What are cardiac monitors? Cardiology Basics

What are cardiac monitors? Cardiology Basics

Cardiac monitors are devices with displays to show ECG, heart rate and other parameters on a continuous basis, usually used in the intensive care unit, emergency department, ambulances or operation theatre. Earlier cardiac monitors had just ECG and heart rate displays.

Current multi parameter monitors have invasive and non-invasive blood pressure, respiration, pulse oximetry, pacemaker sensing and various other monitoring possibilities. It can give out alarms if heart rate or any other parameter is beyond the set limits. Alarms should be taken considering the current physiological state of the person. Someone with continuous tachycardia due to illness will need a higher upper rate cut-off to avoid frequent alarms.

Sometimes the number of alarms is so many that ICU staff may develop “alarm fatigue” and stop responding to alarms. Hence alarm limits should be set appropriately, and monitoring should be done only when essential. Several of the alarms are triggered by poor signals on the ECG channel. This can be avoided by checking the 12 lead ECG and choosing monitor leads with best QRS voltages. Poor electrode contact is another reason, which can be avoided by cleaning the contacts and changing the disposable patches once a day or if damaged.

ICU central monitors are now commonplace in most intensive care units. They are connected to bedside monitors either by wired circuits or wireless links. They can display from a selection of various patient monitoring parameters depending on their configuration. Central monitors also have facility to store physiological data in the hard disk, typically for 72 hours. This enables specialist review of an arrhythmic event at a later time.

Most monitors display continuous ECG monitoring, sometimes more than one channel, depending on the programming, heart rate, respiratory rate, non-invasive and / or invasive blood pressure, pulse oximetry tracing and its instantaneous value (SPO2) and end tidal carbon dioxide (ETCO2). ETCO2 monitoring can be done with a mainstream device attached to the ventilator tubing or a sidestream device in the monitor, which draws a sample from the ventilator tubing.

Various alarm settings are available for each parameter and the alarms can be disabled if needed in case of false alarm, either from the bedside or from the central location. But be careful to check the physiological state of the patient before muting an alarm, to avoid a catastrophe. Muting of alarms is usually time limited so that it will unmute itself after a certain time period, for safety reasons, so that a different true alarm is not missed.