Diagnostic Accuracy of Computed Tomography Angiography as Compared to Conventional Angiography in Patients Undergoing Noncoronary Cardiac Surgery

Abstract

Objective:

To compare the diagnostic accuracy of multi-slice computed tomography (MSCT) angiography with conventional angiography in patients undergoing major noncoronary cardiac surgeries.

Materials and Methods:

We studied fifty major noncoronary cardiac surgery patients scheduled for invasive coronary angiography, 29 (58%) female and 21 (42%) male. Inclusion criteria of the study were age of the patients ≥40 years, having low or intermediate probability of coronary artery disease (CAD), left ventricular ejection fraction (LVEF) >35%, and patient giving informed consent for undergoing MSCT and conventional coronary angiography. The patients with LVEF <35%, high pretest probability of CAD, and hemodynamically unstable were excluded from the study.

Results:

The diagnostic accuracy of CT coronary angiography was evaluated regarding true positive, true negative values. The overall sensitivity and specificity of CT angiography technique was 100% (95% confidence interval [CI]: 39.76%–100%) and 91.30% (95% CI: 79.21%–97.58%). The positive (50%; 95% CI: 15.70%–84.30%) and negative predictive values (100%; 95% CI: 91.59%–100%) of CT angiography were also fairly high in these patients.

Conclusion:

Our study suggests that this non-invasive technique may improve perioperative risk stratification in patients undegoing non-cardiac surgery.

INTRODUCTION

Coronary artery disease (CAD) is the emerging cause of morbidity and mortality in developing world. Conventional coronary angiography has been the gold standard investigation for the diagnosis of CAD. It provides an excellent resolution for visualization of the coronary arteries for catheter-based or operating interventions.[1] Although the association of this technique with major complications such as mortality is highly uncommon, it is frequently associated with various cardiac and noncardiac complications.[2]

Computed tomography (CT) coronary angiography is a promising technique for the evaluation of CAD noninvasively.[3] It assesses disease within the coronary artery and provides qualitative and quantitative information about nonobstructive atherosclerotic plaque burden within the vessel wall. Thus, CT angiography-based disease evaluation may provide clinically more significant information than conventional angiography. The introduction of multi-slice computed tomography (MSCT) technology such as 64-slice, 128-slice, 256-slice, and now 320-slice MSCT has produced a high diagnostic accuracy of CT coronary angiography.[4] It has consistently showed to have a very high negative predictive value (well above 90%) in ruling out patients with significant CAD defined as coronary luminal stenosis of >50%.[5,6]

The American College of Cardiology/American Heart Association recommends that coronary angiography should be performed before valve surgery in men aged >40 years, women aged >35 years with coronary risk factors and in postmenopausal women.[7] The prevalence of CAD in patients undergoing valve replacement is 20–40% in developed countries. In the previous studies, the incidence of angiographically proven CAD in acquired valvular diseases has been shown to vary widely from 9% to 41%.[8] In aortic stenosis, the incidence of CAD was reported to be as high as 37%.[9] Hence, the accurate diagnosis of CAD in valvular patients holds high clinical importance.

We aimed to report the diagnostic performance of 128-slice CT coronary angiography in 50 patients undergoing for major noncoronary cardiac surgery referred for diagnostic invasive coronary angiography to assess the extent and severity of coronary stenosis.

MATERIALS AND METHODS

During January 2013 to December 2014, we enrolled fifty major noncoronary cardiac surgery patients scheduled for invasive coronary angiography who fulfilled the following inclusion criteria of age ≥40 years, having low or intermediate probability of CAD, left ventricular ejection fraction (LVEF) >35%, and patient giving informed consent for undergoing MSCT and conventional coronary angiography. Those having any contraindication for contrast injection, LVEF <35%, high pretest probability of CAD, and hemodynamic instability were excluded from the study. Patients with heart rates of >70 bpm received (unless they had known overt heart failure or electrocardiogram (ECG) atrioventricular conduction abnormalities) a single oral dose of 100 mg metoprolol 45 min before the scan. Patients with heart rates of >80 bpm received an additional oral dose of metoprolol if not contraindicated. If the patient was anxious, then lorazepam was used if not contraindicated.

All patients were scanned with a 128-slice CT scanner (Siemens, somatom definition AS) equipped with a new feature in MSCT technology, so-called z-axis flying-focus technology. The central 32 detector rows acquire 0.6-mm slices, and the flying-focus spot switches back and forth between 2 z positions between each reading. Two slices per detector row are acquired, which results in a higher oversampling rate in the z-axis, thereby reducing artifacts related to the spiral acquisition and improving spatial resolution down to 0.4 mm. A bolus of 65–80 mL contrast material (omnipaque) was injected through an arm vein at a flow rate of 5 mL/s. A bolus tracking technique was used to synchronize the arrival of contrast in the coronary arteries with the initiation of the scan. To monitor the arrival of contrast material, axial scans were obtained at the level of the ascending aorta with a delay of 10 s after the start of the contrast injection. The scan was automatically started when a threshold of 150 Hounsfield units was reached in a region of interest positioned in the ascending aorta. Images were reconstructed with ECG gating to obtain optimal, motion-free image quality.

Conventional coronary angiography evaluation

All scans were performed within 2 weeks of the MSCT coronary diagnostic angiogram. A single observer unaware of the multi-slice CT results identified coronary lesion as a single vessel, double vessel, or triple vessel disease. All lesion, regardless of size, were included for comparison with CT coronary angiography. Lesions were classified as having nonsignificant disease (luminal irregularities or <50% stenosis) or as having significant stenosis. Stenosis was evaluated in two orthogonal views and classified as significant if the mean lumen diameter reduction was 50% using a validated quantitative coronary angiography (QCA).[10]

Computed tomography coronary angiography evaluation

All scans were analyzed independently by a radiologist and a cardiologist who were unaware of the results of conventional coronary angiography. Total calcium scores of all patients were calculated with dedicated software and expressed as Agatston scores. The Agatston score is a commonly used scoring method that calculates the total amount of calcium on the basis of the number, areas, and peak Hounsfield units of the detected calcified lesions. All available coronary segments were visually scored for the presence of > 50% considered as significant stenosis. Maximum intensity projections were used to identify coronary lesions and (curved) multiplanar reconstructions to classify lesions as significant or nonsignificant. Disagreement between observers was resolved by consensus.

Statistical analysis

Data were analyzed using statistical system SPSS version 20 software (Chicago, IL, USA). The diagnostic performance of CT coronary angiography for the detection of significant lesions in coronary arteries with QCA as the standard of reference is presented as sensitivity, specificity, positive and negative predictive values, and positive and negative likelihood ratios with the corresponding exact 95% of confidence interval (CIs). Comparison between CT and conventional coronary angiography was performed on the two level vessel by vessel (no or any disease per vessel), and patient by patient (no or any disease per patient).

RESULTS

In this study, 29 (58%) subjects were female, and 21 (42%) were male showing an average age of 50.36 ± 8.39 years. The overall prevalence of CAD in the study population was 8%. Of fifty patients 24 (48%), 13 (26%), eight (16%), and five (10%) underwent mitral valve replacement, double valve replacement (DVR), aortic valve replacement, and other surgeries, respectively. High distribution of CAD risk factors such as hypertension (24%), smoking (22%), and dyslipidemia (18%) was observed in the study group. The mean creatinine level was 0.766 ± 0.17 and average dye used in conventional angiography was 48.5 ± 26.6 whereas for CT angiography it was 72.8 ± 6.32. Average radiation dose in conventional coronary angiography and MSCT coronary angiography was 5.2 mSv and 9.2 mSv, respectively.

The majority of the patients had sinus rhythm (68%), whereas atrial fibrillation was found in 32% of the subjects. Patients included in the study had low to intermediate probability of CAD. In this study, three patients had complications after conventional angiography. Complications were of local site hematoma, acute kidney injury managed conservatively, and acute heart failure. A patient who developed hematoma was obese female patients with body mass index >30 kg/m². The patient suffered from pseudoaneurysm, had hospitalized for 9 days, which leads to increased morbidity and cost of hospital stay. None of the patients had a complication after CT coronary angiography. One patient needed repeat CT angiography due improper scan.

The diagnostic accuracy of CT coronary angiography was evaluated regarding true positive, true negative values and is presented in Table 1. The overall sensitivity and specificity of CT angiography technique was 100% (95% CI: 39.76%–100%) and 91.30% (95% CI: 79.21%–97.58%), respectively [Table 2]. The positive predictive value (50%; 95% CI: 15.70%–84.30%) and negative predictive value (100%; 95% CI: 91.59%–100%) of CT angiography were also fairly high in these patients.

Table 1.

Diagnostic test evaluation

Table 2.

Diagnostic accuracy of computed tomography angiography according to sensitivity and specificity

DISCUSSION

Recent reports from multiple studies demonstrated that recent-generation MSCT scanners showed promise for noninvasive detection of coronary stenosis[11,12,13,14] However, until now no studies were found regarding the clinical efficacy or prognostic value of 128-slice CT coronary angiography versus conventional invasive coronary angiography in the diagnosis of patients planned for major noncoronary surgeries such as DVR, Bentall, atrial septal defect closure, etc.[15,16] In our study, we reported 8% CAD prevalence in patients planned for major noncoronary cardiac surgery. We performed conventional and MSCT coronary angiography in all patients and the results showed that CT coronary angiography with invasive coronary angiography as the reference standard had a considerably high sensitivity (100%) and specificity (95.65%).

The health economic model using invasive coronary angiography as the reference standard showed that at a pretest probability of CAD of 70% or lower, CT coronary angiography resulted in lower cost per patient with a true positive diagnosis. At a pretest probability of CAD of 70% or higher, invasive coronary angiography was associated with a lower cost per patient with a true positive diagnosis.[17]

In our study population, two patients developed local site complications in the form of hematoma and pseudoaneurysm after conventional angiography. None of the patients developed drug complication after MSCT coronary angiography. Hence, MSCT coronary angiography will be more favorable in female obese patients with intermediate likelihood of CAD. Hence, MSCT coronary angiography will be cost-effective in patients of valvular heart diseases.[18]

However, CT angiography suffers from a drawback that average amount of dye used in MSCT coronary angiography were 72.8 ± 6.32 ml which is higher than average amount of dye required for conventional angiography (48.6 ± 26.6 ml). Hence, the use of CT coronary angiography could not be used in patients with known renal dysfunction, where reduction of contrast dye load is highly advocated.

CONCLUSION

Our results show that 128-slice CT coronary angiography is a reliable technique to detect coronary stenosis in patients planned for noncoronary cardiac surgery. Although there has been important technological progress in the development of CT coronary angiography, its clinical application remains limited. A study wth large numbers of patients is required for the recommendation of only CT coronary angiography for the coronary evaluation in major non-cardiac surgeries.

Financial support and sponsorship

U.N. Mehta Institute of Cardiology and Research Center (Affiliated to BJ Medical College, Ahmedabad, Gujarat, India).

Conflicts of interest

There are no conflicts of interest.