ECG Basics Flashcards
What length of time is 1 small square?
0.04 seconds or 40 ms
What length of time is 1 big square?
0.2 seconds or 200 ms
What is the standard paper speed?
25 mm/sec
What are the possible origins of a narrow complex QRS?
Sinus, atrial or junctional origin
What are the possible origins of a wide complex QRS?
Ventricular origin or supraventricular with aberrant conduction
Lead I
0 degrees (to the left, straight across)
Lead aVF
+90 degrees (straight down)
Lead II
+60 degrees
Lead III
+120 degrees
Lead aVL
-30 degrees (towards the left arm)
Lead aVR
-150 degrees (to the right arm)
Normal QRS axis?
+90 degrees to -30 degrees
Left axis deviation?
-30 degrees to -90 degrees
Right axis deviation?
+90 degrees to 180 degrees
Extreme/Indeterminate axis deviation?
180 degrees to -90 degrees
What is the normal P wave axis range?
0 degrees to +75 degrees
Which lead are p waves normally biphasic in?
V1
Which lead are P waves usually inverted in?
aVR
Which leads are the best to look for atrial abnormalities in?
Inferior leads (II, III and aVF) and V1 (P waves are most prominent in these leads)
The first 1/3 of the p wave corresponds to ____ activation, the final 1/3 corresponds to ____ activation; the middle 1/3 is ____
Right atrial
Left atrial
A combination of the two
What is the criteria for right atrial enlargement?
P wave height > 2.5 mm
What is the criteria for left atrial enlargement?
P wave longer than 120 ms (3 small boxes)
What is the criteria for right atrial enlargement in lead V1?
Initial positive deflection of p wave > 1.5 mm
What is the criteria for left atrial enlargement in lead V1?
Widening (>40 ms) and deepening (>1 mm deep) of terminal negative portion of the P wave
The presence of broad, notched (bifid) P waves in lead II can signify what?
Left atrial enlargement (classically due to mitral stenosis)
The presence of tall, peaked P waves in lead II can signify the presence of what?
Right atrial enlargement (usually due to pulmonary HTN)
What is a classic sign that there is a non-sinus origin of p waves on an ECG?
P-wave inversion in the inferior leads (II, III, aVF)
What is the origin of p waves that are inverted in the inferior leads (II, III, aVF) and PR interval <120?
AV junction
What is the origin of p waves that are inverted in the inferior leads (II, III, aVF) and the PR interval is greater than or equal to 120 ms?
Origin is within the atria (ectopic atrial rhythm)
What does the presence of multiple p wave morphologies indicate?
There are multiple ectopic pacemakers within the atria and/or AV junction
When is multi focal atrial rhythm diagnosed?
If 3 or greater P wave morphologies are seen
When is multi focal atrial tachycardia (MAT) diagnosed?
If 3 or greater different p wave morphologies are seen and the rate is equal to or greater than 100
What is a Q wave?
Any negative deflection that precedes an R wave
Where are small Q waves normally seen?
In the left sided-leads: I, aVL, V5 and V6
Which leads are Q waves not normally seen in?
Right sided leads (V1-V3)
What are signs of pathological Q waves? (List 4)
1) > 40 ms wide (1 small box)
2) > 2 mm deep
3) > 25% of depth of QRS complex
4) Seen in leads V1-V3
Absence of Q waves in leads V5 and V6 are most commonly due to what?
Presence of LBBB
List 3 key R wave abnormalities
1) Dominant R wave in V1
2) Dominant R wave in aVR
3) Poor R wave progression
What are some possible causes of a dominant R wave in aVR? (List 4)
1) Poisoning with sodium-channel blocking agents (e.g. TCAs)
2) Ventricular Tachycardia
3) Dextrocardia
4) Incorrect lead placement (left and right arm leads reversed)
T waves are usually upright except in which leads?
Leads aVR and V1
What are hyperacute T waves? What can they be a sign of?
Hyperacute T waves are usually broad or asymmetrically peaked
They can be seen in the early stages of a STEMI (often preceding the appearance of ST elevation and Q waves)
What T wave morphology is expected in a bundle branch block? What is this phenomenon called?
T wave inversion is usually seen following a QRS pattern suggestive of a bundle branch block or in cases of right/left ventricular hypertrophy
This phenomenon is called “appropriate discordance”, referring to the fact that abnormal depolarization (such as in a bundle branch block) should be followed by abnormal repolarization
What are the two main causes of biphasic T waves? How do they differ?
1) Myocardia ischemia 2) Hypokalemia
In myocardia ischemia, the T waves go up and then down. In hypokalemia, the T waves go down and then up
What is Wellens syndrome? What is it specific for?
Wellens syndrome is a pattern of inverted or biphasic T waves in V2-3 in patients presenting with/following ischemic sounding chest pain.
It is highly specific for critical stenosis of the LAD
Differentiate Type A and Type B Wellens syndrome
Type A: Biphasic T waves (in V2-V3) with the initial deflection positive and the terminal deflection negative
Type B: Deep, inverted T waves (in V2-V3) that are largely symmetric
What are two instances that can cause T waves to have a “double peak”?
1) Prominent U waves fused to the end of the T wave (as seen in severe hypokalemia)
2) Hidden p waves embedded in the T wave (as seen in sinus tachycardia and various types of heart block)
Flattened T waves are non-specific but their presence may represent what? (List 2)
1) Ischemia (if dynamic or in contiguous leads)
2) Electrolyte abnormality (e.g. hypokalemia if generalized)
Which leads are U waves generally best seen in?
Leads V2 and V3
When are U waves classified as “prominent”?
> 1-2 mm or 25% of the height of the T wave
What are 4 drugs or drug classes that can be associated with prominent U waves?
1) Digoxin
2) Phenothiazines
3) Class 1a antiarrhythmics (quinidine, procainamide)
4) Class III antiarrhythmics (sotalol, amiodarone)
When is U wave inversion abnormal? What is this specific for?
U wave inversion is abnormal in leads with upright T waves
Inverted U waves are very specific for myocardia ischemia in patients presenting with chest pain (may be the earliest marker of unstable angina and evolving myocardial infarction)
What is a J wave?
List some possible causes (list 3)
Small notched wave at the J point
Hypothermia, hypercalcemia, Takotsubo
What is an epsilon wave?
Where is it best seen?
An epsilon wave is a small deflection buried towards the end of the QRS complex.
It is best seen in the ST segment of V1 and V2; can be present in V1-V4
What causes an epsilon wave?
Post-excitation of myocytes in the right ventricle
What is an epsilon wave a characteristic finding of?
An epsilon wave is a characteristic finding in patients with arrhythmogenic right ventricular dysplasia (ARVD)
What is the normal PR interval?
Between 120-200 ms
If the PR interval is > 200 ms, ____ is said to be present
First degree heart block
PR interval < 120 ms suggests ____ or ____
the presence of an accessory pathway between the atria and ventricles
AV nodal (junctional) rhythm
Define a junctional rhythm. What are characteristic p wave findings in a junctional rhythm?
A junctional, or AV nodal, rhythm is a narrow complex, regular rhythm that arises from the AV node.
P waves are either absent or abnormal (e.g. inverted) with a short PR interval (<120 ms)
PR segment elevation or depression can be indicative of what 2 conditions?
Pericarditis
Atrial ischemia
The QT interval is ______ to heart rate
inversely proportional
The QT interval ____ at faster heart rates
shortens
The QT interval ____ at slower heart rates
lengthens
What is the QTc an estimation of?
The corrected QT interval (QTc) is an estimate of the QT interval at a standard heart rate of 60 bpm
QTc is prolonged if > ____ in men or > ___ in women
> 440 in men
460 in women
What are some causes of a prolonged QTc? (List 5)
Hypokalemia
Hypomagnesemia
Hypocalcemia
Hypothermia
Medications/Drugs
Myocardial ischemia
Congenital long QT syndrome
What are some causes of a short QTc (<350 ms)? List 2
Hypercalcemia
Digoxin
Congenital short QT syndrome
What are some causes of ST segment elevation? (List 5)
Acute myocardial infarction
Coronary vasospasm
Pericarditis
Benign early repolarization
LBBB
LVH
Ventricular aneurysm
Raised intracranial pressure
List the septal leads
V1-V2
List the anteroseptal leads
V3-V4
List the lateral leads
Lead I, aVL, V5-V6
List the inferior leads
Lead II, III and aVF
Name the mnemonic for reciprocal ST changes
PAILS
Where are the reciprocal changes for a posterior ST elevation?
Anterior leads (PAILS)
Where are the reciprocal changes for an anterior ST elevation?
Inferior leads (PAILS)
Where are the reciprocal changes for an inferior ST elevation?
Lateral leads (PAILS)
Where are the reciprocal changes for a lateral ST elevation?
Inferior or Septal lead changes (PAILS) (Only bidirectional letter in mnemonic)
Where are the reciprocal changes for a septal ST elevation?
Posterior lead changes (PAILS)
Acute pericarditis causes widespread concave ST segment elevation with _______ in multiple leads
PR segment depression
In LBBB, LVH, RBBB and RVH, the ST segments and T waves show _____ because they are directed _____ to the main vector of the QRS complex
Appropriate discordance
Perpendicular
In LBBB and LVH, RBBB and RVH if a QRS complex has a deep S wave, what are the likely effects on the ST segment and T wave morphology?
ST elevation and upright T waves
In LBBB, LVH, RBBB and RVH, if a QRS complex has a dominant R wave, what are the likely effects on the ST segment and T wave morphology?
ST depression and T wave inversion
What is the Brugada sign?
ST elevation and partial RBBB in V1-2 with a “coved” morphology
Ventricular pacing causes ST segment abnormalities identical to that seen in _____ (______)
LBBB
Appropriate discordance
Raised intracranial pressure may cause ST segment depression or elevation with _____ T wave ____
Deep
Inversion
What are some causes of ST depression? (List 5)
Myocardial ischemia
Reciprocal change in STEMI
Digoxin effect
Hypokalemia
RBBB
RVH
LBBB
LVH
Ventricularly paced rhythm
Horizontal or downsloping ST depression >= ___ mm at the J-point in >= ____ contiguous leads indicates myocardial ischemia
0.5 mm
2 contiguous leads
Posterior MI manifests as horizontal ST ____ in V1-V3 and is associated with ____ T waves and ____ R waves
depression
upright
tall
Upsloping ST depression in the precordial leads with prominent De Winter T waves (tall, prominent, symmetrical T waves in the precordial leads) is highly specific for ______
Occlusion of the LAD
Widespread ST depression with ST elevation in aVR is seen in _____ and _____
left main coronary artery occlusion
severe triple vessel disease
Supraventricular tachycardia typically causes widespread horizontal ST ____, most prominent in the _____ (___)
depression
left precordial leads (V4-V6)
In sinus rhythm with frequent ventricular ectopic beats, the narrow beats are ___ in origin and the broad complexes are ____ in origin
sinus
ventricular
What is the Sokolov-Lyon criteria?
What is it used for?
S wave depth in V1 + tallest R wave height in V5-V6 is > 35 mm. This is used to help diagnose LVH
The QRS is said to be low voltage when the amplitude of all the QRS complexes in the limb leads are < ___ mm OR the amplitudes of all the QRS complexes in the precordial leads are < ____ mm
limb leads -> 5 mm
precordial leads -> 10 mm
What is the most important cause for Electrical Alternans?
The most important cause is a massive pericardial effusion in which the alternating QRS voltage is due to the heart swinging back and forth within a large fluid-filled pericardium
