deeper Q waves: leads 3, aVR
In what leads should you not see a Q wave?
Leads V1-V3
What may lead to a Q wave in V3 lead, and what else may you see?
Pulmonary embolism
- S waves in lead 1
- inverted T wave in lead 3
What are pathological Q waves?
> 1 small square WIDE
2 small squares DEEP (except leads 3 and aVR)
-depth more than 1/4 the height of the susequent R wave
What is another name for severe ischaemia?
Unstable angina
Which 2 diseases have the same ECG changes?
Unstable angina and NSTEMI
What is the difference between a NSTEMI and unstable angina and how do you differentiate them?
UA: an acute coronary syndrome. Angina at rest, increasing in frequency, longer in duration
NSTEMI: actual cardiac muscle damage NOT through entire wall (sub-endocardial)
Blood test for myocyte necrosis: troponin
What are the ECG changes in NSTEMI and unstable angina?
ST segment depression
T wave inversion
In which leads are T waves normally not upright?
V1 and aVR
In what leads do T wave inversions occur?
In leads consistent with anatomical regions perfused by a specific coronary artery
e.g. inferior wall of heart supplied by right coronary artery, via posterior descending artery, atheroslcerosis here will lead to changes in leads facing inferior aspect of heart (leads 2,3 and aVF)
What happens to an ECG during stable angina?
ST depression during exercise due to stable atherosclerotic plaque causing fixed narrowing of coronary artery
-ECG changes will reverse at rest
What are the tests to see if a patient has stable angina?
Exercise stress test (treadmill)
Dobutamine stress test (chemically induced)
What are the signs and symptoms of someone with hypokalaemia?
- muscle weakness (can’t repolarise as fast)
- respiration depression
- ascending paralysis
- palpitations
- cardiac arrest
- arrythmias
- myocardial hyperexcitability
What is the ranges for moderate/severe hypokalaemia?
Moderate: <3 mmol/L
Severe: <2.5 mmol/L
What do you see in an ECG of someone who has hypokalaemia (low potassium outside the cells)?
-peaked P waves
-T wave flatenning/inversion
-U waves
Takes longer for repolarisation due to inactivation of K+ channels
What is hyperkalaemia?
> 5mmol/L of potassium
What are the pathophysiological effects of hyperkalaemia?
-resting membrane potential becomes less negative
-causes some voltage gated Na channels to be inactivated
-heart becomes less excitable
-conduction problems can occur
Lead to:
-generalised muscle weakness
-respiratory depression
-ascending paralysis
-palpitations/arrythmia/cardiac arrest
What do you see in an ECG of someone who has hyperkalaemia?
- tall tented t waves
- loss of p wave as you lose atrial depolarisation
- widening of QRS
- QRS continues to widen
