Which of the following conditions may result in tachycardia?
a. Toxic conditions of the heart
b. Increased body temp.
c. Sympathetic nerve stimulation
d. All of the Above
e. B and C only
d. All of the Above
Circus movements are the basis of heart fibrillation. Which of the following statements is not true? a. Fibrillation may occur when the refractory period of the muscle is greatly shortened b. Fibrillation may occur when the pathway around the circle is too short c. Fibrillation may occur when the conduction velocity slows down d. Fibrillation may occur when the heart becomes dilated
b. Fibrillation may occur when the pathway around the circle is too short
What is the definition of Tachycardia?
Fast heart rate (> 100 beats/min)
What are the causes of Tachycardia?
Increased body temp Stimulation of the heart by sympathetic nerves Toxic conditions of the heart
The results of Endogenously Mediated Tachycardia (i.e. exercise) include:
Increased HR Increased cardiac output Reduced filling time, but stroke-volume does not fall (ejection fraction increases)
The results of Pathologically mediated tachycardia include:
Increased HR Decreased cardiac output
What is the definition of Bradycardia?
Slow heart rate (
What are the causes of Bradycardia?
Athletic heart Vagal stimulation Extremely sensitive carotid baroreceptors in carotid sinus syndrome
Identify the ECG
Sinus Bradycardia
What type of signals alternately increase and decrease number of impulses transmitted through sympathetic and vagus nerves to the heart?
Spillover signals
From medullary repiratory center into vasomotor center during inspiratory and expiratory respiratoty cycles
What is this called?
Sinus Arrhythmia
Characteristics of Sinoatrial Block (5):
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
Ventricles will still fill but won’t have last third of pumping effect from atria
Identify the ECG
Sinatrial nodal black (lead III)
What are conditions that cause atrioventricular blockage?
Ischemia of AV node or AV bundle fibers through coronary insufficiency
Compression of AV bundle by scar tissue or clacified portions of the heart
Inflammation of the AV node or bundle
Extreme stimulation of the heart by the vagus nerve
What are the two types of incomplete atrioventricular block?
First-degree
Second-degree
What is the normal P-R time interval?
0.16 sec
What determines if a patient has a first degree incomplete heart block?
When the P-R interval increases to geater than 0.20 seconds
What determines a Second-Degree block?
P-R time intercal increases to 0.25 to 0.45 secs
Atrial P wave is present but QRS-T wave may be missing, resulting in dropped beats of the ventricle
Identify the ECG
Prolonged P-R interval (first degree A-V heart block) (lead II)
Identify the ECG
Second degree A-V block
Describe what happens in a complete atrioventricular block
(WARNING: Very wordy)
Ventricles establish their own signal
No relation between rate of P waves and rate of QRS-T complexes
Duration of block is highly variable (secs to weeks)
After AV conduction ceases, ventricles may not start beating on their own for 5-30 secs
Resumption of the ventricular beat may be due to parts of the Purkinje system acting as an ectopic pacemaker
Patients often faint due to lack of blood to brain until ventricles escape
The periodic fainting spells are reffered to as
Stokes-Adams Syndrome
Identify the ECG
Complete A-V block
A partial intraventricular black is referred to as what?
“electrical alternans”
What does the term “electrical alternans” refer to?
An alteration in the amplitude of P waves, QRS complexes, or T waves
Identify the ECG
Partial Intraventircular Block (electrical alternans)
Most premature contractions are the result of:
ectopic foci
Give examples of ectopic foci (3)
Local ischemic areas
Calcified plaques
Irritation of the conduction system or nodes
Identify the ECG
Atrial Premature Beat
Identify the ECG
A-V nodal premature contraction
Define Paroxysmal Tachycaradia
Heart becomes rapid in paroxysms
Identify the ECG
Atrial paroxysmal tachycardia
Identify the ECG
Ventricular paroxysmal tachycardia
Explain the Basis for 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 stiumlated by the existing depolarization waves
What is Fibrillation?
Twitching (usually slow) of individual muscle fibers in the atria or ventricles and also in recently denervated skeletal muscle fibers
What causes fibrillation?
Fibrillation occurs as a result of circus movements
What is a circus movement?
When the impuls travels around in a circle
Name three different conditions that cause 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 shorteded
Explain a how the length of the pathway around the circle (ventricles) being too long can create a circus movement
When a pathway is too long, often because of a dilated heart, the impulse takes longer to get back to the starting point, and the muscle is no longer in its refractory period and can therefore undergo another depolarization
What can be the cause of a circus movement occuring because of a slowed velocity (but same length pathway)?
Blockage of Purkinje system, ischemia, or high potassium levels
What can be the cause of a circus movement occuring due to a shortened refractory period?
May occur in response to drugs such as epinephrine
May occur after repetitive electrical stimulation
Identify the ECG
Ventricular fibrillation
Atrial Fibrilation
The atrial muscle fibers are separated from the ventricular muscle fibers by the cardiac fibrous skeleton
May occur seperate from ventricular fibrillation
Causes of atrial fibrillation
Enlargement of the atria (i.e. due to valve lesions)
Inadequate emptying of the ventricles causing blood to back up into the atria
Identify the ECG
Atrial Fibrillation