0071643192.pdf

■ Ventricular mechanoreceptors are stimulated.

■ Vagal tone and sympathetic tone ↓.

■ Syncope occurs.

MYOCARDIALPERFUSIONIMAGING

■ Radionuclide testing
■ Thallium or technetium-99m marker is infused during ACS symptoms
or at maximal exertion.
■ Marker is taken up by myocardium in proportion to blood flow, so areas
of poor perfusion are demonstrated.
■ A perfusion defect both at rest and during stress (irreversible defect) =
old infarction.
■ A perfusion defect that occurs only during stress (reversible) =
myocardial ischemia.
■ Technetium-99m has the advantage of allowing for delayed imaging
(up to 3 hours) compared to immediate imaging required with
Thallium.

GRADEDEXERCISESTRESSTESTING

■ Bruce protocol: Exercise pace and/or incline of treadmill increases every
3 minutes.
■ ECG response: ST segment abnormalities are evaluated by
■ Time of onset of abnormality
■ Time of resolution
■ Magnitude of depression or elevation
■ Vital signs: Peak heart rate, blood pressure
■ Higher risk of CAD if
■ Cannot complete 6 minutes of exercise
■ Ischemia in first 3 minutes
■ Drop in SBP
■ ST depression in multiple leads
■ Exercise-induced angina
■ Value of test depends on pretest probability of CAD: Low-risk patients
commonly have false-positive tests.
■ Should not be done in the setting of unstable angina, MI, severe HTN,
uncontrolled dysrhythmias, severe aortic stenosis

PHARMACOLOGICSTRESSTESTING

■ Variety of agents used for patients who cannot complete exercise stress test
for a variety of reasons
■ Inotropic agents
■ Dobutamine: HR without exercise
■ Concurrent echo examined for evidence of LV hypokinesis.
■ Vasodilators: Persantine, adenosine
■ These agents decrease flow to the coronary arteries, exposing areas of
decreased uptake on thallium scan.

ELECTRONBEAMCT

■ New technology that allows for calculating the degree of calcium build-up
in the coronary arteries (calcium score)
■ High calcium score =high likelihood of CAD.
■ May be a good screening tool to exclude CADin the ED patient

→

→

CARDIOVASCULAR EMERGENCIES

Tilt-table testing is primarily

used in the evaluation and

treatment of vasovagal

syncope.

Myocardial perfusion defects

present both at rest and

during stress =old infarction.

Exercise stress testing should

not be performed in the

setting of unstable angina,

severe HTN, or severe aortic

stenosis.