OHCEPS - ECG Flashcards
The 6 chest leads examine the heart how?
In a TRANSVERSE plane:
- V1-V2 –> looking at the RV.
- V3-V4 –> At the septum and anterior aspects of the LV.
- V5-V6 –> At the anterior and lateral aspects of the LV.
P wave represents atrial depolarization and it a positive (upwards) deflection - except?
In aVR.
Q wave?
So called if the first QRS deflection is negative (downwards).
Pathological Q waves may be seen in infarction.
R wave?
The first positive (upwards) deflection - may or may not follow a Q wave.
S wave?
A negative (downwards) deflection following the R wave.
HR - How to calculate from ECG?
HR can be calculated by dividing 300 by the number of large squares between each R wave (with machine trace running at the standard speed of 25mm/sec and deflection of 1cm/1mV.
3 large squares between R waves = ?
100 HR.
5 large squares between R waves = ?
60 HR.
Normal rate ?
60-100/min.
PR interval?
- From the start of the P wave to the start of the QRS complex.
- This represents the inbuilt delay in electrical conduction at the AV node.
- Normally <0.20 sec (5 small squares at standard recording speed).
QRS complex?
Width of the QRS complex - Normally <0.12sec (3 small squares at standard rate).
R-R interval?
- From the peak of one R wave to the next.
2. This is used in the calculation of HR.
QT interval?
- From the start of the QRS complex to the end of the T wave.
- Varies with HR.
- Corrected QT=QT/square root of the R-R interval.
- Corrected QT should be 0.38-0.42sec.
Rhythm of the ECG - What to look?
Is the rhythm (and the time between successive R waves) regular or irregular?
Cardiac axis - what is it?
Refers to the overall direction of depolarization through the ventricular myocardium in the coronal plane.
Normal cardiac axis?
Lies between -30 and +90 degrees.
Cardiac axis deviation - Can be seen in healthy individuals?
Yes:
Right axis deviation if tall and thin.
Left axis deviation if short and stocky.
Which leads should be used to accurately determine the cardiac axis?
Leads I, II, III.
Etiology of axis deviation - Left axis deviation (
- LV hypertrophy
- LBBB
- Left anterior hemiblock (anterior fascicle of the left bundle).
- Inferior MI
- Cardiomyopathies
- TV atresia
Etiology of axis deviation - Right axis deviation (>+90).
- RV hypertrophy
- RBBB
- Anterolateral MI
- RV strain (pulm. embolism)
- Cor pulmonale
- Fallot’s tetralogy (PV stenosis)
What is a heart block?
Disturbance of the normal conduction through the AV junction.
Etiology of heart block?
- IHD
- Idiopathic fibrosis of conduction system
- Cardiomyopathies
- Inferior/anterior MI
- Drugs
- Physiological (1st degree) in athletes
Drugs that cause heart block?
- Digoxin
- Beta blockers
- Verapamil
First degree heart block?
PR interval fixed but prolonged at >0.20 sec (5small squares at standard ratee).
Second degree heart block - Mobitz I?
- PR interval becomes progressively longer after each P wave until an impulse fails to be conducted at all.
- The interval then returns to the normal length and the cycle is repeated.
- Also known as the Wenkenbach phenomenon.
Second degree heart block - Mobitz II?
- PR interval is fixed but NOT EVERY P wave is followed by a QRS.
- The relationship betweenP waves and QRS complex may be 2:1, 3:1, or random.
Third degree heart block?
Also called complete heart block.
- There is no conduction of the impulse through the AV junction.
- Atrial and ventricular depolarization occur independently of one another.
- Each has a separate pacemaker triggering electrical activity at different rates.
QRS complex shape in 3rd degree heart block?
The QRS complex is an abnormal shape as the electrical impulse does not travel through the ventricles via the normal routes (see ventricular escape).
Hint about 3rd degree block?
In 3rd degree heart block P waves may be seen “merging” with QRS complexes if they coincide.
Hint about 3rd degree heart block?
If in doubt about the pattern of P waves and QRS complexes, mark out the P wave intervals and the R-R intervals separately, then compare.
P waves best seen in?
Leads II and V1.
What happens in RBBB?
Conduction through the AV node, bundle of His, and left bundle branch will be normal but depolarization of the RV occurs BY THE SLOW ELECTRICAL CURRENT THROUGH THE MYOCARDIAL CELLS.
What is the result of RBBB?
The result is delayed right ventricular depolarization giving a second R wave known as “R prime” (R’).
RBBB suggests what?
Pathology in the right side of the heart, but can be a normal variant.
RBBB - ECG changes?
- “RSR” pattern seen in V1.
- Cardiac axis usually remains normal unless left anterior fascicle is also blocked (“bifascicular block”) which results in left axis deviation.
- T wave is DOWN in anterior chest leads (V1-V3).
Some causes of RBBB?
- Hyperkalemia
- Congenital heart disease (Fallot)
- Pulmonary embolus
- Cor pulmonale
- Fibrosis of conduction system
LBBB what happens?
Conduction through the AV node, bundle of His, and right bundle branch will be normal but depolarization of the LV occurs by the slow spread of electrical current through myocardial cells.
LBBB result?
The result is delayed LV depolarization.
Can LBBB be seen in normal individual?
ALWAYS PATHOLOGICAL.
LBBB - ECG changes?
- M pattern seen in V6.
2. T wave down in lateral chest leads (V5-V6).
Some causes of LBBB?
- HTN
- IHD
- Acute MI
- AV stenosis
- Cardiomyopathies
- Fibrosis of the conducting system
Some causes of sinus bradycardia?
- Drugs
- Sick sinus rhythm
- Hypothyroidism
- Inferior MI
- Hypothermia
- Incr. intracranial pressure
- Physiological (athletes)
Drugs that cause bradycardia?
- Beta blockers
- Verapamil
- Amiodarone
- Digoxin
Sinus tachycardia - ECG features?
- Ventricular rate >100 (usually 100-150 beats per minute).
2. Normal P wave before each QRS.
Drugs that cause tachycardia?
- Epinephrine
- Caffeine
- Nicotine
Some causes of sinus tachycardia?
- Drugs
- Pain
- Exertion
- Anxiety
- Anemia
- Thyrotoxicosis
- Pulmonary embolus
- Hepatic failure
- Cardiac failure
- Hypercapnia
- Pregnancy
- Constrictive pericarditis
Supraventricular tachycardias are?
Tachycardias (>100) arising in the atria or in the AV node.
–> As conduction through the bundle of His and ventricles will be normal (unless there is other pathology in the heart), the QRS complexes appear normal.
4 main causes of supraventricular tachycardia that you should be aware of?
- A-fib
- A-flutter
- Junctional tachycardia
- Re-entry tachycardia