Review

Continuing Medical EducationNature Clinical Practice Cardiovascular Medicine (2005) 2, 217-223
doi:10.1038/ncpcardio0154  
Received 18 November 2004 | Accepted 25 February 2005

Technology Insight: hand-carried ultrasound cardiac assessment—evolution, not revolution

Bruce J Kimura* and Anthony N DeMaria  About the authors

Correspondence *Noninvasive Cardiology, Scripps Mercy Hospital, University of California, San Diego, 4060 Fourth Avenue, Suite 206, San Diego, CA 92103, USA

Email kimura.bruce@scrippshealth.org

Summary

Hand-carried ultrasound devices can enhance the art of bedside physical examination by increasing diagnostic accuracy, detecting disease at an earlier stage, and improving triage and referral of patients. Although limitations of device cost and portability can be overcome with technologic advances, the shortage of standardized imaging and training opportunities now needs to be addressed to move the technique forward. Cardiologists are the best-qualified subspecialists to design and teach a simplified training program for bedside use of hand-carried ultrasound devices to assess the cardiovascular system.

Review criteria

We identified the papers on which to base this review through extensive searches of the PubMed database, using the keywords "hand-carried" and "hand-held", as well as by inputting the names of investigators in this area, recalled through personal knowledge of the field and of recent contributions. English-language, full-text articles published between the years 1978 and 2004 were included.

Keywords:

diagnosis, hand-carried ultrasound scanning, screening

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Introduction

The practice and teaching of physical examination techniques have evolved slowly since Hippocrates' time and have been virtually unchanged since the invention of the stethoscope nearly two centuries ago. Of the modern imaging techniques that could rejuvenate the 'hands-on' art of physical examination, only ultrasound has been proven safe, is portable and provides immediate data. The advent of hand-carried ultrasound (HCU) devices has provided an opportunity to improve bedside examination. As a consequence, however, controversy has arisen regarding the definition of a formal comprehensive echocardiogram, the training and scope of practice of physicians using the device, and reimbursement for HCU use. This review discusses the value and limitations of HCU use at the bedside to detect cardiovascular disease, and describes an example of an evidence-based cardiovascular ultrasound assessment.

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Development of the technology

Miniaturization of ultrasound equipment can be viewed as natural technologic progression; prototypical HCU devices were introduced over 20 years ago.1 Following in the footsteps of laptop and palm-sized personal computers, some ultrasound systems are now ultraportable, battery-driven devices the size and weight of a small textbook (Table 1). Much of the space and footprint taken up by traditional cart-based machines was dramatically reduced in the first-generation portable devices, by elimination of extensive keyboards, processing hardware and display screens, videotape recorders and storage space. Despite the limited screen size and variation in Doppler color maps, the current HCU devices, when used by cardiovascular specialists or experienced sonographers, are considered acceptably accurate compared with standard echocardiography,2, 3 with minor discordances being due largely to the subjective interpretation of images.

Table 1 Commercial miniaturized, battery-operated ultrasound systems for cardiac or vascular applications.
Table 1 - Commercial miniaturized, battery-operated ultrasound systems for cardiac or vascular applications.
Full tableFigures & Tables indexDownload PowerPoint slide (272K)

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How should hand-held devices be used?

When the current types of HCU devices were introduced 5 years ago, the clinical pathway by which to apply them had not yet been defined. Thus, a revolutionary technology was introduced into an already highly competitive ultrasound-device market, spurring publications and discussion as to the appropriate model of use for HCU devices.4 Soon after its introduction, an expert panel of echocardiographers recommended that this technology be used only for standard indications, by practitioners experienced in echocardiography.5

Cardiac physical examination with the stethoscope is unrestricted in current clinical practice, and has largely evolved into a screening method for echocardiography referral. As such, its status has been reduced from a definitive diagnostic technique to a brief, cursory practice, and medical trainees now seem to perform auscultation with less accuracy than previous generations.6 In today's hurried health-care environment of noisy emergency, intensive-care and patient-care areas, the detection of soft gallops or changing murmurs is even more challenging than in the past. Echocardiograms are frequently ordered based on indications related to the patient's chief complaint, history or initial ancillary testing. HCU can supplement the physical examination, reviving the central role of initial bedside diagnosis.7

Images of cardiac structure recorded on HCU are well suited for storage and wireless transmission and are complementary to auscultative sounds, which are often indicative of dynamic function. In addition, many structural abnormalities are not readily detectable by auscultation, such as early atherosclerosis and pericardial effusion, and are better screened for by ultrasound techniques. The use of HCU to increase the accuracy of physical examination has the potential to detect cardiovascular disease at an earlier stage, improve triage and subspecialty referral, and to eliminate unnecessary testing generated by inaccurate auscultation.

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Which physicians should use the devices?

The intuitive answer to who should use HCU devices is simple: the physicians for whom HCU assessment improves bedside evaluation. Logically, the benefit gained will relate to the individual's expertise in bedside evaluation and echocardiography. An expert with the stethoscope, such as a cardiologist, in a quiet examination room might be little helped by use of HCU, despite his expertise in imaging. Conversely, the hurried emergency room physician in an unavoidably noisy environment could benefit greatly, despite only a basic knowledge of ultrasonography.

Studies have documented the benefit of limited cardiac ultrasound assessment by novices8, 9 and experts10 in detecting specific findings on standard echocardiography. In only a few studies has the additional benefit of HCU after auscultation been investigated, compared with echocardiography as the gold standard.11, 12, 13 No study has yet compared HCU with physical examination as an assessment for appropriate referral for standard echocardiography. This outcome might be appropriate, since a significant abnormality on brief HCU or physical examination should trigger a full investigation with standard echocardiography to assess all findings.

The technique of teaching physical examination to novices has remained unchanged for centuries, usually consisting of representative findings being demonstrated to student groups around the beds of patients. By contrast, the electronic era can make teaching HCU rapid and individualized, with in-device libraries or online educational methods. Innovative teaching techniques can facilitate quick learning of basic ultrasound screening examinations by receptive practitioners. For example, with use of an on-screen circular phantom as an aid to diagnose an enlarged left atrium, 16 medical residents were able to detect left-atrial sizes of 4.0 cm or larger with over 80% accuracy after only 1 h of instruction (unpublished data). Visual training with a videoclip library and a template-matching approach successfully taught 13 medical students the difficult task of estimating left-ventricular ejection fraction.14 So far, of the more than 40 publications on HCU, seven have formally described the accuracy of HCU devices when used by novices; they have involved a total of 96 novice participants who collectively performed 1,484 HCU assessments (Table 2).12, 15, 16, 17, 18, 19, 20 Despite variation in training regimens and study endpoints, these initial reports demonstrate the feasibility of training noncardiologists to use HCU devices effectively for limited applications.

Table 2 Summary of HCU training studies for cardiovascular examination.
Table 2 - Summary of HCU training studies for cardiovascular examination.
Full tableFigures & Tables indexDownload PowerPoint slide (309K)

The maximum impact of HCU examination on health care will rest upon its development into a general diagnostic technique in primary-care medicine. Because of time constraints in both the training of physicians and examination of patients, the HCU assessment of the cardiovascular system for general practice must be limited to easily-obtained echocardiographic windows with maximal sensitivity to detect clinically important diagnoses.

Distillation of the information in a comprehensive echocardiogram to a simplified screening assessment is difficult and requires the cardiologist's knowledge of the clinical accuracy of each ultrasound method, its ease of application, the target diseases to screen for, and the time constraints of clinical practice. Simplified limited echocardiographic examination assessments, when performed by experts, can detect the target diagnosis as well as significant incidental findings.21 We have mathematically modeled this ultrasound screening strategy,22 applied it to consecutive echocardiography referrals to rule out mitral-valve prolapse,23 and extended the application to all cases referred for echocardiography.24 We found that initial limited ultrasound scanning could save costs through improvements in referral for echocardiography, resulting in a 70% reduction in unnecessary echocardiography studies being performed, while missing significant findings in less than 5% of low-risk cases. Importantly, referral by noncardiologists and outpatient status were statistically associated with normal echocardiograms, and therefore were ideal characteristics to target for prereferral HCU screening. Conversely, in patients with a high rate of abnormalities, such as those in the intensive-care unit, routine direct referral for standard echocardiography if immediately available might be more effective than initial HCU assessment.

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Development of a cardiovascular HCU examination for primary care

The limited ultrasound screening strategy can be expanded to routine in-office examination of asymptomatic outpatients, to detect disease states that are clinically significant but have previously required expensive or invasive diagnostic examinations. Carotid atherosclerosis, left-ventricular systolic dysfunction, and abdominal aortic aneurysm are three such disorders for which treatment can prolong life, even in an asymptomatic state, and that can be screened for with an HCU device.

Imaging the carotid arteries for subclinical atherosclerosis

Identification of the extracranial carotid artery in longitudinal and transverse imaging can be learned by novice users in about 1 h.16 Of all potential applications for HCU, screening for subclinical atherosclerosis in the carotid bifurcation will probably save the most lives and typifies point-of-care ultrasound screening. No amount of physical examination or laboratory testing can detect the presence of early, nonobstructive atheroma in the carotid arteries. Yet, the presence of even minimal atherosclerosis in the carotid arteries elevates a patient's risk to that of a coronary heart disease (CHD) equivalent.25 Unlike MRI or CT scanning, ultrasonography can be quickly applied to examine the arterial bifurcation, which is prone to develop disease, often years before clinical cardiac events occur. For the large number of patients with intermediate LDL-cholesterol values, the determination of a CHD risk equivalent can lead to lipid-lowering therapies being started and the risk of CHD events being decreased. In addition, being able to visualize the atheroma on the screen can have an emotional impact on patients that might improve adherence to treatment.

Screening for asymptomatic left-ventricular dysfunction

The parasternal long-axis view of the left ventricle has a long history of diagnostic use and can be achieved by novices.12 Overall sensitivity and specificity of this view for identifying abnormal echocardiography studies exceed 70%.24 Unlike apical views, landmarks for transducer application are easily located along the sternum, frequently without completely disrobing the patient. Clinical evidence supports treatment of left-ventricular systolic dysfunction by administration of angiotensin-converting-enzyme inhibitor therapy when left-ventricular ejection fraction is lower than 40%, even in asymptomatic patients.26

Physicians and sonographers have been able to screen successfully for left-ventricular systolic dysfunction in the community with HCU devices.27, 28 From the same images, left-atrial size can be assessed; left-atrial enlargement can signify the presence of multiple cardiac abnormalities that raise left-atrial pressure, and has prognostic implications.29 Septal-wall thickness can be measured to screen effectively for moderate left-ventricular hypertrophy in a patient with episodic hypertension or for hypertrophic cardiomyopathy as a part of the athlete's preparticipation physical.30, 31, 32 Pericardial effusion can be detected, even in the post-thoracotomy state.33

Imaging the abdominal aorta for aneurysm

Ultrasonography is an accepted technique to screen for abdominal aortic aneurysm, especially in at-risk elderly patients. Palpation is often limited by obesity and detects only advanced disease. Use of HCU by nontraditional users (internists or emergency room doctors) enables effective screening for a lower threshold of aortic dilatation.34, 35, 36 The transducer is placed in a longitudinal plane in the subcostal view and both the abdominal aorta and inferior vena cava are identified with tilting of the transducer. Respiratory dynamics of the inferior vena cava provide important information to estimate central venous pressures.37

Other sites of potential clinical value: a growing list

In the thorax, ultrasonography can quickly identify pleural effusions38 and interstitial pulmonary edema.39 A limited ultrasound imaging protocol for deep-venous thrombosis requires vein compression at only two sites per lower extremity, and has been validated for use by physicians in the emergency department.40 Primary diagnosticians might also use HCU devices to evaluate breast lumps and abnormalities found on pelvic examination, thyroid nodules and bladder postvoid residual volumes, and to screen for cholelithiasis or to improve measurement of liver, spleen and kidney size.

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Limitations of HCU

Cost is a significant limitation of current HCU devices, although cost savings for institutions and patients resulting from the lowering of the number of unnecessary outpatient echocardiography referrals by noncardiologists might justify device purchase. Few studies have addressed the cost effectiveness of HCU bedside diagnosis.23, 41 Since there is currently no payer reimbursement for the above examinations, many individual practitioners choose not to purchase an HCU device. Hospital systems can provide shared devices to help guide the care of inpatients42, 43, 44 and the critically ill,45, 46 and improve triage in the emergency department.47 One possible solution for outpatient application, given the general utility of the devices to examine multiple organ systems during one procedure, is to structure reimbursement as a small surcharge for ultrasound assistance, perhaps tempered by an annual limitation in the frequency of billing for this procedure per patient and physician. Such reimbursement would modify the standard payment for evaluation and management because examinations would be lengthened and increased in complexity, but would not erode standard definitions, nor infringe upon payments for comprehensive echocardiography or vascular studies in which detailed measurements are taken and reports generated.

HCU devices are still too large to hold and image simultaneously and slightly cumbersome to carry on daily hospital rounds. In the future, however, further miniaturization might produce wireless pocket-sized or around-the-neck devices that could be carried effortlessly and potentially transmit data.

Finally, the lack of available formal training is a critical limitation to the widespread acceptance of HCU. Evidence-based imaging protocols and competency criteria have not yet been formally accepted. Although ultrasound itself is not harmful, a false-negative diagnosis could lead to medicolegal liability, and a false-positive diagnosis could result in unnecessary testing and anxiety for patients. Similar risks, however, are already seen with stethoscopic assessment, and well-designed ultrasound screening assessments are likely to reduce the inaccuracies of physical examination. In summary, HCU limitations can be overcome by physicians' efforts to teach and refine the technique, lobbying for reimbursement for ultrasound-assisted physical examination, and market-driven research and development to improve device cost and portability.

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Conclusions

The emergence of an ultrasound-assisted physical examination, tailored by the individual physician to his or her own physical examination skills and mix of patients, is not hard to imagine.48, 49 For example, the focused abdominal sonography for trauma (FAST) scan has already been created for emergency medicine specialists to evaluate blunt abdominal injury, and includes a subcostal view of the heart.50 All such limited cardiovascular applications of bedside ultrasonography are clearly not equivalent to the results of echocardiography, but each is useful to screen for structural abnormalities that typically elude physical diagnosis and can provide life-saving data before the acquisition of more formal, comprehensive studies. In terms of the cardiovascular assessment, after auscultation a brief ultrasound scan of three sites would add less than 10 min to an examination and provide screening for early atherosclerosis, left-ventricular systolic dysfunction, left-atrial enlargement, left-ventricular hypertrophy, abdominal aortic aneurysm and elevation of central venous pressure in the primary-care setting.

Despite trends toward laboratory point-of-care testing, history-taking through remote questionnaire, or widespread total-body screening with CT or MRI, it is reassuring that the intimate patient–physician interaction of physical examination is being maintained and appropriately modernized by ultrasound technology. Initial published experience supports proceeding with further refinements in HCU devices and investigation and promotion of bedside ultrasound use by all physicians. Critical to the success of the technology will be a concerted multispecialty effort to formulate simplified, evidence-based instructions for ultrasound examinations, and to provide instructional support to colleagues practicing HCU in primary-care medicine. As recognized since Hippocrates' era, teaching each other has been, and will always be, a vital method by which we learn and advance. With regard to HCU, it is the vital component now needed for the continued evolution of bedside examination.

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Competing interests

Bruce J Kimura has in the past been a sponsored speaker for Agilent and SonoSite, who both manufacture hand-carried ultrasound devices. He has also received a temporary equipment loan from SonoSite, Inc. Anthony N DeMaria has in the past received grants and has been an ad hoc advisor or sponsored speaker for almost all companies that make ultrasound devices.

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Subject areas under which this article appears: Imaging and other investigations