Monitoring equipment

The technology for cardiac monitoring has improved greatly since 1967. Event detection algorithms are able to alarm for sustained tachycardias and bradycardias. Detection of a cardiac QRS requires not only amplitude recognition but also discrimination between noise and slower upstroke depolarizations. New sophisticated analysis systems are capable of 'learning' the normal QRS morphology and then detecting, displaying, storing, and counting different QRS morphologies, runs, and patterns. Pacing stimulus artifacts can be magnified to allow pacemaker analysis. Computer digitization of the ECG signal has allowed storage of an entire 24-h display in a Holter or full-disclosure format. Reports can be printed which display graphics for heart rate and supraventricular and ventricular ectopy.

Monitoring systems have been developed by several manufacturers. To ensure that different telemeters meet optimum requirements for ECG monitoring, the American Heart Association has developed recommendations for standardized lead placement, instrumentation performance, and personnel training. The American Heart Association recommends that at least two leads be monitored. Multiple-lead display facilitates detection of P waves, QRS-axis changes, and ST-segment changes (ischemia may be manifest in only one plane). Multiple-lead display also minimizes data loss due to noise. Detection algorithms developed by various manufacturers are tested against standardized rhythm databases according to protocols established by the Association for the Advancement of Medical Instrumentation. The American Heart Association Database, The Massachusetts Institute of Technology Database, and the European Society of Cardiology ST-T Database are among the most widely used.

However, we have observed many examples of failure to alarm during life-threatening arrhythmias, no matter how sophisticated the telemeter monitoring system. Automated alarm systems are imperfect. An ECG display is of little value unless the ability to detect and respond to arrhythmias is present. Arrhythmia detection software must be sensitive and specific. If the system is not sufficiently sensitive, arrhythmias will be missed. If the system is very sensitive but not sufficiently specific, frequent alarms for noise may make the staff less apt to respond in a 'boy who cried wolf' syndrome. To overcome some of these problems of instrumentation, we favor using a monitor watcher, i.e. a person trained in arrhythmia recognition who watches the ECG displays in order to alert nursing staff to rhythm abnormalities. In the National Survey of Continuous Electrocardiographic Monitoring in United States Hospitals, 55 per cent of hospitals employed a monitor watcher in their

'step-down' or telemetry unit (Jenkinsand George 1.9.9.5.). The monitor watcher need not possess a registered nurse degree. Forty-four per cent of hospitals indicated that they employed monitor technicians. ICU monitoring does not necessarily require a monitor watcher since nursing personnel are usually at the bedside. The National Survey found that only 29.5 per cent of hospitals utilized a monitor watcher in the ICU. Vigilance to the monitors can be physically and mentally challenging. A monitoring station should be quiet and free from frequent interruptions. The space should be comfortable with the monitors at eye level and with desk space for documentation. The number of monitors watched by a single individual should be limited and should be directly proportional to the sophistication of the arrhythmia detection system. Provided that the system has good sensitivity and specificity, 24 tracings can be watched by a single individual.

As previously mentioned, equipment is only one part of an ECG monitoring unit. Appropriate life-support systems including defibrillators, temporary pacing, and medications are required to treat serious arrhythmias. Lifesaving equipment should be accompanied by nurses and physicians fully trained in cardiac resuscitation and advanced cardiac life support. Patients who are placed on cardiac monitors for the detection of life-threatening arrhythmias should remain monitored by escorts when taken to tests at remote sites.

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