Exam II Flashcards
What is a vector?
An arrow the points in the direction of the electrical potential generated by the current flow. Arrowhead points in positive direction. Length of the arrow is proportional to to the voltage of the potential.
In the ECG shown below, which of the following heart activities is represented?
a) sinus tachycardia
b) sinus bradycardia
c) complete AV block
d) incomplete second degree block with dropped beats
b
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
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
What are the axes for the three leads on the ECG?
Lead I:
R= negative
L= positive
direction= 0 degrees
Lead II (right arm and left leg): A= negative L= positive direction= 60 degrees
Lead III (left arm and left leg): A= negative L= positive direction= 120 degrees
What will voltages be in accordance to the lead directions with the vector of the heart?
- when vector of heart is perpendicular to axis of lead, the voltage recorded in the ECG is very low
- heart vector has almost same axis as the axis of the lead, the entire voltage will be recorded
- instantaneous mean vector: the summated vector of the generated potential at a particular instant
- reference vector is horizontal and extends to left side
What is the vector of the heart in relation to the zero reference point?
59 degrees (mean electrical axis of the heart)
What is the vectorial analysis of the T wave?
- the greatest portion of the ventricles to repolarize first is the outer surface near the apex
- endocardial cells normally repolarize last
- ventricular vector during repolarization is toward the apex of the heart
- normal T wave in all three bipolar leads is POSITIVE
What is the vectorial analysis of the P wave?
- atrial depolarization begins in the sinus node
- vector direction is generally in the direction of the axes of the three limb leads
- ECG is normally positive in all three leads
What is the vectorial analysis of the atrial T wave?
- spread of depolarization through atrial muscle is slower than in ventricles
- musculature around sinus node becomes depolarized a long time before the musculature in the distal parts of the atria
- sinus node is the first to become repolarized
- at the beginning of repolarization, the sinus node is positive with respect to the rest of the atria
- obscured by QRS wave
What are the names of the leads utilized for an ECG?
six standard leads (V1-V6)
three augmented leads (aVR, aVL, aVF)
What can cause the heart’s axis to move?
ventricular conditions:
- change in position of heart in the chest
- hypertrophy of one ventricle
- bundle branch block
- fluid in pericardium
- pulmonary emphysema
What can cause an increased voltage of the QRS wave in the bipolar leads?
- occurs when the sum of the voltages of all the QRS complexes of the leads is greater than 4mV
- most common cause is hypertrophy of the ventricle
What causes a decreased voltage of the QRS wave in a ECG?
- caused by cardiac myopathies
- conditions surrounding the heart
With hypertrophy of the heart is the QRS shortened or lengthened? What can cause this abnormality?
lengthened from 0.06-0.08 to 0.09-0.12
Causes:
- destruction of the cardiac muscle and replacement by scar tissue
- multiple small local blocks in the conduction impulses at the many points in the Purkinje system
What characterizes a current of injury? The “trademark”
- causes part of the heart to remain partially or totally depolarized all the time
- current of injury flows between the pathologically depolarized and the normally polarized areas, even between heartbeats
- the wave will begin above or below the J line due to the fact that the injured part is depolarized
What abnormalities cause an injury current?
- mechanical trauma
- infectious processes
- ischemia (most common cause)
How does a current of injury affect the QRS wave?
-abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles
What is the J point?
the reference point for analyzing current of injury
What is tachycardia and what are some causes?
-fast heart rate (greater than 100 bpm)
Causes:
- increased body temperature (heart rate increase about 10bpF or 18bpC)
- stimulation of the heart by sympathetic nerves (due to loss of blood and state of shock)
- toxic conditions of the heart (results in weakening of the myocardium)
What is the difference between endogenously (exercise) and pathologically mediated tachycardia?
Endogenously:
- heart rate increases and cardiac output increase
- filling time is reduced but stroke volume does not fall
- systolic interval is reduced allowing for more diastolic filling time
- sympathetic and skeletal muscle pump increase venous return to help maintain ventricular filling
Pathological:
- heart rate increases
- cardiac output decreases
- no muscle pump
- mean atrial pressure decreases and activates the sympathetic nervous system, which occurs after the fact and is unable to compensate
What is bradycardia and what are some of the causes?
-slow heart rate (less than 60 beats/min)
Causes:
- athletic heart
- vagal stimulation
- extremely sensitive carotid baroreceptors in carotid sinus syndrome
What is the respiratory type of sinus arrhythmia?
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 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
- no SA node, picks up AV node rhythm