Abstract Background A Science Advisory from the American Heart Association implores clinicians to always consider equivalent tests which do not use ionizing radiation. Intersocietal guidelines describe only two scenarios where a nuclear stress test is the only option for non-invasive evaluation: left bundle branch block (LBBB) and ventricular-paced rhythm; otherwise, treadmill EKG and stress echocardiography are feasible. This study sought to measure our compliance with appropriate use criteria,6 and then to apply our own Novel Radiation Sparing Approach (NRSA) to measure what percentage could have been evaluated without radiation. Methods The appropriateness of each referral for nuclear stress testing was evaluated using the AUC. Our NRSA was then applied, reserving a grade of ‘appropriate’ for patients with LBBB, pacemaker, or known resting wall motion abnormalities. The rate of appropriate referrals was then compared using McNemar’s test. Results We analyzed 423 consecutive referrals between Aug 2010 and Feb 2012. Median age was 64 yr; males comprised 57.2% of all patients; and 64.8% were outpatient. Chest pain and dyspnea were the most common reasons for referral. The rate of appropriate referrals at our facility using the AUC was 93.6%. When applying our NRSA, nuclear stress testing was the required or ‘appropriate’ test in only 17.7% of our patients (p < 0.001, McNemar’s test). Conclusions According to the current AUC, our facility is referring patients appropriately for nuclear stress testing. However, by reserving nuclear stress testing primarily for patients with LBBB, pacemaker, and baseline wall motion abnormalities, we can reduce radiation exposure to our patients while still providing appropriate evaluation. INTRODUCTION The use of medical radiation in the USA has increased nearly 6-fold from the 1980’s to 2006.1 A significant part of this increase is accounted for by the increase in nuclear stress testing. The National Council on Radiation Protection and Measurements estimates that myocardial perfusion imaging (MPI) accounts for more than 10% of the entire cumulative effective dose to the U.S. population from all sources, excluding radiotherapy.1,2 A single standard MPI protocol at our center exposes a patient to an effective dose of 9 milliSieverts (mSv) of radiation; the equivalent of 150 chest radiographs (a standard chest radiograph exposes a person to 0.06 mSv of radiation). The Biologic Effects of Ionizing Radiation (BEIR) VII report looked specifically at the risk estimates for cancer and other health effects from exposure to ionizing radiation. They found that the lifetime attributable risk (LAR) of incidence and mortality for all solid cancers and leukemia from a dose of 100 mSv of radiation was 1/100.2,3 Often, patients will undergo several MPI stress tests during their lifetime, in addition to other tests requiring ionizing radiation such as computed tomography (CT) and standard radiographs, thereby increasing their lifetime risk of adverse effects. As a result, a 2009 American Heart Association (AHA) Science Advisory stated: “Among equivalent tests, the one that exposes that patient to the least amount of radiation should be chosen… Among younger patients, imaging modalities without radiation exposure should be preferred if possible.”5 These statements are in accordance with the ALARA principle; as low as reasonably achievable. Current appropriate use criteria (AUC) for cardiac radionuclide imaging (CRNI) from the American College of Cardiology (ACC) and AHA explain in detail under what conditions a nuclear stress test is felt to be appropriate but do not give significant attention to possible carcinogenesis related to medical radiation.4 Treadmill stress testing is still a valid test in patients with normal baseline electrocardiogram (EKG) and ability to exercise. In many patients though, cardiac imaging is necessary to add to the EKG and blood pressure data collected during a routine treadmill stress test. Among others, the more common reasons to add imaging are: abnormal baseline EKG, inability to exercise thus requiring pharmacologic stress, and the clinician’s desire to define the location and overall burden of disease. Also, it is well established that stress testing using echocardiography has similar diagnostic accuracy and clinical indications as nuclear stress testing.7 Supported in part by the 2002 ACC/AHA Chronic Stable Angina guidelines,8 it is our opinion that there are only a few situations where nuclear stress testing is the required modality for cardiac stress testing requiring imaging: left bundle branch block (LBBB) on baseline EKG, cardiac pacemaker, and wall motion abnormality on previous cardiac imaging. These three situations all involve abnormal motion of the left ventricle at rest, which makes stress echocardiography very difficult to interpret, thus requiring the myocardial perfusion images (that are independent of wall motion) at which nuclear stress testing excels. It is from this line of thinking that we developed this novel radiation sparing approach (NRSA). While we anticipate that there are certain situations where a clinician will prefer a nuclear stress test over stress echocardiogram, our research sought to review 400 consecutive patient referrals applying both published AUC and a NRSA, in which we reserve the radiation and increased cost of nuclear stress testing for those patients with LBBB, cardiac pacemaker, and known baseline wall motion abnormality. METHODS Subsequent to receipt of IRB approval, we reviewed the electronic medical records of 423 consecutive patients seen in the Nuclear Medicine stress testing laboratory at the Naval Medical Center San Diego between August 2010 and February 2012. No patients were excluded. We examined the electronic medical record on each patient to apply the 2009 AUC for CRNI in order to measure the rate of appropriate use. We then measured what percentage of patients required nuclear stress testing while using our NRSA. Patients with LBBB on EKG, cardiac pacemaker, or wall motion abnormality on previous imaging were graded as appropriate for nuclear stress testing. STATISTICAL ANALYSIS The overall rates of appropriate referrals were compared using McNemar’s test for statistical significance. To compare appropriate referral rates based on physician specialty, a Fisher’s Exact Test contingency table was used. RESULTS Median age was 64 yr. Males comprised 57.2% of the patients referred for stress testing. The majority of patients (64.8%) were outpatient. Angina, dyspnea, and atypical chest pain were the most common reasons for referral, details are shown in Table I. Table I. Reasons for Referral Chest pain/angina 211 (49.9%) Dyspnea 80 (18.9%) Atypical chest pain 46 (10.9%) Arrhythmia/abnormal EKG 30 (7.1%) Anginal equivalent 16 (3.8%) Heart failure 11 (2.6%) Preoperative evaluation 7 (1.7%) Syncope 4 (0.9%) Other 18 (4.3%) Chest pain/angina 211 (49.9%) Dyspnea 80 (18.9%) Atypical chest pain 46 (10.9%) Arrhythmia/abnormal EKG 30 (7.1%) Anginal equivalent 16 (3.8%) Heart failure 11 (2.6%) Preoperative evaluation 7 (1.7%) Syncope 4 (0.9%) Other 18 (4.3%) Table I. Reasons for Referral Chest pain/angina 211 (49.9%) Dyspnea 80 (18.9%) Atypical chest pain 46 (10.9%) Arrhythmia/abnormal EKG 30 (7.1%) Anginal equivalent 16 (3.8%) Heart failure 11 (2.6%) Preoperative evaluation 7 (1.7%) Syncope 4 (0.9%) Other 18 (4.3%) Chest pain/angina 211 (49.9%) Dyspnea 80 (18.9%) Atypical chest pain 46 (10.9%) Arrhythmia/abnormal EKG 30 (7.1%) Anginal equivalent 16 (3.8%) Heart failure 11 (2.6%) Preoperative evaluation 7 (1.7%) Syncope 4 (0.9%) Other 18 (4.3%) The rate of appropriate referrals using published AUC was 93.6%. That rate of appropriateness dropped to 17.7% (p < 0.001) when the radiation sparing approach was applied. Cardiology referred 86.5% of the patients for testing, and had a higher rate of appropriateness (19.6%) in comparison to non-cardiologists when applying the NRSA although this difference did not meet statistical significance (cardiology vs. internal medicine (IM), p = 0.09; cardiology vs. family practice (FP), p = 0.06). Details on appropriate use are shown in Table II. Table II. Rate of Appropriate Referrals Number of Referrals AUC Appropriate NRSA Appropriate Total 423 396 (93.6%) 75 (17.7%) p < 0.001 Cardiology 368 347 (94.3%) 72 (19.6%) IM 31 30 (96.8%) 2 (6.5%) Cardiology vs. IM: p = 0.09 FP 24 19 (79.2%) 1 (4.2%) Cardiology vs. FP: p = 0.06 Number of Referrals AUC Appropriate NRSA Appropriate Total 423 396 (93.6%) 75 (17.7%) p < 0.001 Cardiology 368 347 (94.3%) 72 (19.6%) IM 31 30 (96.8%) 2 (6.5%) Cardiology vs. IM: p = 0.09 FP 24 19 (79.2%) 1 (4.2%) Cardiology vs. FP: p = 0.06 Table II. Rate of Appropriate Referrals Number of Referrals AUC Appropriate NRSA Appropriate Total 423 396 (93.6%) 75 (17.7%) p < 0.001 Cardiology 368 347 (94.3%) 72 (19.6%) IM 31 30 (96.8%) 2 (6.5%) Cardiology vs. IM: p = 0.09 FP 24 19 (79.2%) 1 (4.2%) Cardiology vs. FP: p = 0.06 Number of Referrals AUC Appropriate NRSA Appropriate Total 423 396 (93.6%) 75 (17.7%) p < 0.001 Cardiology 368 347 (94.3%) 72 (19.6%) IM 31 30 (96.8%) 2 (6.5%) Cardiology vs. IM: p = 0.09 FP 24 19 (79.2%) 1 (4.2%) Cardiology vs. FP: p = 0.06 CONCLUSIONS As described previously, multiple studies have shown an association between medical radiation and increased lifetime attributable risk of malignancy. As a result, a 2009 AHA Science Advisory exhorts clinicians to minimize radiation use whenever possible. Unfortunately, there are three separate AUC from the AHA/ACC, one for each of the major forms of stress testing, yet none of these views medical radiation as a significant factor when determining appropriateness of the test. Our results demonstrate that according to the current AUC for CRNI, we are referring patients appropriately for nuclear stress testing. However, a very large difference in the rate of appropriate referrals (93.6% with AUC vs. 17.7% with NRSA; Table II) appears when applying a novel approach intended to minimize patient exposure to medical radiation. We believe that the remainder of patients may have undergone stress testing without being exposed to radiation. This is of obvious importance to all patients, particularly to young females. Of note, the youngest of our 181 female patients was 32 yr of age, and 27 of them (14.9%) were age 55 yr or younger. It is precisely this group that incurs the greatest lifetime attributable risk from medical radiation. Also of interest is the difference in referral patterns between cardiologists, internists, and family practitioners. While one could argue that the vast majority of referrals were not warranted when applying the more stringent NRSA, cardiologists appeared relatively more likely than internists and family practitioners to order nuclear stress testing appropriately, although this did not reach statistical significance (Table II). A limitation of our study is that other reasons may exist for ordering a nuclear stress test, thus each center should individualize this NRSA as needed. These potential reasons include: inadequate stress echocardiogram facilities at one’s center, unwillingness to use dobutamine in a patient (ie. atrial fibrillation or a previous reaction to this medication), difficulty obtaining echo images in certain patients (ie. obesity, chronic obstructive pulmonary disease), and clinician preference. Of note, the widespread use of ultrasound contrast agents that allow visualization of the left heart make obesity and chronic obstructive lung disease less of an issue. Another potential limitation is that our patient sample was obtained at a single center. Our data show that according to the current AUC for CRNI, we are referring patients appropriately for nuclear stress testing. We believe these criteria are too liberal and allow for the unnecessary exposure of medical radiation to our patients and additional financial cost to our health care system. Future AUC need to examine all three major forms of cardiac stress testing together and take medical radiation and financial cost into account when determining appropriateness. This will in turn have a real impact on our patients and health care system. REFERENCES 1 Mettler FA , Thomadsen BR , Bhargavan M , et al. : Medical radiation exposure in the US in 2006: preliminary results . Health Phys 2008 ; 95 : 502 . Google Scholar Crossref Search ADS PubMed 2 Monson RR , Cleaver JE , Abrams HL , et al. : Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII – Phase 2 Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, National Research Council. ISBN: 0-309-53040-7, 424 pages, ( 2006 ). 3 Einstein AJ , Weiner SD , Bernheim A , et al. : Multiple testing, cumulative radiation dose, and clinical indications in patients undergoing myocardial perfusion imaging . JAMA 2010 ; 304 ( 19 ): 2137 – 44 . Google Scholar Crossref Search ADS PubMed 4 Faletra FF , D’Angeli I , Klersy C , et al. : Estimates of lifetime attributable risk of cancer after a single radiation exposure from 64-slice computed tomographic coronary angiography . Heart 2010 ; 96 : 927 – 32 . Google Scholar Crossref Search ADS PubMed 5 Gerber TC , Carr JJ , Arai AE , et al. : Ionizing radiation in cardiac imaging: a Science Advisory from the American Heart Association Committee on Cardiac Imaging of the Council on Clinical Cardiology and Committee on Cardiovascular Imaging and Intervention of the Council on Cardiovascular Radiology and Intervention . Circulation 2009 ; 119 : 1056 – 65 . Google Scholar Crossref Search ADS PubMed 6 Hendel RC , et al. : ACCF/ASNC/ACR/AHA/ASE/SCCT/SCMR/SNM 2009 appropriate use criteria for cardiac radionuclide imaging . Circulation 2009 ; 119 : e561 – 87 . Google Scholar PubMed 7 Fleischmann KE , et al. : Exercise echocardiography or exercise SPECT Imaging? A meta-analysis of diagnostic test performance . JAMA 1998 ; 280 : 913 – 20 . Google Scholar Crossref Search ADS PubMed 8 Gibbons RJ , Abrams J , Chatterjee K , et al. : ACC/AHA 2002 guideline update for the management of patients with chronic stable angina – summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on the Management of Patients With Chronic Stable Angina) . Circulation 2003 ; 107 : 149 – 58 . Google Scholar Crossref Search ADS PubMed Author notes The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. Government. Published by Oxford University Press on behalf of Association of Military Surgeons of the United States 2018. This work is written by (a) US Government employee(s) and is in the public domain in the US.
Military Medicine – Oxford University Press
Published: Nov 5, 2018
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