Download Chapter10_Detailed_Answers

Chapter 10
Detailed Answers to Assess Your Understanding
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b:
The impulse that generates the heartbeat originates from the SA node. It then
spreads across the atria from right to left, depolarizing the tissue and causing both atria to
contract. The impulse then activates the AV node, which is normally the only electrical
connection between the atria and the ventricles. Impulse conduction is delayed as it passes
through the AV node allowing the atria to finish contracting and pushing any remaining
blood from their chambers into the ventricles. The impulse then spreads through both
ventricles via the Bundle of His, right and left bundle branches, and the Purkinje fibers
causing a synchronized contraction of the primary pumping chambers of the heart, and
thus, the pulse.
b:
SA node depolarization includes the gradual depolarization of the SA node that
occurs because of a slow inflow of Ca++ into the cell without a corresponding outflow of K+.
b:
The SA node is the primary pacemaker of the heart during normal heart activity.
c:
Depolarization and repolarization of non-pacemaker myocytes takes place over five
phases with depolarization occurring during Phase 0.
d:
Palpitations are the most common symptom of cardiac dysrhythmias. They are an
abnormal sensation felt with the heartbeat. People describe feeling their heart skip a beat
or give an occasional extra strong beat. Palpitations may be infrequent, frequent, or
continuous. Other signs and symptoms of dysrhythmias include low blood pressure,
lightheadedness and shortness of breath. Symptoms are signs of disease or injury. They are
noticed by the patient.
b:
If the patient has a slow heart rate that is producing a low blood pressure, we would
describe it as symptomatic bradycardia. As a general definition, symptomatic can mean
showing symptoms, or it may concern a specific symptom. In this context we think of
someone who is symptomatic as being a patient who is experiencing compromised cardiac
output and in need of treatment. This can also be called unstable bradycardia.
Types of dysrhythmias with the corresponding characteristics. a. Bradycardia is a heart
rate less than 60 beats per minute. b. Tachycardia is a heart rate greater than 100 beats per
minute. c. Premature complexes are impulses that appear early. d. Dropped beats or QRS
complexes occur when the SA node fails to initiate an impulse or from a partial or
intermittent block at the AV node.
b:
(False) Increased parasympathetic tone causes decreased automaticity. It does this
through slowing the automaticity of SA node discharge and impulse conduction through
the AV node. The areas of the heart most affected by the parasympathetic fibers are the SA
node; atria; AV junction; and to a small extent, the ventricles. The parasympathetic branch
of the autonomic nervous system is carried through the vagus nerve and releases the
neurotransmitter acetylcholine. It is therefore referred to as the cholinergic system.
Causes or mechanisms with the corresponding characteristics. a: Increased automaticity is
spontaneous depolarization of the myocytes that occurs more quickly than normal. b. Reentry
occurs when an electrical impulse goes back into a conduction pathway rather than moving from
one end of the heart to the other and then terminating. c Triggered beats occur with problems at
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the level of the ion channels in individual heart cells and leads to partial repolarization which can
cause repetitive ectopic firing. d: Proarrhythmia is a new or more frequent occurrence of
preexisting dysrhythmias that are brought about by antidysrhythmic therapy.
b:
Dysrhythmias that arise from the atria include atrial fibrillation. Other atrial
dysrhythmias are: PACs, wandering atrial pacemaker, atrial tachycardia, supraventricular
tachycardia (SVT), multifocal atrial tachycardia, and atrial flutter.
a:
AV heart blocks include 3rd degree AV block. Other types are 1st degree AV block,
2nd degree AV block, Types I and II, 3rd degree AV block and atrioventricular dissociation.
b:
The preferred lead for identifying cardiac dysrhythmias is lead II.
d:
Physical maneuvers slow the rate at which the SA node fires by stimulating the
parasympathetic nervous system
b:
Synchronized cardioversion is used to treat symptomatic tachydysrhythmias.
a:
Drugs that block the effects of the parasympathetic nervous system are used to treat
bradycardia. Atropine is a drug commonly used to treat bradycardia in the clinical setting.
Antidysrhythmic medications with their actions. a. Class I drugs - Reduce the influx of Na+
ions into the cells during phase 0 of the action potential, which minimizes the chance of
Na+ reaching its threshold potential and causing depolarization. b. Class II drugs - Block the
sympathetic nervous system. Most agents in this class are beta blockers. They depress SA
node automaticity and produce increased AV nodal refractoriness (making it resistant to
stimulation). c. Class III - Block the efflux of K+ during Phase 3 of the action potential and
prolong repolarization and the refractory period. d. Class IV - Inhibit the movement of Ca++
ions during Phase 2 of the action potential, prolonging conductivity and increasing the
refractory period at the AV node.
c:
The patient in the scenario at the beginning of the chapter experienced a sudden
onset of tachycardia at a rate of 220 BPM. This was likely paroxysmal tachycardia as its
self-termination was witnessed by the paramedics.
a:
During the tachycardia the patient was symptomatic. He suddenly felt a pounding in
his chest (palpitations), became lightheaded, and then slumped to the floor. He was also
hypotensive (having a BP of 90/60) and breathing faster than normal.
b:
Reentry was the likely cause of this dysrhythmia. Reentry occurs when an electrical
impulse reenters a conduction pathway (often in a retrograde or reverse manner), rather
than moving from one end of the heart to the other and then terminating. Reentry circuits
are responsible for a number of dysrhythmias, including atrial flutter, most paroxysmal
supraventricular tachycardia, and ventricular tachycardia