Ragnar Granit Institute, Tampere University of Technology,. P.O.Box692, FIN-3310I Tampere, Finland. P. MAKYNEN. Tampere University Hospital, Department ...
COMPUTERIZED SYSTEM FOR STANDARD ELECTROPHYSIOLOGY STUDIES AND ABLATION TREATMENT OF THE HEART
H.P. VANTTINEN, J.J. NOUSIAINEN, J.A. MALMIVUO Ragnar Granit Institute, Tampere University of Technology, P.O.Box692, FIN-3310I Tampere, Finland P. MAKYNEN Tampere University Hospital, Department of FIN-33101 Tampere, Finland
Cardiology,
A large amount of data is acquired during a standard electrophysiology (EP) study. For this reason a computerized data acquisition, analysis and archiving system for EP studies of the heart is a valuable aid for cardiologists in diagnosing arrhythmias and for researchers in collecting data for various purposes. We have developed a system for standard EP studies and ablation treatment running under Windows on a standard PC. The number of channels, temporal accuracy and amplitude precision of the system are sufficient for clinical use. The user-friendly nature of this software, its reliability and quick adaptation to rapidly changing situations during the EP study, are essential in minimising exposure times and discomfort to the patient. Our system supports the most common EP study methods such as the measurement of V-A conduction times to localise structures like accessory pathways supporting re-entrant arrhythmias. It can also be used during catheter RF-ablation treatment to monitor the ablation and its effects. The built-in ablation monitoring capability is a great advantage, enabling combined EP study and ablation treatment, thus reducing exposure times and the total time needed per patient. For clinical use, the software includes versatile tools for reducing the amount of data acquired (i.e. storing only interesting findings and deleting unnecessary data). For research purposes, the system allows long recordings containing, for example, long stimulation series. The system also has a number of automatic data analysis tools, including facilities to recognise pacing series, study anterograde and retrograde conduction and detect refractoriness. Our system is already in regular clinical use at Tampere University Hospital (TUH) and has been used successfully during standard EP studies and ablation treatments.
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Introduction
Cardiac electrophysiology (EP) studies are a relatively new technique for diagnosing arrhythmias. The first His-potential measurement was performed by Scherlag et. al. in 1969 and present-day standard EP studies are based on this successful experiment. The power of this invasive method is that the phenomena are recorded where they occur, i.e. on the endocardium. EP studies are especially effective in localising and studying mechanisms supporting re-entrant arrhythmias, which are often caused by inborn accessory pathways1. A great advantage of the catheter method is that once the structure supporting the arrhythmia has been localised, transcatheter RF-ablation treatment can be applied to destroy the structure. Despite the invasive nature of the EP study, it is a safe method to study and treat arrhythmias in those patients who are 257
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susceptible to life threatening arrhythmias and usually it does not lead to complications. Thus, only a short recovery time is required after the treatment. Currently, similar systems for EP studies are quite expensive. Thus, a low-cost system with sufficient properties to test the electrophysiologic properties of the heart and to monitor RF-ablation would facilitate the more widespread use of these studies and ablation treatment. 2
System Description
The Electrophysiology Studies (EPS) for Windows software3 was developed to meet the requirements of standard clinical EP studies. The goal was to make a very easyto-use Windows application which could be run on inexpensive standard hardware and could be used to control the data acquisition processor and store the data acquired for subsequent analysis. Microsoft Windows® 3.1 (or higher) was chosen for the environment, because it is the most widespread operating system and Windows applications have many common features. Thus, it is quite easy to adopt the use of a new application if the most frequently required functions work in a familiar manner. An initial version of this software2 was developed under DOS. The system requirements adequate for standard clinical EP studies are real time data acquisition, storage and display of 16 channels with a sampling rate of at least 500 Hz and built-in basic data analysis functions. However, at the moment the software is capable of acquiring and storing the data from 24 channels and displaying 1 to 16 arbitrarily chosen signals in real time. The hardware consists' of a standard 120 MHz Pentium PC with 32 MB RAM, 1.3 GB hard disk and highperformance video card with 2 MB VRAM using a 1024 x 768 pixel resolution and 256 colors. Data is acquired using a 16 channel data acquisition processor, DAP 1200/4, which performs the necessary A/D conversion and stores the data in an FIFO buffer, from where it is read into the computer's memory by the EPS for Windows software. The current system also includes an analog video splitter to divide the video signal so that multiple monitors can be used. In addition the software includes various tools for data analysis, management and archiving. The EPS for Windows software has three main operating modes: analysis, monitoring and recording (Figure 1). In both monitoring and recording modes, data acquisition is enabled. The difference between these two modes is that in monitoring mode, the acquired data is stored only in memory in a loop of 60 seconds, while in recording mode the data is stored both in memory and on disk. The 60 s loop buffer allows interesting events that occurred during the last 60 seconds to be saved. In analysis mode, data acquisition does not take place and all the analysis, data management and printing functions are available. During data acquisition most of these functions are disabled, because using them would severely disturb the data acquisition process and some data could be lost.
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The user can study individual recordings by scrolling the signals back and forth by small increments or screen-by-screen. The user can measure time intervals on the display, make annotations for printout, compare and group signals together, hide uninteresting signals temporarily, rename signals easily and change the amplification and/or horizontal time scale if necessary. The results of certain predefined measurements, selected from the menu, are automatically stored in the study report. Other results are copied onto the clipboard, so that they can be pasted into the desired field of the report editor. Additionally, the results and annotations are stored in a memory metafile, so they can also be shown in the printout. EPS for Windows is also useful during transcatheter RF-ablation treatment. It can be used to monitor impedance and temperature during the ablation. There' is also a separate operating mode for ablation treatment where all ablations are recorded automatically according to changes in impedance level. The software also automatically adds two seconds of pre- and post-ablation ECG in order to facilitate the study of ablation effect. To facilitate the management of recordings, the software maintains a list of recordings in chronological order. Comments in the recordings can be edited and one or more recordings can be deleted by selecting them from the list and pressing a two key shortcut. All these data management functions are also available during data acquisition. Other functions available during data acquisition are heart rate monitoring and insertion of bookmarks. Analysis functions available after data acquisition include recognition of stimulation series, detection of refractoriness and automatic detection of anterograde and retrograde conduction. In analysis mode, the user can copy arbitrary sections and views from a recording and a 60 s buffer into a new recording which is then added to the list. Artefacts or peaks in the signals with large amplitudes that disturb other signals can be cut away by applying a clip function that removes peaks exceeding a user-defined threshold. The software allows very long continuous recordings by dividing them automatically into shorter recordings of 200 seconds' duration. This aids in data analysis and management. EPS for Windows allows the user to customise and save system settings for various types of study, or according to personal preferences. Other tools include file preview, file conversion for importing raw binary data files into EPS for Windows and a bookmark manager for adding/removing bookmarks and attaching comments to them. There are several printing options for formatting printouts, including a running time scale and standard scales of 2.5 cm/s, 5 cm/s and 10 cm/s. The file format used by the software is very suitable for archiving the studies, for example on CD-R discs. All data, including recordings, bookmarks, current settings, the study report with patient and study information, are saved in a single binary file which can be compressed using routinely available compression applications, down to as little as 30% of the original size.
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Figure 1: Flowchart showing the operating modes of EPS for Windows. 3
Results
The system has been developed in association with the Department of Cardiology at Tampere University Hospital. Between August 1996 and June 1997, an average of two EP studies/ablations per week have been performed at TUH using EPS for Windows. This system requires no exotic hardware or software. Thus, its operation and maintenance costs are low. The ability of the software to combine standard EP study methods and ablation monitoring can reduce exposure time and the total time needed per patient. This is also more comfortable for the patient. References 1. R.N. Fogoros in Electrophysiologic Testing (Blackwell Scientific Publications, 1991). 2. J.J. Nousiainen in Report No. 2/1994 (Ragnar Granit Institute, Tampere University of Technology, Tampere, 1994). 3. H.P. Vanttinen in Interactive System for Electrophysiological Testing of the Heart (Ragnar Granit Institute, Tampere University of Technology, Tampere, 1995). 4. B.J. Scherlag et. al, Circulation, B 39, 13 (1969).
