Q. What are primary indications for pharmacologic stress?
The primary indications for pharmacologic stress are inability to exercise or the desire to identify viable myocardium. Dobutamine infusion to a peak dose of 40 µg/kg/min is the most commonly used pharmacologic stressor, and increases myocardial oxygen
consumption through increments in inotropic state, heart rate (usually to 120-140 beats/minute), and blood pressure (by 30-40 mm Hg with peak pressures of 170-180 mm Hg). Serious complications occur in about 3:1000.
Vasodilator agents (adenosine to 0.18 mg/kg/min and dipyridamole to 0.84 mg/kg) are less commonly used for pharmacologic stress echo, and work by the induction of coronary steal, which occurs in the setting of severe or extensive coronary disease. The haemodynamic effects of these stressors are minor, and the most common side effects of dipyridamole and adenosine are headache and dyspnoea, respectively; serious side effects occur in about 1:1000 patients. Atropine may be added if the response to dipyridamole is negative, and other protocols involve combination of dobutamine with a vasodilator.
For diagnostic indications,the sensitivity of dobutamine echo is somewhat greater, especially in patients with single vessel disease. From a prognostic angle,a strong evidence base supports both pharmacologic tests. Side effects occur with similar frequency with dipyridamole and dobutamine, although serious problems are more likely with dobutamine. Dobutamine stress is a better choice for those with asthma or untreated conduction system disease, while dipyridamole stress is preferable in patients with serious arrhythmias or severe hypertension.