ECG Flashcards
Leads 2, 3 and aVF are what type of leads?
Inferior leads - they’re near the inferior wall of the heart
This part receives blood from the Right coronary artery
Leads 1, aVL, V5 and V6 are what type of leads?
Lateral leads - the lateral part of the heart receives blood from the left circumflex artery
V1 and V2 are what type of leads?
Septal leads
V3 and V4 are what type of leads?
Anterior leads
The septal and anterior parts of the heart are supplied by which artery?
LAD
Left anterior descending
When calculating rate, 1 big box apart equates to what rate?
300bpm
so R waves 2 big boxes apart = 150bpm, etc
What causes atrial flutter?
When ectopic focus (i.e. an irritated atrial myocyte) contracts at about 250-300bpm - this is atrial rate
Ie SAN isn’t really regulating the contraction
What causes atrial fibrillation
Multiple ectopic foci in atria all firing at once
Atrial rate is 350-450 bpm
If atrial fibrillation no reliable way of estimating HR because heart is just quivering
Bundle branch block results in what?
Wide QRS complexes
How might we tell a 3rd degree heart block
P wave with no following QRS complex
How long is a PR interval?
PR interval = from START of P wave to START of QRS complex
Usually 0.12-0.2 seconds (3-5 little boxes)
What may cause longer/shorter PR intervals?
- Irritable atrial cell (length of PR interval depends on how far it is from AVN)
- First degree heart block - where the conduction travels slower through AVN
How long is a QRS complex
Usually less than 0.1s (2.5 little boxes)
What may cause changes in QRS complex duration
Ventricular ectopic focus (e.g. irritated ventricular cell)
If ventricular cell contracts the contractions go through slow muscle cells rather than electrical conduction system = QRS wider
Intermediate = 0.1-0.12s
Prolonged >0.12s
The QT interval represents ventricular systole (i.e. depolarisation to repolarisation). How long should it be?
Roughly half a cardiac cycle or less
What are some causes of a prolonged QT interval
Medications (Eg amiodarone) or inherited mutations (Eg LQT1/LQT2/LQT3)
How can a QRS vector become larger?
If there is a larger myocardium layer - e.g. hypertrophic cardiomyopathy
How can a QRS vector become smaller?
If the myocardium gets damaged - e.g. heart attack
Aside from hypertrophic cardiomyopathy or heart attack, what else may influence the average QRS vector?
Obesity (vectors more left)
Thin (vectors more right)
What is a normal axis for the heart?
- 30 to +90 degrees
i. e. QRS should be positive in lead 1 and aVF OR positive lead 1 and slightly negative in QRS
What is left axis deviation and what are its causes?
When the ECG axis is between -30 to -90
Can be caused if LV hypertrophies or RV damaged
What is right axis deviation and what are its causes
ECG axis between +90 to + 180
When the RV hypertrophies or when LV damaged
What is extreme right axis deviation
When ECG axis is from +180 to -90 degrees
Can occur when there is an ectopic focus which causes depolarisation to start from LV
If the “transition zone” (i.e. isoelectric points) shift from V3/V4 to V1/2 then what does this suggest?
Suggests that heart is rotated towards persons right - e.g. due to RV hypertrophy
If the transition zone (i.e. isoelectric points) shift from V3/4 to V5/6 what does this suggest
Heart rotated towards persons left i.e. LV hypertrophy
What may shift the QRS transition zone to the right?
MI of the left side of the heart
or right sided cardiac hypertrophy
(vice versa for left)
Right atrial enlargement shows up in an ECG as?
What are the causes of right atrial enlargement?
Large P wave in V1 and 2. Also large P wave in leads 2, 3 and aVF.
Causes include stenotic tricuspid valve
Left atrial enlargement shows up in an ECG as?
What are the causes of leftt atrial enlargement?
2 p waves in Lead 2
Biphasic (peak and trough) p wave in lead v1
Caused by stenotic mitral valve
What are the ECG signs of RV hypertrophy?
Dominant R wave in lead V1
Dominant S wave in lead v5
Often accompanied by some right axis deviation
Give a cause of RV hypertrophy
Pulmonary hypertension
LV hypertrophy has almost the opposite features of RV hypertrophy. So what are the ECG features
Dominant S wave in v1 (and ST elevation)
Dominant R wave in v5 (and ST depression + t wave inversion)
What are the causes of LV hypertrophy
Systemic hypertension
What are the 2 types of ischaemia/infarction of the heart?
Transmural (entire thickness of myocardium) or subendocardial (innermost layer of myocardium)
What is a giveaway sign of subendocardial ischaemia?
ST depression (can be upward/downward sloping or horizontal)
Leads 1, 2, v4, v5 and v6 affected
What does a CURVED ST depression indicate?
Digitalis effect - i.e. patient takes digoxin
Transmural ischaemia arises from atherosclerotic plaques that rupture. When may transmural ischaemia show up?
Unstable angina or NSTEMI
NSTEMI leaks out troponin and CK-MB
What are the ECG signs of transmural ischaemia
ST depression and T wave inversion in contiguous chest leads (v2-6)
What are the ECG signs of subendocardial infarction
ST depression and T wave inversion
Troponins and CK-MB increased
Transmural infarction occurs when coronary artery is completely blocked for e.g. 20 mins. What are the ECG signs
T wave inversion OR hyper acute T waves in 2 contiguous leads and ST elevation. May also get a pathologic Q wave
Transmural infarction suggests STEMI
Name 3 causes of ST elevation that are not MI
Coronary artery vasospasm
LV hypertrophy
Pericarditis
Septal wall infarctions show pathologic Q waves in which leads?
V1 and V2
Anterior wall infarction shows pathologic Q wave in which leads
V3 and V4
Anterolateral wall infarction shows pathologic Q wave in which leads?
V3-6, leads 1 and aVL
Subendocardial infarction DOES NOT show pathologic Q waves. Also which lead is not reliable for showing pathologic Q waves?
aVR
Pathologic Q waves can be caused by what other than transmural infarction?
Remember they linger longer than ST elevation or T wave inversion
Left BBB, Wolff Parkinson White syndrome
