ECG Abnormalities Flashcards
Where can electrical rhythms arise from?
SA node,
atrium,
AV node (= supraventricular rhythms),
ventricles (= ventricular rhythms)
When a normal QRS complex is present, what does this tell you?
Normal ventricular depolarisation
When electrical rhythm originates from the ventricles what change can be seen on an ECG?
Wide QRS complexes (>3 small boxes) –
rhythms from diff loci will have diff shapes
What is chaotic atrial depolarisation and how does it appear on an ECG?
due to multi atrial foci = no P waves = wavy baseline
impulses arrive at AV, only some conducted, ventricles depolarise/contract normally
What is ‘Heart Block’ and its common causes?
Delay/failure of conduction of impulses from atrium to ventricles via AV node and bundle of his
causes = acute MI, degenerative changes
What is first degree heart block?
Normal P wave, but slow conduction at AVN/bundle of His
= prolonged PR interval, QRS normal
What is second degree heart block type 1?
Mobitz type 1 = progressive lengthening of the PR interval, until 1 P wave is not conducted
What is second degree heart block type 2?
Mobitz type 2 = PR interval normal, but sudden non-conduction of QRS
What is third degree heart block?
SAN normal but impulses not conducted to ventricle = ventricular pacemaker takes over = ventricular escape rhythm = wide QRS, no relationship between P waves and QRS = random placement
What is a ventricular ectopic beat?
Ectopic foci in ventricles = abnormal conduction pathway = slower depolarisation = wider QRS
What is ventricular tachycardia and how does it appear on an ECG?
VT = 1 ectopic foci that has caused >3 consecutive ventricle depolarisations = risk of VF
What is ventricular fibrillation and how does it appear on an ECG?
VF = numerous ectopic foci = abnormal/chaotic/fast ventricular depolarisation = no co-ordinated contraction = no CO = cardiac arrest
What is the diff between ventricular tachycardia and fibrillation?
T = 1 ectopic foci, still have CO. F = numerous ectopic sites, no CO
What tissue is most at risk due to reduced myocardial perfusion from coronary atherosclerosis?
Sub endocardial muscle – due to being the furthest away from the blood supply on the epicardial surface
What is STEMI and when is it seen?
ST segment elevation myocardial infarction = complete occlusion = muscle injury extends full thickness from endocardium to epicardium = abnormal current during depolarisation
How does acute STEMI present on an ECG?
ST elevation in leads facing MI, which merges with tall broad T waves
What are the persistent changes that can be seen on an ECG due to MI?
Q waves develop = muscle necrosis = window is now open for the electrode to measure the Q wave produced from the septal L to R depolarisation, ST elevation still present
What does hyperkalaemia do to the RMP?
RMP less –ve (more depolarised)
What does hypokalaemia do to the RMP?
RMP more –ve (hyper polarised)
How does hyperkalaemia present on an ECG?
RMP less –ve = inactivates some Na+ channels = heart becomes less excitable = conduction problems.
High T wave –> prolonged PR interval, depressed ST –> atrial standstill, intraventricular block, abesent p wave –> VF
How does hypokalaemia present on an ECG?
Low T wave, high U wave, low ST segment = each new feature added with lowering potassium
What is the cardiac axis?
Average direction of spread of the ventricular depolarisation = usually downward and to the left: -30 to +90 degrees
What is left axis deviation?
Overall direction of ventricular depolarisation = upward and to the left: associated with = conduction block of anterior branch of left bundle, inferior MI, LV hypertrophy
What is right axis deviation?
Overall direction of ventricular depolarisation = downwards and to the right: associated with RV hypertrophy
How should you report an ECG?
Rhythm Rate PR interval QRS interval QT interval P wave (LA or RA enlargement) Description of QRS complex ST segment T wave Axis
How does atrial fibrillation present on ECG?
no p waves
wavy baseline with QRS
How does VF appear on ECG?
no QRS
completely wavy recording
