Lecture 8 Cardiac Arrhythmias Flashcards
Tachycardia
Fast Heart rate (>100 beats/min)
What causes Tachycardia
Increased body temperature stimulation of the heart by sympathetic nerves Toxic conditions of the heart
How much does heart rate increase with body temperature
Increases about 10 beats per degree F increases about 18 beats per degree C
The heart may be stimulated by the sympathetic nerves for increase heart rate due to what
loss of blood and/or decreased state of shock
During endogenously mediated tachycardia does stroke volume fall
No
What happens during endogenously mediated tachycardia (i.e. Exercise)
Heart rate increases, Cardiac output increases, filling time is reduced but stroke-volume does not fall
what happens during pathologically mediated tachycardia
heart rate increases, cardiac output decreases
Bradycardia
HR less than 60 beats/min
What are some causes of Bradycardia
Athletic heart Vagal Stimulation Extremely sensitive carotid baroreceptors in carotid sinus syndrome
What are respiratory type of Sinus arrhythmia: Spillover signals
form medullary respiratory center into vasomotor center during inspiratory and expiratory respiratory cycles - these signals alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart
What kind of block causes a sudden cessation of the P wave
Sinoatrial block
What are the characteristics of a sinoatrial block
Sudden cessation of the P-waves Resultant standstill of atria Ventricles pick up a new rhythm, usually originating in the AV node Rate of QRS is slowed but not otherwise altered
what are some conditions that cause an Atrioventricular block
-Ischemia of AV node or AV bundle fibers through coronary insufficiency - Compression of AV bundle by scar tissue or calcified portions of the heart - Inflammation of the AV node or bundle - Extreme Stimulation of the heart by the vagus nerves
Characteristics of a Incomplete First-Degree AV block
The P-R interval is increased to greater than 0.20 seconds
Characteristics of a incomplete second-degree AV block
P-R interval is increased to 0.25 to 0.45 seconds Atrial P wave is present but QRS-T wave may be missing, resulting in dropped beats of the ventricle 2:1 rhythm or other variations may develop
Characteristics of Complete AV block
- ventricles establish their own signal (usually AV node) - No relation between the rate of the P waves and the rate of the QRS-T complexes - Duration of the block is highly variable (seconds to weeks) - After AV conduction ceases, ventricles may not start beating on their own for 5 to 30 seconds - Resumption of the ventricular beat (=ventricular escape) may be due to parts of the Purkinje system acting as an ectopic pacemaker - after a complete block occurs, patients will often faint due to lack fo blood to the brain until the ventricles escape - These periodic fainting spells are referred to as Stokes-Adams syndrome
what is Ventricular escape
Resumption of the ventricular beat
what may lead to ventricular escape
Parts of the Purkinje system acting as an ectopic pacemaker
After AV conduction ceases, ventricles may not start beating on their own
for 5-30 seconds
What is Stokes-Adam Syndrom
Period fainting spells due to lack of blood to brain secondary to complete AV block
What is a partial Intraventricular block normally referred to as
Electrical Alternans
what is a Electrical alternans
Partial intraventricular block an alternation in the amplitude of P waves, QRS complexes, or T waves
What are premature contractions
Contractions that occur before they should
What are the main causes of premature contractions
Ectopic foci: - Local ischemic areas - Calcified Plaques - Irritation of the conduction system or nodes
What is Paroxysmal Tachycardia, how long does it last, and how does it end?
Heart becomes rapid in paroxysms paroxym begins suddenly and lasts for a few seconds, minutes, hours, or longer Paroxysm ends suddenly Pacemaker of the heart instantly shifts back to the sinus node
Each block on the x-axis is how many seconds
0.2 seconds, each smaller block is 0.04 seconds
Each large block on the x-axis is how many mV
0.5 mV, each smaller block is 0.1mV
what is fibrillation
twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers.
Fibrillation occurs as a result of what
circus movements
What are the 3 different conditions that case the impulse to travel around the circle
- the pathway around the circle is too long - The length of the pathway remains constant but the velocity of the conduction slows down - The refractory period of the muscle might become greatly shortened
What is the effect of the pathway around the circle (ventricles) being too long
The impulse takes longer to get back to its starting point, and the muscle is no longer in its refractory period and can undergo another depolarization
When causes the length of the pathway to remain normal, but the conduction velocity of the impulse is slowed down
Usually occurs because of the blockage of the Purkinje system, ischemia, or high potassium levels
What may cause the refractory period of the muscle to shorten
may occur in response to drugs such as epinephrine may occur after repetitive electrical stimulation
What are some causes of atrial fibrillation
Enlargement of the atria ( due to valve lesions) -Inadequate emptying of the ventricles causing blood to back up into the atria
Atrial muscle fibers are separated from the ventricular muscle fibers by the __________
Cardiac fibrous skeleton
Can ventricular and atrial fibrillation occur separate form one another
Yes
Bradycardia
Sinoatrial block
First degree A-V block
(Prolonged P-R interval)
Second degree A-V block
(Prolonged P-R interval with Dropped beat)
Complete A-V block
(no relation between the rate of the P waves and the rate of the QRS-T complexes)
Partial intraventricular block (electrical alternans)
(Alternation in the amplitude of the Pwaves, QRS complexes, or T waves)
Atrial premature beat
A-V nodal premature contraction
Atrial paroxysmal tachycardia
Ventricular paroxysmal Tachycardia
Atrial Fibrillation
Ventricular fibrillation
