Guide to Cardiac Diagnosis – Stress Echo
Dr Ben Jacobson
Treadmill Stress Echocardiogram
The vast majority of cardiac stress testing is performed in adults with suspected or known coronary artery disease (CAD). In patients who are able to exercise with an interpretable ECG and no contraindications, a standard stress ECG test is often a first line investigation. For the detection of CAD, large meta-analyses report a sensitivity of 67% and a specificity of 72%. The addition of an imaging modality (echocardiography or nuclear imaging) adds significant diagnostic accuracy, and there are advantages and limitations of each modality. It is often not clear which is the most appropriate investigation for certain patients.
Stress echocardiography has become a major non-invasive diagnostic modality for patients with suspected or known coronary artery disease. It is also established in the assessment of valvular heart disease. It provides a very useful prognostic tool to predict mortality and cardiovascular outcomes and gives significantly higher discriminatory abilities than stress ECG. The main competing modality is nuclear myocardial perfusion imaging, which is slightly more sensitive than stress echo (87% vs. 85%) but has a lower specificity (64% vs. 77%). Disadvantages include high radiation exposure (particularly relevant in
younger patients), a much longer procedure time and significantly higher cost. In severe triple vessel disease, “balanced ischaemia” with perfusion imaging can result in a false negative.
Echocardiography provides additional information on cardiac structure and function, including: left ventricular size, wall thickness, ejection fraction, atrial volumes, pulmonary artery pressure and valvular or pericardial disease. Diagnostic accuracy is limited in situations where there is poor image quality (obesity or chronic lung disease). Many patients are suitable for both standard stress ECG testing or stress echo. The best choice for a patient needs consideration of the pretest probability of disease and additional information available from echo that will assist in diagnosis and management. For example in a young, low risk patient, an equivocal result on stress ECG may not require any further testing based on exercise and clinical data. If the pretest probability is higher, an equivocal result will usually warrant further testing. In these situations a stress echo is the better initial investigation.
Additionally, stress echocardiography is preferred:
- When exertional dyspnoea or chest pain is the main complaint
- In diabetic patients
- In patients with known ischaemic heart disease (with or without prior MI)
- In women (higher rates of false positive stress ECG)