ECGs 2 Flashcards
Which ECG leads look at the inferior side of the heart?
Lead II
Lead III
aVF
Which ECG leads look at the lateral side of the heart?
Lead I
aVL
V5
V6
Which ECG leads look at the anterior side of the heart?
V1-V4
Which ECG leads look at the right side of the heart?
V1
V2 (partly)
What is the first rule of ECGs?
The PR interval is between 0.12 & 0.2 sec (3 -5 small squares)
How long should the PR interval be?
Between 0.12 & 0.2 sec (3 -5 small squares)
-Rule 1
What is a long PR interval suggestive of?
First degree heart block
What is a short PR interval a sign of?
Pre-excitation (Accessory pathway)
OR
AV nodal (Junctional) rythm
What is the second rule of ECGs?
The QRS duration is <0.12 sec (<3 small squares)
How wide should the QRS complex be?
<0.12 sec (<3 small squares)
-Rule 2
What can cause a wide QRS?
Broad complexes may be ventricular in origin or due to aberrant conduction secondary to:
Bundle branch block (RBBB or LBBB)
Hyperkalaemia
Poisoning with sodium-channel blocking agents (e.g. tricyclic antidepressants)
Pre-excitation (i.e. Wolff-Parkinson-White syndrome)
Ventricular pacing
Hypothermia
Intermittent aberrancy (e.g. rate-related aberrancy)
What are the complex morphologies of LBBB shown in V1 and V6?
V1can be:
-‘W’ shaped
-Small r wave with deep S
-Absent R wave and deep Q wave
V6 can be:
-‘M’ shaped
-Notched
-Broad and monophasic
-RS pattern
What axis deviation is seen with LBBB?
Left
What causes narrow QRS complexes?
Narrow (supraventricular) complexes arise from three main places:
-Sino-atrial node (= normal P wave)
-Atria (= abnormal P wave / flutter wave / fibrillatory wave)
-AV node / junction (= either no P wave or an abnormal P wave with a PR interval < 120 ms)
If a narrow complex rythm is present with a normal P wave where is it most likely to originate from?
The SA node
If a narrow complex rythm is present with abnormal P waves where is it most likely to originate from?
Abnormal OR fluttering OR fibrillating P wave:
Atria
Abnormal P wave with a short PR (<120ms):
AV node / junction
If a narrow complex rythm is present with absent P waves where is it most likely to originate from?
AV node/junction
What is the third rule of ECGs?
The QRS complex should be predominantly upright in leads I & II
In which leads should the QRS complex be predominantly upright?
Leads I & II
-Rule 3
When are Q waves considered pathological?
If they are:
> 40 ms (1 mm) wide
2 mm deep
25% of depth of QRS complex
Seen in leads V1-3
What are pathological P waves usually a sign of?
Pathological Q waves usually indicate current or prior myocardial infarction, especially when present with ST elevation and/or T wave inversion.
Differential diagnoses include:
- Myocardial infarction
-Cardiomyopathies (Hypertrophic (HCM), infiltrative myocardial disease)
-Rotation of the heart (Extreme clockwise or counter-clockwise rotation)
In which leads can Q waves be normal?
Small Q waves are normal in most leads
Deeper Q waves (>2 mm) may be seen in leads III and aVR as a normal variant
Where are Q waves not normally present (in the absence of pathologies)?
V1-V3
What can predominantly negative QRS complexes in some chest leads be caused by?
Axis deviation - caused by a number of pathologies, can be normal variants.
What is the fourth rule of ECGs?
QRS & T waves tend to have the same general direction in the limb leads
In which leads should the QRS and T waves have the same general direction?
The limb leads
-Rule 4
What are the characteristics of normal T waves?
Upright in all leads except aVR and V1
Amplitude < 5mm in limb leads, < 10mm in precordial leads (10mm males, 8mm females)
Duration relates to QT interval
What amplitude is considered abnormal for T waves?
More than 10mm in males and 8mm in females
What is the fifth rule of ECGs?
Confirm that aVR is negative (if not check limb lead placement)
What is the sixth rule of ECGs?
The R wave in the precordial leads must grow from V1 to at least V4
How is R wave progression assessed on ECGs?
The R wave should grow from V1 to at least V4
-Rule 6
What can cause poor R wave progression?
Prior anteroseptal MI
Left Ventricular Hypertrophy (LVH)
Right Ventricular Hypertrophy (RVH)
Dilated cardiomyopathy
May be a normal variant
“Crap R, crap heart”
What is the seventh rule of ECGs?
The ST segment should start isoelectric except in V1 & V2 where it may be slightly elevated
In which leads may there be some slight normal ST elevation?
V1 & V2
-Rule 7
What is the ST elevation criterea for MIs?
New ST segment elevation at the J point in at least two contiguous leads of ≥ 2 mm in men or ≥1.5 mm in women in leads V2-V3 and/or of ≥ 1 mm in other contiguous chest leads or the limb leads.
How much ST elevation are you looking for in leads V2-V3?
≥ 2 mm in men or ≥1.5 mm
How much ST elevation are you looking for in contiguous chest leads other than V2-V3 or the limb leads?
≥ 1 mm in men and women
What reciprical changes might you expect to have in an anterior STEMI?
ST depression in inferior leads (mainly III and aVF)
In which MIs might you not see reciprical changes?
Anterior STEMIs that do not involve high lateral leads.
What is the eighth rule of ECGs?
The P waves should be upright in I, II & V2 to V6
In which leads are atrial abnormalities most easily seen, why?
Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF) and lead V1, as the P waves are most prominent in these leads.
