Lecture 08 Cardiac Arrhythmias Flashcards
What can cause tachycardia?
Increased body temperature - increase 10 beats/F degree
Stimulation of the heart by sympathetic nerves - due to loss of blood and/or state of shock
Toxic conditions of the heart - weakening of myocardium
What is tachycardia?
Fast heart rate greater than 100 beats/min
What is bradycardia?
Slow heart rate less than 60 beats/min
What are causes of bradycardia?
Athletic heart
Vagal stimulation
Extremely sensitive carotid baroreceptors in carotid sinus syndrome
What are spillover signals?
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 the heart
What is sinus arrhythmia caused by?
Spillover signals
What is 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 conditions causing 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
What is incomplete atrioventricular block first degree?
Normal P-R time interval = .16 sec
When P-R interval increases to greater than .20 seconds (slower heart beat), then the P-R interval is prolonged and has first degree block
What is second -degree block?
P-R interval time increases to .25 to .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
What is complete AV block?
Ventricles establish their own signal
No relation between the rate of the P waves and rate of 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
What is ventricular escape?
When there is a resumption of the ventricular beat that may be due to parts of the Purkinje system acting as the ectopic pacemaker
What is Stokes-Adams syndrome?
After a complete AV block occurs, patients will often faint due to lack of blood to the brain until the ventricles escape and the periodic fainting spells are referred to the syndrome
What is partial intraventricular block referred to as?
Electrical alternanas
What does electrical alternans mean?
An alternation in the amplitude of P waves, QRS complexes, or T waves
What are causes of premature contractions?
Ectopic foci
Local ischemic areas
Calcified plaques
Irritation of the conduction system or nodes
What is paroxysmal tachycardia?
Heart becomes rapid in paroxysms and begins suddenly and lasts for a few seconds, minutes, hours or longer
They end suddenly
Pacemaker of the heart instantly shifts back to the sinus node
What does electroshock defibrillation do?
Sends a very strong voltage throughout the heart that stops everything and gives the SA node a chance to recuperate and restart the rhythm
Why in a normal ventricular depolarization do the waves die out?
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 in recently denervated skeletal muscle fibers?
What causes fibrillation in the heart?
Circus movements
What are the three different conditions that cause the impulse to travel around the circle in circle movements?
pathway around the circle is too long
Length of the pathway remains constant but the velocity of the conduction slow down
The refractory period of the muscle might become greatly shortened
What occurs when the pathway around the circle (ventricles) 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
In normal conditions, by the time the impulse returns its starting point, in what state is the heart muscle in?
Refractory period
Even if the length of the pathway remains normal, what is the cause of the conduction velocity of the impulse is slowing down
Usually occurs because of the blockage of the Purkinje system, ischemia, or high potassium levels
How do circus movements occur when the refractory period of the muscle is shortened?
May occur in response to drugs such as epinephrine
May occur after repetitive electrical stimulation
True/False
Atrial muscle fibers are linked to the ventricular muscle fibers by the cardiac fibrous skeleton, therefore ventricular and atrial fibrillation must occur together.
False, they are separated and may occur separate from one another
What are the 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
