Advances in Cardiac Computed Tomography

Abstract

Background

Cardiac computed tomography (CT) is essential for the diagnosis of coronary artery disease and structural heart abnormalities. Conventional cardiac CT requires electrocardiographic (ECG) synchronization to reduce motion artifacts, which is challenging and time-consuming.

Early Reports Summary

Advances in CT technology have enabled high-quality imaging without ECG synchronization. This report describes 2 cases where non-ECG–synchronized cardiac CT was successfully performed, reducing preparation time and improving suitability for patients with physical or cognitive limitations.

Discussion

Non-ECG–synchronized cardiac CT streamlines imaging and reduces patient burden. Its effectiveness may be limited in cases of frequent arrhythmia or very high heart rates. Additional studies are needed to explore its clinical applications.

Novelty

This is the first report of non-ECG–synchronized cardiac CT, demonstrating its potential as a novel diagnostic tool.

Take-Home Messages

Non-ECG–synchronized cardiac CT improved efficiency and reduced patient burden. Additional research is required to understand its clinical applicability.

Visual Summary

Cardiac computed tomography (CT) is an important diagnostic tool used to assess coronary artery disease and structural abnormalities of the heart.¹ Conventional cardiac CT requires electrocardiographic (ECG) synchronization to suppress motion artifacts caused by cardiac motion and improve image accuracy. ECG synchronization allows optimal timing within the heartbeat cycle to be identified, resulting in clear images with minimal motion artifacts.² Cardiac CT is therefore a useful noninvasive test used for detecting atherosclerotic plaques and performing morphologic assessment of the coronary arteries.³ In guidelines from Europe⁴ and the United States,⁵ cardiac CT has received a Class I recommendation for use as a first-line test in patients with chest pain. However, ECG synchronization poses several challenges. To implement it, electrodes must be placed on the patient’s body surface to capture the appropriate ECG waveform. This process requires time before the examination, which can be an issue when rapid imaging is required, as in emergency situations. In addition, the application of ECG leads may be difficult in patients with cognitive dysfunction or dermatologic conditions, which can complicate the examination.

Take-Home Messages

• •Non-ECG–synchronized cardiac CT enables rapid, high-quality imaging while reducing patient burden, especially in emergency situations or for patients with physical or cognitive limitations.
• •Advances in CT technology have provided a promising alternative to conventional ECG-synchronized imaging, offering improved efficiency and flexibility in clinical practice.

In recent years, significant advances in CT technology have led to machines with wide detectors that cover the entire heart, as well as with rapid x-ray tube rotation speeds that improve temporal resolution. In addition, the introduction of technology to reduce motion artifacts that occur at high heart rates and in the presence of arrhythmias has contributed to an improvement in the accuracy of cardiac CT. These technological advances can provide good images without the need to wear an ECG device (non-ECG–synchronized cardiac CT). In this report, we describe 2 cases in which non-ECG–synchronized cardiac CT was useful. This case report was approved by the Ethics Committee of Minamino Cardiovascular Hospital (approval number MJ-085).

Case Summaries

Case 1

History of presentation

A 56-year-old man presented with chest and back pain. Laboratory tests showed an abnormal white blood cell count of 9,260 cell/μL, a C-reactive protein concentration of 1.09 mg/dL, and a D-dimer concentration of 5.4 mg/L. At the time of the visit, the patient’s blood pressure was 170/112 mm Hg, indicative of hypertension. Arrhythmias were not observed on 12-lead ECG. The heart rate during the examination was 57 beats/min.

Past medical history

The patient’s surgical history included the Bentall procedure for aortic root rupture.

Differential diagnosis

On the basis of the symptoms and laboratory findings, aortic dissection was suspected and emergency CT was performed.

Investigations

Although an accurate assessment of the ascending aorta was warranted, the patient opted for non-ECG–synchronized cardiac CT to shorten the examination time. CT was performed using the Revolution Apex Elite system (GE HealthCare) with a tube voltage of 120 kV and automatic exposure control. The tube rotation speed was 0.23 seconds. Detector collimation was set to 256 × 0.625 mm (total coverage: 160 mm along the z-axis). The x-ray coverage was determined by the simulated pulse of the CT system, which was set on the basis of the patient’s heart rate. A pulse oximeter was placed on the patient’s finger to monitor heart rate in the CT room. Just before the scan, the heart rate was 70 beats/min (corresponding to an R—R interval of 857 ms); therefore, retrospective imaging was performed with a margin of 10% for 940 ms. After acquisition, reconstruction was performed using Smart Phase (GE HealthCare), a system that automatically detects the optimal cardiac phase (Figure 1). In addition, SnapShot Freeze 2.0 motion artifact reduction technology (GE HealthCare) was applied using the Advantage Workstation VolumeShare 7.0 (GE HealthCare) (Table 1). After imaging of the heart, helical imaging was also performed from the chest to the pelvis for detailed evaluation of the heart and the aorta.

Figure 1.

Setting the Exposure Range Using Simulated Pulses

Simulated pulses can be set by the CT scanner to any heart rate waveform. This allows the unit to reproduce the patient’s heart rate waveform without the need for ECG. However, as the heart rate measured before the examination and the heart rate at the time of imaging may differ, x-rays are exposed with a margin of 10%. The phase with the least motion artifacts is selected using Smart Phase. This electrocardiogram is a simulated electrocardiogram set by the CT scanner that differs from the actual electrocardiogram recorded during patient scanning. CT = computed tomography; ECG = electrocardiography.

Table 1.

Equipment List

Computed tomography scanner: Revolution Apex Elite (GE HealthCare)

Workstation: Advantage Workstation VolumeShare 7.0 (GE HealthCare)

Workstation: REVORAS (Ziosoft)

The obtained images had no motion artifacts in the ascending aorta and coronary arteries (Figures 2A to 2C). Although no abnormalities were visualized in the ascending aorta, a dissection was observed from the descending aorta to the common iliac artery (Figures 2A and 2D). Four-dimensional heartbeat data were obtained by reconstructing the acquired data at 10% intervals (Video 1). The volume CT dose index and dose-length product were 39.0 mGy and 639.5 mGy·cm, respectively. This imaging method eliminated the need for conventional ECG-synchronized imaging, which decreased the preparation time and patient burden.

Figure 2.

Imaging in Case 1

(A) Axial cardiac CT image showing the dissected descending aortic lumen (arrowheads). Volume rendering of the (B) cardiac and (C) coronary curved planar reconstruction allows coronary artery lesion evaluation without motion artifacts. (D) The helical CT volume rendering image from the chest to the pelvis shows the entire aortic dissection. CT = computed tomography; LAD = left anterior descending artery; LCx = left circumflex artery; RCA = right coronary artery.

Management

The patient was hospitalized, and blood pressure control was implemented.

Outcome and follow-up

The patient was discharged after 1 month of hospitalization and treatment. The clinical course was favorable thereafter, and no complications were observed.

Case 2

History of presentation

An 87-year-old woman presented with chest pain. No abnormalities were found on laboratory tests or echocardiography. Arrhythmias were not observed on 12-lead ECG. The heart rate during the examination was 78 beats/min.

Past medical history

The patient had a history of percutaneous transluminal angioplasty for arteriosclerosis obliterans, and cognitive impairment was also suspected during CT.

Differential diagnosis

Angina was suspected on the basis of the patient’s symptoms, and coronary artery assessment was performed by cardiac CT.

Investigations

Because of her cognitive impairment, we were concerned about the possibility of the patient removing the ECG leads during scanning. Therefore, non-ECG–synchronized imaging was performed as described above. The patient’s heart rate was 85 beats/min; therefore, the acquisition was performed over a 777-ms time window. Imaging provided a detailed evaluation and showed significant stenosis in the high lateral wall branch and left circumflex artery branch #13 (Figures 3A to 3C). The volume CT dose index and dose-length product were 31.3 mGy and 500.7 mGy·cm, respectively. This method provided high-quality images in a patient who may not have tolerated wearing ECG leads.

Visual Summary.

Description of Non-ECG–Synchronized Cardiac CT and Take-Home Messages

CT = computed tomography; ECG = electrocardiographic.

Figure 3.

Imaging in Case 2

(A) The cardiac CT volume rendering image shows no motion artifacts. (B) Maximum intensity projection and (C) curved planar reconstruction images show stenotic lesions in the HL branch (yellow arrowhead) and the LCx branch #13 (red arrowhead). CT = computed tomography; HL = high lateral; LAD = left anterior descending artery; LCx = left circumflex artery; RCA = right coronary artery.

Management

The patient underwent coronary angiography at another hospital, and percutaneous coronary intervention was performed on the left circumflex artery.

Outcome and follow-up

Antiplatelet therapy was administered after percutaneous coronary intervention, and the patient progressed well with an uneventful course.

Novelty of the Submission

The 2 cases presented here illustrate the usefulness of non-ECG–synchronized cardiac CT. This method has several advantages over conventional imaging techniques that require ECG synchronization. It does not require the placement of ECG electrodes, thus reducing examination preparation time. This allows rapid diagnosis, especially in emergency situations. In addition, highly accurate nonsynchronized images can be obtained in patients with physical or cognitive limitations.

However, this method is also associated with several limitations. Motion artifacts and poor image quality may be a problem in patients with a high frequency of arrhythmias or an extremely high heart rate. Therefore, ECG-synchronized imaging should be carefully applied on the basis of the patient’s pathology and the purpose of the examination. In addition, as the R-wave cannot be detected because of the lack of ECG synchronization, data for a single heartbeat must be acquired to obtain reliable images, resulting in increased radiation exposure to the patient.

Future Directions

Future research should focus on expanding the clinical applications of non-ECG–synchronized cardiac CT in more diverse patient populations, including those with arrhythmia or very high heart rates. Studies investigating the long-term outcomes of patients undergoing non-ECG–synchronized cardiac CT could provide valuable insights into its safety and diagnostic accuracy compared with conventional methods. Furthermore, non-ECG–synchronized cardiac CT can, currently, only be performed with the CT system used in this study. However, with advancements in the temporal resolution of CT and motion artifact suppression techniques, it is expected that non-ECG–synchronized cardiac CT will soon become possible using equipment from other manufacturers.

Conclusions

The imaging method described in this report may help reduce patient burden and improve cardiac CT examination efficiency. To our knowledge, this is the first reported experience of non-ECG–synchronized cardiac CT. Therefore, additional studies are needed to clarify its clinical scope and applicability.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Appendix

Video 1

Four-Dimensional Images of the Cardiac Cycle