Cardiovascular Imaging and Diagnostic Testing
Items probe test selection for a given pretest probability, recognition of artefacts and limitations, and the specific diagnostic signatures of echocardiography, CT, and magnetic resonance.
Choosing the test
- Low pretest probability: coronary CT angiography or calcium scoring; a calcium score of zero carries a very low event rate.
- Intermediate probability: stress imaging (echocardiography, SPECT, or perfusion MRI) or CT angiography depending on age, calcium burden, and rhythm.
- High probability or known disease: functional testing for ischaemia burden and viability.
Modality strengths
- Echocardiography: first-line for ejection fraction, valves, effusion, and pulmonary pressures; strain detects subclinical dysfunction.
- CMR: late gadolinium enhancement patterns - subendocardial follows a coronary territory and indicates infarction, mid-wall indicates dilated cardiomyopathy, epicardial indicates myocarditis, and patchy septal enhancement suggests sarcoidosis; T1 mapping detects diffuse fibrosis and T2 mapping detects oedema.
- CT: calcium score, coronary anatomy (CAD-RADS), aortic pathology; beta-blockade and nitrates improve image quality.
- Nuclear imaging: perfusion and viability; radiation exposure is around 10 mSv.
Stress testing limits
- Exercise ECG is unreliable with LBBB, paced rhythm, left ventricular hypertrophy with strain, digoxin, or pre-excitation; use imaging instead.
- Dobutamine stress echocardiography assesses viability through contractile reserve.
Worked example
A 55-year-old with atypical chest pain, normal ECG, and no history of disease has a low pretest probability. Coronary CT angiography shows a calcium score of zero and no plaque, so no further testing is needed and risk-factor modification continues.
Traps
- A positive exercise test in a patient with LBBB is not diagnostic of ischaemia.
- Severe calcification limits CT angiography specificity; functional testing is preferred.
- Anaphylaxis to iodinated contrast requires premedication or an alternative modality.