Non-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study

Opportunistic screening at chest computed tomography: literature review of cardiovascular significance of incidental findings

Background and Objective

Several incidental cardiovascular findings are present in a routine chest computed tomography (CT) scan, many of which do not make it to the final radiology report. However, these findings have important clinical implications, particularly providing prognosis and risk-stratification for future cardiovascular events. The purpose of this article is to review the literature on these incidental cardiovascular findings in a routine chest CT and inform the radiologist on their clinical relevance.

Methods

A time unlimited review of PubMed and Web of Science was performed by using relevant keywords. Articles in English that involved adults were included.

Key Content and Findings

Coronary artery calcification (CAC) is the most common incidental cardiac finding detected in a routine chest CT and is a significant predictor of cardiovascular events. Noncoronary vascular calcifications in chest CT include aortic valve, mitral annulus, and thoracic aortic calcifications (TAC). Among these, aortic valve calcification (AVC) has the strongest association with coronary artery disease and cardiovascular events. Additional cardiac findings such as myocardial scar and left ventricular size and noncardiac findings such as thoracic fat, bone density, hepatic steatosis, and breast artery calcifications can also help in risk stratification and patient management.

Conclusions

The radiologist interpreting a routine chest CT should be cognizant of the incidental cardiovascular findings, which helps in the diagnosis and risk-stratification of cardiovascular disease. This will guide appropriate referral and management.

Field of view of mapping catheters quantified by electrogram associations with radius of myocardial attenuation on contrast-enhanced cardiac computed tomography

BACKGROUND

Contrast-enhanced cardiac computed tomography (CE-CT) provides useful substrate characterization in patients with ventricular tachycardia (VT).

OBJECTIVE

The purpose of this study was to describe the association between endocardial electrogram measurements and myocardial characteristics on CE-CT, in particular the field of view of electrogram features.

METHODS

Fifteen patients with postinfarct VT who underwent catheter ablation with preprocedural CE-CT were included. Electroanatomic maps were registered to CE-CT, and myocardial attenuation surrounding each endocardial point was measured at a radius of 5, 10, and 15 mm. The association between endocardial voltage and attenuation was assessed using a multilevel random effects linear regression model, clustered by patient, with best model fit defined by highest log likelihood.

RESULTS

A total of 4698 points were included. There was a significant association of bipolar and unipolar voltage with myocardial attenuation at all radii. For unipolar voltage, the best model fit was at an analysis radius of 15 mm regardless of the mapping catheter used. For bipolar voltage, the best model fit was at an analysis radius of 15 mm for points acquired with a conventional ablation catheter. In contrast, the best model fit for points acquired with a multipolar mapping catheter was at an analysis radius of 5 mm.

CONCLUSION

Myocardial attenuation on CE-CT indicates a smaller myocardial field of view of bipolar electrograms using multipolar catheters with smaller electrodes in comparison to standard ablation catheters despite similar interelectrode spacing. Smaller electrodes may provide improved spatial resolution for the definition of myocardial substrate for VT ablation.

Infarct characterization using CT

Myocardial infarction (MI) is a major cause of death and disability worldwide. The incidence is not expected to diminish, despite better prevention, diagnosis and treatment, because of the ageing population in industrialized countries and unhealthy lifestyles in developing countries. Nowadays it is highly requested an imaging tool able to evaluate MI and viability. Technology improvements determined an expansion of clinical indications from coronary plaque evaluation to functional applications (perfusion, ischemia and viability after MI) integrating additional phases and information in the mainstream examination. Cardiac computed tomography (CCT) and cardiac MR (CMR) employ different contrast media, but may characterize MI with overlapping imaging findings due to the similar kinetics and tissue distribution of gadolinium and iodinated contrast media. CCT may detect first-pass perfusion defects, dynamic perfusion after pharmacological stress, and delayed enhancement (DE) of non-viable territories.

New insight into scar-related ventricular tachycardia circuits in ischemic cardiomyopathy: Fat deposition after myocardial infarction on computed tomography--A pilot study

BACKGROUND

Myocardial fat deposition (FAT-DEP) has been frequently observed in regions of chronic myocardial infarction in patients with ischemic cardiomyopathy. The role of FAT-DEP within scar-related ventricular tachycardia (VT) circuits has not been investigated.

OBJECTIVE

This pilot study aimed to assess the impact of myocardial FAT-DEP on local electrograms and VT circuits in patients with ischemic cardiomyopathy.

METHODS

Contrast-enhanced computed tomography was performed in 22 patients with ischemic VT. Electroanatomic map points were registered to the corresponding contrast-enhanced computed tomography images. Myocardial FAT-DEP was identified and characterized using a postprocessing image overlay that highlighted areas below 0 Hounsfield units (HU). The mean attenuation of local myocardial regions corresponding to sampled electrograms was measured on short-axis images. The associations of mean attenuation with bipolar and unipolar amplitudes, left ventricular wall thickness, and VT circuit sites were investigated.

RESULTS

Of 1801 electroanatomic map points, 519 (28.8%) were located in regions with FAT-DEP. Significant differences were observed in mean intensity (23.2 ± 35.6 HU vs 81.7 ± 21.9 HU; P < .001), bipolar (0.75 ± 0.83 mV vs 2.9 ± 2.4 mV; P < .001) and unipolar (3.1 ± 1.7 mV vs 7.4 ± 4.3 mV; P < .001) amplitudes, and left ventricular wall thickness (5.2 ± 1.7 mm vs 8.2 ± 2.5 mm; P < .001) between regions with and without FAT-DEP. Lower HU was strongly associated with lower bipolar and unipolar amplitudes (P < .0001, respectively). Importantly, FAT-DEP was associated with critical VT circuit sites with fractionated or isolated potentials.

CONCLUSION

FAT-DEP was associated with electrogram characteristics and VT circuit sites. Further work will be needed to determine whether FAT-DEP plays a causal role in the generation of ischemic scar-related VT circuits.

Assessment of the myocardium with cardiac computed tomography

The imaging of myocardial disease is of increasing importance for cardiologists from all subspecialties, for diagnosis, risk stratification, or to facilitate therapy. While the gold standard modalities for such assessment are cardiac magnetic resonance and echocardiography, these are not universally suitable. Cardiac computed tomography (CT), well-established for the assessment of coronary artery disease (CAD), can be of value in the assessment of myocardial pathology, due to excellent patient compatibility and tolerability, high spatial resolution, and acceptable tissue characterization. This review considers the value and limitations of CT in the assessment of the myocardial sequelae of CAD, and for patients with a variety of other cardiomyopathic diseases, depicts some of the common findings, and considers current developments in this area.

Myocardial perfusion imaging with cardiac computed tomography: state of the art

Cardiac computed tomography (CCT) has become an important tool for the anatomic assessment of patients with suspected coronary disease. Its diagnostic accuracy for detecting the presence of underlying coronary artery disease and ability to risk stratify patients are well documented. However, the role of CCT for the physiologic assessment of myocardial perfusion during resting and stress conditions is only now emerging. With the addition of myocardial perfusion imaging to coronary imaging, CCT has the potential to assess both coronary anatomy and its functional significance with a single non-invasive test. In this review, we discuss the current state of CCT myocardial perfusion imaging for the detection of myocardial ischemia and myocardial infarction and examine its complementary role to CCT coronary imaging.

A direct comparison of the sensitivity of CT and MR cardiac perfusion using a myocardial perfusion phantom

Background

Direct comparison of CT and magnetic resonance (MR) perfusion techniques has been limited and in vivo assessment is affected by physiological variability, timing of image acquisition, and parameter selection.

Objective

We precisely compared high-resolution k-t SENSE MR cardiac perfusion at 3 T with single-phase CT perfusion (CTP) under identical imaging conditions.

Methods

We used a customized MR imaging and CT compatible dynamic myocardial perfusion phantom to represent the human circulation. CT perfusion studies were performed with a Philips iCT (256 slice) CT, with isotropic resolution of 0.6 mm³. MR perfusion was performed with k-t SENSE acceleration at 3 T and spatial resolution of 1.2 × 1.2 × 10 mm. The image contrast between normal and underperfused myocardial compartments was quantified at various perfusion and photon energy settings. Noise estimates were based on published clinical data.

Results

Contrast by CTP highly depends on photon energy and also timing of imaging within the myocardial perfusion upslope. For an identical myocardial perfusion deficit, the native image contrast-to-noise ratio (CNR) generated by CT and MR are similar. If slice averaging is used, the CNR of a perfusion deficit is expected to be greater for CTP than MR perfusion (MRP). Perfect timing during single time point CTP imaging is difficult to achieve, and CNR by CT decreases by 24%–31% two seconds from the optimal imaging time point. Although single-phase CT perfusion offers higher spatial resolution, MRP allows multiple time point sampling and quantitative analysis.

Conclusion

The ability of CTP and current optimal MRP techniques to detect simulated myocardial perfusion deficits is similar.

Hypodense regions in unenhanced CT identify nonviable myocardium: validation versus 18F-FDG PET

PURPOSE

The aim of the present study was to evaluate the accuracy of hypodense regions in non-contrast-enhanced cardiac computed tomography (unenhanced CT) to identify nonviable myocardial scar tissue.

METHODS

Hypodense areas were visually identified in unenhanced CT of 80 patients in the left ventricular anterior, apical, septal, lateral and inferior myocardium and CT density was measured in Hounsfield units (HU). Findings were compared to (18)F-fluorodeoxyglucose uptake by positron emission tomography (FDG PET), which served as the standard of reference to distinguish scar (<50 % FDG uptake) from viable tissue (≥50 % uptake).

RESULTS

Visually detected hypodense regions demonstrated a sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 74, 97, 84 and 94 %, respectively. A receiver-operating characteristic (ROC) curve analysis revealed a cutoff value of mean HU at <28.8 for predicting scar tissue with an area under the curve of 0.93 yielding a sensitivity, specificity, PPV and NPV of 94, 90, 67 and 99 %, respectively.

CONCLUSION

Hypodense regions in unenhanced cardiac CT scans allow accurate identification of nonviable myocardial scar tissue.

Risk stratification of non-contrast CT beyond the coronary calcium scan

Coronary artery calcification (CAC) is a well-known marker for coronary artery disease and has important prognostic implications. CAC is able to provide clinicians with a reliable source of information related to cardiovascular atherosclerosis, which carries incremental information beyond Framingham risk. However, non-contrast scans of the heart provide additional information beyond the Agatston score. These studies are also able to measure various sources of fat, including intrathoracic (eg, pericardial or epicardial) and hepatic, both of which are thought to be metabolically active and linked to increased incidence of subclinical atherosclerosis as well as increased prevalence of type 2  diabetes. Testing for CAC is also useful in identifying extracoronary sources of calcification. Specifically, aortic valve calcification, mitral annular calcification, and thoracic aortic calcium (TAC) provide additional risk stratification information for cardiovascular events. Finally, scanning for CAC is able to evaluate myocardial scaring due to myocardial infarcts, which may also add incremental prognostic information. To ensure the benefits outweigh the risks of a scanning for CAC for an appropriately selected asymptomatic patient, the full utility of the scan should be realized. This review describes the current state of the art interpretation of non-contrast cardiac CT, which clinically should go well beyond coronary artery Agatston scoring alone.

CT of coronary heart disease: Part 1, CT of myocardial infarction, ischemia, and viability

OBJECTIVE

This article reviews the CT-based approaches aimed at the assessment of myocardial infarction, ischemia, and viability described in the recent literature.

CONCLUSION

Rapid advances in CT technology not only have improved visualization of coronary arteries but also increasingly enable noncoronary myocardial applications, including analysis of wall motion and the state of the myocardial blood supply. These advancements hold promise for eventually accomplishing the goal of comprehensively evaluating coronary heart disease with a single noninvasive modality.