ECG Interpretation Flashcards
P wave
Atrial depolarization
PR interval
time for the atrial depolarization and conduction from the SA node to the AV node, normal is .12 to .20 seconds
QRS complex
Ventricular depolarization and atrial repolarization, normal is .06 to .10 seconds
QT interval
time for both ventricular depolarization and repolarization , ranges from .20 to .40 and depends on HR
ST segment
Isoelectric period following QRS when the ventricles are depolarized
T wave
Ventricular repolarization
Where does atrial depolarization begin?
SA node…and spreads normally throughout electrical conduction system
Premature atrial contractions (PAC)
Occur when an ectopic focus in the atrium initiates an impulse before the SA node, p wave is premature with abnormal configuration
PAC: Clinical Significance
Very common and generally benign but can progress to atrial flutter, tachycardia, or fibrilation
May occur in normal heart due to caffeine, smoking, stress, alcohol and any type of heart disease
Atrial flutter
Ectopic, very rapid atrial tachycardia
Atrial rate of 250-350 beats.min; ventricular rate dependent upon AV node conduction
Saw toothed p waves
Atrial flutter: Clinical Signifigance
Occurs with valvular disease (especially mitral), ischemic heart disease, cardiomyopathy, HTN, acute MI, chronic obstructive lung disease, and pulmonary emboli
Stagnation of blood may predispose to thrombi in the atria
Palpitations, lightheadedness, and angina due to rapid rate
Atrial fibrilation
Common arrythmia where the atria are depolarized b/w 350-600 times/min
ECG shows irregular undulations of ECG baseline without discrete p waves
A-fib: Clinical Signifigance
Occurs in healthy hearts and in patients with coronary artery disease, HTN, and valvular disease
Stagnation of blood may predispose to thrombi in the atria
Palpitations, fatigue, dyspnea, lightheadedness, syncope, and chest pain
1st degree AV block
PR interval is no longer than.2 seconds but relatively constant from beat to beat
1st degree AV block: Clinical Signifigance
No symptoms or significant changes in cardiac function
PR interval mat become prolonged for many reasons including medications that suppress AV conduction
2nd degree AV block
AV conduction disturbance in which impulses b/w the atria and ventricles fail intermittently
What are the 2 major types of 2nd degree AV block?
Mobitz type I block aka Wenckeback block
Mobitz type II block
2nd degree AV block: Clinical Signifigance
Mobitz I- progressive prolongation of PR interval until one impulse is not conducted (generally benigh)
Mobitz II- consecutive PR intervals are the same and normal followed by nonconduction of one or more impulses, more serious condition
In Mobitz type II block, what happens to cardiac output if HR is slow?
Decrease in CO with the blocked impulse, 2nd degree AV block can lead to 3rd degree AV block
3rd degree AV block (complete heart failure)
All impulses are blocked at the AV node and non are trasmitted to the ventricles
The atria and ventricles are paced independently; atrial rate > ventricular rate
3rd degree AV block: Clinical Signifigance
Considered a medical emergency requiring a pacemaker
If the ventricular rate is too slow, the cardia output drops and the pt my faint
What are some common causes of a 3rd degree AV block?
Degenerative changes of the conduction systems, digitalis, heart surgery, and acute MI
