ECG patch monitors for assessment of cardiac rhythm abnormalities.

The primary goal of long-term monitoring is the improvement of diagnostic yield. Despite the clear utility of Holter monitoring in clinical cardiology, issues of relatively low diagnostic yield, cost and inconvenience have motivated the development of ultra-portable devices referred to as ECG patch monitors. Although the "gold standard" for assessing cardiac rhythm abnormalities remains a 12-lead Holter, there is an increasing interest in portable monitoring devices that provide the opportunity for evaluating cardiac rhythm in real-world environments such as the workplace or home. To facilitate patient acceptance these monitors underwent a radical miniaturization and redesign to include wireless communication, water proofing and a patch carrier for attaching devices directly to the skin. We review recent developments in the field of "patch" devices primarily designed for very long-term monitoring of cardiac arrhythmic events. As the body of supporting clinical validation data grows, these devices hold promise for a variety of cardiac monitoring applications. From a clinical and research standpoint, the capacity to obtain longitudinal cardiac activity data by patch devices may have significant implications for device selection, monitoring duration, and care pathways for arrhythmia evaluation and atrial fibrillation surveillance. From a research standpoint, the new devices may allow for the development of novel diagnostic algorithms with the goal of finding patterns and correlations with exercise and drug regimens.

The subcutaneous defibrillator.

OPINION STATEMENT: Prevention of sudden cardiac death (SCD) remains an important clinical problem. Currently, therapeutic goals for SCD prevention include identification of high risk patients and aggressively treating comorbidities underlying. However, many patients remain at increased risk despite optimal medical management (eg, coronary artery disease and cardiomyopathy) whereas others have nonmodifiable risk for sudden death (eg, arrhythmogenic right ventricular dysplasia/cardiomyopathy, Brugada syndrome, long QT syndrome, and hypertrophic cardiomyopathy). In such patients, device therapy with an implantable defibrillator remains the most effective therapy for SCD prevention. However, implantable cardioverter defibrillators (ICDs), which are typically implanted with at least 1 lead placed within the heart, are associated with risks related to device implantation, as well as the presence of chronic endovascular leads. The durability of chronic leads is variable and can require either new leads to be placed or require lead extraction, which is associated with significant morbidity and mortality. The recently developed subcutaneous ICD (S-ICD) does not rely on any component to be placed within the heart or vasculature and therefore may mitigate the risks associated with endovascular leads. Therefore, it may be preferred for patients who are young, have inherited channelopathies, are immunocompromised, have indwelling catheters, or in whom venous access is obstructed or unfavorable due to congenital heart disease. Though long-term data regarding S-ICD performance are not yet available it may prove to be an effective therapeutic option for prevention of SCD.

New devices for very long-term ECG monitoring.

Present day 24-h Holter monitors have been shown to miss many arrhythmias that may occur infrequently or under specific circumstances. The advancement in electronic and adhesive technologies have enabled the development of first generation wearable long-term 14-day patch ECG monitors that attach directly to the skin and require no electrodes and wires to operate. This new technology is unobtrusive to the patients and offers them unprecedented mobility. It enables very long-term monitoring of critical patients while they are carrying out daily activities. The monitors are waterproof, offer good adhesion to the skin and can operate as either recorders or wireless streaming devices.

Recent innovations in the development of magnetic resonance imaging conditional pacemakers and implantable cardioverter-defibrillators.

The first generation of magnetic resonance conditional pacemakers and implantable cardioverter-defibrillators has finally arrived in clinical practice after many years of development. These devices have been optimized to properly function within magnetic fields of 1.5 T and ensure safe operation in controlled environments. Further progress is needed to develop a new generation of magnetic resonance imaging (MRI) conditional devices that can operate in higher powered MRI machines (3 T) which produce clearer images.

New developments in the treatment of severe drug resistant hypertension.

The purpose of this paper is to review the state-of-the-art of renal denervation system technology for treatment of drug resistant hypertension. We describe an investigational device that is currently tested in an on-going clinical trial. The denervation device uses the RF thermal ablation catheter attached to the RF generator. The RF catheter is inserted into the renal artery and positioned in the vicinity of the efferent and afferent parasympathetic innervations. Renal denervation is a minimally invasive, localized procedure and the procedural and recovery times are very short. The entire procedure lasts about 40 min. In early clinical trials, the systolic blood pressure in 87% of patients who underwent the denervation procedure resulted in an average blood pressure drop of greater than 10 mm Hg. The procedure has no systematic side effects, and appears to be beneficial in the management of hypertension in patients refractory to pharmacological therapy.

Subcutaneous implantable cardioverter-defibrillator (S-ICD).

Current state-of-the art implantable cardioverter-defibrillator (ICD) systems have been proven to be safe and effective in treating ventricular arrhythmias leading to cardiac death. ICDs require placement of at least one lead in, or on, the heart. Surgical placement under fluoroscopy and the ongoing presence of the transvenous leads within the patient's heart are associated with a significant proportion of the complications related to this well-established and highly effective therapy. A new ICD has been developed that is implanted entirely subcutaneously (S-ICD), thus eliminating the need for lead placement in or on the heart and simplifying surgery by eliminating the need for imaging equipment. Recent clinical studies suggest that the S-ICD system provides a viable alternative to conventional transvenous devices that may reduce barriers to treatment and lead to the wider adoption of this life-saving therapy.

Integrated heart failure telemonitoring system for homecare.

The integrated telemonitoring system (ITS) for homecare has been designed to improve quality of care as measured by increased nursing productivity, improved patients' clinical and behavioral outcomes and reduction of cost. The system incorporates managerial, organizational, operational and clinical tasks optimized for delivery of quality care through telemonitoring. A secure, multi-modal computer network that integrates homecare nurses, patients and those who care into one seamless environment has been developed. The network brings together a new generation of small, hand-held, wireless terminals used by nurses and patients with a HIPPA-compliant electronic patient record system at the caregiver's site. Wireless terminals use Gobi multi-standard networking technology for connectivity to any available wireless network. The unique features of ITS include a) picture recognition technology capable of extracting numeric data from in-home physiological signal monitor displays that include blood pressure, weight, oxygen saturation, transmission of lung sounds, and capturing echocardiography and electrocardiography data from mobile units; b) in-home caregiver-assisted interactive examinations of signs and symptoms that include visual impressions of ankle swelling, jugular vein distension measurement, and weight gain; c) video-conference capability, facilitating face-to-face two-way communication of nursing personnel with the patients. The ITS network has been designed to improve patients' clinical and behavioral outcomes, increase nursing productivity, and reduce the cost of homecare. Patients' co-operation and compliance has been achieved through use of easy-to-use videoconferencing terminals.

New material for implantable cardiac leads.

UNLABELLED: Cardiac function management devices, including implantable pacemakers and implantable defibrillators, include at least 1 cardiac lead having an electrode for making contact with a portion of the heart. It has been previously shown that the braided multifilament wire electrodes have a high failure rate both for sensing of spontaneous heart activity and for safe heart stimulation. Therefore, it is desirable to have cardiac leads made of materials with mechanical and electrical properties to insure safe pacemaker function. We have developed a new fiber material suitable for implantable cardiac leads with superior high modulus, high mechanical strength, and excellent electrical conductivity. METHODS: The material comprises poly(p-phenylene benzobisoxazole) fibers plated with gold by using an electroless plating method. Due to the difficulty in plating gold directly on organic and inorganic fibers, gold plating was carried out on the surface of silver-plated fibers. RESULTS: The morphology of plated fibers was studied by x-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, and electrochemical polarization measurements. It was found that gold was uniformly plated on the poly(p-phenylene benzobisoxazole) fiber, and the gold-plated fibers have good corrosion resistance. The electrical conductivity of the gold-plated fibers was higher than 4 x 104 S/cm, and its tensile strengths and Young moduli were greater than 1.9 and 130 GPa, respectively, when estimated in terms of a single-fiber strand. CONCLUSIONS: The metal-clad polymer fibers have advantages over conventional metal cardiac leads in flexibility, weight savings, mechanical strength, durability, and tailored electrical conductivity. Therefore, the combined engineering properties of the new fiber afford implantable cardiac lead applications at reduced diameter while having higher strength. Furthermore, the new fiber can be terminated just like a regular metal wire with the choice of ultrasonic bonding, crimping, or band connection.

Estimation of regional end-systolic wall stress during exercise in coronary artery disease.

Estimating left ventricular wall stress has recognized applications, but formulae for global stress cannot be applied to ischemic ventricles. A mathematic method for estimating regional stress in infarcted ventricles has been described. The hypothesis tested was that exercise-induced ischemia increases end-systolic wall stress. Subcostal four-chamber echocardiograms were recorded at rest and during peak symptom-limited exercise in 19 controls and 41 patients with chest pain undergoing coronary arteriography. Centerline regional wall motion and regional end-systolic wall stress were measured at rest and at peak exercise. The normal controls had increased wall motion with exercise, but wall stress remained low. All 32 of the patients with coronary artery disease (> or = 50% diameter narrowing) had wall motion abnormalities with exercise, but the sensitivity of identifying right coronary artery obstructions was poor. Patients with coronary disease had higher regional stress at peak exercise than did the controls. The sensitivity of identifying lesions in all three coronary arteries (0.95 to 1.0) was better than that for wall motion (p < 0.04). The specificity of wall stress needs to be tested in a larger population. Exercise-induced ischemia causes increased regional end-systolic wall stress that reflects its distribution in patients with coronary artery disease. These changes can be measured non-invasively during exercise echocardiography.

Echocardiographic design of a multicenter investigation of free-living elderly subjects: the Cardiovascular Health Study.

The Framingham study has shown by M-mode echocardiography that left ventricular hypertrophy is a powerful, independent predictor for the development of coronary heart disease and that increased left atrial dimension has been associated with an increased risk of stroke. No previous population-based study has evaluated the risk factor correlates and predictive value for coronary heart disease and stroke of two-dimensional and Doppler, as well as M-mode, echocardiography. The Cardiovascular Health Study is a multi-year prospective epidemiologic study of 5201 men and women older than 65 recruited from four geographic sites in the United States. The main objectives of incorporating echocardiography were to determine whether echocardiographic indices, or changes in these indices, are (1) correlated with traditional risk factors for coronary heart disease and stroke; and (2) independent predictors of morbidity and mortality for coronary heart disease and stroke. Echocardiographic measurements of interest include those related to global and segmental left ventricular systolic and diastolic structure and function and left atrial size. For each subject, a baseline echocardiogram was recorded in super-VHS tape using a standard protocol and equipment. All studies were sent to a reading center where images were digitized and measurements were made using customized computer algorithms. Calculated data and images were stored on optical disks to facilitate retrieval and future comparisons in longitudinal studies. A second echocardiogram is scheduled in year 7, with a goal of determining whether changes in cardiac anatomy or function over a 5-year period are important predictors of morbidity or mortality from coronary heart disease and stroke. Quality control measures included standardized training of echocardiography technicians and readers, technician observation by a trained echocardiographer, periodic blind duplicate readings with reader review sessions, phantom studies, and quality control adults.

Pitfalls in the display of color Doppler jet areas: combined variability due to Doppler angle, frame rate, and scanning direction.

UNLABELLED: The Doppler color jet area depicting a regurgitant or shunt lesion may be useful in estimating its severity. However, color jet area may be affected by technical factors. We studied the combined effects of Doppler angle, frame rate, and scanning direction on the Doppler color jet area of a free jet with 10-mL injection. RESULTS: (1) Angle effects: color flow area was 11.7 +/- 2.0 cm2 at a Doppler angle of 20 degrees , and 2.3 +/- 1.2 cm2 at an angle of 60 degrees , when other parameters were kept constant (frame rate = 12 frames/sec, reverse scanning direction). (2) Frame rate effects: with other parameters kept constant (Doppler angle = 20 degrees , reverse scanning direction), color flow area was 11.7 +/- 2.0 cm2 at a rate of 12 frames/sec and 6.5 +/- 1.8 cm2 at 6 frames/sec. (3) Scanning direction effects: with other parameters kept constant (Doppler angle = 20 degrees , frame rate = 9 frames/sec), color flow area was 7.3 +/- 1.1 cm2 with scanning in the reverse direction, and 20.5 +/- 1.6 cm2 with scanning in the forward direction. (4) Combined effects: In our in vitro studies, the maximum color flow area was 20.5 +/- 1.6 cm2, and the minimum area was 1.5 +/- 0.2 cm2 (nearly twelve-fold). CONCLUSIONS: Doppler color jet area correlated inversely with Doppler angle (P less than 0.01) and directly with frame rate (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Do Doppler color flow algorithms for mapping disturbed flow make sense?

It has been suggested that a major advantage of Doppler color flow mapping is its ability to visualize areas of disturbed ("turbulent") flow, for example, in valvular stenosis or regurgitation and in shunts. To investigate how various color flow mapping instruments display disturbed flow information, color image processing was used to evaluate the most common velocity-variance color encoding algorithms of seven commercially available ultrasound machines. In six of seven machines, green was reportedly added by the variance display algorithms to map areas of disturbed flow. The amount of green intensity added to each pixel along the red and blue portions of the velocity reference color bar was calculated for each machine. In this study, velocities displayed on the reference color bar ranged from +/- 46 to +/- 64 cm/sec, depending on the Nyquist limit. Of note, changing the Nyquist limits depicted on the color reference bars did not change the distribution of the intensities of red, blue, or green within the contour of the reference map, but merely assigned different velocities to the pixels. Most color flow mapping algorithms in our study added increasing intensities of green to increasing positive (red) or negative (blue) velocities along their color reference bars. Most of these machines also added increasing green to red and blue color intensities horizontally across their reference bars as a marker of increased variance (spectral broadening). However, at any given velocity, marked variations were noted between different color flow mapping instruments in the amount of green added to their color velocity reference bars.(ABSTRACT TRUNCATED AT 250 WORDS)

A technique to evaluate the performance of computerized ECG analysis systems.

No objective method to test computerized ECG systems has been available. Until now, tests have been conducted separately for instrumentation and algorithms. Hence, to facilitate objective verification and testing of modern computerized ECG equipment, a dedicated high resolution, low noise instrument (an "electronic test patient") has been developed. The purpose of this communication is to describe this new instrument and its electrocardiographic database. The instrument is designed not to cause any disturbances to the original ECG signals in the frequency range from 0 to 1 kHz. The input channels accommodating standard 12-lead and 3-lead Frank systems are sampled simultaneously at 10 kHz each with 90 dB dynamic range. The overall RMS noise figure of the instrument is 1 microV. The integral part of the instrument is a high resolution, high bandwidth minidatabase consisting of selected A-type and B-type verified electrocardiograms such as infarctions, ventricular hypertrophies, atrial fibrillations, etc. The minidatabase was collected with the aid of a computerized ECG system, which has a program for searching for specific electrocardiographic diagnosis. Each database record consists of simultaneous electrocardiographic signals of all standard leads and Frank leads, and a validated diagnostic report. A system under test is typically connected via its patient cable to the analog output of the instrument. The testing is performed with reference to the validated ECG from the database. In that way, our minidatabase is compatible with any electrocardiographic system. The only similar database assembled for testing purposes is that of the CSE group.(ABSTRACT TRUNCATED AT 250 WORDS)