Cardiac arrhythmas Flashcards
Define Tachyardia
Fast heart rate (>100 beats/min)
What are some causes of Tachycardia?
- increased body temperature
- stimulation of the heart by the sympathetic nerves
- toxic conditions of the heart
Define Bradycardia
Slow heart rate (<60 beats/min)
What are some causes of bradycardia?
- athletic heart
- vagal stimulation (parasympathetic stimulation)
- extremely sensitive carotid baroreceptors in carotid sinus syndrome
What arrhythmia is present?
Atrial fibrillation
What arrhythmia is present?
Atrial paroxysmal tachycardia
What arrhythmia is present?
Atrial premature beat
What arrhythmia is present?
A-V nodal premature contraction
What arrhythmia is present?
Complete A-V block
What arrhythmia is present?
Partial intraventricular block
What arrhythmia is present?
First degree A-V heart block
What arrhythmia is present?
Second degree A-V block
What arrhythmia is present?
Sinoatrial nodal block
What arrhythmia is present?
Sinus bradycardia
What arrhythmia is present?
Tachycardia
What arrhythmia is present?
Ventricular fibrillation
What arrhythmia is present?
ventricular paroxysmal tachycardia
What are some physiological results of endogenously mediated tachycardia?
- heart rate increases
- cardiac output increase
- filling time is reduced but stroke volume does not fall
What are som physiological results of pathologically mediated tachycardia?
- heart rate increases
- cardiac output decreases
What are spillover signals?
Signals sent from the medullary respiratory center into the vasomotor center during inspiratory and expiratory respiratory signals
- These signals alternately increase and decrease the number of impulses transmitted through sympathetic and vagus nerves through the heart
What are the characteristics of a sinoatrial block?
- sudden cessation of P waves
- resultant standstill of atria
- ventricles pick up a new rhythm, usually in the AV node
- rate of QRS is slowed but not otherwise altered
What would be some conditions that would cause an atrioventricular block?
- ischemia of AV node od Av bundle fibers through coronary insufficieny
- 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
What are the two types of incomplete atrioventricular block?
- First-degree
- second-degree
What characterizes a first-degree A-V block?
When P-R interval increases to greater than 0.20 sec. (normal is 0.16)
What is the normal P-R time interval?
0.16 sec
What characterizes a second-degre A-V block?
- P-R interval increases to 0.25 to 0.45 sec
- 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
Periodic fainting spells due to a complete A-V block is referred to as what?
Stokes-Adam syndrome
Patients will often faint due to a lack of blood to the brain until the ventricles escape because of what type of block?
A complete A-V block
A partial intraventricular block is can be also referred to as what?
Electrical alternans
What term refers to an alteration in the amplitude of P waves, QRS complexes, or T waves?
Electrical alternans
Most premature contractions result from what?
Ectopic foci in the heart
Name 2 of the 3 possible causes of ectopic foci.
- local areas of ischemia
- calcified plaques
- toxic irritation of the conduction system or nodes
What does the term paroxysmal mean?
It means that the heart rate becomes rapid in paroxysms
What are some characteristics of paroxysmal tachycardia?
- paroxysms beigin suddenly and can last for seconds, minutes, hours, or longe
- paroxysms end suddenly
- pacemaker of the heart instantly shifts back to the sinus node
What is the physiological basis behind fibrillation?
The normal ventricular depolarization waves die out because the heart muscle that has already contracted is in the refractory period and cannot respond to being stimulated by the existing depolarization waves
What is fibrillation?
The twitching (usually slow) of individual muscle fibers in the atria or ventricles and also recently denervated skeletal muscle fibers.
Fibrillation occurs as a reult of these?
Circus movements
List 2 of the 3 conditions that cause the impulse to travel in around the circle (circus movements)?
- 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 do circus movements occur if the pathway around the cirle is too long?
By the time to impulse returns to its starting point the originally stimulated muscle will no longer be in the refractory period and the impulse will continue around the circle again and again.
-Chareacteristic of dilated hearts
Whay do circus movements occur when the length of the pathway remains constant but the velocity of the conduction slows down?
An increased amount of time will elaspe before the impulse returns to its original position. By this time, the originally stimulated muscle might be out of the refractory period, and the impulse can continue around the circle again and again.
-Characteristic of blockage of the Purkinje system, ischemia, or high potassium levels.
Why do circus movements occur when the refractory period of the muscle is shortened?
With a shorter refrractory period the impulse could continue around the circle again and again.
- May occur in reponse to drugs such as epinephrine or after repetitive electrical stimulation
The atrial muscle fibers are seperated from the ventriculoar muscle fibers by the _______ _______ _______?
Cardiac fibrous skeleton
True or False: ventricular and atrial fibrillation may occur seperate from one another?
True
What are some causes for atrial fibrillation?
- Enlargement of the atria (due to valve lesions)
- Inadequate emptying of the ventricles causing blood to back up into the atria
