Stress Echocardiography: Methodology

General Test Protocol

During stress echocardiography (SE), electrocardiographic leads are placed at standard limb and precordial sites, slightly displacing (upward and downward) any leads that may interfere with the chosen acoustic windows. A 12-lead electrocardiogram (ECG) is recorded in resting condition and each minute throughout the examination. An ECG lead is also continuously displayed on the echo monitor to provide the operator with a reference for ST-segment changes and arrhythmias. Cuff blood pressure is measured in resting condition and each stage thereafter. Echocardiographic imaging is typically performed from the parasternal long- and short-axis, apical long-axis, and apical four- and two-chamber views. In some cases, the subxiphoid and apical long-axis views are used. Images are recorded in resting condition from all views and captured digitally. A quad-screen format is used for comparative analysis. Echocardiography is then continuously monitored and intermittently stored. In the presence of obvious or suspected dyssynergy, a complete echo examination is performed and recorded from all employed approaches to allow optimal documentation of the presence and extent of myocardial ischemia. These same projections are obtained and recorded during the recovery phase after cessation of stress (exercise or pacing) or administration of the antidote (aminophylline for dipyridamole, β-blocker for dobutamine). An ischemic response may occasionally occur late, after cessation of drug infusion. In this way, the transiently dyssynergic area during stress can be evaluated by a triple comparison: stress versus resting state, stress versus recovery phase, and at peak stress. It is critical to obtain the same views at each stage of the test. Analysis and scoring of the study are usually performed using a 16- or 17-segment model of the left ventricle and a 4-grade scale of regional wall motion analysis. Regional wall motion is semiquantitatively graded from 1 to 4 as follows: 1 = normal, 2 = hypokinetic, 3 = akinetic, and 4 = dyskinetic. Wall motion score index (WMSI) is the sum of individual segment scores divided by the number of interpretable segments.

Diagnostic endpoints of SE testing are maximum dose (for pharmacologic) or maximum workload (for exercise testing), achievement of target heart rate, obvious echocardiographic positivity (with akinesis of two or more left ventricular segments), severe chest pain, or obvious electrocardiographic positivity (with >2 mV ST-segment shift). Submaximal nondiagnostic endpoints of SE testing are nontolerable symptoms or limiting asymptomatic side effects such as hypertension, with systolic blood pressure greater than 220 mm Hg or diastolic blood pressure greater than 120 mm Hg; symptomatic hypotension, with a greater than 40–mm Hg drop in blood pressure; supraventricular arrhythmias, such as supraventricular tachycardia or atrial fibrillations, and complex ventricular arrhythmias, such as ventricular tachycardia or frequent, polymorphic premature ventricular beats.

Specific Test Protocols

The most frequently used stressors for echocardiographic tests are exercise, dobutamine, and dipyridamole. Table 51.1 lists some of the advantages and disadvantages of exercise versus pharmacologic stress. Table 51.2 lists the required equipment and protocols for the various forms of SE.