Carotid Ultrasound and the Emergency Department Physician : A Validation Study

This study aims to determine whether Emergency Department (ED) physicians can use an abbreviated bedside ultrasound protocol to accurately evaluate the condition of the carotid arteries. Our primary outcome was the accuracy with which the ED study predicted a category of stenosis as compared to the degree of stenosis based on a formal carotid ultrasound. The secondary outcome was the accuracy with which the ED physician measured peak systolic velocity (PSV) as compared to the measurements obtained during a formal ultrasound study, the current gold standard. We trained four emergency medicine residents and one emergency medicine attending physician to perform an abbreviated carotid ultrasound protocol which measured the peak systolic velocity (PSV) of the internal carotid artery (ICA) and the common carotid artery (CCA) bilaterally and requires the practitioner to calculate the ratio of the two (PSV ICA/PSV CCA). Forty-five adult patients > 55 years old were enrolled from December 2010 to January 2012, presenting with chief complaints of TIA, syncope, or near-syncope within 24 hours of their emergency room visit. The measurements and ratios obtained by our emergency physicians compared to those obtained by the formal ultrasound study all had p-values > . 05, and thus were not statistically significant. This pilot study was meant to be a preliminary look carotid disease in the emergency setting. Our findings confirm that properly trained emergency physicians are capable of performing the abbreviated carotid ultrasound protocol accurately. Background Cerebrovascular disease is the third most common cause of mortality in the developed world, with an estimated prevalence of 794 deaths per 100,000 (1). The incidence of TIA in particular was estimated by a population-based study to be 240,000 cases per year in the United States, with males and persons of African American descent demonstrating the highest rates of TIA among studied groups (2). In turn, hospitals continue to be strained from the growing number of patients requiring inpatient hospitalizations and extended stays in rehabilitation facilities for recovery from stroke and TIA. Additionally, patients presenting with TIA pose several dilemmas for the ED clinician. First, the transient nature of the symptoms often forces the physician to rely on history alone instead of a history coupled with concrete physical exam findings. The differential diagnosis is clouded with the transient nature of TIA symptoms and the additional considerations of “non-ischemic” etiology with similar clinical presentations: seizure, syncope, and migraine. (3) A second dilemma involves the determination of risk for a subsequent stroke. Investigators have developed prediction tools for the short term, namely the ABCD2 score (4,5). Regardless of clinical risk score, patients with highgrade carotid stenosis are at increased risk of stroke following a TIA. A study of 1707 patients with TIA noted 10% of patients returning to the same ED with a CVA within 90 days of the index TIA. Of this group of patients returning with CVA, approximately 50% had subsequent stroke within 2 days of the index TIA (3). The North American Symptomatic Carotid Endarterctomy Trial (NASCET) demonstrated a 90-day stroke risk of 20.1%, with most of the risk accruing within the first 20 days after the index TIA (6). Moreover, on multivariate analysis, including adjustment for ABCD2 score, the only independent predictor of early stroke risk (within 7 days) was the presence of large vessel occlusive disease (HR 5.9; 95% CI 2.2 to 15.9) (6). There is level I evidence that severe (>70%) symptomatic extracranial carotid stenosis should be re-vascularized with carotid endarterectomy as quickly as feasible after TIA or minor stroke (7, 8). More specifically, the internal carotid artery plays a clinically significant role in TIA and stroke, as stenosis greater than 70% increases the threat for a TIA or stroke (9). One study noted a 1.7% per year incidence of stroke among the 500 patients evaluated, and 5.5% per year incidence of stroke among those patients with ICA stenosis greater than 75%. Surgical intervention (via carotid endarterectomy) for clinically significant ICA stenosis can provide between 5-11% overall risk reduction for subsequent ipsilateral stroke between 30 days -2 years following the surgery, based on prospective data available thus far (10-13). Because of this risk and the need to identify those at greater risk than others, multiple prediction rules have been created, namely the ABCD score. However, the ability of clinical risk scores to identify treatment urgent patients, such as those with carotid stenosis requiring revascularization has not been established (14). Furthermore, regardless of clinical risk scores, patients with highgrade carotid stenosis are at increased risk of stroke following a TIA independent of any other factor (15). Based on the existing literature that outlines increased patient risk for high-grade carotid stenosis, our study group was motivated to create and initiate a protocol in which the ED physician may be able to assess the carotid arteries for patients with clinically relevant presentations for TIA and stroke (16, 17). This study attempts to create and validate an ultrasound protocol for assessing the carotid arteries, and correlate its accuracy and reliability when compared to a formal carotid ultrasound performed in the ultrasound department by trained sonographers (18, 19). If validation is successful, we propose that low risk patients, (those with combined low-risk score and negative or low grade stenosis on ultrasound) to be successfully discharged home with outpatient follow up. Those patients with high-risk extra cranial carotid stenosis could then be promptly referred to the in-house vascular surgeon (2024). Purpose/Hypothesis This study aims to determine whether Emergency Department (ED) physicians can use an abbreviated bedside ultrasound protocol to accurately evaluate the condition of the carotid arteries. If we can prove the ED physician is reliably accurate, this quick diagnostic test may be used in the future to identify previously undiagnosed high-risk patients, reduce the inpatient hospital stay for low-risk patients, or potentially eliminate the need for a follow-up visit as an outpatient. In order for the emergency physician to evaluate carotid artery stenosis there must be a protocol that is brief enough to allow safe and accurate estimation of carotid stenosis in a short amount of time. Because of time constraints in the emergency department, it is rare that the ED physician would have more than 5-10 minutes to complete an ancillary study in the department. We chose to abbreviate the formal ultrasound protocol by utilizing the peak systolic velocity (PSV) measurements using continuous color wave Doppler ultrasound and calculating ratios from those PSV values. Based on existing standardized criteria, these ratios can be translated directly into an estimate of internal carotid artery stenosis. Methods This pilot study enrolled 45 patients from December 2010 to January 2012. Patients were eligible for the study if they were aged 55 years and older presenting with a chief complaint consistent with the study definitions of TIA, syncope, near-syncope within 24 hours of their emergency room visit. Study definitions include the following: TIA defined as a sudden focal loss of neurologic function involving the brain or retina, supplied by a specific vascular territory, with complete recovery within 24 hours (25). Syncope was defined as a transient loss of consciousness (T-LOC) due to transient global cerebral hypoperfusion characterized by rapid onset, short duration, and spontaneous complete recovery. (26) Near-Syncope was defined as the sensation or subjective feeling that the patient was near total loss of consciousness. Four resident emergency medicine residents and one attending completed a brief hour long training module designed to standardize the ultrasound protocol for the study. A certified ultrasonographer from our institution’s radiology department provided this training to all the study personnel that performed scans on study patients. Patients under 55 years of age or presenting with acute stroke (ischemic or hemorrhagic), previous carotid endarterectomy, or those with a recent carotid ultrasound study within the last 6 months were excluded. Specifically, those with a recent carotid ultrasound study must have a report that is easily accessed by the ED physician at the primary investigation site, with the report resulted in the hospital electronic medical record at the primary investigation site, or any site affiliated with the primary investigation site (i.e. a hospital-affiliated vascular lab). If it was determined by the admitting physician that the patient did not require a formal carotid ultrasound as a part of their workup, the patient was considered ineligible for the study. Informed consent was obtained per our institutional IRB protocol, and patient information was protected per IRB specifications. In the case of altered or demented patients, and those unable to consent for themselves, consent was obtained by a healthcare proxy or medical power of attorney. Admitting physicians and patients were blinded to the results of the research study scan. The first ultrasound evaluation by the study team members was performed in the emergency department after the patient was admitted. The second ultrasound exam was performed by a trained ultrasonographer in our radiology department during the patient’s inpatient workup, as per the current standard of care. This is a lengthier exam and has been thoroughly described elsewhere (14, 27). Based on current standards, PSV is measured in the internal carotid artery (ICA) as well as the common carotid artery (CCA). These measurements are then used to calculate a ratio of the peak systolic velocities ICA/CCA, whic