Module 12 Exam Material Flashcards
Arrhythmias
Disorders of formation or conduction (or both) of electrical impulses within heart
Arrhythmias can cause disturbances in
Can cause disturbances of
Rate
Rhythm
Both rate and rhythm
Arrhythmias potentially alter
blood flow and cause hemodynamic changes
How are arrhythmias diagnosed?
by analysis of electrographic waveform
Electrical Stimulation
Depolarization
Mechanical Stimulation
Systole
Electrical Relaxation
Repolarization
Mechanical Relaxation
Diastole
What does the P wave represent?
The electrical impulse starting in the SA node and spreading through the atria. Therefore, the P wave represents atrial depolarization
What does the QRS complex represent?
Represents ventricular depolarization.
Not all QRS complexes have all three waveforms
When a wave is less than 5 mm in height, small letters (q, r, s) are used; when a wave is taller than 5 mm, capital letters (Q, R, S) are used to label the waves.
The QRS complex is normally less than 0.12 seconds in duration.
Describe the Q wave
The Q wave is normally less than 0.04 seconds in duration and less than 25% of the R-wave amplitude.
Describe the R wave
The R wave is the first positive deflection after the P wave, and the S wave is the first negative deflection after the R wave
What does the T wave represent?
Represents ventricular repolarization (when the cells regain a negative charge; also called the resting state)
It follows the QRS complex and is usually the same direction (deflection) as the QRS complex
Atrial repolarization also occurs but is not visible on the ECG because it occurs at the same time as ventricular depolarization (i.e., the QRS).
What does the U wave represent?
thought to represent repolarization of the Purkinje fibers; although this wave is rare, it sometimes appears in patients with hypokalemia (low potassium levels), hypertension, or heart disease.
If present, the U wave follows the T wave and is usually smaller than the P wave. If larger in amplitude, it may be mistaken for an extra P wave.
How is the PR interval measured?
measured from the beginning of the P wave to the beginning of the QRS complex and represents the time needed for sinus node stimulation, atrial depolarization, and conduction through the AV node before ventricular depolarization.
What does the ST segment represent?
represents early ventricular repolarization, lasts from the end of the QRS complex to the beginning of the T wave.
The beginning of the ST segment is usually identified by a change in the thickness or angle of the terminal portion of the QRS complex.
The end of the ST segment may be more difficult to identify because it merges into the T wave. The ST segment is normally isoelectric (see later discussion of TP interval).
It is analyzed to identify whether it is above or below the isoelectric line, which may be, among other signs and symptoms, a sign of cardiac ischemia.
What does the QT interval represent?
represents the total time for ventricular depolarization and repolarization, is measured from the beginning of the QRS complex to the end of the T wave.
Many medications commonly given in the hospital can cause prolongation of the QT interval (QTc), placing the patient at risk for a lethal ventricular arrhythmia called torsades de pointes.
Describe isolelectric line.
When no electrical activity is detected, the line on the graph remains flat;
Normal Electrical Conduction
SA node (sinus node)
AV node
Conduction
Bundle of His
Right and left bundle branches
Purkinje fibers
Depolarization = stimulation = systole
Repolarization = relaxation = diastole
What is the RR interval used to determine?
ventricular rhythm
What is the PP interval used to determine?
atrial rhythm
Normal Sinus Rhythm
Electrical conduction that begins in the SA node generates a sinus rhythm. Normal sinus rhythm occurs when the electrical impulse starts at a regular rate and rhythm in the SA node and travels through the normal conduction pathway.
Normal Sinus Rhythm characteristics
Ventricular and atrial rate: 60 to 100 bpm in the adult
Ventricular and atrial rhythm: Regular
QRS shape and duration: Usually normal, but may be regularly abnormal
P wave: Normal and consistent shape; always in front of the QRS
PR interval: Consistent interval between 0.12 and 0.20 seconds
P:QRS ratio: 1:1
Sinus Bradycardia
Sinus bradycardia occurs when the SA node creates an impulse at a slower-than-normal rate.
Causes of Sinus Bradycardia
Lower metabolic needs (e.g., sleep, athletic training, hypothyroidism)
Vagal stimulation (e.g., from vomiting, suctioning, severe pain)
Medications (e.g., calcium channel blockers [e.g., nifedipine, amiodarone], beta-blockers [e.g., metoprolol])
Idiopathic sinus node dysfunction
Increased intracranial pressure,
Coronary artery disease, especially myocardial infarction (MI) of the inferior wall.
Sinus Bradycardia characteristics
Ventricular and atrial rate: Less than 60 bpm in the adult
Ventricular and atrial rhythm: Regular
QRS shape and duration: Usually normal, but may be regularly abnormal
P wave: Normal and consistent shape; always in front of the QRS
PR interval: Consistent interval between 0.12 and 0.20 seconds
P:QRS ratio: 1:1
Sinus Tachycardia
Sinus tachycardia occurs when the sinus node creates an impulse at a faster-than-normal rate
Causes of Sinus Tachycardia
Physiologic or psychological stress (e.g., acute blood loss, anemia, shock, hypervolemia, hypovolemia, heart failure, pain, hypermetabolic states, fever, exercise, anxiety)
Medications that stimulate the sympathetic response (e.g., catecholamines, aminophylline, atropine), stimulants (e.g., caffeine, nicotine), and illicit drugs (e.g., amphetamines, cocaine, ecstasy)
Enhanced automaticity of the SA node and/or excessive sympathetic tone with reduced parasympathetic tone that is out of proportion to physiologic demands, a condition called inappropriate sinus tachycardia
Autonomic dysfunction, which results in a type of sinus tachycardia referred to as postural orthostatic tachycardia syndrome (POTS). POTS is characterized by tachycardia without hypotension, and by presyncopal symptoms such as palpitations, lightheadedness, weakness, and blurred vision, which occur with sudden posture changes
How is the TP interval measured?
measured from the end of the T wave to the beginning of the next P wave—an isoelectric period
How is the PP interval measured?
measured from the beginning of one P wave to the beginning of the next P wave. The PP interval is used to determine atrial rate and rhythm.
How is the RR interval measured?
measured from one QRS complex to the next QRS complex. The RR interval is used to determine ventricular rate and rhythm
Sinus Tachycardia Characteristics
Ventricular and atrial rate: Greater than 100 bpm in the adult, but usually less than 120 bpm
Ventricular and atrial rhythm: Regular
QRS shape and duration: Usually normal, but may be regularly abnormal
P wave: Normal and consistent shape; always in front of the QRS, but may be buried in the preceding T wave
PR interval: Consistent interval between 0.12 and 0.20 seconds
P:QRS ratio: 1:1
DOES NOT START AND END SUDDENLY
Sinus Arrhythmia
Occurs when the sinus node creates an impulse at an irregular rhythm; the rate usually increases with inspiration and decreases with expiratio
Causes of sinus arrhythmia
Nonrespiratory causes include heart disease and valvular disease, but these are rare.
Sinus Arrhythmia Characteristics
Ventricular and atrial rate: 60 to 100 bpm in the adult
Ventricular and atrial rhythm: Irregular
QRS shape and duration: Usually normal, but may be regularly abnormal
P wave: Normal and consistent shape; always in front of the QRS
PR interval: Consistent interval between 0.12 and 0.20 seconds
P:QRS ratio: 1:1
Medical Management of Sinus Arrhythmia
Sinus arrhythmia does not cause any significant hemodynamic effect and therefore is not typically treated.
