Teaching Case

An 81-year-old woman, known to have coronary artery disease, ulcerative colitis, diabetes mellitus, hypertension, and chronic atrial fibrillation, presented to the emergency department with chest pain and dyspnoea on the day of her scheduled WATCHMAN device implantation procedure for her ongoing atrial fibrillation. Electrocardiogram (ECG) showed ST elevations in contiguous leads. Her WATCHMAN procedure was then postponed.

Coronary angiography showed total occlusion of the first obtuse marginal artery following which percutaneous coronary intervention (PCI) was performed. Low-dose spectral-detector CT (SDCT) was obtained four days post-MI. The early (Figure 1) and delayed (Figure 2) conventional CT images showed no gross abnormality. In contrast, low monoenergetic images (40 keV) revealed a significantly large perfusion defect involving the lateral left ventricular myocardium and papillary muscle (Figure 3). Additional spectral methods, such as iodine and effective Z-atomic number mapping techniques, emphasised this elusive finding (Figure 4).

Clinical Perspective

Patients presenting with sudden-onset chest pain and dyspnoea, especially with a known history of coronary artery disease, should be suspected of an acute coronary syndrome event with an ECG performed instantly. If the ECG shows the findings of acute coronary syndrome, coronary angiography is pursued. However, there is always a possibility of other differentials, including acute pulmonary embolism, for which CT imaging helps.

Imaging Perspective

As stated earlier, SDCT was performed on this patient. Usually, the protocol for prospective-gated contrast-enhanced chest CT includes an arterial scan (at 45% of the R-R interval) and a delayed phase scan after 60 seconds. Due to her complex past medical history and elevated creatinine level, the decision was made to utilise an extremely low dose of contrast material: 25cc of Isovue-370 (Bracco Diagnostics, USA).

This case emphasises utilising SDCT in patients with suspicious myocardial insult and with a high risk of acute kidney injury due to contrast angiography. SDCT employs a single high tube potential beam and a dual-layer detector in order to acquire dual-energy data. This simultaneous acquisition of images with different energy levels allows for material decomposition. Thus, spectral maps can be generated [1,2]. Dual-energy CT, harnessed as a method of assessment for myocardial perfusion, has been proven to be effective in the literature [3,4]. Furthermore, compared to conventional CT images, low monoenergetic images of dual-energy CT have improved intravascular enhancement and image contrast [5]. Results of a recent prospective clinical trial of 34 stable patients, who underwent SDCT (40 KeV) for detection of myocardial infarction, demonstrated a sensitivity and specificity of (92.3%) and (90.5%) respectively per patient, and specificity and NPV of (96.8%) and (93.7%) respectively per myocardial segment [6].

According to our knowledge, a dedicated study on the assessment of myocardial perfusion using the novel method of SDCT has not been published yet. Our case presents the advantages of SDCT in the evaluation of myocardial ischemia in a very low contrast dose examination. We believe that spectral maps can serve as an important adjunct tool in interpreting cardiac examinations performed with a very low contrast dose.

Outcome

The case highlights the utility of spectral CT in assessing subtle myocardial perfusion defects. Further studies using SDCT should be conducted to adopt this technique in ischemic heart disease.

All patient data have been completely anonymised throughout the entire manuscript and related files.