Cardiac Conduction Disorders: Rhythm and Rate Flashcards
Manifested by multiple P wave shapes and PR intervals
wandering pacemaker
Describe SA node beats
smooth upright P waves
Describe non-SA node beats
flattened, notched, biphasic (S-shaped) or inverted P waves
Wandering pacemaker: ________ contraction is normal, so the QRS complex is ______ width and height
Wandering pacemaker: ventricular contraction is normal, so the QRS complex is normal width and height
What may precipitate a wandering pacemaker
reduced SA node firing
Most common in very young, very old, athletes, rarely causes symptoms or requires treatment
wandering pacemaker
EKG characteristics of wandering pacemaker
- rate <100
- P wave shape varies
- Irregular ventricular rhythm
Occurs when tachycardia occurs at the same time as wandering pacemaker
multifocal atrial tachycardia
EKG characteristics of multifocal atrial tachycardia
- rate >100
- P wave shape varies
- Irregular ventricular rhythm
Caused by very rapidly firing ectopic atrial foci
atrial fibrillation
What does very rapidly firing ectopic atrial foci result in?
results in uncoordinated, ineffective, irregular atrial contraction
What is the irregular atrial contraction due to?
due to occasional impulses resulting in AV node discharge
How long does atrial fibrillation last?
may occur suddenly and last for minutes to days OR be permanent
EKG characteristics of atrial fibrillation
- P waves absent
- usually normal QRS width
- Irregularly irregular rhythm
- continuous chaotic atrial spikes
occur after the controlling automaticity focus (usually the SA node) stops pacing (“sinus arrest”)
escape rhythms
occurs when a transient pacer escape occurs and resumes after one beat
escape beat
occurs when the SA node stops firing
sinus arrest
occurs when another atrial pacer takes over the rhythm
atrial escape rhythm
EKG change with atrial escape rhythm
- different P wave
- same QRS
Occurs when the AV node (or a nearby focus) takes over following sinus arrest
junctional escape rhythm
EKG change with junctional escape rhythm
- loss of P wave (buried in another wave) OR P wave may occur before or after QRS wave
- unusual P wave shape
- QRS complex usually unchanged
Occurs when pacing fails to occur from more superior pacers (e.g., SA, AV) and automaticity foci in the ventricles take over
ventricular escape rhythm
EKG change with ventricular escape rhythm
- loss of P wave or P wave not conducting
- wide QRS complex
What do ventricular escape rhythms usually result from?
ventricular automaticity focus activation
Following sinus ____ (or block) another _____ will take over, resulting in an ______ _____.
Following sinus arrest (or block) another pacer will take over, resulting in an escape beat.
originate early from an “irritable” automaticity focus
premature beats
Causes of atrial and junctional focus irritability include:
- Epinephrine
- Sympathetic stimulation
- B1 stimulants (caffeine, amphetamines, cocaine)
- Drugs (excess digitalis, ethanol)
- Hyperthyroidism
- Cardiac stretch (heart failure)
- Low oxygen
Which automaticity foci are particularly susceptible to low oxygen tension, hypokalemia, excess stretch, etc?
ventricular automaticity foci
usually result in a change in rhythm (shortened) followed by a prolonged period after which the SA node resets and takes over
premature atrial beats/contraction (PAB, PAC)
EKG change with premature atrial beats
-different shaped P wave with normal QRS wave
arise from an irritable atrial focus, causing premature atrial depolarization
premature atrial beats
What are some other EKG changes that may result from premature atrial beats?
- May result in aberrant ventricular conduction if one bundle branch has not repolarized fully (wide QRS)
- If AV node does not conduct the PAB, a QRS complex is absent
occurs when each normal beat is followed by an abnormal PAB
atrial bigeminy
occurs when two normal beats are followed by an abnormal PAB
atrial trigeminy
Premature beats may originate at an irritable automaticity focus in the AV node (junction), resulting in what?
premature junctional beat
EKG changes with premature junctional beat
- Occur prematurely – early
- P waves may be buried in the QRS wave, occur before or after, or not be conducted
- The QRS complex may be normal, or wider than normal due to incompletely repolarized bundle branches
result when an irritable ventricular automaticity focus fires unexpectedly
premature ventricular contractions
EKG changes with premature ventricular contractions
- Occur prematurely
- No P wave
- The impulse is slowly transmitted to the rest of the ventricles through the myocardium, producing a wide QRS wave and bizarre T wave
Why does it take a long time for full depolarization to cure with premature ventricular beats?
Because the ventricular wall conducts slowly (via cardiomyocyte conduction rather than through the conduction system)
What does the shape of the wave depend on for premature ventricular beats?
The shape of the wave will depend on where the depolarization begins
What generally follows a PVC? Why?
there is generally a compensatory pause as the ventricles repolarize
Why might there be P waves occurring with PVC?
There may be P waves occurring from independent atrial depolarization
Why might multiple PVCs may occur?
if the ventricular automaticity focus is very irritable (e.g., poor oxygenation, epinephrine, β-agonists)
What may multiple PVCs result in?
- ventricular bigeminy
- ventricular trigeminy
- ventricular tachycardia
If all PVCs originate from the same ____ the QRS waves will have the same _____.
If all PVCs originate from the same focus the QRS waves will have the same shape.
If the PVCs originate from _____ foci the ____ waves will look different.
If the PVCs originate from multiple foci the QRS waves will look different.
