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