Sinus rhythm Flashcards
What are the factors that affect sinus rhythm?
- Position of electrodes
- How the heart lies electrically and physically
- Thickness of heart muscle walls
- Rate of travel
- Rate of depolarisation/ repolarisation
- The pathway the electrical activity takes
Describe the P wave
P wave represents atrial depolarisation via P cells that contain automaticity, these are pacemaker cells.
We cannot see SA node on 12 lead ECG, we can see depolarisation of atria’s
P wave represents atrial depolarisation
2 components of P wave, has the right & left atrial component
No longer than 0.08 of a second, no taller than 0.25mV’s
Describe the significance of the shape, duration & amplitude of the P wave
Abnormal if there are no P waves in any leads
The P wave is typically smooth and rounded, reflecting a regular, coordinated atrial depolarization. It is generally positive (upright) in leads I, II, aVF, and often in V3 to V6.
In some leads, such as aVR, the P wave may appear inverted (negative), as the electrical impulses are traveling away from the lead’s view.
The normal amplitude of the P wave is usually less than 2.5 mm (in most leads).
Increased amplitude (taller P waves) may indicate right atrial enlargement, while wider or more prolonged P waves (greater duration) may suggest left atrial enlargement.
Describe the PR interval
PR interval is beginning of P wave to first pos/negative deflection
Conduction is slowed to prevent contraction of atrias & ventricles simultaneously
Av node protects the ventricles. PR segment should be isoelectric, should be 0, no electrical charge
PR interval is not always followed by an R wave, but by the 1st deflection
Refractory period of AV node protects the patient, how long AV node takes to recover protects the ventricles from fibrillating
Describe the significance of the duration of the PR interval
Normal range for PR interval 0.12-0.2
PR interval needs to be consistent in each complex
Too short of a PR interval suggests pathology
Too long of PR interval suggests a block
Effects of exercise/tachycardia on PR interval
PR interval shortens
Describe the QRS complex
QRS represents the depolarisation of the ventricles, Heart depolarises inside out, endo to epicardium
R wave increases in amplitude from V1 to V6, known as R wave progression
R wave progression, if R wave peaks e.g., in V4 it should dip in V5, normal anatomy
The appearance of the QRS complex can vary in different ECG leads. In lead I, the QRS complex is often positive, indicating normal conduction. In lead V1, the complex may show more of a negative deflection, reflecting the initial depolarization of the ventricles.
Describe the importance of the QRS duration
The normal duration of the QRS complex is less than 0.12 seconds (120 milliseconds).
If the QRS complex lasts longer than this, it can indicate a conduction delay or abnormality, such as bundle branch block.
Abnormalities in the shape, duration, or amplitude of the QRS complex in certain leads can help in diagnosing specific heart conditions.
Describe the QRS frontal axis (hexaxial system)
These limbs leads look at how the heart lies electrically in the frontal plane
This is known as the hexaxial reference system,
Uses lead I,II,III & AVL,AVR, AVF
-30 to +90 is normal
Something less than –30 is left axis deviation
Something greater than +90 is right axis deviation
How do you determine the QRS axis from an ECG?
- Identify the QRS Complex in leads I and aVF:
Look at the QRS complex in lead I (which is horizontal) and aVF (which is vertical). - Determine the direction of the QRS complex:
If the QRS is positive (upward deflection) in both leads, the axis is normal.
If the QRS is positive in lead I but negative in aVF, the axis is leftward, suggesting left axis deviation (LAD).
If the QRS is negative in lead I but positive in aVF, the axis is rightward, suggesting right axis deviation (RAD).
Define the J point
The J point on an ECG represents the junction between the termination of the QRS complex and the beginning of the ST segment. It marks the approximate end of depolarization and the beginning of repolarization. The J point elevation can also be seen in benign early repolarization (BER).
Describe the ST segment
ST segment should be within a millimetre of the isoelectric point, you measure from J point to beginning of T wave, interested when it is elevated or depressed
ST changes indicate ischaemia
The ST segment begins at the end of the QRS complex (after the S wave) and ends at the start of the T wave (the beginning of ventricular repolarization).
It represents the electrical transition period between the depolarization (contraction) of the ventricles and the start of repolarization (relaxation).
Describe the significance of ST changes
A flat or normal ST segment suggests normal heart function.
ST elevation:is typically associated with acute myocardial infarction (MI), or a heart attack. It suggests that a portion of the heart muscle is ischaemic
ST depression: is commonly a sign of myocardial ischemia, where the heart muscle is not receiving enough blood and oxygen,
Describe the QT interval
The duration of the QT interval can vary depending on the heart rate. It is usually measured in milliseconds (ms).
The normal QT interval duration for adults is typically between 0.35 to 0.45 milliseconds.
However, it is adjusted for heart rate (because the QT interval shortens with higher heart rates and lengthens with slower heart rates).
Medications: Certain drugs, especially those that affect the electrical conduction of the heart (e.g., some antiarrhythmics, antidepressants, and antipsychotics), can prolong the QT interval.
Describe the significance of a changes in duration of the QT interval
Normal QT interval: A normal QT interval indicates proper timing for the ventricles to contract and relax.
Prolonged QT interval: If the QT interval is abnormally long, it can increase the risk of dangerous arrhythmias, like torsades de pointes, a type of life-threatening tachycardia. Causes of prolonged QT can include electrolyte imbalances (e.g., hypokalemia), drugs (e.g., antiarrhythmics, antidepressants), and congenital syndromes (e.g., long QT syndrome).
Shortened QT interval: A shortened QT interval can be associated with conditions such as hypercalcemia, or digitalis toxicity, and sometimes certain inherited disorders.
Describe the T wave
The T wave repolarizes the ventricles from the epicardium to the endocardium.
Normal T wave is asymmetrical and should have the same polarity to R wave, it should not be 2/3 taller than R wave
T waves have a slow ascent and steep descent
Describe the significance of different shaped T waves
T waves are very sensitive to ischaemia
Peaked T wave: This can suggest hyperkalemia (high K+) which can be life threatning
Inverted T wave: Can suggest a heart condition or myocardial ischaemia, it can be a normal T wave for some pateints
Flat or absent T wave: indicates a problem with the repolarisation process, this can suggest electrical imbalance or pericarditis
Describe the R-R interval
R-R interval is the duration between 2 consecutive R waves.
The R wave is the tall, upward deflection in the QRS complex, which represents the electrical impulse that leads to the contraction of the ventricles
It is calculated by counting the number of small squares & multiplying by 0.04
Normal range is between 0.6 to 1.0 seconds
Describe the significance of changes to the duration of an R-R interval
In healthy heart: R-R interval should be consistent to reflect normal HB & sinus rhythm
Long R-R suggests bradycardia, slower HR or conduction issues
Short R-R interval suggests tachycardia or arrhythmias
Irregular R-R intervals suggest problems with conduction causing arrhythmias e.g., AFIB
How is HR calculated?
Measured using R-R interval
HR=60/R-R interval
Define the criteria for sinus rhythm
P wave must have normal morphology in given lead, to be typical for that patient & typical for that lead
P wave must come before QRST, With only one P wave per QRST
PR interval must be in range of 0.12-20ms
QRS complexes must occur & be withing 0.12ms , which have a morphology typical for the patient and typical for the lead, must have the same morphology for a lead, axis must be –30 to +90,
T waves should have equal polarity to R waves
PQRST must repeat itself
