ECG LP 02 Flashcards
P WAVE
Small, rounded wave.
Positive in most standard leads (especially DII) except aVR where is always negative,
and V1 and V2 where is frequently biphasic with a first positive phase and a second negative part.
P wave electrical axis = between 0° and +90°, more frequently between 45° and 60°)
=> P wave is frequently taller in DII than in the other leads.
Duration = 0.08 – 0.10 (0.11) sec.
Amplitude = 1- 2.5 mm, except V1 and V2 where is less than 2 mm.
PQ (PR) SEGMENT
From the end of P wave to the beginning of QRS.
Normally, it’s an isoelectric segment situated on the isoelectric line.
Represents the conduction time of the impulse through the AV node, Hiss bundle,
branches and Purkinje network.
Normal duration = 0.04 – 0.10 sec.
It varies with the heart rate (HR): it shrinks at higher frequencies and vice versa.
PQ (PR) INTERVAL
From the beginning of the P wave to the beginning of the QRS.
Represent the conduction time of the impulse from the sinus node to the ventricular myocardial cells.
Duration = 0.12 - 0.20 sec.; it also varies with frequency, secondary to PQ segment variations.
Short PQ interval – preexcitation syndrome.
Long PQ interval – first degree AV block.
QRS COMPLEX (I)
- Is the expression of ventricular depolarization.
- A normal ventricular complex is formed by angular waves, with abrupt and straight lines.
- The first negative wave is called q wave.
- The first positive wave is called R wave; if there are more than one we call them r’, r’’.
- The negative wave that appears after the positive wave is called S wave.
- A complex formed by a single negative wave is called QS wave/complex.
- If the amplitude of the wave is rather high the wave is marked with capital letter; if the wave is rather small it is marked with small letter.
Duration = 0.06 (0.08) – 0.10 sec.
0.10 – 0.12 sec. = left ventricular hypertrophy;
>0.12 = bundle branch block;
QRS COMPLEX (II)
The height of the waves: it may vary normally from person to person, with age,
position of the heart, thickness of the thoracic wall, etc.
In the frontal plane leads:
- R < 20mm (2mV)
- DIII R < 18 mm
- aVL R < 12 mm
In the precordial leads:
- R wave should be the tallest in V5, but less than 25 mm
- r wave should be the smallest in V1 and less than 5mm
- S wave should be the deepest in V2, but no more than 25 mm
- Ratio: r/S < 1 in V1 and V2 and R/s> 1 in V5 and V6
q wave is considered normal if is < 3mm in V5, V6 and < ¼ of the height of R wave with duration of less than 0.04 sec.
Electrical axis of QRS complex is between 0° and 90° (extreme normal variants -20° and + 100°).
R PEAK TIME (INTRINSECOID DEFLECTION).
When depolarization stimulus reaches subepicardial cells it determines the downward side of the last positive wave of the complex and it’s called intrinsicoid
deflection.
The time measured from the beginning of ventricular complex until the last positive peak is called R peak time.
R peak time is measured in the precordial leads: in V1, V2 where reflects the time it takes for the depolarization stimulus to travel in the width of RV wall, and in V5, V6 where reflects the time needed for the impulse to reach the subepicardial region of
the LV wall.
Normal values: V1, V2 <0.03 sec V5, V6 <0.05 sec.
ST SEGMENT
Limited by the end of ventricular complex and the beginning of T wave.
Although it is normally a segment situated on the isoelectric wave (with small normal
variations described later), during the time of ST segment there is electrical activity:
there are ventricular territories that are still depolarizing and there are ventricular territories that begin to repolarize.
The sum of this opposite activities is almost equal territories that begin to repolarize.
The sum of this opposite activities is almost equal
so it appears as 0 on ECG tracing.
The beginning of ST segment is named the ”j” point.
Normally, the ”j” point and ST segment are situated on isoelectric line, or beneath isoelectric line with maximum 0.5 mm. Another normal possibility is a slight elevation of ST segment, with maximum 2 mm above isoelectric line, in V1 and V2.
T WAVE
It’s the graphic expression of ventricular repolarization.
It is a rounded (slow) wave and asymmetrical: with a slower ascending slope and a more abrupt descending one.
Duration = 0.15 – 0.30 sec.
Amplitude = usually 2 – 6 mm but sometimes more, up to 10 mm.
Electrical axis of T wave is between 0° and 90°; it forms with the QRS axis a narrow angle < 40°.
T wave is normally positive in most standard leads, except:
- aVR where it is negative;
- DIII where it can be very flat or even negative;
- V1, V2, V3 where it can be negative in children and young adults.
U WAVE
Sometimes, after T wave (after 0.04’’), another small wave appears = u wave;
It is small wave (amplitude <1/4 of the T wave), with same orientation as T wave (positive);
It is seen especially with slower heart rates.
A few meanings have been attributed: repolarization of Purkinje cells;
- repolarization of the papillary muscles;
- depolarization wave determined by the stretching in ventricular wall during the rapid ventricular filling (stretch mediated depolarization) – most likely to be true.
QT INTERVAL
It is measured from the beginning of the ventricular complex until the end of the T wave.
Its normal duration depends on cardiac rate. There are several formulas that calculate corrected QT interval based on RR interval:
QTc = QT/ RR 2 (Bazett)
QTlc (Framingham) = QT + 0.154 (1-RR)
QTc (Fridericia) = QT/ RR 3 Normal values <0.44’’
HEART RATE (HR)
Number of beats (QRS complexes) per minute (60 sec)
For a regular rhythm, HR is calculated dividing 1 minute by RR interval: 60’’/ (RR)’’ = 60’’/ (0.04’’x (RR) mm) = 1500/ (RR) mm.
For irregular rhythms it is better to make an average with 3-4 RR intervals
CALCULATING QRS ELECTRICAL AXIS – IT IS PERFORMED IN FRONTAL PLANE:
Search for an equiphasic complex = sum of the positive waves is equal to the sum of negative waves.
If there is an equiphasic complex in a lead (e.g. DIII) that means that the electrical axis of QRS complex is perpendicular on the axis of that lead, so in our example the QRS axis is parallel with aVR (the lead that is perpendicular on DIII).
Then, we observe the complex in aVR: if the complex in aVR is negative the QRS axis in on the negative segment of aVR a.k.a. at +30° and if it’s positive in aVR the QRS axis will be at -150°.
CALCULATING QRS ELECTRICAL AXIS (II)
!!!!!!!!!
If we don’t find an equiphasic complex:
We observe the aspect of QRS in the leads that are reciprocal perpendicular one on other:
D I and aVF D II and aVL D III and aVR
We look at first at the ventricular complexes in DI and aVF:
1. If the ventricular complex is positive ( the sum of positive waves> sum of negative waves) in DI ( this means that the QRS axis is projected on the positive segment of DI) and if the QRS complex is positive in aVF then the QRS axis is between 0° and +90° = normal
2. If the ventricular complex is positive in DI and negative in aVF → the QRS axis is between 0° and -90° = left axis deviation
3. If the ventricular complex is negative in DI and positive in aVF → the QRS axis is between +90° and 180° = right axis deviation
4. If the ventricular complex is negative both in DI and in aVF → the QRS axis is between -90° and 180° = extreme right axis deviation
5. We repeat the process for the other couples of leads (D II and aVL / D III and aVR).
ANALYSIS OF ECG (I)
HR – must be calculated. Is it normal/higher/lower?
P wave: general aspect; is it a sinus P?; duration, amplitude, axis.
PQ segment: is it isoelectric? Is it the same length all of the ECG trace?; duration.
PQ interval: duration - is it normal/longer/shorter; is it constant at all time?
QRS complex: general aspect: are normal/abnormal morphologies; amplitude, indices of amplitude (White-Block, Sokolov-Lyon, etc.) are there any abnormalities regarding voltage: too high/too small waves?;
duration of ventricular complex + R peak time in V1, V2; V5, V6;
electrical axis of QRS complex;
are there pathological Q waves?
ANALYSIS OF ECG (II)
ST segment: is it isoelectric (or within normal variations); is it elevated/depressed?
T wave: general aspect: is it positive/negative, rounded + asymmetrical/pointed + symmetrical? Duration, amplitude, electrical axis; is it in concordance with QRS complex?
QT interval – duration (preferably corrected using one of the correction formulas).
Rhythm: is it sinus rhythm? If not, what is it?
Sinus rhythm (SR) is present if there are P waves of sinus aspect (positive in almost all leads, especially DII, except aVR where is negative and V1+V2 where is often
biphasic), all followed by a ventricular complex, and a constant AV conduction (there is P in front of each QRS complex and PR is constant) and a HR between 60 and 100 beats/minute (for adults).
