ELECTROCARDIOGRAPHY AND CARDIAC ARRHYTMIAS Flashcards
Which four condition does the heart need to function properly?
- Contraction of the muscle cells must occur at regular intervals and be synchronized
- Ventricular contraction must be forceful
- Heart valves must be competent allowing one-directional flow
- Ventricles must fill adequately during systole
What are the two different system of cells in the heart?
Myocardial cells and pacemaker cells
What does the myocardial cells do?
Generate the contractile force necessary to propel blood through cardiac system
What does pacemaker cells do?
Provide electrical stimulus necessary to initiate contraction
What are the four components of the conduction system?
Sinoatrial node/sinus node
atrioventricular node
Bundle of His
Purkinje Fibers
Where and what does the sinoatrial node do?
Superior/Posterior wall of right atrium
Initiate each electrical impulse and governs the heart rate.
Where and what does the atrioventricular node do?
Located at the AV junction
It delays the transmission to bundle of HIS so it allows the valves to open.
Where and what does the bundle of His do?
Septum and divides into the right bundle branch and the left bundle branch.
Allows the impulse to be rapidly transmitted throughout ventricles.
Where and what does the Purkinje fibre do?
Network of conducting strands that lie beneath endocardium.
Responsible for conduction of impulses of the myocardial cells.
What does the P wave represents?
Atrial depolarization
What are some characteristic of the P wave?
Gently rounded
Less than 3mm, width less than 0.11 sec
Normally upright in leads I,II, AVF and V4 though V6
Negative AVR and can be in V1
What does PR interval represent?
Time required for depolarization of the atria to the onset of depolarization of the ventricles.
What are some characteristic of the PR interval?
Measured fro beginning of P wave to beginning of the QRS.
Normal Range 0.12-0.2 second.
What does the QRS complex represent?
Ventricular depolarization.
What are some characteristic of the QRS interval?
Less than 0.1 sec
Duration 0.1-0.11 sec is incomplete BBB
Greater than 0.12 is complete BBB or intraventricular conduction abnormality.
What are some characteristic of the ST segment?
Horizontal and isoelectric
ST elevation or depression of 1mm or more can show underlying cardiac pathology
Slight displacement of the ST segment can occur as normal
What does the ST segment represents?
Completion of ventricular depolarization and beginning of ventricular depolarization.
What does the T wave represent?
Ventricular Repolarization
What are some characteristic the T wave?
Same direction of QRS complex
Slightly rounded and asymmetrical, smooth take off
minor or flat
abnormal if invested
What are some characteristic
of the QT interval?
Measured from beginning of the QRS to the end of the T wave
normal ranges 0.35-0.45secs
What does the QT interval represents?
Total time required for both repolarization and repolarization.
What is the U wave?
Small deflection following T wave, significance unknown!
You’re doing great!
Keep Going!
EKG Criteria for sinus Rhythm?
HR 60-100
P waves: identical/normal, regular rhythm, consistent PR interval of 0.1-0.2 sec
Each P wave is followed by QRS complex