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Imaging
During regional myocardial ischemia, non-ischemic segments may treadmill, however, since some patients find cycling in the supine
demonstrate compensatory hypercontractility, preserving global position very difficult.
ventricular systolic function. In the setting of CAD, the absence of
improvement of global systolic function during stress associated with Dobutamine Stress Echocardiography
left ventricular enlargement is a marker of severe ischemia, The underlying principle of dobutamine SEcho (DSE) is that
suggesting multivessel involvement.  A global decrease in  left adrenoreceptor stimulation will augment heart rate, blood pressure,
ventricular  function in response to stress, however,  may be due to contractility, and myocardial oxygen demand. Hemodynamic response
other causes such as hypertension or cardiomyopathy. In the vast to dobutamine and exercise are not absolutely identical. In fact, changes
majority of patients, once the stressor is eliminated, ischemia in venous return and heart rate response are more pronounced with
resolves and wall motion abnormalities recover rapidly. Sometimes exercise, while dobutamine provokes a greater augmentation in
contractile dysfunction may persist for 30 minutes or longer, however, myocardial contractility.
suggesting the presence of more severe ischemia.
Current state-of-the-art DSE exam involves various stages of either
Stress Echocardiography low- or high-dose protocols, with increments from 5 to 40μg/kg/min,
The combination of stress testing and echocardiography—SEcho— with each stage lasting  three minutes. Echocardiographic second
has assumed an important role in the diagnosis of CAD. The harmonic images are acquired at each stage to determine new wall
appearance of a new stress-induced regional  wall motion  motion  abnormalities, worsening of pre-existing abnormalities, or
abnormality, readily identified by echocardiography, allows the enhanced wall motion. The protocol should not be stopped because
of the induction of minor  wall motion  abnormalities, as the chance
to identify multivessel CAD increases when maximal stress testing
The appearance of a new stress-induced
is pursued.
regional wall motion abnormality, readily
One of the limitations of DSE is the failure to achieve 85% of age-
identified by echocardiography, allows the
predicted maximum heart rate. Several reports have shown that the
addition of atropine to peak-dose dobutamine (in doses of 0.25mg up
detection of ischemia, and its location
to a maximum of 1mg) is safe and beneficial in patients without
may be used to predict the stenosed
symptoms and echo signs of ischemia who developed inadequate
heart rate responses.
2
It is especially beneficial in those taking beta-
coronary vessel.
blockers and those in whom second-degree heart block develops
during tachycardia.
2
Moreover, anti-anginal medical therapy (in
particular beta-blockers) strongly reduces the diagnostic accuracy of
detection of ischemia, and its location may be used to predict the all forms of stress; therefore, discontinuation of the drug at the time
stenosed coronary vessel. The types of stress employed fall into two of testing is recommended to avoid a false-negative result.
basic categories: exercise and pharmacological.  SEcho with
pharmacological stress can be performed with either dobutamine or Side effects of dobutamine include anxiety, flushing, and palpitations
vasodilator stressors (dipyridamole or adenosine), dobutamine due to premature ventricular or atrial contractions and brief episodes
being  the best studied and most widely clinically available. Other of non-sustained ventricular tachycardia. Occasionally, dobutamine
forms of stress, such as atrial pacing in patients with a permanent induces paradoxical hypotension and  left ventricular  outflow
pacemaker, are less frequently used. obstruction with systolic anterior motion of the mitral valve. The half-
life of dobutamine is short, so side effects can be readily reversed
Exercise Stress Echocardiography through termination of the infusion. In severe cases, a short-acting
SEcho with exercise testing can be performed either on a treadmill or intravenous beta-blocker such as esmolol or metoprolol is effective.
by stationary (upright or supine) cycle ergometry. Exercise induces an Despite the use of high-dose protocols, DSE is an exceptionally safe
increase in heart rate, blood pressure, myocardial contractility, and procedure in appropriate patients, with serious complications such as
cardiac work, increasing oxygen demand. life-threatening arrhythmias or myocardial infarction occuring  in
approximately three in 1,000 patients.
3
Treadmill exercise is the most common form of stress testing in the US.
In this context, echo imaging is performed before and immediately after Dipyridamole and Adenosine Stress Echocardiography
treadmill exercise without affecting the exercise portion of the test. Dipyridamole inhibits adenosine uptake, inducing endogenous
Ischemia may resolve quickly after termination of the exercise, so all adenosine accumulation. The stimulation of adenosine receptors
post-exercise images should be obtained within one to two minutes. induces potent regional vasodilatation, which is significantly less
pronounced in those areas supplied by stenotic coronary arteries. Flow
The primary advantage of bicycle exertion is the ability to acquire is diverted away from abnormal regions (coronary steal), and this
images during the exercise protocol, particularly at peak stress, phenomenon of blood flow maldistribution produces ischemia in those
avoiding the potential problem of rapid recovery after termination of regions with a precarious flow balance. Vasodilator stressors have a
exercise. The attainable workload with a bicycle is lower than with a negative chronotropic and dromotropic effect and no relevant
38 US CARDIOLOGY