Stress echocardiography. Part I: Stress echocardiography in coronary heart disease

Stress test may be performed on a treadmill or a cycle ergometer in a sitting or semi-recumbent position on the left side. Bruce protocol is used for treadmill: step increments by 25 W every 3 minutes until termination criteria are reached (85% of max heart rate, contractility disorders, severe anginal pain, ST elevation in ECG, and maximum stress load).

Stress-pacing echocardiography can be performed in patients with a permanently implanted pacemaker. The pacemaker is externally programmed at 100-110 impulses/min and then increased by 10 impulses/min every 3 minutes until 85% of maximum age predicted heart rate is reached, or a target rate of 150 impulses/min or maximum rate for a given pacemaker is reached. A rapid stress-testing protocol includes two stages: 3 minutes of stimulation at 100 impulses/min and 3 to 5 minutes of 85% of maximum age predicted heart rate. In the case of grade II or III AV block, particularly during atrial stimulation, atropine (a total dose of 2 mg) may be used until 1:1 conduction is reached. The accuracy of the test in the assessment of coronary heart disease is very high, comparable to other stress echo tests. This is a non-invasive, safe and well-tolerated test that may be discontinued at any time. This technique should be considered in every patient with a pacemaker.

Unfeasibility or non-diagnostic result of stress ECG (failure to reach target heart rate during the test, left bundle branch block, stimulatory rhythm, resting repolarization abnormalities, skeletal diseases, lower limb atherosclerosis) is the most common indication for stress echocardiography. Stress and pharmacological tests show similar diagnostic sensitivity, specificity and accuracy in ischemia. The choice of stressor depends on limitations and contraindications, as well as preferences and experience in a given facility. According to guidelines, stress echocardiography has priority over stress electrocardiography, and exercise stress test is the first-choice option in patients able to exercise. Pharmacological or pacing stress test is performed in other patients. Coronary drugs (including beta-blockers) should be discontinued before the test unless contraindicated. Image acquisition in at least three basic projections, i.e. parasternal in the long and short axis, apical four-chamber, two-chamber, and long axis, is performed at each stage with simultaneous recording of heart rate and arterial blood pressure. Doppler parameters are recorded as part of simultaneous valvular assessment. Recording standardized cardiac cross-sections that are identical throughout the entire test is important for comparative analysis.

Segmental contractility analysis is based on left ventricular division into 17 or 16 segments. Each segment is scored between 1 and 4 (1 – normokinesia, 2 – hypokinesia, 3 – akinesia, 4 – dyskinesia), which allows calculation of the left ventricular contractility index at each stage (wall motion score index, WMSI – total score for segments visualized/number of segments visualized). Reduced contractility in at least two segments is considered a positive result, indicative of ischemia. This does not apply to dyskinesia of a segment that is akinetic at rest as this segment may be passively ‘pushed out’ as a result of hyperkinesia of other ventricular elements. Contractility assessment should include centripetal movement and, most of all, systolic thickening of segments. A large number of segments with poor contractility, contractility disorders in areas supplied by more than one coronary artery (multivessel disease), significant deterioration of contractility (e.g. transition from normokinesia to akinesia or dyskinesia), short time between test onset and ischemia, long-lasting regression of contractility disorders at rest, and left ventricular dilation during exercise are indicative of very severe ischemia. Absence of provoked contractility disorders using the full protocol indicates a negative result. The absence of new contractility disorders in the event of premature test discontinuation due to serious arrhythmia, excess increase in blood pressure above 220/120 mm Hg, a decrease in blood pressure below 90 mm Hg (or by 30 mm Hg below baseline) and patient’s request are considered a non-diagnostic result.

Patients with significant ischemic left ventricular systolic dysfunction and reversible contractility disorders (involving at least four left ventricular segments) present with lower perioperative mortality, higher improvement of regional and general contractile function after invasive treatment, a lower number of heart failure symptoms and lower mortality compared to patients with irreversible contractility disorders. An intravenous infusion of low-dose dobutamine (usually 5 and 10 µg/kg/min, 20 µg/kg/min, or 2.5, 5, 7.5, 15, 20 µg/kg/min) administered at 3-minute (or 5-minute) stages, is used for the assessment of myocardial viability. Improved contractility of a given segment during dobutamine infusion indicates its viability. Continuation of dobutamine infusion in accordance with the protocol at doses of up to 40 µg/kg/min is recommended. A two-phase response including initial contractility improvement (at low dobutamine doses), followed by impairment (at higher doses) is specific for preserved viability of myocardial segment supplied by a stenotic coronary artery and is considered to be the most precise prognostic indicator of improved left ventricular contractility after revascularization.

Stress echo is recommended for the diagnosis of ischemic heart disease: high-dose dobutamine test in the case of contraindications, pacing stress echo in patients with pacemaker, and dipyridamole test for the assessment of coronary flow reserve. Chest pain in patients with intermediate probability of coronary artery disease, inability to perform physical exercise and non-diagnostic resting or exercise electrocardiography are indications for stress echo. The test is also used in symptomatic patients after revascularization or patients qualified for revascularization for functional assessment of coronary artery stenosis. Lowdose dobutamine test is usually performed in patients after myocardial infarction or with moderate-to-severe left ventricular dysfunction to assess myocardial viability before potential revascularization.