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  •    Myocardial perfusion imaging inaccurate in assessing coronary artery disease in patients with atrial fibrillation
    Anand Deshmukh, MD, Creighton University, Omaha, NE.

    Coronary artery disease (CAD) is an important risk factor for atrial fibrillation (AF) and is associated with poor prognosis patients with AF. Exercise testing with or without echocardiogram, pharmacologic stress testing with echocardiogram, myocardial perfusion imaging with single photon emission computed tomography (MP-SPECT) are some of the methods for detection of CAD in patients with AF before referring them for coronary angiogram (CAG). Role of MP-SPECT in detection of CAD in patients with AF needs further investigation.

    Smit et al. conducted an observational study over 3 year period on consecutive AF patients that were referred for MP-SPECT. AF patients were age and gender matched with patients without AF. Patients with prior CAG or known CAD were excluded in both the groups. MP-SPECT study was done using exercise or pharmacological stress testing.  Primary end point was MP-SPECT studies with only unambiguous signs of ischemia that were considered positive. Secondary endpoints were CAG performed on patients with positive study and coronary interventions done during the follow up period. During the 3-year study period, 129 consecutive patients with AF were compared with 124 consecutive controls without AF. Mean ages of the overall cohort was 65 years, approximately half were males. Diabetes was more common in control group whereas NYHA class III/IV heart failure, non-ischemic cardiomyopathy and valvular heart disease were more common in AF group. Size of left atrium was larger in AF group. There were differences in the two groups in terms of pharmacological therapy due to obvious reasons.  MP-SPECT was conducted more frequently in AF group. There was no significant difference in the positive MP-SPECT outcomes between the two groups (11% vs. 17%, p=0.16). During mean follow up of 7 months, significant CAD and percutaneous coronary interventions were more common in control group compared AF group. A positive MP-SPECT outcome was related to higher yield of significant CAD in control group than in the AF group (67% vs. 15%, p =0.006). Presence of AF at the time of the study did not influence the positive outcome of the study or subsequent presence of significant CAD.

    What makes this study significant is that investigators tried to validate the presence or absence of significant CAD in patients with AF and positive MP-SPECT outcomes. However the specificity of MP-SPECT for detection of CAD in patients with AF is much lower than quoted in the literature that makes us wonder about the methodology. Results of MP-SPECT study are subject to bias and authors fail to define an “unambiguous” positive study. The study patient population is small. Although control group had higher yield of significant CAD than the AF group, rhythm itself cannot be accounted for explanation of this outcome as half of the patients in AF group had no AF or aflutter at the time of the study. This makes us wonder if the differences in the yield were solely due to the variation in the baseline characteristics such as diabetes and nonischemic cardiomyopathy. The study is subject to selection bias as only patients referred for MP-SPECT were included. Furthermore, CAG was not performed in all the patients with positive MP-SPECT outcome. In nutshell, this study reveals limitations of MP-SPECT imaging in patients with AF and larger randomized studies are needed to assess the role different non-invasive imaging to accurately diagnose CAD in patients with AF.

    Reference:

    Smit MD, Tio RA, Slart RH, Zijlstra F, Van Gelder IC. Myocardial perfusion imaging does not adequately assess the risk of coronary artery disease in patients with atrial fibrillation. Europace. 2010 May;12(5):643-8.


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