8 Handheld Echocardiography
Although technology has transformed almost all aspects of our daily lives, the bedside cardiac physical examination uses technology that is almost 200 years old. In 1816, embarrassed to examine an obese young woman by putting his head to her chest, René Théophile-Hyacinthe Laennec rolled a sheet of paper, then placed one end over her precordium and the other to his ear. Thus, the stethoscope was born.1 The sphygmomanometer for measurement of blood pressure dates back to 1881, when it was invented by Samuel Siegfried Karl Ritter von Basch. It is with these two ancient tools that most physicians approach a patient at the bedside to this day. In the interim, the explosive growth of medical technology has spawned relatively inexpensive, miniature ultrasound machines, which can be taken to the bedside and allow immediate imaging across several medical specialties.
Background
In 1978, J. R. Roelandt proposed the first miniaturized HCU system.2 Since that time, bulky keyboards, large monitors, and video recorders have now been replaced by touch pads, flat screens, and digital storage devices. The American Society of Echocardiography defines an HCU device as a small ultrasound machine typically weighing less than 6 pounds that can obtain images and data.3 Since that publication in 2002, advances in ultrasound technology have incorporated all the capabilities expected of a full sized system into these small machines (Fig. 8-1).4–6
Types of Echocardiographic Instruments
Currently, there are four basic types of echocardiographic systems (Table 8-1):
1. Large, very expensive systems carrying the most advanced instrumentation, capable of two-dimensional (2D), M-mode imaging, designated contrast settings, color flow Doppler, pulsed-wave (PW) and continuous-wave (CW) Doppler, tissue Doppler imaging, tissue harmonic imaging, speckle strain imaging, stress echocardiography formats, and broadband multifrequency imaging with image processing and digital storage, as well as volumetric (three-dimensional [3D], four-dimensional [4D]) imaging and transesophageal, intravascular, and intracardiac echocardiography. These systems typically are based in a hospital echocardiography laboratory or large office practice, with an instrument cost over $250,000.
2. Compact, smaller version of the full-sized systems that are more portable and less expensive, but have most of the features available on larger systems. Some are capable of transesophageal echocardiography (TEE) but lack volumetric (3D) imaging. With a compact system, resolution and penetration may be less robust with a lower cost between $100,000 and $150,000. These systems are usually located in an echocardiography laboratory or cardiology office but also are offered in smaller, battery-powered options that can be attached to a cart or separated and carried for portability.
3. Handheld or hand-carried ultrasound (HCU) devices are small, light, battery powered, less expensive systems with good 2D imaging quality and full Doppler capabilities, often with digital and wireless communication, some with stress and TEE options. These systems can be cart mounted or hand carried and may be in an office, emergency department, or hospital setting to provide “point-of-care” ultrasound with multiprobe capability. HCU systems cost between $50,000 and $100,000, depending on options.
4. Palm-sized devices are very small. They can truly be held in one hand and viewed on a small screen and have potential as a smartphone application. These devices can image in 2D, with a caliper for measurement, usually with no or limited color flow Doppler and no electrocardiographic gating. They are relatively inexpensive for their size and capability, around $10,000, and can be used for point-of-care screening or as a true “echo-stethoscope.”
TABLE 8-1 Classification of Currently Available Echocardiography Machines According to Size and Function
| Echocardiography Machines | Capabilities |
|---|---|
| Stationary high-end systems | Full range of standard echocardiographic modalities and measurements (MM, 2D, PW, CW, Color, TDI, TEE), and advanced modalities (3D, contrast) |
| Mobile (smaller machines on wheels, middle range technology) | Full range of standard echocardiographic modalities and measurements (MM, 2D, PW, CW, Color, TDI, TEE) |
| Portable (small machines that can be carried by a person) | Basic, standard echocardiographic modalities and measurements (MM, 2D, PW, CW, Color) |
| Handheld or pocket-size imaging devices | Limited functions (2D, Color) and measurement package |
Color, Color Doppler; MM, M-mode; PW, pulsed ware; TDI, tissue Doppler imaging.
From Sicari R, Galderisi M, Voigt JU, et al: The use of pocket-size imaging devices: a position statement of the European Association of Echocardiography. Eur J Echocardiogr 12:85-87, 2011.
These echocardiographic systems can be separated on the basis of performance capability, size, weight, and cost. Some of the smaller systems can perform a full examination, whereas the palm-sized units can be applied for screening of left ventricular (LV) function, wall thickness, chamber size, hypertrophy, pericardial effusions, and abdominal aortic aneurysms (Fig. 8-2). Ultimately, the choice of system to use will vary with the goal of the examination, the skill and experience of the persons performing the imaging, and its interpretation (Table 8-2). Typically, complete and compact echocardiography systems are used by cardiologists in the context of an echocardiography laboratory. The focus of this chapter is the use of hand-carried and palm-sized echocardiography systems outside the echocardiography laboratory by health care providers in other specialties. The two most important considerations in the clinical use of these smaller, readily accessible, heavily promoted systems are (1) the technical performance of the imaging device and (2) the appropriate level of skill and training to acquire and interpret the images.
Reliability and Accuracy
The reliability and accuracy of the hand-carried ultrasound devices have been validated in studies comparing their performance to full-size systems with images obtained by skilled technicians or physicians. Vourvouri and colleagues7,8 demonstrated greater than a 90% concordance between results using an HCU and a standard full-size system in the echocardiographic evaluation of LV size and function with older-generation hand-carried devices including the OptiGo (Philips Healthcare, Andover, Mass.) and Sono-heart (Sonosite, Bothell, Wash.). Vourvouri and co-workers9 also imaged 300 consecutive patients referred to a cardiologist with a hand-carried device. Agreement between the HCU device (OptiGo) and the standard system for the detection of major abnormalities was excellent (98%). However, even this level of agreement may be suboptimal in the clinical setting, because the HCU did miss 4% of the major findings.
Because of limitations in penetration and resolution, HCUs may underestimate severity of wall motion abnormalities in patients with poor ultrasound tissue penetration, which is often a problem in overweight or obese patients. In general, the quality of the images obtained with an HCU device correlates directly with the skill and experience of the personnel acquiring and interpreting the images. Cardiology fellows had 100% agreement between HCU and conventional echocardiography on qualitative assessment of LV systolic function and a 94% concordance for LV end-diastolic dimension and interventricular septal thickness, with an ultrasound imaging time of only 6 ± 2 minutes.10 Therefore, with proper training, HCU devices represent a valuable alternative to standard echocardiographic systems for well-trained personnel in some specific clinical applications.
Even the smallest palm-sized devices, potentially true cardiac “stethoscopes,” have been evaluated against more sophisticated echocardiographic systems. Dalla Pozza and colleagues11 used three small ultrasound devices in a pediatric population. The two larger HCU systems (a laptop-sized Philips p50 and a compact Philips CX 50) had excellent image accuracy (93%) compared to full echocardiography instruments; however, the palm-sized device (ACUSON P10, Siemens Healthcare, Malvern, Pa.) had only a 64.5% accuracy. Prinz and Voigt12 compared the diagnostic accuracy of a palm-sized device (Vscan, GE Healthcare), used for imaging by an experienced cardiologist in 349 routine patients with varying LV function, to that of two laptop-sized HCU systems (either a Vivid 7 or E9, GE Healthcare). The palm-sized HCU showed excellent correlation in the evaluation of regional wall motion, visual ejection fraction, LV wall thickness and dimensions, and valve regurgitation (Fig. 8-3). These studies corroborate that HCUs and even palm-sized devices can be used by experienced, qualified sonographers and physicians for routine clinical cardiac imaging and may represent a valuable alternative to standard echocardiographic systems, for certain applications.
Ultrasound “Stethoscope”
The concept of a stethoscope is that the physician listens to the patient’s heart sounds to deduce clinical and hemodynamic information from the noise created by blood flow and valve motion. Echocardiography has the potential to work like a stethoscope by using (ultra)sound waves to create images of the heart and visualization of blood flow that provide more accurate data than can be obtained from the acoustic sounds appreciated with a conventional stethoscope. Integrated into the physical examination, the HCU or palm device, as an ultrasound stethoscope, facilitates rapid identification of cardiac abnormalities (e.g., valve disease, chamber dilation, hypertrophy, pericardial effusion, or wall motion abnormalities). This can eliminate more sophisticated, costly studies and expedite appropriate therapeutic interventions (Figs. 8-3 to 8-5).13–15 The Naples Ultrasound Stethoscope in Cardiology study16 demonstrated that whereas the physical examination diagnosed cardiac abnormalities in 38.2% of patients, the addition of a palm-sized echocardiography examination increased the detection of cardiac abnormalities to 69.7%. The goal of promoting these very portable palm-sized or HCU systems is not to replace the comprehensive, carefully done Doppler echocardiographic examination, a detailed anatomic and hemodynamic evaluation, but to complement and improve the physical examination.17
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