Cardiac Monitor

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Cardiac Monitor

Definition

The cardiac monitor is a device that shows the heart's electrical activity as a wave pattern on a monitor. It is a bedside monitor.

Purpose

The cardiac monitor continuously shows the cardiac rhythm and sends the electrocardiogram (EKG) tracing to a main monitor in the nursing station. Most commonly used in emergency rooms and critical care areas, cardiac monitoring allows for continual observation of several patients. Aside from monitoring cardiac patients, continuous monitoring is useful for observation of postoperative patients, patients with severe electrolyte imbalances, and other unstable patients. Continuous cardiac monitoring allows for prompt identification and initiation of treatment for cardiac arrhythmias and other conditions.

Precautions

The American Heart Association warns of potential interference between some pacemakers and cardiac monitors. Minute ventilation rate-adaptive pacemakers can occasionally interact with certain cardiac monitoring and diagnostic equipment, causing the pacemakers to pace at their maximum-programmed rate. Minute ventilation is sensed in rate-adaptive pacemakers by technology known as bioelectric impedance measurement (BIM). Many medical devices in addition to pacemakers use this technology. When one of these devices is used on a patient with an active, minute ventilation rate-adaptive pacemaker, the pacemaker can erroneously interpret the mixture of BIM signals created in the patient, resulting in an elevated pacing rate. Cardiac monitors, echocardiograph equipment, apnea monitors, respiration monitors, and external defibrillators are common devices that may use BIM technology.

Description

The monitor provides a visual display of the patient's heart rhythm, which is particularly useful information during heart attacks, when patients can develop lethal cardiac arrhythmias. The monitor sounds an alarm if the patient's heart rate goes above or below a predetermined number. An automatic blood pressure cuff and a pulse oximeter, which measures the oxygen saturation in the blood, are also included with some monitors.

Equipment required for continuous cardiac monitoring includes:

cardiac monitor
monitor cable
leadwires
electrodes
dry washcloth or gauze pad
alcohol sponges

Preparation

All electrical equipment and outlets are grounded to avoid electrical shock and artifact (electrical activity caused by interference). The nurse should plug in the monitor, turn on power, and connect the cable if not already attached. He or she should connect the lead wires to the proper position and ensure that color-coded wires match the color-coded cable. If the device is not color coded, the right arm (RA) wire should be attached to the RA outlet, the left arm (LA) wire attached to the LA outlet, and so forth. The nurse should open the electrode package, and attach an electrode to each lead wire. The hands should be washed and the procedure should be explained to the patient. Privacy should be ensured for the patient, and the patient should be clean and dry to prevent electrical shock.

Next, the chest should be exposed and the sites selected for electrode placement. Using the rough patch on the electrode, a dry washcloth, or gauze pad, each site should be rubbed briskly until it reddens, but care should be taken not to damage or break the skin. Dead skin cells are removed in this manner, thereby promoting better electrical conduction. Patients who are extremely hairy may need to be shaved prior to application of the electrodes. An alcohol pad is used to clean the sites in patients with oily skin. Areas should dry completely to promote good adhesion. Alcohol should not become trapped beneath the electrode, as this can lead to skin breakdown. In addition to oily skin, diaphoretic skin can cause interference in the recording. To minimize this interference, the electrode site should be rubbed with a dry 4×4 gauze pad before application. The backing of the electrode should be removed, and the gel inspected. If the electrode has dried out, which can happen if the electrode package is opened before immediate use, it should be discarded and another used. The nurse should apply one electrode to each site, press one side of the electrode against the skin, and pull gently. Then, the opposite side of the electrode should be pressed against the skin. The nurse should press two fingers on the electrode in a circular pattern to affix the gel and stabilize the electrode, then repeat for each electrode. To avoid potential artifact, do not place the electrodes on bony prominences or hairy areas.

Aftercare

After placing all electrodes, the nurse should observe the monitor and evaluate the quality of the tracing, making size and tracing position adjustments as needed. He or she should confirm that the monitor is detecting each heartbeat by taking an apical pulse and comparing the pulse to the digital display. The upper and lower alarm limits should be set according to institutional policy, and the alarm activated. A rhythm strip should be recorded for the medical record, and labeled with patient name, room number, date, time, and interpretation of the strip.

Complications

There is a potential for skin breakdown at the electrode placement site. The patient may be allergic to the adhesive used, or the electrode may have been left on the skin too long. The electrodes should be removed and new electrodes applied, using hypoallergenic electrodes if necessary.

Results

A normal cardiac tracing shows a regular rate and rhythm with no deviations in the QRST complex (the combined waves of an electrocardiogram). Abnormal results may include bradycardia, or tachycardia, accompanied by the alarm. Q waves (the short initial downward stroke of the QRST complex) are abnormal, and may or may not signal an infarction.

Some causes of noninfarction Q waves are:

ventricular hypertrophy
ventricular preexcitation (Wolff-Parkinson-White syndrome)
cardiomyopathies
pulmonary embolism
incomplete left bundle branch block

Causes of changes in ST Segment (part of the EKG between the QRS complex and the T wave) and T Wave (deflection in an EKG that represents electrical activity of the ventricular repolarization) include:

aberrant conduction
amyloidosis
bundle branch block
cardiomyopathy
cocaine vasospasm
electrolyte disturbances
intracranial hemorrhage
myocardial metastases
myocarditis
paced rhythm
pancreatitis or acute abdomen
pericarditis
physical training
Printzmetal's angina
pulmonary embolism
tachycardia
ventricular aneurysm
ventricular hypertrophy
ventricular rhythms
Wolff-Parkinson-White syndrome

Alarm signals are abnormal and must be investigated. A false high alarm rate may be caused by skeletal muscle activity or by the monitor incorrectly interpreting large T waves as a QRS complex, which would double the true heart rate. The electrodes should be repositioned as needed to ensure that the electrode is not over a major muscle mass and that QRS complex is larger than the T wave. A false low alarm rate may be due to patient movement, or poor contact between electrodes and skin. Electrodes should be reapplied as needed. Artifact is a common abnormal finding, and may be caused by improperly placed electrodes, patient movement, static electricity, seizures, anxiety, or chills. The position of electrodes should be checked and static-causing bed linen changed. The cables should not have exposed connectors.

Health care team roles

Cardiac monitoring is usually ordered by a physician. A nurse practitioner or physician assistant can place the electrodes on the patients body. A nurse provides ongoing care during the monitoring, assesses patient to determine hemodynamic effects of rhythms, and intervenes for dysrhythmias as appropriate. The nurse also instructs the patient and family about the cardiac monitor's use.