Introduction

Although Moore’s law of increasing computing capabilities (including processing power and memory) has propelled the development of all imaging modalities, its most tangible manifestation has been in the field of ultrasonography. Unrestrained by the physical limitations (gantry size and power requirements) of the other modalities, echocardiography machines have evolved from large, cumbersome pieces of equipment to handheld echocardiography (HHE) devices that are the size of a mobile phone ( Fig. 46.1 ).

Progressive reduction in the size of ultrasound devices.

The original devices were large and of limited mobility. Echocardiograms became more mobile, eventually being transferred to equipment about the size of a laptop. Handheld devices represent the fruits of ongoing miniaturization, and are analogous in size to a smartphone.

Modified from Marwick TH. The future of echocardiography. Eur J Echocardiogr. 2009;10(5):594–601.

Three aspects of miniaturization have been particularly important for HHE. The display interface has benefited tremendously from technological evolution—cathode ray tube monitors have been replaced by lightweight, high-resolution liquid crystal display (LCD) screens. Developments in microprocessors have led to a shift in the balance between hardware and software so that it is closer to the transducer, usurping some of the functionalities previously performed by the scanner ( Fig. 46.2 ). Likewise, there has been a progressive drop in the size of digital beamforming components from 1 μm to 100 nm. Freeing the handheld device from the ECG leads through fixed time acquisitions or more complex tracking iterations using mitral annular movement of speckle tracking has led to increased portability and reduced size.

Changes in the balance between hardware and software.

The blue boxes indicate system functionality that has been transferred to software or microprocessors. The yellow boxes show steps performed by digital application-specific integrated circuits. The receive (RX) beamforming component has also been incorporated into software applications, and the remainder of the boxes contain analog signal processing units that have been incorporated into the probe itself, thereby reducing volume required on the display end.

Modified from Thomenius KE. Miniaturization of ultrasound scanners. Ultrasound Clin. 2009;4(3):385–389.

The inextricable connection between energy transmitted by a system and the information gained has led powerful, high-end systems to hold an advantage over their battery-dependent counterparts. These power-to-performance issues have benefited from greater efficiency of systems and greater integration, although the limitations imposed by their size continue to leave HHE at one end of the spectrum of ultrasound devices.

Current Handheld Devices

A modern HHE device is characteristically lightweight, portable, and can fit into a coat pocket—in contrast to previous miniaturized models. These devices provide B mode grayscale imaging and in some cases color Doppler. Unlike their fully functional mobile (but non-HHE) counterparts, which are essentially complete echocardiographic devices, most HHE devices do not provide spectral Doppler. They also have smaller screens and a display that is lower in resolution than standard echocardiographic devices ( Fig. 46.3 ). Their various properties are described in Table 46.1 . It is important to remember that comparison with standard echocardiography is only reasonable if these devices are touted as a replacement for echocardiography rather than an extension of the physical examination.

Currently available “handheld” devices.

The technical capabilities of the (A) AcusonP10 (Siemens, Mountain View, California), and (B) Vscan (GE Medical Systems, Milwaukee, Wisconsin) are listed in Table 46.1 .

[A] Courtesy Siemens; B, Courtesy GE Healthcare.

The limitations of HHE are related to the imaging modes, processing, display, and ability to do measurements. None of the devices have continuous-wave Doppler, and only one has pulsed-wave Doppler capability. Because Doppler wave-form analysis is a cornerstone in the severity assessment of valvular and diastolic heart disease, this represents an important (and potentially avoidable) limitation. The high-resolution display of high-end devices provides high-fidelity images that are difficult to reproduce on HHE devices. Finally, post-acquisition analysis and measurements are a key component of analysis. Although three devices enable measurement of distances and area, volumetric assessments are not possible. Adjustment of imaging parameters such as zoom, changing focal point, narrowing sector width to improve frame rate, changing mechanical index for contrast studies, harmonic imaging, changing dynamic range or grayscale maps, and changing frequency are all currently unavailable on such devices. Future iterations may overcome some if not all of these limitations, but currently there is a clear difference between a standard echocardiogram and HHE equipment.

The Learning Curve

The acquisition of information from the traditional physical examination is less reliable than in former times. HHE is a potential replacement for bedside diagnosis, but ultrasonography has not been as well taught and is currently restricted to certain physicians, surgeons, and sonographers. The relative cost, portability, and applicability of HHE devices make them ideal for more widespread dissemination. However, for those unfamiliar with echocardiography, there needs to be a learning process and assessment of competence. The recommended training requirements for performance and reporting of echocardiography are summarized in Table 46.2 .

Clearly Level 2– and 3–trained individuals will readily adapt to HHE; both American Society of Echocardiography (ASE) and European Association of Echocardiography (EAE) recommend that experienced cardiologists and sonographers should be able to use handheld devices. Miniaturization of technology has outpaced training and accreditation guidelines, and ultrasonography has moved from the field of radiologists and subspecialty physicians to residents and general physicians. The ASE advises additional training for Level 1–trained individuals and EAE recommends additional training for cardiologists not fully conversant with echocardiography. The American College of Emergency Physicians (ACEP) has addressed the role of focused cardiac ultrasound (FCU) in the emergency department and provided guidelines on the acquisition and interpretation of ultrasound images on a range of diagnostic possibilities. At an earlier stage in training, HHE can also be used as teaching aide to visualize anatomy and physiology at the bedside. Wittich demonstrated that 79% of medical students could produce a satisfactory parasternal long axis (PLAX) image within 3 weeks of didactic and practical sessions. It seems feasible to use HHE to acquire images and interpret basic cardiac function early during medical school.

There have been multiple previous comparisons of HHE and physical examination—a recent example is summarized in Table 46.3 . There is clear incremental value of HHE over the traditional physical examination; the area under the receiver operating characteristic (ROC) curve was 1.97 for physical examination, 2.42 for ECG and physical examination, and 6.23 for HHE-based echocardiography.

Handheld ultrasonography can be applied to any organ system, although for the purposes of this chapter it will refer solely to the examination of the cardiovascular system. FCU is a specific adaptation—involving HHE—that provides a “Focused examination of the cardiovascular system performed by a physician using an ultrasound as an adjunct to the physical examination to recognise specific ultrasonic signals that represent a narrow list of potential diagnosis in specific clinical settings.” This must be differentiated from limited transthoracic echocardiography, which refers to a reduced number of images performed on a standard and thus a high-end machine by an echocardiographer with appropriate qualifications and interpreted by a cardiologist with the necessary level of experience. The training recommendations on FCU by the ASE comprise three educational components—a didactic component (ultrasound physics, basic cardiac anatomy and views), practical training (image acquisition and correction of technique by experienced echocardiographers), and image interpretation. Recent literature has demonstrated that electronic modules were equivalent to didactic teaching, but there is no substitute for “hands-on” sonographer-based training, or the use of a training log to track the number of successful echocardiographic interrogations for specific cardiac pathologic conditions. There is considerable variation in the duration of training programs depending on the level of experience of operators, opportunity to scan, time, and resources. The length of the learning curve is variable. General practitioners with 8 hours of supervised training using HHE were able to assess left ventricle (LV) function with a sensitivity of 83% and a specificity of 78%. A regression model based on more than 230 HHE examinations performed and interpreted by 30 residents and audited against cardiologists’ measurements suggested improvements every 10 scans and that 30 scans would result in a minimal overall difference. It must be noted that with all R values of less than 0.2, the fit and predictive value of the model was limited.

Validation of Handheld Devices

Table 46.4 summarizes the literature reporting sensitivity, specificity, or agreement between HHE and standard echocardiography. Reported levels of sensitivity, specificity, agreement, and weighted Kappa values, depend on multiple factors including technology used (availability of color Doppler, ability to make measurements), skill level of the operator and interpreter (echocardiographer/cardiologist vs. internist/general resident) and the exact target. Categorical evaluations (presence vs. absence of pathology) are likely to be more robust than quantitative evaluations (e.g., severity of a valvular lesion). The variability in Table 46.4 also reflects that in addition to the progressive development of HHE, there has been an evolution of standard echocardiography over time, with a shifting paradigm toward quantitative analysis using tools such as strain, 3D volumetric analysis, and a focus on quantitative assessment of Doppler waveforms. The variation in agreement despite evolution of handheld technology does not necessarily represent a decline in diagnostic ability; rather, it is testament to the evolution of high-end echocardiography.

A consensus statement published by the ASE found that the use of HHE for assessment of LV enlargement (6 studies), LV hypertrophy (8), LV systolic function (19), left atrium (LA) enlargement (9), right ventricle (RV) enlargement (3), RV systolic function (6), pericardial effusion (11), and inferior vena cava (IVC) size (2) have all been well validated. Similarly, recent literature has attempted to categorize accuracy of HHE as excellent (Sn ≥ 90%, Sp ≥ 95%) including studies by nonexperts, good (Sn ≥ 90%, Sp ≥ 95%) by experts, fair (Sn ≈ 80%, Sp≈ 80%), and variable. Using this categorization, HHE for detection of pericardial effusion was considered to have excellent accuracy. Good accuracy was demonstrated for LV size, LV systolic function, regional wall motion abnormalities (RWMA), ultrasound lung comets, pleural effusion, and abdominal aortic aneurysm (AAA) detection. The accuracy was deemed fair for LA size and assessment of the presence and severity of aortic and mitral valve disease. The accuracy of HHE for RV and IVC assessment was considered to be quite variable.

Suggested Protocol

HHE may be used for a targeted assessment, for example, IVC diameter, a limited examination (apical views only), or a more comprehensive assessment. Any protocol recommendations need to balance the comprehensiveness of an examination with expediency.

Clearly the clinical context will determine the best approach and duration of echocardiography. In an emergent setting such as cardiac arrest, HHE can be used to guide resuscitation. Images can be acquired in the 5- to 10-second window during pulse check or between defibrillations, with the aim to exclude potential causes, including hypovolemic shock (small cavity with contact of ventricular walls), saddle pulmonary embolism (dilated, dysfunctional RV, systolic flattening of septum), cardiogenic shock (markedly reduced ejection fraction [EF]), or pericardial tamponade. The detection of a significant pericardial effusion can be achieved easily and rapidly as shown in Fig. 46.4 .

Use of handheld echocardiography to identify pericardial effusion.

In this subcostal view, the effusion can be recognized as loculated and moderate in size.

The international consensus has recommended a systematic approach of obtaining multiple views in a protocoled manner. HHE does not require the execution of all views used on standard echocardiography. The suggested views for an FCU examination include subcostal long axis, subcostal IVC, parasternal long axis, parasternal short axis, and apical four chamber. Clearly these recommendations should be seen as the minimum necessary number of views and have been designed to limit duration of the examination in time-sensitive scenarios. When appropriate, we also recommend the acquisition of apical two- and three-chamber views. In a time-limited examination, there is a need to employ whichever views are necessary to answer the clinical question, informed by the insight that all may not be possible with HHE ( Fig. 46.5 ). If the device is equipped with color, then this should be employed in each view as well.

Suggested views for handheld echocardiography.

(1 and 2) Parasternal long axis view (PLAX) and parasternal short-axis view (PSAX) (including modified views of pulmonary, tricuspid valve, and short-axis sweep for LV function and regional wall motion assessment. (3, 4, and 5) Apical views 2ch, 3ch, 4ch as illustrated and 5ch for AR, AS assessment. (6) Subcostal long-axis and IVC views 7) aortic arch view.

Documentation of results is also necessary. The ASE has recommended that in addition to identification data and results, limitations of the study and recommendations for additional studies should be reported. A suggested template is shown in Fig. 46.6 .

Proposed handheld echocardiography report.

In addition to a description of all valves and chambers, the report should include commentary about particular limitations and guidance for additional testing.

From Mehta M, Jacobson T, Peters D, et al. Handheld ultrasound versus physical examination in patients referred for transthoracic echocardiography for a suspected cardiac condition. JACC Cardiovasc Imag. 2014;7(10):983–990.

Quantitative Assessment with Handheld Echocardiography

The size of a regurgitant jet by color Doppler and its temporal resolution are influenced by transducer frequency, settings such as gain, output power, Nyquist limit, and depth of the sector. HHE devices do not have the ability to significantly change these settings. The predominant strength of handheld echocardiography lies in its immediate ability to facilitate bedside decisions based on “eye-balling” chamber size, function, and severity of valvular lesions. However, a semiquantitative approach can also be implemented depending on the features available on a device.

Visual estimation and template matching have been the predominant manner with which to evaluate EF. However, semiquantitative approaches including linear measurements ( Fig. 46.7 ), with the Teichholz or Quinones formula to calculate EF, or mitral annular systolic plane excursion (mitral annular plane systolic excursion [MAPSE]; normal MAPSE is greater than 11 mm for women and greater than 13 mm for men) can be employed. In the future, models incorporating speckle tracking technology, initialized and constrained by a deformable model may offer an automated approach to assessment of the severity of LV dysfunction with HHE. The assessment of volume status may be assisted by evaluation of IVC size, and pulmonary congestion may be identified by the detection of “lung comets” caused by fluid in the interlobular septa ( Fig. 46.8 ). The use of IVC collapsibility and lung comets facilitate differentiation of cardiogenic from pulmonary causes of dyspnea.

Approach to the patient with left ventricle (LV) dysfunction.

Multiple views should include measurement of LV size, recognition of mitral regurgitation and its severity, and measurement of left atrium enlargement.

Lung ultrasound for evidence of pulmonary congestion.

This “comet tail” phenomenon is thought to be a consequence of fluid in the pulmonary septa.

As a means to facilitate more accurate determination of valvular heart disease, Beaton et al. have modified the classification of pathological valvular lesions by the World Heart Federation (WHF) ( Table 46.5 ). HHE-acquired examples of mitral regurgitation (MR) (see Fig. 46.7 ) and aortic regurgitation ( Fig. 46.9 ) can be assessed using this methodology. The importance of nonstandard views is demonstrated in a patient with carcinoid syndrome with moderate pulmonary and severe tricuspid regurgitation ( Fig. 46.10 ).

TABLE 46.5

Modification of World Heart Federation Criteria to Recognize Significant Mitral Regurgitation and Aortic Regurgitation

Criteria	Pathologic MR	Pathologic AR
	Seen in 2 views	Seen in 2 views
2012 WHF criteria	In at least 1 view jet length >2 cm	In at least 1 view, jet length >1 cm
	Velocity >3 m/sec for one complete envelope	Velocity >3 m/s in early diastole
	Pansystolic jet in at least 1 envelope	Pansystolic jet in at least 1 envelope
Modified criteria
	Seen in 2 views	Seen in 2 views
	In at least 1 view jet length >2 cm	In at least 1 view, jet length >1 cm
	Pansystolic jet (by color Doppler)	Pansystolic jet (by color Doppler)

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