Sensitivity and specificity are similar to exercise stress testing.
Use when a patient is unable to exercise, has low exercise tolerance, has had a recent MI. It is also frequently used in patients with LV pacers and patients with LBBB. Imaging is required in patients with LBBB since the electrocardiogram (ECG) will not be interpretable for ischemia.
Pharmacologic Stress Agents: Vasodilator vs. Positive Inotrope / Chronotrope
Pharmacologic stress testing can be done using a vasodilator or a drug with positive inotropic/chronotropic effects.
The choice of drug (s) used to stress depends on three things: 1) patient characteristics 2) the kind of stress imaging study being done, 2) provider/institutional preferences.
Because the sensitivity of the stress ECG alone in patients who undergo pharmacologic stress is very low, pharmacologic stress always combines ECG analysis with an imaging modality.
Vasodilators
The vasodilator stress agents increase coronary blood flow through their effects on adenosine A2A receptors.
- Adenosine.
- Dipyridamole;
- Regadenoson (Lexiscan)
- Binodenoson, and
- Apadenoson
***Vasodilators will reveal CAD, but not tell you if the patient is ischemic.
Vasodilators are the preferred pharmacologic stress agent for radionuclide myocardial perfusion imaging (MPI) studies and can be combined with low-level exercise.
The Vasodilators may precipitate bronchospasm and bradycardia and so are contraindicated (absolutely or relatively) in:
- Pronounced active bronchospastic airway disease (since these drugs may stimulate adenosine A2B receptors, which cause bronchospasm)
- Significant hypotension (since these drugs lower the blood pressure)
- Sick sinus syndrome and high-degree AV block (since these drugs may worsen preexisting conduction disease) without a functioning pacemaker
- Unstable or complicated acute coronary syndrome (an increased risk for ischemic events is present with all stress modalities)
Caffeine should be withheld 12 hours and Theophylline for 48 hours before vasodilator stress since these agents can decrease the effectiveness of vasodilators.
Inotropes and Chronotropes
Dobutamine is a synthetic catecholamine that stimulates beta1-adrenergic receptors with the effect of increasing the heart rate (chronotropic effect) and myocardial contractility (inotropic effect).
Dobutamine is the preferred pharmacologic stress agent for stress echocardiography and is the second-line pharmacologic stress agent for stress radionuclide MPI studies.
Because dobutamine may precipitate tachyarrhythmias, it has the following contraindications:
- Sustained or frequent ventricular arrhythmias and atrial fibrillation with RVR
- Recent MI (within one to three days) or unstable angina
- Hemodynamically significant left ventricular outflow tract obstruction
- Aortic dissection
- Moderate to severe systemic hypertension (resting systolic blood pressure >180 mmHg)
Atropine is often used together with dobutamine in patients who do not achieve target heart rate. Atropine given blocks acetylcholine at parasympathetic sites in smooth muscle. The combination results in near maximal coronary vasodilatation, with a significant increase in myocardial blood flow comparable to that caused by dipyridamole in young healthy patients.
*** Note: Half-life of Adenosine: < 10 seconds.