Chapter 18
The Cardiovascular System: The Heart
691
(myocardium) of the heart; sometimes follows an untreated
streptococcal infection in children. May weaken the heart and
impair its ability to pump effectively.
Paroxysmal atrial tachycardia (PAT)
Bursts of atrial contractions
with little pause between them.
Ventricular tachycardia (VT
or
V-tac)
Rapid ventricular
contractions that are not coordinated with atrial activity.
Related Clinical Terms
(continued)
or a malfunction of the papillary muscles. One or more of the
mitral valve flaps become incompetent and billow into the leF
atrium during ventricular systole, allowing blood regurgitation.
Occasionally requires valve replacement surgery.
Myocarditis
(mi
0
o-kar-di
9
tis;
myo
5
muscle,
card
5
heart,
itis
5
inflammation) Inflammation of the cardiac muscle layer
Donald Ayers, a 49-year-old male, was
the driver of the bus involved in the
accident on Route 91. He was brought
into the ER with blunt trauma to the
chest. Paramedics noted that the driver’s seatbelt had broken
and that he was found lying under the instrument panel. Initially
unresponsive, Mr. Ayers regained consciousness and complained
of chest, epigastric, and left upper quadrant pain. Examination
revealed mild tachycardia (110 bpm) and a blood pressure of
105/75 mm Hg. An exam 10 minutes later showed a rapid change
in blood pressure (80/55 mm Hg) and HR (130 bpm) along with
muffled heart sounds, a thready (weak) pulse, and bulging neck
veins. Soon after, the patient began to complain of a sudden
onset of pain that radiated into his back from the injury site. The
patient described the pain as “sharp, stabbing, and tearing” and it
continued to increase.
1.
Mr. Ayers’s pulse is described as “thready.” What might this
indicate with respect to this patient’s stroke volume?
2.
Mr. Ayers’s HR increased from 110 to 130 bpm. What effect will
this have on his cardiac output? Explain your reasoning.
Mr. Ayers’s blood pressure continued to drop, so doctors
ordered a chest X ray, ECG, and spiral CT scan (a rapid CT
technique). These diagnostic tests revealed four fractured ribs,
an enlarged mediastinum, and pericardial effusions (fluid in the
pericardium) producing cardiac tamponade.
Mr. Ayers was scheduled for emergency surgery.
3.
Beginning with the concept of end diastolic volume (EDV),
explain the effect that the fluid in the pericardium is having on
the stroke volume of Mr. Ayers’s heart.
4.
Muffled heart sounds are quieter and less distinct. Explain how
changes in EDV can result in muffled heart sounds.
5.
The final diagnosis in this case is a dissection (tear) of the aorta.
From what you know about the anatomy of the heart, where in
the aorta do you think the tear is located? Explain your answer.
6.
Why did Mr. Ayers’s neck veins bulge?
(Answers in Appendix H)
Case Study
Cardiovascular System: The Heart
18
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