ECG Module Flashcards
What is the 9 step method?
Rhythm
Rate
P-wave
PR interval
QRS complex
ST segment
T wave
QT Interval
Axis
How do you determine if the rhythm is regular or irregular in an ECG?
Check the time/distance between P waves and R waves:
*Hint, use a piece of paper or similar
Regular rhythm: Time/distance is the same between P-P and R-R.
Irregular rhythm: Time/distance varies between P-P and R-R.
What is an ectopic beat?
Signals causing contraction that occur outside the normal pathway
What are the ECG features of normal sinus rhythm?
Regular rhythm at a rate 60-100 bpm.
Each QRS complex is preceded by a normal P wave.
Normal P wave axis: upright lead I and II, inverted in aVR.
PR interval remains constant: 0.12-0.20 sec (3-5 small boxes).
QRS complexes < 100 ms wide or 0.06-0.10 sec (1.5-2.5 small boxes)
What are variations on sinus rhythm?
Sinus tachycardia: resting HR > 100 bpm in adults.
Sinus bradycardia: resting HR < 60 bpm in adults.
Sinus arrhythmia: beat-to-beat variation in the PP interval that produces irregular ventricular rates
Sinus arrhythmia can result from the respiratory cycle
How is rate calculated?
Regular rhythm: 1500/(small boxes) between PP or RR intervals
Irregular rhythm: number of P waves or QRS complexes within 30 boxes multiplied by 10
30 box method is accurate within ±10 bpm
What are the characteristics of a normal P wave?
Upright in Lead II that precedes each QRS complex. Should appear small, rounded, and symmetrical
What is the normal range for the PR interval?
0.12-0.20 seconds or 3-5 small boxes
What indicates right atrial enlargement?
Peaked P wave (P pulmonale).
Amplitude:
>2.5 mm in Leads II, III, and aVF
>1.5 mm in V1 and V2
What is a biphasic P wave?
When current flows perpendicular to the lead as seen in V1. Indicated by the wave travelling over and under the isoelectric line
What indicates left atrial enlargement?
P Mitrale.
Lead II:
- Bifid P wave > 40 ms between peaks
- Total P wave > 110 ms
V1:
- Biphasic P wave, terminal negative portions > 40 ms
- Biphasic P wave, terminal negative portion > 1 mm deep
What happens if a P wave changes?
Reveals the changed path of conduction across the atrium
What is happening to the signal if a P wave is upside down in Lead II
In Lead II the signal is travelling away from the ventricles. No longer in sinus rhythm
What is the normal duration for the PR interval
0.12-0.20 sec; 3-5 small boxes. Consistent
What does a prolonged PR interval suggest (>0.20 sec)
First degree AV block
What can you do if P waves aren’t visible?
Look for retrograde (inverted) P waves, can be located anywhere between the J point and terminal part of the T wave
What are the types of second-degree AV block?
Mobitz type I - Wenckebach block
Mobitz type II
What defines second-degree Av block (Mobitz type I - Wenckebach)?
Repeated cycles of gradually increasing PR interval until an atrial impulse (P wave) is blocked in the AV node and QRS complex does not appear
What defines second-degree AV block (Mobitz type II)?
Intermittently blocked atrial impulses (no QRS after P wave) but with constant PR interval
What defines third-degree AV block?
All atrial impulses (P waves) are blocked at the AV node.
An escape rhythm arises which may have narrow or wide QRS depending on origin.
No relation between P waves and escape rhythm QRS.
Atrial rhythm is typically faster than escape rhythm although both rhythms are typically regular.
What is an escape rhythm?
When the sinus node fails to produce an impulse and there is no electrical communication between atria and ventricles due to 3rd degree AV block.
Ventricles initiate their own rhythm to maintain cardiac output otherwise cardiac arrest occurs.
What are the characteristics of a normal QRS complex?
0.06-0.10 sec; 1.5-2.5 small boxes.
- Positive (I, II, III, aVF, aVL, V5, V6)
- Biphasic (V3, V4)
- Negative (aVR, V1, V2)
Should be narrow (less than 3 boxes), sharp, pointy.
Measured from first deflection of QRS to J point.
What can a wide QRS complex tell? (>0.12 sec)
LBBB/RBBB. Axis deviations (ventricular hypertrophy)
What are the characteristics of a normal ST segment?
Measured between the and of QRS (J point) and onset of T wave.
Measured 0.06 sec; 1.5 boxes to the right of the J point (J-60)
Isoelectric
What does it mean if the ST segment is not isoelectric?
Not in line (isoelectric) with the PR interval
- Depression (upsloping, horizontal, down sloping) indicating myocardial ischemia. Up to 2 mm is okay.
- Elevation (concave, convex, horizontal) indicating myocardial infarction. 1 mm is concerning.
Clinical significance of ST-segment depression.
Considered depressed when 1 mm or more below isoelectric line. Indicates myocardial ischemia or digoxin toxicity. 2 mm is considered okay for this class
Clinical significance of ST-segment elevation.
Considered depressed if 1 mm or more above isoelectric line. Indicates myocardial infarction. 1 mm is concerning.
What are some types of ST-segment depressions?
- Upsloping: normal finding during physical exercise provided that T waves are not inverted. Hyperventilation can cause similar findings.
- Horizontal: typical of ischemia
- Down sloping: typical of ischemia
What are some types of ST-segment elevation caused by ischemia?
- Convex
- Straight upsloping
- Straight horizontal
- Straight down sloping
What does the shape of ST-segment indicate?
- Convex: typical of ischemia (sad face)
- concave: normal finding in all populations (happy face) although check for symptoms of potential MI
ST-segment measurement site
ST deviation is measured in the J point and compared with the PR interval (baseline)
What are some benign common findings for ST elevation?
Elevation is commonly seen across populations particularly in V2-V6.
Concavity (happy face) with T wave intersection
Causes of ST elevation?
Normal male/female patter
Ischemia
STEMI
Causes of ST depression?
Ischemia
Non-ST segment elevation myocardial infarction (NSTEMI)
Hyperventilation
Tachycardia
Left/right ventricular hypertrophy
Causes of waves/deflections in the J point (J wave syndrome)?
Brugada syndrome
Early repolarization
What does the T wave signify?
Ventricular repolarization/recovery
What are the characteristics of a normal T wave?
Follows QRS complex
<5 mm (I, II, III)
< 15 mm (precordial)
Typically round, smooth, and asymmetrical
What are the ECG deflections of a normal T wave?
- upright (I, II, V2, V3, V4, V5, V6, aVL, aVF)
- Inverted or flat (aVR, V1)
- Usually upright (variable) in lead III
What are some types of normal T wave variations?
Biphasic
Bifid/notched
Broad/slow
Flat
What are some indications of pathological T wave variants?
New T wave inversion (old ECG comparison). symmetrical and deep (>3 mm).
Inversion during exercise is always pathological. Indicates ischemia.
Dynamic inversions seen with acute ischemia
Fixed inversions are seen following infarction, associated with pathological Q waves
What should be seen on an ECG in relation to T waves?
Concordant with QRS complex
Positive in most leads
Progression should be normal in precordial leads
High amplitude (highest in II, V2, V3)
Common findings of T waves.
Normal variants
T wave inversion without simultaneous ST deviation
T wave inversion with simultaneous ST deviation
High T waves
What does T wave inversion without simultaneous ST deviation indicate?
Not a sign of ongoing ischemia, possible post-ischemic
Wellen’s syndrome
cerebrovascular insult (bleeding)
Pulmonary embolism
Perimyocarditis
Cardiomyopathy
What do T wave inversions with simultaneous ST deviation indicate?
Acute (ongoing) myocardial ischemia
Causes for High T waves?
Normal variant
early repolarization
Hyperkalemia
LBBB
May be seen in very early phase of STEMI
What is the QTc?
Correction of QT interval for heart rate
What is the QT interval?
Measurement from beginning of QRS to end of T wave.
Indicates entire depolarization to repolarization of the ventricles
What is Bazett’s QTc correction?
QTc = QT duration / sqrt (RR interval)
QT duration = small boxes40
RR interval = small boxes0.04. Or HR / 60
What are the normal limits of Bazett’s correction?
QTc > 540 ms confers 1.7x increase risk of cardiac event
QTc > 640 ms confers a 2.8x increased risk of cardiac event
What are U waves?
Late phase ventricular repolarization after T wave indicated by small, rounded deflection from isoelectric line
Not to be mistaken for P waves
What is the normal QTc duration for men and women?
<0.45 sec (men); <0.46 sec (women)
What could prolonged QTc interval cause?
Malignant arrhythmias (torsade de pointes, a type of ventricular tachycardia)
What are some common findings of QT intervals?
Acquired QT prolongation
Congenital QT prolongation
What are some findings of acquired QT prolongation?
Anti-arrhythmic drugs
Psychiatric medications
Antibiotics
Hypo-kalemia/calcemia/magnesemia/thyroidism/thermia
Myocardial ischemia
Cardiomyopathy
Bradycardia
What is the cardiac axis?
It’s the direction of the hearts electrical activity. Changes in axis can indicate L/R ventricular hypertrophy
How do you determine the cardiac axis?
Observe lead I and aVF and determine if QRS complex is more/mostly positive or negative
What is seen in Lead I and aVF for normal cardiac axis?
Lead I (positive QRS)
aVF (positive QRS)
What is seen in Lead I and aVF for left cardiac axis deviation?
Lead I (positive QRS)
aVF (negative QRS)
What is seen in Lead I and aVF for right cardiac axis deviation?
Lead I (negative QRS)
aVF (positive QRS)
What is seen in Lead I and aVF for extreme cardiac axis deviation?
Lead I (negative QRS)
aVF (negative QRS)
What do changes in the cardiac axis indicate?
Doesn’t indicate much on its own although can help provide information on identifying pathologies including:
- BBB
- R/L chamber hypertrophy
- Myocardial injury
- Pacemaker
What is one way to differentiate noise from atrial fibrillation?
If P waves exist in multiple leads and at the same time (aVL, aVF, lead II, aVR (inverted)) this means the signal can be contributed to noise.
If not P waves exist with a shaky baseline then can mean AF
What does it mean if a deflection seen on an ECG is positive, negative, or biphasic/flat?
- Positive = signal is travelling towards a lead
- Negative = signal is travelling away from a lead
- Biphasic/flat = signal is travelling parallel to a lead
What indicates normal sinus rhythm?
Regular rhythm
Normal HR
Normal PR interval
Normal QRS
What are green flags for exercise in atrial arrhythmias?
Normal sinus rhythm
Sinus bradycardia
Sinus tachycardia
Sinus respiratory arrhythmia
Premature atrial complex (PAC)
Non-conducted premature atrial contraction (non-conducted PAC)
What are amber flags for exercise in atrial arrhythmias?
Sinus block (sinoatrial block)
Sinus arrest/pause
Atrial bigeminy
What are red flags for exercise in atrial arrhythmias?
Sustained atrial tachycardia or supraventricular tachycardia (SVT)
What are the anterior leads and what’s the associated coronary artery?
V1-V4. Left Anterior Descending Artery (LAD)
What are the inferior leads and what’s the associated coronary artery?
Leads II, III, aVF. Right Coronary Artery (RCA)
What are the lateral leads and the associated coronary artery?
Lead I, aVL, V5, V6. Circumflex Artery + LAD
What is the difference between unifocal and multifocal wave?
Unifocal have similar wave morphologies, multifocal has varying wave morphologies
