Comparison of Dual-Energy CT Derived Myocardial Delayed Enhancement with Magnetic Resonance Imaging in Patients with Cardiomyopathy-Related Heart Failure

Keywords

heart failure - cardiomyopathy - cardiac magnetic resonance - late gadolinium enhancement - dual energy - myocardial delayed enhancement

Introduction

Cardiovascular diseases (CVD) are one of the leading causes of mortality and morbidity in developed and developing nations. With improving life expectancy and advancements in health care, the elderly population worldwide is growing, causing heart failure (HF) to be a major public health issue contributing to both disability and death.[1] The estimated prevalence of HF in India is approximately 1% of the total population. This burden is likely to be even more, given the fact that India accounts for 16% of the global population, 25% of the global share of coronary heart diseases (CHD), and approximately 120 million individuals with hypertension. CVD would be the leading cause of morbidity and mortality in India in the coming future.[2]

Cardiomyopathies (CMP) are a heterogenous group of diseases involving myocardium causing CVD-related death and progressive HF-related disability. Among the various CMP, dilated cardiomyopathy (DCM) is the commonest heart muscle pathology, being the third most common cause of HF commonly warranting heart transplantation.[3] Diagnosis of the exact etiology of CMP is important as it directly decides treatment and predicts the prognosis of the patient.[4]

In the present clinical settings, cardiac magnetic resonance imaging (CMRI) is the gold standard imaging tool for the assessment of myocardial diseases such as CMP using gadolinium as contrast agent.[5] CMRI is used for cardiac imaging in HF patients to evaluate the underlying cause with assessment of myocardial “late gadolinium enhancement” (LGE) for the identification and characterization of myocardial fibrosis, myocyte death, or inflammation. Iodinated and gadolinium-based contrast agents exhibit similar pharmacokinetics and myocardial wash-in and wash-out phenomenon. Some researchers have used myocardial delayed enhancement (MDE) at computed tomography (CT) for characterization of the myocardium, but this was not widely accepted as its diagnostic performance was inferior to CMRI.[6]

It is also pivotal to establish the diagnosis of coronary artery disease (CAD) in patients with CMP as the presence of CAD carries worse prognosis as compared with patients without CAD. The presence or absence of CAD is a deciding factor to plan for therapeutic revascularization which, may improve clinical symptoms and the prognosis of the disease.[7]

Although CMRI provides very high-quality images for myocardial assessment, it cannot be used for evaluation of every patient owing to its numerous contraindications (pacemakers, stents, claustrophobia, vascular grafts), which lead to waste of resource and time of the patient and provides no help in diagnostic evaluation.[8] In this study, we propose that as compared with CMRI, cardiac dual-energy CT (DECT) can be helpful in patients who are unable to undergo CMRI, by offering a comprehensive one-step coronary vascular and myocardial characterization assessment.

Our goal in this study was to compare the MDE patterns in DECT with CMRI as the gold standard and added advantage of coronary vasculature assessment for screening and quantification of atherosclerosis if present.

Material and Methods

This prospective analytical study was conducted over a period of 1.5 years (July 2020 to December 2021). Ethical clearance was obtained from the Institutional Ethical Committee.

A total of 30 adult patients with CMP presenting with HF and diagnosed with myocardial scar through LGE on CMRI evaluation were included in the present study. Subsequently, these patients underwent a comprehensive cardiac CT (DECT coronary angiography + MDE detection sequence; [Fig. 1]).

Fig. 1 Flow diagram. Abbreviations: CMRI, cardiac magnetic resonance imaging; LGE, late gadolinium enhancement; MDE, myocardial delayed enhancement.

CMRI was performed with a 3-T machine (Philips Ingenia), installed at the Advanced Cardiac Centre, in PGIMER, Chandigarh. A dedicated phased array surface coil was used. In all patients, breath hold imaging with electrocardiographic (ECG) gating and triggering was performed. LGE images were acquired approximately 15 minutes after dynamic perfusion sequence in various planes. CT imaging was performed in the dual-energy mode with 194-slice dual-source Siemens Somatom Force ECG-gated machine. After 8 to 10 minutes of DECT coronary angiography, cardiac DECT for MDE assessment was done using prospective electrocardiographically gated axial scanning at the mid-diastolic phase. The radiologist analyzing the CT images was blinded to the CMRI images.

Statistical Analysis

The statistical analysis was performed with Statistical Package for Social Science (SPSS) software (version 24; IBM, Armonk, NY, United States). The normality of data was checked using the Shapiro–Wilk test. For univariate analysis, the results were presented as frequency and percentages. The chi-squared test was used to find the association between the covariates and the dependent factors. Sensitivity and specificity were calculated for comparing the two diagnostic techniques, whereas kappa statistics was used to calculate the agreement between the diagnostic ability of two different techniques. Intraclass correlation coefficients were further classified as follows: poor agreement (<0.70), fair agreement (0.70–0.79), good agreement (0.80–0.89), and high agreement (>0.89).

Results

A total of 30 participants who were diagnosed to have CMP-related HF with LGE who subsequently underwent DECT were included in the present study. The mean age of the patients was 45.93 ± 13.61 (range: 18–65) years. The patients were grouped into two age groups, 18 to 45 years and older than 45 years, with 47 and 53% being in the former and later groups, respectively. The majority of them were males at 22 (73%), and 8 patients were females (27%). All the patients were symptomatic at the time of the study, with 93.3% (n = 28) having clinically significant dyspnea. Based on imaging findings, functional assessment, and LGE pattern analysis of 30 patients using CMRI, four subtypes of CMP were identified ([Table 1]). Dilated CMP (DCMP)was seen among 19 patients (63.3%), postischemic CMP in 8 patients (26.7%), hypertrophic cardiomyopathy (HCM) in 2 (6.7%) patients, and restrictive CMP in 1 (3.3%) patient. All 30 patients were detected to have LGE on CMRI. The patterns of LGE identified are described in [Table 2]). The midmyocardial LGE type was the most common type of LGE seen in 17 patients (56.7%), followed by subendocardial LGE, which was seen in 6 patients (20%). Transmural LGE was seen in four patients (13.3%) and patchy LGE was seen in three patients (10%). The subendocardial and transmural patterns were grouped together as the ischemic pattern and the rest were grouped into the nonischemic pattern. Hence, 20 patients (66.7%) were detected to have a nonischemic pattern and 10 patients (33.3%) were found to have an ischemic pattern of LGE.

Table 1 Types of cardiomyopathies diagnosed on cardiac magnetic resonance imaging (CMRI)

Cardiomyopathy type	No. of patients	Percent
Dilated cardiomyopathy	19	63.3
Postischemic cardiomyopathy	8	26.7
Hypertrophic cardiomyopathy	2	6.7
Restrictive cardiomyopathy (sarcoidosis)	1	3.3

Table 2 Late gadolinium enhancement (LGE) patterns detected in cardiac magnetic resonance imaging (CMRI)

LGE type	No. of patients	Percent
Subendocardial	6	20
Transmural	4	13.3
Midmyocardial	17	56.7
Subepicardial	0	0
Global endocardial	0	0
Patchy	3	10

Types of LGE pattern were identified and compared with various subtypes of CMP as identified in CMRI. In patients with DCMP (17 patients), midmyocardial LGE was seen in 17 patients (90%), 1 patient (5%) showed transmural LGE, and 1 patient (5%) showed patchy LGE.

Among the patients with postischemic CMP (8 patients), six patients (75%) showed subendocardial pattern and two patients (25%) showed a transmural pattern of LGE. In HCM patients (2 patients), one showed transmural LGE and one showed patchy LGE. One patient with restrictive CMP secondary to sarcoidosis showed patchy LGE.

Based on CT coronary angiography, 10 patients (33.3%) were diagnosed with CAD and 3 patients (10%) were detected to have triple-vessel disease. The left anterior descending (LAD) artery was the most involved vessel by atherosclerosis, seen in nine patients (90%) who had CAD, followed by right coronary artery (RCA) in five patients (50%).

After CT coronary angiography, a 10-minute delayed scan was acquired of cardiac region in the dual-energy mode, and two sets of images were reconstructed: iodine density map images and virtual monochromatic (VM) images. Iodine density map images and VM images were assessed to look for MDE detection and pattern classification. Out of 30 patients, 23 patients (76.7%) showed MDE on the iodine map and 20 patients (66.7%) showed MDE on VM images. The MDE pattern was identified and classified on both the iodine map and VM images and a comparison was made with LGE in MRI, with the latter being the gold standard. The left ventricular segment-wise comparison was done between LGE on CMRI with MDE in cardiac DECT as per the AHA-17 segment model ([Tables 3] and [4]). Based on the comparative analysis, the diagnostic accuracy of the iodine density map and VM images as compared with LGE in CMRI was found to be 76 and 66%, respectively, with substantial interobserver agreement (p < 0.001). The sensitivity and specificity of VM images as compared with iodine density maps were 86.96 and 100%, respectively. Interclass correlation was performed, which yielded a kappa value of 0.757, suggesting statistically significant results.

Table 3 Comparative analysis between late gadolinium enhancement (LGE) in cardiac magnetic resonance imaging (CMRI) with myocardial delayed enhancement (MDE) in dual-energy computed tomography (DECT) using the American Heart Association 17 (AHA-17) segment model

Patient number	LGE type	AHA segment	MDE on iodine map type	AHA segment	MDE on VM images type	AHA segment
1	Transmural	13	Transmural	13	Transmural	13
2	Patchy	1, 4	Patchy	4	Not detected
3	Midmyocardial	3, 9	Midmyocardial	3, 9	Not detected
4	Patchy	1, 2, 5, 6, 11, 12	Patchy	1, 2, 5, 6	Patchy	1, 2, 5, 6
5	Midmyocardial	9, 14	Midmyocardial	9, 14	Midmyocardial	9, 14
6	Transmural	10, 15, 16	Transmural	10, 15, 16	Transmural	10, 15, 16
7	Transmural	3	Transmural	3	Transmural	3
8	Subendocardial	7, 8	Subendocardial	7, 8	Subendocardial	7, 8
9	Subendocardial	2, 3	Subendocardial	2, 3	Subendocardial	2, 3
10	Midmyocardial	17	Not detected		Not detected
11	Transmural	13, 14, 15, 16, 17	Transmural	13, 14, 15, 16, 17	Transmural	13, 14, 15, 16, 17
12	Midmyocardial	9, 10	Not detected		Not detected
13	Patchy	8, 9, 10, 11, 12	Patchy	8, 9	Patchy	8, 9
14	Subendocardial	7, 8, 9, 10, 13, 14	Subendocardial	7, 8, 9, 10, 13, 14	Subendocardial	7, 8, 9, 10, 13, 14
15	Subendocardial	8, 9, 14, 15	Subendocardial	8, 9, 14, 15	Subendocardial	8, 9, 14, 15
16	Midmyocardial	4, 10	Midmyocardial	4, 10	Midmyocardial	4, 10
17	Midmyocardial	3, 4	Not detected		Not detected
18	Subendocardial	11, 12	Subendocardial	11, 12	Subendocardial	11, 12
19	Midmyocardial	3, 9	Midmyocardial	3, 9	Midmyocardial	3, 9
20	Midmyocardial	1, 4, 7, 10, 13, 15	Midmyocardial	1, 4, 7, 10, 13, 15	Midmyocardial	1, 4, 7, 10, 13, 15
21	Midmyocardial	5	Midmyocardial	5	Midmyocardial	5
22	Midmyocardial	8, 9	Not detected		Not detected
23	Subendocardial	1, 2, 3, 7, 8, 9, 13, 14	Subendocardial	1, 2, 3, 7, 8, 9, 13, 14	Subendocardial	1, 2, 3, 7, 8, 9, 13, 14
24	Subendocardial	8, 9, 13, 14	Subendocardial	8, 9, 13, 14	Subendocardial	8, 9, 13, 14
25	Midmyocardial	1	Not detected		Not detected
26	Subendocardial	3, 9	Subendocardial	3, 9	Subendocardial	3, 9
27	Midmyocardial	8, 9, 10	Not detected		Not detected
28	Midmyocardial	9, 10	Not detected		Not detected
29	Midmyocardial	7, 8, 9, 13, 14, 17	Midmyocardial	7, 8, 9, 13, 14, 17	Midmyocardial	7, 8, 9, 13, 14, 17
30	Subendocardial	9	Subendocardial	9	Subendocardial	9

Table 4 Iodine density maps and Virtual monochromatic imaging cross tabulation

			Iodine density map on CT: MDE (myocardial delayed enhancement) present, Y: 1; N: 0		Total
			0	1
Virtual monochromatic on CT: MDE present, Y: 1; N: 0	0	Count	7	3	10
		% within virtual monochromatic on CT: MDE present, Y: 1; N: 0	70.0%	30.0%	100.0%
		% within iodine density map on CT: MDE present, Y: 1; N: 0	100.0%	13.0%	33.3%
	1	Count	0	20	20
		% within virtual monochromatic on CT: MDE present, Y: 1; N: 0	0.0%	100.0%	100.0%
		% within iodine density map on CT: MDE present, Y: 1; N: 0	0.0%	87.0%	66.7%
Total		Count	7	23	30
		% within virtual monochromatic on CT: MDE present, Y: 1; N: 0	23.3%	76.7%	100.0%
		% within iodine density map on CT: MDE present, Y: 1; N: 0	100.0%	100.0%	100.0%

Discussion

Cardiac MRI Evaluation

Pattern-based LGE identification helps in establishing the diagnosis of CMP types and provides etiological information depending on the selective region of the myocardium affected by LGE. The subendocardial and transmural patterns are attributed to the ischemic type of CMP, and the midmyocardial, subepicardial, and patchy type of LGE are linked to nonischemic causes of CMP.[9]

On CMRI, 19 of 30 patients were diagnosed with DCMP, 8 with postischemic CMP, 2 with hypertrophic CMP, and 1 with sarcoidosis-related secondary CMP. This is in concordance with the prevalence of various CMP in the population.[3]

LGE Patterns in Study Population

Midmyocardial LGE was observed as the most common type of LGE pattern seen in 17 patients (56.7%). This is in concordance with the present study population having a predominant DCMP phenotype ([Fig. 2]). The remaining two patients having DCMP showed transmural and patchy LGE patterns, respectively.

Fig. 2 A 29-year-old man presented with New York Heart Association (NYHA) grade III heart failure diagnosed with dilated cardiomyopathy on MRI. (A) On short axis, late gadolinium enhancement (LGE) view, midmyocardial LGE seen as linear hyperintensity involving septal left ventricular (LV) wall at the mid-cavity level (yellow arrow). (B) On corresponding dual-energy CT image, iodine map image obtained after a 10-minute delay after contrast injection shows iodine entrapment at the same location (yellow arrow).

Subendocardial LGE was the next in line seen in six patients (20%), followed by transmural seen in four patients (13.3%), and patchy type of LGE seen in three patients (10%; [Figs. 3] and [4]).

Fig. 3 A 51-year-old man presented with New York Heart Association (NYHA) grade III heart failure with history of myocardial infarction (MI) and Percutaneous coronary intervention to left anterior descending and right coronary artery (PCI-LAD/RCA) 9 months ago diagnosed with postischemic cardiomyopathy on MRI. (A) On short axis late gadolinium enhancement (LGE) view, there is thinning of septal left ventricular (LV) wall with subendocardial LGE seen as linear hyperintensity involving septal LV wall at the mid-cavity level in the LAD territory (yellow arrow). On corresponding dual-energy CT image, (B) iodine map and (C) virtual monochromatic (VM) images obtained at 40 keV after a 10-minute delay after contrast injection show iodine entrapment in the same location (yellow arrow). (D–F) CT coronary angiography and 3D volume rendered images show patent stents in proximal LAD and RCA, with no residual occlusive plaque seen.

Fig. 4 A 59-year-old man presented with New York Heart Association (NYHA) grade III heart failure with a history of on/off chest pain and angina on exertion for 1 year diagnosed postischemic cardiomyopathy on MRI. (A) On short axis late gadolinium enhancement (LGE) view, there is thinning of septal left ventricular (LV) wall with subendocardial LGE seen as linear hyperintensity involving septal LV wall at the mid-cavity level in the left anterior descending (LAD) artery territory (yellow arrow). (B, C) On corresponding dual-energy CT image, iodine map and virtual monochromatic (VM) images obtained at 40 keV after a 10-minute delay after contrast injection show iodine entrapment in the same location (yellow arrow). (D) CT coronary angiography shows eccentric noncalcified soft plaque in the proximal LAD causing moderate stenosis (red arrow). Another eccentric calcified plaque is seen in the mid-LAD causing mild stenosis.

Therefore, the ischemic type of LGE is seen in 10 patients (33.3%) and the nonischemic type in 20 (66.7%) patients according to CMRI.

Dual-Energy Cardiac Computed Tomography

Computed Tomography Angiography

Ten patients (33.3%) were found to have CAD, and 90% of them had a Coronary artery disease-Reporting and Data System (CAD-RAD) score of ≥3 attributed to the incidence of postischemic CMP seen in the present study population. The LAD artery is the major epicardial vessel supplying the anterior two-thirds of the interventricular septum and half of the left ventricular myocardium as it is considered the most critical vessel supplying the myocardium.

Myocardial Delayed Enhancement Detection

DECT has been used to evaluate the myocardial scar in a few studies earlier. Ohta et al[10] performed a prospective study and used DECT for imaging MDE in 44 adult patients with HF with LGE in MRI as the reference standard, and iodine density and VM images were reconstructed. This study showed very high consistency between the presence and the extent of DECT delayed enhancement and MRI LGE with iodine density images (having an accuracy of 95.5%) and low keV VM images (accuracy: 93.3%).

Chang et al[11] used DECT-based VM images for the evaluation of MDE in 40 patients of CMP and concluded that DECT-based 70-keV VM images provided excellent MDE assessment owing to improved image quality and reduced artifacts.

Segment-wise analysis of the left ventricle was done for LGE and MDE detection. Regions were calculated as segments as per the 17-segment AHA model leaving the apical segment as it is supplied by all the three major epicardial coronary arteries.[12]

In our study, using computer-based reconstruction software, iodine density map and VM images were obtained for each patient. In the VM imaging, 40-keV low-energy images were reconstructed as iodine shows bright hyperdense enhancement on the lowest keV images owing to K-edge of iodine being 33.2 keV.[13]

In this study, out of 30 patients who were detected to have LGE on CMRI, 23 patients were found to have MDE on the iodine map in a similar location and 20 were found to have MDE on low-energy VM images.

In relation to identifying individual subtypes of LGE, DECT shows excellent performance in detecting ischemic and patchy forms of MDE. Iodine density map images showed 100% accuracy in determining the ischemic and patchy type of MDE in our study, whereas low keV VM images showed 100 and 66% accuracy in picking up the ischemic and patchy types of MDE.

However, low diagnostic performance was seen on DECT in detecting midmyocardial MDE in patients having primary DCMP. Iodine density maps and low keV VM images showed a diagnostic accuracy of 59 and 47%, respectively.

The mechanisms for midmyocardial LGE in DCMP is postulated to be the result of multiple factors such as genetic predisposition, exposure to toxins and pathogens, microvascular ischemia, and abnormal modulation of immune and metabolic responses such as overactivity of the renin angiotensin aldosterone system. In our cohort of 19 patients of DCMP, 17 patients had midmyocardial fibrosis. However, the exact pathophysiology, which leads to midmyocardial myofibrosis, is not well understood.[14]

In the case of ischemia-related CMP, following myocardial infarction (MI), there is myocyte injury and death, which further initiate a proinflammatory response through the immune cascade involving complement activation, reactive oxygen species production, and activation of inflammasomes. Thereafter, the release of proinflammatory mediators (such as cytokines and chemokines) induces inflammatory cells into the MI zone and enhances inflammatory response. The infiltrating leukocytes target the viable border zone of the infarction, extending ischemic cell death centrifugally from the subendocardial to the subepicardial region, like a ripple effect created by a droplet falling on water.[15]

In our study cohort, an 18-year-old patient with DCMP had normal CT coronary artery angiography, but showed transmural apical LGE ([Fig. 5]). In the study done by Francone,[16] cases of DCMP showing subendocardial or transmural enhancement were attributed to a previous MI in the absence of significant CAD. In our study cohort, there was one patient of sarcoidosis presenting with HF and showing patchy LGE ([Fig. 6]). Myocardial inflammation in granulomatous diseases such as sarcoidosis may show any pattern of LGE depending on the region of inflammation not attributing to any vascular territory. There is expansion of extracellular space by inflammatory cells and cytokines. On DECT, the patchy type of MDE was excellently detected.

Fig. 5 An 18-year-old woman presented with New York Heart Association (NYHA) grade III heart failure diagnosed dilated cardiomyopathy on MRI. On (A) vertical long axis late gadolinium enhancement (LGE) view and (B) horizontal long axis view, transmural LGE was seen as a hyperintensity involving the left ventricular (LV) apex (yellow arrows). On corresponding dual-energy CT image, (C, D) iodine map and (E, F) virtual monochromatic images at 40 keV obtained after a 10-minute delay after contrast injection show iodine entrapment in the same location consistent with transmural myocardial delayed enhancement (yellow arrows). All three epicardial coronary vessels were normal.

Fig. 6 A 49-year-old man, known case of pulmonary sarcoidosis, presented with New York Heart Association (NYHA) grade III heart failure with pedal edema and chest pain diagnosed with sarcoidosis-related secondary cardiomyopathy on MRI. (A, B) On short axis late gadolinium enhancement (LGE) view, there are patchy areas of LGE diffusely scattered in the left ventricular (LV) myocardium not confirming to any vascular territory (yellow arrows). On corresponding dual-energy CT image, (C, D) iodine map and virtual monochromatic (VM) images obtained at 40 keV after a 10-minute delay after contrast injection show patchy areas of iodine entrapment (yellow arrows). All three epicardial coronary vessels were normal. (E) CECT of the chest, mediastinal window, shows mediastinal lymphadenopathy in the pretracheal and right paratracheal location. (F) Lung window image does not show any abnormality in lung parenchyma.

Conclusion

CMRI-based LGE detection is the gold standard in identification, assessing, and characterizing the myocardium in CMP-related HF patients. DECT with iodine density maps and VM images provide excellent diagnostic yield in cases of ischemia-related CMP and can be used as a “one-step” investigation to evaluate the patients with suspected ischemia-related HF. In our study, there was excellent diagnostic performance of dual energy–based MDE detection in cases of ischemia- and sarcoidosis-related CMP.

Limitations

There are few limitations to this study as it was a single-center study with a small sample size. Further studies with a larger population might be necessary to confirm our results.

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