(a)The anteroseptal wall of the heart is supplied by the left anterior
descending coronary artery (LAD). An acute MI is identified by ST eleva-
tion in leads V 1 , V 2 , and V 3 .(b)The anterior wall of the heart is also sup-
plied by the LAD and an infarct exhibits ST elevations in leads V 2 , V 3 , and
V 4 .(c)The lateral wall of the heart is supplied by the left circumflex coro-
nary artery (LCA) and an infarct exhibits ST elevations in leads I, aVL, V 5 ,
and V 6 .(e)A posterior MI refers to the posterior wall of the left ventricle.
It occurs in 15% to 20% of all MIs and usually in conjunction with inferior
or lateral infarction. The figure below summarizes the distribution.
11.The answer is c.(Flowers, 2005.)The patient has costochondritis,
an inflammatory process of the costochondral or costosternal joints that
causeslocalized pain and tenderness.Any of the seven costochondral
junctions may be affected, and more than one site is affected in 90% of
cases. The second to fifth costochondral junctions are most commonly
involved. In contrast to myocardial ischemia or infarction, costochondritis
is a benign cause of chest pain, often with an insidious onset, and is an
important consideration in the differential diagnosis for chest pain. Of
note, 5% to 7% of patients with cardiac ischemia also have chest-wall ten-
derness. The onset is often insidious. Chest-wall pain with a history of
repeated minor trauma or unaccustomed activity (eg, painting, moving
furniture) is common. The goal of therapy is to reduce inflammation. NSAIDs
are typically prescribed.
(a)The patient has no cardiac risk factors and his ECG and chest radi-
ograph are normal. (b)This is a regime for ACS. (d)This is not a first-line
therapy. Corticosteroid injection may lead to bone degradation. (e)The
patient does not need to be observed.
12.The answer is e.(Tintinalli, pp 198-199.)WPW syndromeis caused
by an accessory electrical pathway (ie, Bundle of Kent)between the
atria and ventricles. The primary significance of WPW syndrome is that it
predisposes the individual to the development of reentry tachycardias. The
classic ECG findings include a short PR interval (< 120 msec), widened
QRS interval (> 100 msec),and a delta wave(slurred upstroke at the
beginning of the QRS). When conduction occurs anterograde down the AV
node and then retrograde up the accessory pathway (orthodromic), the ECG
will appear normal. When the impulse occurs anterograde down the acces-
sory pathway and retrograde up the AV node (antidromic), the QRS complex
will be wide. In the presence of antidromic conduction (conduction first
30 Emergency Medicine