understanding ECG Flashcards
Valve component (heart sound)
The first heart sound (lub) occurs when the atrioventricular (AV) valves close and the second heart sound (dub) is heard when the semilunar valves close.
This phenomenon is due to the fact that the electrical event in cardiac activities takes place before the mechanical event.
Rate
- 1 small square = 0.04 seconds
- 1 large square (5 small squares) = 0.2 seconds
- Slow/Irregular rhythms: count the number of QRS complexes in a ten-second strip and x6 (beats per minute)/ 6 sec strip x 10
- Regular rhythms: 300 ÷ number of large squares between each R wave
Reciprocal Changes (and what are the original leads)
Septal
leads V1 and V2 - normal
V7, V8, V9 - reciprocal (posterior)
- If you see ST elevation in the septal leads, check the posterior leads for reciprocal depression.
Reciprocal Changes (and what are the original leads)
Lateral
Leads I, aVL, V5, and V6 - normal
Leads V1 and V2 - reciprocal (septal)
- If you see ST elevation in the low lateral leads (v5 & v6), check the septal leads for reciprocal depression.
Reciprocal Changes (and what are the original leads)
Inferior
Leads II, III, and aVF - normal leads
Leads I and aVL- reciprocal (high lateral)
- If you see ST elevation in the inferior leads, check the high lateral leads for reciprocal depression.
Reciprocal Changes (and what are the original leads)
Anterior
V3 & V4 - normal leads
Leads II, III, and aVF - reciprocal (inferior)
- If you see ST elevation in the anterior leads, check the inferior leads for reciprocal depression.
Anterior
V3, V4
Septal
V1, V2
Lateral
Lead 1, aVL, V5, V6
Inferior
Lead 2, Lead 3, aVF
V6
Lateral
Left circumflex
V5
Lateral
Left circumflex
V4
Anterior
Left Coronary Artery
V3
Anterior
Left coronary Artery
V2
Septal
Left Anterior Descending Artery
V1
Septal
Left Anterior Descending artery
aVF
Inferior
Right Coronary artery
aVL
Lateral
Left circumflex
aVR
nothing
Lead III
Inferior
Right side coronary artery
Lead II
Inferior
Right coronary artery
Lead I
Lateral
Left circumflex
Which 3 leads do you move to look at the posterior ECG?
V4, V5, V6
12 Lead ECG Placement
V9
Lateral to the spinal Colom in the 5th intercostal space
12 Lead ECG Placement
V8
The base of the scapular in the 5th intercostal space (avoid placing over bony scapular)
- midway between V7 and V8)
12 Lead ECG Placement
V7
left posterior axillary line in the 5th intercostal space
12 Lead ECG Placement
V5
Is placed on the anterior axillary line in the same place as V4
Or midway between v4 and v6
12 Lead ECG Placement
V3
Is placed mid-way between V2 and V4
12 Lead ECG Placement
V6
Is placed on the mid-axially line in the same plane as V4
12 Lead ECG Placement
V4
Is placed in the 5th intercostal space mid-clavicular line
12 Lead ECG Placement
V2
Is placed in the 4th intercostal space left of the sternum
Where to find:
Find the suprasternal notch, then the angle of louis (bump, where the manubrium and body of the sternum meet). The angle of louis is equal to the 2nd rib. Once you palpate the second rib, continue to move down each rib to find the 4th intercostal space (which is below the 4th rib OR can be described as between the 4th and 5th rib).
12 Lead ECG Placement
V1
Is placed in the 4th intercostal space right of the sternum
Where to place:
Find the suprasternal notch, then the angle of louis (bump, where the manubrium and body of the sternum meet). The angle of louis is equal to the 2nd rib. Once you palpate the second rib, continue to move down each rib to find the 4th intercostal space (which is below the 4th rib OR can be described as between the 4th and 5th rib).
QRS wave measurements
- Normal value of <0.12 seconds
- If prolonged >0.12 seconds, may indicate rhythm of ventricular origin, or aberrant conduction of a supraventricular complex
-Should be monomorphic across the ECG
-Q wave: left to right depolarisation of interventricular septum
PR wave measurements
- Normal value of 0.12 – 0.2 seconds.
- If prolonged >0.2 seconds, indicative of first-degree heart block.
Normal P wave
Measurements
- Has a monophasic, upright shape in Lead II
- Has a normal value of 0.08 – 0.10 seconds
- Should precede the QRS complex in a normal sinus rhythm.
Rhythm
Regular or Irregular?
If Irregular:
- Regularly Irregular (pattern) or
- Irregularly Irregular (no pattern)?
Fold a 10-second strip in
half - hold the strip up to the light and match the tips of the QRS complex:
- Do they all match evenly? Regular
- Do they not match at all? Irregular
Use a ruler to measure the distance
between two consecutive QRS complexes. Is this distance equal between ALL QRS complexes?:
- Yes: Regular
- No: Irregular
The T wave
what it does
The T wave represents ventricular repolarisation.
It represents the repolarisation of the ventricles. We don’t see atrial repolarisation as this is superseded (hidden) by QRS complex. Repolarisation occurs slower through larger muscle mass
It should be upright and rounded.
If it is inverted, it may indicate damage to the myocardium (heart muscle).
The ST segment
what it does
The ST segment is the gap between the QRS complex and the T wave. It represents the end of ventricular depolarisation during which ventricular systole occurs.
It represents the period between ventricular depolarisation and repolarisation.
It should be in line with the baseline (the line between the T wave and the next P wave).
The isoelectric section between the end of the S wave (J point) and the beginning of the T wave
- If it is below the baseline (depressed) it indicates myocardial ischemia (lack of oxygen to the heart).
- If it is above the baseline (elevated) it indicates myocardial infarction (cell damage to the heart).
The QRS complex
what it does
The QRS complex represents ventricular depolarisation. It represents the electrical depolarisation of the ventricles.
It should be pointed and narrow.
- If it is wide this indicates a conduction delay in the bundle branches.
- If there is no P wave and the QRS complex is WIDE this generally indicates that the rhythm is being generated in the ventricles.
- If there is no P wave and the QRS complex is NARROW this generally indicates the rhythm is being generated in the AV node.
The PR interval
what they are
The PR interval represents atria depolarisation and the delay in the AV node. It represents electrical conduction from the SA node through to the AV node, where the impulse is slowed down. (Delayed conduction through AV node).
If it is too long this indicates a disease of the AV node. If this is too short, it can indicate that an additional conduction path is bypassing the AV node.
P waves
explanation of what they are
The P wave represents atrial depolarisation (atrial contraction). It represents the SA node firing and electrical depolarisation of the atria.
There should be a P wave before every QRS complex. The P wave should be upright and rounded as pictured.
An abnormal P wave indicates that the rhythm is still originating in the atria but not in the SA node, or there is an abnormality in how the atria are depolarising.
An absent P wave, or a P wave that comes after the QRS indicates that the rhythm is not originating anywhere in the atria.
