Cardiac Arrhythmias Flashcards
Circus movements are the basis of heart fibrillation. What is true of them?
Fibrillation may occur when the pathway around the circle is too short
What is Tachycardia?
Fast heart rate
What does the heart rate have to be to be considered tachycardia?
> 100 beats/min
What is bradycardia?
slow heart rate
What heart rate defines bradycardia?
What causes bradycardia?
- athletic heart
- vagal stimulation
- extremely sensitive carotid baroreceptors in carotid sinus syndrome
What are the characteristics of a sinoatrial block
- sudden cessation of 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 the conditions causing the atrioventricular block?
- ischemia of AV node or AV bundle fibers through coronary insufficiency
- compress 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 and second-degree
What are the characteristics of a first-degree incomplete atrioventricular block?
when P-R interval increases to greater that 0.20 seconds, the P-R interval is prolonged
What is the characteristics of a second-degree incomplete atrioventricular block?
- P-R time interval increases to 0.25 to 0.45
- 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.
What are the characteristics of complete atrioventricular block?
- ventricles establish their own signal
- no relation between the rate of the P waves and the rate of the QRS-T complexes
- Duration of the block is highly variable
- After AV conduction ceases, ventricles may not start beating on their own for 5 to 30 seconds
- resumption of the ventricular beat may be due to parts of the purkinje system acting as an ectopic pacemaker.
Whats the periodic fainting spells caused by complete atrioventricular blocks cause lack of blood to the brain known as?
Stokes-Adams syndrome
Whats the resumption of the ventricular beat called when a complete atrioventricular block occurs?
Ventricular escape
What are the characteristics of the partial intraventricular block?
- referred to as electrical alternans
2. alternation in the amplitude of P waves, QRS complexes, or T waves
What are three ectopic foci that causes of premature contractions?
- local ischemic areas
- calcified plaques
- irritation of the conduction system or nodes
What is fibrillation?
the twitching of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers
What are three different conditions that cause the impulse to travel around the circle in 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 conditions may result in tachycardia?
Toxic conditions of the heart
Increased body temperature
sympathetic nerve simulation
How many beats does heart rate increase for every 1 degree F and C?
10 beats and 18 beats respectively
Why does an increase in body temperature cause tachycardia?
Increases the metabolism of the SA node thus increasing its excitability
What is endogenously mediated tachycardia?
Heart rate increase due to exercise or activeness
What are three characteristics of endogenously mediated tachycardia?
- Heart rate increase
- Cardiac output increases
- filling time is reduced but stroke-volume does not fall
What are pathologically mediated tachycardia’s characterists?
Heart rate increases
Cardiac output decreases
