dipyridamole n BBB Qs - woodywoodpecker

[ArchivalUser]

Dipyridamole is often used during nuclear cardiac
stress tests. Based on the pathophysiology of myocardial
ischemia and the mechanism of action of dipyridamole,
in which circumstance might the stress test underestimate
the degree of ischemic tissue?
A. Three-vessel high-grade obstruction
B. Bradycardia
C. Left bundle branch block
D. Osteoarthritis
E. Right coronary artery 99% occlusion
V-62. A 62-year-old female with a history of chronic left
bundle branch block is admitted to the coronary care unit
with 4 hours of substernal chest pain and shortness of
breath. She has elevation of serum troponin-T. She receives
urgent catheterization with angioplasty and stent placement
of a left anterior descending (LAD) artery lesion.
Three days after admission she develops recurrent chest
pain. Which of the following studies is most useful for detecting
new myocardial damage since the initial infarction?
A. Echocardiogram
B. Electrocardiogram
C. Serum myoglobin
D. Serum troponin-I
E. Serum troponin-T

[ArchivalUser]

DD

[ArchivalUser]

DC

[ArchivalUser]

OOPS!
1 A
2 D

[ArchivalUser]

1.B
2.A

[ArchivalUser]

The answer is A. Dipyridamole inhibits the activity of adenosine deaminase
and phosphodiesterase, which cause an accumulation of adenosine and coronary artery
vasodilation. Where there is significant obstructive coronary disease, there is a pressure gradient
between prestenotic and poststenotic segments, and the poststenotic vascular bed dilates
to allow for preserved coronary blood flow. Higher degrees of obstruction cause
maximal poststenotic vasodilation. In nonaffected regions of myocardium, there is no distal
vasodilation. Dipyridamole, by disproportionately dilating nonobstructed areas of myocardium,
is useful as a pharmacologic agent to differentiate ischemic from nonischemic
tissue. Where there is high-grade, three-vessel disease, the usefulness of dipyridamole or
adenosine infusion is limited by (1) baseline maximal vasodilation, and (2) lack of ability to
differentiate affected from nonaffected regions of myocardium. Dipyridamole testing is
helpful in identifying ischemic tissue in a single-vessel territory. Intraventricular conduction
abnormalities limit the use of electrocardiography or echocardiography as a stressimaging
technique. Dipyridamole, as a pharmacologic stressor, is not affected by heart rate
and may be particularly useful for patients who are unable to exercise.


The answer is C. Myoglobin is released from ischemic myocardial cells
and appears in serum within hours. It has a very short half-life in serum as it is excreted
rapidly in the urine. Serum myoglobin returns to normal within 24 h after an infarction.
Therefore, in this patient a new elevation of myoglobin would be helpful in distinguishing
new myocardial necrosis. Troponin-I and troponin-T are more specific markers of
myocardial necrosis but have a long half-life in the circulation. They may remain elevated
for over a week after an acute MI. Therefore, they are not as useful for detecting new or
recurrent injury. In the presence of a preexisting left bundle branch ECG is of limited
utility in detecting new ischemia. Serial echocardiograms may detect new wall motion
abnormalities that suggest new ischemia or infarction, but in the absence of a prior study
a single echocardiogram would have limited utility in this patient.

[ArchivalUser]

thanks great Q

[ArchivalUser]

thank