through the bypass tract), the normal slowing effect of the AV node is lost
and rapid ventricular response rates (> 200 beats per minute) can occur. The
most dangerous circumstance is in atrial fibrillation where impulses occur at
a rate greater than 300 beats per minute. This can quickly lead to ventricular
fibrillation.
(a)Ventricular tachycardia may be difficult to distinguish from WPW.
In a young patient with classic ECG findings, however, WPW is more
likely. Nonetheless, it is prudent to avoid AV nodal blocking agents in any
wide complex tachycardia. (b)Atrial flutter will have flutter waves that
take on a sawtooth pattern. (c)Atrial fibrillation is an irregular rhythm.
(d)LGL syndrome is classified as a preexcitation syndrome (similar to WPW)
in which a bypass tract is present. LGL is characterized by an individual who
is prone to tachydysrhythmias and has a PR interval less than 120 msec.
Unlike WPW, the QRS complex is normal (no delta wave).
13.The answer is a.(Rosen, pp 1727-1731.)The patient has life-threatening
hyperkalemia.His ECG shows a wide QRS complex, peaked T waves, and
no P waves. At any moment the patient’s rhythm can go into ventricular fib-
rillation or asystole. There are many symptoms of hyperkalemia that are
often difficult to discern from those of the primary condition that precipi-
tated the hyperkalemia. Patients may begin with lethargy and weakness and
progress to paralysis and areflexia. If there are no ECG abnormalities in a
patient with hyperkalemia, treatment can start with potassium binding
resins (eg, Kayexalate). However, this patient requires immediate adminis-
tration of calcium because he has an unstable cardiac rhythm. Calcium (glu-
conate or chloride)antagonizes the effects of potassium in the myocardium
and briefly stabilizes the cardiac membrane. However, calcium will not lower
the potassium level; in order to promote transcellular shifts and removal
from the body, other measures will also be required.
(b)Insulin works to redistribute excess potassium from the extracellular
to the intracellular compartment thereby lowering the serum concentration
transiently. Dextrose is given to prevent hypoglycemia. Sodium polystyrene
sulfonate (Kayexalate) is a definitive treatment for hyperkalemia because it
removes potassium from the body. However, the process is not immediate
and takes between 30 minutes and 2 hours for the results to show. The other
definitive treatment for hyperkalemia is dialysis. (c)Aspirin should be
administered to all patients who are having coronary-related chest pain. Indi-
viduals with an ECG consistent with ST-elevation MI should be taken to the
catheterization laboratory. (d)Though this patient presents with global
Chest Pain and Cardiac Dysrhythmias Answers 31