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Introduction
Due to limited resources and increasing demand in healthcare, technological advances and their application to clinical practice undergo careful evaluation with regards to both their safety and cost-effectiveness.
Several studies have suggested that the availability of hand-held portable ultrasound equipment, not only may increase the diagnostic accuracy of physicians, but can allow earlier disease detection, triage improvement and facilitate patient referral.1) However, the availability of these miniaturized hand-held ultrasound devices has raised several questions with regards to their current and future use in clinical practice.
Despite being an innovative technology, important issues arise with regards to their realistic use. Questions such as their true diagnostic use, the training needed to operate them, whether they can extract reliable information comparable to conventional echocardiography machines and their cost-effectiveness are still a matter of ongoing research. This is the main scope of this manuscript.
Interestingly, national and international bodies2)3) issued 6statements clarifying their views on the use of these hand-held echo machines. Although there is a clear consensus that these devices cannot be used as substitutes to the standard echocardiography, their exact role in clinical practice remains to be defined. The aim of this review manuscript was to summarize the types and utility of portable devices.
Types of Hand-Carried Ultrasound Devices
The concept of portable echocardiography originates from as early as the 1970s, were the first descriptions of "ultrasonic stethoscope" appeared in the literature.4)5) Since then, technological developments allowed the production of a range of echocardiography devices, ranging from mobile systems equipped with all standard modalities to the newer miniature "pocket" devices.3)
Evidently, the functions and capabilities of each device are different, prompting the European Association of Echocardiography to clearly differentiate between different types of portable echo machines. Important technical functions such as the color-flow Doppler and spectral Doppler are not available in all hand-held portable devices.
The newer pocket-sized portable echocardiography machines are small devices similar to the size of a smart phone and may be easily carried by a healthcare professional. They are battery operated and may provide diagnostic quality 2D, with color Doppler imaging in real-time.3) Images may be stored and may be transferred offline in a digital format. Their small size and low weight, allow them to be considered truly hand-held portable devices, easily carried by a healthcare professional.
Use of Pocket-Sized Portable Echocardiography Devices
There have been a number of studies assessing the clinical effectiveness of portable echocardiography devices. They have suggested that these devices may be safely used to enhance the diagnostic accuracy of cardiovascular examination and proposed their use in various clinical settings. Furthermore, since their introduction in clinical practice, several studies have compared these new pocket-sized echo devices with the standard, high quality transthoracic echocardiography devices, suggesting a high level of correlation in terms of basic diagnostic accuracy.
Improvement of diagnostic accuracy when added to clinical examination
Studies have previously demonstrated the limitations of the cardiovascular examination, and also highlighted the reduced emphasis on clinical examination skills in modern medical education.6)7) Various groups have also demonstrated that portable echocardiography may be used as an extension of the physical examination, enabling more accurate assessment of the cardiovascular system and often resulting in the modification of the initial diagnosis and management.8)9) More specifically, hand-held echocardiography has been shown to serve as a valuable tool in addition to clinical examination, in the detection of various cardiac abnormalities such as left ventricular (LV) dysfunction, LV hypertrophy, pericardial effusion, valvular heart disease and right atrial pressure (Table 1).
Although extrapolation of this data to the newer pocket-sized machines should be done with care given the technical differences among the "hand-held portable echo machines", it is not surprising that similar levels of additional diagnostic benefit seemed to be gained from the use of the newer pocket-sized devices.10)11)12)
Appreciating the true benefit gained by the use if these devices seems to be a challenging task. A study by Spencer et al.,8) demonstrated that the use of portable echocardiography increased the diagnostic accuracy of cardiologists by 50% for major cardiovascular abnormalities, whereas a more recent study by Galderisi et al.,10) using a pocket-sized device showed a "theoretical" additional diagnostic power of 31.5%. More importantly, a study by Cardim et al.,12) not only demonstrated an additive clinical value over clinical examination, but showed various other benefits such as reducing the need for unnecessary standard echocardiography and discharge rate from the outpatient clinic.
The diagnostic benefit gained from these seems to apply to a range of healthcare professionals ranging from fully qualified cardiologists,13) internal medicine residents,14) junior doctors and medical students.11)15)16) Interestingly, Kobal et al.15) showed that with the use of a hand-held echo device, the ability of medical students to detect various cardiac abnormalities, including valvular heart disease, LV dysfunction, enlargement, and hypertrophy was significantly greater to that of experienced cardiologists physical examination.
It could also be argued that the true impact that pocket-sized echo machines may have on the diagnosis and management of patients, extends beyond the field of cardiology patients. Indeed, a study by Mjolstad et al.17) demonstrated that the addition of pocket-sized examination of < 10 min to usual care (cardiac and abdominal ultrasound), corrected the diagnosis in almost 1 of 5 patients admitted to a medical department.
How well do the latest pocket-sized devices compare to standard transthoracic echocardiography?
There is an increasing body of evidence comparing the diagnostic accuracy of the pocket-sized echo devices with standard, high quality echocardiography (Table 2). Several studies have demonstrated that these newer devices are not only easy to operate, but in appropriate conditions may provide diagnostic yield similar to that of standard echocardiography, with regards to basic echo parameters.
Most studies concluded that the images acquired with the new devices have very good correlation with standard echocardiography, especially with regards to the assessment of the LV, regional wall motion abnormalities, valvular abnormalities and pericardial effusions. It is however widely accepted, that despite their impressive diagnostic accuracy in identifying significant cardiac pathology, these devices do not provide a substitute for standard transthoracic echocardiography (sTTE) due to their limited technical capabilities.
Assessment of the left ventricle
Most studies comparing the quality of pocket-sized echo devices have used the assessment of the LV as a primary endpoint. Liebo et al.18) compared the images obtained from 97 patients with those obtained from sTTE. Their group demonstrated that the images were adequate for interpretation of the LV ejection fraction in 95% of cases, regional wall motion abnormalities in 83%, whereas LV end-diastolic dimension in 95% of the studies. Compared to standard echocardiography, interpretation of the images by cardiologists had accuracy greater than 90% for all of the above LV parameters. Similar results were published by Andersen et al.,19) after demonstrating that the pocket-sized echocardiography had almost perfect correlation with sTTE with regards to global and regional LV function r (95% confidence interval): 0.95 (0.90–0.99) and 0.92 (0.83–0.98), respectively. Fukuda et al.20) also showed an excellent correlation between pocket-sized echo and sTTE with regards to assessment of LV dimensions and fractional shortening when experienced ultrasonographers performed the scan.
Studies also demonstrated a good correlation with sTTE with regards to the LV assessment when the scan was performed by a non-specialist. Culp et al.21) demonstrated that a cardiology fellow with a 2-month experience in echocardiography was able to visually estimate the ejection fraction of the LV at an adequate degree, with a good correlation with sTTE. Furthermore, another study assessing the ability of medical students to acquire images with pocket-sized transthoracic echocardiography (pTTE), showed good agreement between pTTE and sTTE with regards to the assessment of global LV function.22)
Assessment of valvular heart disease
There is a general consensus that among the various cardiac parameters estimated, assessment of valvular heart disease appears to be one of the most limited functions of these pocketsized devices, with slightly reduced correlation with sTTE findings. Prinz and Voigt23) reported an overestimation of the severity of valvular regurgitation. In their study, no valve stenosis was missed, whereas all valve regurgitations missed were graded as mild with sTTE. Kitada et al.24) demonstrated an overestimated severity of valvular regurgitation in 17% of cases, who also highlighted the fact that no valvular stenosis was missed by pTTE. Finally, another study showed a modest underestimation of valvular pathology, especially with regards to the classification of aortic stenosis.19)
Certainly, the lack of spectral Doppler and the lower resolution of the pocket-sized devices, are thought to be the main limiting factors in the assessment of valvular heart disease. However, Kono et al.25) demonstrated that when pTTE was used by an experienced operator, there was a very good correlation with sTTE in the assessment of mitral and tricuspid regurgitation. Furthermore, their group reported that the sensitivity and specificity of pTTE in detecting more than moderate mitral and tricuspid regurgitation was greater than 95%.
Assessment of other cardiac structures
The assessment of the pocket-sized echo device in its ability to detect other cardiac structures such as right ventricle, the atria, pericardium and the great vessels has also been studied in various studies. Most studies showed excellent correlation with sTTE in the diagnosis of pericardial effusions18)19)20)23)24) whereas the assessment of right ventricular function was also found to have a good correlation with sTTE.19) Some groups reported difficulties in the visualization of the inferior vena cava and the right atrial size.18)19) This could be partly explained by the inability of these devices to show the cyclicity of the cardiac and respiratory phases, as well as the lack of other features such as M-mode and electocardiography timing.
Who Should Operate the Pocket-Sized Echo Devices
Evidently, the small size and limited technical features of these devices render them simple and convenient to use. Since these pocket-sized echo devices became available, several groups attempted to assess the training required for their safe use by various healthcare professionals with different levels of experience in echocardiography (Table 1 and 2). Training programs ranging from 2 hr bedside tutorials to several hours of didactic and practical training seem to have been used in different studies resulting in variable outcomes.
Studies using experienced operators in echocardiography (cardiologists, ultrasonographers) demonstrated that only minimal training is needed before these devices can be used to their maximal potential. In spite of the fact that most studies using inexperienced trainees such as medical students, demonstrated an impressive improvement in both diagnostic benefit compared to clinical examination alone11)15)16) as well as a satisfactory correlation with sTTE images,22) the widespread application of pTTE in clinical practice needs careful consideration. Studies have described the steep learning curve associated with the use of these devices,22)26) but have also emphasized the role of echocardiography experience in both acquisition and interpretation of findings with pTTE. Galderisi et al.10) demonstrated significant differences in both sensitivity and specificity of the diagnostic accuracy of pTTE between trainees and expert operators, whereas the majority of studies directly comparing the pTTE with sTTE used expert operators.
In view of the significant role of previous echocardiography experience in the appropriate use of pTTE, the European Society of Echocardiography has recommended that non-cardiologists should undergo dedicated training and revision of basic cardiac physiology, before the use of these devices. Furthermore, they proposed the idea of training specifically designed for this class of devices as a mandatory certification process, setting a clear standard of technical skill needed to operate them.3)
Discussion
Even though hand-held portable echo devices have been available for more than a decade, the introduction of new pocket-sized echo devices have raised new questions with regards to their clinical use. There is a growing body of evidence suggesting that not only these devices can provide a valuable diagnostic tool that can complement the clinical examination, but under certain conditions these devices can provide a limited but very reliable echocardiographic assessment. Furthermore, studies using these newer devices suggested a role in reducing the need for standard echocardiography and discharge rate from outpatient clinics.12) Combining the evidence derived from this growing number of studies is a challenging task. Not only most of these studies included a very small number of patients, but there is a significant heterogeneity between them in terms of the type of portable devices used, the clinical setting, the training of the operator involved as well as their actual primary outcomes. Extrapolation of data derived from studies done using "hand-held portable devices" to the new pocket-sized machines should be done with caution. For example, the lack of colour Doppler in some models would have a significant effect on their diagnostic abilities, such as the assessment of valvular heart disease, whereas the lack of spectral Doppler results in a less complete assessment of the LV.
Although studies have already shown that their use by nonexpert healthcare professionals yielded an additional diagnostic benefit, it seems clear that the clinical purpose for the use of these devices should be primarily determined by the expertise of the operator. Indeed, if these devices are used appropriately, ensuring a standardized training and competence level for non-expert operators, their scope for clinical application is wide. This can range from their use in the emergency department and acute medical assessment unit, facilitating the assessment of common cardiovascular pathologies such as LV systolic dysfunction, valvular heart disease and elevated central venous pressure, to their use by cardiologists on the coronary care unit. Evidently, their use in other clinical settings such as ambulances, community activities and outpatient settings is also a possibility, although a distinction of their diagnostic purposes should be made given the variability of operator experience.
The introduction of new technology in clinical practice is part of the process that allows the evolution of modern medicine. The use of these pocket-portable echo devices provides an additional tool, which if used appropriately has the potential of improving the standards of practice.
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