Cardiac dual-source CT for the preoperative assessment of patients undergoing bariatric surgery

Clinical Radiology 68 (2013) e154ee163

Contents lists available at SciVerse ScienceDirect

Clinical Radiology journal homepage: www.clinicalradiologyonline.net

Cardiac dual-source CT for the preoperative assessment of patients undergoing bariatric surgery A. Tognolini a, *, C.S. Arellano a, W. Marfori a, J.W. Sayre a, b, J.L. Hollada a, J.G. Goldin a, E.P. Dutson c, S.G. Ruehm a a

Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, USA Department of Biostatistics, Fielding School of Public Health, University of California, Los Angeles, USA c Department of Surgery, David Geffen School of Medicine, University of California, Los Angeles, USA b

article in formation Article history: Received 22 May 2012 Received in revised form 2 November 2012 Accepted 12 November 2012

AIM: To assess the diagnostic value of coronary dual-source computed tomography (DSCT) as a comprehensive, non-invasive tool in the preoperative cardiac evaluation of patients undergoing bariatric surgery. MATERIALS AND METHODS: Thirty consecutive obese [average body mass index (BMI): 45
7.6, range: 35e59] patients (24 women; six men; median age: 52
15 years) were enrolled in this institutional review board (IRB)-approved, Health Insurance Portability and Accountability Act of 1996 (HIPAA)-compliant prospective study. Calcium scoring (CaS) and electrocardiography (ECG)-gated images of the coronary arteries were obtained with a large body habitus protocol (120 kV; 430 mAs; 100 ml iodinated contrast medium at 7 ml/s injection rate) on a DSCT machine. Qualitative (four-point: 1 ¼ excellent to 4 ¼ not delineable) coronary segmental analysis, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) measurements were performed. The presence and degree of vascular disease (four-grade scale: mild to severe) was correlated with CaS and cardiovascular (CV) risk stratification blood tests. In patients with severe stenosis (>70%), findings were compared with cardiac nuclear medicine imaging (single photon-emission computed tomography; SPECT) imaging. RESULTS: The average HR, enhancement, and quality score were 64
7 beats/min, 288
66 HU and 1.8
.5, respectively. Ninety-three percent (417/450) of the coronary segments were rated diagnostic. The SNRs and CNRs were 17
9 and 12
7 for the right coronary artery; 17
8 and 12
7 for the left main coronary artery; 16
9 and 11
7 for the left anterior descending coronary artery; and 15
7 and 10
6 for the left circumflex coronary artery. Ten of the 30 patients (33%) demonstrated coronary artery disease (CAD) of which two (6%) showed three-vessel disease. Four (13%) patients showed severe disease: in three of which the presence of significant stenosis was confirmed by SPECT and by catheter angiography in the fourth patient. Neither the CaS, nor the CV risk stratification tests showed significant correlation with presence or degree of CAD (p > 0.05). CONCLUSIONS: Coronary DSCT is a robust alternative imaging tool in the preoperative assessment of patients undergoing bariatric surgery. Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

* Guarantor and correspondent: A. Tognolini, Diagnostic Cardiovascular Imaging, UCLA, Peter V. Ueberroth Building, Suite 3371, 10945 LeConte Avenue, Los Angeles, CA 90095, USA. Tel.: þ1 310 206 4711; fax: þ1 310 825 0880. E-mail address: [email protected] (A. Tognolini). 0009-9260/$ e see front matter Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.crad.2012.11.003

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

Introduction Approximately 68% of the American adult population is reported to be overweight (BMI 25 kg/m2) and nearly half of these (33.8% total) are obese (BMI 30 kg/m2). Within that subset, the greatest increase in the past two decades has been in the highest BMI category (BMI 40 kg/m2) meaning that not only does the population have a higher incidence of obesity, but the group that is increasing at the most rapid rate is the subset of the most obese individuals.1 According to recent National Institutes of Health (NIH) statistics, obese individuals have a 50e100% increased risk of death from all causes compared to normal weight individuals. Most of the increased risk is due to cardiovascular disease. Life expectancy of a moderately obese person could be shortened by 2e5 years, whereas morbidly obese men may reduce their life expectancy by almost 13 years.2 Bariatric surgery (or weight-loss surgery) is considered intermediate- to high-risk surgery, due to patientassociated co-morbidity and surgery-related complications. Most patients considered for bariatric surgery suffer from various degrees of functional cardiac impairment and pre-surgical assessment of cardiovascular risk factors is typically requested. Despite the published guidelines from the American College of Cardiology (ACC)/American Heart Association (AHA),3 the need for preoperative cardiac testing is often based on clinical judgment, and the overall utilization of objective tools for preoperative cardiovascular risk assessment in the obese patient population remains controversial. Stress echocardiography and single photon-emission computer tomography (SPECT) imaging or positronemission tomography (PET) myocardial perfusion imaging are the most frequently used techniques for non-invasive cardiac assessment; however, their accuracy in this population has been shown to be often compromised.4 In recent years, advancements in multidetector helical computed tomography (MDCT) have increased the diagnostic accuracy of coronary artery imaging, particularly after the introduction of the newer-generation DSCT machines.5 The utilization of a dedicated obesity protocol, which uses additional data sampling by expanding the data acquisition for each tube from a quarter to a half rotation, allows improvement in the signal-to-noise ratio (SNR) and contributes to enhanced image quality in the large body habitus population.6 In contrast to other non-invasive imaging methods, cardiac DSCT has the advantage of providing both functional and anatomical information for the preoperative cardiovascular risk assessment in a highrisk obese patient population and could serve as a comprehensive imaging technique for pre-bariatric surgery cardiac work-up.

e155

Act of 1996 (HIPAA)-compliant prospective study. Informed consent was obtained from all subjects. Adult (>18 years) patients meeting the eligibility criteria for bariatric surgery and undergoing clinical preoperative work-up were included in the study; pregnant women or patients with serum creatinine >1.6 mg/dl (141.4 mmol/l) or previous severe reaction to iodinated contrast media were excluded. All bariatric surgery candidates were evaluated for cardiovascular risk factors by an institutional Preanaesthesia Evaluation Service (PES), which included a complete blood count, blood chemistry, and evaluation of coagulation factors, as well as a blood lipid panel [total cholesterol, low-density lipoprotein (LDL) cholesterol, highdensity lipoprotein (HDL) cholesterol, and triglycerides], fasting glucose and haemoglobin A1C in all patients for the assessment of cardiovascular risk factors. The measured values of cholesterol (total, LDL, and HD), triglycerides, fasting glucose, and haemoglobin A1C were correlated with the presence and degree of coronary artery disease (CAD) at computed tomography angiography (CTA). Additional cardiac testing was considered following the Institutional PES guidelines for bariatric surgery patients (Fig 1). Stress SPECT myocardial perfusion imaging and conventional cardiac echocardiography were performed in a subset of six and nine patients, respectively, in accordance to the aforementioned guidelines. For heart rate reduction, a single dose of oral metoprolol (50 mg) was administered 1e2 h prior to DSCT imaging in patients with a heart rate exceeding 65 beats/min. All patients received a single dose of sublingual nitroglycerine (400 mg) for coronary dilatation approximately 5e6 min prior to the scan. Using a first-generation 64 section DSCT machine (Somatom Definition, Siemens Healthcare, Forchheim, Germany), a standard calcium scoring (CaS) acquisition (120 KV, 430 mAs) followed by helical electrocardiography (ECG)-gated acquisition using a large body habitus protocol (DSXXL_Coronary CTA; image reconstruction temporal resolution: 165 ms) of the coronary arteries was obtained. Coronary CTA was acquired following the administration of 100 ml (7 ml/s injection rate) of iodinated contrast medium (iopamidol 370 mg iodine/ml; Isovue 370, Bracco, Milan, Italy) followed by 50 ml saline (7 ml/s injection rate) utilizing a bolus-tracking technique (CARE Bolus, Siemens Healthcare) with a region-of-interest (ROI; 150 HU) in the left ventricle (LV). Acquisition parameters were as follows: 32  0.6 mm collimation; 0.75 mm section thickness; 0.33 s gantry rotation time; 120 kV tube voltage; 430 mAs quality reference tube current. For all studies, the doseelength product (DLP) was recorded. The estimated radiation dose (mSV) was calculated according to the European Guidelines on Quality Criteria for Computed Tomography7 based on the DLP and correspondent conversion coefficient (chest: k ¼ 0.017 mSv/mGy.cm).

Materials and methods

Image analysis

Thirty consecutive obese patients (24 women; six men) were enrolled in this institutional review board (IRB)approved, Health Insurance Portability and Accountability

Multi-planar reformations, maximum-intensity projections, and volume-rendered images were evaluated by two independent readers (S.R. and A.T., with 12 and 4 years of

e156

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

Figure 1 Guidelines for cardiac testing before bariatric surgery. MET, metabolic equivalents; HR, heart rate; CPAP, continuous positive airway pressure; MI, myocardial infarction; TIA, transient ischaemic accident; CHF, cardiac heart failure, LBBB, left branch bundle block; LVH, left ventricular hypertension.

experience in cardiovascular imaging, respectively) on a separate workstation (Leonardo Multi-Modality Workplace, Siemens Healthcare; Vitrea, Vital Imaging; Aquarius, TeraRecon, Inc, Foster City, CA, USA). A total of 450 segments were analysed. Coronary arterial analysis comprised 15 segments: proximal, middle, and distal right coronary artery (PRCA, MRCA, and DRCA); posterior descending coronary artery (PDA); left main coronary artery (LM); proximal, middle, and distal left anterior descending coronary artery (PLAD, MLAD, and DLAD) and its main diagonal branches (D1 and D2); proximal, middle, and distal left circumflex coronary artery (PLCX, MLCX, and DLCX) and its main obtuse marginal branches (OM1 and OM2). In the case of a left dominant coronary system, the PDA was regarded as a separate artery segment. LV ejection fraction was calculated from the multiphasic CT data in all patients and correlated echocardiography or stress SPECT myocardial imaging.

Quantitative image analysis Qualitative analysis was based on the following fourpoint score: 1 ¼ excellent, 2 ¼ diagnostic quality, mild-

moderate blurring, 3 ¼ poor quality, non-diagnostic due to severe artefacts (blooming from calcified plaques, perivenous streak artefacts), 4 ¼ vessel not delineable, nondiagnostic. The HU values, obtained by positioning a ROI in the centre of each analysed segment, were averaged between readers. Proximal coronaries SNR [mean vascular attenuation/image noise (IN)] and contrast-to-noise ratio (CNR: (mean vascular attenuation e mean soft-tissue attenuation)/IN) were calculated. IN was defined as the standard deviation (SD) of a 3 cm ROI in the pre-sternal air.

Diagnostic performance Vascular disease was graded as follows: grade 1: absent, grade 2: mild (atherosclerotic irregularity of the vascular wall/mild stenosis: 10 to 49%), grade 3: moderate (stenosis: 50 to 69%), or grade 4: severe (stenosis >70% to occlusion). CT findings of severe stenosis were considered true positive when standard of care myocardial imaging (SPECT) showed a perfusion defect in the corresponding vascular territory (Fig 2). The composition of plaques causing significant stenosis was analysed. Additional incidental cardiovascular and extra-vascular findings were

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

e157

Figure 2 A 56-year-old obese patient (BMI ¼ 54) who was a candidate for bariatric surgery. DSCT curved reformat image (a) shows high-grade (>70%) stenosis of the proximal RCA. A mid-LV short axis axial image (b) shows a perfusion defect in the RCA territory (infero-lateral wall) at SPECT.

recorded. Further, the impact of the CT findings on patient management and outcome were determined.

Statistical analysis Statistical analysis was performed using SPSS 18.0 statistics software (SPSS, Chicago, IL, USA). The Spearman correlation analysis was utilized to test significance of the relationship between abnormal laboratory tests [total cholesterol >200 mg/dl (5.18 mmol/l), LDL cholesterol > 130 mg/dl (3.4 mmol/l), HDL cholesterol <35 mg/dl (0.9 mmol/l), triglycerides >200 mg/dl (2.26 mmol/l), fasting glucose >115 mg/dl (6.4 mmol/l), and haemoglobin A1C >7.5% (59 mmol/mol)] and the presence of disease as well as between elevated CaS (Ca >11 with percentile for sex and age >50%) and the presence and degree of disease. The correlation between heart rate and BMI with the CT image SNR and CNR were also tested for statistical significance using a Spearman’s correlation test. The correlation between ejection fraction measurements between CT and conventional echocardiography and CT and SPECT myocardial imaging was tested using a Pearson’s correlation test. A p-value <0.05 was considered statistically significant.

Results Coronary DSCT was successfully performed in all 30 prospectively enrolled patients. Patients median age and BMI were 52
15 years and 45
7.6 (range: 35e59), respectively. Eight patients out of 30 (27%) were in the WHO obesity class II (35  BMI  39.99) bracket and 22/30 (73%) met the criteria for WHO obesity class III (40). The average heart rate during the scan was 64
7 beats/min. Fourteen out of the 30 subjects (47%) who were enrolled in the study ultimately underwent bariatric surgery. The median blood test values were as follows:

total cholesterol ¼ 173
84 mg/dl (4.4
2.1 mmol/l); LDL cholesterol ¼ 102
50 mg/dl (2.6
1.3 mmol/l); HDL cholesterol ¼ 44
24 mg/dl (1.13
0.6 mmol/l); tri glycerides ¼ 100
99 mg/dl (1.13
1.11 mmol/l); fasting glucose ¼ 107
58 mg/dl (5.9
3.2 mmol/l); haemoglobin A1C ¼ 6.2
3.4% (45
34 mmol/l). None of the laboratory tests showed a statistically significant correlation with the presence (p > 0.05) or degree of CAD (p > 0.05). A positive CaS (mean value: 333
336) was found in 11/ 30 patients (36%) with four patients having a CaS in the 90th percentile (761
622). In nine of 11 patients (30%) the CaS represented a value greater than the 50th percentile for same sex/age subjects: no statistically significant correlation with stenosis of any degree (p ¼ 0.51) or severe disease according to CTA (p ¼ 0.62) was demonstrated. The average DLP for the coronary CTA scans was 1217
174 mSv/ mGy.cm and the corresponding calculated effective dose was 20
3 mSv.

Qualitative analysis Individual segments’ qualitative scores and relative attenuation (HU) are reported in Table 1. Ninety-six percent (417/450) of the coronary segments were rated diagnostic with an average quality score of 1.8
.5 on a four-point scale (1 ¼ excellent; 2 ¼ diagnostic quality, mildmoderate blurring; 3 ¼ poor quality, non-diagnostic due to severe artefacts; 4 ¼ vessel not delineable, non- diagnostic). The non-diagnostic segments, which were the result of severe artefacts or insufficient contrast medium opacification, comprised 33/450 (7%) segments of which 94% were either distal segments of the main coronary arteries (11/33) or secondary branches (20/33).

Quantitative analysis The average vessel enhancement was 288
66 HU. The SNR and CNR were as follows: RCA ¼ 17
9 versus 12
7,

e158

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

Table 1 Individual segments image quality score and attenuation. Vessel segments

Quality score

HU

Non-diagnostic segments: 33/450 (7%)

PRCA MRCA DRCA PDA LM PLAD MLAD DLAD D1 D2 PLCx MLCx DLCx OM1 OM2

1.3 1.6 2.1 1.4 1.3 1.8 1.9 2.0 2.1 1.7 1.7 1.9 1.7 2.2 2.2

374 328 227 390 372 285 199 221 212 336 305 224 320 238 253

4 3 3 7 2 4 4 6

PRCA, MRCA, and DRCA, proximal, middle, and distal right coronary artery; PDA, posterior descending coronary artery; LM, left main coronary artery; PLAD, MLAD, and DLAD, proximal, middle, and distal left anterior descending coronary artery and D1 and D2, its main diagonal branches; PLCX, MLCX, and DLCX proximal, middle, and distal left circumflex coronary artery and OM1 and OM2, its main obtuse marginal branches.

LM ¼ 17
8 versus 12
7, LAD ¼ 16
9 versus 11
7, and LCX ¼ 15
7 versus 10
6. Both SNR and CNR values are comparable to published data related to coronary CTA imaging in an average-size population4 whereas the SNR was shown to be superior to published values obtained with a dedicated obesity protocol and comparable technique.3 Furthermore, the present analysis demonstrated that SNR and CNR were both heart rate and BMI, independent with the only exception for the relationship between CNR in the proximal LAD and BMI (p ¼ 0.48).

Diagnostic performance Eleven out of the 30 patients (36%) had CAD; five of them (45%) showed three-vessel CAD. Four (three males and one female) out of the 30 (13%) patients showed severe CAD (>70% stenosis) on coronary CTA; in three out of the four (75%) the diagnosis correlated with the presence of a perfusion defect at cardiac SPECT (Myoview), which, however, was interpreted as shifting breast attenuation on the independent clinical read. In the fourth patient, with severe disease on coronary CTA, the diagnosis was confirmed by catheter angiography (see details in Table 2). In all four patients presenting with severe CAD, all the plaques responsible for the severe stenosis were mixed plaques with predominantly non-calcified components. In all three male patients presenting with severe CAD, catheter angiography was performed and the diagnosis was confirmed and followed by revascularization therapy. Two out of the three patients were still regarded candidates for bariatric surgery. The fourth patient demonstrated a sub-occlusion of the mid-RCA with preserved distal run-off; a tracer reduction was diagnosed at SPECT, which was interpreted as breast attenuation artefact and the patient was cleared for surgery based on the clinical SPECT read. In one additional patient

(female) with a fixed perfusion defect (SPECT) but no evidence of CAD on coronary CT angiography, the perfusion defect on SPECT was interpreted as an artefact and the patient was cleared for surgery.

Functional parameters The average ejection fraction calculated from the multiphasic CT images was 65.3
14.8. In the sub-group of nine patients with available ECG correlation, the mean LV ejection fraction was 64.4
8.8% on CT versus 62.3
4.2% on ultrasound (Pearson correlation ¼ 0.62; p ¼ 0.09) whereas in the subgroup of six patients with available SPECT correlation, the mean LV ejection fraction on CT was 65.6
10.1% versus 66.3
11.9% on SPECT (Pearson correlation ¼ 0.17; p ¼ 0.73). Additional findings by DSCT included a small atrial septal defect in a patient with unexplained paroxysmal atrial tachycardia and aortic valve thickening, which demonstrated significant aortic regurgitation at echocardiography.

Discussion Obesity is an independent risk factor for cardiovascular disease and about two-thirds of patients who have had a myocardial infarction have been shown to have a higher than normal BMI.8 Obesity can promote the development and progression of CAD by directly altering multiple atherogenic metabolic patterns, but also by increasing the risk for associated co-morbidities such as diabetes, dyslipidemia, hypertension, and obstructive sleep apnoea, which can further promote cardiovascular disease.9,10 Lifestyle changes including diet and exercise are not always effective in controlling body weight, especially in severe and morbidly obese patients. Bariatric surgery comprises different surgical procedures (most commonly Roux en-Y gastric bypass, vertical sleeve gastrectomy, adjustable band or bilio-pancreatic diversion/duodenal switch) on the gastrointestinal tract with the goal of achieving sustained weight loss in morbidly obese patients, and has been proven to be an effective and durable tool in fighting obesity-related complications.11 Due to strict eligibility requirements, only about 50% of bariatric surgery candidates who seek it out ultimately undergo surgery; of those individuals who meet surgical screening criteria and would stand to incur direct health benefits from undergoing surgery, fewer than 1% are evaluated by a surgeon. This low rate is mostly due to fear of surgery and lack of commitment to a complete lifestyle change (All the individuals evaluated for surgery are required to lose from 5e10% of their initial weight. Attend mandatory classes and undergo a psychological evaluation). Another important contributing component is the inability to meet pre-surgical cardiovascular clearance. In 2004, a meta-analysis of more than 22,000 weight-loss surgery patients, demonstrated the dramatic impact that bariatric surgery has on reducing post-surgical co-morbidities such as diabetes, hyperlipidaemia, hypertension, and sleep apnoea in more than 80% of the patients.12 According

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

e159

Table 2 Demographics and imaging findings. ID

Sex

Age

BMI

No. non-diagnostic segments

CT findings

SPECT findings

Cath-angio

1

F

49

46

-

Negative

n/a

2 3

F M

68 56

34 54

-

Negative Negative

4 5 6 7

F F F F

52 54 49 65

34 48 45 39

1 -

Mild LAD Mild non-calcified plaque RCA Moderate LAD; mild LCX; mild RCA Sub-occlusion RCA; mild LAD; mild LCX

8 9 10

F F M

50 33 65

60 46 36

3 -

11 12 13 14

M F F M

55 28 28 50

55 44 37 51

-

Negative Negative Multiple patent by-pass; antero-apical sub-endocardial defect/myocardial thinning. Thyroid mass. Severe RCA Negative Negative High-grade narrowing proximal to LAD stent

15 16 17 18

F F F F

56 29 57 53

39 52 46 43

2 2 -

Negative Negative Negative Antero-lateral and septal sub-endocardial perfusion defects

19

F

35

35

-

20 21 22

F F F

36 58 58

48 43 41

2 -

n/a n/a n/a

n/a n/a n/a

23 24 25 26 27 28 29 30

F M F F F F M F

41 45 55 56 48 65 42 46

43 59 52 40 62 40 48 64

6 6 3 8

Small patent foramen ovale/atrial septum defect (ASD). Negative Mixed plaque LAD (20% stenosis) Diffuse coronary atherosclerotic changes. Non-calcified plaque of LAD (50% stenosis). Mild LAD Negative Negative Negative Negative Negative Negative Negative

Mild reversible perfusion defect anterior wall, most likely shifting breast attenuation n/a Patchy stress perfusion basal inferior wall; no definitive evidence of defect n/a n/a n/a Mild reversible perfusion defect anterior wall, most likely bowel movement artefact n/a n/a Reversible stress defect on the lateral antero-apical left ventricular wall n/a n/a n/a Overall negative nuclear stress but technically difficult n/a n/a n/a Reversible perfusion defect anterior wall, most likely shifting breast attenuation n/a

n/a n/a n/a n/a n/a n/a n/a n/a

n/a n/a n/a n/a n/a n/a n/a n/a

n/a n/a

n/a n/a n/a n/a

n/a n/a n/a

Stent placed n/a n/a Additional stent placed n/a n/a n/a n/a

n/a

BMI, body mass index; CT, computed tomography; SPECT, single photon-emission computed tomography; Cath-angio, catheter angiography; LAD, left anterior descending coronary artery; RCA, right coronary artery; LCX, left circumflex coronary artery; n/a, not applicable.

to the AHA and ACC, obesity is a major modifiable cardiovascular risk factor for secondary prevention of CAD.13 Due to the procedures themselves and to the related co-morbidities often coexisting in obese patients, bariatric surgery has been classified as intermediate- to high-risk non-cardiac surgery and, therefore, pre-surgical assessment of cardiovascular risk factors is advised.8,9,14 Myocardial SPECT imaging with the utilization of different tracers, most commonly Tc99melabelled agents such as MIBI (Cardiolite, Bristol-Myers Squibb Medical Imaging, North Billerica, MA) or Tetrofosmin Tc-99m (Myoview, GE Healthcare, Arlington Heights, IL, USA)1e9 is utilized in most Institutions as the non-invasive test of choice for the assessment of patients with chest pain or elevated risk for coronary artery disease. Despite its widespread utilization, this technique can present some challenges in the patient with a larger body size: it has been

shown20 that the most common SPECT attenuation artefacts are those seen as anterior defects in women with large breasts and inferior defects in obese patients with large abdomens.4,15e17 A study from Hansen et al.4 on a population of 607 patients, 38% of whom were obese, also showed that the false-positive rate, when compared to catheter angiography, was significantly higher in obese patients, leading to a significant reduction in the accuracy of quantitative SPECT imaging in such a population.4 The most accurate test for the assessment of CAD still remains coronary catheter angiography, which, however, is invasive and may not be easily feasible in such patients due to technical challenges and elevated risk of severe periprocedural complications.18,19 Coronary CTA has become a robust, non-invasive diagnostic tool for the detection of CAD, although up until the

e160

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

advent of DSCT technology20,21 it’s accuracy has been shown to be decreased in obese patients due to increased image noise.21e23 Recent studies have shown the improved image quality and diagnostic accuracy of DSCT technology even in larger size patients.6,23,24 Brodoefel et al.24 showed the superior stability of the first-generation DSCT (two 64 section detectors, 83 ms temporal resolution) in the setting of elevated BMI. In their series, the authors attributed the

heightened diagnostic image quality, even at higher BMI, to the doubling of temporal resolution (83 ms for the firstgeneration DSCT machines) and subsequent reduction of motion artefacts with DSCT. The diagnostic value, when compared to coronary CTA, was not significantly affected by the BMI level, consistent with the results of another study from Alkadhi et al.25 The major advantage of utilizing a standard (i.e., average body

Figure 3 Chest topogram in a female patient (58-years-old, height: 5 feet, weight: 226 pounds, BMI: 42, HR: 64) demonstrates the physiognomy of the large body habitus patient undergoing coronary CT (a). Curved reformatted images of the LCX (b), LAD (c), and RCA (d) are shown as an example of excellent image quality (SNR: 20, 30, and 34, respectively, and CNR: 10, 22, and 25, respectively).

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

sized individuals) cardiac DSCT mode resides in the ability of scanning with a short acquisition window of 83 ms (64 detector system) or 67 s (128 detector system), but such a high temporal resolution might not be adequate for the examination of severely obese patients. As Chinnaiyan et al.,26 as well as Leschka et al.6 illustrated in their series on morbidly obese patients (mean BMI of 44.8
5.6 and 46.3
8.3, respectively), the utilization of a modified ‘‘cardio-obese’’ acquisition mode with adjustable time resolution for DSCT coronary imaging can be advantageous in patients with morbid obesity. With this alternative acquisition mode, a larger data range per measurement system, ranging from a quarter rotation (i.e., 83 ms for a 64 section DSCT) to half a rotation (i.e.,165 ms)

e161

can be used to accumulate more x-ray photon attenuation data per image, trading off temporal resolution for image noise reduction. The population included in the present series (mean BMI: 45
7.6) showed similar results in terms of average diagnostic segments (94%) and image quality (Figs 3 and 4) than previous studies on a similar population.23 The results of the present study demonstrate that more than 30% of the present population had CAD of various degrees with no statistically significant correlation with CaS (p > 0.05); likewise, none of the laboratory tests performed for cardiovascular risk stratification demonstrated a significant correlation with the severity of CAD, highlighting the challenge of cardiovascular risk stratification in this patient population. As shown in Table 2, in three of the four patients

Figure 4 (a) Chest topogram of a male patient (48-year-old, height: 5 feet, 5 inches; weight: 385 pounds, BMI: 62, HR: 60) along with the curve reformatted images of the LCX (b), LAD (c), and RCA (d) of the largest patient in the present series, show diagnostic image quality, on average, despite the higher noise level (SNR: 17, 12, and 12, respectively, and CNR: 12, 6, and 5, respectively).

e162

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163

with severe CAD at CTA, a defect corresponding to the territory of the severely stenotic coronary artery was indeed visualized at SPECT imaging, but falsely attributed to attenuation artefacts. This underlines the importance of the availability of anatomical information regarding CAD location and severity, which may improve the diagnostic accuracy in the bariatric/obese patient population. Additionally, CTA is able to provide information on left ventricular function and plaque composition, as well as volumetric measurements of pericardial and epi-cardial fat, which recent studies have suggested has a direct (paracrine) influence on plaque development.27e30 One of the main obstacles to a widespread preoperative use of CTA is the concern for radiation exposure. Although the radiation exposure for such a dedicated protocol is higher compared to a standard protocol, it is still within the range of radiation exposure values reported (8e25 mSv) for 64-section CTCA,24 which is similar to other diagnostic tests used in cardiology.31 It should be noted that the estimated radiation dose in obese patients presumably overestimates the true radiation dose due to increased distance from the skin to the organs of interest.32 The ICRP (International Commission on Radiological Protection) provides recommendations and guidance on protection against the risks associated with ionizing radiation.33,34 As well described from Brenner et al.,35 the effective dose is meant to be a measure of “radiation detriment”, and it represents summed organ doses, each weighted with committeegenerated numbers, which are a mix of cancer incidence, cancer mortality, life shortening, and hereditary effects, and do not take in account age-dependent and sex-dependent factors. Additionally, very often in the literature the effective dose (weighted average over the entire body) and equivalent dose (dose to a given organ), both measured in millisieverts, are confused with one another. For this reason, the same authors have recently suggested that the concept of effective dose should be more appropriately replaced by “effective risk” (i.e., summed organ doses, each weighted with actual epidemiologically-based cancer risks for ageand sex-related population).35 In summary, cardiac DSCT with the outlined obesity protocol appears to be a valuable diagnostic tool for comprehensive cardiac assessment in the preoperative evaluation of patients undergoing bariatric surgery. The present study supports the value of coronary DSCT in an obese patient population and its feasibility as an alternative, robust tool in the preoperative assessment of patients undergoing bariatric surgery.

References 1. Flegal KM, Carroll MD, Ogden CL, et al. Prevalence and trends in obesity among US adults, 1999e2008. JAMA;303:235e41. 2. NIDDK Weight-control Information Center: US Department of Health and Human Services. Statistics related to overweight and obesity. NIH Publication No. 03e4158. Bethesda: NIH; 2003. 3. Eagle KA, Berger PB, Calkins H, et al. ACC/AHA guideline update for perioperative cardiovascular evaluation for noncardiac surgerydexecutive summary a report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines

4.

5.

6.

7.

8.

9. 10. 11. 12. 13.

14.

15.

16.

17. 18. 19.

20. 21.

22. 23.

24.

25.

26.

(Committee to Update the 1996 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery). Circulation 2002;105:1257e67. Hansen CL, Woodhouse S, Kramer M. Effect of patient obesity on the accuracy of thallium-201 myocardial perfusion imaging. Am J Cardiol 2000;85:749e52. Kerl JM, Bauer RW, Maurer TB, et al. Dose levels at coronary CT angiographyda comparison of dual energy-, dual source-, and 16-slice CT. Eur Radiol;21:530e37. Leschka S, Stinn B, Schmid F, et al. Dual source CT coronary angiography in severely obese patients: trading off temporal resolution and image noise. Invest Radiol 2009;44:720e7. Bongartz G, GS, Jurik AG, et al. European Guidelines on Quality Criteria for Computed Tomography. EUR 16262. The European Commission’s Study Group on Development of Quality Criteria for Computed Tomography Luxembourg. Luxembourg: European Commission; 2000. Romero-Corral A, Montori VM, Somers VK, et al. Association of bodyweight with total mortality and with cardiovascular events in coronary artery disease: a systematic review of cohort studies. Lancet 2006;368:666e78. Krauss RM, Winston M, Fletcher RN, et al. Obesity: impact of cardiovascular disease. Circulation 1998;98:1472e6. Shamsuzzaman AS, Gersh BJ, Somers VK. Obstructive sleep apnea: implications for cardiac and vascular disease. JAMA 2003;290:1906e14. Glatt D, Sorenson T. Metabolic and bariatric surgery for obesity: a review. S D Med 2011:57e62. Spec No. Buchwald H, Avidor Y, Braunwald E, et al. Bariatric surgery: a systematic review and meta-analysis. JAMA 2004;292:1724e37. Smith Jr SC, Blair SN, Bonow RO, et al. AHA/ACC guidelines for preventing heart attack and death in patients with atherosclerotic cardiovascular disease: 2001 update. A statement for healthcare professionals from the American Heart Association and the American College of Cardiology. J Am Coll Cardiol 2001;38:1581e3. Burke GL, Bertoni AG, Shea S, et al. The impact of obesity on cardiovascular disease risk factors and subclinical vascular disease: the MultiEthnic Study of Atherosclerosis. Arch Intern Med 2008;168:928e35. Duvall WL, Croft LB, Corriel JS, et al. SPECT myocardial perfusion imaging in morbidly obese patients: image quality, hemodynamic response to pharmacologic stress, and diagnostic and prognostic value. J Nucl Cardiol 2006;13:202e9. Freedman N, Schechter D, Klein M, et al. SPECT attenuation artifacts in normal and overweight persons: insights from a retrospective comparison of Rb-82 positron emission tomography and TI-201 SPECT myocardial perfusion imaging. Clin Nucl Med 2000;25:1019e23. Gugliotti D, Grant P, Jaber W, et al. Challenges in cardiac risk assessment in bariatric surgery patients. Obesity Surg 2008;18:129e33. Cohen MG, Alfonso C. Starting a transradial vascular access program in the cardiac catheterization laboratory. J Invasive Cardiol 2009;21:11Ae7A. Hildick-Smith DJ, Walsh JT, Lowe MD, et al. Transradial coronary angiography in patients with contraindications to the femoral approach: an analysis of 500 cases. Catheter Cardiovasc Interv 2004;61:60e6. Flohr TG, McCollough CH, Bruder H, et al. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006;16:256e68. Nakashima Y, Okada M, Washida Y, et al. Evaluation of image quality on a per-patient, per-vessel, and per-segment basis by noninvasive coronary angiography with 64-section computed tomography: dualsource versus single-source computed tomography. Jpn J Radiol; 29:316e23. Malhotra V. The approach to cardiac CT imaging in obese patients is not “one size fits all”. J Cardiovasc Comput Tomogr 2009;3:43e4. Raff GL, Gallagher MJ, O’Neill WW, et al. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol 2005;46:552e7. Brodoefel H, Tsiflikas I, Burgstahler C, et al. Cardiac dual-source computed tomography: effect of body mass index on image quality and diagnostic accuracy. Invest Radiol 2008;43:712e8. Alkadhi H, Scheffel H, Desbiolles L, et al. Dual-source computed tomography coronary angiography: influence of obesity, calcium load, and heart rate on diagnostic accuracy. Eur Heart J 2008;29:766e76. Chinnaiyan KM, McCullough PA, Flohr TG, et al. Improved noninvasive coronary angiography in morbidly obese patients with dual-source computed tomography. J Cardiovasc Comput Tomogr 2009;3:35e42.

A. Tognolini et al. / Clinical Radiology 68 (2013) e154ee163 27. Mahabadi AA, Massaro JM, Rosito GA, et al. Association of pericardial fat, intrathoracic fat, and visceral abdominal fat with cardiovascular disease burden: the Framingham Heart Study. Eur Heart J 2009;30:850e6. 28. de Vos AM, Prokop M, Roos CJ, et al. Peri-coronary epicardial adipose tissue is related to cardiovascular risk factors and coronary artery calcification in post-menopausal women. Eur Heart J 2008; 29:777e83. 29. Gorter PM, de Vos AM, van der Graaf Y, et al. Relation of epicardial and pericoronary fat to coronary atherosclerosis and coronary artery calcium in patients undergoing coronary angiography. Am J Cardiol 2008;102:380e5. 30. Gorter PM, van Lindert AS, de Vos AM, et al. Quantification of epicardial and peri-coronary fat using cardiac computed tomography; reproducibility and relation with obesity and metabolic syndrome in patients suspected of coronary artery disease. Atherosclerosis 2008;197:896e903.

e163

31. Hesse B, Tagil K, Cuocolo A, et al. EANM/ESC procedural guidelines for myocardial perfusion imaging in nuclear cardiology. Eur J Nucl Med Mol Imaging 2005;32:855e97. 32. Schroeder S, Achenbach S, Bengel F, et al. Cardiac computed tomography: indications, applications, limitations, and training requirements: report of a Writing Group deployed by the Working Group Nuclear Cardiology and Cardiac CT of the European Society of Cardiology and the European Council of Nuclear Cardiology. Eur Heart J 2008;29:531e56. 33. Valentin J, editor. The 2007 recommendations of the International Commission on Radiological Protection. Annals of the ICRP, publication 103. The International Commission on Radiological Protection. 34. International Commission on Radiological Protection. The 1990 recommendations of the International Commission on Radiological Protection. Annals of the ICRP, publication 60. Oxford UPP. 35. Brenner DJ. Effective dose: a flawed concept that could and should be replaced. Br J Radiol 2008;81:521e3.