Exam 2 – Cardio Ch 13 Flashcards
What are causes of cardiac arrhythmias?
Abnormal rhythmicity of the pacemaker
Shift of pacemaker from sinus node
Blocks at different points in the transmission of the cardiac impulses
Abnormal pathways of transmission in the heart
Spontaneous generation of abnormal impulses from any part of the heart
What are normal causes of sinus arrhythmia?
Increase in heart rate during inhalation
Decrease in heat rate during exhalation
Autonomic input associated with respiration
What are abnormal sinus rhythms?
Tachycardia
Bradycardia
Define tachycardia
Fast heart rate is greater than normal range
What causes tachycardia?
Increased body temperature
Sympathetic stimulation (blood loss, reflex stimulation of the heart)
Toxic conditions
How does increased body temperature cause tachycardia?
Due to increased rate of metabolism of sinus node which in turn directly increase its excitability and rate of rhythm
Define bradycardia
Slow heart rate lower than normal range
Why is bradycardia present in some athletes?
They have a large stroke volume
What can cause bradycardia?
Vagal stimulation
What is carotid sinus syndrome?
Especially sensitive syndrome that easily triggers vagal stimulation
Define sinoatrial block
In rare instances impulses from SA node are blocked before it enters atrial muscle
What does sinoatrial block cause cessation of?
P wave
What is the new pacemaker in sinoatrial block?
Region of heart with the next fastest discharge rate, usually AV node
Due to cessation of P waves in sinoatrial block, what is occasionally seen?
Atrial standstill
Define atrioventricular block
Impulses through AV node and AV bundle are slowed down or blocked
What causes atrioventricular block?
Ischemia
Compression
AV nodal/AV bundle inflammation
Excessive vagal stimulation
What is the AV bundle also known as?
Bundle of HIS
Describe incomplete heart block first degree block
Long space between P wave and QRS
Prolonged PR interval
What can the PR interval not be longer than in a first degree block?
RR interval
Cannot be longer than space between two beats
Why is a first degree block considered incomplete?
Delay of conduction from atria to ventricles but not actual blockage of conduction
Describe second degree incomplete block
PR interval increased
What is Mobitz Type ! or Wenkebach second degree block?
PR gets longer with each beat until a beat is dropped
What is Mobitz Type 2 second degree block?
Some impulses pass through AV node and some do not thus causing “dropped beats”
Fixed number of nonconducted P waves for every QRS complex
What happens to atria speed in second degree incomplete block?
It beats faster than ventricles
What species tends to have mild second degree block at rest?
Horses
Describe third degree complete block
Total block through AV node or AV bundle
How are the P waves in a third degree complete block?
Completely dissociated from QRST complexes
AV dissociation
What happens to ventricles in third degree complete block?
Ventricles escape and AV nodal rhythm ensues Spontaneously establish their own signal, usually originating in AV node or AV bundle
Is there a relation between rhythm of P waves and QRST complex in third degree complete block?
No because ventricles escape control from atria and beats at its own natural rate
Describe Stokes-Adams syndrome
Fainting associated with complete AV block
How is the complete AV block in stokes-adams syndrome?
It comes and goes
What happens to ventricles in stokes-adams syndrome?
Ventricles stop contracting for 5-30 seconds because of overdrive suppression meaning they are used to atrial drive
Why does the patient faint from stokes-adams syndrome?
Because of poor cerebral blood flow
What does the ventricle escape in stokes-adams syndrome?
AV nodal or AV bundle rhythm (15-40 beats/min)
What will correct stoke-adams syndrome?
Pacemaker
What happens to the impulse in incomplete intraventricular block (electrical alternans)?
Sometimes blocked and sometimes not in peripheral portions of purkinje system resulting in abnormal QRS waves
What can cause incomplete intraventricular block?
Ischemia
Myocarditis
Digitalis toxicity
What is incomplete intraventricular block associated with?
Pleural and/or pericardial effusions in animals
What happens to the PR interval in premature atrial contractions?
Shortened if ectopic foci originating the beat are near AV node
Where does the impulse travel in premature atrial contractions?
Through AV node and back toward sinus node causing discharge of the sinus node
Next sinus discharge will thus be late
How does an early contraction affect the heart?
It doesn’t allow the heart to fill with blood causing a low stroke volume and a weak radial pulse
How does Av nodal or AV bundle premature contractions affect the P waves?
Early and inverted
Missing
Late and inverted
When the P wave is early and inverted, where is the premature contraction in the AV junction?
High AV junction
When the P wave is missing, where is the premature contraction in AV junction?
Mid AV junction
When the P wave is late and inverted, where is the premature contraction in AV junction?
Low AV junction
Where does the impulse travel in a AV junctional premature contractions?
Backward into atria
What happens to the QRS in premature ventricular contractions?
QRS is prolonged because impulse is conducted through muscle which has slow conduction
What happens to the QRS voltage in premature ventricular contractions?
High because one side depolarizes ahead of the other
What happens to the T wave in premature ventricular contractions?
Inverted because slow conduction causes the area to first depolarize to also repolarize first (opposite of normal)
What causes T wave premature ventricular contractions?
Cigarettes
Coffee
Lack of sleep
define paroxysmal
A series of rapid heart beats suddenly start and then suddenly stop
What can stop atrial paroxysmal tachycardia?
Vagal reflex
Quinidine or procainmide or lidocaine
What happens to the P wave in atrial paroxysmal tachycardia?
Inverted if origin is near AV node
How does atrial paroxysmal tachycardia?
Occurs by re-entrant pathways
What autonomic discharge occurs in atrial paroxysmal tachycardia?
High sympathetic discharge
What is an atrial flutter?
Single large impulses wave travels around area in one direction
What is the atrial contraction speed in an atrial flutter?
200-350 beats/min
When will the AV node not pass signal in atrial flutter?
Not pass signal until 0.35 seconds elapses after previous signal
Therefore, atria may beat 2 or 3 times as rapidly as ventricle
What does atrial fibrillation most often occur without?
Ventricular fibrillation
What is the most frequent cause of atrial fibrillation?
Atrial enlargement due to AV valve dysfunction
This causes a long pathway of conduction which is favorable for circus movements
What happens to the efficiency of ventricular pumping because of atrial fibrillation?
Decreased 20-30 percent
Why does an irregular, fast heart rate occur in atrial fibrillation?
Because of irregular arrival of cardiac impulses at AV node
What does atrial fibrillation sound like?
Tennis shoes in a dryer
When does ventricular paroxysmal tachycardia occur?
Usually does not occur unless there has been ischemic damage
What can fix the problem of ventricular paroxysmal tachycardia?
Quinidine increases refractory period of cardiac muscle
When do circus movements occur in ventricular fibrillation?
If pathway is long
If conduction velocity is decreased
If refractory period is shortened
What causes a long pathway in ventricular fibrillation?
Dilated heart
What causes decreased conduction velocity in ventricular fibrillation?
Blockade of purkinje system
Ischemia of muscle
High K+ levels
What causes shortened refractory period in ventricular fibrillation?
Epinephrine release
What is ventricular fibrillation compared to?
Bag of worms
Why is ventricular fibrillation considered a bag of worms?
Some parts of ventricle contract while others relax thus little blood flows out of heart
What is ventricular fibrillation caused by?
Electrical shock or cardiac ischemia
What is ventricular defibrillation?
1000 volts direct current is applied for a few thousandths of a second
Which parts of the heart become refractory during ventricular defibrillation?
All parts of the heart become refractory and remain quiescent for 3-5 seconds until new pacemaker is established
What happens to the heart if used later than one minute after fibrillation?
The heart is too weak to defibrillate and may have to be hand-pumped/CPR
When does cardiac arrest usually occur?
Due to hypoxic conditions in the heart which prevents muscle and conductive fibers from maintaining their electrolyte gradients
Look at ventricular fibrillation diagram
Look at ventricular fibrillation diagram
Look at all EKG pictures
Look at all EKG pictures
