Hand-Carried Cardiac Ultrasound: Background, Instrumentation, and Technique
- Bruce J. Kimura, MD
Background
Despite the contributions of echocardiography to cardiac diagnosis over the past three decades, the recent development of hand-held ultrasound devices may herald an unprecedented era—one of ultrasound physical examination. The immediate clinical value of data rapidly obtained from miniaturized devices disrupts the standard conventions of echocardiography and represents a substantial change in the traditional philosophy and goals of cardiac ultrasound imaging. An examination obtained using an ultrasound stethoscope is best done by the physician as a directed search for simplified ultrasound signs and not one to define and measure all normal and abnormal structures. This focused approach greatly reduces the length and complexity of the examination and represents a fundamental difference with the practice of echocardiography. Focused cardiac ultrasound (FCU) has been differentiated from limited echocardiography in an expert consensus document of the American Society of Echocardiography ( Table 19.1 ). In FCU practice, the physician limits the number of views to only those focused to one clinical issue, as compared with a limited echocardiogram, in which the user is responsible for all diagnoses, primary and incidental, manifest on each of a limited number of views. In limited echocardiography, the requirements of quantifying, reporting, archiving, and billing make the use of pocket-sized ultrasound devices untenable; whereas in FCU, results can be charted as a part of the physical examination simply as positives or pertinent negatives. As a new technique, the definition of FCU has important implications for physician competency and scope of practice, patient expectations, and medicolegal risk.
| Limited Echocardiogram | FCU | |
|---|---|---|
| Patients | Any adult patient | Defined scope of practice |
| Location of imaging | Any location | Defined scope of practice |
| Image protocol | Skill to perform any view, but only selected views may be required | Limited number of views |
| Equipment | Full function (M-mode, 2D, color Doppler, spectral Doppler, TDI, contrast), ECG-gated | 2D minimum |
| Transducers | Multiple | Single |
| Measurements | Advanced quantification | None or linear measurement |
| Acquisition | Sonographer or level II/III echocardiographer | Physician with FCU training |
| Interpretation | Echocardiographer; all pathology and normal structures within imaging view | Physician with FCU training defined, limited scope |
| Image storage | DICOM format, archived for easy retrieval and review | Only for select indications (see text) |
| Documentation | Formal report meeting ICAEL standards | Documentation as brief report or as part of PE, depending on indication |
| Billing | 93308 | None |
Instrumentation
The form of pocket-sized ultrasound stethoscopes follows their intended function by maximizing portability and simplicity for frequent, brief applications. Four pocket-sized devices are currently approved by the U.S. Food and Drug Administration (FDA) ( Fig. 19.1 ). Common features include rechargeable battery as power source, small screen, limited user interface for entering patient information, docking station for archiving studies to a computer, and viewing software. At the present time, additional features vary by manufacturer and include color or spectral Doppler feature, interchangeable transducers, and even smartphone or tablet connectivity. Image presets are available to allow quick boot up for cardiac, abdominal, or OB-GYN imaging. The presence of either a color or spectral Doppler feature provides the user with at least the ability to determine whether an anechoic region is a cyst or vessel, and arterial and venous flow patterns can be visually distinguished on a gross level. For the more advanced user, color Doppler can also be used to identify valvular regurgitation and grossly estimate severity. Pulsed wave spectral Doppler can potentially be used to assess diastolic filling patterns. Battery life generally provides 1 to 2 hours of continuous imaging, further promoting quick-look application and recharging every 1 to 2 days. Future developments may involve transducer technology and interfacing and capitalize on the advancements made in mobile phone technologies; these include touch screen or voice commands, and wireless and cordless connectivity. Remote real-time imaging and telementoring has already been reported as a feasible and inexpensive method for health-care delivery and training. In summary, unlike fully featured, laptop-sized echocardiographic platforms, ultrasound stethoscopes have limited measurement capabilities and are not designed for formal echocardiographic studies.
Currently, a first-generation pocket-sized device is the most expensive device a physician will routinely carry, generally selling in the United States for around $8000. No specific payer reimbursement exists for use of these devices to augment bedside examination. However, cost-savings to health-care systems have been projected by improving diagnostic efficiency in echocardiographic referral and appropriateness of triage or consultation. At the current price, partnerships, call groups, hospital departments or floors, and clinics often share a device, but a reduction in price of these devices will likely be necessary for purchase by individual physicians. As a benefit of ongoing studies of the cost utility of these ultrasound devices, insights into the economic and prognostic value of both traditional and ultrasound-augmented cardiac physical examination may ultimately be revealed.
Technique
To date there is no consensus on the best technique for using these ultrasound devices, and those currently employed can be categorized by two different philosophies of imaging, resulting in the creation of (1) many different sets of diagnosis-based, symptom-based, or “focused” imaging protocols for specific clinical indications; or (2) a single simplified general examination to augment physical examination. As to the former, the burgeoning nature of this field has created initial diversity in practice. For example, there are more than 15 separate acronyms and imaging protocols to use for unexplained hypotension in the emergency and critical care literature. The development of each imaging protocol to answer a specific clinical question has inherent difficulties in (1) compromising between the potentially opposing needs for brevity and highest diagnostic sensitivity, and (2) determining liability associated with disregarding significant yet incidental findings. Unlike the one-size-fits-all, comprehensive imaging philosophy for standard echocardiography, currently published limited, quick-look, or focused imaging protocols have been tailored by the specific clinical needs, patient presentations, and disease prevalence within different subspecialties. If such heterogeneity continues, user training will be variable, and a standardized curriculum would be difficult to develop for medical education. Memorization of multiple, often unrelated imaging protocols, each with its own specific accuracies and limitations, would become necessary for each physician’s particular practice and patient mix.
Another approach is to employ bedside ultrasound to augment the physical examination and model its use as a general examination for all patients during all presentations. Physical examination findings, such as a sustained apical impulse, gallop sounds, rales, and elevated jugular venous pressure, are time-honored targets that underlie our knowledge of cardiac physiology and direct bedside diagnosis. A brief, multitargeted ultrasound survey can improve detection of left ventricular systolic dysfunction, left atrial enlargement, pulmonary edema, pleural effusions, and elevated central venous pressures. Each of these targets has been shown to have diagnostic and/or prognostic value when detected by ultrasound and represent the fundamental pathologies that have long been embedded in formative thinking at the bedside. Clinical synthesis of these basic ultrasound findings earlier in the diagnostic process can help form a more accurate cardiopulmonary differential diagnosis. A logical search for a few ultrasound signs may be simpler to teach and memorize than the sets of unrelated, focused examinations to rule in or rule out specific diagnoses. In the future, one could imagine that both imaging philosophies would coexist, starting with the fundamental teaching of a basic ultrasound physical examination to all physicians; specific, diagnosis-based, focused examinations could be left for subspecialty or advanced use, which is similar to our current practice of physical examination. A variety of ultrasound targets pertinent to cardiovascular medicine can be detected by a quick look with an ultrasound stethoscope ( Box 19.1 ). Proponents have suggested that improved bedside examination would reduce unnecessary testing and provide more accurate initial diagnoses. Opponents have questioned whether current bedside practice, which relies on the sensitivity of patient history and biomarker testing and the specificity of physical examination, would benefit enough from ultrasound to offset the costs of such practice.
