Feature | February 21, 2011| Dave Fornell

Trends in ECG Stress Test Systems

The Philips StressVue system offers a wireless patient module for patient comfort and software that gives a clear indication of ST anomalies and morphology changes.

Recent advances in electrocardiogram (ECG) stress testing systems include better waveform analysis algorithms, improved connectivity with electronic medical records and wireless lead systems to untether patients from the machines. In addition, Web-based software and ECG management systems are making it possible to access ECG stress reports and waveforms from anywhere at any time. Wider use of common formats, such as XML and PDF, also allows patient information to be forwarded in information systems or by e-mail to referring physicians.

Recent Industry News

In October 2010, Cardiac Science began offering sudden cardiac arrest risk assessment software on its Quinton Q-Stress cardiac stress systems. Through a partnership with Cambridge Heart, systems now incorporate a microvolt T-wave alternans (MTWA) module to help detect a patient’s risk for sudden cardiac arrest.

Also in late 2010, Cardiac Science released two new cardiac stress test systems. The Quinton 9500 and 9550 systems optimize space in either a wall-mount or cart configuration. They also offer wireless data acquisition and better electronic medical record (EMR) connectivity. One-button navigation and an optional touch screen make the systems intuitive to use, facilitating efficient workflow and reducing training.

Opto Circuits, an Indian company that develops and manufactures healthcare equipment and interventional products, purchased Cardiac Science in October. The transaction is expected to open several new global markets for Cardiac Science’s products and will enhance Opto Circuits’ product offering and presence in the United States.

Mortara and Angeion Corp. introduced the Ultima CardiO2 metabolic stress testing system in May 2010. It combines an integrated 12-lead ECG and a pulmonary assessment system. The system is supposed to enhance testing capabilities with breath-by-breath analysis.

Nihon Kohden entered the market with the introduction of stress software for its Model 1550A/S ECG. All 12 leads are viewed simultaneously during stress testing. Averaged dominant complexes are displayed to the left of each lead for easier viewing of ECG morphology changes as the stress test protocol advances stage-by-stage.

Connectivity

Unlike imaging and healthcare IT, which adopted the DICOM and HL7 format standards, ECG vendors never agreed on a standard for waveforms. The result is an array of file formats for ECGs, including DICOM, XML, TIFF, JPEG, GDT, PDF, ZIP, DVD and others.

Mortara standardized on the DICOM imaging format for its ECG and stress test waveforms. Philips and Cardiac Science also offer optional DICOM formats. This enables easy compatibility with picture archiving and communications systems (PACS) and most cardiovascular information systems, which operate using DICOM.

Cardiac Science offers HL7 and DICOM compatibility on its Quinton Q-Stress. The company said these formats allow compatibility with virtually any EMR, hospital information system (HIS), PACS and many ECG management systems, including GE Muse.

Some systems will interface text data using an HL7 interface, but the reports and waveforms are usually saved in a different format. Several vendor-neutral ECG management systems standardize on XML file formats. Many reports are also saved and/or exported as PDFs.

Before purchasing a stress system, hospitals should ask what formats are used to save the ECG waveforms. They should also find out what formats are accepted by their current or planned ECG management systems to ensure good interoperability.

Untethering Patients

Wireless technology has allowed patients to be freed from the usual bundle of wires tethering them to the ECG system when they are exercising. Wireless leads allow freedom of movement for the patient and clinician. The technology also helps eliminate artifacts due to cable movement.

Mortara’s X12+ transmitter (about the size of smartphone) digitally sends diagnostic-quality, 12-lead ECG data without the need for a conventional tethered patient cable. Mortara’s WAM (wireless acquisition module) also provides freedom of movement. A single button press at the WAM acquires an ECG or prints a rhythm strip.

Analysis Software

Many stress systems offer optional ECG interpretation software for both adult and pediatric patients. Schiller’s systems offer risk stratification tools such as thrombolysis, heart rate variability and signal-averaged ECG. It recognizes high-frequency late potentials using signal averaging and high pass filtering. The Cardiac Science Quinton Q-Stress system offers the Analytic Spectral Method (ASM) to detect every-other-beat patterns unique to patients at increased risk by analyzing the ECG in the frequency or spectral domain. The company says using frequency is more superior at filtering out noise and artifact than using timing alone. The system also uses a proprietary algorithm and baseline wander.

Several vendors also offer filtering software to reduce noise, signal distortion and motion artifacts in the waveforms, even at high speeds and steep grades. Some systems come with lead quality detection and/or offer checklists to aid electrode placement to improve lead quality.

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