Blake_Physio_08_Cardiac Arrhythmias Flashcards
Tachycardia:
Definition
Causes
Fast heart rate (>100bpm)
Causes:
Increased body temp
Sympathetic Stimulation
Toxic conditions of the heart
Heart rate increases about ____ beats per degree F, or ____ beats per degree C.
10, 18
Endogenousely mediated tachycardia (6)
- Heart rate increases
- Cardiac output increases
- Filling time is reduced but stroke-volume does not fall
- sympathetic stimuli contractility increases
- systolic interval is reduced
- Sympathetic stimulus and skeletal muscle pump increases venous return to maintain ventricular filling.
Pathologically mediated tachycardia: (4)
- heart rate increases
- cardiac output DEcreases
- Mean atrial pressure decreases => sympathetic system does not increase contractility => unable to compensate
- no skeletal muscle pump to increase venous return.
Bradycardia:
Definintion
Causes (3)
- Slow heart rate
- athletic heart
vagal stimulation
carotid sinus syndrome (over sensitive baroreceptors)
Respriratory Type of Sinus Arrhythmia:
Spillover signals: (2)
- From 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 heart
Sinoatrial block: Characteristics: (4)
- Sudden cessation of P waves [visible on ECG]
- Resultant standstill of atria
- Ventricles pick up a new rhythm, usually from AV node
- Rate of QRS is slowed but not otherwise altered.
Atrioventricular Block: Conditions Causing: (4)
- Ischemia of AV node or AV bundle fibers through coronary insufficiency
- Compression of AV bundles 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
Incomplete Atrioventricular Block:
First Degree: (2)
- P-R interval Increases in length with slower heartbeat and decreases with faster heartbeat
- When P-R interval increases to greater than 0.2 sec, the P-R interval is prolonged and patient has first degree incomplete heart block.
When _____ interval increases to greater than _____ sec, the _____ interval is _________ and patient has _______, _________ heart block.
P-R, 0.2, P-R, prolonged, first degree, incomplete
Incomplete Atrioventricular Block:
Second Degree: (3)
- P-R interval 0.25-0.45 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
Where are Ventricals signaled from in a complete atrioventricular block?
Ventricals establish their own signal (usually the AV node)
What is the relationship between the rate of the P waves and the rate of the QRS-T complexes during a complete atrioventricular block?
There is no relation between rate of P and rate of QRS-T during a complete atrioventricular block.
After AV conduction ceases, ventricles may not start beating on their own for ____ to______ sec
5-30sec
Resumption of the ventricular beat (ventricular escape) may be due to parts of the _________ system acting as an _________ ___________
Purkinje, ectopic pacemaker
After a complete atrioventricular block occurs, patients will often _______ due to __________ until the ventricals _________
faint due to lack of blood to the brain until the ventricals escape.
Periodic fainting spells due to complete atrioventricular block is called _________
Stokes-Adams-Syndrome
Partial intraventricular blocks are also referred to as _________
electrical alternans
Electrical alternans refers to_______
and alternation in the amplitude of P waves, QRS complexes, or T-waves
Premature contractions are the result of (3)
Ectopic foci such as:
local ischemic areas,
calcified plaques,
irritation of the conduction system or nodes
Paroxysmal Tachycardia: (3)
Heart becomes rapid in paroxysms:
- Paroxysm begins suddenly and lasts for a few seconds to hours or longer.
- Paroxysm ends suddenly
- Pacemaker of the heart instantly shifts back to the sinus node
Basis of Fibrillation
the normal ventricular depolarization waves die out because the heart muscle that has already contracted is in the REFRACTORY PERIOD and canot respond to being stimulated by the existing depolarization waves.
Fibrilation is ________________________________
the twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers
Fibrilation occurs as a result of _______________
circus movements
Circus movements: Three conditions that cause them
- the pathway around the circle is too long
- the velocity of conduction is slowed down
- the refractory period of the muscle might become greatly shortened
Circus Movements: Occur when the pathway around the circle (ventricles) is too long because: (2)
- Normally, by the time the impulse returns to its starting point, the heart muscle will be in the refractory period.
- If the pathway is too long, often because of a dilated heart, 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.
3 factors that cause circus movements by slowing the conduction velocity of the impulse.
Blockage of the Purkinje system,
ischemia,
High potasium levels.
2 factors that may cause circus movements due to shortening of the refractory period:
- drugs such as epinephrine
- repetitive electrical stimulation
Atrial Fibrillation (2 facts)
- Atrial muscle fibers are separated from the ventricular muscle fibers by the cardiac fibrous skeleton.
- Ventricular and atrial fibrillation may occur separate from one another.
Why are atrial muscle fibers unaffected by ventricular fibrillation?
Atrial muscle fibers are separated from the ventricular muscle fibers by the cardiac fibrous skeleton.
Causes of atrial fibrillation: (2)
- Enlargement of the atria (i.e. due to valve lesions)
- Inadequate emptying of the ventricles causing blood to back up into the atria
