Multislice Computed Tomography in the Exclusion of Coronary Artery Disease in Patients with Presurgical Valve Disease

jc large iconBACKGROUND: Multislice computed tomography (MSCT) has shown high negative predictive value in ruling out obstructive coronary artery disease. Preliminary studies in patients with valvular heart disease (VHD) have demonstrated the potential of MSCT angiography (CTA) in such patients, precluding need for invasive angiography (XA). However, larger prospectively designed studies, including patients with atrial fibrillation and incorporating dose reduction algorithms, are needed.

METHODS: To evaluate the clinical utility of 64-slice CT in the preoperative assessment in patients with VHD, we prospectively studied 452 consecutive patients undergoing routine cardiac catheterization for eligibility. Two hundred thirty-seven patients underwent both MSCT and XA. Segment-based, vessel-based, and patient-based agreement between CTA and XA was estimated assuming that “nonevaluable” segments were positive for significant coronary stenosis.

RESULTS: In a patient-based analysis, sensitivity, specificity, positive predictive value, and negative predictive values of CTA were 95%, 89%, 66%, and 99%, respectively; in vessel-based analysis, 90%, 92%, 48%, and 99%, respectively; and in segment-based analysis, 89%, 97%, 38%, and 100%, respectively. No significant differences were found between patients with or without atrial fibrillation. A CAC value of 390 was the best cutoff for the identification of patients with positive or inconclusive CTA (which would not be exempted from XA in the clinical setting).

CONCLUSIONS: In the preoperative assessment of patients with predominant VHD, the diagnostic accuracy of 64-slice CTA for ruling out the presence of significant coronary artery disease is very good even when including patients with irregular heart rhythm. Using this approach, CAC quantification before CTA can be successfully used to identify patients who should be referred directly to XA, sparing unnecessary exposure to radiation.

PMID: 19808611

Posted in Computed Tomography, Journal Club Selections and tagged , , .

4 Comments

  1. Interesting work, give more support to the use of coronary CTA to diagnose obstructive coronary artery disease during pre-operative evaluation of patients with valvular heart diseases.
    An additional interesting piece of information was that screening for coronary artery calcifications may allow exclusion of patients with indeterminate CTA (those who had calcium score > 390). Therefore, allowing a referral of those patients to invasive coronary angiography.

  2. Another important finding of the study is that the negative predictive value of CTA was high in all 3 analysis (patient-, vessel-, or segment-based) in a large cohort of patients with both a relatively high mean age (67±10) and using ECG dose-modulation.

  3. This study, which included 237 pts (those who received both MSCT and XA) with multiple valve pathologies, was read by our group with interest, as there is a significant volume of patients at our hospital receiving intervention for valve pathology. The strong NPV of coronary CTA makes it an attractive preoperative modality for patients with valve pathology and low to intermediate probability of coronary artery disease. This role has typically been filled by coronary catheterization, with the goal of improving perioperative and long term outcomes in patients with significant CAD, as these patients could undergo combined valve and coronary bypass surgery at time of operation. The improved performance of MSCT in recent years makes it an alternate preoperative imaging modality, and represented the thrust of this paper.

    DISCUSSION POINTS:

    1) The inclusion of patients with atrial fibrillation in this cohort was a point of interest (32/237). The authors noted no significant differences in MSCT imaging results between patients with and without AF, however a higher radiation dose was observed (due to inability to use tube current modulation). The authors conclude that the ability of CT to exclude CAD in pts with AF is very good. We felt that the small numbers of patients with AF do make generalization of these findings somewhat limited. Also, our own experience with scanning patients in with arrhythmia is not as robust as reported in this study. More caution/assessment on case by case basis is more in-line with our current approach.

    2) Another point of interest was the use of calcium score in decision making, with a proposed cut off >400 CAC. Coronary calcium remains a significant challenge in coronary CTA, even with the latest generation of scanners. One of the proposed benefits of using coronary calcium score is identifying patients with calcium levels that will preclude the use of CTA in ruling out significant coronary disease, and thereby saving these patients the radiation dose and contrast load. However, the radiation doses now achievable with the use of prospective gating (which has become more widely available since the time of this study) and more dose restrictive versions of tube current modulation make estimated dose significantly lower, and diminish the benefit of performing a CAC on all patients. Additionally, the logistics become more complicated in a busy clinical setting, where patients might conceivably be given an IV and rate controlling medications after the CAC, but not in other instances.

    3) The endpoint of this study was comparison of MSCT with invasive angiography (XA). This is reasonable, as it is a modality that is a frequently utilized preoperative modality. However, a future, and perhaps more telling step would be to eventually evaluate is clinical outcomes of patients receiving valve surgery who have been assessed preoperatively by MSCT.

    4) The high NPV values observed on this study were in keeping with the results of multiple investigations that have noted the ability of CTA to rule out significant disease, particularly in properly selected patients (low to intermediate pre test suspicion). The modest PPV is not unexpected, given the results of prior investigators, as well as the decision to assign unevaluable segments as positive.

    5) Limitations of this study as reported by the authors include patients scheduled for elective valve surgery and without known CAD were included. Also, patients with heart rates >85 were excluded. With some scanners (notably, ones with dual source capacity) this rate could likely be higher. This was performed at a single center with experience in MSCT. Our own experience supports the concept that centers with more experienced technologists and physicians generate more appropriate and higher quality cardiac CT examinations/interpretations. The low prevalence of CAD noted in this population is unlikely to be replicated in North America, which would impact results; however careful selection of patients that are referred for CTA could help mitigate this.

    Overall, we found this to be an interesting study, with compelling results to further advance the role of cardiac CT in the clinical setting, particularly in centers with reasonable experience/volume in CTA and a population undergoing valve surgery.

    Prepared by Michael Bolen, MD

  4. The study supports the utilization of coronary artery calcium scoring as an important tool to guide which patients would benefit more from going straight to cardiac catheterization. To some degree, this study validates what some Institutions have been doing already based on the excellent negative predictive value of CTA.

    Specific discussion points:

    1. The study confirms the high negative predictive value of CTA for detection of obstructive coronary artery disease in a subset of patients with valve disease, most of them with aortic valve disease which shares some of the same pathophysiologic pathways of CAD.

    2. The utilization of tube current modulation in patients with atrial fibrillation resulted in the expected reduction of mean radiation dose to the patients without a trade-off in the capacity to exclude disease.

    3. The most common valvular heart disease is calcific aortic stenosis. This subgroup of patients has higher coronary calcium scores and would benefit more from cardiac catheterization. Should CTA be exclusively used in patients with mitral valve disorders, or those with aortic disease secondary to bicuspid valves? It would have been useful to know the correlation of between the anatomy of the aortic valve (trileaflet vs bicuspid) and the CAC. Young patients with valvular heart disease and at a low risk of atherosclerotic heart disease would benefit the most from coronary artery assessment by CTA prior to surgery.

    4. To some, the most interesting aspect of the paper was the utilization of CAC as a gatekeeper for the utility of CTA. While a very interesting, and potentially a radiation and cost saving algorithm, its logistics do not seem very realistic for a busy imaging center.

    Prepared by Juan C Brenes, MD and Jacobo Kirsch, MD

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